Effect of Frequency, Environment, and Temperature on Fatigue Behavior of E319 Cast-Aluminum Alloy: Small-Crack Propagation

Abstract

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°C and 250°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.

Effect of Frequency, Environment, and Temperature on Fatigue Behavior of E319 Cast Aluminum Alloy: Stress-Controlled Fatigue Life Response

“…[7,15] The observed effect of frequency on S-N behavior is likely attributable to an environmental effect on fatigue crack growth rate. [6] For E319 cast aluminum alloys, the number of cycles required to cause failure is determined by the crack growth rate. As reported in the companion work, [6] the crack growth rate at ultrasonic frequency is lower than at conventional frequency due to lower water exposure (characterized by the ratio of water partial pressure over test frequency, P/f) at ultrasonic frequency and, therefore, the less hydrogen-induced increase of fatigue crack growth rate.…”

“…We have examined the effect of frequency, environment, and temperature on fatigue crack propagation behavior of E319 cast aluminum alloy and proposed a modified environmental superposition model to characterize the fatigue crack growth rate in various environments for E319 cast aluminum alloy in a companion article. [6] Here, the S-N behavior of E319 cast aluminum alloy is examined at 20 kHz and 75 Hz at 20°C, 150°C, and 250°C to understand the potential effect of frequency and environment at both room temperature and elevated temperature. The modeling approach is extended to predict the S-N behavior in various environments.…”

Fatigue at high number of cyclic loads: Testing methods and failure mechanism

“…The influence of the test frequency on various aluminium casting alloys was investigated in [3,4]. The deviations in fatigue strength that were observed between those carried out at low test frequencies (f = 75 Hz) and high test frequencies (f = 20 kHz) are explained due to the influence of the ambient medium.…”

“…The deviations in fatigue strength that were observed between those carried out at low test frequencies (f = 75 Hz) and high test frequencies (f = 20 kHz) are explained due to the influence of the ambient medium. In [4] a model is developed based on investigations in [16]. In the investigation the difference in fatigue life arising from the test frequency is reduced by the humidity, as measured by the partial pressure of water vapour p. By changing the quotient (p/f) a good correlation between the fatigue tests carried out at different frequencies could be achieved in [3,4].…”

Current developments and trends on structural durability

“…The result for cast aluminium is shown in Fig. 14 [23]. Some of the often discussed frequency effects in VHCF-testing at 20 kHz ultrasonic driven test equipments might be influenced by this effect, if surface failure occurs.…”