RESIDUAL-STRESSES IN SCS-6 BETA-21S COMPOSITES

Residual stress profiles were determined using X-ray diffraction (XRD) procedures in SCS-6/Beta-21S composites in unidirectional [0](4) cros s-ply [0/90](s), and quasi-isotropic [0/+/-45/90](s) lay-ups by sequen tially electropolishing matrix layers off the outer surface. These exp erimental results were compared with the finite element model (FEM) ca lculations. Generally, the longitudinal stresses in the unidirectional [0](4) composite was almost twice the transverse stresses, while for the cross-ply [0/90](s) composite, the longitudinal and the transverse stresses were similar in magnitude. The stress profile for the quasi- isotropic [0/45/90](s) lay-up were intermediate between the unidirecti onal and cross-ply composites. These results show the strong influence of the underlying ply on the residual stresses in the outer ply. A 90 degrees ply has greater influence than a 45 degrees ply on the outer 0 degrees ply of the composite.