Study On Optimization Design Of Pentamode Metamaterials And Selective Laser Melting Forming

Pentamode metamaterials(PMs),also called pentamode structures,are a special kind of engineering structural materials.Only one eigenvalue in its elastic matrix is nonzero.Compared with the conventional lattice structures,pentamode metamaterials have stronger designability,fluid-like characteristics and regulation ability of multi-physical properties.Therefore,pentamode metamaterials have more extensive potential applications.However,due to the high complexity of pentamode metamaterials,it is difficult to fabricate pentamode metamaterials by traditional manufacturing processes.Additive manufacturing technology can fabricate any complex shape components and has significant advantages for fabricating pentamode metamaterials.The research on additive manufacturing of pentamode metamaterials mainly faces following scientific problems:(1)the influence mechanism of geometric parameters of two-dimensional honeycomb-like pentamode metamaterials on mechanical properties is not clear;(2)the influence of topological shapes of three-dimensional diamond-like pentamode metamaterials on manufacturing accuracy,mechanical properties and biological mass transport performances is ambiguous;(3)the strengthening mechanism of gradient design on mechanical and mass transport properties of three-dimensional diamondlike pentamode metamaterials needs to be studied.Given the above problems,the following research contents have been carried out:(1)A two-step optimization method was proposed to design the two-dimensional honeycomb-like pentamode metamaterials with load-bearing and acoustic functions.The effects of Selective Laser Melting(SLM)process and geometric parameters on the properties of Ti-6Al-4V honeycomb-like pentamode metamaterials were studied.With the increase of the strut width,the pentamode metamaterials change from plastic buckling deformation to brittle fracture deformation under compression load and the critical size of the transition was0.12 mm.Based on the Johnson-Cook model,a material constitutive model of SLM pentamode metamaterials was proposed for finite element simulation of compression mechanics.The influence of geometric parameters on the mechanical properties of honeycomb-like pentamode metamaterials was clarified.The mechanical properties prediction model of honeycomb-like pentamode metamaterials was established.(2)The design and SLM forming method of three-dimensional uniform diamond-like pentamode metamaterials with different topologies were proposed.The manufacturing accuracy,static compression mechanical response and biological mass transport performance of uniform diamond-like pentamode metamaterials were analyzed.The influence mechanism of strut topology and volume fraction of the pentamode unit cell on fabrication accuracy and mechanical properties was revealed.The enhancement mechanism of the mass transport performance of biological scaffolds by the double-cone topological design was elucidated.The double-cone strut increased the internal complexity of the structure,thus enhancing the permeability.A cooperative regulation model for geometric properties,mechanical properties and mass transport properties of diamond-like pentamode metamaterials was revealed.(3)The deformation law of the layer-by-layer fracture in compression process of graded diamond-like pentamode metamaterials was revealed.The strengthening mechanism of gradient design on the energy absorption performance of diamond-like pentamode metamaterials was clarified.Compared with uniform diamond-like pentamode metamaterials,the energy absorption performance of gradient diamond-like pentamode metamaterials was improved by 77.73%.Based on the Iso-stress model in composite structures and the modified Gibson-Ashby model,the mechanical performance of gradient diamond-like pentamode metamaterials was accurately predicted.Based on the hydrodynamic model,the enhancement mechanism of gradient design on the mass transport performance of diamond-like pentamode metamaterials was quantitatively analyzed.Compared with uniform diamond-like pentamode metamaterials,the permeability of gradient diamond-like pentamode metamaterials was improved by 27.27%.In this paper,based on the optimal design and SLM forming research of two-dimensional honeycomb-like and three-dimensional diamond-like pentamode metamaterials,the manufacturing accuracy,static compression mechanics and biological mass transport performance for two-dimensional and three-dimensional,uniform and gradient pentamode metamaterials are systematically analyzed,which has laid an important theoretical foundation of SLM-manufactured pentamode metamaterials for their engineering applications.