Joint design alterations for adhesive bonding

When designing the Elise, Lotus made the decision to use an aluminium spaceframe both to save weight and for cosmetic reasons. Instead of conventional joining techniques it was decided that adhesive bonding would be the best method of providing accuracy, repeatability and additional weight savings.

TWI was called into the project early on and worked with the car manufacturer on joint design. A study of the joints established the relationship between stress concentrations and the aspect ratio of the joint. With this information, together with existing work from Lotus on quantified suspension loads, it was possible to begin to quantify the bond areas.

But TWI's contribution went beyond providing the best design for bonded joints. It also served to reassure Lotus about the testing of these joints. It is far better to concentrate on perfecting the bonding process than to put time and effort into examining failed bonds.

'TWI helped us get over some of our qualms about the testing process for adhesives,' said Lotus' Daryl Greig. 'They convinced us that the greatest effort should go into creating a bullet-proof process rather than spending £500 000 on equipment to test the bonds'.

Today, one of Lotus' adhesively bonded chassis is displayed in a prominent position in the atrium of TWI's corporate headquarters.