276 E.G. Koricho et al. • On the other hand, a pre-cycled hybrid bolted joint exhibits improvement of joint strength over the as-fabricated hybrid bolted joint. This surprising result could be explained by a combination of few phenomena. Firstly, because of the presence of the resin insert, the bolt carries the applied load uniformly, so that both the bolt and the washer could be favorably stressed through work hardening and their proof loads/yield strengths increase accordingly. Secondly, after one million of cycles, the resin may act as a cushioning media between the laminate and the bolt that would allow the load to transfer smoothly during tensile shear loading. Thirdly, the matrix in the composite adherend may be undergoing micro-degradation allowing the fibers to align in the load direction during the fatigue cycling. Upon postfatigue quasi-static testing, these aligned fibers may increase the stiffness and strength of resulting joints relative to their non-cycled counterparts. Further experimental work combined with realistic modeling and numerical simulations can aid in understanding the underlying phenomena. Generally, the conventional and hybrid bolted composite joints under quasi-static and fatigue loadings have shown complex behaviors. However, the observations from the experimental data and their correlations with failure could provide valuable information for better design of innovative composite joints and related components in various applications. Besides, more complex tailored inserts that contain other resins, adhesives, particulates, and fibres could play a significant role in improving the fatigue life of joints and facilitate lightweighting of vehicles and other devices. References 1. http://www.plasticsnews.com/ 2. Heimbs, S., Schmeer, S., Blaurock, J., Steeger, S.: Static and dynamic failure behaviour of bolted joints in carbon fibre composites. Compos. A: Appl. Sci. Manuf. 47, 91–101 (2013) 3. Saunders, D.S., Galea, S.C., Deirmendjian, G.K.: The development of fatigue damage around fastener holes in thick graphite/epoxy composite laminates. Composites 24(4), 309–321 (1993) 4. Crews Jr., J.H.: Bolt-bearing fatigue of a graphite/epoxy laminate. In: Kedward, K.T. (ed.) Joining of Composite Materials, ASTM STP 749, pp. 131–144. American Society for Testing and Materials, Baltimore (1981) 5. Herrington, P.D., Sabbaghian, M.: Fatigue failure of composite bolted joints. J. Compos. Mater. 27(5), 491–512 (1993) 6. Fu, M., Mallick, P.K.: Fatigue of hybrid (adhesive/bolted) joints in SRIM composites. Int. J. Adhes. Adhes. 21, 145–159 (2001) 7. Haq, M., Khomenko, A., Cloud G.: Novel hybrid fastening system with nano-additive reinforced adhesive inserts. In: SEM 2014 Annual Conference and Exposition on Experimental and Applied Mechanics, Greenville, 2–5 June 2014 8. Haq, M., Cloud, G.: Flexible hybrid fastening system. In: SEM 2013 Annual Conference and Exposition on Experimental and Applied Mechanics, Chicago, 3–5 June 2013 9. Belingardi, G., Paolino, D.S., Koricho, E.G.: Investigation of influence of tab types on tensile strength of E-glass/epoxy fiber reinforced composite materials. Procedia Eng. 10, 3279–3284 (2011)
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