RESIDUAL THERMAL-STRESSES IN 3 CONCENTRIC TRANSVERSELY ISOTROPIC CYLINDERS - APPLICATION TO THERMOPLASTIC-MATRIX COMPOSITES CONTAINING A TRANS CRYSTALLINE INTERPHASE

A theoretical model for built-in residual thermal stresses in three co ncentric, transversely isotropic, cylinders is presented. The scheme i s an extension of earlier work by Nairn, who considered the case where only the central cylinder possesses such particular form of orthotrop y, the two other (external) cylinders being isotropic. The generalizat ion proposed here enables study of the thermal stresses in fiber-reinf orced composite materials containing transversely isotropic interphase s and matrices. In particular, the longitudinal thermal stress present in the fiber prior to a single-fiber fragmentation experiment is foun d to be compressive in nature and in some cases is high enough to indu ce extensive fiber fragmentation. The number of such preexisting break s varies strongly as a function of the Weibull shape parameter of the fiber compressive strength distribution, and of the fiber volume fract ion. Alternatively, the fiber Weibull shape parameter in compression m ay be predicted from fitting procedures, using experimental results th at include the number of fiber breaks versus either the thermal decrem ent or the fiber volume fraction. General implications for high-fiber- content composites are discussed. The effect of interface thickness on the residual thermal stresses is discussed for the particular case of transcrystalline interphases, with assumed morphologies for alpha and beta isotactic polypropylene. (C) 1997 Elsevier Science Limited.