Micromechanics of recycled composites

Transcription

1 Monday, 21 st August 2011 Micromechanics of recycled composites for material optimisation and eco-design Soraia Pimenta S T Pinho, P Robinson

2 Motivation Introduction recycled Composites: sustainable key for the future 100 CF use (1000 ton/year) Recycled Carbon Fibre Ltd Boeing 25 Acmite Market Intelligence,

3 Recycling CFRP Introduction CFRP waste Recycled Carbon Fibre Ltd. Boeing Pyrolysis / Oxidation / Solvolysis Recycled CFs Similar response (vs. virgin) 223 GPa 3.6 GPa For a fraction of the cost! /kg 3-10 kwh /kg E f X f price energy

4 Recycling CFRPs for structural applications Introduction wheelhouse Pickering et al., U. Nottingham, 2009 door panel Janney et al., Mater. Innov. Tech., 2009 F3 car structure arm rest George et al., Boeing 2009 Meredith et al. U. Warwick, 2009

5 Recycling CFRPs for structural applications Introduction Material optimisation Understanding response Design methods Damage tolerance Fracture toughness

6 Objective Introduction Understanding Experimental Fracture toughness of recycled CFRP Modelling Design framework for engineers Guidance for material optimisation

7 Experimental Introduction Experimental Conclusions

8 Materials Experimental CFRP waste Recycled CFRPs A B C

9 Mechanical properties Experimental Stiffness E T /ρ 10 6 m 2 /s 2 Strength X C /ρ 10 3 m 2 /s A B C Al GFRP 0 A B C Al GFRP

10 Microstructure Experimental Multiscale reinforcement single clean fibres + bundles with residual matrix 0.5 mm

11 Architecture Experimental Different degrees of bundling Bundle width distribution 100% 80% 60% 40% 20% 0% 0.5 mm 0.5 mm A B C Bundle width (mm) 0.5 mm

12 Toughening mechanisms Experimental Compact tension testing Fractography Optical microscopy SEM analysis

13 CT tests Experimental Fracture toughness vs. fracture surface G c kj/ m A Crack extension (mm)

14 Experimental Failure of bundles Bundle pull-out Single-fibre pull-out Multiscale Self similar

15 Failure of bundles Experimental Defibrillation Hierarchical failure 500 μm 100 μm 50 μm

16 CT tests Experimental Fracture toughness vs. fracture surface G c kj/ m B Crack extension (mm)

17 CT tests Experimental Fracture toughness vs. fracture surface G c kj/ m C Crack extension (mm)

18 Fracture toughness Experimental Comparison G c kj/ m Bundles Toughness C B A Crack extension (mm)

19 Introduction Experimental Conclusions

20 Objective Understanding Experimental Fracture toughness of recycled CFRP Modelling Design framework for engineers Guidance for material optimisation

21 Physical basis Toughening mechanisms: pull-out & failure Multiscale problem Consistent mechanisms throughout the scales

22 Strategy Energy dissipation fibre / bundle Probability of failure vs. pull-out Integration over microstructure G c = 1 A s Ω Prob F W F + Prob PO W PO dω

23 Probability of failure Prob F Challenge: Fibre / Bundle strength distribution with size effects Debonding stage

24 Probability of failure Prob F Approach: extending the Weakest Link Theory Length Filament count 100% F(σ) 75% 50% 25% 0% σ (GPa)

25 Probability of failure Prob F Failure of bundle with 2 fibres Perfect plastic matrix Stress concentrations within recovery distance Final failure requires matrix yielding between breaks

26 Probability of failure Failure of bundles Prob F Probability of failure of 2-fibres bundle F 2 u = 1 1 F 1 u F 1 u 2 1 F 1 u 1 F 1 k F i + 1 = f F(i) Hierarchical failure

27 Probability of failure Prob F Results 100% F i (σ) X avg (GPa) 8k 2 Increasing interfacial strength 75% MPa 50% 4 input 52 MPa Okabe & Takeda (2002) 25% 0% single fibre σ (GPa) ,000 1,000,000 n f

28 Strategy Energy dissipation fibre / bundle Probability of failure vs. pull-out Integration over microstructure G c = 1 A s Ω Prob F W F + Prob PO W PO dω

29 Bundle fracture work W F Challenge: size effect on toughness G UD (kj/m 2 ) Laffan et al Laffan et al. (2010) Laffan et al t (mm)

30 Bundle fracture work Approach W F Fractal fracture surface Self-similar failure

31 Bundle fracture work W F Pull-out length 2.5 avg l PO (mm) 0 lpo 1 l PO l PO i

32 Bundle fracture work W F Validation W F = l PO t μ l PO x dx avg l PO (mm) G UD (kj/m 2 ) Laffan et al. (2010) CoV = 22% CoV = 14% Increase fibre strength variability i t (mm)

33 Strategy Energy dissipation fibre / bundle Probability of failure vs. pull-out Integration over microstructure G c = 1 A s Ω Prob F W F + Prob PO W PO dω

34 Pull-out work FE simulation W PO

35 Pull-out work W PO Pull-out of inclined fibres Beam theory fibre deflection v (4) = k el E I v v (4) = 0 Elastic reaction q el = k el v l emb k el v x l uns = x s PO δ =

36 Pull-out work W PO Pull-out of inclined fibres Beam theory fibre deflection v (4) = k el E I v v (4) = 0 Elastic reaction q el = k el v Pin-load based solution Contact pressure p el θ cos θ q el Frictional dissipation p el (θ) q el t θ θ w

37 Pull-out work Validation W PO W PO (10 6 J) k el = 20 GPa k el = 9.5 GPa k el = 4 GPa FE modelling 0.0 Fu & Lauke φ ( )

38 Strategy Energy dissipation fibre / bundle Probability of failure vs. pull-out Integration over microstructure G c = 1 A s Ω Prob F W F + Prob PO W PO dω

39 Validation Experimental G c kj/ m C B A Crack extension (mm)

40 Validation 100% 75% 50% F 1 (σ) Single fibre tensile tests PDF Architecture characterisation orientation ( ) 25% % σ (GPa) 100% CDF % 60 P (mn) 0% length (mm) Single fibre pull-out tests 100% 50% CDF u (μm) 0% width (mm)

41 Validation Experimental vs. G c kj/ m C B A Crack extension (mm)

42 Parametric studies 5 4 = 1.00 = 0.75 A 3 = = Crack orientation, ( ) 2 1

43 Parametric studies Fibre modulus Measured modulus Fibre strength Measured strength C Fibre modulus (GPa) Fibre strength (GPa)

44 Conclusions Introduction Experimental Conclusions

45 Conclusions Conclusions Understanding Multiscale reinforcement Role of fibre bundles Toughening: pull-out & fracture Self similar mechanisms Fracture toughness of recycled CFRP Design framework for engineers Guidance for material optimisation Recycled + Virgin? Modelling Probabilistic model Hierarchical bundle strength Fractal fracture surfaces Pull-out of inclined fibres / bundles

46 Acknowledgments Conclusions Funding Portuguese Foundation for Science and Technology Materials and consultancy H.K.Wong & S.J.Pickering, University of Nottingham P.George & W.Carberry, The Boeing Company Collaboration from Imperial students J.Castella-Martin & H.Wazni

47 Monday, 28 th August 2011 Micromechanics of recycled composites for material optimisation and eco-design Soraia Pimenta S T Pinho, P Robinson