The role of bedding angle on the mechanic properties and failure modes of shale under cyclic loading and unloading conditions is unclear. This study conducted uniaxial cyclic loading and unloading tests on shales from the Longmaxi Formation with different bedding angles (θ = 0°, 22.5°, 45°, 67.5° and 90°), and characterized their damage evolution through both AE and charge signals. Results show that the compressive strengths are higher, and the loading cycles are more in specimens with θ = 0° and 90° than those with θ = 22.5°, 45° and 67.5° during cyclic loading tests, resulting in a silent period of signaling presented in former but not in latter θ. Both AE and charge signals can well reflect the major damages in time-domain analysis, while only charge signals can characterize the minor damages at the silent stages by continuous wavelet transforming into time-frequency plots, leading to their advantages in characterizing the damage evolution in specimens with θ = 0° and 90°, but not with θ = 22.5°, 45° and 67.5°. These differences can be attributed to their different signal acquirement mechanisms. These findings highlight the effectiveness of charge signals in characterizing the shale damage evolution under loading and unloading conditions.

中文翻译：

---

表征层理角对循环装卸下页岩损伤影响的电荷信号


层理角对循环加卸载条件下页岩力学性质和破坏模式的影响尚不清楚。本研究对不同层理角 （θ = 0°、22.5°、45°、67.5° 和 90°） 的 Longmaxi 组页岩进行了单轴循环加载和卸载试验，并通过声发射和电荷信号表征了它们的损伤演变。结果表明，在循环加载试验中，θ = 0° 和 90° 的试件的抗压强度更高，加载循环次数比 θ = 22.5°、45° 和 67.5° 的试件更大，导致前一个 θ 出现信号沉默期，而后 θ 则没有。声发射信号和电荷信号都能很好地反映时域分析中的主要损伤，而只有电荷信号可以通过连续小波转化为时频图来表征无声阶段的轻微损伤，因此在表征 θ = 0° 和 90° 的试样损伤演变方面具有优势，而在 θ = 22.5°、45° 和 67.5° 时则不然。这些差异可归因于它们不同的信号获取机制。这些发现强调了电荷信号在表征加载和卸载条件下页岩损伤演变方面的有效性。