MEANWHILE. ThermoPlastic composites Research Center TPRC proprietary

Transcription

1 Processing and propertiese of thermoplastic composite materials Remko Akkerman 1

2 SCIENCE AND TECHNOLOGY I have not the smallest molecule of faith in aerial navigation other than ballooning, or of the expectation of good results from any of the trials we heard of. So you will understand that I would not care to be a member of the Aeronautical Society. Lord Kelvin, replying to an invitation from Major B. F. S. Baden-Powell to join the Royal Aeronautical Society, Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible. Simon Newcomb, All attempts at artificial aviation are not only dangerous to human life, but foredoomed to failure from the engineering standpoint. Engineering Editor, The Times, The scientist describes what is; the engineer creates what never was. - Theodore von Kármán 2

3 MEANWHILE 3

4 AEROSPACE DEVELOPMENTS Composites share 1978 PEEK invention (ICI) 1982 US patent 4

5 AEROSPACE DEVELOPMENTS Composites share 50% by weight Increasing build rates Automated manufacturing Challenges in processing and materials 1978 PEEK invention (ICI) 1982 US patent 5

6 THERMOPLASTIC COMPOSITES Characteristics Light weight High toughness No chemistry during part manufacturing Excellent fire, smoke and toxicity performance Solvent resistant Corrosion resistant Infinite shelf life Suited for recycling Suited for welding (no adhesives needed) Rapid processing (only heating and cooling). For large series production

7 THERMOPLASTIC COMPOSITES Nevertheless Light weight High toughness No chemistry during part manufacturing Excellent fire, smoke and toxicity performance Solvent resistant Corrosion resistant Infinite shelf life Suited for recycling Suited for welding (no adhesives needed) Rapid processing (only heating and cooling). For large series production

8 CURRENT DEVELOPMENTS Aerospace Applications of TPCs 7000 parts on A

9 COMPOSITES DESIGN Enabled by a wealth of manufacturing processes Material where it is needed in the direction where needed Fibres dominate material properties in the fibre direction Ideally: fibre orientation fibre/matrix properties component properties 9

10 COMPOSITES DESIGN Interrelations: Processing, Properties & Performance process settings fibre orientation fibre/matrix properties product geometry composite properties product properties

11 COMPOSITES DESIGN Looking a bit further. Properties & Performance Mechanical Stiffness Strength Static Impact Fatigue (Hygro)thermal Optical Acoustic Results of Processing Fibre orientation distribution + Residual stresses Partial crystallisation Potentially also defects! Degradation / oxydation Porosity Fibre waviness Delaminations. 11

12 COMPOSITES DESIGN For optimum part quality: 1. Designed & controlled fibre orientation and resulting properties (subject to material & processing constraints) 2. Defect prediction and mitigation Design For Composite Manufacturing 12

13 KEY: F(m,p), ) determined by structure (multiscale) 13

14 KEY: The structure is determined by the processing history Raw Materials Laminates Blanks Assembly Impregnation Consolidation Fibre placement Forming Overmoulding Joining Pre-Preg Component 14

15 EVOLVING STATE AND STRUCTURE Fibre orientation and distribution Consolidation (void generation, migration and dissolution; lamination/healing) Crystallinity Degradation (matrix, fibre, interphase) Residual stresses. 15

16 FULFILLING THE TPC PROMISES Maturing the technology Robust Automated Processing Shorter Cycle Times CAE Tools process We need the whole value chain application material al design 16

17 VALUE CHAIN APPROACH TPRC member base 17

18 RESEARCH CHARACTERISTICS Mechanisms Experimental Characterisation Multi scale Multi physics Constitutive Equations Vacuum Bag Consolidation Stamp Forming Tailored Blanks (AFP & Forming) Overmoulding Material & Process Modelling Design Tools Optimisation of Material Process Design 18

19 Vacuum Bag Consolidation Erik Krämer

20 METHOD Observe waviness formation in AS4-PEEK Light source High resolution camera Vacuum Press plate Glass plate Thermocouples Composite Steel caul sheet 20

21 OBSERVATIONS 23

22 20 C 340 C 24

23 340 C 400 C 25

24 400 C 270 C 26

25 270 C 20 C 27

26 OBSERVATIONS Heating phase Below TT mmmmmmmm : No fiber movement At TT mmmmmmmm : Sudden waviness formation Above TT mmmmmmmm : Minor fiber movement Cooling phase Waviness severity gradually increases New waves are formed Below 270 C, no further fiber movement Viscosity ++ Modulus ++ 28

