Evaluation of the Orthotropic Behavior in AN Auxetic Structure Based on a Novel Design Parameter of a Square Cell with Re-Entrant Struts (original) (raw)
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Auxetic material is a unit cell structure arranged in a cellular pattern such that it gives negative Poisson's ratio. The cellular structure expands when stretched and contracts when compressed. It is different from regular structure. Cellular auxetic structure exhibits some unique characteristics like high strength, light weight, impact damping capabilities, high energy absorption and reduced stress concentration effect etc. due to the number of unit cells arranged in a network. These unique characteristics provides potential applications in aerospace, military protection equipment, medical, textile and automobile field. Although different cellular auxetic structures are analyzed and studied because of their stress concentration effect, strength to weight ratio and negative Poisson's ratio etc., there is need of development of new cellular structure to improve these properties. The aim of our work is to focus on stress concentration effect of cellular arrowhead shaped auxetic structure. In this work, the cellular arrowhead shaped auxetic structure is modelled and the stress concentration effects and the stress distribution patterns are studied by using Finite Element Analysis (FEA) in ANSYS software. It is compared with the cellular honeycomb (re-entrant honeycomb) auxetic structure [1]. It led to the conclusion that cellular arrowhead shaped auxetic structure has reduced stress concentration effect as compared to the reentrant honeycomb auxetic structure. Overall stress distribution patterns of cellular arrowhead shaped auxetic structure are good in comparison with the re-entrant honeycomb auxetic structure.
Cellular Arrowhead Shaped Auxetic Structure with Significantly Reduced Stress Concentration Effects
Auxetic material is a unit cell structure arranged in a cellular pattern such that it gives negative Poisson's ratio. The cellular structure expands when stretched and contracts when compressed. It is different from regular structure. Cellular auxetic structure exhibits some unique characteristics like high strength, light weight, impact damping capabilities, high energy absorption and reduced stress concentration effect etc. due to the number of unit cells arranged in a network. These unique characteristics provides potential applications in aerospace, military protection equipment, medical, textile and automobile field. Although different cellular auxetic structures are analyzed and studied because of their stress concentration effect, strength to weight ratio and negative Poisson's ratio etc., there is need of development of new cellular structure to improve these properties. The aim of our work is to focus on stress concentration effect of cellular arrowhead shaped auxetic structure. In this work, the cellular arrowhead shaped auxetic structure is modelled and the stress concentration effects and the stress distribution patterns are studied by using Finite Element Analysis (FEA) in ANSYS software. It is compared with the cellular honeycomb (re-entrant honeycomb) auxetic structure [1]. It led to the conclusion that cellular arrowhead shaped auxetic structure has reduced stress concentration effect as compared to the reentrant honeycomb auxetic structure. Overall stress distribution patterns of cellular arrowhead shaped auxetic structure are good in comparison with the re-entrant honeycomb auxetic structure.
Unit Cell Modelling of Auxetic Structure
Journal of Minerals and Materials Characterization and Engineering, 2022
Auxetic material structures exhibit a negative Poisson ratio. The structure expands in the axial and transverse directions under tensile loading and vice versa under compression loading. Many fabricated designs for auxetic materials exist such as re-entrant hexagonal, chiral, and arrowhead geometries. This paper studies the unit cell of the re-entrant hexagonal geometry to understand how changing the internal angle and fillet radius of the structure affects the Poisson's ratio. The material chosen for this study is acrylonitrile butadiene styrene (ABS) due to its availability and frequent use in additive manufacturing. The study was based on finite element analysis. It is observed that the direction of load applied to the unit cell affects the unit cell strain, Poisson's ratio, and maximum load capacity before failure responses. It is noticed that the re-entrant cell starts by showing a standard non-auxetic behavior until it reaches a specific axial strain value. A quadratic correlation is identified between axial and transverse strain. Designing an auxetic structure starts with understanding the behavior of a unit cell structure. The auxetic structure design is a complex process that requires a compromise between auxetic property to be achieved and load capacity via avoiding stress concentration zones.
Study of auxetic beams under bending: A finite element approach
Materials Today: Proceedings, 2020
Materials with a negative Poisson's ratio are termed as auxetic materials. A negative Poisson's ratio implies a lateral strain in accordance to a longitudinal strain under application of load, that is, it expands laterally when under tensile load and contracts under compressive loading. The key feature that imparts the auxetic behavior to a structure is its geometry. This paper initially discusses about the single cell honeycomb and re-entrant configurations. Analytical formulations are used to calculate the Poisson's ratio for various structures and numerical analysis is carried out using the ABAQUS software. Further, various beam configurations such as homogeneous, truss and auxetic re-entrant structures are investigated under four point bending to understand the scope of application of these structures and to observe their behavior when employed in a practically significant entity. The auxetic beam is found to have lowest level of stress in most of the regions. This paper also discusses the reasons why there is a need for a combined analysis of these auxetic structures using Experimental/Numerical and analytical methods.
Investigation of Modified Auxetic Structures from Rigid Rotating Squares
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Auxetic structures exhibit unusual changes in size, expanding laterally upon stretching instead of contracting. This paper presents this effect in a failsafe mode in structures made of rigid squares. We applied the concept of auxetic structures made of rigid rotating squares (from Grima and Evans) and offer a novel solution for connecting them. By introducing axes of rotation on the surface of the squares, a reliable working system is obtained, free from stress, in which the squares can come into contact with each other and completely cover the surface of the structure, or, in the open position, form regularly arranged pores. Herein, we present a new 2D auxetic metamaterial that is mathematically generated based on a theoretical relationship of the angle between the edges of a square and the position of the axis of rotation. Physical models were generated in the form of a planar structure and in the form of a circular closed structure. Such physical models confirmed our initial cons...
International Journal of Solids and Structures, 2018
Under compression, auxetic open cell cellular solids may lose auxeticity due to instability and/or selfcontact between the ribs. This study explores the limiting strains for preserving auxetic effects for auxetic open cell materials of two different cellular structures: re-entrant honeycomb and the 'missing-rib' type chiral cellular solids. Experiments of the 3D printed specimens, periodicity analysis, and ellipticity analysis showed that, under compressive loads, the auxetic effects and the limiting compressive strain for auxeticity are mutually exclusive. In other words, the limiting compressive strain has to be reduced if larger auxetic effect is desired, vice versa. It was found that compared with re-entrant honeycombs, due to chirality-induced rotation, the chiral cellular solids can preserve auxetic effects under much larger compressive strain (> −10-30%).