Browsing by Author "Kalwak, Gordon"

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    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, Nik
    Z-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.
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    Soft body impact on composites: delamination experiments and advanced numerical modelling
    (Elsevier, 2021-03-20) Selvaraj, Jagan; Kawashita, Luiz F.; Kalwak, Gordon; Hallett, Stephen R.
    Cohesive interface elements have become commonly used for modelling composites delamination. However, a limitation of this technique is the fine mesh size required. Here, a novel cohesive element formulation is proposed and demonstrated for modelling the numerical cohesive zone with equal fidelity but fewer elements in comparison to a linear cohesive element formulation. The newly proposed formulation has additional degrees of freedom in the form of nodal rotations which when combined with the use of multiple integration points per cohesive element, allows for delamination propagation to be modelled with increased stability. This element formulation is introduced with an adaptive modelling method, termed Adaptive Mesh Segmentation (AMS). To demonstrate its effectiveness under impact loading the new model is applied to a soft body beam bending test. This test, containing a delamination pre-crack, uses inertial constraints and results in a dynamic stress state when impacted by a gelatin cylinder.