Effect of residual stress on the bending response of L-shaped composite laminates

Abstract

Residual stresses after manufacturing are critical in fiber-reinforced composite materials, since they may contribute significantly premature failure. In this study, the effect of residual stress on the out-of plane strength of corner sections of L-shaped laminates was investigated. The composite laminates with different thicknesses, and stacking sequences were manufactured in an autoclave and four-point bending tests were conducted on the samples. In order to investigate the internal damage of the samples, optical microscopy technique was used. A combined four step model was introduced, which includes the evaluation of residual stress and four-point bending analysis of the laminates. Residual stresses were calculated in the first three steps and quasi-static tests were simulated in the last step. In the last step, Cohesive Zone Model and Hashin’s failure criteria were used for interlaminar and intralaminar failure respectively. According to the results, residual stresses do not change the region and the type of initial failure mode. However, residual stresses decrease the initial failure load for cross-ply (XP) samples. Also, they change the magnitude of the hoop stress values for unidirectional (UD) samples. The models predicted stiffness and the location of delamination well for UD samples and the location of matrix tensile failure for XP samples.