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在测定某些钢材,例如35CrMoA,42CrMo,20CrMnTi,50CrMoA和轨钢的疲劳裂纹扩展门槛值时,普遍认为当三点弯曲试样的α/W<0.2时,ΔK_(th)值α/W(?)的减少而降低,只有当0.2<α/W<0.5时,ΔK_(th)值才趋于稳定.本文作者应用边界配置法计算了三点弯曲试样裂纹尖端应力场无奇异性的均匀横向分量,即应力双轴参数T.指出当三弯试样α/W<0.2时,T值很大.ΔK_(th)和T两者控制了对疲劳扩展有重要影响的过程区和塑性区.建议在测定三点弯曲试样的ΔK_(th)值时宜选用α/W=0.3～0.5.
When measuring the fatigue crack propagation thresholds of some steels, such as 35CrMoA, 42CrMo, 20CrMnTi, 50CrMoA and rail steel, it is generally accepted that when the three-point bending specimen α/W<0.2, the ΔK_(th) value α/W ( )) decreases and decreases only when 0.2<α/W<0.5, the value of ΔK_(th) tends to be stable. The authors use the boundary configuration method to calculate the uniform stress field at the crack tip of a three-point bending specimen with no singularity. The transverse component, ie, the stress biaxial parameter T., indicates that when the three-curve specimen α/W<0.2, the T value is large. Both ΔK_(th) and T control the process and plastic zones that have an important influence on fatigue expansion. It is recommended to use α/W=0.3～0.5 when measuring the ΔK_(th) value of the three-point bending specimen.