一种与路径相关的多轴低周疲劳寿命预测方法

已有研究指出,与比例加载相比,非比例加载下某些金属材料虽然没有明显的附加强化现象,但疲劳寿命却明显缩短.利用附加强化系数和非比例度因子修正的等效应变法,无法反映此类材料非比例加载下的寿命缩短现象,导致预测寿命通常偏于危险.为更好地预测不存在明显附加强化现象材料的多轴非比例疲劳寿命,引入寿命缩减因子的概念,并结合非比例度因子对ASME等效应变范围进行了修正,提出一种新的多轴低周疲劳寿命预测方法.为了便于应用,明确了寿命缩减因子的确定方法.针对不同加载路径,发展了一种基于最小法向应变范围的非比例度因子计算方法,并给出了多轴加载一般情形下最小法向应变范围的计算步骤.利用304不锈钢12种非比例加载路径下的试验数据验证了所提非比例度因子计算方法的精度,并与已有方法进行了对比分析,发现所提方法可以更好的描述加载路径的非比例程度.利用10种材料(包括7种不存在明显非比例附加强化现象的材料)的试验数据对所建疲劳寿命预测模型进行了验证,结果表明预测结果与试验结果吻合较好.

A path-dependent multiaxial low cycle fatigue life prediction model

Existing experimental results showed that, for some metallic materials, nonproportional loading resulted in significantly shorter lives while no additional nonproportional cyclic hardening was observed. The equivalent strain method modified by additional hardening coefficient and nonproportionality factor cannot be used to correlate the fatigue data of these materials, which usually gives nonconservative predictions. To overcome this shortcoming, a new multiaxial low cycle fatigue life prediction model on the basis of the ASME effective strain range is proposed by introducing the fatigue life reduction factor and nonproportionality factor. The procedure was also proposed to determine the fatigue life reduction factor. A new equation is proposed to calculate the nonproportionality factor on the basis of the minimum normal strain range. Procedures to determine the minimum normal strain range are presented for the general multiaxial loadings. The proposed method is verified by the measured data of 12 kinds of nonproportional loading paths. In contrast to the existed method, the proposed one can be better used to describe the nonproportionality of the loading path. The accuracy of the proposed fatigue life prediction method is systematically checked by the experimental data found in literature for 10 different metallic materials (including 7 kinds of material showing no additional nonproportional cyclic hardening) under various constant amplitude multiaxial loading paths.