Evaluation of Creep-Fatigue Behavior under Multiaxial Loading Based on the Overstress Concept

为建立多轴载荷条件下的蠕变-疲劳寿命预测方法进行了研究。详细研究了多轴蠕变疲劳条件下的变形和破坏行为。用固溶处理的304不锈钢制备了中空圆柱形试件，并在650ﾟC的空气中进行了应变控制拉扭试验。此外，还对同一材料在650ﾟC空气和高真空环境中进行了单轴推拉应变控制蠕变-疲劳试验，并对试验结果进行了应力-应变响应分析，得到了超应力和内应力，以明确非弹性变形行为与这些应力分量的关系。即使峰值应力各向同性，超应力和内应力也会导致各向异性的发展。超应激的时间依赖行为表现为变化的…由于法向应力分量与剪切超应力分量的比率较大，所以Ge更大。结果表明，超应力的剪切分量控制非弹性变形的时变分量，超应力的法向分量控制非弹性变形的时变分量。此外，应力松弛行为至少由两个部分组成：一个是超应力松弛，另一个是内应力松弛。对于蠕变疲劳破坏行为，超应力的非弹性应变积分控制着蠕变-疲劳损伤的时间无关分量。此外，超应力的最大可分辨剪切分量控制与环境无关的损伤分量。环境效应包含在与时间无关的损伤分量中，并由超应力的分解法向分量控制，损伤的时变分量用最大主超应力分量的时间积分很好地描述。得到了适用于考虑环境影响的多轴加载条件下的蠕变-疲劳寿命预测方程。较少

A research has been made in order to establish a creep-fatigue life prediction procedure under multiaxial loading condition. Deformation and failure behaviors under the multiaxial creepfatigue condition were studied in detail. Hollow cylindrical test specimens were prepared with solution annealed 304 stainless steel and were subjected to a strain controlled tension-torsion under proportional loading at 650ﾟC in air. Additionally, uniaxial push-pull strain controlled creep-fatigue tests were also made with the same test material at 650ﾟC in air and in high vacuum environment.Analyses were made with stress-strain responses of the test results to obtain the overstress and the internal stress in order to make clear the relation between the inelastic deformation behaviors and those components of stress.A development of anisotropy was observed with the overstress and the internal stress even though the peak stresses showed isotropy. The time dependent behavior of the overstress showed a chan … More ge due to the ratio of normal versus shear overstress components. It was concluded that the shear component of the overstress controls the time-independent component of the inelastic deformation and that the normal component of the overstress controls the time-dependent component of the inelastic deformation. Additionally, It was made clear that the stress relaxation behavior is composed of, at least, two components: one is the relaxation of the overstress and the other is the relaxation of the internal stress. The former occurs with a high stress relaxation rate to cease within a short time duration,, however, the latter has a slow relaxation rate to last for long time.Regarding the creep fatigue failure behavior, the inelastic strain integration of the overstress controls the time-independent component of the creep-fatigue damage. Furthermore, The maximum resolved shear component of the overstress controls the environment free component of the damage. The environmental effect is included in the time-independent damage component and is governed by a resolved normal component of the overstress.The time-dependent component of the damage is well described with the time integration of the maximum principal overstress component. Obtained is the creep-fatigue life prediction equation which is available for the multiaxial loading condition including the environmental effect. Less