27 DISCUSSION Driving forces for waviness formation (Heating) At melting point: Prepreg deconsolidation (residual stress, potentially moisture release) Driving forces for increasing waviness (Cooling) Between 370 C C: Tool shrinkage Also the prepreg is a structure with a process history 29

28 Stamp Forming Sebastiaan Haanappel & Ulrich Sachs

29 STAMP FORMING The process 31

30 STAMP FORMING Advancing TPC Technology From Fabrics to Unidirectionals 32

31 DEFORMATION MECHANISMS UD laminates 33

32 1. INTRA-PLY BEHAVIOUR CHARACTERISATION & CONSTITUTIVE MODEL UD shear testing: torsion bar (rheometer) η' [Pa s] ω [rad/s] Cetex Thermo-Lite TC

33 2. INTER-PLY BEHAVIOUR CHARACTERISATION & CONSTITUTIVE MODEL Tool/ply & Ply/ply testing 35 mm 8 mm Pneumatic actuator Automatic alignment 85 mm 50 mm Fixed platen Movable platen 35 R Akkerman et al, Texcomp 2010, p

34 2. INTER-PLY BEHAVIOUR Ten Cate UD C/PEEK tool/ply P=10 kpa P=50 kpa Peak Steady state

35 3. BENDING CHARACTERISATION & CONSTITUTIVE MODEL Kirchhoff transverse shear both 37

36 3. BENDING CHARACTERISATION UD carbon/peek Rate variation Temperature variation 38

37 IMPLEMENTATION Numerical aspects: Very high anisotropy Highly Sensitive to Fibre Directions Use exact (non linearised) strain definition Shear Locking for non-aligned meshes Stiff systems Consistent Tangent Operators to prevent divergence Multi-layer approach With discrete layers Including bending, intra- & inter-ply behaviour 40

38 APPLICATION & RESULTS 41

39 APPLICATION & RESULTS Small shear strains predicted in wrinkle freee areas ε xy Diagonal shear patterns are recognised in both simulation and experiment Waviness in mesh near critical spots with local wrinkling in practise Simulation ε xy Global wrinkling correctly predicted Experiment 42

40 MANUFACTURING DEFECTS Ply splitting/transverse cracks Matrix degradation Voids Dry spots Delaminations Surface defects (due to severe traction or resin squeeze out) Contamination Fibre distortions (folds, wrinkles and waviness) Fibre breakage What can we predict already? And what can we learn from our simulations? 36

41 CONSOLIDATION Dominated by the Pressure Distribution Laminate thickness variation Tool deflection Thicker due to inplane shear Thinner due to stretching 44

42 WRINKLES Developing during the process Excess material can lead to a buckled region, a possible starting point for a fold or wrinkle. The buckled region can develop in various ways 45

43 WRINKLES Developing during the simulation Incomplete tool closure Out-of-plane deformation is dependent on the laminate element size. Large wrinkles or folds can still be visualized by the mesh Medium wrinkles or folds will show only a bump in the mesh Small wrinkles can hardly be visualized by the mesh Large Small Medium Real ply/laminate Simulated ply/laminate 46

44 WRINKLES Large Medium Small Folds Alternating shear Compressive fibre stress 48

45 FIBRE TENSION Consolidation defects and cavity clearance Local high fibre tensions in corners can lead to fiber migration and thinning This can lead to a local cavity clearance This can lead to resin flow (squeeze) into a void cavity 49

46 FIBRE TENSION Consolidation defects and cavity clearance Examples of resin squeeze out: 50

47 FIBRE TENSION Bridging Bridging is accompanied with fibre tension Schematic drawing of bridging Fibre tension Example: Traction due to tool/ply friction High fibre stresses Matrix-rich areas (Poor consolidation) 51

48 PLY SPLITTING (UD) or transverse cracks in woven fabrics Fibres and matrix are not separately modelled, hence splitting is indicated at a more global level in the simulation model. Large transverse strains indicate ply splitting Elements represent homogenized material Tensile strain 52

