Residual thermal stresses in three 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 concentric, transversely isotropic, cylinders is presented. The scheme is an extension of earlier work by Nairn, who considered the case where only the central cylinder possesses such particular form of orthotropy, the two other (external) cylinders being isotropic. The generalization proposed here enables study of the thermal stresses in fiber-reinforced composite materials containing transversely isotropic interphases and matrices. In particular, the longitudinal thermal stress present in the fiber prior to a single-fiber fragmentation experiment is found to be compressive in nature and in some cases is high enough to induce extensive fiber fragmentation. The number of such preexisting breaks varies strongly as a function of the Weibull shape parameter of the fiber compressive strength distribution, and of the fiber volume fraction. Alternatively, the fiber Weibull shape parameter in compression may be predicted from fitting procedures, using experimental results that include the number of fiber breaks versus either the thermal decrement 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.