department of mechanical engineering weikeong teng 0703555

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Department of Mechanical Engineering

Weikeong TENG 0703555

MEng in Mechanical Engineering

Comparison of Composite material with Finite Element Analysis

Final Year Project 2010/ 2011

Supervisor: Dr Phil Harrison

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Abstract

This project will give a brief overview of composite materials. Three possible composite

manufacturing methods that can fabricate bike frame are discussed. Twintex specimen made

from vacuum bagging is tested using British Standard (BS) test guides. This is compared

against FEA which is used to predict the specimen property.

The second part of the project deals with manufacturing a composite bike. It discusses how the

bike mould gets coated with primer and lacquer. Additionally, the bike frame in CAD drawing

was converted from a solid geometry part to a surface geometry. This was imported from IGES

format into Abaqus to produce the shell bike frame. Finally, FEA was performed on the

composite bike at basic level of analysis.

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Table of Contents

Abstract...................................................................................................................................... 2

Acknowledgements .................................................................................................................... 9

1. Introduction of the Project ..................................................................................................10

1.1 Objective .....................................................................................................................11

2. Introduction to composites .................................................................................................12

2.1 Composite materials ...................................................................................................12

2.1.1 Fibre reinforcements ............................................................................................12

2.1.2 Matrix ...................................................................................................................12

2.1.3 Laminates ............................................................................................................12

2.2 Fibre architecture ........................................................................................................13

2.2.1 Fibre Volume fraction ...........................................................................................13

2.2.2 Rule of mixtures ...................................................................................................13

2.2.3 Halpin- Tsai equations .........................................................................................14

2.3 Micromechanical composite property ..........................................................................15

3. Manufacturing processes ...................................................................................................17

3.1 Wet layup ....................................................................................................................18

3.2 Vacuum bagging .........................................................................................................19

3.3 Vacuum infusion .........................................................................................................20

4. Bike mould .........................................................................................................................21

4.1 Steps to complete coating of bike mould .....................................................................22

4.2 Manufacturing process for the bike frame ...................................................................23

4.3 Bike ribs ......................................................................................................................24

4.4 Trial test on sample mould ..........................................................................................25

4.4.1 Sample mould without lacquer coating .................................................................25

4.4.2 Sample mould with lacquer coating ......................................................................26

5. Composite specimen Test ..................................................................................................27

5.1 Twintex specimen .......................................................................................................27

5.2 Three Point Bend Test ................................................................................................28

5.2.1 Bending results in the force deflection .................................................................29

5.2.2 Bending results in flexural stress strain ................................................................30

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5.3 Tensile Test ................................................................................................................31

5.3.1 Tensile results in force displacement ...................................................................32

5.3.2 Tensile results in stress strain ..............................................................................33

6. Numerical Analysis ............................................................................................................34

6.1 Hand calculation: Three point bend test ......................................................................34

7. Finite Element Analysis ......................................................................................................37

7.1 FEA: Three point bend ................................................................................................38

7.1.1 Case 1 (Laminates at [0, 90, 45, -45, 90, 0] °) ......................................................38


7.1.3 Case 3 (Loading force) ........................................................................................45

7.1.4 Comparison FEA: Three point bend cases ...........................................................49

7.1.5 Comparing the bending results of FEA to experiment ..........................................50

7.2 FEA Tensile: ...............................................................................................................51



7.2.4 Comparison FEA: Tensile Cases .........................................................................61

7.2.5 FEA Tensile: steel ................................................................................................62

7.2.6 Comparing the tensile results of FEA to experiment.............................................63

8. Things need to be done before FEA: bike frame ................................................................64

8.1 Shell geometry from SolidWorks .................................................................................64

8.2 Importing CAD file in Abaqus ......................................................................................66

8.2.1 Importing bike frame using ACIS format ...............................................................67

8.2.2 Importing bike frame using IGES format ..............................................................68

9. FEA: Bike frame .................................................................................................................69

9.1 Errors occurred in the simulation of bike frame ...........................................................69

9.2 Solution to solve the errors .........................................................................................70

9.3 Successful simulated bike frame with random loading magnitude ...............................73

9.4 Triangular (Tri) mesh elements ...................................................................................74

10. Discussion ......................................................................................................................75

11. Conclusion .....................................................................................................................76

12. Future works ..................................................................................................................77

Reference .................................................................................................................................78

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Appendices ...............................................................................................................................79

Appendix A: Ribs drawings (all dimensions are in mm) .........................................................79

Appendix B: Mesh density .....................................................................................................81

Appendix C: Extract surface geometry from CAD model in SolidWorks .................................83

Appendix D: Solution for ‗layup orientation was coincided to the shell normal‘ errors ............85

Appendix E: Steps for the Bike frame in FEA.........................................................................88

Appendix F: Mesh type Tri elements .....................................................................................93

List of Tables

Table 1: Property of e-glass and polypropylene ........................................................................15

Table 2: Micromechanical property of the composite lamina .....................................................15

Table 3: Comparison of composite property between Biaxial and Twintex ................................16

Table 4: Comparison of Three point bend results ......................................................................50

Table 5: Comparison of tensile results ......................................................................................63

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List of figures

Figure 1: Schematic of Wet layup [8] .........................................................................................18

Figure 2:Schematic of Vacuum bagging [9] ...............................................................................19

Figure 3: Schematic of Vacuum infusion [10] ............................................................................20

Figure 4: Physical data of ebaboard60-1 [11] ............................................................................21

Figure 5: Mould coated with primer Figure 6: Mould coated with lacquer .............................22

Figure 7: Ribs in half bike shell .................................................................................................24

Figure 8: Primer mould Figure 9: Vacuum bagging Figure 10: Specimen ..............25

Figure 11: Mould with lacquer Figure 12: Hand wet layup Figure 13: Coating was ripped .26

Figure 14: Twill woven Twintex material ....................................................................................27

Figure 15: Top surface: dull textile Figure 16: Base surface: flat shiny .................................28

Figure 17: Bend specimen ........................................................................................................28

Figure 18: Bend specimen on the bending machine ..................................................................28

Figure 19: Bend test_ force deflection .......................................................................................29

Figure 20: Bend test_ flexural stress strain ...............................................................................30

Figure 21: Dog-bone tensile specimens ....................................................................................31

Figure 22: Tensile specimen clamped in test jig ........................................................................31

Figure 23: Tensile test_ force displacement ..............................................................................32

Figure 24: Tensile test_ stress strain .........................................................................................33

Figure 25: Schematic of a beam on two supports ......................................................................34

Figure 26: Schematic 2nd moment of area in rect. .....................................................................34

Figure 27: Schematic of tensile structure ..................................................................................36

Figure 28: Bend specimen with partition lines ...........................................................................38

Figure 29: Material property setting ...........................................................................................38

Figure 30:Case 1_Composite layup ..........................................................................................39

Figure 31: Symmetric and antisymmetric angle-ply laminates [2] ..............................................39

Figure 32 Seeds alone the edges of the parts ...........................................................................40

Figure 33: Supports BC is highlighted in red .............................................................................40

Figure 34: Supports BC .............................................................................................................40

Figure 35: Mid-span BC is highlighted in red .............................................................................41

Figure 36 Mid-span BC .............................................................................................................41

Figure 37: Bend specimen in displacement ...............................................................................41

Figure 38: Bend specimen in resultant force .............................................................................42

Figure 39: Bend specimen Case 1: stress strain ......................................................................42

Figure 40: Case 2_Composite layup .........................................................................................43



Figure 43: Loading points represent in red dots ........................................................................45

Figure 44: Supports BC is highlighted in red .............................................................................46

Figure 45:Supports BC ..............................................................................................................46

Figure 46: Load condition is highlighted in red dots ...................................................................46

Figure 47 Load condition ...........................................................................................................46

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Figure 48: Bend specimen in displacement ...............................................................................47



Figure 51: Comparisons of bending test ....................................................................................49

Figure 52: Tensile specimen .....................................................................................................51

Figure 53: Material property setting ...........................................................................................52

Figure 54: Composite layup ......................................................................................................52

Figure 55: Mesh tensile specimen .............................................................................................53

Figure 56: Bottom BC of tensile specimen ................................................................................54

Figure 57: Reference point BC of Tensile specimen .................................................................54

Figure 58: Top BC of tensile specimen .....................................................................................55

Figure 59: Tensile model in displacement Figure 60: Tensile model in reaction force ............56

Figure 61:Tensile specimen Case 1_stress strain .....................................................................56

Figure 62: Case 2_tensile Composite layup ..............................................................................57

Figure 63: Tensile specimen Case 2_stress strain ....................................................................57

