Smart design wins bonding challenge

A team of mechanical engineers at Coventry University has won a competition to design the strongest aluminium beam using adhesives. Dean Palmer was one of the judging panel A student design competition, recently won by a team of four mechanical engineers studying for a masters degree at Coventry University, demonstrated the value of good teamwork, always designing for manufacture and how to use finite element analysis to design a more effective, stronger aluminium beam bonded using adhesives. The challenge, set by Huntsman Advanced Materials, was to design and build a bonded beam with the objective of achieving the highest load at yield under testing. Each of the twelve universities that entered the challenge, was allowed to submit two beams manufactured from the materials supplied. The beam itself had to be at least 400mm long, with the top surface flat and at least 25mm wide. The maximum height was 150mm but there was no minimum height. The beams had to be manufactured from no more than two sheets of L165 aluminium, 300mm long by 300mm wide by 1.5mm thick, plus the adhesive for bonding, Araldite 2011. Bonding was the only permitted method of fastening and the adhesive was not to be used to fill voids other than those in normal bond lines. Students were allowed to consult with Huntsman technical staff during the project and seek guidance on curing cycles and pre-treatment methods. The testing of the beams took place at TWI in Cambridge using a special electro-pneumatic testing machine. The beams (twelve in total) were tested for maximum flexural load at yield (local or general) in three-point flexure. The lower supports were 300mmm apart and the central loading bar had a diameter of 10mm. The loading rate was 5mm/minute. The results were interesting. The winning beam from Coventry University attained a maximum loading of 66kN in a little over 67 seconds of testing time. The total weight of the beam was 732g. Prior to bonding, the team had abraded the surfaces to maximise the bond strength of the adhesive. Rectangular and squat in shape but with sloping ends at its thickest point, the construction consisted of 11 aluminium laminate sheets bonded together. The beam had a very stable structure and was very symmetrical. According to one of the judges, Stuart Thompson, technical support manager at Araldite Structural Adhesives, "Coventry's winning entry was the only one to utilise the diagonal dimension of the supplied aluminium sheet to obtain the required beam length of 400mm in one continuous piece of aluminium. In achieving this, all subsequent aluminium had to be cut from the remaining triangular pieces, which necessitated the bonding of ever smaller strips of aluminium." It was also apparent during and after testing that the beam was held together for so long due to its aluminium plates being in shear and the adhesive being in tension. The winning team consisted of George Constandinides, David Munoz, George Xrysakis and Jedsada Kraikosol. George Xrysakis told Eureka: "It took us around one week for the design and analysis work, plus three to four days to manufacture the beams. We used Catia and Solidworks for 3D modelling and Cosmos for FEA work. The latter was particularly helpful as it highlighted to us where we had to place extra material to combat the high stress points on the beam." According to the team, overall planning and design evaluation work, including the clamping arrangement, took up around 70 to 80% of the time. Constandinides commented: "We worked well as a team and took our initial design ideas from structural beams. Design for manufacture was also key as we were limited to certain manufacturing methods at Coventry. Second place went to a team from Northumbria University whose design was somewhat reminiscent of a weighing scale - but of much sturdier construction. Pieces of aluminium that had been either bent, folded or cut resulted in a design that was different to all the other entries, especially as there was no bond line control and so substantial adhesive had been used. The beam weighed 781g and achieved a very credible 57kN and lasted on the testing machine for a surprising 71 seconds. Other entries came from Bath University, University College London, Sheffield Hallam University, De Montfort University Leicester and Loughborough University.