environmental study on gfrp composite laminates · 2017. 6. 30. · dr.m.satyanarana gupta...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 6, June 2017, pp. 480–493, Article ID: IJMET_08_06_050

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

ENVIRONMENTAL STUDY ON GFRP

COMPOSITE LAMINATES

G. Dhanajayan

Assistant Professor, Aeronautical Department,

MLR institute of technology, Hyderabad, India

Veeranjaneyulu Kalavagunta, V.Vamshi, Dr.M.Satyanarana Gupta

Aeronautical Department,

MLR institute of technology, Hyderabad, India

ABSTRACT

This paper investigates the structural behavior of composite material under

different environment conditions. The mechanical properties of composite materials

may vary when the material is exposed to high temperature, high humidity

environments. Therefore, in order to utilize the full potential of composite materials,

their performance at elevated temperatures and at high moisture content must be

known. The objective of this investigation was to evaluate the changes in the tensile

strength and flexural strength of composite materials exposed to fresh water, 3%

NaCl, and engine oil in which the temperature is maintained about 60oC and 95%

relative humidity. Hot-air oven is used to maintain the above condition. The flexural

and tensile strength were tested for period of 2, 4 and 8 days after continuous aging.

The results of mechanical deformation in the GFRP samples were studied and

compared for above environmental condition.

Key words: Composites, Accelerated aging, GFRP, Humidity

Cite this Article: G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and

Dr.M.Satyanarana Gupta Environmental Study on Gfrp Composite Laminates

International Journal of Mechanical Engineering and Technology, 8(6), 2017, pp.

480–493.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6

1. INTRODUCTION

Fibers or particles embedded in matrix of another material are the best example of modern

day composite material, which are mostly structural.

Though fiber composites have been in use for many years in application of aircraft,

marine, automobile etc. but still there is little information available on their environmental

impacts.

G.Dhanajayan, Veeranjaneyulu Kalavagunta, V.Vamshi and Dr.M.Satyanarana Gupta


The strength of composites may be hindered as a result of different environmental

interaction. As recent study under accelerating aging shows that the tensile and flexural

strength of composite resins demonstrate lower values after immersed and test in water, NaCl

and engine oil as compared to dry condition due to their absorption.

Accelerated testing is an approach for obtaining more information from a given test time

than would normally be possible. It does this by using a test environment that is more severe

than that experienced during normal equipment use. Since higher stresses are used,

accelerated testing must be approached with caution to avoid introducing failure modes that

will not be encountered in normal use. The strength of a material in bending, expressed as the

stress on the outermost fibers of a bent test specimen, at the instant of failure is called flexural

strength. The tensile strength of a material is the maximum amount of tensile stress that it can

be subjected to before failure.

2. DESIGN AND FABRICATION OF GFRP LAMINATES

Laminates are composite material where different layers of materials give them the specific

function to perform. Fabrics have no matrix to fall back on, but in them, fibers of different

compositions combine to give them a specific character. Reinforcing materials generally

withstand maximum load and serve the desirable properties.

A. Hand lay-up method

Hand lay-up is a simple method for composite production. A mould must be used for lay-up

parts unless the composite is to be joined directly to another structure. The mould can be as

simple as a flat sheet or have infinite curves and edges. For some shapes, moulds must be

joined in sections so they can be taken apart for removal after curing. Before lay-up, the

mould is prepared with release agent to insure that the part will not adhere to the mould.

Reinforcement fibers can be cut and laid in the mould. It is up to the designer to organize

the type, amount and direction of the fibers being used. Resin must then be catalyzed and

added to the fibers. A brush, roller or squeegee can be used impregnate the fibers with the

resin. The lay- up technician is responsible for controlling the amount of resin and the

quantity of saturation.

B. Raw Materials Used

Epoxy resin - ARALDITE LY 556 Hardener - HY 951

Figure 2.1 Epoxy Resin and Hardener

Glass fiber - Bidirectional woven textile

Environmental Study on GFRP Composite Laminates


Figure 2.2 Bidirectional woven textile

C. Fabrication of Material

The fabrication of the polymer matrix composites was done at room temperature. The

required ingredients of resin and hardener were mixed in beaker and the mixture used to

laminate the material. A ten layered structure was formed as per ASTM standards. Then the

material kept for 24hrs to set properly.

