C. Mercer

An investigation of short and long fatigue crack growth behavior of Ti-6Al-4V

Abstract This paper presents the results of a study of the effects of positive stress ratios on the propagation of long and short fatigue cracks in mill annealed Ti–6Al–4V. Differences between the long fatigue crack growth rates at positive stress ratios (R=Kmin/Kmax=0.02–0.8) are attributed largely to the effects of crack closure. Microstructurally short fatigue cracks are shown to grow at stress intensity factor ranges below the long crack fatigue threshold. Anomalously high fatigue crack growth rates and crack retardation are also shown to occur in the short crack regime. Differences between the long and the short crack behavior at low stress ratios are attributed to lower levels of crack closure in the short crack regime.

An investigation of fatigue crack growth in a cast lamellar Ti48Al2Cr2Nb alloy

The results of a study of fatigue crack growth in a lamellar gamma titanium aluminide alloy are presented in this paper. Differences in the fatigue crack growth behavior at 25, 450 and 700°C are shown to be associated with the combined effects of different fracture modes/crack-tip deformation mechanisms and oxide-induced crack closure under cyclic loading. Crack-tip deformation was found to occur by conventional slip at 25°C. At 450 and 700°C, however, crack-tip deformation occurs via a duplex mode of slip and micro-twinning within lamellae. A higher fatigue threshold at 700°C is attributed partly to the effects of oxide-induced crack closure.

A probabilistic framework for the modeling of fatigue in a lamellar XDTM gamma titanium aluminide alloy

Abstract This paper presents a probabilistic framework for the modeling of fatigue damage in a gamma titanium aluminide alloy (Ti–45Al–2Mn–2Nb +0.8 vol% TiB2). This includes: empirical stress-life and fracture mechanics approaches to the estimation of material reliability or the risk of failure. Empirical reliability functions are obtained initially from multiple stress-life experiments designed to identify the statistical distributions that best describe the measured variabilities in fatigue life. Fracture mechanics-based reliability functions are also derived using statistical distributions that characterize the measured variabilities in fatigue crack growth data obtained from fatigue crack growth experiments in the long crack regime. The anomalous behavior of short cracks is then discussed before assessing the implications of the current work for the design of engineering structures and components from gamma-based titanium aluminides.