Stress-driven method bio-inspired by long bone structure for mechanical part mass reduction by removing geometry at macro and cell-unit scales

International audienceMass reduction is a main issue in mechanical design. Over millions of years, Nature had to face this issue.Nature came up with an efficient solution using a stress-driven structure to reduce the mass of bones whilesaving their mechanical performances. This optimized structure is used in several species and persiststhroughout Evolution. Thus, it may be considered as optimal for this issue. In this article, a method bio-inspired from both bone medullar cavity and trabecular structure is proposed to reduce the mass of partssubjected to mechanical stresses. The objective of this method is to provide high mass reduction, just likebone does. First, the method removes iteratively unloaded areas of material from the mechanical part tomimic the medullar cavity structure. Second, a final mass reduction is done integrating small holes bio-inspired from trabecular structure in the remaining material. An experimental validation was carried out on atorsion disc and provided a 60% mass reduction. Using this mass reduction rate, the topology optimizationmethod was used to define a standard geometry to evaluate the mechanical performances of the proposedmethod. Experimental results highlight that regarding torsional stiffness, the bio-inspired part is 27% stifferthan the standard on

Performance domains of bio-inspired and triangular lattice patterns to optimize the structures’ stiffness

Mass reduction of mechanical systems is a recurrent objective in engineering, which is often reached by removing material from its mechanical parts. However, this material removal leads to a decrease of mechanical performances for the parts, which must be minimized and controlled to avoid a potential system failure. To find a middle-ground between material removing and mechanical performances), material must be kept only in areas where it is necessary, for example using stress-driven material removal methods. These methods use the stress field to define the local material removal based on two local parameters: the local volume fraction vf and the structural anisotropy orientation β. These methods may be based on different types of cellular structure patterns: lattice-based or bio-inspired. The long-term objective of this study is to improve the performance of stress-driven methods by using the most efficient pattern. For this purpose, this study investigates the influence of vf and β on the mechanical stiffness of three planar cellular structures called Periodic Stress-Driven Material Removal (PSDMR) structures. The first, taken from the literature, is bio-inspired from bone and based on a square pattern. The second, developed in this study, is also bio-inspired from bone but based on a rectangular pattern. The third is a strut-based lattice pattern well documented in the literature for its isotropic behavior. These three patterns are compared in this study in terms of relative longitudinal stiffness, obtained through linear elastic compressive tests by finite element analysis. It is highlighted that each PSDMR pattern has a specific domain in which it performs better than the two others. In future works, these domains could be used in stress-driven material removal methods to select the most adequate pattern or a mix of them to improve the performances of parts