Figure 64: Load condition of the tensile specimen .....................................................................58

Figure 65: Bottom BC of tensile specimen ................................................................................58

Figure 66: Reference point BC of Tensile specimen .................................................................59

Figure 67: Top BC of tensile specimen .....................................................................................59

Figure 68: Tensile specimen in displacement Figure 69: Tensile specimen in reaction force .60

Figure 70: Tensile specimen Case 3_stress strain ....................................................................60

Figure 71: Comparisons of Tensile test .....................................................................................61

Figure 72: Top BC of tensile steel .............................................................................................62

Figure 73:Steel specimen stress strain .....................................................................................62

Figure 74: Bike frame with rear suspension housing Figure 75: Rear suspension housing ...64

Figure 76: Bike frame after removing the suspension housing ..................................................64

Figure 77: Half Bike frame in solid geometry .............................................................................65

Figure 78: Half Bike frame in shell geometry .............................................................................65

Figure 79: Bike frame model and error message. ......................................................................67

Figure 80: Bike frame shell model .............................................................................................68

Figure 81: Error message .........................................................................................................69

Figure 82: Fibre and normal directions overlapped with each other. ..........................................70

Figure 83: Before correction_ red circles highlights the changes errors.....................................71

Figure 84: After correction_ yellow circles highlights the changes made. ..................................72

Figure 85: Bike frame in displacement, U2 ................................................................................73

Figure 86: Bike frame in reaction force, RF2 .............................................................................73

Figure 87: Triangular element mesh of the bike frame ..............................................................74

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List of figures in Appendices A 1: Bottom rib1 drawing ...........................................................................................................79

A 2: Bottom ribs 2 drawing ........................................................................................................79

A 3: Rear rib drawing ................................................................................................................80

A 4: Top rib drawing ..................................................................................................................80

B 1: Bending test No of elements against RF ............................................................................81

B 2: Bending test No of elements Against RF ...........................................................................81

B 3: Tensile no of elements against RF .....................................................................................82

B 4: Tensile no of elements against RF .....................................................................................82

C 1: Offset surface function .......................................................................................................83

C 2: Offset parameters ..............................................................................................................83

C 3: Hide the solid body ............................................................................................................84

C 4: Verify the surface body ......................................................................................................84

D 1: Identify the region with errors.............................................................................................85

D 2: Fibre orientation with the error ...........................................................................................85

D 3: Edit composite layup .........................................................................................................86

D 4: Ply orientation before amendment D 5: Ply orientation after amendment .....................86

D 6: Region with errors .............................................................................................................87

E 1: Import parts .......................................................................................................................88

E 2: Create parts from IGES file ................................................................................................88

E 3: Create datum E 4: Type of datum system ......................................................88

E 5: Partition .............................................................................................................................89

E 6: Edit material property .........................................................................................................89

E 7: 5 region for the composite layup ........................................................................................90

E 8: Seedlings on the bike geometry .........................................................................................91

F 1: Seeding on the part ............................................................................................................93

F 2: Element type ......................................................................................................................93

F 3: Mesh controls ....................................................................................................................94

F 4: Mesh Tri element on the bike .............................................................................................94

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Acknowledgements

I would like to thank several people for their help, advices throughout the duration of the project.

My supervisor, Dr Phil Harrison for his guidance and patience, and also provide resources

during the project.

Mr. John Davidson for his help in performing the experiments and tabulated the experiment data

for the project.

Mr. Brian Robb and the technical workshop staff for their work on making the ribs.

Mr John Kitching (Acre Rd wind tunnel) for his help in completing lacquer coating on the left bike

moulds.

Qusai Hatem (Post grad) for sharing his experiences in Simpleware and give me advice

modelling in FEA.

Farag Ali (Post grad) for his guidance and help us in the composite manufacture process.

Niall Morton for his help in verifies and comparing in the experiment and in FEA results.

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1. Introduction of the Project

The whole aim of the project is to design and manufacture a composite wheelchair. The project

itself will cover a broad foundation of engineering prospects from creating a new design of

composite wheelchair, manufacturing a composite wheelchair, using finite element analysis

(FEA) to predict the product‘s performance at its service conditions, and finally testing the

composite wheelchair to validate the results from FEA.

In order for us to achieve this goal we have to start from entry level. First, we needed to

understand the general overview on composite materials. The composites manufacturing

processes were briefly discussed which included their advantages and disadvantages.

Composites specimens were made during the course of the project and were tested to obtain its

mechanical property. With the use of FEA, the results were compared and verified against test

results, and learn how accurate the FEA can predict the performance of the structures or

products in working environments.

In this part of project, the main focus was manufacturing a composite bike frame. As the

wheelchair is like a box of trusses, the bike frame is more ideal as it is a single-piece space

frame. This would make it easier to obtain the mechanical property through the testing.

Manufacturing a composite bike would also cover all aspects of design process, manufacturing

process, simulating bike frame in its service environments in FEA and testing the bike frame

physically.

Hence, this project would be a perfect foundation and reference for the future work in design

and manufacture of a composite wheelchair.

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1.1 Objective

This project will cover,

Brief overviews on Composite materials

Learn composite manufacturing processes in the market

The steps for preparing bike tooling mould

Physical testing: Three point bend and Tensile testing

Numerical analysis: Hand calculations and FEA

Compare results of Physical testing with Numerical analysis

Model composite bike frame in shell geometry in FE

Fabrication of the composite bike

Testing the bike frame (tensile or compression tests and etc.)

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2. Introduction to composites

2.1 Composite materials

Composites are made up of at least two materials. Reinforcement (fibres, particles, flakes, and

fillers) provides stiffness and strength to the composite structure, while embedded in Matrix for

bonding. When composites are well-engineered, they exhibit better mechanical properties than

would each individual material. Composites are known for its high stiffness and strength to

density ratio. In this project, the main focus is on Polymer Matrix Composites [1] (PMCs) which

is based on polymer matrix: thermoset and thermoplastic commonly reinforced with glass or

carbon fibres.

2.1.1 Fibre reinforcements

Fibre reinforcements have high stiffness and low density. Its main function is to carry the loads

along their longitudinal directions. Carbon and glass are used extensively in polymer matrix

composites.

2.1.2 Matrix

The functions of the matrix are to transfer stresses between the fibres reinforcement and protect

the fibres from any mechanical or environmental damages. The popular resin matrices are

epoxy, polyester, polyurethane, and vinyl ester.

2.1.3 Laminates

Laminates are composite materials that are stacked in different layers/ plies of fabric

reinforcement materials to give them the specific character of a composite to perform a specific

function. Composite fabric configurations are in continuous fibre, plain woven or twill woven.

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2.2 Fibre architecture

2.2.1 Fibre Volume fraction

Fibre volume fraction identified the actual volume content of fibre in a composite [3].

The fibre volume fraction is calculated as

𝑓 =𝜌𝑚𝑤𝑓

𝜌𝑓𝑤𝑚 + 𝜌𝑚𝑤𝑓

Where

f = Volume fraction of fibers

Wf = Weight of fibers

Wm = Weight of matrix

ρf = Density of fibers

ρm = Density of matrix

2.2.2 Rule of mixtures

The composite stiffness is simply a weight mean between moduli of the two components,

depending only on the fibre volume fraction [2]. It is also applicable to Poisson‘s ratio.

𝐸1 = 1 − 𝑓 𝐸𝑚 + 𝑓𝐸𝑓

𝑣12 = 1 − 𝑓 𝑣𝑚 + 𝑓𝑣𝑓

Where

f = Volume fraction of fibers

E1 = Young‘s modulus along longitudinal direction

Ef = Young‘s modulus of fibers

Em = Young‘s modulus of matrix

v12 = Poisson‘s ratios

vf = Poisson‘s ratios of fibers

vm = Poisson‘s ratios of matrix

(2.1)

(2.2)

(2.3)

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2.2.3 Halpin- Tsai equations

Halpin–Tsai equations are a set of empirical expressions that enable the property of a

composite material to be expressed in terms of the properties of the matrix and reinforcing

phases together with their proportions and geometry [2].The equations were accurate estimates

in most cases.

𝑀

𝑀𝑚=

1 + 𝜉𝑛𝑓

1 − 𝑛𝑓

Where

𝑛 = 𝑀𝑓

𝑀𝑚 + 1

𝑀𝑓

𝑀𝑚 − 1

In the above equations M = composites modulus (e.g. E2, G12, or ν23), Mf = fibre modulus (e.g.

Ef, Gf, νf), and Mm = matrix modulus (e.g. Em, Gm, νm). The parameter ξ is a measure of fibre

reinforcement in the composite and depends on various conditions such as loading and fibre

packing geometries.

