| The thesis addresses the issue of possible debonding of faces of a sandwich plate under hail-like impact conditions. The interface stresses are considered responsible for the debonding, and to design against this possibility, it is necessary to determine them correctly. The problem is addressed by constructing a FE program to accomplish the following tasks. (i) To analyse a circular sandwich plate as a three dimensional axisymmetric structure, supported at periphery and subjected to a central static load equivalent to the dynamic impact load. Since no plate theories are used, through-the-thickness stresses, from top to bottom, are determined accurately. (ii) To determine the interface stresses uniquely and correctly, an axisymmetric bimaterial interface element was developed and incorporated in the constructed FE program. The standard FE programs do not determine these stresses unambiguously. (iii) To determine the extent of debonding, the program uses an interface shear stress failure criterion. The possibility of interface separation and the impossibility of their inter-penetration are accounted for by means of a gap element. Based on this failure criterion, the program determines, for a given load, the debonding radius by means of iterative analyses. The equivalent static load used in the analysis is determined by an energy balance equation taking into account the mass, velocity, modulus, and radius of the spherical impactor, as well as the properties of the sandwich plate. The results are expected to be of general usefulness in the design of aircraft structures against hail impact damage. |
