Papers by Keyword: Unsymmetric Laminates

Abstract: Residual internal stresses arise during thermal processing of thermoplastic composites due to differential shrinkage of stacked orthotropic plies and can lead to defects such as shape distortion, microcracking or delamination. In the current study, a comprehensive thermomechanical model for predicting residual stresses and strains in semicrystalline thermoplastic composites is presented with specific application to unidirectional Carbon fiber reinforced LM-PAEK composite laminates. The model is based on an incremental Classical Laminate Theory (CLT) framework that incorporates temperature-dependent material properties and accounts for both thermal and crystallization-induced shrinkage effects. Material characterization is performed to measure key temperature-dependent properties: thermomechanical analysis (TMA) is used to measure the transverse thermal expansion coefficient (CTE) and crystallization shrinkage upon cooling from melt state, dynamic mechanical analysis (DMA) to obtain the transverse modulus. The stress-free temperature, the temperature at which residual stresses begin to develop, is identified through curvature evolution measurements of unsymmetric laminates using image analysis. The model validation is performed via curvature measurements of unsymmetric cross-ply laminates using laser scanning techniques, demonstrating good agreement between model predictions and experimental measurements.

Abstract: Unsymmetric composite laminates were benefit to reducing the structure weight of some aircrafts. However, the cured unsymmetric laminates showed distortion at room temperature. Therefore, predicting the deformation before using the unsymmetrical composite is very important. In this study an attempt was made to predict the shapes of some unsymmetric cross-ply laminates using the finite element analysis (FEA). The bilinear shell-element was adopted in the process. Then the simulation results were compared with the experimental data. The studies we had performed showed that the theoretical calculation agreed well with the experimental results, the predicted shapes were similar to the real laminates, and the difference between the calculated maximum deflections and the experimental data were less than 5%. Hence the FEA method was suitable for predicting the warpage of unsymmetric laminates. The error analysis showed that the simulation results were very sensitive to the lamina thickness, 2 α and (T.

Abstract: An analytical model was established by means of Ritz method to calculate the cured shape of cross-ply unsymmetric composite laminates. A number of experiments of Carbon/Epoxy laminates were conducted. It was found in the experiment that the warped surface could be a multiple-value function, which should be studied further. The result of calculation correlates well with the experimental result except the regions very near the laminate edge. The conclusion is instructive to manufacture of composite laminates.