Browsing by Author "Liu, B. G."

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    High strain rate compressive response of ultra-high molecular weight polyethylene fibre composites
    (Elsevier, 2019-04-20) Liu, B. G.; Kandan, Karthikeyan; Wadley, H. N. G.; Deshpande, V. S.
    The mechanisms of deformation during the dynamic in-plane compression of 〖[0^o/〖90〗^o]〗_n (cross-ply) ultra-high molecular weight polyethylene (UHMWPE) fibre composites with polymeric matrices have been investigated for strain rates in the range 0.01 s^(-1) to 4000 s^(-1). The measured strain rate sensitivity was mild for strain rates less than about 100 s^(-1), but increased sharply at higher rates. X-ray computed tomography and optical microscopy revealed that over the range of strain rates investigated here, the deformation mechanism was kinking (micro-buckling) of the plies with a kink band width of about 1 mm. Ply delamination was also observed, but only during softening phase of the response after the peak strength had been attained. To gain a mechanistic understanding of the observed strain rate sensitivity, finite element (FE) simulations were used to model the compression experiments. For these calculations, each specimen ply was explicitly modelled via a pressure-dependent crystal plasticity framework that accounts for the large shear strains and fibre rotations that occur within each ply in the kink band. Calculations were conducted in the limits of perfectly-bonded and completely un-bonded plies. Good agreement between measurements and predictions was obtained when plies were assumed to be perfectly bonded, confirming the hypothesis that ply delamination plays a small role in setting the peak strength as well as the compressive response of the composite at moderate levels of applied strain. The calculations also show that misalignment of the specimen between the compression platens strongly influences the compression response and especially the initial stiffness. Importantly, the FE calculations reveal that over the range of strain rates investigated here, inertial stabilisation has a negligible contribution to the strong rate sensitivity observed for strain rates above 100 s^(-1) and that this sensitivity is primarily associated with the strain rate sensitivity of the polymeric matrix.
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    ItemOpen Access
    Out-of-plane compressive response of additively manufactured cross-ply composites
    (Cambridge University Press, 2020-03-06) Farukh, Farukh; Liu, B. G.; Yogeshvaran, R. N.; Kandan, Karthikeyan
    Digital manufacturing was employed to 3D print continuous Carbon, Glass and Kevlar fibre reinforced composites in Unidirectional (UD) [0°], Off-axis ±45° and Cross-ply [0°/90°] layup sequence. These 3D printed composites were subjected to quasi-static, in-plane tension and out-of-plane (compression and shear) loading. The tensile strength of 3D printed Carbon, Glass and Kevlar UD laminates was significantly lower than that of 3D printing filaments used to manufacture them. The type of fibre (brittle/ductile) reinforcement was found to be governing the shear yield strength of 3D printed composites despite having the same Nylon matrix in all the composites. Out-of-plane compressive strength of the 3D printed Carbon and Glass fibre reinforced composites was independent of specimen size. Contrary to that, Kevlar fibre composites showed a pronounced size effect upon their out-of-plane compressive strength. A combination of X-ray tomography and pressure film measurements revealed that the fibres in 3D printed composites failed by ‘indirect tension’ mechanism which governed their out-of-plane compressive strength. To gain further insights on the experimental observations, Finite Element (FE) simulations were carried out using a pressure-dependent crystal plasticity framework, in conjunction with an analytical model based on shear-lag approach. Both FE and analytical model accurately predicted the out-of-plane compressive strength of all (Carbon, Glass and Kevlar fibre reinforced) 3D printed composites.
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    ItemOpen Access
    OUT-OF-PLANE COMPRESSIVE RESPONSE OF ADDITIVELY MANUFACTURED CROSS-PLY COMPOSITES
    (2018-09-10) Yogeshvaran, R. N.; Liu, B. G.; Farukh, Farukh; Kandan, Karthikeyan
    Digital manufacturing is employed to 3D print continuous Carbon, Glass and Kevlar fibre reinforced composites in [0°/90°] layup sequence. These 3D printed composites subjected to quasi-static, out-of-plane compression loading. The out-plane compressive strength of the 3D printed Carbon and Glass fibre reinforced composites were independent of specimen size. By contrast, the Kevlar fibre composites have shown a pronounced size effect upon their out-of-plane compressive strength. By using pressure film measurements, it is shown that there exists a shear-lag zone at the periphery of the specimen which governs the out-of-plane compressive strength of the 3D printed composites. To gain further insights on the experimental findings, Finite Element (FE) simulations are carried out using a pressure-dependent crystal plasticity framework. An analytical model is also developed to link the out-of-plane compressive strength of the 3D printed composites to their mechanical properties. Both FE and analytical model accurately predict the out-of-plane compressive strength of 3D printed composites.