Nondestructive evaluation of interfacial damages in composite materials

Abstract

The high stress concentration near the interface of fiber-matrix in composite materials causes the accumulation of the interfacial damages and the degradation of mechanical properties of the materials. In this paper, by using the residual surface displacement data, we evaluate the microscopic damages in terms of Somigliano's dislocations in composites near the interface caused by a series of unknown loadings. The goal of this research is to monitor the processes of the damage evolution near the interface and to relate this microscopic damage to the degradation of the macroscopic mechanical properties of the materials.The problem is an inverse problem, which is substantially different from the conventional forward analysis of structural mechanics. Therefore, the uniqueness and stability must be considered. It is proved that the residual fields and all the characteristic quantities along the interface, such as displacement jumps (Somigliano's dislocations), are uniquely determined by the residual surface displacements. It follows that the traction free parts of the interface correspond to cracks, the normal displacement jumps indicate debonding and the tangential displacement jumps measure the interfacial sliding. A special technique is utilized to stabilize the numerical calculations.