A study on the load capacity of the bolted friction grip joint

Abstract

For the simple friction grip joint consists of two joined parts, one of which is tapped and bolted with the other with a bolt, the load capacity (Here, this is expressed by n described below) of the friction grip joint is analyzed using the strength of materials, and FEM analysis is carried out on 10 cases, which result in the following conclusions. [Here, F:Bolt axial tension, μCS : Friction coefficient on the contact surfaces between joined parts and also on the bolt bearing surface, WSCr : Critical applied shear force without any slip, n : Equivalent number of contact surface (=WSCr /FμCS).] (1) Introducing the shear spring constant of the bolt KBS and that of the joined part KCS, the theoretical equation to calculate the load capacity n, which contains only KBS and KCS, is derived. (2) The load capacity nth, calculated by the theoretical equation substituting KBS and KCS obtained through FEM analysis, coincides very well with nFEM obtained through FEM analysis. Therefore, it is concluded that the theoretical equation to calculate n using KBS and KCS is correct. (3)According to this theoretical equation, to increase the load capacity n, it is necessary to develop the joint structure which gives smaller KCS/KBS. (4) The maximum load capacity n=2 is obtained only under KCS=KBS in the case of the concentrated shear load applied on the upper corner of the joined part. (5) The problem left to predict n is to derive the equation that can accurately calculate KCS. (6) From the results of this analysis, the number “q F”, which is described in VDI 2230 Part 2 and corresponds to n, is judged to be too large from the viewpoint of slip.

Keywords

• friction joint
• fixing
• screw
• stiffness
• reliability
• finite element method
• design engineering