两级加载下两焊点拉剪点焊接头的损伤

对带有两个焊点的拉剪点焊试样进行了两级变幅疲劳加载,应力幅和平均应力均不相等.结果表明,两级变幅加载下存在应力次序效应.在低—高加载时存在"锻炼效应",线性累积损伤的值大于1;在高—低加载时存在"过载效应",高—低加载下的线性累积损伤值也大于1.在高—低加载方式下,高水平应力作用后,低水平应力剩余疲劳寿命大于按线性疲劳累积损伤法则所估算的剩余寿命,低应力作用下的剩余寿命甚至大于低应力单独作用下的全寿命.高—低加载下的线性累积损伤结果表明,焊点边缘更象是一个缺口.

Damage of two-spot welds under two level loading

Two level loadings of unequal stress amplitude and unequal mean stress were applied on the two-spot tension-shear spot welds.Experimental results show that there exists stress sequence effect under two-level loading.There exists exercise effect under low-high loading,the damage accumulated by linear damage accumulation rule is higher than 1;there exists overload retardation under high-low loading,the damage accumulated by linear damage accumulation rule is also over 1.Under high-low loading,residual lives under low stress level are longer than residual life calculated from linear damage accumulation rule;some residual fatigue lives are even longer than total life under low stress alone.The damage accumulation result under high-low loading indicates that the periphery of spot welds behaves as a notch.