49 LESSONS LEARNT From using the software It is not only about improving algorithms, but also about understanding the results Users will benefit from better defect indicators (FLD for composites?) Challenging, both experimentally and analytically! 53

50 STAMP FORMING SIMULATION Concluding remarks Current software provides: 1. Reliable results can be obtained for the fibre orientation distribution (subject to material & processing constraints) 2. Useful indicators for a range of defects Further research needed? 1. (always) Better constitutive models 2. Further defect indicators 54

51 Tailored Blank Manufacturing Tjitse Slange

52 TAILORED BLANK MANUFACTURING Background Traditional blank Uniform lay-up Trimming scrap Tailored blank Local reinforcement Thickness Orientation (Near) net-shape Increased performance Reduced weight, scrap & cost Rapid automated lay-up 56

53 TAILORED BLANK MANUFACTURING Critical issues 1) Quality of the tailored blank (required) 2) Discrete thickness steps and discretised contours 3) Positioning accuracy 57

54 1) LAMINATE QUALITY Quality evolution 58

55 1) LAMINATE QUALITY Tape quality evolution Prepreg As received (carbon/peek) A B C

56 1) LAMINATE QUALITY Tape quality evolution Prepreg Deconsolidated A B C

57 1) LAMINATE QUALITY Laminate quality evolution Laminate (A) after AFP deconsolidated after stamp forming

58 1) LAMINATE QUALITY Laminate quality evolution Laminate (B) after AFP deconsolidated after stamp forming

59 1) LAMINATE QUALITY NDI after AFP+stamp forming 20 bar, 390 C Consolidation pressure, blank temperature reference: Pressconsolidated d Consolidation quality improves 20 bar, 390 C 20 bar, 420 C 100 bar, 390 C 100 bar, 420 C after AFP + stamp forming 63

60 1) LAMINATE QUALITY Conclusion Press formed tailored blank carries the history of the prepreg (geometry / thickness & frozen-in stresses) and the blank manufacturing processing steps 67

61 2) DISCRETE THICKNESS STEPS Stamp consolidation of ply drops How to consolidate the gaps? Rapid AFP blanks, stamped at T blank = 420 C, P cons = 100 bar 4 ply drops, different orientations 68

62 2) DISCRETE THICKNESS STEPS Before stamping Large voids in pockets due to rapid placement 69

63 2) DISCRETE THICKNESS STEPS Influence of Orientation (after stamp forming) Transverse flow of plies with fibres parallel to the drop (90 between 0 or 0 between 90, but also 0 between ±45 ) Transverse flow 70

64 2) DISCRETE THICKNESS STEPS Influence of Orientation (after stamp forming) Transverse flow of plies with fibres parallel to the drop (90 between 0 or 0 between 90, but also 0 between ±45 ) Matrix flow 71

65 2) DISCRETE THICKNESS STEPS Influence of Orientation (after stamp forming) Transverse flow of plies with fibres parallel to the drop (90 between 0 or 0 between 90, but also 0 between ±45 ) Matrix flow 72

66 DEMONSTRATOR TAILORED SPAR 73

67 DEMONSTRATOR TAILORED SPAR Blank design and lay-up Near net-shape 200 mm/s AFP minimum fiber length: ~100mm Marking for blank-tooling alignment check Trimmed blank 75

68 DEMONSTRATOR TAILORED SPAR Stamp forming Tooling engraving + laser cross for alignment check Cycle time 5 min 76

69 DEMONSTRATOR TAILORED SPAR Consolidation quality Ply-drops well consolidated (visual inspection only, no microscopy) 78

70 DEMONSTRATOR TAILORED SPAR Consolidation quality: C-scan No defects observed (3 of 5 scanned) GKN/Fokker quality standard approved Ply-drops Alignment marks Reference mark 79

71 DEMONSTRATOR TAILORED SPAR Forming defects In-plane waviness near inner radius Ply splits at bottom side 80

72 DEMONSTRATOR TAILORED SPAR Warpage All spars show same twist direction, but magnitude varies 81

73 DEMONSTRATOR TAILORED SPAR Discussion Cavity vs blank thickness is critical Draft angle in the flange inplane shear thickness increase Increased flange thickness High traction in flange Lack of pressure in web Predictive modelling can help to identify these issues: Ply splits Small wrinkles Dry spots if locally the laminate pressure is too low 82

