Abstract: A method of estimating normal stiffness of joint is presented. By profilometer, profile data of coarse surface are obtained and then planar joint model of finite element is established, which is based on elastic-plastic contact analysis including friction between coarse surfaces. By penalty function method, stress, displacement and contact area in contact layer are calculated when load pressure is 0～0.8 MPa. Results of numerical analysis indicate that real contact area of coarse suface rapidly increases under lower pressure and slowly increases under high pressure. When pressure is 0.8 MPa，ratio of real contact area to nominal contact area is only 0.3%, real area of contact is far less than nominal area of contact. At the same time, maximum of normal contact stress is 924 MPa and maximum of Mises stress is 434 MPa, material nearby the contact spot is in plastic state and stress is much higher than substrate. Normal contact stiffness of analysis model depends on contact stiffness of a few contact spots, which depend on profile of contact spots. In experimental results of contact specimens with different dimension, normal stiffness of joint accords with normal stiffness from numerical analysis, which indicates the method is valid.

Key words: Coarse surface, Contact, Finite element, Joint, Stiffness