LAMINATION RESIDUAL STRAINS AND STRESSES IN HYBRID LAMINATES.

The influence of hybridization in angle-ply laminates on curing residual strains and stresses was investigated. The specimens were graphite/Kevlar 49/epoxy and graphite/S-glass/epoxy laminates of various stacking sequence variations of the basic left bracket plus or minus 45/0//2 right bracket //s construction. The plus or minus 45 degree plies and in some cases half the 0 degree plies, were graphite/epoxy. Residual strains were determined experimentally following previously developed techniques. It was found that stacking sequence had no influence on measured residual strains. Residual stress computations show that at room temperature the transverse to the fibers residual stresses exceed the static strength for the graphite plies and reach values up to 75% of the transverse strength for the glass plies. The residual stresses in the Kevlar plies are high enough to cause early transverse failure of these plies before the laminate is cooled down to room temperature.