Shear avalanches in metallic glasses under nanoindentation: Deformation units and rate dependent strain burst cut-off

Abstract

Articles you may be interested in Microstructure and nonlinear signatures of yielding in a heterogeneous colloidal gel under large amplitude oscillatory shear Strain rate effects in beryllium under shock compression AIP Conf. Abstract. Attractive colloidal particles are trapped in metastable states such as colloidal gels at high attraction strengths and attractive glasses and high volume fractions. Under shear such states flow via a two step yielding process that relates to bond and cluster or cage breaking. We discuss the way the structural properties and related stress response are affected by the shear rate. At low rates colloidal gels yield during start-up shear essentially in a single step, exhibiting a single stress overshoot due to creation of compact flowing clusters. With increasing shear rate a second stress overshoot, linked with further cluster breaking up to individual particles, is becoming more pronounced. We further present the age dependence of the two step yielding and wall slip effects often taking place during rheological experiments of colloidal gels. The latter is related both with the shear rate dependent gel structure as well as the time evolution of the near wall structure.

Serrated flow behaviors of a Zr-based bulk metallic glass by nanoindentation

“…Wang et al 11 found that under nanoindentation plastic flow the cut-off of the strain burst size, corresponding to the shear avalanche size, was associated with the deformation unit size and loading rate in the glassy phase after a statistical analysis of strain bursts in five metallic glasses to study SOC (self-organize to a critical state) behavior. 12 Sun et al 13,14 demonstrated that the plastic deformation could develop into a self-organized critical state characterized by intermittent power-law distributed shear avalanches in ductile BMGs.…”

Flaw-induced plastic-flow dynamics in bulk metallic glasses under tension

“…It has been reported that Zr-based BMGs have particular values of the constants A (≈9.5) and β (≈0.40) under compression9. The change of the constants A and β in the single-side-notched specimens indicates that the shear avalanche profile can be affected by the change of the notch size and shape, which usually occurs in the specimens with different composition935, or under an external disturbance9. Additionally, the cut-off load drop ( ΔL c ) decreases as the notch radius increases.…”

Abnormal devitrification behavior and mechanical response of cold-rolled Mg-rich Mg-Cu-Gd metallic glasses

“…In particular, it can be speculated that the serrations of Mg 85 are smaller in amplitude and larger in numbers than those of Mg75, which means that the size of strain bursts and shear avalanche in Mg85 can be smaller than those of Mg75 due to different structural stability depending on fragility. To clarify this speculation, we carried out a statistical analysis on the strain burst size (S) by considering the distribution of the strain burst which is irregularly and stochastically changing across the as-spun and cold-rolled Mg75 and Mg85 ribbons, attempting to acquire a better understanding of the mechanism in the intermittent pop-in events depending on local structural instability [31]. Thus, first we eliminate the influences from the increase of indentation depth (h) in the pop-in events.…”

“…The fitting parameters, b and S c , reflect the profile of the shear avalanche in MGs. b is associated with the degree of universality of the power-law relation, which characterizes the tendency of MGs to form jamming state, making cooperative motion of concordant regions [31]. S c corresponds to the critical size (avalanche size) of strain burst, shear banding behavior was also investigated by analyzing compressive stress-strain curves of Zr-based MG samples having brittle to ductile transition [33].…”