Basic Contact Mechanics

Many real fretting problems involve the contact of components of great complexity, such as the flanged joints depicted in the pipework photograph, fig. 2.1. In cases such as this it is really quite impossible to consider modelling the contact by anything other than a numerical method, and the technique chosen will in many cases be the finite element method. It must be remembered when doing such modelling that care needs to be exercised: not only must a carefully refined mesh in the neighbourhood of the contact be incorporated, but many other aspects need to be carefully studied, too. In the flanged joint, for example, what is the pre-load provided in the bolts? Are the contacting bodies elastically similar? How is the size of the contact patch determined — and is it known a priori? Which components adhere to each other, i.e. experience no relative displacement at any point, and which experience frictional effects? What is the history of loading experienced, i.e. do normal and tangential loads arise at the same time, or is there a phase shift between the maximum normal and tangential components of loading? These questions are often difficult to answer, but we hope that a consideration of the idealized problems presented in this and the next chapter will provide the analyst with physical insight. This will facilitate the choice of the correct boundary conditions for the investigation of complex real problems.