Synthesis of contact-aided compliant mechanisms for non-smooth path generation

Topology optimization is used in this paper for the systematic synthesis of contact-aided compliant mechanisms that trace prescribed, non-smooth paths in response to a single, monotonically increasing input force. Intermittent contact interactions that enable these mechanisms to exhibit non-smooth responses also lead to algorithmic difficulties when the techniques from the synthesis of ordinary compliant mechanisms are used to design contact-aided compliant mechanisms. A sequential optimization approach based on a regularized normal contact model for large displacements is used in this work to circumvent these difficulties and to enable the use of computationally efficient, gradient-based optimization methods. We use an objective function based on Fourier shape descriptors, which allows the designer to emphasize different aspects of the design intent (such as the shape, the size and the orientation of the output path) separately. A variable-stiffness input spring is used to allow the synthesis procedure to choose the appropriate magnitude of the input force. An arc-length finite element solver and heuristic measures that guard against local and global instabilities add to the robustness of the synthesis procedure as demonstrated by the two design examples presented in this paper

A stress-based approach to the optimal design of structures with unilateral behavior of material or supports

The paper presents a stress-based approach that copes with the optimal design of truss-like elastic structures in case of unilateral behavior of material or ground supports. The conventional volume-constrained minimization of compliance is coupled with a set of local stress constraints that are enforced, all over the domain or along prescribed boundaries, to control the arising of members with tension-only or compression-only strength. A Drucker–Prager failure criterion is formulated to provide a smooth approximation of the no-tension or no-compression conditions governing the stress field. A selection strategy is implemented to handle efficiently the multi-constrained formulation that is solved through mathematical programming. Benchmark examples are investigated to discuss the features of the achieved optimal designs, as compared with problems involving material and ground supports with equal behavior in tension and compression. Numerical simulations show that a limited set of constraints is needed in the first iterations to steer the solution of the energy-driven optimization towards designs accounting for the prescribed assumption of unilateral strength