试验测定和分析了YB-MD-3有机玻璃的等幅疲劳裂纹扩展规律和疲劳裂纹扩展门槛值。结果表明对较厚的中心裂纹板试件用带压缩的循环载荷能够预制出质量稳定的穿透裂纹;显示了平均应力对疲劳裂纹扩展特性影响的特殊规律以及负应力比循环下压缩部分对裂纹扩展的加速作用;探讨了常温下低频加载时频率变化对YB-MD-3有机玻璃疲劳裂纹扩展的影响。

An experimental study of stable fatigue crack propagation behavior and the measurement of fatigue crack propagation thresholds of YB-MD-3 PMMA plates was carried out at room temperature.During the preparation of initial through fatigue cracks for M(T)specimens,load cycles with compressive portion demonstrates better quality than usual tension-tension loading.The fatigue crack propagation rate in Paris's region for certain load ratio shows good correlation with a straight line in double logarithmic da/dV-ΔK coordinate.The da/dN and the slope of the straight line increases with the increase of load ratio.For the negative load ratios,however,the compressive portion in load cycles accelerates the crack growth.A proper formulation to these effects is unavailable.The fatigue crack propagation rate in YB-MD-3 plates is also sensitive to the change of load frequency at room temperature,even for very low frequencies,say,1Hz and 2Hz.