bristol composites institute (accis) research speakers ... · pseudo-ductility of unidirectional...

Chair: • Marco Longana

• Ian Gent

Bristol Composites Institute (ACCIS) Research

Showcase: Session 2Speakers:• Aakash Paul (presentation not included)

• Putu Suwarta• Rita Palumbo• Jiajia Shen• Alexis Kordolemis

Pseudo-ductility of Unidirectional Thin-Ply Hybrid Composites in Longitudinal Compression

Putu Suwarta, Gergely Czél, Mohamad Fotouhi, Jakub Rycerz, Michael R. Wisnom

ACCIS conference 2018

22-11-2018

1

STIFF & LIGHTWEIGHT

2

Advantages:

Carbon Fibre Composites

Disadvantages:

BUT Failure is BRITTLE & CATASTROPHIC

Pseudo‐ductility of Unidirectional Thin Ply Hybrid Composites in Longitudinal Compression

3DUCTILITY for Safety

Gradual and progressive failure

Visible deformation beforefailure

High Performance Ductile Composites Technology


4The HiperDuct Challenge

• Is it possible to create high performance composites that showductile or pseudo‐ductile response??

• To impart gradual failure in composites.• Retain high strength and stiffness in various loading condition.• Adding benefits:‐ Benign failure‐ Increased damage tolerance‐Warning of overloading‐ Greater work of fracture


5Challenge in Compression

• Is it possible to impart gradual failure of composites inlongitudinal compression?

• To explore the pseudo-ductile behavior of UD glass/thin plycarbon hybrid composites in longitudinal compression.

• To understand the key micro-mechanisms active in UDglass/carbon hybrids under longitudinal compression.


6Compression Properties of Composites

• Typical failure mode in compression : brittle and sudden.

• Stress‐strain curve ofcarbon/epoxy under longitudinalcompressive loading [1].

• Kink band governed by shearinstability [1].

• Dictate final failure incompression.


7Specimen Geometry for Longitudinal CompressionSpecimen

ConfigurationWidth

nominal[mm]

Thickness nominal[mm]

Glass Layers

Carbon Layers

s

[SG1/(C1/SG1)17] 10 3.31 18 17 12.5[SG1/(C2/SG1)17] 3.83 34 10.8[SG1/(C3/SG1)17] 4.35 51 9.5

Slenderness ratio :

Lg : gauge length = 12 mm

t : nominal thickness

To avoid buckling, s should be below 20[2]


8TABLE I. FIBRE PROPERTIES OF THE APPLIED UD PREPREGS [3]

Fibre type Manufacturer E ρ εt σt

( GPa) (g/ cm3) ( % ) ( GPa )

Torayaca M55JB Toray 540 1.91 0.8 4.02

FliteStrand S ZT S‐glass Owens Corning 88 2.45 5.5 4.8‐5.1

TABLE II. CURED PLY PROPERTIES OF THE APPLIED UD PREPREGS [3]

Prepreg type Fibre mass per unit area (g/m2)

t Vf Ei εt εc

( m) (%) (GPa) (%) (%)

M55 carbon/epoxy 30 30.5 52 280a 0.6b 0.26b

S‐glass/epoxy 190 155 51 45.7 3.98 [5] 2.33b

a calculated for the given volume fraction.b based on manufacturer’s data for 60% carbon fibre volume fraction.


9Experimental Technique

Imperial College compression test rig

Strain measurement using video gauge:

Speckle pattern for deformation tracking


10Stress-Strain Curve


11


Change in Slope due to Fragmentation

[SG1/(C1/SG1)17]

[SG1/(C2/SG1)17][SG1/(C3/SG1)17]

Interrupted test at -0.80% strain

Interrupted test at -0.41%

12Progressive Failure under Compression• 4PB testing to study the damage

behavior of UD hybrids undercompression [3]


13Fragmented Carbon Layers

• Optical microscopy images ofcarbon layer cracks showingsliding displacement.

Carbon strain: ‐1.2%0%


14Micro-Damage Mechanisms

• Carbon layers were still able to transfer axial load between them through thefragmented surface.

• The load between glass/epoxy and carbon/epoxy layers is transferred primarilythrough direct compression mechanism.

• Sliding displacement is responsible for local delamination.

