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No abstract

Auxetic structures have attracted attention in energy absorption applications owing to their improved shear modulus and enhanced resistance to indentation. On the other hand, four-dimensional (4D) printing is an emerging technology that is capable of 3D printing smart materials with additional functionality. This paper introduces the development of a NiTi negative-Poisson’s-ratio structure with superelasticity/shape memory capabilities for improved ballistic applications. An analytical model was initially used to optimize the geometrical parameters of a re-entrant auxetic structure. It was found that the re-entrant auxetic structure with a cell angle of −30° produced the highest Poisson’s ratio of −2.089. The 4D printing process using a powder bed fusion system was used to fabricate the optimized NiTi auxetic structure. The measured negative Poisson’s ratio of the fabricated auxetic structure was found in agreement with both the analytical model and the finite element simulation. A finite element model was developed to simulate the dynamic response of the optimized auxetic NiTi structure subjected to different projectile speeds. Three stages of the impact process describing the penetration of the top plate, auxetic structure, and bottom plate have been identified. The results show that the optimized auxetic structures affect the dynamic response of the projectile by getting denser toward the impact location. This helped to improve the energy absorbed per unit mass of the NiTi auxetic structure to about two times higher than that of the solid NiTi plate and five times higher than that of the solid conventional steel plate.

No abstract

The bio-inspired porous metallic scaffolds have tremendous potential as artificial bone substitutes. In this work, a radially graded lattice structure (RGLS), which mimic the structures of natural human bones, were designed and processed by laser powder bed fusion (LPBF) of martensitic Ti-rich TiNi powder. The morphologies, mechanical properties, deformation behaviour, and biological compatibility of RGLS samples were characterised in comparison to those in the uniform lattice structure. The results demonstrated that RGLS has superior biomechanical properties and biological compatibility than the uniform structures, which highlights a novel strategy for improving the performance of additively manufactured artificial implants.