Very High Cycle Fatigue of a Cast Aluminum Alloy: Size Effect and Crack Initiation
- PDF / 3,271,483 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 25 Downloads / 219 Views
JMEPEG https://doi.org/10.1007/s11665-018-3617-y
Very High Cycle Fatigue of a Cast Aluminum Alloy: Size Effect and Crack Initiation Hongqian Xue, Zhidan Sun, Xianjie Zhang, Tao Gao, and Zhi Li (Submitted July 7, 2017; in revised form June 30, 2018) Fatigue properties of an Al-Si-Cu cast alloy were investigated with life up to very high cycle fatigue regime. Particular attention was given to specimen size effect and fatigue crack initiation mechanism. Uniaxial fatigue tests with constant amplitudes were carried out by using ultrasonic fatigue testing machine operating at 20 kHz, compared to the results obtained by using conventional hydraulic fatigue machine at 35 Hz. In order to evaluate the size effect, two sets of specimens with different dimensions were used. The results show that the fatigue strength of the studied alloy decreases with the increase in specimen size. Scanning electron microscopy observation of fracture surfaces revealed that most fatigue cracks initiated from microstructural defects such as porosity located on specimen surface or in subsurface. Weibull statistical analysis of fatigue data accounting for size effect was performed to predict the fatigue life of the AlSi-Cu alloy in the very high cycle regime. Good agreement was found between the fatigue life prediction and the experimental data. Keywords
Ai-Si-Cu alloy, fatigue crack initiation, size effect, VHCF, Weibull analysis
1. Introduction The use of aluminum-silicon-copper (Al-Si-Cu) cast alloys in automotive structural applications is fast growing because of a number of distinct benefits of these alloys. Such benefits include low mass density, excellent castability and high resistance to wear. In service, some engine components are subjected to low amplitude cyclic loading due to vibrations. As the number of cycles to failure is very large, the components should be designed to endure until 109 or 1010 cycles under similar loading conditions. Therefore, understanding the fatigue properties of these alloys in high and very high cycle regimes is a valuable asset to design durable components. Ultrasonic fatigue instrumentation, operating at a frequency of 20 kHz, has been used, since decades, to examine the very high cycle fatigue (VHCF) properties of materials, which allows to significantly reduce the testing time duration (Ref 13). Most studies to date regarding VHCF have been carried out based on the ultrasonic fatigue testing technique. The effectiveness of this technique for testing cast aluminum has been demonstrated by Mayer and Caton (Ref 4-6) who reported fatigue results in the regime of 108-109 cycles for cast AlSiMg0.3 alloy and 319 cast aluminum. Numerous studies (Ref 7-15) have shown that porosity has the most critical effect on the fatigue strength of Al-Si cast alloys, as it generally acts as a preferential site for fatigue crack initiation. Porosity
reduces the time for crack initiation by creating a high stress concentration and is thus mainly responsible for the decrease of fatigue life of these alloys. Since porosity distr
Data Loading...