FF

Glass/epoxy

Glass/epoxy

Carbon/epoxy

Sliding Localdelamination

Specimen’s top surface


[4]

15Strain vs Carbon Layer Thickness

• Energy release rate increases with the thickness of carbon layers.• Delamination occurs at lower strain with increasing thickness of carbon

layers.


16Conclusions

• Pseudo‐ductile behaviour under longitudinal compression has been obtained for

[SG1/(C1/SG1)17] and [SG1/(C2/SG1)17] laminates.

• The responsible mechanisms for decrease of stiffness for [SG1/(C1/SG1)17] and

[SG1/(C2/SG1)17] laminates was carbon fibre fragmentation and dispersed

delamination.

• The carbon layers fragmented at a lower strain than in tension.

• After carbon layers fragmented the stress rises further due to the ability of the

layers to still transfer load.

• The different damage behaviours underpin the crucial role of carbon layer

thickness and carbon/glass volume ratio in unidirectional glass/carbon hybrid

laminates under longitudinal compressive loading.


17References

1. Daniel ,I.M., Hsiao, H.M., Is there a thickness effect on compressive strength ofunnotched composite laminates?” , Int. Journal of Fracture, vol. 95, no. 6, pp.143–158, 1999

2. Häberle, J. G. and F. L. Matthews, “An improved technique for compressiontesting of unidirectional fibre-reinforced plastics; development and results,”Composites, 25(5): 358–371, 1994

3. G. Czél, M. Jalalvand, M.R. Wisnom, Hybrid specimens eliminating stressconcentrations in tensile and compressive testing of unidirectional composites,Composites Part A: Applied Science and Manufacturing, 91, pp.436-447, 2016

4. G. Czél, P.Suwarta, M. Jalalvand, M.R. Wisnom, Investigation of the compressionperformance and failure mechanism of pseudo-ductile thin-ply hybrid composites,21st International Conference on Composite Materials, Xi’an, 20-25th August 2017

[email protected]

18

Putu Suwarta

Thank you for your attention!

Acknowledgements

A multi-scale-reinforced sandwich panel for vibroacoustic applications

Rita Palumbo

11th ACCIS Annual Conference

22/11/2018

1

Main target: inclusion of vibroacoustics design rules at early stages of products development, through the use of periodic

media.

VIPER project2

European Joint Doctorate network focused on VIbroacoustics of PERiodic media

November the 22nd, 2018

11th ACCIS annual Conference

Project consortium3

Beneficiaries

Academic and industrial partners

ESR project duration: 36 monthsTime to spend on Secondments: 10 months

12 Early Stage Researchers (ESRs)



ESRs4

ESR project duration: 36 monthsTime to spend on Secondments: 10 months

• Primary focus on scientific research• Exposure to the non-academic sector• Secondments• Curricular trainings• Extra-curricular trainings (transferable skills)• Technical schools twice a year• Special sessions within conferences• Social events and networking



ESR 8 – PhD position within VIPER5

Main Institution:University of Bristol, Bristol Composites Institute

Supervision:Fabrizio Scarpa, Professor of Smart Materials & StructuresDmitry Ivanov, Senior Lecturer in Aerospace Engineering

Joint Institution:Ecole Centrale de Lyon, Laboratory of Tribology and Systems Dynamics (LTDS),

Vibro-Acoustics and Complex Media Research Group (ViAME)

Supervision:Mohamed Ichchou, Professor of Solid MechanicsOlivier Bareille, Associate Professor

Partners:Prof. Noureddine Atalla Dr. Luca LanziSupervision:



ESR 8 – Research contribution to VIPER6

www.stressebook.com/solid‐metal‐versus‐sandwich‐panels/ http://www.econcore.com/en/marketshttps://www.limetech.asia/

https://www.polskieradio.pl/

High bending stiffness

Low density Versatility - skins

and core’s materials

Wide range of applications



Sandwich panels


High specific bending stiffness

Sandwich panelsGood mechanical performances

Poor vibroacoustic behaviour

Main thesis objective: manufacturing of a sandwichpanel with enhanced vibroacoustics performances.Methods: adoption of novel materials andmanufacturing techniques.




