An uneven strain model for analysis of residual stress and interface stress in laminate composites

An uneven strain model was proposed to analyze the residual stress and interfacial stress in laminates. Results suggested that the residual stress caused by the difference of thermal expansion coefficient between two adjoining layers is a function of the relative location in the laminates, instead of being a constant value. In addition, both shear stress and normal stress existed in the interface, and they varied with the distance to the interfacial boundaries. Calculations based on experiments containing different material types of laminate composites and indentation crack sizes were conducted. Results indicated that the maximum residual stress and interfacial tensile stress occurred at the center of a laminate, while the maximum interfacial shear stress and compressive stress normal to the interface occurred near the boundary of the laminates.