(2.4)

(2.5)

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2.3 Micromechanical composite property

The composite specimens (Twintex) for testing were made from E-glass and polypropylene.

However, there is no information on the property of the raw materials (E-glass and

polypropylene filaments) on the Twintex website. Therefore, the generic E-glass [4] and

polypropylene [5] properties were taken from the online material information resource- MatWeb.

Since the micromechanical property of Twintex was calculated using genetic materials; as a

result its calculated property would be off its original property.

The table below has shown the genetic materials property which was needed for the composite

calculation.

f, Volume fraction of fiber:

0.35

Ef, Young’s modulus of fiber:

72.4GPa

Em, Young’s modulus of matrix: 1.21GPa

Vf, Poissons ratio of fibre:

0.2

Vm, Poissons ratio of matrix: 0.3

Gf, Shear modulus of fibre:

30GPa

Gm, Shear modulus of the matrix: 0.538GPa

Table 1: Property of e-glass and polypropylene

A single (uniaxial, continuous fibre) lamina property can be calculated from the equations (2.3),

(2.4), and (2.5). The lamina property would be used in the material selection in finite element

(FE) modelling.

E11 (Pa) E22 (Pa) v12 G12 (Pa) G13 (Pa) G23 (Pa)

2.61E+10 3.02E+09 2.65E-01 1.09E+09 1.09E+09 1.15E+09

Table 2: Micromechanical property of the composite lamina

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First of all, the calculated property was based on a single uniaxial lamina. Twintex are twill

woven fabrics which are biaxial, crimped laminates. There was no reference or online material

that could calculate biaxial woven composite fabric. Composite materials were tested to

determine their properties. In order to compare the property of Twintex, biaxial non-crimped

laminates was used. The properties of two unidirectional lamina stack in the orientation of

[0/90]° were averaged to give the ‗estimated biaxial laminates property‘. In the table shown

below, the tensile modulus between estimated biaxial and Twintex were quite close. However,

the possions ratio and shear modulus differences were significant.

Comparison: Biaxial Twintex [7]

E11 14.56GPa 14 GPa

E22 14.56GPa 13 GPa

v12 0.265 0.1

G12 1.09GPa 1.7 GPa

G13 1.09GPa 1.8 GPa

G23 1.15GPa 1.7 GPa

Table 3: Comparison of composite property between Biaxial and Twintex

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3. Manufacturing processes

There are wide variety manufacturing processes available to the composites manufacturer for

selection and production of the cost efficient products. Each fabrication process has its

advantages and disadvantages. The manufacturing team needs to consider several factors

before selecting the most efficient manufacturing process [6]. The factors are listed below:

User needs

Performance requirements

Size of the product

Surface complexity

Appearance

Production rate

Total production volume

Economic targets

Limitations

Labor

Materials

Tooling/assembly

Equipment

This part of project focuses on three feasible manufacturing processes for the fabrication of

composite bike frame: Wet Layup, Vacuum Bagging and Vacuum Infusion. The next few pages

will describe and identify the advantages and disadvantages of each process. This is followed

by a discussion on the ideal manufacture method for the bike frame.

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3.1 Wet layup

Figure 1: Schematic of Wet layup [8]

Resins are impregnated by hand into fibers/fabrics on the mould. With the use of the rollers or

brushes, air bubbles are removed and resin is evenly distributed across the fabrics. The

laminates are left to cure in room temperature or oven [8].

Advantages

i) Easy and commonly used method

ii) Low cost tooling

iii) Wide choice of suppliers and material types

Disadvantages

i) Resin mixing, laminate resin contents, and laminate quality are reliant on the skills and

experiences.

ii) High void contents in the finish product.

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3.2 Vacuum bagging

Figure 2:Schematic of Vacuum bagging [9]

Vacuum bagging is an extension of the wet layup process where pressure is applied to the

laminates in order to improve its consolidation. This is achieved by sealing a vacuum film over

the wet laid-up laminate and onto the mould. The air under the bag is extracted by a vacuum

pump and thus up to one atmosphere of pressure can be applied to the laminate to consolidate

[9].

Advantages

i) High fibre content laminates can be achieved than the Wet layup process.

ii) Lower void contents are achieved.

iii) Better fibre wet-out due to pressure and resin flow throughout laminates.

Disadvantages

i) Adds cost both in labor and in disposable materials

ii) A higher level of skill is required by the operators

iii) Mixing and control of resin content still largely determined by operator skill

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3.3 Vacuum infusion

Figure 3: Schematic of Vacuum infusion [10]

In vacuum infusion, fabrics are stacked to the desired laminates orientation. The fibre stack is

then covered with peel ply and breather fabric. The resin flow channels were placed precisely

over the mould. The whole mould is vacuumed, allowing resin to flow into the laminate. The

resin was distributed uniformly across the whole laminate aided by resin flowing easily through

the channels [10].

Advantages

i) Much lower tooling cost due to one half of the tool being a vacuum bag, and less

strength being required in the main tool.

ii) Large components can be fabricated.

iii) Cored structures can be produced in one operation.

Disadvantages

i) Relatively complex process to perform well.

ii) Resins must be low in viscosity, thus comprising mechanical properties.

iii) Un-impregnated areas can occur resulting in scrapping the whole product.

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4. Bike mould

The common composite bikes are composite fabrics, wrapped around core foam that holds the

bike shaped. This could be another approach for manufacturing composite bike. The idea is to

create the male bike half tooling moulds. Then, by using one of mentioned manufacturing

processes, the left and right composite bike shells produced were bonded together using

adhesive. Thus, a hollow coreless bike frame is produced.

The bike frame was designed by a previous FYP student (Alan Easdale). The bike mould was

CNC out of tooling foam, ebaboard60-1 [11]. The ebaboard60-1 properties were high in

strength, good edge strength, high heat resistance, good resistance against solvent and very

well workable (contains no abrasive fillers).

Figure 4: Physical data of ebaboard60-1 [11]

The right side of the bike mould was coated with cellulose lacquer in the last FYP. Alan was not

able to complete the left side of the bike mould with the coating in time, because the left bike

mould was damaged. In this project, Niall Morton and I would need to prepare and prime the left

bike mould at the garage in the James Watt building and John Kitching would finish off the

lacquer coating in Acre Rd wind tunnel.

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4.1 Steps to complete coating of bike mould

Steps taken to finish coating the bike mould:

1. Wet-sand the whole mould with 240 or 480 grade of sand papers.

2. Using blower or damp cloth to removes and dust, basically to keep it clean.

3. Spray cellulose/ acrylic primer (purchased by Niall) evenly on the mould in a well

ventilated room when possible, and then leave the mould to dry.

4. Repeated step 1 to step 3 about 3 to 4 times, till the mould has achieved desired

smoothness.

5. It is best to use a spray gun to apply a thin layer of cellulose lacquer as the final

protective coat.

6. Sand lightly by using 800 grades sand paper to smooth lacquer coat.

Figure 5: Mould coated with primer Figure 6: Mould coated with lacquer

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4.2 Manufacturing process for the bike frame

The surface geometry of the bike mould is quite complex. Performing vacuum infusion is a

challenge - planning resin distribution channels along the complex geometry takes lots of

experience. Due to lack of skills and experiences, there will be a high percentage that the resin

will not be distributed uniformly on the composite fabrics across the mould. Thus the laminates

would be scrapped and materials would be wasted.

Therefore, it is the best to fabricate the bike frame using Vacuum Bagging. The advantage with

vacuum bagging is using the brushes to apply the resin on fabrics. The composite fabrics can

be wetted uniformly and even at the curvature edges. Any excess resin can be absorbed by

breather cloth and extracted through vacuum hose. With 1 atmospheric pressure, laminates are

consolidated in the curing process.

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4.3 Bike ribs

Bike frame will be made from bonding two composite shells. Ribs are necessary since the bike

shells will be bonded together and need to be properly aligned. The ribs should be made out of

low density material which does not add too much weight on the bike. In project context, the ribs

were made from ebaboard60-1. The position of the ribs was picked out of convenience. Each rib

was designed to have a 5mm thickness. The dimensions of the ribs were taken from the bike

CAD drawing depends on the ribs position on the bike. Hence, the bike frame is of non-uniform

geometry. The ribs drawing can be found in Appendix A. The ribs are in blue while attached to

the left half bike frame in grey as shown in the figure below.

Figure 7: Ribs in half bike shell

Tri rib

Top rib

Bottom rib 1

Bottom rib 2

Rear rib

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4.4 Trial test on sample mould

Before the composite bike was fabricated using the bike moulds, a couple of trial tests on the

sample moulds (e.g. mould with primer coating and the other mould with lacquer coating) were

tested to ensure the laminates could be removed cleanly with ease.

