| Plasticity induced closure and its effect on the fatigue growth of short cracks were investigated analytically in a high strength titanium alloy at room temperature and in a nickel base alloy at elevated temperature. The analysis consisted of subjecting a single-edge cracked specimen with an initial crack length of.001 inch to cyclic loads and allowing the crack to propagate.A two-dimensional plane stress finite element code with constant strain triangles was used. The Bodner-Partom Viscoplastic Flow Law was incorporated to handle non-linear material behavior. Relations in this model are integrated through time by an Euler extrapolation scheme. The overall solution technique is the residual force method. Changing boundary conditions are incorporated through the use of a crack closure algorithm as well as a crack growth procedure.Numerical simulations involved subjecting TI-6246 at room temperature (time-independent behavior) to cyclic loads having maximum nominal stresses of 60 and 90 percent material yield strength, load ratios of The formation of a plastic wake and the effects of plasticity induced closure were observed. Differences between cracks grown through cyclic loading and those with no fatigue crack growth were investigated. Strain related characteristics were highly dependent upon previous loading history, whereas stress related characteristics were relatively insensitive to previous loading history. |
