On thermal-expansion properties of more-orthotropic prepreg laminates with and without interleaf layers

More-orthotropic laminates are increasingly used in today's carbon-fiber-epoxy composite airframe structures. A recent study reported on a considerable discrepancy between measured and calculated coefficients of thermal expansion (CTEs) for M21E/IMA prepreg laminates, which was found to increase with the laminates' degree of orthotropy xi = E-x/E-y. In this paper it is analyzed whether the observed effect is related to more-orthotropic laminate stackings in general or to the particular inner laminate architecture of M21E/IMA laminates, which is characterized by discrete interleaf layers. Therefore, a quasi-isotropic and three more-orthotropic laminates, made from 8552/AS4 and M21E/IMA prepreg, were analyzed by means of thermo-mechanical analysis (TMA) and classical-laminate theory (CLT). Calculated and measured CTEs are compared and the effect of orthotropy is quantified. Potential affectations of TMA measurements and CTE determination due to edge effects and sample size are examined by means of finite-element analyses.