The effects of combined external pressure and cyclic bending on the pipe buckling mechanism are investigated by experiments and finite element analysis. Ten experiments are conducted and it is found that the loading paths of external pressure and cyclic bending have a great influence on the buckling pressure of thick-walled pipes. The loading path of pressure followed by cyclic bending (p→ck) is more dangerous than that of cyclic bending followed by pressure (ck→p). The material properties of kinematic hardening, loading application and mesh convergence are taken into consideration in rigorous FE models. The reason of the critical loading path is revealed from the aspects of section ovality and stress-strain accumulation. Sensitivity analysis is conducted on the loading patterns and axial tension. With the application of axial force, the pipe laying process is simulated more precisely which shows that pipe buckling capacity is more sensitive to the bending cycles in the presence of axial force. The comparison between numerical results and present specification shows that the API specification is conservative in predicting the collapse pressure of thick-walled pipes (D/t = 15–21) whose underestimation is about 11%~37% under the effect of cyclic bending.

通过实验和有限元分析研究了组合外部压力和循环弯曲对管道屈曲机制的影响。进行了10次实验，发现外压和循环弯曲的加载路径对厚壁管的屈曲压力影响很大。压力后循环弯曲（p → ck）的加载路径比循环弯曲后压力（ck → p）的加载路径更危险。）。在严格的有限元模型中考虑了运动硬化、加载应用和网格收敛的材料​​特性。从截面椭圆度和应力应变累积方面揭示了临界加载路径的原因。对载荷模式和轴向张力进行敏感性分析。随着轴向力的应用，管道铺设过程被更精确地模拟，这表明管道屈曲能力在存在轴向力的情况下对弯曲循环更敏感。数值结果与现有规范的比较表明，API规范在预测厚壁管（D/t  =15-21）的坍塌压力时是保守的，在循环弯曲的影响下，其低估率约为11%~37%。