STUDY on MICRO MECHANISM of FRACTURE by ULTRASONIC METHOD

超声法研究断裂微观机理

基本信息

批准号：
62550043
负责人：
SATOH KATSUHIKO
金额：
$ 1.22万
依托单位：
UNIVERSITY of TOKYO
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

The fracture process of most ductile metals generally consists of three stages; i) voids nucleation at the second phase particle sites either due to cracking of the particles of decohesion between the particles and the matrix, ii) the voids growth under the multi-axial stress state, and iii) the voids coalescece leading to the final fracture.In the present project, the void nucleation and growth process is experimentally studied, based on the real time observation of void density by ultrasonic method and also by the examination of dimple distribution on the fracture surface. In the experiment, tensile fracture test of mild steel was performed. Several kinds of materials were chosen to examine the effect of the concentration of the second phase particles which can be the void initiation sites. The shape of the specimen used in the test was a circular cross-section bar with a circumferential notch. Speci-mens without notch were also used. The size of the notches was changed to obtain dif … More ferent tri-axial stress states. Tensile fracture test was conducted by an instron type testing machine at a quasi-static strain rate. The mode of fracture was a typical cup and corn type. The etched section along the center axis indicates that a small region near the fracture cross-section is highly deformed and the voids are concentrated at a thin layer along the fracture section. Tensile fracture test of ductile mild steel changing the stress triaxiality and impurity concentration has shown the following results by the observation of the dimple distribution on the fracture surface.1) In case of rather rich impurity material, the number and area densities of the main dimples increase with the stress triaxiality and they approach to limited values.2) In case of high purity material, the number density of the dimples does not depend on the stress triaxiality. The area density increases with the stress triaxiality.The real time measurements of the ultrasonic wave attenuation have consistent results with the above, and also revealed that the nucleation and growth process of the voids do not start untill very close to the fracture instant after the development of large plastic deformation. Concerning to the attenuation measurement, the attenuation due to the voids and cleavage have not been distinguished so far, however, the method of changing the frequency might be able to overcome this problem. The above obtained results can qualitatively be explained by assuming a microscopic mechanism of voids nucleation and growth process, which includes the mutual interference of the voids. Less

金属的断裂过程通常由粘附粒子的三个阶段组成，颗粒和基质，ii）多轴应力状态下的空隙生长，iii）导致最终骨折的空隙死亡。基于超声法的实时观察，以及在实验中的凹槽表面的检查。空白的坐姿是带有圆周缺口的圆形横截面。杯子和玉米类型。裂缝表面上的凹痕分布。1）如果有相当丰富的材料，则tress tress tress toreaxiality的数量和面积密度对有限的值。2）al，酒窝的数量密度不取决于应力三方性。面积密度随应力三轴性而增加。超声波一致的时间测量结果与上述空隙的上述和生长过程的启动不会非常接近裂缝内部，从而使大型塑性变形的发育均未达到衰减测量。空隙和裂解已被区分了，可以通过假设成核和生长过程来解释上述问题的质量。