Characteristics of the design surface of damage tolerance parameters and their relation to shape optimisation

The design surfaces for residual strength and fatigue life establish that a design based on damage tolerance parameters poses a well-behaved optimisation problem with a well-defined minimum/maximum region. The design space was found to be flat for both residual strength and fatigue life, enabling the specification of design tolerances. The optimum values of the stress intensity factor and the fatigue life obtained from the design space agreed well with those determined using various optimisation methods. It is shown that a design space exploration can provide a systematic way to reduce the weight of a structure by adopting a 'feasible non-optimal' solution that meets the design criteria, rather than aiming for the 'optimal' (best) solution.