THERMAL PULSE-INDUCED EDGE CRACKING OF COATINGS BASED ON TIME-FRACTIONAL HEAT CONDUCTION

Edge cracking due to thermal shock is a common failure mode of coatings that seriously affects their protective performance, so it is crucial to accurately predict the thermally induced growth behavior of edge cracks. In this paper, based on the Caputo time-fractional heat conduction model, the crack driving force for an edge crack in the coating is investigated under a heat flow pulse. Firstly, the closed-form solutions are obtained for transient temperature and thermal stresses by using techniques of Laplace transform and finite cosine integral transform. Secondly, the thermal stress intensity factor (TSIF) for an edge crack is determined by using the principle of superpostion and weight function method. The dependence of TSIF is examined on such parameters as the fractional-order, normalized crack length as well as normalized time. The results show that, the peak value of the TSIF increases as the fractional-order increases. Compared with the case of fractional order super-diffusion due to a heat flow pulse, the classical Fourier thermal diffusion underestimates the crack driving force for an edge crack, while compared with the case of fractional order sub-diffusion, the classical Fourier thermal diffusion overestimates the crack driving force. Under a heat flow pulse, the peak value of TSIF for a shorter edge crack is higher and thus shorter edge cracks are more prone to propagation.