4 research outputs found
Mathematical modeling of auxetic systems : bridging the gap between analytical models and observation
The Poissonâs ratio, a property which quantifies the changes in thickness when a material is stretched and
compressed, can be determined as the negative of the transverse strain over the applied strain. In the scientific
literature, there are various ways how strain may be defined and the actual definition used could result in a
different Poissonâs ratio being computed. This paper will look in more detail at this by comparing the more
commonly used forms of strain and the Poissonâs ratio that is computable from them. More specifically, an attempt
is made to assess through examples on the usefulness of the various formulations to properly describe what can
actually be observed, thus providing a clearer picture of which form of Poissonâs ratio should be used in analytical
modelling.peer-reviewe
A novel mechanical metamaterial exhibiting auxetic behavior and negative compressibility
Auxetics (negative Poissonâs ratio) and materials with negative linear compressibility
(NLC) exhibit the anomalous mechanical properties of getting wider rather than thinner when
stretched and expanding in at least one direction under hydrostatic pressure, respectively. A novel
mechanismâtermed the âtriangular elongation mechanismââleading to such anomalous behavior is
presented and discussed through an analytical model. Amongst other things, it is shown that this
novel mechanism, when combined with the well-known ârotating squaresâ model, can generate giant
negative Poissonâs ratios when the system is stretched.peer-reviewe
Auxetic-inspired honeycomb macrostructures with anomalous tailormade thermal expansion properties including ânegativeâ heat-shrinking characteristics
Negative thermal expansion (NTE) materials and structures exhibit the anomalous property
of shrinking rather than expanding when heated. This work examines the potential of multimaterial
planar re-entrant and non-re-entrant honeycombs to exhibit anomalous thermal
expansion properties. Expressions for the coefficient of thermal expansion as a function of
the geometric parameters and intrinsic thermal expansion properties were derived for any
in-plane direction. It was shown that re-entrant honeycombs, a metamaterial which is well
known for its auxetic characteristics, can be made to exhibit NTE in specific directions
when constructed from conventional positive thermal expansion (PTE) materials, provided
that the slanting ligaments expand more than the vertical ligaments when heated and that
the geometry is amenable. Conversely, it was shown that the construction of such
honeycombs from NTE components will not necessarily result in a system which
exhibits NTE in all directions. Furthermore, conditions which result in honeycombs
demonstrating zero thermal expansion (ZTE) coefficients in specific directions were
also explored.peer-reviewe
The multidirectional auxeticity and negative linear compressibility of a 3D mechanical metamaterial
In this work, through the use of a theoretical model, we analyse the potential of a specific
three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit
a negative Poissonâs ratio for an arbitrary loading direction. Said analysis allows us to assess its
suitability for use in applications where materials must be able to respond in a desired manner to
a stimulus applied in multiple directions. As a result of our studies, we show that the analysed system
is capable of exhibiting auxetic behaviour for a broad range of loading directions, with isotropic
behaviour being shown in some planes. In addition to that, we show that there are also certain
loading directions in which the system manifests negative linear compressibility. This enhances its
versatility and suitability for a number of applications where materials exhibiting auxetic behaviour
or negative linear compressibility are normally implemented.peer-reviewe