mohammad ali kouchakzadeh

This paper discusses the topic of probabilistic analysis of composite laminates rectangular plates containing a central circular hole under static tensile load. First, According to the continuum damage mechanics (CDM) approach, structural analysis models, the definition of damage and the treatment of random variables will be explored. Then, the matrix cracking and fiber/matrix debonding damage is modeled and the material constitutive relationships are implemented in the ABAQUS software by the subroutine. The probabilistic methods, first order reliability method (FORM) and second order reliability method (SORM) have been used to analyze the composite plates’ system failure probability. The failure functions and random variables have been obtained according to the CDM approach. Issues arising out of the use of composite material structures, in applications, due to non-homogeneity and anisotropic characteristics, and manufacturing defects will be highlighted, and uncertainties related to the material properties, loads, and boundary conditions will be discussed through examples. It is shown that the scatter in parameter values has a significant effect on damage development in the model.

In this study, a method for uncertainty analysis of laminated rectangular plate made of glass/epoxy with interlaminar crack (delamination) in loading mode I, II and I/II is performed using energy criterion. Limit state functions have been obtained to analyze the reliability of delamination growth in each loading mode according to the concepts of fracture mechanics and energy release rate. By using random variables and limit state functions according to energy criterion, uncertainty assessment will be performed using Response Surface Methodology (RSM). The main idea of the response surface methodology is to approximate the implicit response surface function using an explicit mathematical equation with random variables involved in the limit state function. Since the approximation of the limit state function is explicit, the first/second order reliability method can be used to estimate the probability of failure. It was indicated that in all modes the probability of delamination growth calculated by the surface response method has the highest value. Finally, the effects of initial delamination, laminate layer and loading in different modes on the delamination growth are obtained from the perspective of the reliability of composites laminates.

This study aims to determine the global buckling load of stiffened composite conical shells under axial compression. Stringers stiffen the conical shells in longitudinal and rings in circumferential directions. The boundary conditions are assumed to be simply supported at both ends. At first, the equilibrium equations are obtained using the first-order shear deformation theory and the principle of minimum potential energy. Effects of stiffeners (longitudinal and circumferential directions) are considered using the smearing technique. The resulting equations are solved using the generalized differential quadrature method to obtain the critical buckling load. The acquired results are compared with the finite element method results and other researcher's results available in the literature, and good agreement is observed. The influence of the number of stiffeners and rings, length, radius, semi-vertex angle of the cone, and shear deformation on the shell's buckling behavior is studied. Finally, the optimum number of stiffeners (longitudinal and circumferential directions) to achieve the maximum global buckling load in a cross-ply composite conical shell with various stacking sequences for a specific weight and overall geometry is investigated.

The purpose of this study is to define a piecewise fatigue damage model (PFDM) for the prediction of damage in composite laminates under cyclic loading based on the continuum damage mechanics (CDM) model. Assuming that damage in fiber-reinforced plastic structures accumulates nonlinearly, a piecewise degradation growth function is defined and coupled with CDM and micromechanics approaches. The model divides the damage behavior of fiber, matrix, and fiber/matrix debonding at the ply scale, into three different stages. For generality, a fully multi-stage damage formulation on a single-ply level is employed. The unknown parameters of the PFDM are estimated according to obtained experimental data of damage mechanisms associated with the composites laminate under cyclic loading. To predict multidirectional composite laminates' fatigue life, the proposed model was implemented in Abaqus software by the subroutine. In a validation against experimental data on carbon fiber reinforced material, the model proves to provide a good numerical approximation of the damage during the fatigue loading. The results reveal that by considering the multi-stage process in stiffness reduction, the proposed model can estimate the fatigue life of composite laminate under multiaxial cyclic loading conditions more accurately than the similar model in the literature.

The buckling analysis of rectangular laminated composite plates with an edge delamination under in-plane compressive loading is performed using the finite element method. Such a plate may be considered as a simplified model of stiffener plates of a stiffened panel. The buckling load and buckling mode are obtained by solving an eigenproblem. In an unconstrained analysis, physically inadmissible modes appear because of the overlap between separated sublaminates in the delaminated region. To eliminate overlap, constraints are added iteratively on the entire overlapped area using penalty function method. The validity and superiority of the analysis method in predicting buckling load and buckling mode is shown in comparison with the experimental and analytical results available in the literature. Numerical results show the effect of delamination width and depth and boundary conditions on the buckling load.