Fracture asperities interlock or break during stick slip and ride over each other during stable sliding. The evolution of fracture asperities during the transition between stick slip and stable sliding has attracted less attention, but is important to predict fracture behaviour. Here, we conduct a series of direct shear experiments on simulated fractures in homogeneous polycarbonate to examine the evolution of fracture asperities in the transition stage. Our results show that the transition stage occurs between the stick slip and stable sliding stages during the progressive reduction in normal stress on the smooth and rough fractures. Both the fractures exhibit the alternative occurrence of small and large shear stress drops followed by the deterministic chaos in the transition stage. Our data indicate that the asperity radius of curvature correlates linearly with the dimensionless contact area under a given normal stress. For the rough fracture, a bifurcation of acoustic energy release appears when the dimensionless contact area decreases in the transition stage. The evolution of fracture asperities is stress-dependent and velocity-dependent.

This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

粘连滑动时，断裂粗糙会互锁或断裂，稳定滑动时会相互碰撞。在粘滑和稳定滑动之间的过渡过程中，裂缝凹凸的演变引起了人们的较少关注，但是对于预测骨折行为很重要。在这里，我们对均相聚碳酸酯中的模拟裂缝进行了一系列直接剪切实验，以研究过渡阶段裂缝凹凸的演变。我们的结果表明，在光滑和粗糙裂缝的法向应力逐渐减小的过程中，过渡阶段发生在粘滑和稳定滑动阶段之间。两种裂缝均表现出剪切应力下降大小的交替发生，然后在过渡阶段发生确定性的混乱。我们的数据表明，在给定法向应力下，粗糙表面曲率半径与无量纲接触面积线性相关。对于粗糙的裂缝，当无量纲的接触面积在过渡阶段减小时，会出现声能释放的分叉。断裂粗糙的发展是应力相关和速度相关的。

本文是主题主题“固体材料的断裂动力学：从粒子到地球”的一部分。