Instrumented nanoindentation evaluation of Young modulus alteration caused by induced residual stress fields

This work evaluates the alteration of Young's modulus caused by the induction of residual stress (RE) fields in a set of SAE 1045 Steel specimens by using instrumented nanoindentation. The specimens were subjected to a stress relief to eliminate their prior history caused during the manufacturing process. The importance of this evaluation states in the fact that, in mechanical components, previous residual stresses are accumulated or added to superficial and volumetric stresses generated during subsequent mechanical loads. This characteristic may cause sudden failures or increase service life also. The RE were induced through bending tests and evaluated using the Crack Compliance Method (CCM). During the instrumented nanoindentation, a Berkovich type nanoindenter was used, following the Oliver-Parr method. A differential segment was extracted from the centre of the beam which contains the same stress field distribution as it was also demonstrated with a numerical analysis carried in ANSYS (R). A total of four cases were analysed considering: a) Non previous history, b) with induced RE, c) with the application of the Bauschinger effect (BE) and d) with the induction of RE plus the application of the BE. Differences between Young's modulus and surface hardness values were found for each case.