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Fatigue characteristics of A7075-T651 aluminum material were studied with surface treatment of shot peening. The fatigue life was characterized by two fatigue testing methods, ultrasonic fatigue test (UFT, 20 kHz) and the rotary-bending fatigue test (RFT, 53 Hz). The fatigue life improvement was confirmed by rotary bending fatigue tester. However, the surface modification effects were hardly observed by UFT method. The RFT results validate that the fatigue properties of RFT show a fine congruence regardless of the test machine types. The results of hardness, compressive residual stress, fatigue strength, and mechanical properties of specimen were improved by shot peening.
1. Introduction
Fatigue crack occurs due to the cyclic loading, which will primarily cause progressive and localized damage in materials utilized at automobiles, aircraft, and equipment parts and may lead to permanent fatigue failure. Further, in many cases, the severe deterioration of the key components is mainly caused by the fatigue cracks [1-3].
The use of aluminum alloy A7075-T651 is increasing, in accordance with the current trend of weight reduction, such as the damping and braking system of the aircraft. Thus, the improvement of fatigue strength is required for the high reliability in the extended range of service life.
In that sense, fatigue crack characterization and improvement are of significant importance. There are well known techniques to generate intensive compressive residual stress in the subsurface of materials in order to prevent crack formation and crack propagation. This could dramatically diminish economic losses predominantly that resulted from the infrastructural accidents and the component replacement, since the crack preventing technology is inevitable to prevent the sudden fracture by fatigue [4-6]. Shot peening is one of the ways to improve the fatigue life of the material [7, 8].
Various fatigue tests were in accordance with the magnitude of the impinged steel balls. Previous studies on gigacycle fatigue testing of high carbon chromium steel regarding the durability and processing method of the material were performed with the correlation of shot peening impingement angle and the acceleration [9-11]. This study focused on the fatigue tests in the range of very high cycle fatigue (VHCF) and the fatigue characteristic improvement by the shot peening (SP). SP treatment was carried out to generate a compressive residual stress by altering the SP pressure...