Browsing by Author "Petrinic, Nik"
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Item Open Access Analyzing the failure and damage of FRP composite laminates under high strain rates considering visco-plasticity(Elsevier, 2019-03-19) Eskandari, Sina; Andrade Pires, Francisco M.; Camanho, Pedro P.; Cui, Hao; Petrinic, Nik; Marques, Antonio T.In order to analyze composite structures under dynamic condition or model manufacturing processes in which high strain rates exist, it is important to develop a constitutive model that regards these effects. In this work, a phenomenological approach is used to formulate a continuum damage for composites in presence of high strain rates. Visco-plastic behavior of the composite is taken into account and the deformation of composite structures under dynamic conditions is studied. Effects of dynamic conditions on the material properties including strength and fracture toughness are included in the modeling. The model can capture the effects of strain rate on material behavior and has a good capability in the prediction of the response and final strength of composite laminates in comparison with the experimental data under medium and high rates.Item Open Access Bridging mechanisms of through-thickness reinforcement in dynamic mode I&II delamination(Elsevier, 2017-04-13) Cui, Hao; Yasaee, Mehdi; Kalwak, Gordon; Pellegrino, Antonio; Partridge, Ivana K.; Hallett, Stephen R.; Allegri, Giuliano; Petrinic, NikZ-pin through-thickness reinforcement is used to improve the impact resistance of composite structures; however, the effect of loading rate on Z-pin behaviour is not well understood. The dynamic response of Z-pins in mode I and II delamination of quasi-isotropic IM7/8552 laminates was characterized experimentally in this work. Z-pinned samples were loaded at both quasi-static and dynamic rates, up to a separation velocity of 12 m/s. The efficiency of Z-pins in mode I delamination decreased with loading rate, which was mainly due to the change in the pin misalignment, the failure surface morphology and to inertia. The Z-pins failed at small displacements in the mode II loading experiments, resulting in much lower energy dissipation in comparison with the mode I case. The total energy dissipation decreased with increasing loading rate, while enhanced interfacial friction due to failed pins may be largely responsible for the higher energy dissipation in quasi-static experiments.Item Open Access Coupon scale Z-pinned IM7/8552 delamination tests under dynamic loading(Elsevier, 2019-08-01) Cui, Hao; Mahadik, Yusuf; Hallett, Stephen R.; Partridge, Ivana K.; Allegri, Giuliano; Ponnusami, Sathiskumar A.; Petrinic, NikDynamic impact onto laminated composite structures can lead to large-scale delamination. This can be mitigated by the introduction of through-thickness reinforcement, such as z-pins. Here, mode I & II and mixed-mode delamination tests have been designed and conducted at high loading rate, for both unpinned and Z-pinned coupons to study the effect of rate of loading. It was found that the Z-pins were not effective in delaying the dynamic crack initiation or resisting the dynamic propagation of delaminations shorter than 5 mm. However, the further growth of cracks was substantially delayed by Z-pinning, especially for the pure mode I and mode I dominated failure modes. On the other hand, the effectiveness of Z-pins in shear tests was relatively modest. The mode I dominated delamination resistance of Z-pinned laminates was found to be sensitive to the loading rate.Item Open Access A critical study on impact damage simulation of IM7/8552 composite laminate plate(Elsevier, 2019-01-25) Cui, Hao; Thomson, Daniel; Eskandari, Sina; Petrinic, NikPlate impact tests on IM7/8552 composite laminates with different projectile 10 incident angles and velocities were carried out. Numerical simulations were conducted to 11 predict the impact damage, with both Puck and LaRC failure criteria having been employed in 12 this study. The dynamic failure performance of IM7/8552 lamina was reviewed first, by 13 referring to data obtained from experiments conducted at a range of strain rates. The 14 performance of the assessed modelling approaches was evaluated by comparing the results 15 of simulations against experimentally (quantitatively and qualitatively) acquired projectile 16 velocity, impact load and the failure modes of the plates. It proved to be challenging to model the macroscopic damage of the laminate at elevated projectile velocities; further 18 improvement can be made through enriching the dynamic material data and mitigating the 19 mismatch between the complex fibre architecture and its numerical representation.Item Open Access Dataset for the publication: "Coupon scale Z-pinned IM7/8552 delamination tests under dynamic loading"(Cranfield University, 2019-08-27 15:00) Cui, Hao; R. Hallett, Stephen; Mahadik, Yusuf; K. Patridge, Ivana; Allegri, Giuliano; Anusuya Ponnusami, Sathiskumar; Petrinic, NikDatasets for a paper published in Composites Part A: Applied Science and Manufacturinghttps://doi.org/10.1016/j.compositesa.2019.105565The quasi-static tests were done at velocity of around 0.01mm/sDynamic tests were conducted at norminal velocity of around 4m/s, some of the WDCB tests were done at 7m/s.Item Open Access Determination of the strain-energy release rate of a composite laminate under high-rate tensile deformation in