Residual stress measurement in a ceramic-metallic graded material

This paper presents experimental measurements of the through-thickness distribution of residual stress in a ceramic-metallic functionally graded material (FGM). It further presents an error analysis and optimization of the residual stress measurement technique. Measurements are made in a seven-layered plate with a base of commercially pure titanium and successive layers containing an increasing proportion of titanium-boride, reaching 85% titanium-boride in the final layer The compliance method is employed to determine residual stress, where a slot is introduced using wire electric-discharge machining and strain release is measured as a function of increasing slot depth. Strain release measurements are used with a back-calculation scheme, based on finite element simulation, to provide residual stresses in the FGM. The analysis is complicated by the variation of material properties in the FGM, but tractable due to the flexibility of the finite element method. The Monte Carlo approach is used for error analysis and a method is described for optimization of the functional form assumed for the residual stresses. The magnitude and variation of the resulting residual stress distributions and several aspects of the error analyses are discussed.