Continuous evolution of processing induced residual stresses in composites: An in-situ approach

Abstract

Processing induced residual stresses are often responsible for causing warping, undesired distortion, dimensional instability, and delaminations in composite structures. Monitoring the evolution of residual stresses throughout the cure is essential to understand their effect on the mechanical behavior of the composites. In the present work, a novel in-situ experimental approach is used to measure the dimensional changes in the laminates during cure and combined with temperature-dependent moduli obtained from Dynamic Mechanical Analysis (DMA) to calculate the continuous evolution of residual stresses during composite processing. Five symmetric and asymmetric layup configurations are analyzed to investigate the effect of ply orientation on the residual stress evolution. The maximum average residual stress of 110 MPa in the longitudinal direction is observed for symmetric cross-ply [0/90]s configuration and the maximum average warpage of 1.46 mm is observed for balanced un-symmetric [30/−30/60/−60] layup configuration.