Effetto del pre-stress sul comportamento a fatica di elementi intagliati in acciaio inossidabile

Il trattamento di pretensionamento, o pre-stress, consiste nel sovraccaricare gli elementi di macchina con valori delle forze applicate tali da eccedere localmente, nei punti critici, lo sforzo di snervamento del materiale. In questo modo è possibile generare tensioni residue superficiali di compressione che contribuiscono a migliorare la resistenza a fatica degli elementi trattati. In questo lavoro si analizza il comportamento di provini intagliati di acciaio inox, precedentemente pretensionati e poi sollecitati a fatica assiale. La geometria dei provini è stata disegnata in modo da riprodurre nella maniera più fedele l???andamento degli sforzi nelle zone critiche rispetto all???elemento di macchina considerato. La misura degli sforzi residui e della rugosità, oltre all???analisi delle superfici di frattura hanno permesso di completare la caratterizzazione del comportamento dei provini dopo il trattamento di pre-stress. I risultati sono discussi criticamente e permettono di trarre indicazioni utili in sede di progetto

Photoelastic analysis of surface-cracked elements in presence of Hertzian contact and interposed fluid

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Multiparameter Analysis of The Stress Field Around A Crack Tip

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Sull’utilizzo dell’energia cinetica per produzione additiva: primi risultati di prove di fatica e confronto con lavorazioni SLM

Il cold spray (CS) è una tecnica di rivestimento a freddo in cui la deposizione delle polveri avviene grazie all’impatto ad alta velocità delle particelle contro un substrato e alla conseguente elevata deformazione plastica, con l’instaurarsi delle condizioni di instabilità adiabatica di taglio. Nel presente lavoro sono stati considerati provini in In718 prodotti con CS e con SLM, sottoposti a diversi trattamenti termici, a valle della lavorazione dei provini. La caratterizzazione dei provini ha compreso l’analisi microstrutturale, la misura degli sforzi residui e della la porosità, mentre le prove meccaniche hanno previsto prove di trazione statiche e di fatica assiale. I risultati mostrano caratteristiche e resistenza comparabili a quelle dei provini SLM, suggerendo che il CS, grazie alla minore temperatura del processo e al ridotto impegno energetico, possa divenire una tecnologia additiva alternativa o complementare rispetto alle più consolidate tecnologie laser

Failure analysis of a shaft of a car lift system

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Finite Element Simulation of Shot Peening Coverage with the Special Attention on Surface Nanocrystallization

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High-cycle fatigue strength of a pultruded composite material

Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for large production rates and volumes. For this reason, their use is increasing also in structural applications in civil and mechanical engineering. However, their use is still limited by the partial knowledge of their fatigue behaviour; in many applications it is, indeed, required a duration of many millions of cycles, while most of the data that can be found in literature refer to a maximum number of cycles equal to 3 millions. In this paper a pultruded composite used for manufacturing structural beams is considered and its mechanical behaviour characterized by means of static and high-cycle fatigue tests. The results allowed to determine the S-N curve of the material and to assess the existence of a fatigue limit. Observations at the scanning electronic microscope (SEM) allowed to evaluate the damage mechanisms involved in the static and fatigue failure of the material

3D Reality-Based Survey and Retopology for Structural Analysis of Cultural Heritage

Cultural heritage’s structural changes and damages can influence the mechanical behaviour of artefacts and buildings. The use of finite element methods (FEM) for mechanical analysis is largely used in modelling stress behaviour. The workflow involves the use of CAD 3D models and the use of non-uniform rational B-spline (NURBS) surfaces. For cultural heritage objects, altered by the time elapsed since their creation, the representation created with the CAD model may introduce an extreme level of approximation, leading to wrong simulation results. The focus of this work is to present an alternative method intending to generate the most accurate 3D representation of a real artefact from highly accurate 3D reality-based models, simplifying the original models to make them suitable for finite element analysis (FEA) software. The approach proposed, and tested on three different case studies, was based on the intelligent use of retopology procedures to create a simplified model to be converted to a mathematical one made by NURBS surfaces, which is also suitable for being processed by volumetric meshes typically embedded in standard FEM packages. This allowed us to obtain FEA results that were closer to the actual mechanical behaviour of the analysed heritage asset

Effects of hybrid post-treatments on fatigue behaviour of notched LPBF AlSi10Mg: Experimental and deep learning approaches

Laser powder bed fusion (LPBF) as one of the widely used technologies of additive manufacturing (AM), has a high capability to produce complex geometries such as notched parts in a layer-by-layer manner. LPBF parts in their as built state have inhomogeneous and anisotropic microstructure and poor surface quality. Post-treatments can play a key role in modulating these imperfections. In this study, the effects of four different post-treatments including heat treatment, shot peening and electro-chemical polishing as well as their combination as hybrid treatment were investigated on microstructure, surface and mechanical properties and finally fatigue behaviour of the LPBF V-notched AlSi10Mg samples. Afterward, a deep learning based approach was employed for modelling the fatigue behaviour via artificial neural network. Surface roughness, surface modification factor, hardness, residual stress and porosities were considered as inputs and fatigue life was considered as the output. Model function of the network was generated and the relevant parametric and sensitivity analyses were performed. The results indicated the importance of surface related properties and the notable effect of the surface post-treatments in enhancing the fatigue performance of the LPBF material

Whole family-based physical activity promotion intervention: the Families Reporting Every Step to Health pilot randomised controlled trial protocol

Introduction : Family-based physical activity (PA) interventions present a promising avenue to promote children’s activity, however, high-quality experimental research is lacking. This paper describes the protocol for the FRESH (Families Reporting Every Step to Health) pilot trial, a child-led family-based PA intervention delivered online.  Methods and analysis : FRESH is a three-armed, parallel-group, randomised controlled pilot trial using a 1:1:1 allocation ratio with follow-up assessments at 8- and 52-weeks post-baseline. Families will be eligible if a minimum of one child in school Years 3-6 (aged 7-11 years) and at least one adult responsible for that child are willing to participate. Family members can take part in the intervention irrespective of their participation in the accompanying evaluation and vice versa. Following baseline assessment, families will be randomly allocated to one of three arms: (1) FRESH, (2) pedometer-only, or (3) no-intervention control. All family members in the pedometer-only and FRESH arms receive pedometers and generic PA promotion information. FRESH families additionally receive access to the intervention website; allowing participants to select step challenges to ‘travel’ to target cities around the world, log steps, and track progress as they virtually globetrot. Control families will receive no treatment. All family members will be eligible to participate in the evaluation with two follow-ups (8 and 52 weeks). Physical (e.g., fitness, blood pressure), psychosocial (e.g., social support), and behavioural (e.g., objectively-measured family PA) measures will be collected each time point. At 8-week follow-up, a mixed-methods process evaluation will be conducted (questionnaires and family focus groups) assessing acceptability of the intervention and evaluation. FRESH families’ website engagement will also be explored.  Ethics and dissemination : This study received ethical approval from the Ethics Committee for the School of the Humanities and Social Sciences at the University of Cambridge. Findings will be disseminated via peer-reviewed publications, conferences, and to participating families