4.4.1 Sample mould without lacquer coating

In the first test, a flat piece was cut out from the ebaboard60-1, the same material as the bike

mould which had the exact number layers of primer but without lacquer coat as shown in Figure

8. Vacuum bagging was chosen to make the laminates for the trial test, and it doubled as a

practise session to work with composites. While cleaning the surface using acetone, the primer

coating dissolved and was removed at the same time. This concluded that acetone should not

be used to clean the bike mould. Nevertheless, the test continued with rest of the steps for

vacuum bagging. The materials used for the laminates were plain woven E-glass fabrics and

epoxy. The laminates were left to cure in the oven at 85°c. After 7 hours or so for curing, as you

can see in the Figure 9, the breather cloth did not fully absorb the excess resin from the wet

laminates. There were dry patches left over the breather clothes. Thus, the laminates had high

void contents at the same area of the dry patches. Laminates had to be forcefully torn off as

they were stuck onto the mould. As the result shown in Figure 10, the primer coating was ripped

off with laminates and the laminates were scrapped.

Figure 8: Primer mould Figure 9: Vacuum bagging Figure 10: Specimen

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4.4.2 Sample mould with lacquer coating

In the second test, the other side on the sample mould was coated with the exact layers of

primer and lacquer shown in Figure 11. The mould was waxed and applied with PVA release

agent beforehand the test. The test was to determine whether laminates would be able to

release from the mould. Hand wet- layup in Figure 12 was used to make the laminates in this

test. The laminates used were plain woven E-glass fabrics and epoxy. They were left to cure in

the oven at 85°c. After the laminates were cured in the oven, there were small bubbles

underneath the lacquer coating. This might indicate that lacquer was unfit for high temperature

usage. It seems that with a dry corner on peel ply, removing laminates from the mould was

much manageable. However, the specimen still ripped off the lacquer coating completely as in

the Figure 13.

Figure 11: Mould with lacquer Figure 12: Hand wet layup Figure 13: Coating was ripped

The above occurrence will be discussed with John Kitching. Hopefully, John will have some

answers to it. He might have other suggestions for protective coatings to use on the mould.

27 | P a g e

5. Composite specimen Test

The mechanical property of the composite laminates can be determined through a series of

tests. In the context of this project, three point bend and tensile tests were performed on the

composite specimen. Both test methods were conducted strictly, following the British Standard

institute (BSI) test guides:

Glass fibre reinforced plastics — Flexural test — three point bend method (BS EN 2746:1998)

Glass fibre reinforced plastics —Tensile test (BS EN 2747:1998)

5.1 Twintex specimen

Twintex is a commingled E-glass and polypropylene filaments, pre-impregnated material [7].

The advantage of using Twintex is that the manufacturing method will be a mess free process

as there is no involvement using the low viscosity resin in the process. As heat was applied onto

the Twintex, the polypropylene filaments melted and bonded the E-glass filaments together, and

with pressure, the laminates have better consolidation. Figure 14 is a twill woven Twintex

material was shown below.

Figure 14: Twill woven Twintex material

28 | P a g e

Specimen was made from 3 plies of Twintex which were stacked at fibre orientation of [0/90,

45/-45, 90/0] °. Specimen was fabricated by using vacuum bagging. The cured specimen had

two textile finish surfaces. One was the dull wavy textile at the top surface of the specimen. The

other was the shiny flat was at the base surface.

Figure 15: Top surface: dull textile Figure 16: Base surface: flat shiny

5.2 Three Point Bend Test

According to BS- three point bend method (BS EN 2746:1998). Specimen dimensions were

3mm x 15mm x 20mm (h x w x l). The test was conducted on the 4 piece of specimen with the

results averaged. The radius of supporting beam and loading nose were 9.5mm which was too

big for the specimen. Specimen was compressed by loading cell at the mid-span. The speed of

the downward force was travelled at 1.5 mm/ min.

Figure 17: Bend specimen

Figure 18: Bend specimen on the bending machine

29 | P a g e

5.2.1 Bending results in the force deflection

In the graph below, specimens 1 and 4, and specimens 2 and 3 had similar characteristics.

The curve shows the linearity where the specimen held the loading, and the spiky curve shows

some fibres started to fail and absorbed the energy locally in the laminates. The cause of fibre

pull-out and delamination was due to weak bonding. Thus, delamination is a kind of failure as it

develops inside the laminate. However there will not be any obvious damage on the surface.

Why were the maximum linear forces different? It might be that the preparation of composite

specimen was not cut and finished, exposing the lamina to damage at the cut-edges. This

resulted in broken fibres around the edges and causes failure and damage to propagate.

The standard deviation (SD) bending force applied was 378N, and SD deflection distance was

2.76mm

Figure 19: Bend test_ force deflection

-20

30

80

130

180

230

280

330

380

430

480

0 2 4 6 8 10 12

Fo

rce (

N)

Deflection (mm)

3 Point Bend Test: Twintex

Specimen1

Specimen2

Specimen3

Specimen4

http://en.wikipedia.org/wiki/Fiber_pull-out

http://en.wikipedia.org/wiki/Fiber_pull-out

30 | P a g e

5.2.2 Bending results in flexural stress strain

Flexural stress is the stress at the surface of the material in the middle of the span of the

specimen between supports at any time during the test.

𝜎𝑓 = 3 𝐹 𝐿

2 𝑏 ℎ2

Where

σf= flexural stress (MPa)

F = forced applied (N)

L = length of span (mm)

b = width of specimen (mm)

h = thickness of specimen (mm)

Flexural modulus is the slope of the tangent at the origin of the stress strain curve calculated

from the force deflection curve.

𝐸𝑓 =𝐿3

4 𝑏 ℎ3

∆𝐹

∆𝑑

The SD flexural stress was 201.5MPa and SD flexural modulus was 9.08GPa.

Figure 20: Bend test_ flexural stress strain

-20

30

80

130

180

230

280

-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

FL

EX

UR

AL

ST

RE

SS

(M

Pa)

STRAIN

3 Point Bend Test: Twintex

Specimen 1

Specimen 2

Specimen 3

Specimen 4

(5.1)

(5.2)

31 | P a g e

5.3 Tensile Test

According to BS - tensile test (BS EN 2747:1998). The tensile test was conducted on the 4

pieces of dog- bone shape specimens, and then the results were averaged. The speed of the

pulling force was travelled at 2 mm/ min. Specimen was clamped at the ends tightly, and the

gauge length was approximately 60mm.

Figure 21: Dog-bone tensile specimens

Figure 22: Tensile specimen clamped in test jig

32 | P a g e

5.3.1 Tensile results in force displacement

In the graph below, specimens 1 and 4, and specimens 2 and 3 had similar characteristics.

During the loading, laminates were able to withstand a load as shown in the linear rise in the

loading force. The fibres continue to accumulate damage until some local failures in the

laminate causes it to no longer sustain load, causing the whole specimen to fail.

The average tensile force was 4.8kN and average displacement was 3.57 mm.

Figure 23: Tensile test_ force displacement

-1000

0

1000

2000

3000

4000

5000

6000

-0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Fo

rce (

N)

Displacement (mm)

Tensile Test: Twintex

specimen1

specimen2

specimen3

specimen4

33 | P a g e

5.3.2 Tensile results in stress strain

Tensile stress is tensile load experienced by the specimen at any moment during the test, per

initial unit cross sectional area within the free length.

𝜎 = 𝐹

𝑏ℎ

Modulus of elasticity is quotient of the tensile stress and corresponding strain within the linear

area.

𝜀 = ∆𝐿𝐿𝑜

𝐸 = 𝜎𝜀

The average stress was 106MPa and average tensile modulus was 1.81GPa. The average

tensile modulus was a lot smaller than the flexural modulus, which should not be the case. It

should fall in the range of approximate 20% more than flexural modulus. The tensile test did not

conduct with strain gauges on the specimen. Thus, the strain could not be verified. Perhaps the

change in the gradient near the start of the test might be to due to slipping of the specimens

which cannot be verified. From the initial gradient, the tensile modulus calculated was 4GPa.

Figure 24: Tensile test_ stress strain

-20

0

20

40

60

80

100

120

140

-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Str

ess (

MP

a)

Strain

Tensile Test: Twintex

Specimen 1

Specimen 2

Specimen 3

Specimen 4

(5.2)

(5.3)

(5.4)

34 | P a g e

6. Numerical Analysis

Before modelling in the FEA, it is always best to represent actual product with a simple

schematic drawing and calculating the results from hand calculation. Hand calculated results

can help to validate the results from the FEA.

