Rocks are subjected to different loading rates at different construction stages and engineering applications. The strength of rock usually increases with loading rate. This rate dependency is one of the time-dependent behaviors of rock, whereby the micro-mechanisms are believed to be the subcritical crack growth due to stress corrosions. However, no evidence is provided yet. This study investigated rate effects of rocks through a novel implementation of Parallel-Bonded Stress Corrosion (PSC) model in Discrete Element Method (DEM). Long-term microparameters in PSC are first calibrated through creep test. Then, a series of uniaxial compressive strength, direct tensile strength, and triaxial compressive strength tests are performed, with strain rates ranging from /s to /s. Results show that the uniaxial compressive strength is highly dependent on strain rates which quantitatively matches with the experimental data. At lower strain rate, more subcritical cracks propagate due to longer stress-corrosion reaction time, resulting in a lower strength. Besides, strain rate also influences the failure patterns in post-peak, with single failure plane at lower strain rates and multiple failure planes at higher strain rates. Rate effects are also observed in direct tensile strength tests, with similar rate of increase in strength and a transition in cracking pattern, which align with the experimental data, indicating tension-induced subcritical cracking is the unified underlying micro-mechanism of rate effects for both cases. However, in triaxial compressive strength tests, rate effects become less obvious with increasing confining pressure, consistent with experimental findings, as subcritical crack growth is suppressed in shearing processes.

中文翻译：

---

岩石的速率效应：DEM 建模的见解


岩石在不同的施工阶段和工程应用中承受不同的加载速率。岩石的强度通常随着加载速率的增加而增加。这种速率依赖性是岩石随时间变化的行为之一，据信其微观机制是由于应力腐蚀而导致的亚临界裂纹扩展。但目前尚未提供任何证据。本研究通过离散元法 (DEM) 中并行粘结应力腐蚀 (PSC) 模型的新颖实现来研究岩石的速率效应。 PSC 中的长期微观参数首先通过蠕变测试进行校准。然后，进行一系列单轴抗压强度、直接拉伸强度和三轴抗压强度测试，应变速率范围为/s至/s。结果表明，单轴抗压强度高度依赖于应变率，这与实验数据定量匹配。在较低的应变速率下，由于应力腐蚀反应时间较长，更多的亚临界裂纹会扩展，导致强度较低。此外，应变率还影响峰值后的失效模式，较低应变率时为单一失效面，较高应变率时为多个失效面。在直接拉伸强度试验中也观察到了速率效应，具有相似的强度增长率和裂纹模式转变，这与实验数据一致，表明拉伸诱发的亚临界裂纹是两种速率效应的统一基础微观机制。案例。然而，在三轴抗压强度试验中，随着围压的增加，速率效应变得不那么明显，这与实验结果一致，因为剪切过程中亚临界裂纹扩展受到抑制。