Heavily loaded bonded composite structure: design, manufacture and test of `I beam specimens

The use of adhesive bonding in advanced composite structures offers the potential for considerable weight and cost saving compared to the use of mechanical fasteners. However, confidence must be developed in the ability to design and analyse such structures and in their manufacture to suitable quality standards. The programme of work described here was carried out as a step towards building such confidence. Secondarily bonded `Iʹ beams were designed to carry an ultimate shear flow of 1712 Nm m-1. They were manufactured under factory conditions and predictions were made of their failure loads and modes. The beams were then tested in three- and four-point bending and the outcomes of these tests were compared to predictions. The beams failed at loads comfortably in excess of the target, a shear flow of 2828 Nm m-1 being carried in four-point bending. Failure was a very energetic process leading to a great deal of damage within the test structures. Despite this an attempt was made to inspect the failed beams in an attempt to determine the quality of the bondlines and identify the site of failure.