INTERLAMINAR TENSION STRENGTH OF GRAPHITE-EPOXY COMPOSITE LAMINATES

An L-shaped curved beam specimen and a tension loading fixture were pr oposed to measure the interlaminar tension strength of laminated and t extile composites. The specimen size was 2 x 2 in. (51 x 51 mm). The u se of a standard tension test machine and the introduction of load nea rly at the midthickness were the advantages of the proposed specimen. Modified Lekhnitskii and beam theory equations for calculating interla minar stresses of an L-beam were verified by finite element analysis. The beam theory equation is simple and accurate for mean radius to thi ckness ratios greater than 1.5. The modified Lekhnitskii equations can be used for detailed stress field calculation. AS4/3501-6 graphite/ep oxy unidirectional specimens with thicknesses of 16, 24, and 32 plies were fabricated and tested. The delamination initiation site agreed wi th the calculated maximum interlaminar tension stress location for all three thicknesses. Average interlaminar tension strengths of 16-, 24- , and 32-ply laminates were 47.6, 40.9, and 23.4 MPa, respectively. Re sults of 16- and 24-ply specimens agreed reasonably well with data in literature for a longer size specimen and a different loading fixture. Interlaminar tension strength decreased with increased specimen thick ness and width because of volumetric effect.