Two types of dynamic joint behaviour: theoretical and experimental analysis

The joints in a structure may be a significant source of damping and may have uncertain stiffness properties. Experimental and theoretical investigations are presented that suggest there are two extreme types of bolted lap joint. If the joint has a limited contact patch, due to the bolt stress, then the edges of the contact patch have large static normal stresses which prevent sliding under dynamic loading. Alternatively, if the contact patch occurs naturally, due to bolting two surfaces together, then outside the contact patch the joint interfaces will separate. This type of joint can slip at the edges of the contact patch and this can lead to changes in the stiffness and the generation of significant damping. It is shown that the joint behaviour is nonlinear with damping increasing and stiffness decreasing as vibration amplitudes are increased. It is suggested that all joint damping falls between the extremes of a limited contact patch and a natural contact patch.