1,721,021 research outputs found
Multiscale three-dimensional stress analysis of voids clusters for the modelling of degenerated graphite in cast iron
No full textWe propose a multiscale three-dimensional model for the stress analysis of a cluster of degenerated graphite in spheroidal cast iron. The model allows to study the effect of graphite microstructure on the average stress distribution inside the cluster. At the microscale, precipitates of degenerated graphite are modelled as spheroidal voids. At the mesoscale, clusters of degenerated graphite are viewed as spheroidal inclusions made of equivalent porous elastic material. The equivalent elastic properties of the porous material are calculated using an approach proposed by Tandon and Weng and based on Eshelby's equivalent principle and the Mori-Tanaka's estimate. FE simulations at the microscale and at the mesoscale are performed in order to numerically validate the multiscale model
Utilizzo del parametro JV per la resistenza a fatica di giunti saldati
No full textIn the present work, an exemplified method is proposed for the fatigue assessments of arc welded joints made of steel or aluminum alloy. The fatigue calculation takes into account the JV parameter evaluated at weld bead. On the basis of the characteristic radius ρ*, related to the material, JV is numerically evaluated as an line integral of strain energy density along two consecutive segments located at the point of interest. The method is also applicable to complex welds. Some example are presented for the estimation of the fatigue behavior of welded joints subjected to nominal tensile loading, bending or torsion
Numerical Analysis of Double Riveted Lap Joints
No full textIn a previous work, the fatigue behaviour of different hot riveted joints under fatigue loadings were experimentally calculated. In particular, the experimental data showed a Wöhler curve slope close to five against the slope of three proposed by Eurocode 3. However, two series of shear splice riveted joints showed, at two million cycles, a stress range very close to the value suggested by Eurocode for shear splices that use non-preloaded high-strength bolts. In order to clarify the fatigue behaviour of riveted joints at high- and medium-fatigue regimes, this paper presents a preliminary three-dimensional non-linear FE analysis of a double-riveted lap joint previously analysed experimentally. Different friction coefficients and rivet clamping stress have been taken Into account, as well as the elastoplastic behaviours of the main plate subjected to tensile loadings. The numerical analysis shows that the friction force tends to reduce the range of stresses at the net section during fatigue loadings, and the force distribution or the stress concentration on the rivets is always critical for the external rivet, which is also the case regarding the non-linear behaviour of the material
Una sintesi della resistenza a fatica di giunti saldati in acciaio e lega leggera in funzione dell'energia di deformazione al piede e alla radice dei cordoni
No full textConcentrazione delle tensioni dovuta a disallineamento assiale nei giunti testa a testa
No full textNel presente lavoro viene eseguita una approfondita analisi numerica per analizzare il comportamento a fatica di giunzioni saldate testa a testa con disallineamento assiale. La procedura di calcolo è basata sul metodo del gradiente implicito attuata con le stesse modalità proposte in precedenza per lo studio delle giunzioni saldate ad arco. Viene presentata un’analisi di tipo parametrico al variare dell’entità del disallineamento assiale nella giunzione fornendo dei diagrammi di sintesi utili per il calcolo della resistenza a fatica. Infine, è stato eseguito un confronto con dati sperimentali tratti dalla letteratura di provini saldati testa a testa sollecitati a fatica e caratterizzati da tre diversi livelli di disallineamento assiale. I dati sperimentali sono relativi a provini in acciaio S1100.This paper reports a detailed numerical analysis of the fatigue strength of butt-welded joints with axial misalignment by applying the implicit gradient method. The numerical procedure is implemented similarly to a previous proposed investigation on the arc welded joints. A parametric analysis is proposed by changing misalignment type and quantity and providing some diagrams useful for the fatigue strength assessment. Finally, the paper shows an experimental comparison between the numerical assessment and the experimental fatigue data taken from the literature. The experimental data are some fatigue tests on welded joints made of steel S1100 and characterized by three different levels of axial misalignment
Fatigue crack propagation of planar three-dimensional cracks
No full textIn this paper the Fourier series is used to evaluate mode I Stress Intensity Factors (SIF) in three-dimensional planar flaws based on a distortion transformation of a reference disc. Under the hypothesis of an isolated crack, the SIF at each point of the crack border is calculated to assess the crack shape after propagation according to the crack growth rate equation of Paris and Erdogan. The contour is moved along the outward normal to the crack shape. Many examples are proposed with the aim of predicting the final shape of different types of embedded planar flaws
Previsione della vita a fatica di giunzioni saldate con difetti
No full textIl presente lavoro mette in luce la possibilità di considerare i difetti nelle giunzioni saldate ad arco come semplici concentratori di tensione in aggiunta al cordone di saldatura. La procedura numerica del gradiente implicito, validata in precedenza per le giunzioni integre, viene estesa anche a giunti con disallineamenti, undercuts e porosità. La soluzione tiene conto dello sviluppo tridimensionale dei giunti e delle eventuali difettosità senza introdurre modifiche o esemplificazioni di tipo geometrico rendendo possibile anche analisi numeriche a partire da scansioni tridimensionali che riproducono nel dettaglio il cordone di saldatura
The Stress Intensity Factor of convex embedded polygonal cracks
No full textIn the present work, a simple formula for the evaluation of the stress intensity factor (SIF) of convex embedded polygonal cracks has been proposed. This formula is structured as a correction factor of the Oore-Burns’ equation and is based on accurate three-dimensional FE analysis. Furthermore, a precise formula for a regular polygonal crack has been given
A closed form for the stress intensity factor of a small embedded square-like flaw
No full textIn the present work, the stress intensity factor (SIF) of a small embedded square-like flaw is calculated by means of a procedure based on the Oore-Burns integral. An explicit equation is given to evaluate the SIF along the two axes of symmetry that correspond to the points where the SIF takes its maximum and minimum value on the contour crack. The SIF is calculated in accordance with FE numerical results
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