Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.
The two-parameter Weibull model is used to describe the fiber strength distribution.The stress carried by the intact and fracture fibers on the matrix crack plane during unloading/reloading is determined based on the global load sharing criterion.The axial stress distribution of intact fibers upon unloading and reloading is determined based on the mechanisms of fiber sliding relative to matrix in the interface debonded region.The interface debonded length,unloading interface counter slip length,and reloading interface new slip length are obtained by the fracture mechanics approach.The hysteresis loops corresponding to different stresses considering fiber failure are compared with the cases without considering fiber failure.The effects of fiber characteristic strength and fiber Weibull modulus on the fiber failure,the shape,and the area of the hysteresis loops are analyzed.The predicted quasi-static unloading/reloading hysteresis loops agree well with experimental data.
A straightforward multi-scale boundary element method is proposed for global and local mechanical analysis of heterogeneous material.The method is more accurate and convenient than finite element based multi-scale method.The formulations of this method are derived by combining the homogenization approach and the fundamental equations of boundary element method.The solution gives the convenient formulations to compute global elastic constants and the local stress field.Finally,two numerical examples of porous material are presented to prove the accuracy and the efficiency of the proposed method.The results show that the method does not require the iteration to obtain the solution of the displacement in micro level.
The non-linear behavior of continuous fiber reinforced C/SiC ceramic matrix composites(CMCs)under tensile loading is modeled by three-dimensional representative volume element(RVE)models of the composite. The theoretical background of the multi-scale approach solved by the finite element method(FEM)is recalled firstly.Then the geometric characters of three kinds of damage mechanisms,i.e.micro matrix cracks,fiber/matrix interface debonding and fiber fracture,are studied.Three kinds of RVE are proposed to model the microstructure of C/SiC with above damage mechanisms respectively.The matrix cracking is modeled by critical matrix strain energy(CMSE)principle while a maximum shear stress criterion is used for modeling fiber/matrix interface debonding. The behavior of fiber fracture is modeled by the famous Weibull statistic theory.A numerical example of continuous fiber reinforced C/SiC composite under tensile loading is performed.The results show that the stress/strain curve predicted by the developed model agrees with experimental data.
