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本文介绍了由焊趾始裂的疲劳裂纹的弹-塑性断裂力学解,通过用应变项代替通常的应力项便可将该解用于解决塑性问题。由于引入了有效裂纹长度,该解可用来解释很短裂纹的传播问题。这里的有效裂纹长度是真实裂纹长度再加上l_o值,l_o是材料和材料状态的特征常数。本文也考虑了平均应力和裂纹前沿的形状对由该解得到的强度因子的影响。就焊接试样的弹性和塑性应变场里的裂纹而言,当用该强度因子来表达时,裂纹增长结果与弹性长裂纹的数据非常吻合。当结合包含裂纹增长的所有阶段的传播模型考虑时,用该强度因子对两种钢的对接焊和填角焊试样总寿命的预测也是成功的。对应于对接焊试样破坏时的界限应力等于光滑试样疲劳极限应力除以弹性应力集中系数。然而,填角焊试样的对应于破坏时的应力值却比疲劳极限应力除以弹性应力集中系数所得的值高一些。在这两种应力值之间的各应力下,裂纹将起始于填角焊趾区,但决不会传播至破坏。
In this paper, the elastic-plastic fracture mechanics solution of fatigue crack initiation from weld toe initiation is introduced. This solution can be used to solve the plastic problem by replacing the usual stress term with strain term. Due to the introduction of the effective crack length, this solution can be used to explain the propagation of very short cracks. The effective crack length here is the true crack length plus the l_o value, l_o is the characteristic constant of the state of the material and the material. The paper also considers the effects of the average stress and the shape of the crack front on the intensity factor obtained from this solution. In terms of the elasticity of the welded specimen and the cracks in the plastic strain field, the crack growth results are in good agreement with those of the elastic long crack when expressed by this strength factor. The prediction of the total life of butt-welded and fillet-welded specimens from both steels with this strength factor has also been successful when considered in conjunction with the propagation model for all phases including crack growth. The limit stress corresponding to the failure of a butt welded specimen is equal to the fatigue limit stress of a smooth specimen divided by the elastic stress concentration factor. However, the value of the stress at break corresponding to the fillet weld test is higher than the value obtained by dividing the fatigue limit stress by the elastic stress concentration factor. At these stresses between these two stresses, the crack will begin at the fillet toe zone but will never propagate to failure.