Determination of effective flaw size for fatigue life prediction

Effective flaw sizes (c(i)) for initiation of mechanical failure have been determined for unfilled and filled natural rubber and filled styrene-butadiene rubber by comparing experimental results for failure scenarios with predictions made using fracture mechanics, treating effective flaw size as a fitting parameter. Two independent techniques are used; the different failure scenarios being cyclic fatigue life of tensile strips in one case, and ozone cracking in the other. For the filled rubbers there was a surprisingly large dependence of apparent effective flaw size on the strain amplitude used in the fatigue tests. The fatigue method also called for the crack growth parameters to be determined, and these are compared to values reported in the literature for similar materials.