International Journal of Mechanical Engineering Education Vol 30 No 1 Making and characterizing negative Poisson’s ratio materials R. S. LAKES * and R. WITT ** , University of Wisconsin–Madison, 147 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706-1687, USA. 〈[email protected]〉 * Department of Engineering Physics, Engineering Mechanics Program, Biomedical Engineering Program, Materials Science Program and Rheology Research Center. Author to whom correspondence should be directed. ** Department of Engineering Physics. Received 18th October 1999 Revised 26th August 2000 We present an introduction to the use of negative Poisson’s ratio materials to illustrate various aspects of mechanics of materials. Poisson’s ratio is defined as minus the ratio of transverse strain to longitudinal strain in simple tension. For most materials, Poisson’s ratio is close to 1/3. Negative Poisson’s ratios are counter-intuitive but permissible according to the theory of elasticity. Such materials can be prepared for classroom demonstrations, or made by students. Key words: Poisson’s ratio, deformation, foam, honeycomb 1. INTRODUCTION Poisson’s ratio is the ratio of lateral (transverse) contraction strain to longitudinal extension strain in a simple tension experiment. The allowable range of Poisson’s ratio ν in three dimensional isotropic solids is from –1 to 1 2 [1]. Common materials usually have a Poisson’s ratio close to 1 3 . Rubbery materials, however, have values approaching 1 2 . They readily undergo shear deformations, governed by the shear modulus G, but resist volumetric (bulk) deformation governed by the bulk modulus K; for rubbery materials G K. Even though textbooks can still be found [2] which categorically state that Poisson’s ratios less than zero are unknown, or even impossible, there are in fact a number of examples of negative Poisson’s ratio solids. Although such behaviour is counter-intuitive, negative Poisson’s ratio structures and materials can be easily made and used in lecture demonstrations and for student projects. Such solids become fatter in cross section when stretched. A solid with ν ≈ – 1 would be the opposite of rubber: difficult to shear but easy to deform volumetrically: G K. Negative Poisson’s ratio materials offer a new direction for achieving unusual and improved mechanical performance.
Making and characterizing negative Poisson’s ratio materials
Jun 23, 2023
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