Microstructure and lengthscale effects on fracture

材料断裂预测是影响制造业和运输业的老大难问题，也限制了新型耐断裂材料的开发。其原因在于难以通过实验观察材料的失效，以及断裂过程中涉及的许多微观结构参数。这项建议的总体目标是了解微观结构和断裂性能之间的关系，以便设计出具有更好的抗断裂性能的材料。这种方法的新颖性在于实验技术的独创性，以及实验和建模之间的精确耦合。断裂通常是通过材料中空洞或裂纹的形核、生长和连接而发生的。由于影响裂缝的参数很多，用商业材料研究裂缝是很困难的。为了将这些参数解耦，我们开发了一种简化的材料(或模型材料)，其中断裂过程受到控制。它由金属片组成，其中的空洞是使用脉冲激光人工引入的。人造空隙模仿商业材料中的空隙，但以一种简化和受控的方式。这种由激光打孔技术提供的对空隙大小和位置的控制以前从未实现过，这为更好地了解裂缝提供了许多机会。将对钛、镁和铜的织构、孪生和长度效应进行研究。在2D、扫描电子显微镜和X光计算机断层扫描装置中的原位拉伸测试期间，将监测这些样品中激光钻孔的生长和连接。这项研究计划的结果将有助于我们从根本上理解织构、孪生和长度对骨折的影响。在更实际的层面上，这项研究计划所预期的知识将对工程领域的抗损伤材料的设计产生直接影响，这些领域中的断裂是一个问题，如交通、制造和核工业。

Predicting fracture of materials is a long-standing problem affecting manufacturing and transportation industries, and limiting the development of new fracture tolerant materials. The reasons come from difficulties in experimentally observing failure of materials and from the many microstructural parameters involved in the fracture process. The overall goal of this proposal is to understand the relation between microstructure and fracture properties, in order to design materials with improved fracture resistance. The novelty of the present approach lies in the originality of the experimental techniques and in the precise coupling between experiments and modeling. Fracture generally takes place by the nucleation, growth and linkage of voids or cracks in a material. Using commercial materials to study fracture is difficult due to the large amount of parameters affecting it. In order to decouple these parameters, we have developed a simplified material (or model material) where the fracture process is controlled. It consists of metallic sheets in which voids are artificially introduced using a pulsed laser. The artificial voids mimic voids in commercial materials but in a simplified and controlled fashion. Such control over size and location of the voids provided by the laser drilling technique has never been achieved before and offers many opportunities to better understand fracture. Texture, twinning and lengthscale effects will be investigated in Ti, Mg and Cu samples. Growth and linkage of laser drilled hole in these samples will be monitored during in-situ tensile tests in 2D in a scanning electron microscope and in 3D in an x-ray computed tomography set-up. The outcome of this research program will contribute to our fundamental understanding of texture, twinning and lengthscale effects on fracture. On a more practical level, the knowledge expected from this research program would have a direct impact on the design of damage resistant materials in engineering fields where fracture is an issue such as transportation, manufacturing and nuclear industries.