Local strain re-distribution and stiffness degradation in cross-ply polymer composites under tension

Individual aramid Kevlar 49 fibers were embedded into the 0° ply of transparent cross-ply glass fiber reinforced polymer (GFRP) laminates and used as Raman sensors for the monitoring of the local strain field due to matrix cracking under quasi-static loading. The sensors were placed near the 0/90 interface, and the resulting strain within the 0° ply and its dependence on the geometry of the specimen due to 90° cracking were recorded. The decay of the strain magnification with the distance from the crack front, the residual strain and the axial modulus of elasticity reduction were derived from the strain distributions at each separate level of loading. The results obtained were compared with shear-lag calculations as well as numerical and analytical models.