A Novel Assessment Method for Wrinkle Defects in Composites

Fiber reinforced composite structures have been increasingly used in the field of pressure vessels and piping. Various process-induced defects of composite structures are accumulated during their manufacture processes for the variations of environment temperature and humidity, pre-stress of fiber and curing temperature. Wrinkle defect is one of the most frequently encountered defects in fiber reinforced composite structures. In this paper, a new method for detecting wrinkle defects based on the relation of the displacement fields between flawed and flawless areas is proposed. The orthotropic finite element analysis codes combined with wrinkle model were developed based on Matlab platform to predict structural responses of laminates under three different loading types, including transverse compression, axial tension and bending. The effective elastic moduli disturbed by wrinkles were determined based on a mesomechanics model and a two-step homogenization procedure. Two different wrinkle models including definite and heterogeneous distributed models were considered. It is found that the out-of-plane displacement obviously increases at the wrinkle region under the axial load. The fluctuant displacement fields under axial tensile load can be clearly observed when the heterogeneity wrinkle model is considered. However, the transverse compression cannot produce any displacement distortion. All the results bring us a new idea of non-destructive evaluation for composites, wherein the defects that mainly weakening the stiffness can be detected by measuring the displacement distribution under some specified loads.