Effect of hardening induced by cold expansion on damage fatigue accumulation and life assessment of Aluminum alloy 6082 T6

Abstract

Hole cold expansion (HCE) is an effective method to extend the fatigue life of mechanical structures. During cold expansion process compressive residual stresses around the expanded hole are generated. The enhancement of fatigue life and the crack initiation and growth behavior of a holed specimen were investigated by using the 6082 Aluminum alloy. The present study suggests a simple technical method for enhancement of fatigue life by a cold expansion hole of pre-cracked specimen. Fatigue damage accumulation of cold expanded hole in aluminum alloy which is widely used in transportation and in aeronautics was analyzed. Experimental tests were carried out using pre-cracked SENT specimens. Tests were performed in two and four block loading under constant amplitude. These tests were performed by using two and four blocks under uniaxial constant amplitude loading. The increasing and decreasing loading were carried. The experimental results were compared to the damage calculated by the Miner's rule and a new simple fatigue damage indicator. This comparison shows that the 'damaged stress model', which takes into account the loading history, yields a good estimation according to the experimental results. Moreover, the error is minimized in comparison to the Miner's model.

Damage accumulation near the cold-expanded hole due to high-cycle fatigue by crack compliance method

“…Only a few of publications concern quantitative damage accumulation near cold-expanded holes due to fatigue loading. Available approaches are based on circumstantial damage indicators, which cannot be reliably established proceeding from direct physical measurements [13][14][15]. Implementation of the novel destructive method for quantitative assessment of fatigue damage accumulation in the stress concentration zone accompanied by the influence of residual stresses is the first subject of the present paper.…”

Cold Expansion Process with Multiple Balls—Numerical Simulation and Comparison with Single Ball and Tapered Mandrels

“…For the specific case of the mandrel geometry, there are a wide published research focused on the tapered models [13][14][15][16] but limited investigations on ball geometries [17,18]. The motivation behind the use of ball geometries, as an alternative to tapered mandrels, comes from its consolidated manufacturing process based on their use for ball bearings industry.…”

Fatigue damage and sensor development for aircraft structural health monitoring

“…It was shown, that the density of the persistent slip bands on the sensor's surface is determined by the accumulated fatigue damage [4]. Now, after investigations of the aluminium alloys under fatigue the efficiency of polycrystalline sensors has been proved [5,6]. Appropriate materials for fatigue sensors manufacturing are well known aluminium alloys D16AT, V95, 2024T3, 7075T6, covered by the layer of pure aluminium.…”