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The mechanism of the residual stress relaxation during the fatigue life of shot peened high-strength aluminum alloys was investigated. Experiments were conducted on specimens subjected to three different shot peening treatments and tested under reverse bending fatigue. x-ray diffraction (XRD) measurements were carried out to determine the initial and stabilized residual stress fields. The residual stress field created by the surface treatments has been introduced into a finite element (FE) model by means of a fictitious temperature distribution. The elastic-plastic response of the superficial layers affected by the shot peening treatments has been derived through reverse strain axial testing combined with microhardness tests and implemented in the FE model. The proposed numerical/experimental approach is able to satisfactorily predict the residual stress field evolution. Notably, relaxation has been correctly simulated in the low-cycle fatigue regime and imputed to plastic flow in compression when the superposition of compressive residual and bending stresses exceeds the local cyclic yield strength of the material. Conversely, the residual stress field remains stable at load levels corresponding to the 5×106 cycles fatigue endurance.

The offset between the hole and the centre of the strain-gage rosette is unavoidable, although usually small, in the hole-drilling technique for residual stress evaluation. In this article, we revised the integral method described in the ASTM E837 standard and we recalculated the calibration coefficients. The integral method was then extended by taking into account the two eccentricity components, and a more general procedure was proposed including the first-order correction. A numerical validation analysis was used to consolidate the procedure and evaluate the residual error after implementing the correction. The values of this error resulted limited to a few percentage points, even for eccentricities larger than the usual experimental values. The narrow eccentricity limit claimed by the standard, to keep the maximum error lower than 10%, can now be considered extended by approximately a factor of 10, after implementing the proposed correcting procedure, proving that the effect of the eccentricity is mainly linear within a relatively large range

In this article, the single-point incremental forming of sheet metals made of micro-alloyed steel and Al alloy is investigated by combining the results of numerical simulation and experimental characterization, performed during the process, as well as on the final product. A finite element model was developed to perform the process simulation, based on an explicit dynamic time integration scheme. The finite element outcomes were validated by comparison with experimental results. In particular, forming forces during the process, as well as the final shape and strain distribution on the finished component, were measured. The obtained results showed the capability of the finite element modelling to predict the material deformation process. This can be considered as a starting point for the reliable definition of the single-point incremental forming process parameters, thus avoiding expensive trial-and-error approaches, based on extensive experimental campaigns, with beneficial effects on production time

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