74 DEMONSTRATOR TAILORED SPAR Concluding remarks Promising results Rapid AFP lay-up + stamp forming No additional preconsolidation Reduced scrap & weight: Near net-shape lay-up: 12% Tailoring: 21% (25% part weight) Total material savings: 30% Weight (g) % 30% 25% Pre-forming scrap Post-forming scrap Final part Conclude? 83

75 Overmoulding Mark Bouwman, Jeroen Houwers, Thijs Donderwinkel, Coen Hartjes, Sebastiaan Wijskamp 84

76 OVERMOULDING Process Overview Overmoulding = stamp forming + injection molding Short cycle times Net shape manufacturing Integration of reinforcing ribs / functionality One-step process: forming and injection molding combined into one process Two-step process: forming and injection molding performed separately 85

77 86 Overmoulding partners:

78 WHAT IS THE PART QUALITY? What about geometric accuracy? Shrinkage & Warpage: how much, where, how to correct for this? What about mechanical performance? Of the laminate, the overmoulded resin, and most of all: the interface! Expensive tooling aim for right first time manufacturing 87

79 INTERFACE STRENGTH Overview Goal: develop a simulation tool to predict the interface strength Autodesk Moldflow for injection molding simulation Relatively simple models for strength modelling Polymer interdiffusion Melting behavior D h 1 Experimental characterization: Tensile / shear coupons Overmolded V-shape 0 88

80 INTERFACE STRENGTH Experimental characterization Overmoulded V-shape 3PB of a single rib section: F 4PB of a single rib: F/2 F/2 F/2 F/2 F/2 F/2 Preference for failing on one side (in agreement with healing model) Higher strength Debonding at the interface followed by rib cracking Comparison (verified with high speed fps) with D h? Test Result FEM (Abaqus) 89

81 SHAPE DISTORTIONS Overview Overmoulding = stamp forming + injection moulding Software coupling: AniForm data: - Fiber orientations - Shear angles - Thickness changes - Fiber stresses Thermo-mechanical model for laminate insert: - CTE (T) - Crystallization shrinkage 90

82 SHAPE DISTORTIONS Validation and conclusions Single curved geometry Double curved geometry initial shape warped shape Accuracy of the warpage analysis is significantly improved by including: Thermo-mechanical model for laminate insert Forming induced effects (coupling between AniForm and Moldflow)

83 DEMONSTRATOR MANUFACTURING At TPRC Industrial injection moulding machine suitable for C/PEEK Equipped with KUKA Robot and Krelus IR oven 92

84 DEMONSTRATOR MANUFACTURING Demonstrator geometry and mold Rib-stiffened panel C/PEEK on C/PAEK (Victrex AE250) One-step and two-step process cold runner net-shape 93

85 DEMONSTRATOR MANUFACTURING Overview: Two-step overmolding process Blank: Stamp forming Trimming Overmoulding Shell part remains below T m Insert with lower melting temperature is beneficial for the interface strength 94

86 DEMONSTRATOR MANUFACTURING Overview: One-step overmoulding process Blank: After forming (without injection) Forming + Overmolding Fiber migration & resin squeeze out Sink marks at back side 95

87 DEMONSTRATOR Microscopy cross sections Overmoulding of ribs on a laminate Two-step overmolding process One-step overmolding process 0.5 mm Cracks visible Thin section in radius freezes off quickly Less polymer interdiffusion and less packing Radius is not recommended for two-step process Fiber migration Higher interface strength Influence on laminate performance? Currently investigated 96

88 DEMONSTRATOR Microscopy cross sections Overmoulding of laminate edges Two-step overmoulding process One-step overmoulding process Poor interface strength observed Use material overlap Laminate 0.5 mm Insert penetration by polymer flow Good interface strength 97

89 CONCLUSIONS AND OUTLOOK Overmoulding Conclusions: Processability proven for one-step & two-step C/PEEK on C/PAEK Developed models to simulate: Interface strength Residual stresses and shape distortions Extension to structural performance analysis 98

90 Overall Conclusion

91 CONCLUSION Processing and Properties are tightly linked for Thermoplastic Composites For various processes (OOA, stamp forming, AFP, overmoulding, ) the P rocess Structure P roperty relations are gradually unveiled 100

92 Thank you for your attention Remko Akkerman