On stress-constrained fail-safe structural optimization considering partial damage

This brief note presents some observations about the modelling of stress constraints in fail-safe structural optimization considering local degradation of member properties. An analytical study of a three-bar example demonstrates the impact of the constraint modelling choices on the optimal design. One notable finding is that degradation of one arbitrary member may cause a worse objective function than complete removal of the member. The observation is similar to the singular optimum issue in topology optimization with stress constraints, but applies also to sizing problems. This deserves special attention and should be considered when modelling fail-safe structural optimization with stress constraints.