Dynamics of Britttle Fracture

9802562 Marder 本项目将研究脆性材料中裂纹的动力学，使用单晶硅，因为它是最好的材料，高质量的单晶是丰富的，相对便宜。 PI已经开发了一套实验工具，显着提高运动裂纹的测量。 使用这些工具，他们将收集表征硅脆性断裂的数据，并显示它如何受到原子结构的影响。 这些工具是：1）动态电位降法，它能以120微秒的间隔连续测量裂纹的速度和位置120，000次，精度为± 10米/秒; 2）加载装置，它能对10厘米长的样品施加刚性位移，精度为0.1微米;以及3）X射线形貌，以获得断裂之前和之后的地下条件的图像。 这项研究将测量单晶硅中快速运行的裂纹的速度如何取决于载荷大小、载荷模式、晶面、取向和温度。 还将测量断裂表面上和断裂表面下的裂纹后面的结构。 随着对运行裂纹如何响应外部和原子尺度结构的详细了解，可以解决几个问题，包括微观结构的变化如何使裂纹扩展更加昂贵，并使用这种见解来降低材料的脆性;以及使用断裂表面上或断裂表面下的损伤结构与速度之间的已知相关性来提供断裂的事后分析速度 该跨学科项目由材料研究部陶瓷计划和数学和物理科学理事会多学科活动办公室共同资助。 ***

9802562 Marder This project will study the dyanamics of cracks in brittle materials, using single crystal silicon since it is the best characterized material available, and single crystals of high quality are plentiful and relatively inexpensive. The PIs have developed a set of experimental tools that improve significantly the measurement of cracks in motion. Using these tools they will gather data that characterize brittle fracture of silicon, and show how it is influenced by atomic structure. These tools are 1) a dynamic potential drop method which makes it possible to measure the velocity and location of a crack 120, 000 times in succession at intervals of one twentieth of a microsecond and with accuracy of plus or minus10 meters per second; 2) a loading apparatus capable of applying rigid displacements to a 10 cm long sample with accuracy of 0.1 micron; and 3) X-ray topography to obtain images of subsurface conditions, before and after fracture. The research will measure how the speed of a rapidly running crack in single-crystal silicon depends upon loading magnitude, loading mode, crystal plane, orientation, and temperature. The structures left behind the cracks, both on and below the fracture surface, will also be measured. %%% With a detailed understanding of how running cracks respond to external and atomic-scale structures, several issues can be resolved including how microstructural changes make crack propagation energetically more expensive, and using this insight to reduce the brittleness of materials; and using known correlations between damage structures on or below fracture surfaces with velocity to provide post mortem analysis of fracture velocities. This interdisciplinary project is co-funded by the Ceramics Program of the Division of Materials Research and the Office of Multidisciplinary Activities of the Mathematical and Physical Sciences Directorate. ***