Foam Structures with a Negative Poisson's Ratio

Abstract

A novel foam structure is presented, which exhibits a negative Poisson's ratio. Such a material expands laterally when stretched, in contrast to ordinary materials.

Analytical parametric analysis of the contact problem of human buttocks and negative Poisson's ratio foam cushions

“…In addition to the traditional development of wheelchair cushions (Brienza et al, 1999), negative Poisson's ratio foams are considered here since they give rise to new degrees of freedom which may aid design of better cushions which reduce peak contact pressure. The creation of negative Poisson's ratio foams (Lakes, 1987) is based on changing the shape of foam cell structures to be re-entrant, or bulging inward. Such foams can exhibit negative Poisson's ratio as small as À0.7 for polymer foams, and À0.8 for metal foams.…”

Negative Poisson's Ratio Behavior Induced by an Elastic Instability

“…Discovery and development of materials with negative Poisson's ratio, also called auxetics, was first reported in the seminal work of Lakes in 1987. [1] There is significant interest in the development of auxetic materials because of tremendous potential in applications in areas such the design of novel fasteners [2] , prostheses [3] , piezocomposites with optimal performance [4] and foams with superior damping and acoustic properties [5] . The results of many investigations [6][7] suggest that the auxetic behavior involves an interplay between the microstructure of the material and its deformation.…”

“…Examples of this are provided by the discovery that metals with a cubic lattice [8] , natural layered ceramics [9] , ferroelectric polycrystalline ceramics [10] and zeolites [11] may all exhibit negative Poisson's ratio behavior. Moreover, several geometries and mechanisms have been proposed to achieve negative values for the Poisson's ratio, including foams with reentrant structures [1] , hierarchical laminates [12] , polymeric and metallic foams [13] , microporous polymers [14] , molecular networks [15] and manybody systems with isotropic pair interactions [16] . Negative Poisson's ratio effects have also been demonstrated at the micron scale using complex materials which were fabricated using soft lithography [17] and at the nanoscale with sheets assemblies of carbon nanotubes [18] .…”

Fatigue Properties of Polyurethane Foams, with Special Emphasis on Auxetic Foams, Used for Helicopter Pilot Seat Cushion Inserts

“…The final dimensions of the processed specimens were determined using the thermal method by exposing the specimen to temperature close (but below) the softening temperature of foams. A characteristic parameter of the manufactured foams is the volumetric compression ratio R CV =V p /V a (where V p -initial volume of the foam specimen before processing, V a -final volume of the processed foam) [1]. The final dimensions of processed auxetic foams were 150x150x50 mm.…”

“…1). Secondly, due to the negative Poisson's ratio (NPR), these materials tend to wrap around crumple zones, which is not observed for conventional materials [1].…”