Chapter 33 Fatigue Behavior of Novel Hybrid Fastening System with Adhesive Inserts Ermias G. Koricho, Anton Khomenko, Mahmoodul Haq, and Gary L. Cloud Abstract A novel joining technique that incorporates the advantages of both bonded (lightweight) and bolted (easy disassembly) techniques was invented (Provisional Patent 61/658,163) by Dr. Gary Cloud at Michigan State University. The most basic configuration of this invention consists of a bolt that has a channel machined through the bolt-shaft that allows injection of an insert compound that fills the necessary clearance between the bolt and the work-pieces and acts a structural component. More sophisticated versions of the concept incorporate additional sleeves or inserts. In this paper the fatigue behaviour of composite hybrid bolted joints was studied. Composite plates were bolted with grade-five bolts and preloaded to a torque of 35 N-m. Two types of bolted joint configurations were evaluated. In the first case, a conventional bolted joint was studied. In the second case, pristine SC-15 epoxy resin was used as the structural insert in the hybrid fastening system. The joints were subjected to different fatigue loadings with the maximum loading level up to 80 % of the joint ultimate failure load and stress ratio of RD0.1. Results reveal considerable improvement of fatigue life of the novel fastening system compared with a conventional bolted joint. Keywords Bolted joint • Hybrid joint • Bolt • Composite • Fatigue • Damage 33.1 Introduction With increasingly stringent national and international fleet fuel economy regulations, the use of composite materials for primary vehicle and aircraft structures has been expanding considerably for the last decades. Several automotive and aircraft manufactures have developed composite-intensive components not only to reduce the weight of the structure but also to improve the performance of final products. For example BMW has introduced a composite-body for the BMW i3, using carbon fiber rather than traditional steel, in order to eliminate enough weight to compensate for the weight of the battery packs that power the electric motor while still maintaining safety standards [1]. Further, Airbus and Boeing have built the latest generation of composite-intensive commercial aircraft, the A350XWB and Boeing 787, respectively [2]. Even though considerable progress has been made on adhesive and other joining techniques, the joining of composite structures still depends on mechanically fastened bolted joints that allow the disassembly of parts for repair/replacement. However, bolted joints have their own disadvantages, the main one being that drilling and machining bolt holes causes stress concentrations and delaminations that reduce the resistance of the joint construction to applied loads, and thus its efficiency. Loading conditions, such as type of loading and load configuration, are among the most important factors in designing a joint in a structure. Particularly, the failure behaviour of a bolted joint in a composite structure under fatigue is complex due to the fluctuations of the stress transfer mechanisms through the joint that detrimentally affect the thermo-mechanical behaviour of the composite materials around the hole. Generally, the fatigue damage around bolt holes consists of three types, i.e. hole-wear, damage in the contact surface of the composite, and growth of the delaminations that are induced due to drilling of holes [3]. The material degradation and the hole-wear are caused by the erosion of material around the bolt holeas E.G. Koricho ( ) • A. Khomenko • G.L. Cloud Composite Vehicle Research Center, Michigan State University, 2727 Alliance Drive, Lansing, MI 48910, USA e-mail: ermias.koricho@gmail.com M. Haq Composite Vehicle Research Center, Michigan State University, 2727 Alliance Drive, Lansing, MI 48910, USA Department of Civil and Environmental Engineering, Michigan State University, 2727 Alliance Drive, Lansing, MI 48910, USA © The Society for Experimental Mechanics, Inc. 2016 A.M. Beese et al. (eds.), Fracture, Fatigue, Failure and Damage Evolution, Volume 8, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-21611-9_33 269
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