Abstract Accumulation of the subtle impacts of fatigue-induced rock damage may ultimately trigger rock failure. Probing, understanding and quantifying this behavior is crucial in evaluating the mechanical response under dynamic loading. We conduct cyclic uniaxial compression tests with real-time measurement of ultrasonic velocity to probe the evolution of fatigue-induced damage in shale subjected to cycles of increasing-amplitude and constant-amplitude. The stress-strain response shows hysteretic behavior and hardening effect under cyclic compression. Time of first arrival is used to estimate apparent changes in ultrasonic velocity at incremented maximum stresses. Coda wave interferometry (CWI) is applied to detect the more subtle changes in ultrasonic velocity at minimum stress (10 MPa) under fatigue-loading. Despite a continuous increase in ultrasonic velocity measured at incremented maximum stresses the subtle signal of increasing fatigue-induced damage is apparent in the sensitive CWI signal. This is reflected in the descending trend of ultrasonic velocity, especially the S-wave velocity, observed at the minimum stress (10 MPa) – and may ultimately result in failure. The evolution of ultrasonic velocity is controlled by the competing effects of irreversible healing/closure of micro-fractures, dominating at low-stresses/early-cycles, and counteracted by the creation of fatigue-induced micro-fractures, dominating at high-stresses/late-cycles. The development of fatigue-induced micro-fractures is optimally detected by the multiply-scattered coda waves but is absent in the first arrivals. Dynamic modulus and relative changes in effective velocity inferred from CWI are sensitive and discernable indicators of fatigue-induced damage prior to failure while characteristics of the stress-strain curve and the evolution of elastic moduli are inferior indicators.

中文翻译：

---

使用超声波尾波干涉测量法量化疲劳损伤和失效前兆

摘要 疲劳引起的岩石损伤的细微影响的累积可能最终引发岩石破坏。探索、理解和量化这种行为对于评估动态载荷下的机械响应至关重要。我们通过实时测量超声速度进行循环单轴压缩试验，以探测页岩在振幅递增和恒定振幅循环下疲劳诱导损伤的演变。应力应变响应在循环压缩下表现出滞后行为和硬化效应。首次到达时间用于估计在最大应力增加时超声速度的明显变化。尾波干涉测量法 (CWI) 用于检测疲劳载荷下最小应力 (10 MPa) 下超声速度的更细微变化。尽管在增加的最大应力下测量的超声速度持续增加，但在敏感的 CWI 信号中，疲劳引起的损坏增加的微妙信号很明显。这反映在超声波速度的下降趋势上，尤其是在最小应力 (10 MPa) 下观察到的 S 波速度 - 并可能最终导致故障。超声波速度的演变受微裂缝不可逆愈合/闭合的竞争效应控制，在低应力/早期周期占主导地位，并被疲劳诱导的微裂缝的产生抵消，在高应力/后期周期。疲劳引起的微裂缝的发展最好由多次散射的尾波检测到，但在初至波中不存在。