6.1 Hand calculation: Three point bend test

A beam structure is placed on two supports and force is applied in the middle span.

Figure 25: Schematic of a beam on two supports

M = FL

4

Where

M = Bending moment

F = Force acting on the beam

L = Length of the beam

Second moment of area

I = bd3

12

Figure 26: Schematic 2nd moment of area in rect.

Where

I = second moment of area

b = breadth of cross section

d = depth of cross section

F

(6.1)

(6.2)

N.A.

b

d

35 | P a g e

From General Bending equation

M

I=

σ

y=

E

R

σ = My

I

=FL

4 .

d

2 .

12

bd3

σ = 3FL

2bd2

From the bend experiment, the average applied bending force was 378N.

σ = 3. 378. 48

2.15. 32

The bending stress was σ = 201.6MPa

In the bending FEA, when a bend force of 378N was applied on the bend model, the expected

the stress was 201.6MPa. If the FE stress did not matched, the simulation would be wrong.

(6.3)

(6.4)

36 | P a g e

6.2 Tensile test

The tensile structure is fixed at one end, while a pulling force is applied on the other.

Figure 27: Schematic of tensile structure

σ = F

bh

From the experiment, the average applied tensile force was 4.8kN.

σ = 4800

15. 3

The tensile stress was σ = 106.7 MPa

In the tensile FEA, when a tensile force of 4.8kN applied on the tensile model, the expected

stress was 106.7MPa. If the FE stress did not matched, the simulation would be wrong.

F

37 | P a g e

7. Finite Element Analysis

FEA is a numerical model of design product with any material that will be simulated to mimic the

stresses that might occur in the physical environment. It is able to provide analyses for specific

results such stress, stiffness, displacement and etc. This numerical modeling technique has

helped manufacturers save cost as they can virtually test their product without creating a mock-

up product for testing. FEA is used to verify the proposed design of a product and determine

modifications to meet the specifications or service conditions.

FE models can be made either in solid or planar shell geometry. 3D solid structure is limited due

to the fixed dimensions. However, in a planar shell part, the thickness can be defined and

amend as needed in the section function. This is a major advantage. In this instance, in

designing a composite bike the number layers of laminates will change the wall thickness and

the stiffness of the bike frame. If the bike is modeled as a solid part, the wall thickness would be

fixed and unchangeable in FE. Therefore, all models are designed in the planar shell geometry.

Starting from modeling on bend test and tensile test in FEA, would familiarize myself to the

functions and characteristics in modeling composite material parts in Abaqus. Eventually, I

would be confident in modeling composite bike for the later part of project.

38 | P a g e

7.1 FEA: Three point bend

Three different sets of analyses were simulated in FEA bending. Case 1, the composite layup

angles were [0, 90, 45, -45, 90, 0] °. Case 2, the layup angles were changed to [90, 0, 45, -45,

0, 90] °. A bend specimen would be subjected to compression loading at the top surface, while

bottom of the specimen was subjected to tensile loading. Case 3, by using the load to generate

similar service conditions in the bending test, it would help to verify whether the analysis steps

were correct or not.

7.1.1 Case 1 (Laminates at [0, 90, 45, -45, 90, 0] °)

The bending specimen was model in 3D deformation, planar shell geometry. The specimen

dimensions were length 60mm by width 15mm.The model was partitioned to create supports

and mid-span that would be assigned to its boundary conditions which would be discussed later.

Figure 28: Bend specimen with partition lines

In the material property setting, material type was set to lamina. Composite material property

was taken from the Halpin-Tsai calculations.

Figure 29: Material property setting

39 | P a g e

Modelling the specimen in 3 plies twill woven composite in FE was impossible. The next option

was to model the specimen in 6X unidirectional lamina ply, with each ply 0.5mm thick to form

the wall thickness of 3mm. The orientation of the laminates was set [0, 90, 45, -45, 90, 0] °to

become an antisymmetric angle-ply laminates shown in Figure 28. A bend specimen, at the top

of the specimen was compressed while bottom was subjected to tensile. Thus, outer fibre angle

orientation would affect the bending results. At 0 ° lamina at outer surface, the specimen tends

to handle more bending force.

Figure 30:Case 1_Composite layup

Figure 31: Symmetric and antisymmetric angle-ply laminates [2]

40 | P a g e

Meshing in FE, seeds were markers that position along the edges of the part. Quadrilateral

element S8R5 (8-node curved thin shell, reduced integration, using five degrees of freedom per

node) was assigned in the composite specimen. The mesh density can be modified to its

specified target by changing the number of seeds on the edge. The mesh density would not

affect the results as the reaction forces were only found to vary by 0.0003% with higher mesh

densities. This can be found in Appendix B.

Figure 32 Seeds alone the edges of the parts

The specimen resting on the supports is able to bend around the supports when being push

onto the mid-span. For the supports‘ boundary condition, U3= 0, where specimen was held at

fixed level, the specimen was only able to move along X and Y directions. Whereas when UR1=

UR3= 0 the specimen could not be distorted by twisting, but could rotate at Y-axis.

Figure 33: Supports BC is highlighted in red

Figure 34: Supports BC

41 | P a g e

For the mid-span‘s boundary condition, U3= -0.00276m, the specimen was displaced at an

average of 2.76mm in the 3 point bend test.

Figure 35: Mid-span BC is highlighted in red

Figure 36: Mid-span BC

In the figure of specimen in displacement below, specimen was pushed down and rotated at the

supports axis. This was like the actual three point bend test, how the specimen would behave in

the test.

Figure 37: Bend specimen in displacement

42 | P a g e

To get the total resultant force for FEA, sum of all force at the nodes along mid-span were

required.

Figure 38: Bend specimen in resultant force

As the graph had shown, this was a linear system. The resultant force was 722.8 N. The

young‘s modulus of this composite specimen calculated to be 17.8GPa.

Figure 39: Bend specimen Case 1: stress strain

0

50

100

150

200

250

300

350

400

450

0 0.005 0.01 0.015 0.02 0.025

FL

EX

UR

AL

ST

RS

S (

MP

a)

STRAIN

FE: Bend test

Bending Case 1

43 | P a g e


In Case 2, every features and functions of the bend specimen remained the same as Case 1.

The only change made was the laminates orientation. Twill woven lamina is a biaxial fabric.

Thus, the orientation of the laminates could be set in [90, 0, 45, -45, 0, 90] °. Now, 90°

laminates were the outer surface of the model. This affected the stiffness of the model.

Figure 40: Case 2_Composite layup

44 | P a g e

The displacement was the same as in Case 1. However, the force applied to depress the

specimen was half the value of Case 1.


The resultant force was 355.4N. The young‘s modulus of this composite specimen calculated to

be 8.8GPa. The model stiffness was reduced by half as compared to Case 1. The results will be

discussed further in the comparison of FEA bending.


0

50

100

150

200

250

300

0 0.005 0.01 0.015 0.02 0.025

FL

EX

UR

AL

ST

RS

S (

MP

a)

STRAIN

FE: Bending test

Bending Case 2

45 | P a g e

7.1.3 Case 3 (Loading force)

In Case 3, the model was set in the way where loading force was applied in the mid-span unlike

Case 1 where BC was set to displace the specimen. By using the SD force calculated from the

bending experiment, it would create similar testing conditions to bending test. This would

determine the effects on the specimen and overall results in FE. Thus, the results would relate

better to bending test.

Loading points were created in sets under the assembly module using nodes which would be

needed for loading condition.

Figure 43: Loading points represent in red dots

46 | P a g e

The specimen resting on the supports is able to bend around the supports when being push

onto the mid-span. For the supports‘ boundary condition, U3= 0, where specimen was held at

fixed level, the specimen was only able to move along X and Y directions. Whereas when UR1=

UR3= 0 the specimen could not be distorted by twisting, but could rotate at Y-axis.

Figure 44: Supports BC is highlighted in red

Figure 45: Supports BC

To represent the applied force at the mid-span, concentrated force was used. The average

bending force 378N was distributed uniformly between loading points in the mid-span. 378N

divided into six, each node would have 63N.

Figure 46: Load condition is highlighted in red dots

Figure 47: Load condition

47 | P a g e

In the figure of specimen in displacement below, specimen was pushed down and rotated at the

supports axis. The specimen was displaced 1.45 mm deep in the middle.

Figure 48: Bend specimen in displacement

However, there was no reaction force on the mid-span. Therefore, the resultant force was taken

from the sum of total force acting at nodes along the two supports.