Figure 2.3 Fabrication of Composite

D. Cutting of Samples

A diamond cutter was used to cut each laminate into smaller pieces, having dimensions of

250x25x3mm for tension test and 127x12.7x3mm for flexural test. This was done in

accordance with ASTM standards.

Figure 2.4 Samples



E. Accelerated Environmental Testing In GFRP

The basis for this test as an indicator of the long term behavior of fiber reinforced composites

is that elevated temperature and moisture content accelerate the formation of the products

hydration of the cement in the matrix. Accelerated degradation from the combined action of

temperature and moisture. As a result of these environmental factors, the utility of composite

materials is terminated when the stiffness is reduced sufficiently to cause structural instability,

and/or failure or rupture of the material is induced. The samples are immersed in water, 3%

of NaCl, engine oil and accelerated at a temperature of 60oC and 95% humidity were placed

in a humid chamber. The samples are tested in above condition in time interval for 2, 4 and 8

days.

- - .

Figure 2.5 Accelerated Aging

F. Three Point Bending

The flexural test measures the force required to bend under three point loading conditions.

The data used to select materials for parts that will support loads without flexing. The data is

often used as an indication of a material stiffness when flexed. Since the physical properties

of many materials (especially thermoplastics) can vary depending on ambient temperature, it

is sometimes appropriate test materials at temperature that simulate the intended end user

environment.

Flexural strength:

S=��

��(�)

Where

P = maximum load (N)

L = support span (min)

b = specimen width (mm)

d = specimen thickness (mm)

Figure 2.6 Schematic of 3-point bend



3. TESTING MACHINES

A. Universal Testing Machine

This UTM used to test the tensile properties of unreinforced and reinforced plastics in the

form of standard dumbbell-shaped test specimens when tested under defined conditions of

pre-treatment, temperature, humidity, and testing machine speed.

Specification:

Company Unico

Load capacity 2.5ton

ASTM D638

Speed of test 50mm/min

Figure 2.7 Universal Testing Machine

Figure 2.8 Hot-Air Oven

B. Hot-Air-Oven

Double walled thermostatically controlled: Inner chamber made of aluminium /stainless steel.

Outer body is made of MILD STEEL. Beaded heading elements are placed under the ribs at

the bottom and sides. Temperature controlled by hydraulic thermoset from 10oC above

ambient to 40oC. Dial setting approximate basis. Correct reading as per L-shape thermometer

fitted on the front panel at the top. Suitable to work on 220 volt A.C supply.

4. RESULTS, DISCUSSION AND INTERPRETATION

FRP composites consist of fiber and matrix. The mechanical behavior or performance of the

composites is determined by the local response of the fiber matrix. There is load transfer from



fiber to fibre through the matrix. The region including the contact region between matrix and

fiber extending on both sides, and having some finite thickness called as interphase. The

interphase possesses unique properties to the bulk matrix. It can include impurities un reacted

polymers components non polymerized additives etc. The thickness and properties of this

interphase have crucial impact on the composite properties. Apart from allowing the load

transfer between fibers through matrix, interphase provides a match of chemical and thermal

compatibility between the constituents.

Below are the variations of moisture content with time for different mediums.

A). SAMPLES IMMERSED IN WATER:

Table 1 environmental conditions in water

Test method ASTM D638,D790,D573

Test condition Temperature 60oC, humidity 95%

Room temperature 23oC

Relative humidity 50%

Table 2 variation of mechanical properties

GFRP Before

aging

After Aging in Water

48 hours 96 h0urs 192 hours

Tensile strength, N/mm2 215.3 214.86 208.95 211.63

Flexural Strength, n/mm2 26.40 25.96 24.81 21.97

Difference in Weight, g - 0.2 .36 .41

B). SAMPLES IMMERSED IN 3% NaCl:

