3 Clamping, Interference, Microslip, and Self-Piercing Rivets

Defining the Clamping Force (Bolt Tension). The stress concentrations in a shear joint in the clamping mode depend on both friction and the clamping force or bolt tension, Q_C, (Equation (1.2), Chapter 1.4). Clamping is obtained when the pre-assembly shank height¹, H₀, is less than 2t₀, the combined initial thickness of the two (or three) panels. The shank must then stretch during assembly to accommodate the misfit. The clamping force, Q_C, is the elastic restoring force, which is related to ε, the elastic strain of the shank after assembly:

Where ε = (H − H0)/H0, H is the shank length after assembly, E is the Young's Modulus, and AS is the cross sectional area of the shank. The average shank tensile stress is2:

While the key variable for clamping is the shank strain, ε, it is convenient to use the nominal clamping, %CL, which is easy to evaluate, as a measure of ε: