3-DIMENSIONAL EFFECTIVE MODULI OF SYMMETRICAL LAMINATES

Closed-form expressions of three-dimensional effective moduli of symme tric laminates, which are based on the assumption of constant in-plane strains and constant interlaminar stresses through the thickness, had been proposed by Chou and Carleone (1972) and later re-proposed by Su n and Li (1988). This article modified the effective interlaminar shea r moduli to account for the effect of stacking sequence by assuming th e parabolic distribution of interlaminar sl;ear stresses through the t hickness. In this article, the effective three-dimensional moduli are also re-presented in such forms that it could be seen that several par ticular forms of the rule of mixture apply for individual stiffness or compliance components. As a result, four stiffness invariants and one compliance invariant are developed. The invariance is helpful in chec king the reliability of measurements. The effective moduli predicted b y this article are found to be in good agreement with the experimental data measured by ultrasonic methods.