Dataset for "Frictional Response of Fault Gouge Analogs to Normal Stress Perturbations: Implications for the Microscopic Origin of Rate- and State-Dependent Friction Evolution"

This repository contains the LAMMPS input files and processed numerical data used in the study “Frictional Response of Fault Gouge Analogs to Normal Stress Perturbations: Implications for the Microscopic Origin of Rate- and State-Dependent Friction Evolution”. Normal stress perturbations strongly modulate fault strength and slip behavior. Non-isobaric Rate- and State-Dependent Friction (RSF) laws are widely used to describe frictional responses, yet their applicability and micromechanical origins remain poorly constrained. Using discrete element modeling, we examine the normal stress step responses of quartz and clay analogs with contrasting strength and slip stability, and relate their macroscopic RSF-like behavior to micromechanical processes. The global response agrees with available experiments. Normal stress steps induce a three-stage shear stress response, with an initial linear increase followed by a quasi-exponential rise toward a new steady state. The nonlinear stage of the shear response is slip dependent rather than time dependent, which we interpret in terms of a nearly velocity-independent strain scale over which the contact fabric loses memory. For normal stresses (5–25 MPa), loading velocity (0.0003–1 m/s), and normalized loading stiffness (0.0005–0.009 1/μm), non-isobaric RSF laws broadly capture the shear stress response, with the Slip law underestimating the linear stage and the Aging law overestimating the nonlinear stage. This mismatch reflects a transition from Aging-law-like to Slip-law-like behavior during transients. At steady state, the state variable serves as an effective proxy for contact area, but it does not during transients, even though contact-area evolution more closely resembles the Aging-law state. The RSF parameter \alpha, which describes the normalized nonlinear shear response, is controlled by the macroscopic friction coefficient and particle size distribution. These results provide new insight into the micromechanical mechanisms underlying shear responses and RSF behavior under normal stress perturbations.本仓库包含了研究《断层黏土模拟物在正应力扰动下的摩擦响应：速率与状态依赖摩擦演化微观起源的启示》中所使用的LAMMPS（LAMMPS）输入文件与经处理的数值数据。正应力扰动会显著调控断层强度与滑移行为。非等压速率-状态依赖摩擦（Non-isobaric Rate- and State-Dependent Friction, RSF）定律被广泛用于描述摩擦响应，但其适用性与微观力学起源仍未得到明确约束。本研究借助离散元建模，对强度与滑移稳定性存在显著差异的石英与黏土模拟物的正应力阶跃响应展开分析，并将其宏观类RSF行为与微观力学过程相关联。整体响应与已有实验结果相符。正应力阶跃会引发三阶段剪切应力响应：初始阶段呈线性增长，随后准指数式上升至新的稳态。剪切响应的非线性阶段由滑移主导而非时间主导，我们将其归因于近似与速率无关的应变尺度——在此尺度下接触组构会丧失记忆。在正应力范围（5–25 MPa）、加载速率（0.0003–1 m/s）与归一化加载刚度（0.0005–0.009 1/μm）的参数区间内，非等压RSF定律能够较好地拟合剪切应力响应，其中滑移定律（Slip law）会低估线性阶段的响应，而老化定律（Aging law）则会高估非线性阶段的响应。这种偏差反映出瞬态过程中存在从类老化定律行为向类滑移定律行为的转变。在稳态条件下，状态变量可作为接触面积的有效代理指标，但在瞬态过程中却并非如此——尽管接触面积的演化更贴近类老化定律的状态变量演化。用于描述归一化非线性剪切响应的RSF参数α，由宏观摩擦系数与粒径分布共同控制。本研究结果为正应力扰动下剪切响应与RSF行为背后的微观力学机制提供了全新的认识。