One of the most important issues about the composites behavior in different loading conditions is the initiation and propagation of various damage modes that have significant effects on the application of these materials. Fiber/Matrix debonding is one of the first damage modes that appears in different composites and causes the formation of other damage modes like Matrix cracking. In the present study, by using the cohesive zone model (CZM) as well as an extended finite element method (XFEM) and by applying a transverse loading on different representative volume elements (RVE’s) in micromechanical scale, the effects of initiation and propagation of different damage modes like fiber/Matrix debonding and Matrix cracking will be studied. To this aim, the authors start by studying the behavior of cohesive zone model and validating the applied method by simulating the previous researchs. Then, the effects of cohesive zone on different volume elements will be studied and the results will compare with each other. Finally by entering the effects of Matrix cracking initiation and propagation using the extended finite element method, effects of cohesive zone damage and Matrix cracking will be studied simultaneously based on finite element method and using Abaqus software.

In this paper, an object oriented method is developed for generation, optimization and management of a hydrocarbon (CX Hy) pyrolysisreaction network using a Bond-Electron (BE) Matrix. A computer program was developed using C++ language. This program can provide and generate a pyrolysisreaction network for a wide range of hydrocarbons, including alkanes, olefins, diolefins, cyclic and aromatic compounds, using the linear notation structure of the reactant species. Furthermore, the reaction patterns and pruning methods are considered and a new method is presented for identification of reactants and products. The structural identification of species contained in the network allows one to approximate the species and reactions thermochemical properties by group contribution or semi empirical quantum chemistry methods. The reaction network generated by this method can be used directly for simulation of thermal cracking reactions or as input for thermal cracking simulators such as REACT, CHEMKIN and KINALC.

Due to the mismatch of mechanical properties in composite laminates, propagation of delami-nation is considered as a severe damage mechanism in beams with various lay-up configurations. Delamination can be generated due to Matrix cracking propagation or it can also be initiated due to the manufacturing process before using composite beams. Using a micromechanics model, this study is aimed to investigate the bending moment required for Matrix cracking and induced de-lamination in cross-ply composite beams. To that end, a unit cell is selected from the lamina sur-face in a composite beam containing Matrix cracking and delamination. Later, the governing equation of stress and displacement fields are extracted in the unit cell to calculate the strain energy release rate due to the propagation of Matrix cracking and induced delamination. In or-der to validate this method, the stiffness variations in Carbon-Epoxy cross-ply laminate [90/02]s is examined and the obtained results are compared with the numerical results. It concluded that there is a favorable agreement between the results of the proposed micromechanics model and available numerical results.

Fiber Metal Laminates are new composite structures in which several thin metal sheets and composite layers are connected together. These structures have properties such as high fatigue resistance, high impact resistance and high energy absorption, which have led to a growing use of them in various industries. In this study, damage in FMLs under tensile static loading, including Matrix cracking, delamination induced by Matrix cracking and plasticity in metal layers, was examined. Using the analytical model, stress distribution and energy release rate were extracted in FML containing Matrix cracking and delamination. Numerical modeling of FML containing such damages was also performed. The stress distribution results obtained from the analytical and numerical models were compared, and good agreement between the results was observed. Furthermore, the FML samples were subjected to tensile test and the damages that occurred in them were displayed. By using the analytical model and calculating energy release rate, the Matrix crack saturation and the initiation of delamination at the crack density of 0.38 (the distance between two cracks is 2.7 mm) were extracted. By observing the experimental samples, this crack density was observed in most of the length of the sample, but due to various reasons such as manufacturing defects, in some areas the distance between the cracks was larger than the mentioned value.

In this paper by implementing energy based theory, growth of induced delamination due to Matrix cracking have been studied in symmetric composite laminates subjected to constant in-plane stresses and constant thermal stresses. Two unconstrained and generalized plane strain states have been analyzed here. Matrix cracking as a primary assumption has been supposed in both states and the impact of Matrix cracking and delamination on the stiffness degradation is calculated. Afterwards some thermoelastic constants, which are only depended on, ply material properties of composite lamina are. Then by relating stiffness Matrix elements using these constants, a simple equation due for Gibbs free energy acquired. By differentiating the Gibbs free energy equation for delamination length other simple equation was obtained to compute energy release rate. To verify the obtained results, ANSYS finite element software is used. The obtained results reveal that there is good agreement between the extended and FE approaches.

Unlike other materials, composite laminates have more uncertainty sources, such as uncertainty in the material properties,hence it is very essential to predict the probability of the occurrence of various types of damage modes in composite laminates due to random behaviors of composite structures. Matrix cracking induced delamination (MCID) is one of the catastrophic modes that can occur in composite laminates. In this paper, a new algorithm for probabilistic prediction of MCID based on the concept of energy release rate and its critical value was developed and by applying this proposed framework, the reliability analysis of MCID damage was performed. The limit state function was formulated using a general failure criterion which was developed by the authors of this article, previously. To represent the performance of the proposed algorithm, the probability of the occurrence and growth of MCID in a quasi-isotropic laminate including 45°, , 90°, ,-45°,and 0°,plies under different loading conditions and various stacking sequences was extracted by using first and second order reliability methods (FORM and SORM), . The verification of the obtained probabilities was performed using Monte Carlo simulation (MCS). In addition, some significant results were validated using several experimental data, qualitatively. The effect of variables such as the ply thickness, the level of longitudinal uniaxial stress and the presence of general in-plane stresses on the probability of occurrence and growth of MCID was investigated.

Nondestructive evaluation of mechanical properties and health monitoring of composite structures is of great importance. The aim of this research was to propose a nondestructive evaluation method based on the propagation of Lamb waves to investigate the Matrix cracking damage in laminated cross-ply composites. For this purpose, after developing the finite element model of a glass/epoxy composite, the Lamb wave behavior was studied in two antisymmetric (A0) and symmetric (S0) modes with different excitation frequencies. The dispersion curves of the A0 and S0 modes of the Lamb wave are then obtained by considering different crack densities. It was observed that the effect of Matrix crack density and the loss of mechanical properties of the cross-ply composites on the phase velocity of the S0 Lamb wave mode was higher than that of the A0 mode. Furthermore, the detection of Matrix cracking was better performed using the Lamb wave velocity at high frequencies close to the cut-off frequency. It was observed that the cut-off frequency decreased by increasing the crack density, and the drop in the Lamb wave velocity increased by increasing the number of 90° layers in the cross-ply composite. It was concluded that the Lamb wave propagation simulation method can be used as a virtual laboratory for nondestructive evaluation of composites and detection of Matrix crack density in them.