Non-destructive Detection of a Sintered Tool Material by Impact Repetition

为了预测刀具失效，需要了解刀具材料的断裂特征及其在冲击重复作用下的行为。近年来，各种烧结刀具材料因其具有高温高硬度、低摩擦系数等优良特性而应运而生。断裂特征及其随冲击重复次数的变化是预测刀具失效所必需的，但由于断裂应力的分散性，需要准备大量的试件。该项目的目标是开发一种无损检测断裂应力及其变化-恶化-冲击重复的方法。1.为了研究烧结刀具材料的劣化机理，专门设计了冲击试验机，可以在较宽的温度和冲击持续时间范围内进行断裂和劣化试验。2.劣化机理认为是在硬质颗粒周围产生方向随机的小裂纹。3.讨论了超声波在烧结刀具材料中的传播特性随冲击重复次数的变化规律。劣化程度对波传播的衰减，尤其是横波的衰减影响很大，而横波和横波的传播速度变化不明显。4.根据波的传播特性，还可以检测到断裂应力的散布，这是材料中结构的不同。

In order to predict tool failure, the fracture characteristics of tool material and their behaviors with impact repetition are required. In recent years, many kinds of sintered tool materials come on the stage because of their excellent characteristics, such as high hardness under high temperature and low frictinal coefficient. The fracture characteristics and their change with impact repetition are required for the prediction of tool failure, but an extreme lot of specimen should be prepared bacause of the scatter of their fracture stresses. The object of the project is a development of non-destructive detection method of fracture stress and its change ---deterioration--- with impact repetition. The results from the project are as follows:1. In order to study the deterioration mechanism of a sintered tool material, the impact testing machine is specially designed, by the machine the fracture and deterioration test may be possible under wide temperature and impact duration range. 2. The mechanism of deterioration is considered as the generation of small crack with random direction around hard particles. 3. A change of a characteristics of ultra-sound wave propagation with impact repetion in sintered tool material is next discussed. An attenuation of wave propagation, especially that of shear wave, is greatly affected by the deterioration level, while a change of velocity of the propagation is not seen in both of lateral and ghear waves. 4. A scatter of fracture stress, which is the defference of the structure in the material, may also be detected by the characteristics of the wave propagation.