48 | P a g e

In the results, the resultant force was 378N and tensile stress worked out to be 201.6MPa. Both

the force and stress were the same value as in the hand calculation: bending test. Thus, the

analytical steps to perform in FEA were correct. The young‘s modulus of this composite

specimen was calculated to be 17.4GPa. The tensile modulus was about the same as in the

Case 1. The result was expected, as both cases had the same material property.


0

50

100

150

200

250

0 0.002 0.004 0.006 0.008 0.01 0.012

FL

EX

UR

AL

ST

RS

S (

MP

a)

STRAIN

FE: Bending test

Bending Case 3

49 | P a g e

7.1.4 Comparison FEA: Three point bend cases

Case 1 had double the stiffness than Case2. In a bend specimen, the top surface of specimen

was compressed while bottom surface was under tensile loading. Thus, the outer-fibre angle

orientation would affect the stiffness. When 0 ° lamina (longer fibre length) was at outer surface,

the specimen was be able to withstand higher bending force. While 90 ° lamina (shorted fibre

length) was at outer surface, specimen could handle half amount of bending force in Case 1.

This proves that the laminates orientation had a huge effect on the stiffness of the model in the

bending condition.

Case 1 and 3 had same stiffness value even though they were performed in different load and

boundary conditions. This is expected since both the bend specimens had same material

property and laminates orientation.

Figure 51: Comparisons of bending test

-50

0

50

100

150

200

250

300

350

400

450

-0.005 0 0.005 0.01 0.015 0.02 0.025

FL

EX

UR

AL

ST

RS

S (

MP

a)

STRAIN

Bending test

Bending Case 1

Bending Case 2

Bending Case 3

SD from bending test

50 | P a g e

7.1.5 Comparing the bending results of FEA to experiment

The three point bend FEA had created a high and low boundary for the composite‘s modulus.

The results had taken into account the possible laminates layups that could represent the twill

woven composite. The mean modulus in FEA was 13.25GPa which was 45% higher than the

bending test‘s standard deviation (SD) modulus.

The material which I used in the composite specimen was Twintex, a biaxial crimped fabric. In

crimped fabric, the higher the crimp percentage in the fabric, the lower in the stiffness modulus

[12]. In FEA, I used uniaxial lamina. Hence, the FEA modulus was higher than experiment

modulus.

Since the material property used in FEA already had discrepancies from the Twintex material

property, the percentage of error accumulated in the simulation, resulting in huge differences in

the results between FEA and experiment.

Three point bend

modulus (GPa)

Experiment Specimen 1 9.8

Specimen 2 9.2

Specimen 3 8.5

Specimen 4 8.8

Standard deviation 9.08

FEA

0/90,45/-45,90/0 Case 1 17.8

90/0,45/-45,0/90 Case 2 8.7


Loading 378N Case 3 17.7

Table 4: Comparison of Three point bend results

51 | P a g e

7.2 FEA Tensile:

Three sets of analysis were performed in FEA tensile. Case 1, the composite layup angles were

[0, 90, 45, -45, 90, 0] °. Case 2, the layup angles were changed to [90, 0, 45, -45, 0, 90] °.

Basically, in different laminates layups would identify whether the FEA tensile results would be

affected. Case 3 uses the loading force to generate similar service conditions in the tensile test.

This could also help verify whether perform FEA steps were correct a not.


The tensile specimen was model in 3D deformation, planar shell geometry. The specimen

model dimensions were length 60mm by width 15mm, FEA was focused on the specimen

gauge length. A datum coordinate (local coordinate) and reference point was created, as

highlighted in red in the figure showed below.

Figure 52: Tensile specimen

52 | P a g e

In the material property setting, material type was set to lamina. Composite material property

was taken from the Halpin-Tsai calculation.

Figure 53: Material property setting

The layup orientation was set to datum coordinate that the lamina would be aligned to the

desired axis on the specimen. The orientation of the laminates was set [0, 90, 45, -45, 90, 0] °,

the laminates are antisymmetric.

Figure 54: Composite layup

53 | P a g e

Quadrilateral element S8R5 (8-node curved thin shell, reduced integration, using five degree of

freedom per node) was assigned in the tensile specimen. The mesh density would not affect the

results as the reaction forces only found to vary by 0.0002% with higher mesh densities. This

can be found in Appendix B.

Figure 55: Mesh tensile specimen

The tensile specimen was held down at the bottom end and pulled at the top end in the actual

tensile test. To mimic the test environments, three boundary conditions were defined in the FE

simulation.

54 | P a g e

1st BC, bottom of the specimen was fixed in all axis, except X-axis was allowed to move.

Figure 56: Bottom BC of tensile specimen

2ndBC, reference point in the mid of the bottom edge was set to encastre, lost all its degree of

freedom. The node of bottom edge of specimen would be fixed.

Figure 57: Reference point BC of Tensile specimen

55 | P a g e

3rd BC, top edge was fixed to prevent the edge from twisting from the pulling force. The

specimen was set to displace for 3.57mm in Y-axis.

Figure 58: Top BC of tensile specimen

The tensile model was displaced to 3.57mm. The resultant force was the sum of all forces of the

nodes along the top edge of the model.

56 | P a g e

Figure 59: Tensile model in displacement Figure 60: Tensile model in reaction force

The resultant force was 32.4kN. The stress was 720.8MPa. The young‘s modulus of the tensile

specimen calculated to be 12.1GPa.

Figure 61: Tensile specimen Case 1_stress strain

0

100

200

300

400

500

600

700

800

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Str

ess

Strain

FE: Tensile test

Tensile case 1

57 | P a g e


In Case 2, the tensile specimen layup orientation was [90, 0, 45, -45, 0, 90] °. The layup might

affect the stiffness of the model just like the Case 2_bend test.

Figure 62: Case 2_tensile Composite layup

The resultant force was 32.4kN. The stress was 720.8MPa. The young‘s modulus of the tensile

specimen calculated to be 12.1GPa. For tensile test, the layup orientation did not have any

effect on the stiffness.


0

100

200

300

400

500

600

700

800

0 0.02 0.04 0.06 0.08

Str

ess

strain

FE: Tensile test

Tensile case 2

58 | P a g e

7.2.3 Case 3 (Loading force)

The tensile model was subjected to tensile force at the top edge. In load condition, a pulling

force of 4800N (SD pulling force in the tensile experiment) was applied across the top edge of

0.015m. Using shell edge load condition, the magnitude was 320kN/m which was calculated

from 4.8kN/ 0.015m.

Figure 64: Load condition of the tensile specimen

The tensile specimen was held down at the bottom end and pulled at the top end in the actual

tensile test. To mimic the test environments, three boundary conditions were defined in the FE

simulation.

1st BC, bottom of the specimen was fixed in all axis, except X-axis was allowed to move.

Figure 65: Bottom BC of tensile specimen

59 | P a g e

2ndBC, reference point in the mid of the bottom edge was set to encastre, lost all its degree of

freedom.

Figure 66: Reference point BC of Tensile specimen

3rd BC, top edge was fixed to prevent the edge to twist from the pulling force. As the laminates

were antisymmetric, the specimen would twist when force is applied.

Figure 67: Top BC of tensile specimen

60 | P a g e

The overall tensile displacement was 0.53mm. The resultant force was the sum of the total

reaction force at bottom edge.

Figure 68: Tensile specimen in displacement Figure 69: Tensile specimen in reaction force

The resultant force was 4.8kN. The tensile stress was 106.7MPa. This matches the hand

calculation from the tensile results (refer to Chapter 6.2 tensile test). The young‘s modulus of

the tensile specimen was calculated to be 12.1GPa.


0

20

40

60

80

100

120

0 0.002 0.004 0.006 0.008 0.01

Str

ess

Strain

FE: Tensile test

Tensile case 3

61 | P a g e

7.2.4 Comparison FEA: Tensile Cases

Case 1 and 2 had the same value for the young‘s modulus 12Gpa even though the tensile

specimens were differences in their laminates orientation. This shows that tensile result can be

influenced by the geometry of the model but not the laminates orientation.

As compared to the experiment, the modulus obtained in FEA was much higher. In order to

verify the steps performed in FEA, material property of composite was replaced by steel.

Once the forces applied onto the steel specimen was obtained, the stress could be calculated

and, with the known strain, tensile modulus could be calculated by using Hooke‘s law. Tensile

modulus of the steel specimen would be tabulated and compared to the modulus input in the

material property. If both tensile moduli were matched, the steps in performing FEA for tensile

would be correct.

Figure 71: Comparisons of Tensile test

0

100

200

300

400

500

600

700

800

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Str

ess

Strain

Tensile test

Tensile case 1

Tensile case 2

Tensile case 3

SD from tensile test

62 | P a g e

7.2.5 FEA Tensile: steel

The tensile specimen model remains unchanged but the material property was changed to

steel. Its young‘s modulus was 200GPa and Poisson ratio was 0.3. The boundary condition of

the top edge was set to displace 4mm in Y axis.

