Size-dependent crystal plasticity: from micro-pillar compression to bending

Size-dependent crystal plasticity of metal single crystals is investigated using finite-element method based on a phenomenological crystal-plasticity model, incorporating both first-order and second-order effects. The first-order effect is independent of the nature of the loading state, and described by three phenomenological relationships based on experimental results. The second-order effect is considered in terms of storage of geometrically necessary dislocations, affected significantly by the loading state. The modelling approach is shown to capture the influence of loading conditions on the sample size effect observed in compression and bending experiments. A modelling study demonstrates the subtleness and importance of accounting for first-order and second-order effects in modelling crystalline materials in small length-scales

Effect of graphene-oxide enhancement on large-deflection bending performance of thermoplastic polyurethane elastomer

Thermoplastic polyurethane (PU) elastomers are used as shoe-sole materials due to many excellent properties but their inelastic deformation is a serious deficiency for such applications. Hence, graphene oxide (GO) was introduced into the synthesized thermoplastic PU to produce a GO/PU composite material with enhanced properties. Plastic behaviour of this composite was assessed in cyclic tensile tests, demonstrating reduction of irreversible deformations with the addition of GO. Additionally, in order to evaluate mechanical performance of PU and the GO/PU composite under conditions of large-deflection bending typical for shoe soles, finite-element simulations with Abaqus/Standard were conducted. An elastic-plastic finite-element model was developed to obtain detailed mechanical information for PU and the GO/PU composite. The numerical study demonstrated that the plastic area, final specific plastic dissipation energy and residual height for PU specimens were significantly larger than those for the GO/PU composite. Besides, the addition of GO into the PU matrix greatly delayed the onset of plastic deformation in PU in a large-deflection bending process. The average residual height and final specific plastic dissipation energy for PU were approximately 5.6 and 17.7 times as large as those for the studied GO/PU composite. The finite-element analysis provided quantification of the effect of GO enhancement on the large-deflection bending performance of PU for regimes typical for shoe soles and can be used as a basis for optimization of real composite products