Fracture Kinetics of Thermally Loaded Bodies in Elastic-Brittle State and Criterion of Thermal Stress Resistance

Abstract

For explanation of observable differences in heating and cooling behavior of a body, limiting equilibrium curves of thermally loaded disks with a central and an edge slit, heated or cooled on the lateral area are calculated on the base of linear fracture mechanics. It is established experimentally that the fracture of the body with partial loss of its bearing capacity at cooling and the body total fragmentation at heating is determined by non ℄ uniformity of the body stress state. The quantitative characteristic of the inhomogeneous stress state, taking into account not only the relation of the zones sizes of tension and compression, but also the distribution of stress in these zones, is offered to estimate by an N parameter. The fracture type is characterised by the criterion N_c. At the limiting value N_c, < 0,1 the crack propagation reduces the body strength only partially. A total fragmentation of the body in this case, as well as under mechanical compression, is possible as a result of interaction of equilibriumly growing cracks at stresses 8–12 times exceeding starting stress of crack growth. In determining the limit load-bearing capacity of a body it is practically indispensable to take into account the loading history and the fracture kinetics, i.e., the effect of the intermediate stage of crack development on the final state of the body. For substantiation of advantages of the force fracture approach to the thermally loaded bodies, in comparison with energetic principles, the spreading of cracks and the thermal stress resistance (TSR) is considered under combined influence of thermal and mechanical loading on the body by a calculated and experimental way. It is shown also, that complex fracture kinetics of a finite cylinder, thermally loaded on a local point, can be explained only by the force fracture mechanics.