Figure 72: Top BC of tensile steel

The resultant force was 600kN. The stress was 13.3GPa. The young‘s modulus of the steel

specimen calculated 200GPa. Thus, the steps in performing FEA were correct. This meant the

values from the tensile experiment might be wrong.

Figure 73:Steel specimen stress strain

0

2000

4000

6000

8000

10000

12000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Str

ess

Strain

FE: Tensile test

Steel specimen

63 | P a g e

7.2.6 Comparing the tensile results of FEA to experiment

The FEA tensile results were comparatively higher than tensile experiment. Since the steps

performed in the FEA were proven to be correct, the errors stems from the tensile experiment.

In the experiment, strain was not measured by any apparatus such as strain gauges. However,

it was calculated from change in length divided by the original gauge length of specimen.

Previous FYP tensile experiments [13] were used to evaluate its tensile modulus. The previous

FYP specimens were a tensile tube made of 5 plies of e-glass at [0/90] ° layup orientation. The

tube had an inner diameter of 0.038m and wall thickness of 0.001m and length of 0.1m. The

modulus was calculated from Hooke‘s law.

All the tensile experiment‘s results had much lower value modulus than in FEA. Comparing the

modulus between tensile and bend tests, the modulus were far apart which should be the Case.

Just maybe, the tensile test platform was not compliant to composite testing. The only way to

justify the tensile modulus results in the experiments would be to perform another test with

biaxial strain gauges attached onto the tensile specimens.

Tensile modulus (GPa)

Experiment Specimen 1 2.04

specimen 2 1.63

specimen 3 1.58

specimen 4 1.99


Tensile tube[13] Test 3 and 4 1.8

Test 5 1.16

FEA

0/90,45/-45,90/0 Case 1 12.1

90/0,45/-45,0/90 Case 2 12.1

Loading F 4.8kN Case 3 12.1

Table 5:Comparison of tensile results

64 | P a g e

8. Things need to be done before FEA: bike frame

8.1 Shell geometry from SolidWorks

The CAD of bike is quite complex (provided by Alan Easdale). There is a part that had to be

removed to house the rear suspension due to its angular edges. The angular part was

considered as bad geometry in Abaqus. It would create errors in the simulation as the region

would be badly meshed.

Figure 74: Bike frame with rear suspension housing Figure 75: Rear suspension housing

Figure 76: Bike frame after removing the suspension housing

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The solid bike frame needs to be converted into surface entities. Surface geometry was required

to import in FE, as shell geometry would be much preferred in the bike analysis. The surface

geometry was extracted from the solid bike frame part by using the offset surface under

surfaces function in SolidWorks. The original bike surface was offset by 0mm to create a copy of

the surface. The steps taken to produce the surfaces can be found in Appendix C. The bike

surface was saved in either SAT or IGS format, which could be imported in Abaqus.

Figure 77: Half Bike frame in solid geometry

Figure 78: Half Bike frame in shell geometry

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8.2 Importing CAD file in Abaqus

Since SolidWorks can save the parts/ sketches in either IGES-format file (.igs files) or ACIS-

format file (.sat files), it is best to find out which format would be more appropriate for importing

the CAD in Abaqus.

ACIS-format file has multiple parts. Abaqus is able to import every individual part or merge the

parts as a whole. However, parts of mixed modelling space from an ACIS-format file, such as

solids and axisymmetric surfaces, cannot be imported. In addition, parts of mixed type, such as

deformable bodies and discrete rigid surfaces, cannot be imported [14].

For IGES-format file containing multiple parts, Abaqus can import them as a single part. An

imported IGES part forms the base feature of a new part in Abaqus/CAE. This base feature

cannot be modified directly, but additional features can be added to it, such as a solid extrusion

or a blind cut [15].

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8.2.1 Importing bike frame using ACIS format

When importing the bike frame as a single shell part using ACIS format, the model contained

invalid geometry. The model was still invaild after trying to repair the invalid geometry by either

‗convert to analytical‘ or ‗convert to precise‘.

Figure 79: Bike frame model and error message.

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8.2.2 Importing bike frame using IGES format

IGES format was used to import bike frame as a whole. Apparently, the model imported in

Abaqus was a total success, steps can be found in Appendix E. Thus, it would be best to import

the bike frame in IGES format file. Actually, which format to choose was quite subjective. It

depended on how the parts you want to model in FEA and the complexity of the geometry CAD

file. Since FE is dimensionless, it would follow the dimension of the CAD drawing. The CAD

drawing of the bike was in mm.

Figure 80: Bike frame shell model

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9. FEA: Bike frame

After successfully importing the bike frame into Abaqus, I tried to set up the functions for the

simulation such as material property that was used in the FEA in bending and tensile: composite

layup would be 6 plies of uniaxial laminates at [0, 0, 90, 90, 0, 0] ° and random compressive

loading magnitude of 1000N at the seat post and some boundary conditions to encastre the

front tube and gear pedal regions.

9.1 Errors occurred in the simulation of bike frame

The simulation was terminated due to an error of 15 elements in its layup orientation that

overlapped with the shell normal shown in Figure 81.

Figure 81: Error message

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9.2 Solution to solve the errors

I went through every composite layout orientation in the five regions to identify ―15 elements its

layup orientation that overlapped with the shell normal‖. I zoomed into each region where the

fibre and normal could be distinguished easily until I identified the spot where the fibre and

normal direction overlapped each other (as shown in Figure82 by the red circle).

Figure 82: Fibre and normal directions overlapped with each other.

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In the example shown, composite layup 4 was the main cause for the error. The 90° lamina

conflicted with the shell normal. To resolve this, the datum coordinates of 90° lamina was

changed from ‗Datum csys-7.3‘in Figure 83 to ‗Datum csys-7.2‘ in Fig 84, changing the normal

direction. The full steps can be found in Appendix D.

Figure 83: Before correction_ red circles highlights the changes errors.

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Figure 84: After correction_ yellow circles highlights the changes made.

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9.3 Successful simulated bike frame with random loading magnitude

Once the errors were fixed, I was able to perform the simulation on the bike to obtain the FEA

results. The full steps to complete the analysis can be found in Appendix E.

Figure 85: Bike frame in displacement, U2

Figure 86: Bike frame in reaction force, RF2

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9.4 Triangular (Tri) mesh elements

Using the tri elements to mesh the bike frame would be a better choice. In the Figure 87, the

mesh was much more uniformly distributed across the bike geometry. However, the number of

elements that were created exceeded the Abaqus teaching license. I believe the simulation will

get better results than the quadrilateral mesh elements. Steps for mesh the tri elements can be

found in Appendix F.

Figure 87: Triangular element mesh of the bike frame

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10. Discussion

Material:

Twintex is a twill woven fabric which is crimped. Throughout the project, all calculation of

composite micromechanical property and FEA were based on uniaxial fabric.

Bending test:

The supports and loading nose should use smaller radius as their radius are proportion to the

thickness of the test specimen. It may affect the bending magnitude of the specimen which

could change the modulus slightly, making the test data more accurate.

Tensile test:

The tensile experiment results were too low as compared to the flexural modulus. It is best to re-

run the tensile test with strain gauges.

FEA in tests:

In FEA, I used uniaxial lamina to compensate for the woven fabric that I could not model in

Abaqus. At least, I know the steps took to perform the analysis were correct, because I had

verified those steps by replacing the material with steel. I had also verified the FEA results to the

hand calculation results and they matched.

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Comparison of results:

There was a huge discrepancy in the bending results of the experiments and the FEA. This was

due to the material property and the factor in the crimped Twintex fabrics. The tensile results

could not be verified as there might be errors in the tensile test experiment, making the

comparison invalid. It could be better, if the FEA results managed to match the experiment

results.

FEA of composite bike:

The analysis for the composite bike was barely started. As I was new to SolidWorks, time was

lost while trying to convert the solid bike geometry to surface geometry. Additionally, there were

errors in the fibre orientations conflicting with shell normal. Fortunately, I managed to resolve

this but I ran out of time to do a proper and complete FE analysis on the bike frame.

11. Conclusion

This project covered most of its objectives, i.e. making the composite specimen using vacuum

bagging, testing the composite specimen in bending and tensile, and validating the experiment

results with FEA. However, it was unable to produce the bike frame FEA, make the composite

bike and test it. This was due to the time needed to familiarise myself with the materials and

program such as Abaqus. Hence, I spent the full semester learning the functions of the Abaqus,

working out the right steps to perform composite analysis, getting the results sorted out,

validating them and briefly started on the bike analysis. I wish for more time to carry on working

on this project as I managed to solve the error in the modelling bike.

