Inelastic Analysis of Stress-Strain Response in Engineering Ceramics at Elevated Temperatures

对烧结氮化硅陶瓷进行了高温拉伸试验和拉伸蠕变试验。在试件的规长上加工四个凸点，并在试件的一侧用激光束式伸长仪测量两个凸点之间的位移。在此基础上，建立了陶瓷高温疲劳性能测试系统。然后对烧结后的氮化硅陶瓷在室温~ 1200℃范围内进行了推拉疲劳试验。所得结果总结如下：1。试验温度和位移速率对拉伸应力-应变关系有显著影响。对实测荷载(P)-位移（delta）关系计算的标称应力-应变关系进行了修正，使弹塑性有限元法计算的P -delta曲线与实测值一致。修正后的应力应变关系似乎给出了烧结氮化硅陶瓷在高温下的内在关系。烧结氮化硅陶瓷的蠕变曲线表现为瞬态蠕变阶段，其次是稳态蠕变阶段。根据最小蠕变应变率与标称应力的双对数关系，数据可以用两条直线拟合，且其斜率在高应力区大于低应力区。应力幅值与破坏循环次数之间的关系呈现出所谓的S-N曲线的形状。随着试验温度的升高，S-N曲线的斜率有减小的趋势。

The tensile tests and tensile creep tests were performed for the sintered silicon nitride ceramics at elevated temperatures. The four projections were machined in the gauge length of the specimen, and the displacement was measured between the two projections on one side of the specimen by means of the laser-beam-type extensometer. Furthermore, the new test system was developed for evaluating the fatigue properties of ceramics at elevated temperatures. Then push-pull fatigue tests were performed for the sintered silicon nitride ceramics in the temperature range from room temperature to 1200ﾟC. The results obtained are summarized as follows :1. The tensile stress-strain relationship was markedly influenced by test temperature and displacement rate.2. The nominal stress-strain relationships calculated from the measured load (P)-displacement(delta) relationships were corrected so that the p-delta curve calculated using the elastic-plastic F.E.M agreed with the measured one. The corrected stress-strain relationship seems to give the intrinsic relationship of sintered silicon nitride ceramics at elevated temperatures.3. The creep curves of sintered silicon nitride ceramics exhibited the transient creep period, being followed by the steady creep period.4. According to the relationships between the minimum creep strain rate and nominal stress plotted in double logarithmic scales, the data could be fitted by two straight lines, and their slopes are larger in the higher stress region than in the lower stress region.5. The relationships between stress amplitude and number of cycles to failure showed the shape of a so called S-N curve. The slope of S-N curve, however, had a tendency to decrease with increase in test temperature.