Sub-surface fatigue in mechanical structures affecting their fundamental modes within conventional sensing limits. As per published research, these effects are mostly investigated under dynamic loads on different boundary conditions. Analytical, numerical and empirical studies clearly indicate that the dissipated strain energy during crack propagation affects the modal values of the structure. However, there is still need to perform comprehensive research that can relate the mentioned parameters specifically under thermo-mechanical loads. The cyclic thermal loads along with dynamic loading may represent a more practical loading scheme as experienced on mechanical components or structures. In this research, analytical and numerical modelling will be performed on a structure with different boundary conditions. The structure will be loaded at resonance with a cyclic thermal load applied at the ends. The changes in the modal responses of the structure will be determined during the subsurface crack initiation and propagation. The results will then be compared with the available empirical studies in the literature.