Effect of microalloying via soft and hard random pinning on the yielding transition of amorphous solids under oscillatory shear.

Abstract

We investigate the effects of microalloying via random pinning on the yielding transition under oscillatory shear through extensive computer simulations. Random pinning refers to freezing the relaxation degrees of freedom for a fraction of randomly selected particles, which is often termed as hard pinning. Experimentally, pinning effects can be realized by introducing particles with much larger masses and diameters than the particles in the host medium, which is termed soft pinning. Many multicomponent glasses, especially metallic glasses, are good examples of such systems in which the mass and sizes of constituent molecules can vary considerably. Large molecules in these systems can act like soft pinning particles with respect to other particles due to a large timescale separation in their relaxation process. Using the Kob-Andersen model as our glass former, we create a randomly pinned system by pinning a fraction of the particles permanently, as well as by increasing their masses, thereby creating soft pinning sites. Increasing the fraction of hard or soft pinned particles transforms the system from a fragile to a strong glass former, enabling a systematic investigation of how fragility influences the yielding transition. Our findings reveal significant differences in the yielding behavior between strong and fragile glasses. These findings, along with earlier studies where fragility was tuned by varying the packing fraction in soft-sphere systems, demonstrate a universal relationship between fragility and yielding. Moreover, by varying the spatial dimensions, we demonstrate that the relationship is independent of both the dimensionality and the underlying origin of fragility in these model systems.