CONSIDERATION OF OFF AXIS PLY FAILURE STRAINS IN DETERMINING TENSILE MODULUS OF ANGLE PLY LAMINATES

摘要

In tensile testing angle ply laminates, the off axis plies suffer matrix damage before final fiber failure of the laminate. The matrix failures cause slight deviation from the linear response near this failure strain (0.8 percent), shown as a slight knee that sometimes can be barely noticeable with the naked eye. If the measurement of the modulus using the chord modulus method inadvertently comes too close or spans this failure strain it is possible to introduce significant error in the result. In the present study, a (0/90)ns laminate with 52 percent wt (32 percent v) fiber was constructed from Zentron~R?non-crimp fabric infused with a marine-grade epoxy resin, and cured under vacuum. The resulting tensile modulus of the laminate determined by method ASTM-D3039 spanning 0.2 and 0.8 percent strain resulted in a 7 percent error to the modulus compared to using 0.1 and 0.3 percent strains. Both the revised tensile modulus, and the first ply transverse failure strain indicated as a slight knee in the linear stress-strain response, were in very good agreement to the values predicted from laminate theory.