Effect of frequency, environment, and temperature on fatigue behavior of E319 cast-aluminum alloy: Small-crack propagation

The influence of test frequency on fatigue-crack propagation behavior of small cracks in E319 cast-aluminum alloy was studied using ultrasonic and conventional test techniques. It was observed that fatigue cracks grow faster at 30 Hz than at 20 kHz in air at both 20 degrees C and 250 degrees C. The effect of frequency on the fatigue-crack growth rates was attributed to an environmental effect. For E319 cast-aluminum alloy, fatigue-crack growth rate increases with increasing water exposure (characterized by the ratio of water partial pressure over test frequency, P/f), and this behavior can be estimated using a modified superposition model. The effect of temperature on fatigue-crack growth behavior was primarily attributed to the effect of temperature on Young's modulus and yield strength. The environmental contribution to fatigue-crack growth rates modestly decreases with increasing temperature.