Creating Composites that Fail More Gradually

Programme Grant Michael R. Wisnom A. Bismarck, G. Czél, J. Finley, M. Fotouhi, J. Fuller, M. Jalalvand, W. Lee, M. Longana, S. Pimenta, K. Potter, T. Rev, P. Robinson, M. Shaffer, P. Suwarta, X. Wu, H. Yu Creating Composites that Fail More Gradually Carbon/epoxy composites: STIFF, STRONG BUT failure is SUDDEN & CATASTROPHIC Can we add metal-like DUCTILITY? High Performance Ductile Composite TechnologyHiPerDuCT Programme The HiPerDuCT Challenge To create high performance composites that show ductile or pseudo-ductile response 0 100 200 300 400 500 600 0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 12.00% 14.00% 16.00% Stress (MPa) Strain (%) Al 2024-T3 Quasi-isotropic carbon fibre Ductility •Ability to deform nonlinearly without fracture –To achieve more gradual failure –To redistribute load at stress concentrations •Ideally no loss of elastic modulus –true ductility •Shorter term target: pseudo-ductility with loss of modulus due to damage •Increased toughness, energy absorption are additional benefits •Change in secant modulus is key •Elastic-perfectly “plastic” is ideal –maximises load redistribution •Initial focus on tension, but stiffness and strength in other loading modes must be maintained Mechanisms for creating gradual failure 0 200 400 600 800 1000 1200 0.0 0.2 0.4 0.6 0.8 1.0 Strain [%] Stress [MPa] •Fibre reorientation - using excess length e.g. angle plies •Distributed damage e.g. ply fragmentation •Aligned discontinuous composites –slip at interfaces •Ductile fibres 0 200 400 600 800 1000 1200 1400 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Strain [%] Stress [MPa] Mechanisms for Pseudo-Ductility Fragmentation in hybrid laminates Pseudo-ductile hybrid composites Hybrid s e High strain material Low strain material s e s e Hybridisation in QI laminates •UD hybridisation: [45H/90H/-45H/0H]s •Material dispersed •QI hybridisation: [QIG/QIC/QIG]s •Orientation dispersed Symmetry line 45HQIG Glass Carbon Quasi-isotropic pseudo-ductile laminate •[QIG60/QIC60]s tested in 0, 60 and -60 directions. 0 60 -60 0 60 -60 [60G/-60G/0G /0C/60C/-60C]S Fragmentation Dispersed delamination S2-Glass –0.15 mm T300 Carbon –0.03 mm Fotouhi, Jalalvand, Wisnom, 2017a Suppressing stress concentrations •Open-hole tension and sharp notches Fotouhi, Jalalvand, Wisnom, 2017b Other loading conditions •Off-axis tension at 5,10 & 20° •Indentation and impact: Different from conventional composites. Interesting behavior - under investigation •Fatigue: No significant damage for loads up to 80% of fragmentation initiation strain after 100k cycles for UD and QI hybrids Indenter 0 60 -60 θ 0 150 300 450 600 0 2 4 Stress (MPa) Strain (%) 0° off-axis 10° off-axis A new accurate simple tensile test •Standard methods tend to underestimate tensile strength due to stress concentrations at grips •Hybrids can eliminate stress concentration •Fail in gauge section at much higher strain •1.86% vs. 1.5% for TR30 carbon •Gauge section failure even without end-tabs •Gives correct baseline strain, enables proper evaluation of hybrid effect Czél, Jalalvand, Wisnom, 2016b Hybrid effect •Hybrid effects may be overestimated due to incorrect baseline •There is a significant effect, but only for very thin plies •Due to constraint on critical cluster formation Wisnom et al, 2016b Baseline strain from delaminating hybrids Skyflex TR30 carbon/epoxy Hybrid effect Pseudo-ductile hybrids can take advantage of a greater proportion of the carbon fibre strength distribution UD baseline 1.86% First carbon layer fracture in hybrid 2.17% Start of fragmentation 2.23% Fully fragmented 2.36% Wisnom et al, 2016b Overload sensing •Load carrying surface layer or bonded patch •Strain can be tuned by choice of fibre •Wireless and offline •No special training required Ordinary photos, NOT special NDT Wisnom, Czél, Jalalvand, Potter 2016 Fatigue cycle indicator •Can also be applied to monitor subsequent cyclic loading •After initial fracture, sensor ply will gradually delaminate •Linear relation between damage and number of cycles Increasing number of cycles Delamination area Suwarta, Fotouhi and Jalalvand Standard Sensor activation Overloaded bicycle handlebar EN14781 Standard load: 1000 N Applied load: 2700 N Damage visualised