This letter presents a cellular solid characterized by extreme tailorability of its mechanical response over a large range of macroscopic strains. The proposed periodic structure is based on a hexagonal chiral lattice topology, modified by introducing transverse curvature in the ligaments, key to the resulting unconventional behavior. The resulting topology allows to exploit different levels of structural hierarchy for tailoring the mechanical behavior of the continuous medium. The capability of the initially curved ligaments to change shape under global deformations is exploited to alter the microstructural motions andas a resultthe macroscopic response. We explore the effect of the additional geometrical design parameter, namely the transverse ligament curvature, on the strain-dependent stiffness of the chiral lattice, evaluating its interplay with the conventional attributes defining the chiral topology and assessing the attainable envelope of mechanical responses. Purposely choosing the parameters permits to tailor the behavior of the chiral lattice, enabling extreme variations in stiffness. The possibility to attain effective negative and zero-stiffness regimes over large compressive strains further exemplifies the potential of this design. These unique characteristics can be used to attain specific wave propagation properties, augment structural damping, control vibrations and noise, and tune the deformation of compliant structures.
This paper introduces a shape optimization of wire strands subjected to tensile loads. The structural analysis relies on a recently developed reduced helical finite element model characterized by an extreme computational efficacy while accounting for complex geometries of the wires. The model is extended to consider interactions between components and its applicability is demonstrated by comparison with analytical and finite element models. The reduced model is exploited in a design optimization identifying the optimal shape of a 1 + 6 strand by means of a genetic algorithm. A novel geometrical parametrization is applied and different objectives, such as stress concentration and area minimization, and constraints, corresponding to operational limitations and requirements, are analyzed. The optimal shape is finally identified and its performance improvements are compared and discussed against the reference strand. Operational benefits include lower stress concentration and higher load at plastification initiation.
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