Catastrophic Failure: what controls precursory damage localisation in rocks?

灾难性破坏是脆性地球上各种规模的重要现象，从人类引起的地震活动到自然滑坡，火山爆发和地震。它总是与局部变形区上的较小断层和裂缝形式的结构性损伤集中有关，最终导致系统大小的脆性破坏沿着一个明显的和紧急的断层面。然而，局部化的过程还没有得到很好的理解-较小的裂纹自发地沿着早期的断层平面自组织沿着，往往就在故障之前，但涉及的精确机制尚未确定。许多问题仍然存在，包括：Q1 -裂纹、孔隙和晶界如何与施加的应力场局部相互作用，从而导致在特定位置、方向和时间发生灾难性失效？问题2：准静态和动态过程的相对重要性是什么？和问题3-为什么我们只能在某些情况下检测到灾难性故障的前兆？在这里，我们将直接解决这些问题，通过成像的整个定位过程中，使用新开发的X射线透明变形细胞和快速同步X射线显微断层扫描。我们将在同步加速器中首次以高分辨率可视化本地化过程的性质和演变。我们将故意放慢这个过程，以成像其演变，并调查应变率依赖的基本机制，使用快速电子监测和反馈控制。这将为相关机制提供前所未有的直接观察，包括地震（产生声发射的局部开裂）和抗震（弹性加载和无声的不可逆损坏）过程对结果的贡献。这种创新的技术组合是及时的，可行的，并有可能改变我们对微观过程在控制系统大小故障中的作用的理解。研究结果将为自然和人为地震活动中的类似过程提供解释模型，包括对大型诱发事件风险管理策略的比例模型测试。

Catastrophic failure is a critically-important phenomenon in the brittle Earth on a variety of scales, from human-induced seismicity to natural landslides, volcanic eruptions and earthquakes. It is invariably associated with the structural concentration of damage in the form of smaller faults and fractures on localised zones of deformation, eventually resulting in system-sized brittle failure along a distinct and emergent fault plane. However, the process of localisation is not well understood - smaller cracks spontaneously self-organise along the incipient fault plane, often immediately before failure, but the precise mechanisms involved have yet to be determined. Many questions remain, including : Q1 - How do cracks, pores and grain boundaries interact locally with the applied stress field to cause catastrophic failure to occur at a specific place, orientation and time?; Q2 what dictates the relative importance of quasi-static and dynamic processes?; and Q3 - why can we detect precursors to catastrophic failure only in some cases? Here we will address these questions directly by imaging the whole localisation process, using a newly-developed x-ray transparent deformation cell and fast synchrotron x-ray micro-tomography. We will visualise the nature and evolution of the localisation process structurally and seismically together for the first time at high resolution in a synchrotron. We will deliberately slow the process to image its evolution, and to investigate the strain-rate dependence of the underlying mechanisms, using rapid electronic monitoring and feedback control. This will provide unprecedented direct observation of the relevant mechanisms, including the contribution of seismic (local cracking producing acoustic emissions) and aseismic (elastic loading and silent irreversible damage) processes to the outcome. This innovative combination of techniques is timely, feasible, and is likely to transform our understanding of the role of microscopic processes in controlling system-size failure. The results will provide interpretive models for similar processes in natural and human-induced seismicity, including scale-model tests of strategies for managing the risk of large induced events.