A progressive damage model for 3D woven composites under compression

A progressive damage model is proposed to investigate the damage initiation and evolution of 3D woven composites under uniaxial compression at a micromechanical level. The typical compressive experiments were carried out. Based on the observations, the compression failure modes of 3D woven composites mainly include fiber kinking, transverse failure of fiber tow, matrix fracture, and interfacial debonding. The initial damage criteria are according to the physically based failure criteria for the fiber kinking, the Puck criteria for the transverse failure of fiber tow, and the maximum stress criterion for the matrix. The damage of fiber tow–matrix interfacial is simulated through cohesive contact. Particularly, the fiber’s initial misalignment angle is taken into account in the damage model. The simulated compression results agree well with the experimental ones. The compressive stress–strain response of the 3D woven composite is forecasted. The damage evolution of each constituent of the 3D woven composite is obtained. The results show that the influence of the fiber’s initial misalignment angle on the compression strength of the 3D woven composite needs to be considered.

Temperature effects on transverse failure modes of carbon fiber/bismaleimides composites

The results of experimental and numerical studies on temperature dependence of carbon fiber/bismaleimides composites subjected to transverse tensile load at −120℃, 25℃, 150℃, 170℃, 200℃ are summarized. The scanning electron microscopic fractographs showed that fibers were coated by a small amount of resin along with split resin at −120℃, melted resin attached to fibers is found in the view at 200℃ and naked fibers were observed at room temperature. It is concluded that the interfacial strength reduced with the increase of temperature. Experimental stress versus strain curves showed that modulus decreased with the increase of the temperature, and the obviously nonlinear tendency was observed at 200℃. Employed Mohr–Coulomb criterion to characterize plastic behavior of bismaleimides matrix, representative volume element based on random sequential expansion algorithm was modeled to simulate the entire damage progress with thermomechanical load. The analytical results showed that high stress concentration occurred in the matrix band between closely arranged fibers and became more severe with temperature rising. The percentage of interfacial debonding was larger at room temperature than those at higher and lower temperature. The experimental and analytical results showed that transverse failure modes at different temperature are related to thermal residual stress and the Young’s module of matrix.