For elastic–plastic contacts, we propose a complete description of the plastic strain field beneath the indenter during indentation and scratch with a spherical indenter (with R, the tip radius), as a function of the testing conditions, defined by the geometrical strain, noted a/R (with a, the contact radius), and the local friction coefficient μloc. The main parameter of the description is the level of the plastic deformation imposed during test into amorphous polymeric surfaces, related in first approximation to the ratio a/R. An equivalent average plastic strain, noted (εp)av, is calculated over a representative plastically deformed volume, both for indentation and scratch tests. The equivalent average plastic strain (εp)av, is observed to increase with the ratio a/R, as predicted by the empirical Tabor's rule, but also with the local friction coefficient μloc for a given ratio a/R, especially during scratching. The plastic zone dimensions and the plastic strain gradient developed beneath the moving tip are shown to depend both on the geometrical strain a/R and also on the friction coefficient μloc.

In the present work a new equation to determine the internal material length scale for strain gradient plasticity theories from two independent experiments (uniaxial and nanoindentation tests) is introduced. The applicability of the presented equation is verified for conventional grained as well as for ultrafine-grained copper and brass with different amounts of prestraining. A significant decrease of the experimentally determined internal material length scale is found for increasing dislocation densities due to prestraining. Conventional mechanism strain gradient plasticity theory is used for simulating the indentation response, using experimentally determined material input data as the yield stress, the work-hardening behavior and the internal material length scale. The work-hardening behavior and the yield stress were taken from the uniaxial experiments, whereas the internal material length scale was calculated using the yield stress from the uniaxial experiment, the macroscopic hardness H0 and the length scale parameter h* following from the nanoindentation experiment. A good agreement between the measured and calculated load–displacement curve and the hardness is found independent of the material and the microstructure.

Systematic studies of the deformation mechanisms of multilayer transition metal nitride coatings TiN/CrN, TiN/NbN, and NbN/CrN, and corresponding reference coatings of TiN, NbN, and CrN deposited by a direct current (dc) magnetron sputtering process onto silicon 〈100〉 have been performed. Mechanical characterization was conducted using a combination of microindentation and nanoindentation in the load range 30 to 150 mN and 0.5 to 3.5 mN, respectively. For both load ranges, scanning electron microscopy (SEM) in situ indentation was used to observe the indentation process including any pileup, sink-in, and fracture mechanisms specific to each coating. The coatings’ microstructure, both before and after indentation, was analyzed using transmission electron microscopy (TEM). It was possible to both correlate the indentation load–displacement response to surface roughness effects and fracture modes (substrate and film cracking) and observe deformation mechanisms within the coatings.

In this work, the effects of conical indentation variables on the load–depth indentation curves were analyzed using finite element modeling and dimensional analysis. A factorial design 26 was used with the aim of quantifying the effects of the mechanical properties of the indented material and of the indenter geometry. Analysis was based on the input variables Y/E, R/hmax, n, θ, E, and hmax. The dimensional variables E and hmax were used such that each value of dimensionless Y/E was obtained with two different values of E and each value of dimensionless R/hmax was obtained with two different hmax values. A set of dimensionless functions was defined to analyze the effect of the input variables: Π1 = Pl/Eh2, Π2 = hc/h, Π3 = H/Y, Π4= S/Ehmax, Π6 = hmax/hf, and Π7 = Wp/WT. These six functions were found to depend only on the dimensionless variables studied (Y/E, R/hmax, n, θ). Another dimensionless function, Π5 = β, was not well defined for most of the dimensionless variables and the only variable that provided a significant effect on β was θ. However, β showed a strong dependence on the fraction of the data selected to fit the unloading curve, which means that β is especially susceptible to the error in the calculation of the initial unloading slope.

This work uses crystal plasticity finite element simulations to elucidate the role of elastoplastic anisotropy in instrumented indentation P–hs curve measurements in face-centered cubic (fcc) crystals. It is shown that although the experimental fluctuations in the loading stage of the P–hs curves can be attributed to anisotropy, the variability in the unloading stage of the experiments is much greater than that resulting from anisotropy alone. Moreover, it is found that the conventional procedure used to evaluate the contact variables ruling the unloading P–hs curve introduces an uncertainty that approximates to the more fundamental influence of anisotropy. In view of these results, a robust procedure is proposed that uses contact area measurements in addition to the P–hs curves to extract homogenized J2-plasticity-equivalent mechanical properties from single crystals.

