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One-fourth of the global energy losses are spent to overcome friction, making it particularly important to reduce and minimize friction between contacting materials. Hexagonal close-packed (HCP) metals are an important class of structural materials. It has not been possible to reduce their friction, primarily because of friction-induced dislocation slip and twinning. Here, we find particularly low friction when sliding perpendicular to the a -axis on the basal plane in HCP Mg single crystals. This is in contrast to the common belief that friction is small along the preferred dislocation slip direction (a -axis). This macroscopic low-friction stems from twinning assisted lattice reconstruction sharing a common rotation axis, confirmed by atomistic simulations and strain energy analysis. While sliding along the a -axis and other directions, 〈 c + a〉 dislocation activity accounts for high frictional resistance. By unambiguously decoupling the contributions of dislocation slip and twinning, this discovery reveals potential opportunities in mitigating the energy dissipation at tribological interfaces of HCP metals, e.g. through crystallographic texture design. [Display omitted] [ABSTRACT FROM AUTHOR]

This work presents a theoretical and experimental characterization of shape memory alloy metal rubber (SMA-MR) material. SMA-MR is a novel porous damping solid made of coil entangled nitinol wires. The constitutive model proposed in this work takes into account the geometry of the coils used, the manufacturing parameters of the SMA-MR material together with the thermo-mechanical behavior of the shape memory alloy wires. Metal rubber samples made with nitinol constitutive material are fabricated and tested under different quasi-static loading and temperature conditions. The special characteristics of SMA-MR such as hysteretic behavior, nonlinear stiffness, transverse isotropy, dry friction damping property and temperature dependency are predicted by the model, with the comparison between the theoretical and experimental results yielding discrepancies lower than 5% in the majority of the conditions considered. [ABSTRACT FROM AUTHOR]