X90超高强度输气钢管材料本构关系及断裂准则

针对试制成功的X90输气钢管,进行5种不同圆棒缺口的准静态拉伸试验及应力三轴度计算,发现由于试样缺口存在,应力三轴度值增加2.43倍,断裂应变减少29%,损伤应变能降低71%。利用常规拉伸试验机和Hopkinson拉杆试验装置进行不同应变速率拉伸试验发现,应变速率对断裂应变的影响相对较小,准静态和高速状态下,差异最大约10%。基于Johnson-Cook本构和失效模型,分别建立了考虑应变率效应的X90管线钢本构模型和考虑应变率、应力三轴度的失效模型;同时,基于损伤力学理论,得到了基于塑性均匀延伸率和损伤应变能的X90管线钢断裂准则。基于材料损伤应变能密度临界值不变假设以及试验数据,得到了X90管线钢断裂特征长度与应力三轴度、试样直径之间的关系式。

Constitutive law and fracture criteria of X90 ultrahigh-strength gas-transmission steel pipe material

For trial-produced X90 gas-transmission pipe, quasi-static tensile tests and stress triaxiality calculation were carried out on five kinds of different notched round bars. It has been found that because of sample notch, when stress triaxiality is increased by 2.43 times, fracture strain and damage strain energy will be reduced by 29% and 71% respectively. Universal material testing machine and Hopkinson bar test unit were used for tensile experiments at different strain rates. It has been discovered that strain rate has less effect on failure strain, and in a case of quasi-static state and high-rate state, the largest difference is about 10%. Based on Johnson-Cook constitutive and failure model, X90 steel pipe constitutive model with consideration of stress rate effect was established as well as the failure model considering strain rate and stress triaxiality. Meanwhile, according to damage mechanics theory, X90 pipe steel fracture criterion was obtained on a basis of plastic uniform elongation and damage strain energy. Based on the assumption of constant density critical value of material damage strain energy and test data, the relation expression was obtained between X90 pipe steel fracture characteristic length and stress triaxiality as well as specimen diameter.