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In this work, nanoindentation tests on Nation 117 membranes are conducted under three different sets of loading conditions. The effects of loading/unloading rate, peak load and holding period on the mechanical responses of membranes are analyzed, respectively. The results demonstrate that the creep deformation as well as the modulus and hardness depend on these loading conditions, and appropriately fast loading/unloading rate, long enough holding time, relatively low peak load are essential to minimize the creep effect on the nanoindentation results. By analyzing the variation tendency of reduced modulus and hardness, the optimized loading/unloading rate, holding time and the peak load are >10 [mu]N/s, longer than 20 s and 100 [mu]N for dry Nation 117., INTRODUCTIONConsiderable attention has been paid to the chemical and mechanical properties of perfluorosulphonic acid (PFSA) membranes on the horizon of polymers, particularly Nafion, because of their excellent material properties including [...]

In this paper, discrete element method (DEM) is used to investigate the strength properties and failure modes of QH-E lunar soil simulant at the low confining stress. The deviator stress-axial strain curves and volumetric strain-axial strain curves are obtained based on DEM simulations, which are basically consistent with the experimental results at the low confining stresses, and the lower confining stress is, the closer to the experimental curves will obtain. Moreover, for a given low confining stress, the effects of porosity and friction coefficient on strength properties of QH-E samples are discussed. The results show that the peak stress, residual stress and axial strain corresponding to the peak stress obviously decrease with the increase of the porosity, while slightly increase with the increase of the friction coefficient. Furthermore, the whole failure processes and failure modes at different low confining stresses are also observed by DEM simulations. The simulated results indicate that the V-type shear zone (double shear bands) is the main failure mode at the low confining stress, and then the V-type shear zone gradually changes to a single shear band (along the horizontal direction about 52o) with the increase of the confining stress.

In this paper, we study nanoindentation in Cu64Zr36 metallic glass (MG) nanopillars with different aspect ratios by molecular dynamics simulations. The activation of shear transformation zones (STZs) and the deformation behavior of MG pillars are discussed during nanoindentation loading and unloading processes. Buckling and serrated flow are the two types of deformation behaviors observed during nanoindentation. For large aspect ratio pillars, a sudden stress drop in the load–displacement curve is found that relates to the buckling process, while smaller aspect ratio pillars exhibit large stress fluctuations. The serrated flow is associated with STZ activation. STZs are locally activated, and their number gradually increases with increasing indentation depth during loading, whereas their number decreases during unloading. For pillars with a large aspect ratio, no new STZs are activated and their number decreases rapidly once the indenter has left the sample because of the buckling deformation. In contrast, new STZs are activated for pillars with smaller aspect ratio during the unloading process. Analysis of STZ activation and shear localization reveals an inhomogeneous deformation process and an increase in the degree of structural heterogeneity as the aspect ratio of the pillars increases for both loading and unloading stages. The present work provides an insight into the atomic-scale plastic deformation behavior of MG nanopillars during nanoindentation loading and unloading processes. [ABSTRACT FROM AUTHOR]

A slope is a complex engineering geological body that contains many uncertainties. In the present study, the high rock slope of Duimenshan in Gejiu, China is taken as the research object, and the Monte Carlo method is used to perform the analyses. Firstly, based on a large number of rock mass discontinuities, the Fuzzy C-Means (FCM) clustering algorithm is used to determine the dominant discontinuities. Secondly, the affecting parameters of the rock mass such as cohesion, internal friction angle, horizontal seismic acceleration coefficient, and water-filled depth coefficient are taken as random variables, and the failure probability of the slope and the failure index corresponding to different slope heights and slopes are obtained as the output parameter. The obtained results show that the target reliability index of the slope in a certain range of the slope height is far from the safety value, indicating that the slope is unstable, and the combination of slope height and slope angle affects the reliability of the slope. More specifically, as the slope height and angle increase, the number of samples with a stability coefficient of less than 1 increases, thereby increasing the failure probability of the slope indicating that the slope is stable. It is found that unless the slope height is small, it is the main factor of stability. However, when the slope height exceeds 33 m, the effect of the slope inclination on the stability increases gradually. [ABSTRACT FROM AUTHOR]