点载荷循环加载下红砂岩疲劳破坏特性试验分析

Test and Analysis on Fatigue Failure Properties of Red Sandstone under Cyclic Point Loading

在掘进机截齿破岩、高频破碎锤破岩时,其与岩体的接触面积均很小,相当于点载荷循环加卸载破岩。为了解点载荷循环作用下上限应力对红砂岩疲劳特性的影响,利用MTS Landmark试验系统对红砂岩进行上限应力比分别为0.70、0.80、0.85和0.90的循环点载荷试验。结果表明:在加载波形为渐变正弦波,下限应力比为0.3,加载频率为1 Hz的条件下,红砂岩的疲劳寿命随着上限应力的增大而减小,即上限应力越大,破岩速度越快;红砂岩在点载荷循环加卸载作用下发生破坏时的轴向应变与上限应力所对应的静态应力-应变曲线峰后段的应变相当。

The application of point load is involved in many fields of practical engineerings such as the rock-breaking of boom-type roadheader, high-frequency hammer, etc. As the contact area between the machine and rock mass is very small and can be seen as a point contact, the rock-breaking type is equivalent to cyclic point loading. In order to understand the effect of upper limit stress on fatigue life （the time required for destruction） of red sandstone under the cyclic loading of point load, the MTS Landmark test system is adopted for the fatigue test with different upper limit stress ratios including 0.70, 0.80, 0.85, and 0.90. The experimental result shows that the fatigue lifetime of red sandstone decreases with the increase of upper limit stress when the loading waveform is a gradient sine wave and the lower limit stress ratio and the loading frequency are 0.3 and 1 Hz, respectively. It is also shown that the terminal strain corresponding to fatigue failure is equal to the one corresponding to the point where the post-peak stress-strain curve and the line of the maximum cyclic load intersect, which is called the deformation control law.