Analyses of Tightening Characteristics and Cyclic Stress Amplitude of Studs and Tap Bolts

概要

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When subjected to alternating external forces, a fatigue failure of bolted joint is most likely to occur around the first bolt thread for the case of bolt-nut connections. In the previous paper, the relationship between the external force and the stress amplitude at thread root in bolt-nut connections has been evaluated by three-dimensional finite element analysis, in which the numerical models of bolted joints are constructed so as to accurately take account of the effect of thread helical geometry. In the cases of bolted joints clamped by studs and tap bolts, however, it is reported that fatigue failures frequently initiate around the far-end female threads.In this paper, using the FE models with thread helical geometry, stress amplitude distributions along the thread root of male and female threads are evaluated, aiming to clarify the fatigue failure mechanism of the bolted joints clamped by studs or tap bolts. As a result of parametric calculations, it is demonstrated that the maximum stress amplitude tends to occur around the far-end female threads. Specific stress concentration phenomena, which are inherent to the engaged threads machined along the drilled hole, are also quantitatively clarified.