1,721,049 research outputs found
Study of high strain rate effect on sheet formability based on Nakazima test
No full textThe knowledge of the sheet metals formality is important for the success of the manufacturing processed based on plastic deformation. Even though many industrial processes take place at relatively high speeds, higher than the quasi-static regime ones, few studies are present in the literature on the evaluation of the formability at high speed. In this framework, the present paper aims at studying the effect of the high strain rate on the formability of AA6082 aluminium alloy, characterized by a thickness of 1 mm. An experimental equipment, based on the Nakazima test, mounted on a direct tension-compression Split Hopkinson Bar, has been developed in order to define the formability under dynamic loading conditions. The high strain rate behaviour of the alloy has been compared with the one obtained in quasi-static condition
Tensile behavior and formability of pre‐painted steel sheets
No full textThe present work aims at studying the tensile behavior and formability of pre‐painted steel sheets. To this purpose, uniaxial tensile and hemispherical punch tests were performed in order to analyze the deformation behavior of pre‐painted sheets under uniaxial stretching and biaxial balanced stretching conditions, respectively. Tests were interrupted in order to obtain different strain levels until fracture; at each strain level reached, the occurrence of superficial damages on the paint coating was detected; thinning of the different layers of the pre‐painted sheet was also measured. It was observed that the degree of damage on the paint coating depends on the loading condition; in particular, under uniaxial stretching, the paint coating is able to follow the steel sheet during deformation up to the onset of the necking, whilst, under biaxial balanced stretching, coating exhibits superficial damages before fracture of the sheet
Friction stir welding of AZ31 magnesium alloy thin sheets using “pin” and “pinless” tools
No full textThe present investigation aims at studying the friction stir welding of thin AZ31 magnesium alloy sheets (1.5 mm in thickness). Different tool geometries and process parameters were investigated. In particular, two properly designed tools, with different values of the shoulder diameter, have been used; each of them has been manufactured both with and without the pin (“pin” and “pinless” tool). It was shown that, as the tool characterised by the shoulder with lower diameter (8 mm) is used, the presence of the pin leads to the obtaining of peak stress and ductility values higher than those provided by the “pinless” tool. A strong beneficial effect on both ductility and strength of the joint is obtained by increasing the shoulder diameter (19 mm) even though the “pin” tool configuration is characterized by a very narrow welding window. An investigation has been also carried out in order to evaluate the micro-hardness distributions and the microstructure of the welded joints. A different metal flow can be clearly observed depending on the presence/absence of pin. Moreover, a more homogeneous microstructure is obtained using the “pinless” tool
High-speed deformation of pinless fswed thin sheets in aa6082 alloy
No full textThe high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition
Reuse of Composite Prepreg Scraps as an Economic and Sustainable Alternative for Producing Car Components
No full textIn the present paper, an innovative process for the reuse of carbon fiber prepreg scraps, based on a zero-waste approach, was proposed in order to recovery scraps produced during cutting operations of virgin prepreg rolls. Unfortunately, during the prepreg transformation, about 75% of the materials is discarded due to the inefficiency of the cutting phase. Nevertheless, this prepreg can be reused, in a closed loop system, to produce second life products. In this research, the environmental and economic benefits of implementing a recovery system for prepreg scraps were investigated exploiting Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) techniques. The LCA technique was used to compare the environmental impact of the innovative reclaiming process with the one obtained by the manufacturing process based on the use of virgin prepreg. Typical compression molding process was modeled for both the scenarios and the environmental performances were evaluated exploiting the Cumulative Energy Demand indicators. Moreover, the LCC analysis of the two alternatives was performed for evaluating the economic sustainability of the recycling process
High Strain Rate Behaviour of AA7075 Aluminum Alloy at Different Initial Temper States
No full textThe aim of this work is to study the mechanical properties of alloy AA7075 in both T6
and O temper states, in terms of visco-plastic and fracture behavior. Tension and compression tests
were carried out starting from the quasi-static loading condition 10-3 up to strain rates as high as 2 x
103 s-1. The high strain rate tests were performed using a Split Hopkinson Tension-Compression Bar
(SHTCB) apparatus. The tensile specimens were also subjected to micro-fractography analysis by
Scanning Electronic Microscope (SEM) to evaluate the characteristics of the fracture. The results
show a different behavior for the two temper states: AA7075-O showed a significant sensitivity to
strain rate, with a ductile behavior and a fracture morphology characterized by coalescence of
microvoids, whilst AA7075-T6 is generally characterized by a less ductile behaviour, both as
elongation at break and as fracture morphology. Brittle cleavage is accentuated with increasing
strain rate. The Johnson-Cook viscoplastic model wad also used to fit the experimental data with an
optimum matching
Comparison among the environmental impact of solid state and fusion welding processes in joining an aluminium alloy
No full textThe life cycle assessment (LCA) methodology was used to evaluate the environmental impact of friction stir welding (FSW) of AA5754-H114 aluminium alloy sheets. FSW was performed under different values of rotational and welding speeds to analyse the influence of the process parameters on midpoint category impacts. Pin tool wear and mechanical properties of joints were also evaluated. The functional unit chosen was related to the weld efficiency; furthermore, the weld length was set equal to 170 mm. The pre- and post-processing stages were also considered. Raw materials, energy and all inputs associated with each stage of product life cycle were collected and evaluated to analyse the environmental impact index. The results showed that, irrespective of the rotational speed, the lowest welding speed investigated leads to the highest energy consumption and, consequently, to the highest values of the midpoint category impact. On the contrary, at the highest welding speed, the environmental impact assumes the lowest values. By concerning the rotational speed, its effect on the midpoint category impact is strongly reduced compared to the one given by the welding speed. A performance index, obtained by considering both the midpoint category impact and ultimate tensile strength of the joints, was also defined.
