Nanoindentation was used to examine the impact of impurities and grain boundaries on the mechanical properties of a “model” (110)/(100) grain boundary (GB) interface prepared using direct silicon bonding via the hybrid orientation technique of (110) and (100) p-type silicon wafers. Remarkable differences were found between the mechanical behavior of Fe- and Cu-contaminated samples. The direct silicon bonded wafers contaminated with either Fe or Cu showed opposite effects on mechanical properties, with Fe enhancing the silicon hardness, while Cu contamination induces a gradual weakening. High-resolution transmission electron microscopy was used to verify that the abrupt hardness changes observed during increasing nanoindentation loading is attributed to local deformation induced by the GB interface, Cu precipitate colony induced dislocations, and the abrupt crystallographic orientation change across the GB. The resulting dislocation loop generation facilitated the deformation process during nanoindentation and therefore softened the material.

This study reports on the anisotropic indentation response of α-titanium. Coarse-grained titanium was characterized by electron backscatter diffraction. Sphero-conical nanoindentation was performed for a number of different crystallographic orientations. The grain size was much larger than the size of the indents to ensure quasi-single-crystal indentation. The hexagonal c-axis was determined to be the hardest direction. Surface topographies of several indents were measured by atomic force microscopy. Analysis of the indent surfaces, following Zambaldi and Raabe (Acta Mater. 58(9), 3516–3530), revealed the orientation-dependent pileup behavior of α-titanium during axisymmetric indentation. Corresponding crystal plasticity finite element (CPFE) simulations predicted the pileup patterns with good accuracy. The constitutive parameters of the CPFE model were identified by a nonlinear optimization procedure, and reproducibly converged toward easy activation of prismatic glide systems. The calculated critical resolved shear stresses were 150 ± 4, 349 ± 10, and 1107 ± 39 MPa for prismatic and basal 〈a〉-glide and pyramidal〈c + a〉-glide, respectively.

Indentation methods have been widely used to study bone at the micro- and nanoscales. It has been shown that bone exhibits viscoelastic behavior with permanent deformation during indentation. At the same time, damage due to microcracks is induced due to the stresses beneath the indenter tip. In this work, a simplified viscoelastic-plastic damage model was developed to more closely simulate indentation creep data, and the effect of the model parameters on the indentation curve was investigated. Experimentally, baseline and 2-year postovariectomized (OVX-2) ovine (sheep) bone samples were prepared and indented. The damage model was then applied via finite element analysis to simulate the bone indentation data. The mechanical properties of yielding, viscosity, and damage parameter were obtained from the simulations. The results suggest that damage develops more quickly for OVX-2 samples under the same indentation load conditions as the baseline data.

Novel lightweight intermetallic titanium aluminides, so-called γTiAl, provide good strength and creep resistance up to 700 °C. Their stress–strain behavior at room temperature is however strongly confined in elongation due to their low ductility. For studying the stress–strain behavior of γTiAl, the viscoplastic mechanical properties are determined using spherical indentation testing. The identification problem is solved on the continuum level by neural network analysis, which is based on a unified viscoplasticity model. The identified material parameters are validated by comparing the predicted stress–strain behavior with conventional compression tests at different deformation velocities. It was found that the average response of the indentation tests is in good agreement with the compression tests of round bars. Using a spherical indenter tip of R = 0.2 mm, a small volume is tested, offering possibilities for investigation of local property variations due to processing. The experimental indentation curves exhibited wide hysteresis loops, revealing the existence of pure kinematic hardening. Since tensile fracture strength for γTiAl is very low, microcracking occurred during loading as well as during unloading, significantly contributing to the unloading compliance.