A review of high temperature fracture mechanics for hypervelocity vehicle applications

Abstract

The concept of linear elastic fracture mechanics(LEFM) may be applied to crack growth predictions in various areas of hypervelocity vehicle airframe structures depending upon the structural material and the applied load-temperature profile. The high temperature crack growth work in alloys developed for such applications is still under development. Extensive studies have been conducted to predict crack growth in superalloys and stainless steels to simulate loading conditions in gas turbine engines and nuclear power plants. Time dependent damage may occur in both classes of materials in addition to cyclic damage. The crack growth damage in superalloys is mainly due to environmental degradation while creep deformation plays a dominant role in time dependent cracking in steels. A linear superposition damage concept, initially developed for stress corrosion in high strength steels have shown to correlate crack growth under cyclic sustained loads in most superalloys quite well. Based on the available experimental da ta , it can not be firmly established whether creep, actually accompanies environmental degradation in superalloys. However, LEFM based parameter, stress intensity factor have shown good correlation with the observed data . Relatively, few studies have been conducted to study crack growth under simultaneous variations in temperatures and loads. A simultaneous occurance of temperature and load peaks under load control situations is found to be most damaging in several superalloys. Several studies have reported attempts to use plasticity based retardation models to correlate crack growth due to overloads under isothermal conditions. This paper discusses various crack growth prediction models for elevated temperature effects. Recommendations are made for further elevated temperature structural