Search results for "SISTEMI"
showing 10 items of 2026 documents
Joining Ti6Al4V and AISI 304 through friction stir welding of lap joints: experimental and numerical analysis
2014
The results of an experimental and numerical analysis on Friction Stir Welding of dissimilar lap joints made out of AISI304 and Ti-6Al-4 V thin sheets are presented. The mixed joints, welded with varying process parameters, have been characterized from a mechanical and metallurgical point of view. A numerical model able to take into account the behaviour of the two different materials has been used. The numerical results have been utilized to explain the joint properties and the occurring material flow. The effect of the heat input, tilt angle and sheets mutual position has been investigated. It is found that both hooking defects and tunnels may occur with incorrect choice of process parame…
Beta forging of Ti-6Al-4V: Microstructure evolution and mechanical properties
2013
Titanium alloys are finding an increasing use in the aeronautical field, due to their characteristics of high mechanical properties, lightness and corrosion resistance. Moreover these alloys are compatible with the carbon fibre reinforced plastics that are also finding a wide use in the aeronautical field. On the other hand the use of these alloys implies some drawbacks, for example titanium alloys are often considered more difficult to form and generally have less predictable forming characteristics than other metallic alloys such as steel and aluminum. In this paper was studied both the microstructure evolution and the mechanical properties of a Ti-6Al-4V rolled bar after hot forging. The…
Friction Stir Welding of Tailored Blanks: Investigation on Process Feasibility
2006
Tailor welded blanks (TWBs) are conventionally produced by laser or traditional welding processes. In either case, the joints are created by solid-liquid-solid phase transformations that result in undesirable microstructures and tensile residual stresses detrimental to joint performance. This study investigates feasibility of an alternate joining process, friction stir welding (FSW). The joining of AA7075-T6 blanks of different thickness is investigated through FE analyses and controlled experiments. It is found that for a successful joint, the welding parameters have to be carefully designed so that the resulting metal flow and the temperature history during FSW are consistent for the two …
Investigations on the Mechanical Properties and Formability of Friction Stir Welded Tailored Blanks
2007
Tight competition characterizing automotive industries in the last decades has determined a strong research effort aimed to improve utilized processes and materials in sheet stamping. As far as the latter are regarded light weight alloys, high strength steels and tailored blanks have been increasingly utilized with the aim to reduce parts weight and fuel consumptions. In the paper the mechanical properties and formability of tailored welded blanks made of a precipitation hardenable aluminum alloy but with different sheet thicknesses, have been investigated: both laser welding and friction stir welding have been developed to obtain the tailored blanks. For both welding operations a wide rang…
Beta-forging of Ti6Al4V titanium alloy powders consolidated by HIP: Plastic flow and strain-rate relation
2014
Ti6Al4V is probably the best known and studied titanium alloy, not only for aerospace applications. Nevertheless the deformation behavior still represents a challenge if any modification in the deformation process is required or introduced. This work deals with deformation behavior description of Ti6Al4V HIPped powders during high temperature deformation tests carried on in the Beta-region. Laboratory compression and tensile tests have been coupled with relaxation tests in order to achieve robust data about strain rate sensibility m-coefficient and activation energy Q. These results have been fitted for the assessment of a more general exponential deformation law. The final result is a “Dor…
Fatigue crack growth in 2024-T351 Friction Stir Welded Joints: longitudinal residual stresses and microstructural effects
2009
Abstract The role of longitudinal residual stress on propagation of fatigue cracks was examined in friction stir welds produced in 2024-T351 aluminum alloy. Fatigue crack growth rate was obtained through constant Δ K Iapp tests for notches at different distances from the weld centerline. Subsequently, crack growth was correlated to weld residual stress measured by the cut-compliance method. It was found that residual stresses correspond to low crack growth rates outside the weld zone during fatigue loading. Once in the weld zone, the crack growth was affected by microstructural and hardness changes. Furthermore, weld residual stresses were mechanically relieved and effects on crack propagat…
AA6082-T6 Friction Stir Welded Joints Fatigue Resistance: Influence of Process Parameters
2006
In the paper the results of a wide range of experiments on friction stir welding (FSW) of aluminium alloys are reported. In particular, the AA6082-T6 butt joints fatigue resistance was investigated by varying the most relevant process parameters. In addition, a revolutionary pitch was utilized in order to investigate the effects of the tool rotating speed and the tool feed rate. Observations of the fracture insurgence were developed for different levels of applied load.
FSW of AA2139-T8 Butt joints for aeronautical applications
2011
The effect of process parameters on mechanical and microstructural properties of AA 2139 T8 joints produced by friction stir welding (FSW) was analysed by means of statistical tools. Three different parameters were taken into account: angular speed ( ω), welding speed ( va), and plunging depth ( p); each of them was varied on three levels. Forces and temperatures achieved during the welding were monitored and analysed for all joints. An accurate microstructural analysis was performed: the occurrence of some remarkable defects, typical of FSW, such as tunnel or lack of penetration, was related to actual process parameters adopted. The extension of each FSW characteristic zone was measured a…
Improved FE model for simulation of friction stir welding of different materials
2010
Abstract One of the most relevant aspects of friction stir welding is the possibility to weld different materials. In the present paper, the authors present an improved continuum finite element model for the simulation of friction stir welding processes aimed to obtain T joints, made of a stringer in AA7175-T73511 and of a skin in AA2024-T4. The model, taking into account the thermomechanical behaviours of the two different materials, is utilised to study the occurring material flow and residual stress state. Numerical results are compared with experimental observations: the model is able to predict the material flow, obtaining important information on the joint failure mode.
Solid state bonding mechanics in extrusion and FSW: Experimental tests and numerical analyses
2007
In the paper the authors compare the different solid state bonding mechanics for both the processes of hollow profiles extrusion and Friction Stir Welding (FSW), through the results obtained from a wide experimental campaign on AA6082-T6 aluminum alloys. Microstructure evaluation, tensile tests and micro-hardness measurements realized on specimens extracted by samples of the two processes are discussed also by means of the results obtained from coupled FEM simulation of the processes. ©2007 American Institute of Physics