X-RAY-DIFFRACTION STUDY OF THE FATIGUE BEHAVIOR OF A SHOT-PEENED ALUMINUM-LITHIUM ALLOY

The effect of different shot-peening treatments on the cyclic fluctuat ing bending fatigue behavior of a new aluminum-lithium alloy (the 2091 ) has been investigated. The residual-stresses in-depth profiles have been defined just after the shot peening using mainly the X-ray diffra ction method. To reach a given depth inside the material, the surface layer was removed by electro-polishing. The acquired data had to be th en corrected in older to account for the redistribution of the stresse s during the polishing. Furthermore, this alloy contains up to 15-perc ent intermetallic precipitates. Moreover, the X-rays penetrate deeply inside the material (23 mu m). For these reasons, a special procedure, based on a self-consistent micromechanical scheme, has been developed to correct the acquired data. The stress profiles obtained by this pr ocedure are compared to those obtained by other mechanical experimenta l methods and those calculated by a theoretical shot-peening method. S hot peening improves the life of the material but the surface residual stresses are partially released during the first cycles of fatigue an d are then quickly stabilized.