Uniform Compressive Stress Research Articles

Inelastic Instability and Incremental Theories of Plasticity

A most troublesome paradox has existed for a number of years with respect to buckling in the plastic range. Theoretical considerations and all direct experimental evidence show conclusively that an incremental or flow type of mathematical theory of plasticity is valid. However, the results of plastic buckling tests are well correlated by a simple total or deformation theory 1 4 and bear no resemblance to published predictions of incremental theory. ' The suggestion was made that initial imperfections of shape or loading might well explain this most peculiar result. However, subsequent investigations by several authors seem to have given the impression that excessively large imperfections would be needed and that the answer would be overly sensitive to the magnitude of such imperfections.^' I t is the purpose of this paper to demonstrate that extremely small, and therefore unavoidable, imperfections of shape do account for the paradox in a simple manner. The buckling load is shown to be extremely insensitive to the amount of imperfection. The example chosen is a simplified version of the long rectangular plate hinged along one edge and free on the other under uniform compressive stress at the ends. This is the equivalent of the case of the cruciform column, which has been so disturbing in the past because incremental theory applied to a perfect cruciform column did lead to an entirely incorrect result.

Forest Products Laboratory Technical Notes

Advanced compressor designs today often include blade integrated disc (blisk) rotors, with high demands on aerodynamic performance, resistance againsthigh load levels and foreign object damage (FOD).To increasethe highcycle fatigue (HCF) strength, compressive residual stresses are introduced into the surface and subsurface layer of aerofoil, fillet (transient area between aerofoil and disk) and annulus (intermediate area between aerofoils). For generatingcompressive residual stresses several different industrial production processes are used, beside ultrasonic shot peening, laser shock peening, deep rolling and shot peening wet and dry with glass or ceramic media is shot peening with steel media the mostly used technology. However, depending on the size of the componentaccessibility for tools might be limited and the set-up of economical production techniques challenging for blisk shot peening.This paper gives an introduction into blisk shot peening, a sophisticated mechanical surface technology for treating aerofoil surfaces of blisk rotors using special designed calliper nozzles assolution for introducing uniform residual compressive stress states, as well as consistentshot peening coverage levels.