Energy Absorption Capability and Ductility
The area under the entire load-deflection diagram represents the energy that the structure will absorb during failure. Consideration of this energy is important, especially for dynamic loading, and determines the ductility of the structure. Plastic limit analysis can give no information on the post-peak decline of the load and the energy dissipated in this process. According to plasticity, the load is constant after the peak, and the energy absorption theoretically unlimited. So some form of fracture mechanics is inevitable.