In-Plane Stiffness of Semiauxetic Laminates

In this note it is shown that the combination of conventional laminas (possessing positive Poisson's ratio) and auxetic laminas (possessing negative Poisson's ratio) gives rise to effective in-plane composite laminate Young's modulus that surpasses the rule-of-mixture formula. To enable comparison between the developed model with the rule-of-mixture, the former is presented in such a way that two correction functions exist distinctively for multiplication into the two terms of the rule-of-mixture formula. Each of the two correction functions reduces to a minimum of 1 when all laminas possess equal Poisson's ratio, and the correction functions are greater than one when there exists mismatch in the Poisson's ratios among the laminas in the laminate. Plotted results show that the overshooting of the laminate's effective in-plane modulus is significant for semiauxetic laminates but not for conventional and fully auxetic materials.