1,722,326 research outputs found
Joining of Dissimilar Materials
Full text linkMaterial manufacturers and engineering structure designers are currently focusing new ways to exploit the benefits of light-weight, hybrid materials with improved properties at a low cost. The ability to join dissimilar materials is enabling the design engineers to develop light-weight and efficient automobiles, aircraft and space vehicles.
The objective of this PhD research study was to produce alternative and efficient joining solutions for automotive and aerospace applications. The joining of dissimilar material was experimented to obtain light-weight Fibre Reinforced Polymer (FRP) sandwich composites, Al-foam sandwich (AFS) composites, hybrid dynamic FRP epoxy/polyurethane composites and the joining of Ti6Al4V alloy with and without surface modification to Ceramic Matrix Composite (CMC) and itself.
The joining of Al-foam and Al-honeycomb to FRP skins was performed. The experimental results show that higher flexural properties can be achieved by replacing Al-honeycomb with low-cost Al-foam as a core material in the sandwich structures. Compared to FRP-honeycomb sandwich panels, FRP-Al foam sandwich panels display ~25 % and ~65 % higher flexural strength in a long and short span three-point bending tests respectively.
AFS composites with complete metallic character, to withstand high-temperature application conditions, were produced by soldering/brazing techniques using Zn-based and Al-based joining alloys. A post-brazing thermal treatment was designed to recover the mechanical properties of AFS composites, lost during the soldering/brazing process. The microstructural analysis of the Al-skin/Al-foam interface revealed that the diffusion of joining materials into the joining substrates (Al-sheet and Al-foam) was achieved. Around 80% higher bending load before failure was observed when the AFS specimens produced with Zn-based joining alloys were subjected to flexural load compared to those produced with Al-based joining alloys.
Hybrid dynamic Carbon Fibre Reinforced Polymer (CFRP) composites with enhanced impact properties were produced by exploiting the reversible cross-linking functionalities of dynamic epoxy and dynamic PU resin systems. By joining dynamic CFRP-epoxy and dynamic CFR-PU laminates, hybrid dynamic composite in three different configurations and a non-hybrid composite were obtained. The four dynamic composites were characterised for structural, thermal, flexural and impact properties. The damage initiation upon impact was observed at around 95% higher energy level in the hybrid configuration (CFRP-4), compared to the non-hybrid configuration. The hybrid configuration CFRP-3 responded with around 55% higher perforation threshold energy compared the non-hybrid configuration.
Preliminary work on Adhesive joining of the Ti6Al4V alloy to itself was performed to analyse the effect micro-machining on adhesion and the effect of shape/design of micro-slots on an adhesive joint strength. Three types of micro-slots: V, semi-circle and U-shaped micro-slots were produced on Ti6Al4V sheet surface by using an in-house developed Micro-Electro-Discharge Machining (Micro-EDM) setup. Ti6Al4V alloy specimens with and without micro-machined surfaces were bonded together using a commercial epoxy adhesive. The Single Lap Offset (SLO) shear test results revealed that the micro-slot oriented perpendicular to the applied load displayed ~23 % higher joining strength compared to when the micro-slots were oriented parallel to the applied load. U-shaped micro-slots configuration displayed ~30 % improvement in the joint shear strength compared to the specimens with un-modified surfaces. The fractured surfaces analysis revealed mix (adhesive-cohesive) with cohesive dominated failure in bonded specimens with micro-machined surfaces compared to the as-received where pure adhesive failure was observed.
The joining of CMCs (C/SiC and SiC/SiC) to Ti6Al4V alloy was experimented using active brazing alloy (Cusil-ABA) and Zr-based brazing alloy (TiB590) in a pressure-less argon atmosphere. The CMC-Ti6Al4V joint strength was further improved by modifying the surface of Ti6Al4V alloy using an in-house built Micro-EDM setup. Around 40% higher joining strength was recorded when the Zr-based brazing alloy was used as a joining material compared to the conventional active brazing alloy, Cusil-ABA. Improvement in the joining strength was noticed when the Ti6Al4V surface was modified prior to joining
Joining of AL-6016 to Al-foam using Zn-based joining materials
No full textTo obtain an Aluminium Foam Sandwich (AFS), Al-6016 sheets were successfully joined to a 9 mm thick Aluminium (Al) foam, by using Zinc (Zn) based joining materials (pure Zn and Zn alloy with 2% Al) at 430 °C in argon atmosphere. The microstructure of the joints was analysed by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS). Moreover, three-point bending tests were carried out to evaluate the flexural properties of the AFS components. Current experimental work is focused on optimization of the AFS joining process and the mechanical properties of AFS components
Consumer environmental awareness and purchase intentions. A survey
No full textBesides posing a serious threat to the health and life of the world population, COVID-19, a severe acute respiratory syndrome, has also changed significantly people’s habits concerning transportation. Indeed, the fear of getting infected has provoked a shift from public to personal transportation, which may lead consumers to prefer buying their own cars, rather than using public transport, with a negative impact on the environment. At the same time, however, recent research suggests that COVID-19 might have increased consumers’ environmental awareness, thus paving the way for increased diffusion of electric cars. Nevertheless, we know little about whether and how the growing environmental awareness created by COVID-19 (EAC-19) affects consumers’ (electric vs. gasoline) car purchase intention (EvsG-CPI). To investigate such an impact, we frame the decision to buy an electric vs. gasoline car as an ethical decision, and argue that it is influenced by both rational or deliberated (i.e., individual judgement) and non-rational or emotional (i.e., ethical obligations and subjective norms) factors. Structural Equation Modelling (SEM) results reveal that both a rational path and a non-rational path are at work in explaining the influence of EAC-19 on EvsG-CPI. On the one hand, a rational path is confirmed as the effects of EAC-19 on EvsG-CPI is mediated by ethical judgement. On the other hand, we find that both ethical obligation and subjective norms influence the relationship between EAC-19 and EvsG-CPI by acting simultaneously as mediators in a serial mediation model. Overall, our findings allow marketing scholars, electric car companies, and policy-makers to develop a better understanding of customers’ preferences regarding the purchase of cars in the new normal after the COVID-19 pandemic and, more generally, of the rational and non-rational factors underlying the purchase of environmentally-friendly products. Limitations of the study and avenues for further research are also discussed
Choosing environmentally friendly transportation in the post-Covid-19 era: The role of personal norms.
