Equations are derived for the load/deflection relations, the energy dissipation per cycle, and the instantaneous rate of dissipation. The energy dissipation per cycle is only valid for steady-state cyclic loading, whereas the load/deflection equations and instantaneous dissipation rate are valid for arbitrary loading and take into account the previous loading history. The difference between the instantaneous dissipation rate in a lap joint and the equivalent linear system is illustrated for cases of sinusoidal loading and triangular loading.