ABSTRACT
The incompressibility of rubber vulcanizates during deformation depends on the shape of sample specimen. It is nearly realized if the dimension of sample specimen in tensile direction is much longer than that in perpendicular to tensile direction. On the other hand, if the dimension of sample specimen in tensile direction is comparable to the length of sample in tensile direction or below, a certain compressibility arises because the rubber cannot shrink due to constraint of strain on top and bottom surfaces of sample specimen and, therefore, the volume of the specimen increases as a function of strain. This volume increase originates initially from certain elasticity, later from formation and growth of cavities.
