结合应变硬化定律和连续损伤力学,提出了一种考虑蠕变 3 阶段的本构模型,对 650℃下的哈氏合金X的CT 试样进行了裂纹扩展有限元模拟分析.对比分析了不同蠕变阶段对纯蠕变裂纹扩展的影响,使用考虑蠕变 3 个阶段的本构模型进行了蠕变-疲劳裂纹扩展模拟,讨论了载荷幅值、载荷比和保载时间对裂纹扩展速率的影响,并分析了每种载荷条件对裂纹扩展期间损伤积累的贡献.结果表明:纯蠕变裂纹扩展模拟结果中,考虑所有蠕变阶段的本构模型计算结果与实验结果一致性最高.载荷从 5kN 增加到 7 kN,考虑蠕变第Ⅰ、Ⅱ阶段的裂纹扩展速率平均预测差异由 0.57 增至 0.61,考虑蠕变第Ⅱ阶段和考虑蠕变第Ⅱ、Ⅲ阶段分别由 0.67 减至 0.64、由 0.16 减至0.07.蠕变-疲劳裂纹扩展模拟结果显示,随着载荷幅值从 5kN增大至 7 kN,载荷比从 0.01 增至 0.50,裂纹扩展速率前者增大、后者减小,da/dt-Ct,avg曲线斜率基本不变,同时蠕变损伤占比增大,疲劳和交互损伤占比减小,各加载情况结果的蠕变损伤均占主导,其次为交互损伤,疲劳损伤占比最小.随保载时间从 1s 增加到 1800 s,循环相关的裂纹扩展速率增大,时间相关的扩展速率减小,da/dt-Ct,avg曲线斜率增大,蠕变损伤增大,疲劳损伤减小,交互损伤先增后减,保载时间为 10s时各损伤占比近似相等,保载时间为 1s时疲劳损伤为 83%,保载时间为 600 s时蠕变损伤为96%.
A constitutive model that incorporates the three stages of creep was proposed by combining the strain hard-ening law with continuum damage mechanics.This model was used in finite element simulations of crack propagation in Hastelloy X CT specimens at 650℃.The influence of various creep stages on the pure creep crack propagation behavior was compared.The constitutive model was also applied in simulations of creep-fatigue crack propagation considering the three stages of creep.The impact of load amplitude,load ratio,and hold time on the crack growth rate,as well as the contribution of each loading condition to damage accumulation during crack propagation,were investigated.The findings reveal a high correlation between the constitutive model which considers all creep stages and the experimental results in pure creep crack propagation simulations.As the load escalated from 5 kN to 7 kN,there was an increase from 0.57 to 0.61 in the average prediction differences of crack propagation rate considering creep stages Ⅰ and Ⅱ,whereas the average prediction differences considering creep stage Ⅱ and considering creep stages Ⅱ and Ⅲ witnessed a decrease from 0.67 to 0.64 and from 0.16 to 0.07,respectively.The creep-fatigue crack propagation simulation demonstrated that as the load amplitude increased from 5 kN to 7 kN or the load ratio increased from 0.01 to 0.50,the crack growth rate increased for the former and decreased for the latter.The da/dt-Ct,avg curve's slope remained virtually unchanged,but the proportion of creep damage increased and those of fatigue and interaction damage decreased.Creep damage had the most significant effect on the results of each loading case,followed by interaction damage,whereas fatigue damage had the least impact.As the hold time was extended from 1 s to 1800 s,the cycle-related crack propagation rate grew,the time-related propagation rate fell,and the slope of the da/dt-Ct,avg curve increased.Creep damage increased,fatigue damage decreased,and interaction dam-age initially rose and then declined.The proportion of each damage was approximately equal at a hold time of 10 s,but fatigue damage accounted for 83%at a hold time of 1 s and creep damage accounted for 96%at a hold time of 600 s.