at: 1750 N Fuller and Rev Mechanisms for Pseudo-Ductility Fragmentation in angle-plies Fragmentation in angle plies Thin ply angle-ply laminates: •Highly non-linear stress-strain behaviour •Delaminations suppressed Glass-Carbon hybrid laminates: •[Gn/Cm/Gn] layups •Gradual failure via fragmentation of thin carbon plies Combine mechanisms: •Replace glass by angle ply carbon •Fragmentation and fibre rotation [3] [2] [1] Fuller, Jalalvand, Wisnom, 2016 0 200 400 600 800 1000 1200 1400 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Strain [%] Stress [MPa] Carbon-epoxy, 0.03 mm plies, [±265/0]S Three distinct regions of each curve: 1. Initial laminate modulus Damage free Repeatable loading 2. Stress plateau Gradual failure of 0°plies ±θfibre rotations 3. Further loading of ±θ No further increase in load in 0°plies [±265/0]S 2.5% 3.75% - Initial laminate modulus; - plateau stress level; - pseudo-ductile strain; - strength can all be controlled with layup design. 1.5% Vf = 42% 2.22% pseudo=ductile strain (±265/0)s Cyclic response •Unloading - reloading tests follow monotonic response •Similar hysteresis, permanent deformation Normalised reloading modulus Small reduction in modulus 0 –400 MPa due to fragmentation Mixed carbon types [±25/0/±25] •Ultra-high modulus 0˚plies, intermediate modulus ±25˚ •1.6% pseudo-ductile strain, modulus of 135 GPa •Sub-laminate potentially only 0.15 mm thick Wu et al, 2017 Open-hole tension •Open-hole thin ply laminates. •Often brittle failure with no load redistribution. •Ductile thin ply laminates can redistribute stress. Notch Insensitive “ ” Strains from DIC Tension-tension fatigue •Tensile fatigue testing at a frequency of 2Hz, R ratio of 0.1 with various peak loads. •CT-scans shows no damage after cycling at 80%of syield. •Can be operated at up to 80%of syield for 100,000 cycles. Tubular tension member •Tensile testing –Dimensions: 350 mm x ø55 mm –Skyflex thin carbon, [±266/0]s –Bolted joint configuration. –Video extensometry for strains. Pseudo-ductility successfully demonstrated. Peak load = 89 kN Max strain = 3.1% Pseudo-ductile strain = 1.2% Fuller and Summers Mechanisms for Pseudo-Ductility Discontinuous composites For AFP application Through-thickness tapered end High deformability –increase capability of steering Stretched during the steering Reduction of stress concentration at the ply drop Coriolis For Additive Manufacturing (3D printing) Markforged Adapting the HiPerDiF process to the production of aligned short fibre reinforced thermoplastic towpreg for 3D printing devices. Potential further applications High performance ductile fibres 010 20 30 40 50 0 100 200 300 400 500 600 PVOH-g-SWNT 40 Stress [MPa] Strain [%] BS ISO 11566, 1996 Modulus : ~45 GPa Strength : up to 1400 MPa Strain : up to 60 % Lee and Shaffer Single wall carbon nanotubes offer high strength and stiffness, high strain to failure, if chemistry and processing are optimised Benefits of Ductility and Pseudo-Ductility •Warning of overload or impending failure: noncatastrophic damage, detectable stiffness change •Ability to still carry load after “failure initiation” until structure can be repaired or replaced •Potential to be able to exploit a greater proportion of the fibre’s ultimate strain •Load redistribution around stress concentrations provides notch insensitivity •Potentially less defect sensitive •Greater energy absorption Typical design limit Conclusions - hybrids •Ply fragmentation in thin-ply hybrids creates a pseudoductile response •Can take advantage of the hybrid effect •Fragmentation also in compression •Multi-directional QI pseudoductility •Notch insensitivity –similar unnotched and open hole QI strengths •Can use for overload sensing 0 200 400 600 800 1000 1200 1400 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Strain [%] Stress [MPa] Increasing number of cycles Conclusions - other approaches •Fibre reorientation in thin-ply angle plies creates additional strain •Can be combined with ply fragmentation •Notch insensitive response •HiPerDiF creates highly aligned, high Vf short fibre composites •Can optimise pseudo-ductile response with different fibres and architectures •Potential for high value products from recycled fibres •High performance ductile CNT fibres created •Opens up exciting