From an analysis point of view, it requires a nonlinear static analysis including frictional contact and a cyclic loading based on realistic operation of the structure. Friction needs to be applied in the thread and at the bolt head. Moreover, large rotations and an update of the contact geometry during rotation are also required. PERMAS integrates all these functions to facilitate this kind of analysis. The paper "Experimental and numerical studies of bolted joints subjected to axial excitation" by J. Liu, H. Ouyang, J. Peng, C. Zhang, P. Zhou, L. Ma, M. Zhu, published 2016 in Wear, describes an experimental set-up to detect the pretension loss in case of axial loading of a bolt, which is called relaxation.

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