fibre direction(Elsevier, 2018-05-19) Hoffmann, Justus; Cui, Hao; Petrinic, NikIn order to successfully model design-critical impact loading events on laminated composite structures, the rate-dependency of the composite material has to be correctly reflected. In this context, the rate-dependency of the strain-energy release rate for fibre tensile failure under high-rate loading conditions has not yet been satisfyingly explored. This study employed compact tension specimens consisting of IM7/8552 for dynamic testing on a split-Hopkinson tension bar system. Data reduction was based on the area method . The obtained strain-energy release rate for testing under high-rate conditions was determined to View the MathML sourceGIc,dynf+=82.0±20.8kJ/m2, exhibiting a salient drop compared to its counterpart obtained under quasi-static loading (View the MathML sourceGIc,QSf+=195.8±18.0kJ/m2). Analysis of the strain field surrounding the crack tip using digital image correlation (DIC) suggested a more extensive damage zone for testing under quasi-static than for high-rate loading. A fractographic analysis of the specimens did not indicate any pronounced difference in terms of fracture surface morphology across the two loading rate regimes.Item Open Access Dynamic bridging mechanisms of through-thickness reinforced composite laminates in mixed mode delamination(Elsevier, 2017-11-23) Cui, Hao; Yasaee, Mehdi; Hallett, Stephen R.; Partridge, Ivana K.; Allegri, Giuliano; Petrinic, NikDelamination resistance of composite laminates can be improved with through-thickness reinforcement such as Z-pinning. This paper characterises the bridging response of individual carbon fibre/BMI Z-pins in mixed mode delamination at high loading rate using a split Hopkinson bar system. The unstable failure process in quasi-static tests, was also captured with high sampling rate instruments to obtain the complete bridging response. The energy dissipation of the Z-pins were analysed, and it was found that the efficacy of Z-pinning in resisting delamination growth decreased with an increase in mixed mode ratio, with a transition from pull-out to pin rupture occurring. The Z-pin efficacy decreased with loading rate for all mode mix ratios, due to the changing in failure surface with loading rate and rate-dependent frictional sliding.Item Open Access Dynamic bridging response of through-thickness reinforcement in composite laminates(International Committee on Composite Materials, 2017-12-31) Cui, Hao; Melro, António R.; Mahadik, Yusuf; Yasaee, Mehdi; Allegri, Giuliano; Partridge, Ivana K.; Hallett, Stephen R.; Petrinic, NikThe present experimental study aims to extend the understanding of delamination crack bridging mechanisms in Z-pinned laminates subjected to highly dynamic loading conditions. The bridging response of single Z-pins was characterized with both quasi-static and high loading rate. Standard delamination tests of Z-pinned laminates were carried out at varying velocity. The experimental results at both length scales showed that Z-pin efficiency in improving delamination resistance decreases with increasing loading rate.Item Open Access Dynamic mode II delamination in through thickness reinforced composites(Springer, 2016-09-21) Yasaee, Mehdi; Mohamed, Galal; Pellegrino, Antonio; Petrinic, Nik; Hallett, Stephen R.Through thickness reinforcement (TTR) technologies have been shown to provide effective delamination resistance for laminated composite materials. The addition of this reinforcement allows for the design of highly damage tolerant composite structures, specifically when subjected to impact events. The aim of this investigation was to understand the delamination resistance of Z-pinned composites when subjected to increasing strain rates. Z-pinned laminated composites were manufactured and tested using three point end notched flexure (3ENF) specimens subjected to increasing loading rates from quasi-static (~0m/s) to high velocity impact (5m/s), using a range of test equipment including drop weight impact tower and a split Hopkinson bar (SHPB). Using a high speed impact camera and frame by frame pixel tracking of the strain rates, delamination velocities as well as the apparent fracture toughness of the Z-pinned laminates were measured and analysed. Experimental results indicate that there is a transition in the failure morphology of the Z-pinned laminates from quasi-static to high strain rates. The fundamental physical mechanisms that generate this transition are discussed.Item Open Access Experimental characterisation and numerical modelling of the influence of bondline thickness, loading rate, and deformation mode on the response of ductile adhesive interfaces(Elsevier, 2019-06-21) Lissner, Maria; Alabort, Enrique; Cui, Hao; Rito, R.; Blackman, Bamber R R.K.; Petrinic, NikA new method for characterising the rate-dependent failure of ductile adhesively bonded structures has been developed and used to investigate the different modes of loading of representative interfaces. Furthermore, experimental observations enabled a newly developed cohesive zone model that captures all critical aspects of the observed and quantified behaviour of the adhesive under consideration. In particular, the model is capable of reproducing the conducted experiments by incorporating both the dependence of the deformation rate and the adhesive thickness. For that, computed tomography of the adhesive