Multi-criteria formulations reported previously in topology design of compliant mechanisms address the flexibility and stiffness issues simultaneously and aim at attaining an optimal balance between these two conflicting attributes. Such techniques are successful in indirectly controlling the local stress levels by constraining the input displacement. Individual control on the conflicting objectives is often difficult to achieve with these flexible and stiff formulations. Resultant topologies may sometimes be overly stiff and there is no guarantee for design against failure as local stresses may exceed the permissible yield strength of the constituting material. In this paper, local failure conditions via stress constraints are incorporated in topology optimization algorithms to obtain compliant and strong designs. Quality functions are employed to impose stress constraints on retained material ignoring non-existing regions in the design domain. Stress constraints are further relaxed to regularize the design space to help the KKT conditions-based mathematical programming algorithms yield improved solutions. Examples are solved to corroborate the solutions for failure-free compliant topologies that are much improved than those obtained using flexible and stiff multi-criteria objectives.
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