Nanoindentation is a widely accepted test method for materials characterization. On account of the complexity of contact deformation behavior, design of parametric constitutive models and determination of the unknown parameters is challenging. To address the need for identification of mechanical properties of viscoelastic/plastic materials from nanoindentation data, a combined numerical finite element/optimization-based indentation modeling tool was developed, fully self-contained, and capable of running on a PC as a stand-alone executable program. The approach uses inverse engineering and formulates the material characterization task as an optimization problem. The model development consists of finite element formulation, viscoelastic/plastic material models, heuristic estimation to obtain initial solution boundaries, and a gradient-based optimization algorithm for fast convergence to extract mechanical properties from the test data. A four-parameter viscoelastic/plastic model is presented, then a simplified three-parameter model with more rapid convergence. The end result is a versatile tool for indentation simulation and mechanical property analysis.

Using the extended Hertzian approach (EHA), the “effectively shaped indenter” corresponding to Pharr's concept is described in terms of a parameter set {d0,d2,d4,d6}, which can be determined by a fitting procedure from the unloading curve of an indentation experiment. Owing to the limited accuracy of measurement, a given experimental curve may in principle correspond to more than one such parameter set. Based on indentation experiments with a Berkovich indenter into fused silica, we have investigated the influence of the fitting procedure itself on the results. We suggest a certain manual fitting procedure, which delivered a yield strength Y = (7.1 ± 0.1) GPa independent of the maximum load. Manual fitting always includes some degree of subjectivity, however, both Y and the elastic field as a whole proved to be relatively robust against modifications of the parameter set. We also suggest a preliminary objective procedure, which delivered Y = 6.8 − 7.1 GPa. In addition, we have performed finite element method (FEM) simulations of elastic–plastic indentations of a conical indenter into a von Mises solid with a yield strength of Y = 7.0 GPa. The simulated unloading curve was analyzed using the EHA in the same manner as the experimental curves, and yield strength of 6.95 GPa was obtained being very close to the input value of the FEM.

The present paper deals with the plastic deformation process into metallic materials occurring in the subindenter region during the loading cycle of spherical indentation test. Load–indentation-depth curve and plastic strains field evolution in the region beneath the indenter are examined using finite element analysis (FEA). The FE model was set up and validated by comparison with experimental spherical indentations carried out on two different materials (Al6082-T6, AISI H13) under four different friction conditions, corresponding to friction coefficients equal to 0.0, 0.1, 0.3, and 0.5. It is confirmed that friction effects on load–indentation-depth curves are negligible for the investigated penetration depths, whereas the plastic deformation process is affected by the contact conditions. The investigation shows that, although the L–h curve is not affected by the contact conditions up to medium values of the penetration depth, remarkable effects are produced in the overall plastic core under the indenter. A strong correlation between plastic strains field and friction coefficient is especially observed at low values of this parameter, whereas a saturation of the phenomena is found for medium-high values of the friction coefficient.

The development of nanoindentation test systems with high data collection speeds has made possible a novel type of indentation creep test: broadband nanoindentation creep (BNC). Using the high density of data points generated and analysis techniques that can model the instantaneous projected indent area at all times during a constant-load indentation experiment, BNC can reveal materials properties across a range of strain rates spanning up to five decades (10−4–10 s−1). BNC experiments aimed at measuring activation parameters for plasticity were conducted on three systems: two Zr-based bulk metallic glasses and poly-(methyl methacrylate) (PMMA). The results give insight into the operation of the deformation mechanisms present in the test materials, including the dependence of the deformation rate on the hydrostatic component of the stress for PMMA and the form of the activation energy function for the metallic glasses.

Nanoscale metallic multilayers, comprising two sets of materials—Cu/Nb and Cu/Ni—were deposited in two different layer thicknesses—nominally 20 and 5 nm. These multilayer samples were indented, and the microstructural changes under the indent tips were studied by extracting samples from underneath the indents using the focused ion beam (FIB) technique and by examining them under a transmission electron microscope (TEM). The deformation behavior underneath the indents, manifested in the bending of layers, reduction in layer thickness, shear band formation, dislocation crossing of interfaces, and orientation change of grains, has been characterized and interpreted in terms of the known deformation mechanisms of nanoscale multilayers.