Browsing by Author "Cui, Hao"
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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 Data for the paper "Inter-fibre failure of through-thickness reinforced laminates..."(Cranfield University, 2018-06-18 13:00) Cui, Hao; Yasaee, MehdiData used in the paper " Hao Cui, Antonio R. Melro, Mehdi Yasaee, Inter-fibre failure of through-thickness reinforced laminates in combined transverse compression and shear load, Composites Science and Technology, 2018 "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 inter-fibre failure of unidirectional composite laminates with through-thickness reinforcement(Elsevier, 2019-04-03) Cui, Hao; Yasaee, Mehdi; Melro, António R.Unidirectional composite laminates reinforced in the thickness direction with Z-pins are tested in tension and compression with different off-axis angles at high loading rate. A split Hopkinson bar setup and a high speed imaging system have been used for these dynamic tests. It is found that the inter-fibre strength was reduced by Z-pinning in tension and shear dominated failure modes, and the reduction from dynamic loading conditions is greater than that in quasi-static. However, the laminate strength was not significantly influenced by Z-pinning when loaded predominantly in compression. This difference was caused by the transition of failure mechanisms around Z-pins. The stiffness of the laminate was not affected by Z-pins at elevated strain rates, since the increased epoxy stiffness helped to make up for the stiffness loss due to reduced fibre volume fraction resulting from Z-pins.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 Experimental data for the dynamic inter-fibre failure of composite laminates with through-thickness reinforcement(Cranfield University, 2019-04-10 12:14) Cui, HaoExperimental data as published in "Dynamic inter-fibre failure of unidirectional composite laminates with through-thickness reinforcement" DOI: 10.1016/j.compscitech.2019.04.004Item Open Access Fibre-bridged fatigue delamination in multidirectional composite laminates(Elsevier, 2018-09-28) Yao, Liaojun; Cui, Hao; Sun, Yi; Guo, Licheng; Chen, Xiangming; Zhao, Meiying; Alderliesten, R. C.The influence of fibre bridging on delamination failure in multidirectional composite laminates with different thickness scales is characterized, and the dependence of fibre bridging significance on laminate thickness as well as loading regime is investigated in this paper. Both quasi-static and fatigue resistance curves (R-curve) are experimentally determined to quantify the significance of fibre bridging in delamination growth. The results clearly demonstrate that thickness has effect on the amount of fibre bridging in quasi-static delamination. And the significance of fibre bridging decreases with the increase in laminate thickness. However, the situation for fatigue delamination growth (FDG) is much more complicated. The difference in fibre bridging generation seems to be insignificant in short fatigue cracks and at the plateau state, whereas more bridging fibres can be present in a thinner laminate in-between state. Loading regimes also have significant effect on the amount of fibre bridging. The results clearly demonstrate that more bridging fibres can be generated in quasi-static delamination compared to fatigue. A modified Paris relation proposed by the authors in previous studies is employed in present study to determine fibre-bridged FDG behaviors in multidirectional composite laminates with various thickness scales. All fatigue data locate in a relatively narrow band region of the resistance graph, resulting in a master resistance curve in determining fatigue delamination behaviors. This clearly demonstrates that neither thickness nor fibre bridging has significant effect on fatigue delamination behaviors, if the similarity is well represented.Item Open Access On the rate dependent behaviour of epoxy adhesive joints: experimental characterisation and modelling of mode I failure(Elsevier, 2018-01-10) Lißner, M.; Alabort, E.; Cui, Hao; Pellegrino, Antonio; Petrinic, N.The increasing use of adhesive joints in dynamic applications require reliable measurements of the rate-dependent stress-displacement behaviour. The direct measurement of the stress-displacement curve is necessary when using cohesive models in discretised solutions of boundary value problems in solid mechanics. This paper aims to investigate the rate-dependent tensile failure of adhesive joints by using a new experimental methodology – it relies upon the combination of the stress wave propagation theory and digital image correlation methods on high speed footage to quantify the tensile stress and the dissipated energy respectively. For this purpose, the Split Hopkinson Bar methodology was employed – the experimental configuration was optimised using numerical modelling. To prove the sensitivity of our framework, two different adhesives are characterised at different loading rates: the adhesive failure strength was found to increase considerably with the strain rate, while the plastic deformation of these adhesives was reduced. The film adhesive showed superior performance over the particle toughened one. In the final part, a rate-dependent cohesive zone model is proposed, one which captures the measured behaviour and which has the potential to be used in industrial applications.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 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 Thickness effects on fibre-bridged fatigue delamination growth in composites(Elsevier, 2018-04-16) Yao, Liaojun; Cui, Hao; Alderliesten, R. C.; Sun, Yi; Guo, LichengThis paper provides an investigation on thickness effects on fibre-bridged fatigue delamination growth (FDG) in composite laminates. A modified Paris relation was employed to interpret experimental fatigue data. The results clearly demonstrated that both thickness and fibre bridging had negligible effects on FDG behaviors. Both energy principles and fractography analysis were subsequently performed to explore the physical reasons of this independence. It was found that the amount of energy release of a given crack growth was not only independent of fibre bridging, but also thickness. Fibre print was the dominant microscopic feature located on fracture surfaces, physically making the same energy dissipation during FDG. Furthermore, the present study provides extra evidence on the importance of using an appropriate similitude parameter in FDG studies. Particularly, the strain energy release rate (SERR) range applied around crack front was demonstrated as an appropriate similitude parameter for fibre-bridged FDG study.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.