new possibilities for composites that fail more gradually References Wisnom, MR., 2016. Mechanisms to create high performance pseudo-ductile composites. IOP Conf. Series: Materials Science and Engineering, 139, 012010. doi.org/10.1088/1757-899X/139/1/012010 Czél G., Pimenta S., Wisnom MR. & Robinson P., 2015. Demonstration of pseudo-ductility in unidirectional discontinuous carbon fibre/epoxy prepreg composites Composites Science and Technology, 106, 10–119, doi:10.1016/j.compscitech.2014.10.022 Czel G., Jalalvand M., and Wisnom MR., 2016a. Design and characterization of advanced pseudo-ductile unidirectional thin-ply carbon/epoxy-glass/epoxy hybrid composites, Composite Structures, 143, 362–370, doi:10.1016/j.compstruct.2016.02.010 Czel G., Jalalvand M. & Wisnom MR., 2016b. Hybrid specimens eliminating stress concentrations in tensile and compressive testing of unidirectional composites, Composites Part A, 91, 436-447, doi.org/10.1016/j.compositesa.2016.07.021 Czel G., Jalalvand M., Wisnom MR. & Czigany, T. 2017. Design and characterisation of high performance pseudo ductile all carbon/epoxy unidirectional hybrid composites. Composites Part B, 111, 348-356, doi.org/10.1016/j.compositesb.2016.11.049 Fotouhi M., Jalalvand M. & Wisnom MR., 2017a. High performance quasi-isotropic thin-ply carbon/glass hybrid composites with pseudo-ductile behaviour in all fibre orientations, Composites Science and Technology, submitted. Fotouhi M., Jalalvand M. & Wisnom MR., 2017b. Notch insensitive orientation-dispersed pseudo-ductile thin-ply carbon/glass hybrid laminates, Composites Part A, submitted. Fuller, JD. & Wisnom, MR., 2015. Pseudo-ductility and damage suppression in thin ply CFRP angle-ply laminates Composites Part A, 69, 64–71, doi:10.1016/j.compositesa.2014.11.004 Fuller, JD., Jalalvand, M. & Wisnom MR., 2016. Combining fibre rotation and fragmentation to achieve pseudo-ductile CFRP laminates, Composite Structures, 142, 155–166, doi.org/10.1016/j.compstruct.2016.01.073 References Fuller, JD. & Wisnom, MR., 2017. Ductility and pseudo-ductility of thin ply angle-ply CFRP laminates under quasi-static cyclic loading, Composites Part A, submitted Jalalvand, M., Czél, G. & Wisnom, MR., 2015. Parametric study of failure mechanisms and optimal configurations of pseudo-ductile thin-ply UD hybrid composites, Composites Part A, 74, 123–131, doi.10.1016/j.compositesa.2015.04.001 Longana, M., Ong, N., Yu, H. & Potter, K., 2016. Multiple closed loop recycling of carbon fibre composites with the HiPerDiF (High Performance Discontinuous Fibre) method, Composite Structures, 153, 271-277, doi.org/10.1016/j.compstruct.2016.06.018 Wisnom, MR., Fuller, JD., Suwarta, P. & Czél, G., 2015. Repeated tensile loading of thin-ply pseudo-ductile laminates, American Society for Composites 30th Technical Conference, Michigan, 28-30 Sept 2015 Wisnom, MR., Czel, G., Jalalvand, M. & Potter, KD., 2016a. Pseudo-ductile hybrid composites with overload sensing capability. American Society for Composites 31st Technical Conference, Williamsburg, Virginia. 19-22 September 2016 Wisnom, MR., Czel, G., Swolfs, Y., Jalalvand, M., Gorbatikh, L. & Verpoest, I., 2016b. Hybrid effects in thin ply carbon/glass unidirectional laminates: accurate experimental determination and prediction. Composites Part A, 88, 131139, doi.org/10.1016/j.compositesa.2016.04.014 Yu, H., Potter, KD. & Wisnom, MR., 2014. A novel manufacturing method for aligned discontinuous fibre composites (High Performance-Discontinuous Fibre method) Composites Part A, 65, 175–185 doi:10.1016/j.compositesa.2014.06.005 Yu, H., Longana, ML., Jalalvand, M., Wisnom, MR. & Potter, KD., 2015. Pseudo-ductility in intermingled carbon/glass hybrid composites with highly aligned discontinuous fibres, Composites Part A, 73, 35–44 doi:10.1016/j.compositesa.2015.02.014 Wu, X., Longana, ML., Fuller, JD. & Wisnom, MR., 2017. Reduced notch sensitivity in pseudo-ductile CFRP thin-ply angleply laminates, Composites Part A, submitted. Thank you for your attention! Programme Grant This work was funded under the UK Engineering and Physical Sciences Research Council Programme Grant EP/I02946X/1on High Performance Ductile Composite Technology, a collaboration between Bristol University and Imperial College, London Acknowledgement