Microstructure and lengthscale effects on fracture

材料断裂预测是困扰制造业和运输业的一个长期难题，也限制了新型耐断裂材料的开发。其原因是实验观察材料破坏的困难和断裂过程中涉及的许多微观结构参数。本提案的总体目标是了解微观结构与断裂性能之间的关系，从而设计出具有更高抗断裂性能的材料。本方法的新颖之处在于实验技术的独创性和实验与建模之间的精确耦合。断裂通常是由材料中空洞或裂纹的成核、扩展和连接引起的。由于影响断裂的参数较多，使用工业材料进行断裂研究很困难。为了解耦这些参数，我们开发了一种简化材料（或模型材料），其中断裂过程得到控制。它由金属薄片组成，其中用脉冲激光人为地引入空洞。人造空洞模仿商业材料中的空洞，但以一种简化和控制的方式。激光钻井技术对孔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。将研究Ti、Mg和Cu样品的织构、孪晶和长尺度效应。这些样品中激光钻孔的生长和连接将在二维扫描电子显微镜和三维x射线计算机断层扫描装置的现场拉伸测试中进行监测。这个研究项目的结果将有助于我们对断裂的织构、孪生和长度效应的基本理解。在更实际的层面上，本研究项目所期望的知识将对工程领域的抗损伤材料的设计产生直接影响，这些领域的断裂是一个问题，如交通运输、制造业和核工业。

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.