Fracture Mechanics of Interfaces of Laminates Subjected to Thermal Shock or Low Velocity Impacts

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A laminated plate containing an interior disc-shaped interface crack is considered. The main aim of the present research is to derive the energy release rates, which is the most important parameter that determines the condition of interface crack growth.First, we consider the case when a laminated plate is subjected to thermal shock. A constant heat flux is assumed to be suddenly imposed over the top surface of a laminated plate by, for example, a laser heating. As the temperature is raised, the plate is bent by the through the thickness temperature gradients. The temperature distribution at an arbitrary time t after the initiation of heating has already been known. Utilizing this result and modeling the portion of the plate consisting of the two circular plates above and below the disc-shaped crack as two lapped circular plates hinged at their rims, the deflection of the laminated plate is theoretically determined. It is found that the portion of the plate above the disc-shaped delami … More nation causes local buckling due to radial compressive stress induced by the temperature gradients. It is shown that this buckling would greatly promote the growth of delamination, since the energy release rates become very large.Second, we consider the growth of a disc-shaped interface crack by the low velocity impact. The impact is assumed to be made by the strike of a freely falling rigid column with large mass at the point of the plate surface directly above the center of the disc-shaped crack. Based on the characteristic function expansion methods, the concentrated force applied at the point of collision and the deflection of the plate are theoretically determined as functions of the time t after the instant of impact. By comparing the results with experiments, the present analyses are well confirmed. The energy release rate is also derived as a function of time t. It is shown that the energy release rate becomes about three times larger than that for the case of statically applied load. Less