Residual stresses measurement in engine valves

Abstract

Engine components can develop important therma l gradients during service, producing high inelas- tic strains that modify the stress state and induce re sidual stresses when the components are cooled down to room temperature. A similar process is developed in co mponents subjected to heat treatment or to localized melting and solidification, such as dur ing induction heating for tempering, we lding, brazing, etc.In order to ob- tain the real stress state, and to asse ss the capability of the components to sustain loads, it is mandatory to de- termine the magnitude of the inelastic strains and the resulting residual stre sses. Experimental methods such as X-ray or neutron diffraction and Barkhäusen noise, give in formation only for residual stresses in a thin superfi- cial layer. Other methods, such as st rain-gauges rosettes, require cannot be applied with confidence in parts with complicated shapes. In this work, a layer-removal methodol ogy is presented to determ ine residual stresses in ax- isymmetric components. This method requires measurem ent instruments commonly used by engine component manufacturers, combined with analysis by numerical methods. An application case is presented in order to de- termine the residual stresses at room temperature and the effective stresses, in an internal combustion engine valve during its service.