This paper presents systematic molecular dynamics modelling of Na-montmorillonite subjected to uniaxial compression and unidirectional shearing. An initial 3D model of a single-cell Na-montmorillonite structure is established using the Build Crystal module. The space group is C2/m, and COMPASS force fields are applied. Hydration analysis of Na-montmorillonite has been performed to validate the simulation procedures, where the number of absorbed water molecules varied with respect to the various lattice parameters. A series of uniaxial compression stress σzz and unidirectional shear stress τxy values are applied to the Na-montmorillonite structure. It is shown that the lattice parameter and hydration degree exhibit significant influence on the stress–strain relationship of Na-montmorillonite. The ultimate strain increases with increases in the lattice parameter but decreases in the number of water molecules. For saturated Na-montmorillonite, more water molecules result in a stiffer clay mineral under uniaxial compression and unidirectional shearing.

Microscale testing has enjoyed significant developments, with the majority of testing focused on tensile/compression type tests and little focus on shear testing. With the recent advances in macroscale shear testing, we developed a novel shear structure for evaluating shear properties of bulk materials and films at the microscale. The shear response in single-crystal copper oriented along the [111] direction was found to have a yield strength of ∼180 MPa. Nanocrystalline copper specimens with different orientations showed sensitivity to the film texture with a shear yield strength nearly three times that of single-crystal copper. Shear specimens were fabricated with Cu film–Si substrate interface near the middle of the shear region and compressed to fracture. The shear response showed a mixed behavior of the stiff Si substrate and softer nanocrystalline film and failed in a brittle manner, indicating a response unique to the interface.

The recent decades have seen significant progress in linking the mechanical performance of materials to their underlying microstructure. This article presents an overview of some of these achievements, trends, and challenges. Attention is given to methods initially developed for micromechanics and their gradual evolution toward powerful multiscale methods. Various methods have been proposed for bridging scales in mechanics of materials, all aiming for efficiency and accuracy. Computational homogenization is one of these powerful approaches, now used systematically for the assessment of structure–property relations. Novel solution methods and model reduction techniques provide tools to speed up the structure–property analysis, whereby large-scale computations have been made possible. Truly fast analyses of microstructures may be expected in the near future.

Herein rutile (TiO2) single-crystal surfaces, with (001) and (100) orientations, were indented with hemispherical indenters with radii of 13.5, 5, and 1.4 μm. By converting the load–displacement data to nanoindentation (NI) stress–strain curves, together with microscopic post-indentation observations, we conclude that in the (001) orientation, plastic deformation occurs by the activation of all four {101}<10> slip systems. In the (100) orientation, only two of the four {101}<10 > slip systems, along with {100}<00> slip, are activated. Because the four {101}<10> slip systems in the (001) orientation intersect, the surface is harder and exhibits higher hardening rates after the nucleation of dislocations. The latter are manifested by pop-ins, some of which are large. The pop-in stresses are adequately described by Weibull statistics and were significantly higher for the (001) orientation. The elastic moduli, determined from spherical NI stiffness versus contact radii plots, were 349 ± 5 and 229 ± 4 GPa for (001) and (100) orientations, respectively. Fully spontaneous reversible, stress–strain hysteretic curves—only manifest in the (100) orientation—are attributed to the to-and-fro motion of dislocations comprising incipient kink bands in the {100}<00> slip system.

Over the past two decades, nanoindentation has been the most versatile method for mechanical testing at small length scales. Because of large strain gradients, it does not allow for a straightforward identification of material parameters such as yield and tensile strength, though. This represents a major drawback and has led to the development of alternative microscale testing techniques with microcompression as one of the most popular ones today. In this research, the influence of the realistic sample configuration and unavoidable variations in the experimental conditions is studied systematically by combing in-situ microcompression experiments on ultrafine-grained nickel and finite element simulations. It will be demonstrated that neither qualitative let alone quantitative analyses are as straightforward as they may appear, which diminishes the apparent advantages of microcompression testing.

Recent extensive nanomechanical experiments have revealed that the instantaneous strength and plasticity of a material can be significantly affected by the size (of sample, microstructure, or stressed zone). One more important property to be added into the list of size-dependent properties is time-dependent plastic deformation referred to as creep; it has been reported that the creep becomes more active at the small scale. Analyzing the creep in the small scale can be valuable not only for solving scientific curiosity but also for obtaining practical engineering information about the lifetime or durability of advanced small-scale structures. For the purpose, nanoindentation creep experiments have been widely performed by far. Here we critically review the existing nanoindentation creep methods and the related issues and finally suggest possible novel ways to better estimate the small-scale creep properties.

Uniaxial tensile tests were performed on Cu/Nb multilayered foils to investigate yield strength and grain boundary strengthening in the layered foils at room temperature and in fine-grained Nb at 600 °C. At room temperature, yielding in Cu/Nb multilayered foils is controlled by deformation in both layers, and grain boundary strengthening is observed with a Hall–Petch slope (kRT) of 198 ± 56 MPa·μm1/2 at a strain rate of 10−4 s−1. At 600 °C, yielding in Cu/Nb multilayered foils is controlled by deformation in just the Nb layers. Hall–Petch strengthening is observed over a range of strain rates, but the Hall–Petch slope decreases from 197 ± 71 MPa·μm1/2 for a strain rate of 10−4 s−1 to only 25 ± 40 MPa·μm1/2 for a strain rate of 10−6 s−1. The significant drop in the Hall–Petch slope for Nb with decreasing strain rate indicates a change in the controlling deformation mechanism from dislocation glide to dislocation creep.