1,721,108 research outputs found
Effetto del trattamento di rullatura sulla resistenza a fatica da fretting della connessione forzata albero-mozzo
No full textFretting fatigue of deep rolled shrink fitted samples
No full textThe shrink fitted shaft to hub connection, loaded under bending, experiences Fretting Fatigue at the end of the contact where both stress concentration and microslip are acting. Shrink fitted testing is not standard and common as the bridge type test, however, the round geometry implies no edge effect, the shrinkage and the bending loads can be carefully controlled with strain gages, and the stress distribution easily calculated with finite element analyses. Though the shrink fit compressive state, the cyclic bending introduces tensile stresses, hence the introduction of compressive residual stresses can play a significant role to prevent the initiation and the propagation of the fretting fatigue cracks. Experimental results are reported in the paper where the fretting fatigue strength was remarkably improved after a deep rolling treatment. Numerical analyses even predicted the complete mode I closure of potential fretting fatigue cracks by taking into account the compressive residual stresses. SEM investigation showed how the crack pattern was significantly different with deep rolling, having multiple crack initiation sites and then either coalescence or crack branching. From the modelling point of view, the paper shows that the self-arrest theory cannot be used to assess the fretting fatigue strength, for deep rolled specimens, where the crack remains closed. A better prediction can be obtained with a critical plane multiaxial fatigue criterion, based on the shear stress amplitude, which under a compressive stress state can be more effectively assumed as the driving force of the crack. Consistently the orientation of the plane experiencing the maximum shear stress amplitude was found in agreement with the observed initial crack direction
Analysis of the plane contact with discontinuous curvature
No full textThe analytical solution for the plane contact between nonconforming C 1 profiles with a curvature discontinuity is obtained and discussed. The initial gap between the undeformed profiles was represented by a double parabolic function having the curvature discontinuity within the contact region. On the basis of the analytical solution, the complete analysis of pressure distribution was obtained. A raw technique to find an approximate solution is presented and comparison to the analytic one provided. For the limit case of strong curvature ratio the asymptotic treatment is discussed in terms of consistency with hypotheses claimed
Verifica mediante banco a flessione della misura di tensione residua, in superficie e a bassa profondità, con il metodo del foro
No full textIl metodo del foro per la valutazione delle tensioni residue è stato recentemente sviluppato e migliorato. La valutazione dell’accuratezza del metodo è quindi di notevole interesse. Tuttavia, la misura delle tensioni residue è, per sua natura, non facilmente verificabile. Nonostante siano disponibili in letteratura riscontri positivi con la misura ai raggi X, lo stato di tensione residua può essere poco ripetibile e quindi non si presta ad una verifica di estrema accuratezza. L’utilizzo di un banco a flessione, invece, permette di simulare (come tensione residua) una tensione monoassiale, nota con elevata precisione. Nel presente lavoro, il metodo è stato verificato con successo. Inoltre, è stata verificata l’opportunità di selezionare frese di foratura con fondo piatto, in modo da migliorare la misura nei primi passi di foratura e quindi la previsione delle tensioni residue vicino alla superficie, dove la valutazione è di maggiore interesse
Prove a fatica in piena scala su connessioni di elementi tubolari in alluminio per perforazione petrolifera
No full textStato di tensione ed aspetti di fatica in elementi filettati per perforazione petrolifera
No full textProposal for Tip Relief Modification to reduce Noise in Spur Gears and sensitivity to meshing conditions
No full textIn the paper a new Tip Relief Profile Modification for spur Gears is presented. The topography here proposed is a classical linear profile modification with a parabolic fillet (Linear- Parabolic modification).
The parabolic fillet extension is treated as a parameter and its effect investigated.
The proposed topography is able to take advantages from both Linear, and Parabolic tip relief. The evolution from Linear to Parabolic is discussed in terms of Peak to Peak Transmission Error. Anomalous contact conditions due to particular tip relief modification are reported, and maps are obtained in order to find optimum tip relief by taking into account contact conditions boundaries too
Estensione del metodo integrale, considerando l'effetto di eccentricità, per la valutazione delle tensioni residue con i metodi del foro e della cava anulare
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