Adding Additional Load Paths in a Bonded/Bolted Hybrid Joint

Abstract

compared to the bolt. In all existing designs of hybrid joints, bolts do not participate in taking loads until the complete failure of the bondline. In other words, bolts stay idle until failure in the adhesive part of the joint occurs. It is evident that the main issue of improving the hybrid joint is to come up with a design that would involve bolts in contributing to the load bearing at the joint before failure of the adhesive. Another approach in improving bonded joints was pursued by Qian and Sun [9], who proposed an idea of using separate attachments to provide additional load transfer paths at the joint. In thisproposeddesign,inadditiontoadditionalloadtransferpaths,the localized interfacial stress concentrations near the joint edge are reduced. With the attachments used in double strap joints, the joint strengthincrementwasfoundtobe20–30%comparedtotheconventional double strap joint. A similar approach was employed by Turaga and Sun [10] to improve single-lap bonded joints. Experiments were conducted with aluminum as well as composite adherends. Failure loads for the conventional single-lap joints and single-lap joints with attachments were compared. The strength of the joint with angular attachments was found to be 59% higher than thatoftheconventionaljoint.Thesetwoapproaches[9,10]discussed above indicate that the joint strength of bonded joints can be enhancedsignificantlybyusingattachmentstocreateadditionalload transfer paths at the joint. The present study proposes a new hybrid (bonded/bolted) joint design, which can achieve a substantially higher joint strength compared to the existing hybrid joint design. This new hybrid joint designusesaconceptsimilartothatproposedbyTuragaandSun[10] forbondedsingle-lapjoints.Theproposednewhybridjointdesignis able to activate bolts to load bearing before the adhesive fails, a capability that cannot be achieved by conventional hybrid joints.