Exploration of high and negative Poisson's ratio elastomer‐matrix laminates

Abstract

Elastomer-matrix composites show promise for high Poisson's ratio and negative Poisson's ratio (auxetic) applications due to high orthotropy. There are approximately five orders of magnitude between the axial stiffness of high modulus graphite fibres and the stiffness of low durometer elastomers. Although the maximum Poisson's ratio for isotropic elastomers is 0.5, it is easily shown that inplane Poisson's ratios twice unity can be obtained with a graphite/epoxy angle-ply laminate at 25°. Chou and others have predicted inplane Poisson's ratios greater than 7 for certain cord-rubber combinations. Peel previously predicted inplane Poisson's ratios higher than 32 and less than -60. Preliminary experimental results have produced inplane Poisson's ratios as high as 14. Certain combinations of un-balanced highly orthotropic laminates may also produce inplane negative Poisson's ratios. Inplane Poisson's ratios, experimentally obtained from two laminate configurations with approximately the same axial stiffness are compared. A symmetric, balanced laminate produced an inplane Poisson's ratio of 3.7; while an unbalanced laminate with an equivalent axial stiffness produced an average inplane Poisson's ratio of -1.5. Certain high and negative Poisson's ratio elastomer-matrix laminates appear to have quasi anti-symmetric relationships about 0°, although laminate designers may consider dual angle-ply laminates to be the more likely counterpart to the unbalanced dual angle auxetic laminates. Unbalanced symmetric laminates experience significantly more inplane shear deformation when axially loaded than their balanced counterparts. The high shear may be desirable for damping applications, but less desirable otherwise.

The mechanical properties of plant cell walls soft material at the subcellular scale: the implications of water and of the intercellular boundaries

“…For an isotropic linear elastic material, Poisson's ratio cannot be more than 0.5. However, where two phases exist, as in the cases of a cellular solid or fiberreinforced laminate, Poisson's ratio can be much larger than 0.5 without violating any physical laws [61,62]. In such cases, the high anisotropic value between the phases or the deformation of cellular structures in foam helps to attain unusually high Poisson's or LA ratios.…”

The manufacture and characterisation of a novel, low modulus, negative Poisson’s ratio composite

“…This work is of significant importance as it is the first time reported in the research literature that an auxetic composite has been produced from inherently auxetic fibres, and this has been achieved using standard manufacturing processes and commonly available materials [16,17], though auxetic fibres have been reported and the possibility of such a composite postulated [18,19]. It is therefore conceivable that composites of this nature could be manufactured commercially without the need for developing new manufacturing techniques.…”

“…Interestingly there are signs that auxetic materials may have advantages over conventional equivalents in damping applications [15]. It has been the goal to produce an auxetic composite for some time and some examples exist which rely upon specific stacking sequences of otherwise conventional lamina and fibres [16,17], rather than fibres which are auxetic in their own right. Alderson et al [16,18,19] have also proposed the used of intrinsically auxetic fibres in composites to improve fibre pull out strength, however tests were conducted on single fibres potted in epoxy but a full composite sample was not characterised.…”

Thermal-Mechanical Properties of Epoxy-Impregnated Bi-2212/Ag Composite

“…Loading off axis may result in complicated local stress on the strand. Similar behavior has been reported in study of fiber-reinforced materials loaded along off-axis directions [9]. On the other hand, results measured by gages mounted on epoxy may be considered as an average behavior.…”