Fatigue of hard and bittle materials

对WC-Co硬质合金和氮化硅两种硬质材料进行了拉伸压缩疲劳试验。这些材料表现出与金属完全不同的疲劳特性。WC- co硬质合金的疲劳极限由最大应力决定，且几乎取恒定值，与co含量和WC晶粒大小无关。对氮化硅的疲劳试验表明，受应力比和Co含量的影响，应力比越大，应力范围越小，疲劳寿命越短。这些硬材料之所以表现出与金属相反的趋势，是因为这些硬材料的疲劳性能不仅取决于机械性能，还取决于各种物理和化学性能，而金属的疲劳特性仅取决于机械性能。试验结果表明，该仪器具有良好的精度和在任意应力比下进行拉压疲劳试验的能力，非常适合于高强度材料的疲劳试验。

Tension-compression fatigue tests were made on two kinds of hard materials,WC-Co hardmetal and silicon nitride. It has been found that these materials show completely different fatigue characteristics from those of metals. The fatigue limits of WC-Co hardmetals are determined by the maximum stress and that take almost s constant value, regardless of Co-content and WC grain size. Fatigue tests on silicon nitride have shown, on the effects of stress ratio and Co contents, that the fatigue life will be shorter with larger stress rations and with smaller stress ranges. The reason why these hard materials show the opposite tendency to metals, will be that the fatigue properties of these hard meterials depend not only on mechanical properties but also on various physical and chemical properties, while the fatigue characteristics of metals depend solely on mechanical properties. It has been shown that the newly developed apparatus is very suited to the fatigue tests on hsrdmaterials because of its excellent accuracy and capability of tension-compression fatigue tests at arbitraly stress ratios.