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A. Gent
Goodyear, USA
Elastic Instabilities in Rubber: Aneurysms, Blisters and Wrinkles
Various types of instability are discussed, including the sudden
appearance of internal cavities at a critical dilatant stress (negative
pressure) [1,2] and surface wrinkling caused by compression of a
half-space parallel to the free surface [3,4]. Unrestrained growth of a
cavity in a neo-Hookean solid is predicted to occur at a dilatant stress
of 5E/6, where E is the Young modulus of elasticity. Internal voids
appear suddenly in a variety of experiments when the dilatant stress
approaches this value [2]. Total failure often follows. Adjustments to
the simple theory are needed to account for finite extensibility effects
and the tear energy of cavity growth.
Instability of the surface of a neo-Hookean half-space is predicted to occur at moderate compressive strains, between 33 and 55 % [3]. When an
elastic block is bent, compression occurs in one direction at the inner
surface,and instability would then be expected at 44 %
compression. Experimentally, sharp creases appear suddenly on the inner
surface but at about 35 % compression, when the bending is only about
one-half as severe as predicted [4]. Occurrence of sharp creases might
well pass undetected in service, although they would be potential failure
sites. Also, moving creases (~SSchallamach waves~T) are observed in a
rubber surface underneath a frictional slider [5] and may play an
important role in rubber abrasion.
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