Effect of clamping force on the fatigue behaviour of punched plates subjected to axial loading

In order to analyse the fatigue behaviour of complex structural joints a previous analysis of a simple joint is needed. This paper describes a study of a punched plate, with a simple clamping nut-bolt, subjected to cyclic axial loading. The most important parameters needed to perform a realistic simulation are the clamping force and the coefficient of friction between the joint parts. In order to continuously control the clamping force, a load cell, placed between the bolt and the plate, has been designed. The coefficient of friction between the materials of the nut and the plate has been experimentally obtained. After that, a 3D finite element simulation has been performed in order to obtain the contact stresses between the nut, bolt and the plate originated by clamping and axial loading. Using axial and contact loads, a new 3D finite element analysis has been undertaken in order to simulate the fatigue crack growth from a previously determined engineering initial crack to the final fracture, and S–N curves have been obtained. Numerical S–N curves have been compared with experimental fatigue tests, and good results have been obtained that permit the methodology performed to be applied for simulation of more complex joints subjected to fatigue loads.