On the Choice of Tool Material in Friction Stir Welding of Titanium Alloys

Friction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, is now being successfully used also for magnesium alloys, copper and steels. The wide diffusion the process is having is due to the possibility to weld both materials traditionally considered difficult to be welded or "unweldable" by traditional fusion welding processes due to peculiar thermal and chemical material properties, and complex geometries as sandwich structures and straightening panels. Recently, research is focusing on titanium alloys thanks to the high interest that such materials are getting from the industry due to the extremely high strength-weight ratio together with good corrosion resistance properties. At the moment, the main limit to the industrial applicability of FSW to titanium alloys is the tool life, as ultra wear and deformation resistant materials must be used. In this paper a, experimental study of the tool life in FSW of titanium alloys sheets at the varying of the main process parameters is performed. Numerical simulation provided important information for the fixture design and analysis of results. Tungsten and Rhenium alloy W25Re tools are found to be the most reliable among the ones considered

Network Virtual Machine (NetVM): A New Architecture for Efficient and Portable Packet Processing Applications

A challenge facing network device designers, besides increasing the speed of network gear, is improving its programmability in order to simplify the implementation of new applications (see for example, active networks, content networking, etc). This paper presents our work on designing and implementing a virtual network processor, called NetVM, which has an instruction set optimized for packet processing applications, i.e., for handling network traffic. Similarly to a Java Virtual Machine that virtualizes a CPU, a NetVM virtualizes a network processor. The NetVM is expected to provide a compatibility layer for networking tasks (e.g., packet filtering, packet counting, string matching) performed by various packet processing applications (firewalls, network monitors, intrusion detectors) so that they can be executed on any network device, ranging from expensive routers to small appliances (e.g. smart phones). Moreover, the NetVM will provide efficient mapping of the elementary functionalities used to realize the above mentioned networking tasks upon specific hardware functional units (e.g., ASICs, FPGAs, and network processing elements) included in special purpose hardware systems possibly deployed to implement network devices

On the role of intermetallic and interlayer in the dissimilar material welding of Ti6Al4V and SS 316L by friction stir welding

Joining titanium with stainless steel can lighten the structure of numerous industrial applications. However, a vast disparity of thermal, physical, and chemical properties between these alloys leads to defects in conventional arc welding techniques, viz., brittle intermetallic compounds, pores, cracks, etc. Friction stir welding (FSW) is a renowned solid-state joining technology for creating dissimilar material joints producing visco-plastic material flow at the interface. The present investigation compares the intermetallic layer thickness and properties as a function of the thickness of the Cu interlayer sandwiched in lap joints. Macrostructural and microstructural characterizations were carried out to understand the localized microstructural evolution comprising intermetallic, grain refinement, defects, etc. Mechanical properties were also evaluated for prepared lap joints

On the Choice of Tool Material in Friction Stir Welding of Titanium Alloys

Friction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, is now being successfully used also for magnesium alloys, copper and steels. The wide diffusion the process is having is due to the possibility to weld both materials traditionally considered difficult to be welded or “unweldable” by traditional fusion welding processes due to peculiar thermal and chemical material properties, and complex geometries as sandwich structures and straightening panels. Recently, research is focusing on titanium alloys thanks to the high interest that such materials are getting from the industry due to the extremely high strength-weight ratio together with good corrosion resistance properties. At the moment, the main limit to the industrial applicability of FSW to titanium alloys is the tool life, as ultra wear and deformation resistant materials must be used. In this paper a, experimental study of the tool life in FSW of titanium alloys sheets at the varying of the main process parameters is performed. Numerical simulation provided important information for the fixture design and analysis of results. Tungsten and Rhenium alloy W25Re tools are found to be the most reliable among the ones considered

Material Flow in FSW of T-joints: Experimental and Numerical Analysis

In the paper the authors present the results of both an experimental and a numerical campaign focused on the analysis of the occurring material flow in the FSW of T joints of aluminum alloys. In particular to investigate the metal flow experimental tests and observations has been developed utilizing a thin foil of copper as marker placed between the skin and the stringer. In this way, the actual metal flow occurring during the FSW of T-joints has been highlighted together with the real bonding surface. The acquired information is definitively useful in order to choose effective set of process parameters, improving the process mechanics and avoiding the insurgence of defects

