Crushing Behavior of Graded Auxetic Structures Built from Inverted Tetrapods under Impact

Abstract

In this study, the crushing behavior of auxetic structures built from inverted tetrapods with linearly graded porosity under impact is analyzed both experimentally and computationally. The auxetic samples with linearly graded porosity are fabricated from Ti-6Al-4V alloy powder by the selective electron-beam melting method. A detailed geometrical analysis of the fabricated samples based on micro computed tomography (microCT) scans is performed to determine the variation of strut thickness and other fabrication imperfections. The samples are subjected to high strain rate compression loading in two specimen orientations (specimens with low or high porosity facing the impacting plate) using the powder gun. Appropriate computational models are later developed and validated to provide a more detailed insight into the crushing mechanism of auxetic structures during impact. The experimental and computational results show dependency of the plateau stress inclination (progressive/regressive) on the gradation of the auxetic cellular structures (specimens with low or high porosity in front). These initial results prove that it is possible to tailor the mechanical behavior of a porous structure with introduction of graded porosity, especially in the case of high strain rate impact, where the main deformation occurs at the impacting front.

Auxetics and Other Systems of Anomalous Characteristics

“…crystal of hard spheres with an array of [001]-nanochannels filled by hard spheres of another diameter' by J. Narojczyk et al [20] The simulations show that symmetry of such crystals changes from the cubic to tetragonal one. When spheres inside the inclusions are smaller than spheres forming the crystalline matrix, the changes of Poisson's ratio are qualitatively similar to the changes observed earlier in the Yukawa sphere crystal, that is, the introduction of nanochannels causes simultaneous decrease of the Poisson's ratio for [110] [1][2][3][4][5][6][7][8][9][10]-directions, and its increase for [110][001]-directions. Filling the nanochannels with spheres having diameters greater than that of the spheres in the crystalline matrix, causes a strong decrease of the minimum Poisson's ratio value.…”

“…N. Novak et al [10] in their paper 'Crushing behaviour of graded auxetic structures built from inverted tetrapods under impact' show an experimental and numerical work related to the crushing with a powder gun of additive layer manufactured tetrapod lattices with graded distribution of geometrical properties that lead to local variations of the Poisson's ratios. Here samples made using selective electron beam melting are subjected first to micro-CT and metallurgy characterisation to investigate the effective porosity generated by the manufacturing process.…”

Viscoelastic Properties of Filled Polyurethane Auxetics

“…Nowadays researches are highly interested in methods that enable to increase operation properties of traditional materials by creating structures that possess nonlinear and abnormal distortion properties, up to the point of obtaining adaptive physical reaction of the materials to the external influence [1]. Auxetics, materials with negative Poisson's ratio, can be regarded as abnormities.…”

“…В'язкопружні характеристики наповнених поліуретанових ауксетиків 1 Рівненський державний гуманітарний університет, Рівне, Україна, labor.relax@gmail.com 2 Рівненська медична академія, Рівне, Україна, bordiuk57@ukr.net 3 Рівненський обласний інститут післядипломної педагогічної освіти, Рівне, Україна, v.kukla@roippo.org.ua 4 Національний університет водного господарства та природокористування, Рівне, Україна, v.а.mashchenko@nuwm.edu.ua У роботі представлені експериментальні значення швидкостей поширення поздовжніх і поперечних ультразвукових хвиль та коефіцієнтів їх поглинання, отриманих за допомогою імпульсного імерсійного методу у зразках металонаповнених полімерних ауксетиків з поліуретановою матрицею. На основі отриманих результатів визначені коефіцієнт Пуассона, дійсні та уявні частини комплексних динамічних модулів пружності (модуля Юнга, модуля зсуву, модуля об'ємної деформації) і тангенс кута механічних втрат для поздовжніх, поперечних та об'ємних деформацій.…”

Computational simulation of fracture behaviour in auxetic cellular structure by multiaxial loading

“…Novak et al [12] investigated the effect of the porosity, loading direction and strain rate on the mechanical properties of auxetic cellular structures built from inverted tetrapods. The same author in the article [13] experimentally and computationally investigated the effect of the porosity on the crushing behaviour of graded auxetic structures built from inverted tetrapods. Kramberger et al [14] experimentally and numerical investigated the effect of the shape and distribution of unit cells on the fracture behaviour of 2D (two-dimensional) auxetic cellular structures, under quasi-static loading conditions.…”