| The main objective of the research described herein was to find a method to improve the estimates of mechanical properties--especially elastic properties--in order to reduce the amount of point design testing needed to characterize laminated fiber composites. The specific approach evaluated was "reverse calculation" of the lamina properties from laminate properties for pairs of laminates. Tensile test data with biaxial strain gages were obtained for six to twelve replications for each of seven different laminate configurations of AS4/APC-2 graphite/PEEK. All laminates except the pure 90-deg laminate had between 0 and 25-percent 90-degree plies. The research showed that, for certain pairs of laminates, lamina elastic properties determined from reverse calculation improve the prediction of laminate elastic properties, compared to traditional approaches for obtaining lamina properties (ASTM D3039 and D3518 methods). This is particularly true for the laminate major Poisson's ratio, {dollar}nusb{lcub}xy{rcub}{dollar}, and for the laminate axial modulus, {dollar}Esb{lcub}xy{rcub}{dollar}, at high strains for ductile laminates, which may be very important in such areas of study as fracture mechanics where strains at the edge of a flaw can be very high. The pairs which provided the best correlation had one highly directional laminate with more than forty percent 0-degree plies, and one ductile laminate with 75-percent {dollar}pm{dollar}45-degree plies. |