Selective Laser Melting of Ti6Al4V: Effects of Heat Accumulation Phenomena Due to Building Orientation

Titanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland

Effects of disturbance on sandy coastal ecosystems of N-Adriatic coasts (Italy)

Coastal sand dune landscapes hold habitats of high economic, social and ecological value on a global scale. At the same time, they are among the most threatened ecosystems worldwide, facing escalating anthropogenic pressures, drawing attention to their resilience as a necessary condition for both biodiversity conservation and sustainable development. This study describes the vegetation zonation of the North-Adriatic coastal landscape which suffers from a severe and complex human utilization meanwhile holding high landscape, faunal and floral values. As plant communities, because of their specific nature, are considered good indicators of overall biodiversity and of ecosystem integrity of coastal dune environments, effects of both human and natural disturbance have been analysed through a comparison between real and potential coastal vegetation, using a hierarchical landscape classification approach. To provide a comprehensive framework for sustainable coastal management and development, a multiscale method for the assessment of the conservation status of sandy coastal environment has been applied. The assessing methodology focused first on landscape level by means of structural and compositional indicators. At a more detailed scale, floristic, vegetational and structural aspects of plant communities were analyzed along the main environmental gradient, which develops moving inland from the sea edge. Conservation status of N-Adriatic coastal zonation resulted fairly good at only few sites along the coast, mostly located where urban development and tourism are limited by legislation or simply because of the difficulty in reaching them. Elsewhere, real vegetation is deeply different from the potential zonation: erosion and tourism pressures truncate the first elements of the zonation, while towns and villages, coastal roads, pines plantations and agriculture truncate the last stages and sandy systems are trapped between erosion on the sea side and human settlements inlands, with no space for natural sediment dynamics and communities development

Fuzzy FMECA analysis of radioactive gas recovery system in the SPES experimental facility

Selective Production of Exotic Species is an innovative plant for advanced nuclear physic studies. A radioactive beam, generated by using an UCx target-ion source system, is ionized, selected and accelerated for experimental objects. Very high vacuum conditions and appropriate safety systems to storage exhaust gases are required to avoid radiological risk for operators and people. In this paper, Failure Mode, Effects, and Criticality Analysis of a preliminary design of high activity gas recovery system is performed by using a modified Fuzzy Risk Priority Number to rank the most critical components in terms of failures and human errors. Comparisons between fuzzy approach and classic application allow to show that Fuzzy Risk Priority Number is able to enhance the focus of risk assessments and to improve the safety of complex and innovative systems such as those under consideration

A numerical approach for the modelling of forming limits in hot incremental forming of AZ31 magnesium alloy

Magnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25–400 °C and wall angle in a range of 35–60°. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity

Hybrid prediction-optimization approaches for maximizing parts density in SLM of Ti6Al4V titanium alloy

It is well known that the processing parameters of selective laser melting (SLM) highly influence mechanical and physical properties of the manufactured parts. Also, the energy density is insufficient to detect the process window for producing full dense components. In fact, parts produced with the same energy density but different combinations of parameters may present different properties even under the microstructural viewpoint. In this context, the need to assess the influence of the process parameters and to select the best parameters set able to optimize the final properties of SLM parts has been capturing the attention of both academics and practitioners. In this paper different hybrid prediction-optimization approaches for maximizing the relative density of Ti6Al4V SLM manufactured parts are proposed. An extended design of experiments involving six process parameters has been configured for constructing two surrogate models based on response surface methodology (RSM) and artificial neural network (ANN), respectively. The optimization phase has been performed by means of evolutionary computations. To this end, three nature-inspired metaheuristic algorithms have been integrated with the prediction modelling structures. A series of experimental tests has been carried out to validate the results from the proposed hybrid optimization procedures. Also, a sensitivity analysis based on the results from the analysis of variance was executed to evaluate the influence of the processing parameter and their reciprocal interactions on the part porosity