Effects Of Plastic Straining On Residual Stresses Induced By Shot-peening

Author:  Kirk, D.
Source:  Conf Proc: ICSP-3, (p.213-220)
Doc ID:  1987025
Year of Publication:  1987
The 'skin' of residual compressive stress induced by shot-peening is of primary practical importance. It is this skin of compressive stress, which offsets applied tensile stress, that gives rise to improved service performance in fatigue, corrosion-fatigue and stress-corrosion situations. Any factor which affects surface stress level is therefore very significant. It is well-known that elevated temperature treatments can reduce the level of residual stress in a component. Harmful tensile surface stresses are usefully reduced by 'stress-relief-annealing'. Beneficial compressive surface stresses are also relieved by elevated temperature treatments and are therefore proscribed in standard specifications for shot-peened components. It is less well-known that small plastic strains can drastically affect the residual stress distribution in shot-peened components and therefore should be proscribed. Vohringer has pointed out that, for a shot-peened aluminium alloy (A1Cu5Mg2) both tensile and compressive plastic strains will change the surface stress level. A small applied tensile plastic strain can replace the original compressive surface residual stress with a tensile surface residual stress. Compressive plastic strains, on the other hand, only reduced the level of surface compressive residual stress without reversing its sign. This work is concerned with extending our knowledge of the effects of plastic strain applied to shot-peened material. Only applied tensile strains have been considered since they are known to have a more serious effect than applied compressive strains. Two simple pure materials, copper and nickel were chosen together with three steels - a mild steel (American Flat B), a plain-carbon steel (BS EN8) and a low-alloy steel (BS EN30B). Sub-surface residual stress distribution changes were to be examined for the two pure materials. All of the work was to be carried out on flat tensile test pieces shot-peened on both major surfaces using the same grade of shot.

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