Numerical studies of microstructurally optimized bolts with graded grain size

Demands on fastening bolts in mechanical engineering and automotive industry are discussed in this paper. The possibility of using microstructurally graded material for bolts is derived from this discussion. This material consists of a conventional coarse-grained core or main body and an ultra-fine-grained (UFG) layer surrounding it. Current research focuses on the manufacture of UFG layers by means of incremental metal forming. The examinations were carried out on an UFG material with elevated yield strength. An elasto-plastic model of an M6 bolt, made of aluminum alloy EN AW-6082, was set up and the bolt was loaded with tensile forces. The resulting distributions of stress and equivalent plastic deformation were analyzed. Result of this analysis is a recommendation for an optimum thickness of the ultra-fine-grained layer. Bolts from graded materials can withstand higher loads in the groove of the thread, which is the section with the highest load on the bolt. At the same time high toughness in the bolt’s core is obtained, which allows its use as a safety component.