An Experimental Approach to Understanding Self-Organization of Mode I Defects and Nucleation of Shear Fracture

9805368 Green，II虽然拉伸断裂已经被很好地理解了50多年，但剪切断裂仍然知之甚少，特别是在成核过程方面。 自组织过程的细节，人口的微裂纹演变成一个局部故障，控制故障的方向的因素仍然知之甚少。 随着高压相变诱发断层作用的发现，目前有两种剪切破坏机制可供研究。 虽然这两种机制的基本物理在最精细的尺度上是不同的，但证据表明，在自组织和断层的尺度上，这两种机制的行为是相似的。 这两种机制的比较可以带来新的见解，并且可能可以用于解决涉及另一个的未回答的问题。 特别是，微透镜中的转化材料的诊断外观使得破译自组织过程的尝试比试图区分由“脆性”过程导致的材料中的多代裂纹要简单得多。 本研究将研究Mg 2GeO 4在压力大于2.5 GPa（压力太高，“脆性”过程无法参与）下发生橄榄石-尖晶石转变的失效方法，以绘制出从加载产生的微透镜到自组织过程再到断层的微观结构演化。

9805368Green, IIAlthough tensile fracture has been well understood for more than 50 years, shear fracture remains poorly understood, especially in terms of the nucleation process. The details of the self-organization process by which a population of microcracks evolves into a localized fault, and the factors controlling fault orientation remain poorly understood. With the discovery of high-pressure phase-transformation-induced faulting, there are now two mechanisms of shear failure available for study. Although the fundamental physics of the two mechanisms is different on the finest scale, the evidence suggests that on the scale of self-organization and faulting, the mechanisms behave similarly. Comparison of these two mechanisms can lead to new insights and potentially one can be used to resolve unanswered questions involving the other. In particular, the diagnostic appearance of the transformed material in microlenses makes the attempt to decipher the self-organization process much simpler than attempting to distinguish cracks of many generations in material faulted by "brittle" processes. This study will examine the approach to failure in Mg2GeO4 undergoing the olivine« spinel transformation at pressures greater than 2.5 GPa (pressures too high for "brittle" processes to participate) to map out the microstructural evolution from loading-generated microlenses, through the self-organization process, to faulting.