Abstract
Ultrasonic and conventional fatigue tests were carried out on the AISI-SAE AA7075-T6 aluminum alloy, in order to evaluate the effect of artificial and induced pre-corrosion. Artificial pre-corrosion was obtained by two hemispherical pitting holes of 500-μm diameter at the specimen neck section, machined following the longitudinal or transverse direction of the testing specimen. Induced pre-corrosion was achieved using the international standard ESA ECSS-Q-ST-70-37C of the European Space Agency. Specimens were tested under ultrasonic fatigue technique at frequency of 20 kHz and under conventional fatigue at frequency of 20 Hz. The two applied load ratios were: R = −1 in ultrasonic fatigue tests and R = 0.1 in conventional fatigue tests. The main results were the effects of artificial and induced pre-corrosion on the fatigue endurance, together with the surface roughness modification after the conventional fatigue tests. Crack initiation and propagation were analyzed and numeric models were constructed to investigate the stress concentration associated with pre-corrosion pits, together with the evaluation of the stress intensity factor in mode I from crack initiation to fracture. Finally, the stress intensity factor range threshold ΔKTH was obtained for the base material and specimens with two hemispherical pits in transverse direction.
Highlights
One of the most versatile metal used in industrial applications is aluminum and its alloys; it is the second widely produced metal after steel
The following conclusions be drawn from the present investigation; Ultrasonic fatigue tests werecan obtained on specimens of the aluminum alloy 7075-T6: base material, with two hemispherical pits and pre-corroded
Ultrasonic fatigue tests were obtained on specimens of the aluminumfatigue: alloy 7075-T6: base and with two hemispherical pits; material, with two hemispherical pits and pre-corroded
Summary
One of the most versatile metal used in industrial applications is aluminum and its alloys; it is the second widely produced metal after steel. Its alloys are often used in modern industries: more than 40% of aerospace and aeronautical parts are made of these alloys nowadays [1,2,3,4]. Such industrial applications imply a combination of mechanical loading and corrosion, which leads to stress concentration and failure of the material. In previous numeric investigations [10], it was found that orientation of the corrosion pits regarding the applied load plays a significant role on the stress concentration factors. An important number of studies has been focused to understanding how cracks initiate and propagate in materials influenced by external factors, such as corrosion pitting, surface conditions, temperature and others [10,11,12,13]
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