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12. Future works

To the next Final Year Project student:

Find out more about the crimped fabric and whether it will decrease their properties

compared to uniaxial fabric, if you are dealing with woven composite materials.

If not, best to work with uniaxial or biaxial non-crimped fabrics. Things will be slightly

more simplified. From the point of view, the experiment results will be more compatible

to the FEA results.

When working with tensile test, try to test the specimens with strain gauges. This will

ensure identification of any slippage in the test.

You might do a couple more tests on the flat mould to ensure the laminates can be

removed cleanly from the mould. Regardless, you should still be able to manufacture the

composite bike

Use FE to model the laminates on the bike. This will predict the deformation in the bike

geometry. With this knowledge, you will be able to figure out the layup orientations to

use in fabrication of the composite bike frame.

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Reference

[1] Hull, D. And Clyne, T. W, 1996, an introduction to composite materials, 2nd Edition,

Cambridge University press.

[2] Staab, George H, 1999, Laminar composites, Butterworth- Heinemann

[3] Fibre volume [online] available at http://composite.about.com/library/glossary/f/bldef-

f2200.htm [accessed on 10 January 2011]

[4] E-Glass Fiber, Generic [online] Available at:

http://www.matweb.com/search/DataSheet.aspx?MatGUID=1202140c34e8443bbf273862e24c5

f0e [Accessed on 19 October 2010]

[5] Overview of materials for Polypropylene Copolymer [online] Available

at:http://www.matweb.com/search/DataSheet.aspx?MatGUID=d9c18047c49147a2a7c0b0bb17

43e812 [Accessed on 19 October 2010]

[6] Composites Basics: Composites Manufacturing [online] Available at:

http://www.mdacomposites.org/mda/psgbridge_cb_mfg_process.html [accessed on 10 January

2011]

[7] Twintex® Fabrics, Physical Properties for FEA modelling [online] Available at:

http://www.ocvreinforcements.com/Pages/Physical_Properties_for_FEA_Modeling.asp

[Accessed on 11January 2011]

[8] Wet layup [online] available at: http://www.netcomposites.com/education.asp?sequence=56

[Accessed on 11January 2011]

[9] Vacuum bagging [online] available at:

http://www.netcomposites.com/education.asp?sequence=57 [Accessed on 11 January 2011]

[10] Vacuum infusion [online] available at:

http://www.netcomposites.com/education.asp?sequence=61 [Accessed on 11 January 2011]

[11] ebaboard60-1[online] Available at:

http://www.ebalta.co.uk/products/product_datasheets/ebaboard/modelling_boards/datasheet_uk

_ebaboard_60-1.pdf [Accessed on 12 January 2011]

[12] Sulzer Textil Limited Switzerland, 2001, Fabric Structure, Properties and Testing

[13]Alan Easdale, Manufacture of a carbon composite wheelchair-part1

[14] Abaqus/CAE User's Manual/ 10.7.4 importing parts from an ACIS-format file

[15] Abaqus/CAE User's Manual/ 10.7.7 importing a part from an IGES-format file

http://www.matweb.com/search/DataSheet.aspx?MatGUID=1202140c34e8443bbf273862e24c5f0e

http://www.matweb.com/search/DataSheet.aspx?MatGUID=1202140c34e8443bbf273862e24c5f0e

http://www.matweb.com/search/DataSheet.aspx?MatGUID=d9c18047c49147a2a7c0b0bb1743e812



http://www.mdacomposites.org/mda/psgbridge_cb_mfg_process.html

http://www.ocvreinforcements.com/Pages/Physical_Properties_for_FEA_Modeling.asp%20%20%5bAccessed%20on%2011

http://www.ocvreinforcements.com/Pages/Physical_Properties_for_FEA_Modeling.asp%20%20%5bAccessed%20on%2011

http://www.netcomposites.com/education.asp?sequence=57

http://www.netcomposites.com/education.asp?sequence=61

http://www.ebalta.co.uk/products/product_datasheets/ebaboard/modelling_boards/datasheet_uk_ebaboard_60-1.pdf

http://www.ebalta.co.uk/products/product_datasheets/ebaboard/modelling_boards/datasheet_uk_ebaboard_60-1.pdf

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Appendices

Appendix A: Ribs drawings (all dimensions are in mm)

A 1: Bottom rib1 drawing

A 2: Bottom ribs 2 drawing

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A 3: Rear rib drawing

A 4: Top rib drawing

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Appendix B: Mesh density

In bending test,

Bending test No of elements Reaction Force (N)

100 722.677

30 722.917

14 723.094

B 1: Bending test No of elements against RF

B 2: Bending test No of elements Against RF

722.4

722.5

722.6

722.7

722.8

722.9

723

723.1

723.2

100 30 14

REA

CTI

ON

FO

RC

E (N

)

NO OF ELEMENTS

BENDING TEST

BEND TEST

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In tensile test,

Tensile test No of elements Reaction Force (N)

100 32437.2

30 32444.1

14 32452.6

B 3: Tensile no of elements against RF

B 4: Tensile no of elements against RF

32425

32430

32435

32440

32445

32450

32455

100 30 14

REA

CTI

ON

FO

RC

E

NO OF ELEMENTS

TENSILE TEST

TENSILE TEST

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Appendix C: Extract surface geometry from CAD model in SolidWorks

Step 1: Select the offset surface function.

C 1: Offset surface function

Step 2: In the offset parameters, enter 0mm in the distance setting. The offset faces pick those

faces which you are interested in. Done to click the green tick.

C 2: Offset parameters

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Step 3: The surface was generated in the model tree. In order for you to see the surface body,

the solid body needs to be hidden.

C 3: Hide the solid body

Step 4: Just to verify the surface body is the geometry that you are interested.Done!

C 4: Verify the surface body

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Appendix D: Solution for ‘layup orientation was coincided to the shell normal’ errors

Step 1: Identify the region for the composite layup where fibre and normal directions were

coincided with each other. They were identified in the red circles below.

D 1: Identify the region with errors

Step 2: Identify the error from its source (i.e. which ply does the error belong to).They are

highlighted in the blue.

D 2: Fibre orientation with the error

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Step 3: To correct the error, select the ply and right click to amend to the coordinates system

(csys).

D 3: Edit composite layup

Step 4: In the ply orientation, change the normal direction by choosing either Axis 1 or Axis 2.

D 4: Ply orientation before amendment D 5: Ply orientation after amendment

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Step 5:You might need to check for the conflicing normal again. Now all the fibre orientations

are orthoganal to the shell normal. Done !

D 6: Region with errors

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Appendix E: Steps for the Bike frame in FEA

Step 1: Bike frame was being imported using IGES format.

E 1: Import parts

Step2: Create part from IGES file; change the stitches tolerance from 1 to 0.1(by trial and error).

Then select topology to be shell.

E 2: Create parts from IGES file

Step3: Create local coordinates which will be the orientation of the laminates. Go to toolbar,

select the datum. I chose the datum type as csys and the method to identify the

coordinates I use 3 points. I work with rectangular coordinate system.

E 3: Create datum E 4: Type of datum system

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Step 4: Create partition the frame. This is where you have to decide on the region for the layup

orientation.

E 5: Partition

Step 5: Edit material property (lamina).

E 6: Edit material property

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Step 6: Create no. of composite layups which is depended on the no of regions and type of

lamina you be doing. In this bike frame, I had distinct 5 regions for the composite layup,

and the same layup orientation for the 5 regions.

E 7: 5 region for the composite layup

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Step 7: Edit Composite layup. Create the no. of plies for the region. In the bike frame, you need

to set local coordinates for the fibre direction using the csys and remember to set the

normal direction.

Step 8: Set the normal in the fibre orientation, refer to Appendix D.

Step 9: Global seeds are given by default.

E 8: Seedlings on the bike geometry

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Step 10: Quadrilateral element S8R5 (8-node curved thin shell, reduced integration, using five

degree of freedom per node) was assigned in bike frame.

Step 11: Mesh the bike frame

Step 12: Load and boundary condition will vary that depended on what you are trying to

simulate in FEA. Finally, run the simulation. Done!

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Appendix F: Mesh type Tri elements

Step 1: Assign global seeding to the part.

F 1: Seeding on the part

Step 2: Choice of element type

F 2: Element type

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Step 3: Mesh controls choose tri.

F 3: Mesh controls

Step 4: Mesh the part. Done!

F 4: Mesh Tri element on the bike

department of mechanical engineering weikeong teng 0703555

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