Copula Approach to Multivariate Energy Efficiency Analysis

Data envelopment analysis (DEA) is a method that finds the effectiveness of an existing system using a number of input and output variables. In this study, we obtained energy efficiencies of construction, industrial, power, and transportation sectors in OECD countries for 2011 using DEA. It is possible to achieve the efficiencies in different sectors. However, we aim to find joint energy efficiency scores for all sectors. One of the methods proposed in the literature to obtain joint efficiency is network data envelopment analysis (network DEA). Network DEA treats sectors as sub-processes and obtains system and process efficiencies through optimal weights. Alternatively, we used a novel copula-based approach to achieve common efficiency scores. In this approach, it is possible to demonstrate the dependency structure between the efficiency scores of similar qualities obtained with DEA by copula families. New efficiency scores are obtained with the help of joint probability distribution. Then, we obtained joint efficiency scores through the copula approach using these efficiency scores. Finally, we obtained the joint efficiency scores of the same sectors through network DEA. As a result, we compared network DEA with the copula approach and interpreted the efficiencies of each energy sector and joint efficiencies.

Improvement in joint efficiency with high productivity and narrow weld formation in friction stir welding

High productivity, excellent joint strength and small weld bead make friction stir welding an emerging joining technique to join difficult to weld dissimilar aluminum alloys. Effect of rotational speed, traverse speed and shoulder diameter on the joint strength and elongation of the friction stir welded dissimilar aluminum alloys (AA7475-AA2219) is investigated. In addition, parameters are optimized to obtain joint with narrow weld bead and high joint efficiency using the entropy-weighted technique for order of preference by similarity to ideal solution method. Nine experiments are performed as per the L9 orthogonal array and mechanical properties of the welded joints are measured. Results of the study reveal that optimum values of ultimate tensile strength and percentage elongation are obtained at a rotational speed of 710 rev/min, welding speed of 250 mm/min and shoulder diameter of 10 mm resulting in good joint strength, high productivity and narrow weld bead. From the selected process parameter range, tool shoulder diameter is found to be the most significant parameter. The findings of the present study are discussed in light of the friction stir welding process mechanism, available literature, mechanical testing, microstructure and fractography.

Effect of Tool Rotational Speed and Traverse Speed on Friction Stir Welding of 3D-Printed Polylactic Acid Material

Joining of polymers are usually carried out using adhesives that has a deteriorating quality at elevated working conditions thus limiting its application areas. Friction stir welding (FSW) is a growing solid-state welding technology, with applications including the welding of lightweight materials. FSW was recently introduced for joining thermoplastics materials and found successful. This study attempts in employing FSW to join polylactic acid (PLA)-based 3D printed engineering components and assess the effect of FSW process parameters (tool rotational speed and traverse speed) on the weld property. The present work uses the FSW process to butt weld 5 mm thick 3D printed PLA sheets with taper cylindrical profiled tool. For the experimentation, three different combinations of feed rates and pin rotational speeds are considered. Based on joint efficiency evaluation, it is found that tool rotational speed of 1400 rpm combined with 10 mm/min transverse speed produces the weld with high joint efficiency of 40%.

Comparative assessment on weldability of Al 6061 to polycarbonate for dissimilar sheets placement in friction stir lap welding using sensor signals

The thermoplastic polymers and precipitation hardened aluminium alloys are highly popular in the aerospace and automobile sectors as a replacement of metallic materials to improve the strength to weight ratio. Thus, the unlike aluminium alloy to polycarbonate assembled structures are often necessary for which mechanical fastening and adhesive bonding are the primary methods for joining as fusion welding processes are inadequate. However, the dissimilar joint efficiency is found to be less. Thus, the ultrasonic and friction welding processes are developed. The friction stir welding is one such advanced material stirring technique without any melting of base materials. The present work addresses metallic aluminium (Al6061) to polycarbonate sheet materials joining using friction stir welding in overlap configuration using tapered H13 tool steel. The thrust force with associated tool stirring torque has been acquired in real time during plunging followed by welding phase. The weld bead profile with respective force-torque signals was analysed for the process monitoring. The tensile test has been carried out on the lap welds. The weld interface of the unlike sheets have also been scrutinised. Initially, the aluminium sheet was partially overlapped on polycarbonate for the parametric study. The highest joint efficiency was found to be 40.2% at 1400 rpm tool rotational speed and 75 mm/min traverse speed due to improper material mixing at the weld interface. Therefore, the feasibility of the process have been tested by placing thermoplastic polycarbonate over aluminium alloy through which the joint efficiency was further improved (48.57%) at comparatively low tool rotational speed (1100 rpm) with lower welding speed (55 mm/min) as the minute metallic particles uniformly mixed with melted and solidified polycarbonate due to more uniform torque in the welding phase. The tool stirring torque and axial thrust was found to be higher in this overlap position.

