Sommaire:

A defining mechanical property of amorphous materials, which are abundant in daily life and nature, is the existence of a yielding threshold. In the case of soft materials, flow occurs only when the applied stress exceeds a threshold value. Understanding the mechanisms of yielding and subsequent flow is important for a variety of rheological applications and designing newer materials. During yielding, the glassy materials often respond via formation of inhomogeneous flow patterns. These transient heterogeneities have a finite lifetime depending upon the magnitude of applied shear. We will discuss the transient dynamics that emerge during this onset of flow for various imposed shear protocols. In particular, using extensive simulations for the case of imposed shear-rates, we will demonstrate the occurrence of a transition towards the formation of a percolating cluster of mobile regions. This occurs for all imposed shear-rates and only at low shear rates, these clusters subsequently evolve into a transient (but long-lived) shear band with a diffusive growth of its width, before steady flow is attained.

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