LAUSR

An analytical method is established to estimate the load level when interfacial debonding occurs between fibers and matrix of a composite under an arbitrary load. Only the transverse tensile strength and the components' properties of the unidirectional (UD) composite are required for this estimation. For internal stress analysis based on micromechanics, the homogenized stresses in matrix must be converted into true values because of the nonuniform stress distribution due to embedded fiber. The stress concentration factors (SCFs) of matrix before and after the interfacial debonding are both essential, between which the difference indicates the effect of debonding on the stress fluctuations in matrix. A final true stress is obtained by accumulating the products of stress increments of matrix arising before and after debonding and corresponding SCFs. Letting the predicted transverse tensile strength of a UD composite with an initial perfect and later cracked interface be equal to the measured corresponding value, a critical von Mises stress of matrix at which the interfacial cracks appear is obtained. For a UD composite subjected to an arbitrary load, when the principal stress is positive and the von Mises stress of matrix reaches the critical value, the applied load level when interfacial debonding occurs is determined accordingly. POLYM. COMPOS., 2018. (c) 2018 Society of Plastics Engineers