Of Residual Stresses In Composite Laminates

The micro-and macro- residual stresses at the 0° and 90°directions in the 1aminates were measured quantitatively by the strain gageembedment method in this paper. The laminates were produced by vacuumbag molding method. The residual microstresses of 3218 epoxy-glass fiberlaminate were 8.91MPa at the 0?direction. The residual macrostresses ofsymmetric cross-ply laminate of 32l8 epoxy-g1ass fiber were 0.5MPa at the0irection and 1l.57MPa at the 90irection. The residualmacrostfesses of 32l8 epoxy-glass cloth laminate were -8.17MPa at the0irection and ll.02MPa at the 90irection. The experimental dataagreed fair1y wel1 with the predictions of the classical lamination theory.And some results were proved by the moire fringes interferometry and theX-ray diffraction. The development of the residual strain during the curingprocess has been discussed qualitatively by the strain gage embedmentmethod. The stress free tendency was proved to increase near thq Tg oflaminates and the "g1obal" stress is existed through analyzing thecomposition of the final residual stress by the strain gage method. After theinfluence of the cooling rate on the laminates was investigated, the residualstress was found to decrease with the increase of the cooling rate because ofthe relaxation of the residual stress such as microcrack.