THE NIKU-LARI METHOD AND THE STRESS SOURCE METHOD:APPLICATION TO RESIDUAL STRESS DISTRIBUTION OF SHOT PEENED PLATES

This chapter discusses application of the Niku–Lari method and the stress source method to residual stress distribution of shot peened plates. In industry, shot peening represents a well-known process to improve the fatigue properties of metallic components. As only the surface is plastically deformed by this process, an inhomogeneous deformation takes place, which induces compressive residual stresses in a thin surface layer. These reduce the mean stresses in the surface so that the initiation and early growth of fatigue cracks is retarded. A well-known measure of the shot peening process is the so-called Almen-intensity, that is, the deflection that results when a plate of normed size, called Almen-strip, is shot peened. This chapter introduces a simple procedure to determine the average depth and the average magnitude of the compressive residual stresses. The method involves the shot peening of plates of different thickness under identical conditions. Niku–Lari's method to determine the residual stress profile is based on a measurement of the deflection variation that results if the shot peened layer is removed step by step.