Table .3 environmental conditions in Nacl

Test method ASTM

D638,D790,D573

Test condition Temperature 60oC,

humidity 95%




GFRP Before aging After Aging in 3% Nacl

48 hours 96 hours 192 hours

Tensile strength,

N/mm2 215.3 213.42 207.46 210.23

Flexural Strength,

n/mm2 26.40 25.83 23.75 20.62

Difference in

Weight, g 0.1 .32 .38



c). SAMPLES IMMERSED IN ENGINE OIL

Table .5 environmental conditions engine oil

Test method ASTM

D638,D790,D573

Test condition Temperature 60oC,

humidity 95%




GFRP Before aging After Aging in Engine Oil

48 hours 96 hours 192 hours

Tensile strength, N/mm2 215.3 213.02 206.27 209.48

Flexural Strength,n/mm2 26.40 25.81 22.10 19.83

Difference in Weight, g - 0.1 .2 .32

5. LOAD Vs ELONGATION IN TENSILE STRENGTH TEST

Table .7 Tensile strength test for sample after-48 hrs aging in Engine oil:

Breaking load 14869 N

Elongation at break 2mm

Percent elongation 9.1%

Tensile strength 2171.5kg/sq.cm

213.03MPa

Figure 2.9 Load Vs Elongation in sample after aging in 48-hrs in Engine oil

Table .8 Tensile strength test for sample after-48 hrs aging in 3% NaCl:




Tensile strength 2175.6kg/sq.cm

213.42MPa



Figure 2.10 Load Vs Elongation in sample after aging in 48-hrs in 3% NaCl.

Table .9 Tensile strength test for sample after-96 hrs aging in water




Tensile strength 2129.9kg/sq.cm, 208.95MPa

Figure 2.11 Load Vs Elongation in sample after aging in 96-hrs in water

Table .10 Tensile strength test for sample after-96 hrs aging in Engine Oil:


Elongation at break 2.5 mm

Percent Elongation 11.45 %

Tensile strength 2102.7 kg/sq.cm, 206.27 MPa

Figure 2.12 Load Vs Elongation in sample after aging in 96-hrs in Engine oil.



Table.11 Tensile strength test for sample after-96 hrs aging in 3% NaCl



Percent elongation 12.3 %

Tensile strength 2114.8 kg/sq.cm, 207.46MPa


Table.12 Tensile strength test for sample after -192 hrs aging in water




Tensile strength 2157.3 kg/sq.cm 211.63MPa

Figure 2.14 Load Vs Elongation in sample after aging in 192-hrs in water.

Table .14 Tensile strength test for sample after-192 hrs aging in Engine Oil:


Elongation at break 2 mm



Figure 2.15 Load Vs Elongation in sample after aging in 192-hrs in Engine Oil.



Table 13 Tensile strength test for sample after-192 hrs aging in 3% NaCl:


Elongation at break 2 mm




6. MOISTURE ABSORPTION OF SAMPLES AGING IN DIFFERENT

ENVIRONMENT

6.1. MOISTURE CONTENT IN WATER

The graphical representation shows the absorption of water in the GFRP samples in

accelerated environment.

Figure 2.17 Moisture content Vs square root time in water

6.2. MOISTURE CONTENT IN 3% NaCl

The graphical representation shows the absorption of 3%NaCl in the GFRP samples in

accelerated environment.

Figure 2.18 Moisture content Vs square root time in 3% NaCl



6.3. MOISTURE CONTENT IN ENGINE OIL

The graphical representation shows the absorption of Engine Oil in the GFRP samples in

accelerated environment

Figure 2.19 Moisture content Vs square root time in Engine Oil

7. DEGRADATION IN FLEXURAL STRENGTH OF SAMPLES AGING

IN DIFFERENT ENVIRONMENT

7.1. SAMPLES IN WATER

The following graph shows the degradation in flexural strength of GFRP samples immersed

in water at 60oC with 95% of humidity. The strength were tested in period of time interval 2,

4 and 8 days.

Figure 2.20 Degradation in flexural strength agter aging in water.

7.2. SAMPLES IN 3% NaCl


in 3% NaCl at 60oC with 95% of humidity. The strength were tested in period of time interval

2, 4 and 8 days.

Figure 2.21 Degradation in flexural strength agter aging in 3% NaCl.



7.3. SAMPLES IN ENGINE OIL


in Engine oil at 60oC with 95% of humidity. The strength were tested in period of time

interval 2, 4 and 8 days.