Finally, the environmental sustainability of FSW was compared to the one of two different fusion welding technologies, namely gas tungsten arc welding (GTAW) and laser beam welding (LBW). The results showed that FSW was characterized by midpoint category impacts much lower than those of the GTAW, whilst such discrepancies decreased with the LBW
Effect of printing orientation on mechanical properties of components in stainless steel obtained using the Bound Metal Deposition technology
No full textThe present work aims at studying and analyzing the influence of process parameters on performances of 3D printed components obtained using the Bound Metal Deposition technology. Bound Metal Deposition is one of the latest technologies for metals 3D printing. It consists in an extrusion process in which the parts are fabricated layer-by-layer through the deposition of metal powder held together by wax and polymer binder. After printing, binder is removed using a solvent, and the additively manufactured parts are sintered for their consolidation at temperatures reaching 1400°C for about 40 hours. Tensile specimens in 17-4 PH stainless steel were additively manufactured imposing different printing orientations in order to evaluate the effect of growth orientation angle on the mechanical properties of 3D printed parts. Results have demonstrated that the printing orientation greatly affects the mechanical performances of 3D printed components
Life cycle impact assessment of different manufacturing technologies for automotive CFRP components
No full textA comparative life cycle assessment analysis among pressure bag molding and bag molding with autoclave for the manufacturing of car components in carbon fiber reinforced plastic (CFRP) was carried out. Four scenarios were analyzed: i) autoclave bag molding with aluminum mold, ii) autoclave bag molding with CFRP mold and plastic master, iii) autoclave bag molding with CFRP mold and medium density fiberboard master, and iv) pressure bag molding with aluminum mold. The collected data for life cycle inventory derives from an Italian manufacturer of CFRP car components, scientific references and Ecoinvent database. Cumulative energy demand, global warming potential, ReCiPe midpoint and endpoint methods were used as impact and damage categories for quantifying the environmental impacts of the different manufacturing processes investigated. The results showed that the pre-impregnated composite fibers with thermoset polymer matrix, used as input material for the four investigated scenarios, represents the main source of total environmental impact, due to the use of polyacrylonitrile as a precursor for carbon fibers. The comparison among the environmental assessments of the different scenarios demonstrated that the most impacting process is the autoclave bag molding with composite mold and polyurethane master, whilst the most sustainable process is the autoclave bag molding with aluminum mold
Development and Life Cycle Analyses of Carbon Fiber Reinforced Polymer Tubular Parts for Metal Replacement in Aerospace Applications
Full text linkReducing the weight of aircraft components is a key strategy to improve fuel efficiency and reduce greenhouse gas emissions. Innovative materials such as carbon fiber reinforced polymers (CFRPs) and manufacturing techniques represent a possible solution for improved sustainability in the aerospace sector. In this context, this paper presents the design and the evaluation of the environmental and economic impacts of a CFRP tubular structural component, employed for supporting passenger seats of commercial aircraft, realized with the innovative FW process. At first, a simulation of the winding process was conducted to define the component layers, and then a FEM analysis was performed to identify the optimal layering of the tubular structure to support the defined loads. Subsequently, environmental and economic impacts were evaluated by means of life cycle assessment and life cycle costing methodologies. The comparison between the CFRP tubular structure and traditional aluminum alternative was conducted to identify the most sustainable solution. The analysis showed that the CFRP tubular component resulted in lower environmental impacts than the traditional alternative (i.e., about 70% lower considering the whole life cycle) mainly due to the reduced weight. However, the cost evaluation identified the CFRP alternative as the most expensive solution, with production cost 40% higher than the aluminum alternative
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