延性耗散理论认为，高温疲劳和蠕变产生的材料流动可以用粘性流进行描述，失效判据为Σ动粘性=材料韧性。本文在此基础上提出一种新的疲劳蠕变寿命预测方法，认为只有拉伸应力引起的塑性变形或蠕变变形才构成延性耗散，并提出以拉伸应力达到σmax-(σmaxσa)^1/2 作为开始塑性变形的条件。该方法适用于应力控制模式，且能综合反映应力比、加载速率、拉伸保载时间和平均应变速率的影响。用该方法对1.25Cr0.5Mo钢540℃应力控制下的疲劳区、蠕变区及疲劳蠕变交互作用区的寿命进行预测，预测结果与实测结果吻合较好。
Ductility exhaustion theory premises that material flow caused by loads under fatigue-creep conditions can be described by dynamic viscosity, and the criterion of failure is that dynamic viscosity equals material toughness. A new fatigue-creep life prediction method has been put forward based on ductility exhaustion theory with the assumption that ductility consumption only relates to plastic strain and creep strain caused by tensile stress, and plastic strain occurs only when tensile stress equates with σmax-(σmaxσa)^1/2. The method given is applicable for stress control mode, and includes effects of stress ratio, stress rate, tensile hold time, and mean strain velocity. Applicability of the new method is assessed with fatigue, creep, and fatigue-creep data on 1.25Cr0.5Mo under stress control at 540℃, and the prediction is found to be very satisfactory with a factor of ±×1.25.
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