为了开展多模态缺陷条件下复合材料柱形壳的屈曲特性研究,进行了理想柱形壳在轴压工况下的线性屈曲分析,得出前50阶屈曲失稳模式,即模态缺陷;基于弧长法研究不同模态缺陷条件下复合材料柱形壳的非线性屈曲特性;将有限元分析结果、NASA SP-8007规范计算结果与Bisagni试验结果作对比分析.结果表明:对于轴压柱形壳屈曲问题,第1阶模态缺陷不是最差缺陷,在第1阶模态缺陷条件下求出的非线性屈曲载荷比试验值高出较多;高阶模态缺陷条件下的复合材料柱形壳非线性屈曲计算结果与试验结果最为吻合,两者相差较少;屈曲载荷下降受缺陷形状、幅值双重影响,复合材料柱形壳屈曲计算需考虑多模态问题;NASA求出的屈曲载荷非常保守,低于试验值较多,用NASA方法进行复合材料柱形壳的设计,往往会导致结构笨重、材料浪费、性能降低.
In order to investigate on buckling behavior of some composite cylindrical shells considering multimode imperfections, linear buckling analysis was performed for the perfect cylindrical shell under axial compressed condition to obtain the first fifty buckling modes, defined as mode imperfections.Nonlinear buckling analysis of the cylindrical shell under different mode imperfection was proposed based on the Riks method.Buckling loads calculated using finite element analysis results and empirical method results according to NASA SP-8007 were compared with Bisagni's test results.The results show that the first mode imperfection is not the worst imperfection for composite cylindrical shells under axial compressed condition.Buckling load obtained from the first mode imperfection is much higher than the experimental result.And buckling load obtained from higher mode imperfection agrees well with the experimental result.The decrease of buckling load is influenced by shape and amplitude of imperfection synchronously.The multi-mode effects should be considered on buckling analysis of composite cylindrical shells.Buckling load obtained from NASA is very conservative, which is much lower than the test result.Designing composite cylindrical shells according to NASA always results in heavy structure, material redundancy and poor performance.
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