Effect of Friction Stir Welding Techniques and Parameters on Polymers Joint Efficiency—A Critical Review

The objective of current work is to analyse the influence of different welding techniques and welding parameters on the morphology and mechanical strength of friction stir welds (FSW) in polymers, based on data collected in the literature. In the current work, only articles that provide data on the joint efficiency, or sufficient information to estimate it are considered. The process using conventional tool is presented and compared with new procedures developed for FSW of polymers, such as those using tools with heated stationary shoulder, preheating of the polymer or double-side passage of the tool. The influence of tool rotational speed (w), welding speed (v), tilt angle and geometry of the pin are discussed. This work focuses on the polymers most studied in the literature, polyethylene (PE) and polypropylene (PP). The use of external heating and tools with stationary shoulder proved to be of great importance in improving the surface finish, reducing defects, and increasing the mechanical strength of the welds. The increase in the w/v ratio increased the joint efficiency, especially when using conventional tools on PE. A trend was obtained for conventional FSW, but it was difficult to establish mathematical relationships, because of the variability of welding conditions.

Examination of the Mechanical, Corrosion, and Tribological Behavior of Friction Stir Welded Aluminum Alloy AA8011

Aluminum alloy AA8011 is emerging as a promising material for modern engineering applications in which improved tensile strength, hardness, corrosion-resistance, and wear-resistance of materials are required. Typically, AA8011 alloys are utilized in air-conditioning ducts and heat exchanger fins in ships, leisure boats, luxury vessels, workboats, fishing vessels, and patrol boats. However, the conventional welding of AA8011 is a challenging procedure. In this context, this paper focuses on the development of an effective solid-state welding methodology for AA8011 alloy welding. The AA8011 alloy was friction stir welded by varying the tool rotation speed, traverse speed, and shoulder diameter. The microhardness, tensile strength, joint efficiency, elongation, corrosion rate, and wear rate of the friction stir welded specimens were compared with the base material. Fractography analysis was conducted after the tensile test and surface morphology analysis after corrosion and wear tests, using scanning electron microscopy. The compositional elements in the corroded and worn section of the specimens were analyzed using energy-dispersive X-ray spectroscopy. Based on the joint efficiency as a primary constraint, the optimum process parameters for friction stir welding of aluminum alloy AA8011 have been established as follows: tool rotation speed of 1200 rpm, tool traverse speed of 45 mm/min, and tool shoulder diameter of 21 mm.

Friction stir spot welding of AA5052 with additional carbon fiber-reinforced polymer composite interlayer

In this study, similar aluminum alloys AA5052 with additional carbon fiber-reinforced polymer composite (CFRP) interlayer were selected to investigate the effect of welding parameters (rotational speed and dwell time) on the mechanical properties, joint efficiency, and microstructure of friction stir spot weld joint. The maximum tensile shear load was 1779.6 N with joint efficiency of 14.6% obtained at rotational speed of 2,000 rpm and 2 s dwell time, which is 39.5% higher than the value at low rotational speed 850 rpm and 2 s dwell time. Meanwhile, the maximum microhardness 58 HV was attained in the keyhole region at rotational speed of 2,000 rpm and dwell time of 5 s, which is 22.4% higher compared to low rotational speed. The SEM-EDS results reveal the presence of intermetallic compounds (Al–Mg–C), which enhance the intermetallic bonding between elements.