研究层合板结构基于最终层失效准则的可靠性分析方法,在此基础上,对复合材料层合板可靠性优化设计的方法和算法进行讨论。层合板作为一个系统考虑,其可靠性分析含以下几个步骤:(1)随机载荷和强度参数作为随机变量,利用一次二阶矩法(first order reliability method,FORM)分析单层板的失效概率。(2)假定失效概率最大的单层板首先破坏,然后通过修改刚度矩阵对结构进行再分析,得到剩余结构各单层板的失效概率,从而建立主要失效序列。(3)计算系统的可靠度。在确立复合材料基于最终层失效准则的可靠性分析方法的基础上,以系统可靠度指标最大为目标,研究层合板的可靠性优化问题。建立和发展基于最终层失效准则的复合材料层合板可靠性优化方法以及相应的算法,并对比讨论单变量和多变量优化设计问题。
In conventional reliability-based optimum design of structures, the reliability is computed based on the probability assumption, and the design objective and constraint are considered as deterministic ones. In many cases, however, there exist some fuzzy factors in the design objective and constraint functions. In this paper, the fuzzy reliability and fuzzy constraint are introduced to establish the fuzzy reliability-based optimum model for laminated composites. The examples show that the method developed in this paper can give consideration to both the reliability demand and the economic aspect of a structure. Since the fuzzy reliability-based optimum design is a ＇soft＇ design, the present results provide a new methodology for the effective evaluation of structural reliability and bring us an alternative optimum design idea.
A last-ply failure (LPF) analysis method for laminated composite plates is incorpo- rated into the ?nite element code-ANSYS, and a robust optimum design method is presented. The composite structure is analyzed by considering both in-plane and out-of-plane loads. For a lamina, two major failure modes are considered: matrix failure and ?ber breakage that are characterized by the proper strength criteria in the literature. When a lamina has failed, the laminate sti?ness is modi?ed to re?ect the damage, and stresses in the structure are re-analyzed. This procedure is repeatedly performed until the whole structure fails and thus the ultimate strength is determined. A structural optimization problem is solved with the ?ber orientation and the lamina thickness as the design variables and the LPF load as the objective. Finally, the robust optimum design method for laminates is presented and discussed.
