MECHANICAL-PROPERTIES OF BONDED ELASTOMER DISCS SUBJECTED TO TRIAXIALSTRESS

The aim of this article was to evaluate and analyze the mechanical pro perties of bonded elastomer discs subjected to triaxial stress on an M TS (machine for testing samples) equipment. Several pulling tests were run on an Instron machine using an O-ring type of samples to evalutat e the mechanical properties of testing unfilled nitrile rubber subject ed to uniaxial tension. It was found from the stress-strain curve of t he O-ring samples that a very small stress softening occurred when the maximum strain is less than 200%. It was also found that the stress a nd strain at break does not drastically vary with respect to strain ra te. The initial modulus does not vary with respect to strain rate up t o epsilon = 2 min(-1), and only for large values of epsilon does the m odulus depend on the strain rate. The material used for the uniaxial t ension experiments were bonded between two rigid cylindrical steel pla tes and the specimens were subjected to uniaxial tension on an MTS mac hine. It was found that the initial modulus in tension was smaller tha n in compression. The theoretical predicted initial modulus from Gent' s equation was much larger than experimentally estimated. It was shown that the elastomer in the pancake tests was not incompressible and a value of 0.494 was determined for the effective Poisson's ratio. A mat hematical equation was derived for the effective Poisson's ratio as a function of the volume fraction of voids within the testing material. (C) 1996 John Wiley & Sons, Inc.