Numerical and experimental verification of a technique for locating a fatigue crack on beams vibrating under Gaussian excitation

The stationary vibrations of a beam excited by Gaussian noise are strongly affected by the presence of a fatigue crack. Indeed, as soon as the crack arises the system response becomes non-linear due to crack breathing and a non-Gaussian behaviour is encountered. The paper presents both numerical and experimental investigations in order to assess the capability of the non-Gaussianity measures to detect crack presence and position. Monte Carlo method is applied to evaluate in time domain the higher order statistics of a cantilever beam modelled by finite elements. The skewness coefficient of the rotational degrees of freedom appears the most suitable quantity for identification purpose being …

A linear programming model for optimal subassembly level determination in shipbuilding industry

Shipbuilding industry is an industrial sector characterized by a customized make-to-order production process. The shipbuilding process can be roughly divided into four steps: design, assembly planning, manufacturing and final assembly. In this paper assembly planning is investigated: it consists in subdividing the ship structure into blocks and grand-blocks, thus involving a two levels subassembly generation. Any mechanical assembly process can be decomposed into a set of tasks, each task involving joining two or more components or subassemblies together. The sequence of assembly tasks has a major influence on completion time and resource utilization and it drastically impacts costs and eff…

METODOLOGIA PER IL RILIEVO SIMULTANEO DELL’USURA DIFFUSA E LOCALIZZATA IN CUSCINETTI A ROTOLAMENTO

Aluminium sheet metal scrap recycling through friction consolidation

Abstract In the last decades, several direct-recycling techniques have been developed and investigated in order to avoid material remelting, typical of the conventional aluminum alloys recycling processes. Moreover, the remelting step for aluminum recycling is affected by permanent material losses. Solid-state recycling processes have proven to be a suitable strategy to face such issues. Friction Consolidation is an innovative solid state-recycling technology developed for metal chips. During the process, a rotating die is plunged into a hollow chamber containing the material to be processed. The work of friction forces decaying into heat soften the material and, together with the stirring …

Friction stir extrusion to recycle aluminum alloys scraps: Energy efficiency characterization

Abstract Solid state recycling refers to a group of processes allowing direct recycling of metals scraps into semi-finished product. Their main advantage lies in avoiding the molten state of the material which badly affects the environmental performance of the conventional (remelting based) recycling routes. It is expected that such process category would lower the environmental performance of metals recycling. In this paper, the friction stir extrusion process for aluminum alloy AA 2050 wire production is analyzed under the primary energy demand perspective. The process electrical energy demand is quantified with varying process parameters. An empirical modelling approach was applied and a…

WELDING MISMATCHING INLUENCE ON CRACK PROPAGATION

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as t…

Crack identification in a beam by measure of the responce to white noise

Surface and mechanical characterization of stationary shoulder friction stir welded lap joints: experimental and numerical approach

Friction Stir Welding (FSW) is one of the most used solid-state welding processes in the aeronautical, aerospace, ground transportation and naval fields. Stationary Shoulder Friction Stir Welding (SSFSW) is a recently introduced variant of the process allowing lower heat input into the joints, with beneficial effects in terms of joint mechanical properties, microstructure and top surface finish. In the paper, lap joints produced by SSFSW and made out of AA6082-T6 aluminum alloy sheets have been analyzed with the aim to investigate the effect of the stationary shoulder on the lap joints surface, metallurgical, and mechanical properties. The lap joints produced by SSFSW have been compared to …

Job shop scheduling by a parallel approach

The paper deals with a parallel approach to job shop scheduling by a branch and bound methodology using the lower bound proposed by Ashour and Hiremath. The optimal solution is achieved by an iterative-reductive strategy. At each iteration the algorithm investigates the conflict intervals and it selects a subset of the possible solutions. The makespan value, achieved by the parallel processes, gives the upper limit for the admissible lower bound of the intermediate solutions. Furthermore the best makespan reached by each iteration is reused as a filter to reduce the complexity of the next iteration. The computation is speeded up by a parallel implementation, giving the possibility of distri…