89 research outputs found
Usura da strisciamento a secco della lega di magnesio AM60 contro acciaio rapido rivestito
No full textNel presente lavoro è stato studiato lo strisciamento a secco della lega Mg-6%Al-0.3%Mn (AM60) contro un acciaio rapido (di tipo AISI M2), rivestito con diversi film sottili di nitruri ad alta durezza (TiN, CrN e ZrN), prodotti commercialmente con tecnica PVD. L’intento è stato quello di simulare il processo di foratura della lega di magnesio con punte rivestite e capire quindi i meccanismi tribologici che impongono limiti al processo stesso, soprattutto in relazione alla formazione del tagliente di riporto. Sono state condotte prove nella configurazione blocco (l’acciaio rivestito) contro anello (la lega di magnesio), ad un carico di 200 N e ad una velocità di strisciamento di 0.8 m/s. Queste condizioni sono state scelte per simulare il comportameno tribologico del sistema, con riferimento a prove di foratura precedentemente condotte. I rivestimenti con nitruri non hanno comportato evidenti miglioramenti prestazionali in confronto alle punte in acciaio rapido non rivestito, ma i risultati ottenuti hanno permesso di proporre una metodologia di prova tribologica e delle linee guida per la selezione dei valori ottimali di avanzamento e velocità periferica per la foratura della lega di magnesio AM60
Tensile and bending behavior of sintered alloys: Experimental results and modeling
No full textSintered materials show a different stress-strain behavior when subjected to tensile or compressive loading, the response to compression being characterized by a higher elastic modulus, yield stress, and strain hardening rate. These differences tend to make the bending behavior somewhat more complex to analyze, particularly in the elasto-plastic field, as compared to conventional materials, having equal mechanical properties under tension and compression. As a consequence, the use of widely applied test techniques, such as the Three Point Bending (TPB), becomes more difficult for sintered materials, due to the lack of reliable analytical models capable of evaluating elasto-plastic stress-strain distribution as a function of applied load and deflection. In the present investigation, the results of uniaxial tensile-compressive and bending tests conducted on sintered ferrous alloys characterized by different microstructures and porosity are reported and briefly discussed. Then an analytical model, specifically aimed to analyze the elasto-plastic monotonic behavior of a TPB specimen made with a material having different tensile and compressive properties, is presented. Its predictions as regards load-deflection curves and elasto-plastic stress-strain distributions are compared with the results of TPB tests and of numerical (Finite Element) analysis, showing a fairly good agreement
Influence of post weld treatments on the fatigue behaviour of Al-alloy welded joints
No full textIn this paper the influence of different post welding treatments, such as ageing or shot peening, on the fatigue behaviour of Al-alloy welded joints was investigated. The analysed joints were candidates for car structural applications. Several four point bending fatigue tests were conducted on GMAW specimens subjected to different post weld treatments. The residual stress field acting on specimens was measured by the X-ray diffraction (XRD) technique. The results of tests were discussed with the aid of a finite element model of the specimen aimed to calculate the actual fatigue cycle, also taking account of residual stresses and of their redistribution during the test. This allowed to characterize the fatigue resistance of the joints, taking account of the effective stress acting in the region of crack initiation. (C) 1998 Elsevier Science Ltd. All rights reserved
Investigation of secondary phases effect on 2205 DSS fracture toughness.
No full textThe fracture toughness properties of duplex stainless steels (DSS) are strongly reduced by intermetallic phases, precipitating at 600-1000°C. In this investigation, the embrittlement effect induced by a low content of these phases has been studied in a 2205 DSS, by means of instrumented Charpy V impact testing. Different contents of intermetallic phases have been produced by isothermal treatments at 800-950°C. The microstructure has been analysed by scanning electron microscope/backscattered electron images. The impact test results, the examination of the fracture surfaces and of the cross-sections close to the notch root allows us to elucidate the role of secondary phases contents in reducing impact fracture toughness. When the quantity of secondary phases is 1%, the fracture is completely brittle. The plastic deformation at the notch root and in the resisting section provokes a secondary phase breakage with a high density microcrack formation, inducing an easy nucleation and propagation of the final fracture crack. When the content of secondary phases is between 0·5 and 1%, fracture is mixed. Both the sigma σ and chi χ phases have been found to be responsible for the embrittling of the 2205 DSS, and fracture toughness mainly depends on their density and dimension
Fracture toughness of nitrided layers obtained with different treatment cycles
No full textThis investigation is aimed at developing a methodology for a proper characterization of the fracture toughness of nitrided layers as a function of treatment depth and at assessing the influence of different nitriding cycles on the toughness of nitrided layers
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