Papers by Author: C. Pappalettere

Abstract: In recent years, important innovations have been introduced in Friction Stir Welding (FSW) technology such as, for example, the Laser assisted Friction Stir Welding (LFSW) and in-process Cooled Friction Stir Welding (CFSW). Residual stresses have a fundamental role in welded structures because they affect the way to design the structures, fatigue life, corrosion resistance and many other material properties. Consequently, it is important to investigate the residual stress distribution in FSW where, though the heat input is lower compared to traditional welding techniques, the constraints applied to the parts to weld are more severe. The aim of the present work is to verify the capabilities of both FSW techniques in reduction of the residual stress in aluminium butt joints.

Abstract: The present work present a preliminary study to evaluate the impact response of a new sandwich panel, made up of two polyethylene skins separated by lightweight polyethylene foam. An impact test campaign was conducted on 15 square specimens (side 100 mm, total height 44 mm, average skins height 2.75 mm) with not macroscopic defects, obtained by three homogenous panels. The absorbed energy, the force and the crosshead velocity were recorded during the test. Three level of impact energy were considered. Experimental tests have allowed to obtain the impact energy/acceleration and the peak stress/impact energy diagrams for this material. Moreover, the specimen profile of the section that passes through the impact area was obtained before the test, just after the impact and one hour later for each specimen. Subsequently the experiment was reproduced by means of solid explicit finite element (FE) model in Abaqus. In order to simulate as real as possible the panel behaviour, the skins were modelled as elasto-plastic material while the core was simulated as elastomeric hyperfoam material. The material constants were based on previous experimental data conducted on the same material. After the FEM model validation, the stress-strain resulting maps were plotted.

Abstract: The fatigue strength of real welded structures neither can be covered by formulae or theoretical arguments, nor simply deducted by studying a complex assembly through its elementary components because of the many interactions among different factors governing the phenomenon. In view of this, the support of experimental observations and practical procedures to evaluate the stress/strain magnitude that could lead some components to unsafe working conditions should be preferred, especially in industrial applications where fast and reliable responses are strongly needed.