抄録
The rheological and stochastic characteristics of the fracture of elastomers are hereunder discussed to begin with. For the failure process of elastomers, two hypotheses are proposed, viz.
(a) The flow of the polymer chains in polymeric solids may be effective to disperse the stress concentration around a flaw in the solid.
(b) The probability to grow a catastrophic flaw in the solid may increase by the increase in time interval during the flow.
These two hypotheses will bring reverse effects on the strength of the polymer. A theory on fracture mechanism based on the hypothesis (b) is introduced, and, on this theory, the creep failure process of some elastomers are analyzed according to the theory. In this analysis, two material constants on fracture, by which the failure process is characterized, are obtained by the experiment.
As another application of the theory, the distribution of the breaking stretch ratios in uniaxial extension of constant rate is estimated by the constants obtained by the creep fracture. There is good agreement between the theoretical and the experimental results, but there are cases where the fracture mechanism assumed by hypothesis (a) is also important. It is considered practically that both the mechanisms occur simultaneously.
Secondly, the importance of the research on the strength in multiaxial stressed state is emphasized for the sake of considering the fracture phenomena of elastomers in relation to the micro structures. Some data from a biaxial extension testing of valcanized SBR is introduced and, as a fracture criterion, the following formula is presented
λi≥λB (i=1 or 2)
where λi is stretch ratio along the principal axes (axis 1 and 2 have orthogonal direction to each other), λB is a critical stretch ratio and independent value on any combinations of λi (i=1, 2).
This simple result is discussed in relation to its mechanical property obtained by the biaxial tensile testing.
