Papers by Author: Filippo Gabrielli

Abstract: In this paper, the friction behaviour in a severe bending process of a thick plate was investigated, taking into account both dry and lubricated conditions. Early experimental tests were performed to obtain mechanical properties of the low carbon steel AISI 1006, to be used as input in FE solver. Besides a 3D thermo-mechanical model based on FEM was developed to predict stress and strain distributions and final component dimensions. The second experimental series was composed of a coining process and a forming operation to reach the size of the final part. The analysis and the control of the friction conditions has permitted to obtain a product of higher quality that permitted to avoid all the secondary machining operations previously required.

Abstract: The present investigation deals with the development of a methodology to predict the flow behaviour of the ZM21 magnesium alloy in given intervals of temperature and strain rate by FEM simulation of torsion testing. Equations based on the hyperbolic sine of flow stress and on the multiple linear regression were proposed and implemented into the finite element code. The flow curve shapes obtained by simulation were compared with experimental ones that were not used in the building phase of the equations. It was found that the simulation of torsion tests allows, under given conditions of temperature, strain rate and deformation levels, to obtain flow curve shapes very similar to those obtained by experiments under conditions not included in the building of the models.

Abstract: The thickness effect on formability of AZ31 magnesium alloy sheet has been widely investigated by means of uniaxial tensile tests, performed in the temperature range from 250 to 350°C, with strain rates varying from 10-4 to 10-1 s-1, using samples with different thickness values (from 1.5 to 3.2 mm). A preliminary microstructural study has shown that grain size and morphology are not significantly affected by both sheet thickness and heating just before the deformation step. The experimental results of tensile tests have been analysed in terms of flow curve shape, flow stress and strain to failure levels. They show that, in general, flow stress increases and ductility decreases with increasing sheet thickness even if such influence is strongly related to the temperature and strain rate conditions Finally, the analysis of the Zener-Hollomon parameter vs. peak flow stress data showed that the same mechanisms are operative in the investigated sheets.

Abstract: The formability of friction stir welded AZ31 magnesium alloy sheets was investigated by means of uniaxial tensile and hemispherical punch tests performed under different process conditions. The results of the tensile tests were analysed in terms of flow stress and ductility at different temperature and strain rate; the hemispherical punch tests, carried out at different temperatures, provided the limiting dome height. The formability of FSW-ed blanks was compared to the one exhibited by the base material in order to evaluate the quality of the welded joints.

Abstract: The effect of the process parameters on the sheet formability of AZ31 magnesium alloy has been investigated by means of uniaxial tensile and hemispherical punch tests at different temperatures and strain rates. The results of the uniaxial tensile tests were analysed in terms of flow curves, ductility and microstructural evolution; the constitutive parameters were evaluated and related to the forming limit curves obtained by the hemispherical punch tests carried out at different temperatures and punch speeds.