Semi-analytical mechanical model for FRCM-to-substrate shear bond tests

Abstract

The debonding process of an FRCM reinforcing system from the substrate is studied in a semi-analytical fashion. FRCM is modeled considering independently the central elastic fiber grid and the two thick upper and lower matrix layers, assumed elasto-fragile; matrix and fiber are considered in a monoaxial state of stress; they mutually exchange shear stresses at the interface, this latter characterized by a softening stress-slip relationship; the reinforcement system is then bonded with a rigid substrate by means of a further elastic interface. Under such hypotheses, a simple system of first order non-linear and coupled differential equations is derived and solved by means of a semi-analytical approach. Independent variables are the axial displacements of the three layers (upper and lower matrix, central fiber) and the corresponding axial stresses. The approach is successfully validated against two experimental datasets available in the literature, relying into different FRCM strengthening systems bonded to rigid substrates and subjected to single lap shear tests. The model is able to capture not only the global debonding behavior but also the local one, with a precise prediction along the bond length of the shape of the axial stresses into the different layers, of the interface shear stresses and of the location of the cracks inside the matrix.