4D Printing of NiTi Auxetic Structure with Improved Ballistic Performance.

Hany Hassanin,Mahmoud Ahmed Elsayed,Alessandro Abena,Khamis Essa

doi:10.3390/mi11080745

Hany Hassanin, Mahmoud Ahmed Elsayed + Show 2 more

Open Access

https://doi.org/10.3390/mi11080745

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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.

Highlights

Metamaterials have attracted substantial research interest attention during the past few years as an emerging concept to develop materials with novel properties different from conventional materials, such as negative compressibility, negative Poisson’s ratio, manipulating electromagnetic radiation or sound waves, and negative elasticity
This study aims to introduce a new metamaterial that combines the properties of NiTi and auxetic materials in one structure, which is processed using 4D printing
The predicted results can be compared to other numerical studies reported by Raguraman and coauthors [51] who used a rigid projectile core and shell elements for the plate

Summary

Introduction

Metamaterials have attracted substantial research interest attention during the past few years as an emerging concept to develop materials with novel properties different from conventional materials, such as negative compressibility, negative Poisson’s ratio, manipulating electromagnetic radiation or sound waves, and negative elasticity. The benefits of using auxetic structures in these applications are because of their improved mechanical behavior but because they hold properties such as enhanced energy absorption, shear resistance, and higher indentation resistance [4,5,6]. This has led to the advancement of auxetic metamaterials especially with the emergence of additive manufacturing (AM), which allowed designers to have the geometrical freedom to fabricate structures with a complex and controlled macro/micro-structure

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