: core shear transition frequency

F. Fahy, P. Gardonio, Sound and Structural Vibration: Radiation, Transmission and Response, Academic Press, second edition (2007)

Fundamental indicator of the

macro-behaviour of sandwich panels



Target: increasing as much as possible

Design solutions – topology and material 9

Square cell:• Industrial applications• Easy to model and

manufacture• Focus on the material

Biotex Flax 400gr/m2 2x2 twill :• High vibration damping• Low density• Good environmental impact• Cheap

PFA resin:• Bio-resin• Sustainable• Fire-retardant



Design solutions – viscoelastic inserts10

CNT-reinforced resin:deposited by means of LiquidResin Printing (LRP)

CNT-reinforced resininjected at the corners

• Core stiffening• Core strengthening• Increased vibration

damping (nanotubes stick-slip mechanism)



Results: shear transition frequency11

yz

ATOP ABASE

hCOREATOP

: panel with inserts , : panel without inserts

Results obtained applying Guillaumie’s exact analytic formula, where the shear modulus is evaluated numerically. Core walls lay-up sequence: 0/90



Future work12

• Panels manufacturing for vibroacoustics and static characterization tests

• Vibration and acoustics tests

• Numerical wave propagation characterization

• Static characterization (flatwise compression)

• Materials characterization of flax prepreg and reinforced resin



Acknowledgements13



This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation

programme under the Marie Skłodowska-Curie grant agreement No 675441.

Thank you for your attention!Rita [email protected]

14

Virtual testing of experimental path‐following

Rainer M.J. Groh, Alberto Pirrera, Mark Schenk, Robin M. Neville, Jiajia Shen

Bristol Composites Institute (ACCIS) Conference 201822 November 2018

1

Outline2

• Background

• Method and implementation

• Virtual testing results and verification

• Concluding remarks

3

Background

Force

Deflection

Deflection

Force

Snap-through

Snap-back

• Emerging use of well‐behaved nonlinear structures for shape adaption, energy absorption, energy harvesting, etc.e.g. adaptive structures for flow control (from G. Arena et al. (2018))

4

Disp.

Force

ForceForce

Force Force

Disp.Disp.

Disp. Disp.

Traditional testing methods and limitations

Disp.limit

Disp.limit

Force limit

Force limit

Inaccessible

5

Shape control – decouple disp. and forceProbes Actuation point

Virtual testing environment6

• Key features:

Provides an efficient and economical way to design a experimental setting for nonlinear structures.

Digital twin of the experimental setting (nonlinear structure + probes + actuation point) in the FE package ABAQUS.

Using the arc‐length method to traverse limit points and path‐follow the unstable path.

Modular functionality and versatile for a variety of different structures.

7

Results and verification• Example 1.1: shallow arch with one pair of probes.

8

Results and verification• Example 1.2: shallow arch with different probe locations

Results and verification9

• Example 2: shallow roof with two independent pairs of probes.

Concluding remarks 10

• The proposed experimental path‐following method can traverses limit points and path‐follow along nonlinear unstable equilibrium curves.

• The virtual testing environment provides a robust tool for future experiment design of novel nonlinear structures.

Acknowledgements11

• RMJG is supported by the Royal Academy of Engineeringunder the Research Fellowship scheme [RF/201718/17178].

• AP is funded by the Engineering and Physical Sciences Research Council (EPSRC) under their Research Fellowship scheme [EP/M013170/1].

• RN is supported by the EPSRC under grant number [EP/N509619/1]. • The support of all funders is gratefully acknowledged.

Thank you!Questions?

12

Estimation of microstructural lengths through homogenization of corrugated panelsAlexis Kordolemis, Paul M. Weaver

ACCIS Conference – Research Showcase

22-11-2018

1

Multiscale Analysis2

Corrugated panel Flat Plate (Strain gradient)

Research Showcase – 22/11/2019

ACCIS Conference

Generalised Continuum Theories


ACCIS Conference

3

Cauchy’s postulate: no longer valid

Different theories: Cosserat, micropolar, micromorphic, strain gradient, couple stress, etc.Our analysis: Strain gradient theory

,,ij ij kU U ε ε

Shell Theory – Analytical Solution


ACCIS Conference

4

Thin Shell Theory Governing equationsSolving governing equations for six load cases Closed form expressions for material stiffnesses

Validation with FEA


ACCIS Conference

5

Orthotropic strain gradient theory


ACCIS Conference

6

Constitutive law of a thin flat orthotropic plate

Material stiffness

Models comparison - Energy approach

Thanks for your attention!

[email protected]

7

bristol composites institute (accis) research speakers ... · pseudo-ductility of unidirectional...

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