interface was used to resolve three-dimensionally the adhesive volume. The volume fraction of microscopic voids in the adhesive was introduced into the model to rationalise the observed dependence of the mechanical response of the adhesive upon its thickness. Finally, the cohesive zone model was proven with mixed-mode fracture experiments which demonstrate the model’s ability to simulate more complex deformation regimes.Item Open Access A rate dependent experimental and numerical analysis of adhesive joints under different loading directions(Springer, 2018-09-10) Lißner, Maria; Alabort, Enrique; Erice, Borja; Cui, Hao; Petrinic, NikAdhesively bonded joints subjected to dynamic loading demand reliable and accurate measurement techniques to capture their rate dependent traction–separation behaviour. Particularly challenging is the measurement of damage and failure processes which are fundamental to develop the corresponding cohesive zone models. This paper proposes a new experimental methodology for the characterisation of rate-dependent behaviour of adhesive joints. The results of the adopted approach have been used to calibrate a rate-dependent numerical cohesive model proposed to simulate the failure of adhesive joints. The procedure was benchmarked against quasi-static DCB and ENF experiments.Item Open Access Strain rate dependence of mode II delamination resistance in through thickness reinforced laminated composites(Elsevier, 2017-05-04) Yasaee, Mehdi; Mohamed, Galal; Pellegrino, Antonio; Petrinic, Nik; Hallett, Stephen R.A thorough experimental procedure is presented in which the mode II delamination resistance of a laminated fibre reinforced plastic (FRP) composite with and without Z-pins is characterised when subjected to increasing strain rates. Standard three-point End Notched Flexure (3ENF) specimens were subjected to increasing displacement loading rates from quasi-static (∼0 m/s) to high velocity impact (5 m/s) using a range of test equipment including drop weight impact tower and a Modified Hopkinson Bar apparatus for dynamic three-point bending tests. The procedure outlined uses compliance based approach to calculate the fracture toughness which was shown to produce acceptable values of GIIC for all loading rates. Using detailed high resolution imaging relationships between delamination velocities, apparent fracture toughness, longitudinal and shear strain rates were measured and compared. Confirming behaviours observed in literature, the thermosetting brittle epoxy composite showed minor increase in GIIC with increase in strain rate. However, the Z-pinned specimens showed a significant increase in the apparent GIIC with loading rate. This highlights the need to consider the strain rate dependency of the Z-pinned laminates when designing Z-pinned structures undergoing impact.Item Open Access A study on the longitudinal compression strength of fibre reinforced composites under uniaxial and off-axis loads using cross-ply laminate specimens.(Elsevier, 2019-03-25) Thomson, Daniel; Cui, Hao; Erice, Borja; Petrinic, NikAbstract Longitudinal compression testing of unidirectional FRP laminates remains a challenge due to the difficulty in applying high compressive loads without stress concentrations and boundary effects leading to premature failure. This work aims to critically evaluate different specimen designs and laminate configurations, cross-ply in particular, for the determination of longitudinal compression properties of unidirectional plies. To this end, a comprehensive experimental campaign has been carried out, comparing strength, stiffness, and failure modes across different specimen designs and laminate configurations. The investigated cross-ply specimens produced comparable results without many of the issues observed in the testing unidirectional material and, therefore, are strongly recommended for the determination of longitudinal compressive strength. Finally, the cross-ply material was tested under off-axis compression to study the effects of shear on the longitudinal compression strength using a series of compression specimens cut at different angles between 0 and 15° to the direction of the laminate.Item Open Access A wedge-DCB test methodology to characterise high rate mode-I interlaminar fracture properties of fibre composites(EDP Sciences, 2018-09-07) Ponnusami, Sathiskumar A.; Cui, Hao; Erice, Borja; Pathan, Mehtab; Petrinic, NikA combined numerical-experimental methodology is presented to measure dynamic Mode-I fracture properties of fiber reinforced composites. A modified wedge-DCB test using a Split-Hopkinson Bar technique along with cohesive zone modelling is utilised for this purpose. Three different comparison metrics, namely, strain-displacement response, crack propagation history and crack opening history are employed in order to extract unique values for the cohesive fracture properties of the delaminating interface. More importantly, the complexity of dealing with the frictional effects between the wedge and the DCB specimen is effectively circumvented by utilising right acquisition techniques combined with an inverse numerical modelling procedure. The proposed methodology is applied to extract the high rate interlaminar fracture properties of carbon fiber reinforced epoxy composites and it is further shown that a high level of confidence in the calibrated data can be established by adopting the proposed methodology.