Microstructure and lengthscale effects on fracture

材料的断裂预测是影响制造业和交通运输业的一个长期存在的问题，也限制了新的断裂容限材料的发展。其原因来自于实验观察材料失效的困难和断裂过程中涉及的许多微观结构参数。该提案的总体目标是了解微观结构与断裂性能之间的关系，以便设计具有更高抗断裂性能的材料。本方法的新奇在于实验技术的独创性和实验与建模之间的精确耦合。断裂通常通过材料中空隙或裂纹的成核、生长和连接而发生。由于影响材料断裂的参数较多，使用商业材料研究断裂是困难的，为了使这些参数解耦，我们开发了一种简化材料（或模型材料），在这种材料中，断裂过程是可控的。它由金属片组成，其中使用脉冲激光人为引入空隙。人造空隙模仿商业材料中的空隙，但以简化和受控的方式。这种对激光钻孔技术提供的空隙的尺寸和位置的控制以前从未实现过，并且提供了许多更好地理解断裂的机会。在Ti、Mg和Cu样品中，将研究织构、孪晶和长度效应。这些样品中激光钻孔的生长和连接将在扫描电子显微镜中的2D和X射线计算机断层扫描装置中的3D原位拉伸试验期间进行监测。这项研究计划的结果将有助于我们的基本理解的纹理，孪生和长度尺度对断裂的影响。在更实际的层面上，从这个研究计划预期的知识将有一个直接的影响，在工程领域的抗损伤材料的设计断裂是一个问题，如运输，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.