Development of simplified model for buckling collapse analysis of plates and stiffened plates under cyclic loa

建立了一个计算板和加筋板在面内循环载荷作用下屈曲/塑性破坏行为的简化模型。首先，通过材料试验验证了Dafalias和Popov提出的双面非线性应变硬化模型能够准确地模拟低碳钢在循环载荷作用下的应力应变关系。进行了两端简支角钢柱的循环屈曲试验，并与采用双面模型的有限元分析结果进行了比较。取得了良好的协议。研究还发现，由于面内载荷作用下的应变范围较大以及初始屈曲后的预压应变导致材料韧性下降，局部屈曲区域的裂纹萌生更容易发生在弯曲的压缩侧而不是拉伸侧。进一步对船舶结构中典型的简支矩形板在单轴面内循环载荷作用下进行了有限元分析。人们认识到，拉伸膜应变在卸载边缘的积累可以成为裂纹萌生的触发器。最后，在理想结构单元法（ISUM）的框架内，建立了一个新的简化模型，用于板和加筋板的倒塌分析。通过理想化材料非线性和几何非线性，ISUM模型中的单元比传统有限元模型中的单元大，可以很容易地科普任何类型的应变硬化模型，包括两个表面模型。与有限元分析的比较表明，所提出的模型具有较高的适用性，在船舶结构中的典型板进行面内循环载荷。

A simplified model to calculate the buckling/plastic collapse behavior of plates and stiffened plates under in-plane cyclic loads was developed. First, it was proved by the material test that the two-surface nonlinear strain-hardening model proposed by Dafalias and Popov could accurately simulate the stress-strain relationship of mild steels under cyclic loads. The cyclic buckling test of both-end simply supported angle-bar columns was performed, and the results were compared with the results of Finite Element Analysis (FEA) using the two-surface model. Good agreements were obtained. It was also found that the initiation of crack at the locally buckled region is more likely to take place at the compression-side of bending than the tension sides, as a result of larger strain range due to the action of in-plane load and the deterioration of material toughness due to the pre-compressive strain after initial buckling. The FEA was further performed for a simply supported rectangular plate typical in ship structures, subjected to uni-axial cyclic in-plane load. It was recognized that the accumulation of tensile membrane strain at the unloaded edges could become a trigger to the crack initiation. Finally, a new simplified model for collapse analysis of plates and stiffened plates was developed within in the framework of the Idealized Structural Unit Method (ISUM). By idealizing material and geometrical nonlinearities, larger structural units are defined as an element in ISUM than in conventional FEA.This mode can easily cope with any type of strain-hardening model including the two-surface model. Comparisons with FEA demonstrated the high applicability of the proposed model to typical plates in ship structures subjected to in-plane cyclic loads.