Forming of Adhesive-Bonded Sandwich Sheets with a Rubber Pad
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SANDWICH sheets (SWS) are combinations of thin metallic skins with a soft, nonmetallic core layer. The core layer can be polymer, foam, and composite, and the skin can be steel, aluminum alloys etc. Thin SWS panels, including all metal SWS, are applied in automotive, aerospace, transportation, ship industries for light weight manufacturing.[1] The potential use of steel sandwich panels for ship hull reinforcement has been demonstrated by Withy.[2] Thermal insulation, dampening of vibration, and noise are other benefits of SWS. Although fabrication of SWS has been standardized, their formability and joining are of great concern for manufacturing, and has limited their widespread application. Prior research on formability of sandwich sheet includes study by Kim et al.[3] who analyzed the formability of AA5182/Polypropylene/ AA5182 SWS using limit dome height test and plane-strain tests, and showed it to be better than the base AA5182 sheet. Later, the same SWS was used to fabricate an automotive hood by Kim et al.[4] without surface cracks and instabilities. A key observation during cup deep drawability was the strain-path difference between the inner skin and the outer skin, which was considered mainly
GIRISH KUKREJA and R. GANESH NARAYANAN are with the Department of Mechanical Engineering, IIT Guwahati, Guwahati, India. Contact e-mail: [email protected] Manuscript submitted October 30, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
responsible for the improved formability due to shear deformation created. The effects of skin and core material were also presented.[5] Erichsen cup and drawing tests on 316L-Polyolefin-316L SWS revealed its applicability for automotive applications.[6] The negative effect of polymer core on limit drawing ratio during cup deep drawing of Al-Polypropylene-Al SWS was revealed by Parsa et al.[7] The predictions by the GTN damage model was shown to agree well with experiments. A similar effort was made by Parsa et al.[8] to evaluate the forming limit of SWS, who showed that the forming limit increased with an increase in skin thickness and a decrease in polypropylene core thickness. Kami and Banabic[9] evaluated the formability of Bondal SWS at varying lubricated conditions and blank holding force, and showed improved formability of about 0.33 in near plane-strain limit strain, but observed delamination during deep drawing. Tensile behavior characterization of SWS with Al skin and polypropylene core at room and elevated temperatures revealed that the magnitude of serrations in the flow curves of SWS can be reduced by using a high volume fraction polypropylene core.[10] Engel and Buhl[11] carried out pilot studies on vibration damping SWS made of cold-rolled steel skin, and recommended strategies like reducing the thickness of the outer sheet, and overall thickness of the sandwich to improve the forming quality. They also suggested that the total thickness of the sandwich can be achieved by increasing the number of sheets. The finite element (FE) simulation-based optimization of bending prov
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