Figure 2.23 Degradation in flexural strength agter aging in Engine oil.

8. COMPARISION OF FLEXURAL STRENGTH DEGRADATION IN

DIFFERENT ENVIRONMENT

The following graph shows the degradation of flexural strength in the environment like water,

NaCl, Engine Oil. The strength degradation is high in engine oil compare to water and NaCl.

Figure 2.24 Comparion of Degradation in flexural strength

9. DEGRADATION IN TENSILE STRENGTH OF SAMPLES AGING IN

DIFFERENT ENVIRONMENT SAMPLES IN WATER

The following graph shows the degradation in Tensile strength of GFRP samples immersed in

water at 60oC with 95% of humidity. The strength were tested in period of time interval 2, 4

and 8 days.

Figure 2.25 Degradation in Tensile strength agter aging in water.



9.1. SAMPLES IN 3% NaCl


3% NaCl at 60oC with 95% of humidity. The strength were tested in period of time interval 2,

4 and 8 days.

Figure 2.26 Degradation in Tensile strength agter aging in 3% NaCl.

9.2. SAMPLES IN ENGINE OIL


Engine oil at 60oC with 95% of humidity. The strength were tested in period of time interval

2, 4 and 8 days

Figure 2.27 Degradation in Tensile strength after aging in Engine oil.

10. CONCLUSION

Glass fiber reinforced composite when exposed to degrading atmosphere like 3% NaCl

solution, water and Engine oil, and this exposure generally decreases the mechanical

properties. It was found experimentally by the accelerated aging method the properties

degraded.

The moisture absorption was found to be maximum in water than 3% NaCl and engine oil.

This diffusivity in moisture decreases the mechanical property of composites by decreasing

the saturation of matrix.

The flexural strength decreases periodically in an aging environment. It decreases more in

engine oil, compared to water and 3% NaCl. The percentage of flexural strength reduces in

the following environment, Water-16.7%, 3% NaCl-21.87%, and engine oil-24.88%

The tensile strength decreases for certain period of time and its strength varies continuous

aging process with elevated temperature but it does not attain its original strength. Therefore

when composites are exposed to different environment the tensile strength decreases. The

percentage of decrease of the tensile strength in the following environment: Water by 2.94%,

3% NaCl by 3.64%, engine oil- 4.14%

Therefore the decrease in flexural strength is more than that of tensile strength in

composites due to environmental degradation.



REFERENCES

[1] Neeti “Assessment Of Small Interactions And Structural Gradient At The Interface Of Frp

Composites By Ftir-Imaging And Dsc Techniques” Department of Metallurgical and

Materials Engineering National Institute of Technology Rourkela 2007

[2] S. K. Rege, S. C. Lakkad “Effect of Salt Water on Mechanical Properties of Fibre

Reinforced Plastics”

[3] Lee, H.; Neville, K. Hand Book of Epoxy Resins, McGraw Hill: New York, NY, 1982.

[4] J. J. Lesko, Mike Hayes, Fred McBagonluri, K. Garcia, Environmental-Mechanical

Durability of Glass/Vinyl Ester Composites in Progress in Durability Analysis of

Composite Systems, Proceedings of the International Conference on Durability of

Composites Systems (Duracosys) Blacksburg, VA 1997.

[5] T.P. Meikandaan and Dr. A. Ramachandra Murthy, Flexural Behaviour of RC Beam

Wrapped with GFRP Sheets. International Journal of Civil Engineering and Technology,

8(2), 2017, pp. 452–469.

[6] T. P. Meikandaan and Dr. A. Ramachandra Murthy, Retrofittng of Reinforced Concrete

Beams Using GFRP Overlays. International Journal of Civil Engineering and Technology,

8(2), 2017, pp. 410–417

[7] Hooper, S. J., Toubia, R. F., and Subramanian, R., “Effects of Moisture Absorption on

Edge Delamination, Part I: Analysis of the Effects of Non uniform Moisture Distributions

on Strain Energy Release Rate,”

[8] Parvati T S and Dr. P.S. Joanna, Double Skin Tubular Columns Confined with GFRP.

International Journal of Civil Engineering and Technology, 7(6), 2016, pp.536–543.

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