dong(~7":K~)~ ; HE Jia-wen(~]'~3~:) 2 , CUI Jian-guo(~IIt~) 2 , LI Nian(~j~ ~)2, FU Yong-hui(~7]<~) z, SUN Jun@]~ ~)2 (1.Abstract. The interface plays the central role in the failure analysis of composite laminates, therefore, the interface material properties are taken as the independent parameters. A simple, universal and practicable criterion, i.e. a ratio criterion of strain energy release rate, is proposed to determine the growing direction of a fatigue crack in the composite laminates. The method of arbitrary lines, which is very effective to solve the problems with high gradient feature, is used to analyze the experimental results at the key moments when a crack kinks, turns into the interface, or bifurcates. An approximate method of computing the energy release rate is given. The fatigue fracture tests of composite laminates are carried out, and the numerical predictions of crack growing directions agree well with the experimental results. It is concluded that the methods suggested in this paper are effective to obtain the cracking history and the growing path of a fatigue crack in composite laminates.
The finite element method (FEM) and the boundary element method (BEM) are often adopted. However, they are not convenient to spatially vary thermal properties of functionally graded material (FGM). Therefore, the method of lines (MOL) is introduced to solve the temperature field of FGM. The basic idea of the method is to semi-discretize the governing equation into a system of ordinary differential equations (ODEs) defined on discrete lines by means of the finite difference method. The temperature field of FGM can be obtained by solving the ODEs. The functions of thermal properties are directly embodied in these equations and these properties are not discretized in the domain. Thus, difficulty of FEM and BEM i8 overcome by the method. As a numerical example, the temperature field of a plane problem is analyzed for FGMs through varying thermal conductivity coefficient by the MOL.
Abstract. Responses of structure under impact load are different from quasi-static process and fatigue. Especially when the impact load is cyclic loading and unloading, damage of structure is different form that of structure under single continuous load. Random impact load usually has high peak value, thus material in structure may contain plastic strain, and damage evolution is non-linear. For cyclic loading and unloading, elastic recovery process should be considered. These characteristics make it difficult to compute damage in FEA. In the paper, we use FEM and damage theories to compute cumulative damage of certain metal structure under cyclic loading and unloading, and statistic method is used in load setting. A series of experiments were carried out to verify the simulated results. It is proved that FEM can be used to acquire cumulative damage of structure under cyclic loading and unloading, and the results may be referenced in engineering design.
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