Induction of auxetic response in needle‐punched nonwovens: Effects of temperature, pressure, and time

Abstract

We have examined the effect of temperature, pressure, and time on the magnitude of induced auxetic response in postmanufacture-processed needle-punched nonwovens. Different combinations of these processing parameters -temperatures ranging from room temperature to above the glass transition temperature (T g ) of constituent fibers, pressure of 0.49 or 2.45 MPa, and duration of 4 or 24 h -were used to process these nonwovens. This resulted in some permanent compression (defined as "compression set") and in out-of-plane auxetic behavior of the fabric, both of which were found to be proportional to the severity of the processing conditions employed. Milder processing conditions were found to be insufficient in producing significant compression set and hence produced little or no auxetic response. Using micro-CT and optical video microscopy techniques, it was found that the processing conditions caused the fiber bundles present in needle-punched nonwovens to assume a buckled/tilted state, which opened up during mechanical extension and hence were instrumental in the observed thickness increase.Out-of-plane Poisson's ratio with strain for as-received and treated nonwovens.

Review of Auxetic Materials for Sports Applications: Expanding Options in Comfort and Protection

“…Auxetic fabrics can also be produced from conventional fibres. Out-of-plane NPR has been induced in non-woven fabrics, produced thermo-mechanically [224,225], via compression between two flat, heated plates to tilt and buckle needle punched fibre bundles. The through-the-thickness auxetic samples consist of bent fibre bundles perpendicular to the surface of the fabric.…”

An Accurate Design Equation for the Maximum Deflection in a Class of Auxetic Sectorial Plates

“…In isotropic solids, the bounds for Poisson's ratio are defined as . These bounds imply the possibility of Poisson's ratio being negative; such solids expand in the lateral direction when stretched axially, and have been termed “auxetics.” Pioneering works on auxetics were spearheaded by Lakes, Wojciechowski, and Evans et al Of late auxetics research includes, but not limited to, auxetics in ligament structures, Cosserat elasticity of auxetic foams, wave properties in re‐entrant lattices, phononic band gap design, impact testing of auxetic foams for sports safety, chiral 3D lattices, 3D auxetic structure from intersecting double arrowheads, auxetic response of needle‐punched nonwoven, extrusion of auxetic PP fiber, auxetic properties in cubic materials and porous graphenes, auxetic behavior from nanochannels in degenerate crystals of hard dimers, auxetic composites from 3D textile structure and PU foam, reinforced‐core auxetic assemblies and auxetic gradient composite hexagonal honeycombs, to name a few. For a comprehensive survey on auxetic materials and structures, the reader is referred to a recent review and monograph …”

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