The onset of frictional motion is mediated by the dynamic propagation of a rupture front, analogous to a shear crack. The rupture front nucleates quasi-statically in a localized region of the frictional interface and slowly increases in size. When it reaches a critical nucleation length it becomes unstable, propagates dynamically and eventually breaks the entire interface, leading to macroscopic sliding. The nucleation process is particularly important because it determines the stress level at which the frictional interface fails, and therefore, the macroscopic friction strength. However, the mechanisms governing nucleation of frictional rupture fronts are still not well understood. Specifically, our knowledge of the nucleation process along a heterogeneous interface remains incomplete. Here, we study the nucleation of localized slip patches on linear slip-weakening interfaces with deterministic and stochastic heterogeneous friction properties. Using numerical simulations, we analyze the process leading to a slip patch of critical size for systems with varying correlation lengths of the local friction strength. Our deterministic interface model reveals that the growth of the critical nucleation patch at interfaces with small correlation lengths is non smooth due to the coalescence of neighboring slip patches. Existing analytical solutions do not account for this effect, which leads to an overestimation of global interface strength. Conversely, when the correlation length is large, the growth of the slip patch is continuous and our simulations match the analytical solution. Furthermore, nucleation by coalescence is also observed on stochastic interfaces with small correlation length. In this case, the applied load for a given slip patch size is a random variable. We show that its expectation follows a logistic function, which allows us to predict the strength of the interface well before failure occurs. Our model and observations provide new understanding of the nucleation process and its effect on the static frictional strength.

摩擦运动的开始是由类似于剪切裂缝的破裂前沿的动态传播来介导的。破裂前沿在摩擦界面的局部区域准静态成核，并且尺寸逐渐增大。当达到临界成核长度时，它将变得不稳定，动态传播并最终破坏整个界面，从而导致宏观滑动。成核过程特别重要，因为它决定了摩擦界面失效的应力水平，因此也决定了宏观摩擦强度。然而，控制摩擦破裂锋面成核的机理仍未得到很好的理解。具体而言，我们对沿异质界面的成核过程的了解仍然不完整。这里，我们研究具有确定性和随机异质性摩擦特性的线性滑弱化界面上局部滑移斑的形核。使用数值模拟，我们分析了导致局部摩擦强度相关长度变化的系统产生临界尺寸滑移斑块的过程。我们的确定性界面模型显示，由于相邻滑动斑块的合并，临界成核斑块在具有较小相关长度的界面上的增长是不平滑的。现有的分析解决方案无法解决这一问题，从而导致高估了整体界面强度。相反，当相关长度很大时，滑动补丁的增长是连续的，我们的仿真与解析解匹配。此外，在具有较小相关长度的随机界面上也观察到了通过聚结形成的核。在这种情况下，对于给定的防滑垫尺寸，所施加的载荷是随机变量。我们表明其期望遵循逻辑函数，这使我们能够在发生故障之前很好地预测接口的强度。我们的模型和观察结果为成核过程及其对静摩擦强度的影响提供了新的认识。