FATIGUE CRACK GROWTH-RETARDATION BEHAVIOR OF IN-100 AT ELEVATED-TEMPERATURE

In this investigation the effect of temperature on the fatigue crack growth retardation behavior of IN-100, a nickel base superalloy, when subjected to a single peak tensile overload cycle was examined. Baseline constant load amplitude fatigue crack growth rate (da/dN) and single peak tensile overload testing was conducted at room temperature, 649 and 732°C in laboratory air. As a result of this investigation it was concluded that retardation of fatigue crack growth due to a single peak tensile overload cycle does occur in IN-100 at elevated temperatures. In general, the number of delay cycles decreased as temperature increased. The overload testing was conducted at two baseline stress intensity factor (Kmax) values. It was found that for a given amount of overload, the observed retardation was less for tests conducted at the higher value of baseline Kmax. A new parameter, the Crack Growth Rate Ratio ((da/dN) at KOL/(da/dN) at Kmax, was dev was found that the influence of test environment on the number of delay cycles resulting from a peak tensile overload could be correlated with the ratio of crack growth rate at the overload value of stress intensity to the crack growth rate at the baseline Kmax. The utility of the Crack Growth Rate Ratio as a potential tool for predicting the retardation behavior of a material when operating in a complex environment is discussed. © 1979.