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Title: Effects Of Plastic Straining On Residual Stresses Induced By Shot-peening
Author: Kirk, D.
Source: Conf Proc: ICSP-3, (p.213-220)
Publication year 1987
Document number: 1987025
Number of pages: 8
Abstract:
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.
I
t 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.
T
his 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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