All polymer foams are viscoelastic; for foams used in earplugs, this response is essential to their function. Poisson's ratio was inferred from viscoelastic response of earplug foam in torsion and bending. Poisson's ratio increases with frequency as a result of stress induced air flow. Air within the pores contributes to the overall bulk modulus at high frequency, but not at low frequency at which it easily flows when the foam is deformed. Such behaviour is the opposite of that of solid polymers in which the shear modulus varies with frequency much more than the bulk modulus.
Get full access to this article
View all access options for this article.
References
1.
PipkinA.C.Lectures on Viscoelasticity Theory, Springer Verlag, Heidelberg; George Allen and Unwin, London, (1972).
2.
TschoeglN.W., KnaussW., and EmriI., Poisson's ratio in linear viscoelasticity - a critical review, Mechanics of Time - Dependent Materials, 6, (2002), 3–51.
3.
LakesR.S., and WinemanA., On Poisson's ratio in linearly viscoelastic solids, Journal of Elasticity, 85, (2006), 45–63.
4.
LakesR.S.Foam structures with a negative Poisson's ratio, Science, 235, (1987), 1038–1040.
5.
LakesR.S.The time dependent Poisson's ratio of viscoelastic cellular materials can increase or decrease, Cellular Polymers, 11, (1992), 466–469.
6.
GrossB., Mathematical Structure of the Theories of Viscoelasticity, Hermann, Paris, (1968).
7.
GibsonL.J., and AshbyM.F., Cellular Solids: Structure and Properties, Cambridge: Cambridge University Press (1997).
8.
BiotM.A., General theory of three-dimensional consolidation, J. Applied Physics, 12, (1941), 155–164.
9.
GentA.N., and RuschK.C., Viscoelastic behavior of open cell foams, Rubber Chemistry and Technology, 39, (1966), 388–396.
10.
GardnerR.Jr., Earplugs. US Patent 3,811,437 (1974).
11.
LeeT., LakesR.S., and LalA., Resonant ultrasound spectroscopy for measurement of mechanical damping: comparison with broadband viscoelastic spectroscopy, Review of Scientific Instruments, 71, (2000), 2855–2861.
12.
CalcagnoB., Lopez GarciaM.d.C., KuhnsM., and LakesR.S., On the nonlinear creep and recovery of open cell earplug foams, Cellular Polymers, 27 (8) (2008), 165–178.
13.
SokolnikoffI.S., Mathematical Theory of Elasticity, Krieger; Malabar, FL, (1983).
14.
ChauK.T.Young's modulus interpreted from compression tests with end friction, J. Engng. Mech., 123, (1997), 1–7.