No full textJoining of C/SiC Ceramic Composites to themselves and to Ti-6Al-4V for aerospace applications
No full textJoining of C/SiC for aerospace applications
Full text linkTo join C/SiC to C/SiC with a new, pressure-less composite joining material and technique, for high performance application
Joining of Aluminium Alloy Sheets to Aluminium Alloy Foam Using Metal Glasses
No full textAluminium alloy foam is a lightweight material with high energy absorption properties and can potentially replace bulk Al-components. The aim of this work is to develop a brazing technique to join aluminium facing sheets to aluminium alloy foam to obtain aluminium foam sandwich panels for applications where high service temperature is a requirement. Al-6016 alloy sheets were brazed to aluminium alloy foam using two aluminium based (Al-Cu-Mg and Al-Si-Mg-Ti) metal glasses at 560 °C–590 °C in an argon atmosphere. Microstructure and microhardness profiles of the aluminium alloy sheet/aluminium alloy foam brazed joints were analysed using a microhardness tester and scanning electron microscope equipped with electron dispersion spectroscopy. A three-point bending test was conducted to study the flexural behaviour of the aluminium foam sandwich composite panels
Joining of CFRP and low-CTE glass-ceramics for aerospace applications
No full textJoining of dissimilar materials is a crucial point in aerospace applications; in particular CFRP and low-CTE glass-ceramics that are widely employed in space structures. The main challenge in this context is manufacture light and stable joints able to withstand aerospace conditions. Joining materials for this purpose, in order to be used in aerospace atmosphere, need to be lightweight, with low coefficient of thermal expansion, low moisture absorption, mechanical strength to sustain the component weight and low curing temperature to avoid damage of the composite polymeric matrix. For these reasons use of organic joining materials is limited by their moisture absorption and relatively high CTE values. In this study several inorganic joining materials, such as inorganic cements and pre-ceramic adhesives, were selected and tested. Inorganic cements have the advantage of room temperature curing and low CTE, but the disadvantage of relatively low mechanical properties. For this reason addition of fibers (e.g. glass fibers) to these materials was performed to improve mechanical strength. For ceramic adhesives, curing temperature might damage the polymeric matrix of CFRP, therefore the treatment was modified to preserve the matrix and at the same time ensure sufficient mechanical strength. Joints have been manufactured using the selected inorganic materials and mechanical strength was evaluated with tensile and shear strength tests. Most promising materials were also tested after ageing cycles developed to simulate aerospace conditions. Furthermore surface modification of CFRP was also studied, with different techniques, to improve the adhesion of inorganic materials. Each joining technique and joining material has been studied in order to offer an innovative approach in the field of CFRP/low-CTE glass-ceramic joining. Moreover, selected joining solutions take into account scalability and the possibility to transfer the process to larger structures. This activity was developed in the frame of the H2020-SMS (Sandwich Material and Structure) project
Surface machining of Ti6Al4V by means of Micro-Electrical Discharging to improve adhesive joining
Full text linkThe Micro-Electrical Discharge Machining (Micro-EDM) technique has been employed to machine micro-patterns with shaped micro-slots on Ti6Al4V surfaces. Ti6Al4V substrates, with and without micro-slots, were bonded using a commercial epoxy adhesive. Optical microscopy and SEM were used to observe the micro-patterned Ti6Al4V surfaces before and after joining and to analyse the fracture surfaces after mechanical tests. The joints were mechanically characterised, with and without micro-patterns, by means of Single Lap Offset (SLO) shear tests under compression to understand the effect of differently shaped micro-slots. The effects of the shape of the micro-slots, their interlocking or overlapping, and their orientation, with respect to the applied load, are presented and discussed in terms of mechanical performance of the joints
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