In the bearing mode, a relatively large fastener load, Q, is applied to the small area of contact between the fastener shank and the panel. The area corresponds approximately with the projected area of the shank, A = DS t (where DS is the diameter of the shank and t is the panel thickness). In single fastener row joints, the concentration of load produces peak local stresses, σ*, of order Q/A:

In addition, the stresses are affected by μ, the coefficient of friction, which governs microslip at the joint interfaces and, in the case of lap joints, by the fastener shank diameter-to-panel thickness ratio, DS/t, which affects panel bending. The geometry of the fastener head and its rigidity also play a role because the clamping forces applied by the fastener head reduce panel bending under the head. The number of fastener rows also has a large effect on joint response because, Qi, the actual load transmitted to the fasteners of a particular row, is a fraction fi, of the (total) fastener load: Qi = fi Q. Finally, the residual stresses attending shank-hole interference have major effects. These are described in Chapter 3.3. It follows that the mechanical response of the joint—including the joint compliance, rivet tilt, local stresses, strains, and displacements, the local contact pressure and slip, and the state of the fasteners—depends on the following variables: The material properties of the panels, fasteners, and sealant or adhesive at the joint interfaces, the type of loading—uniaxial or biaxial—and the proximity of free edges are additional variables.