A recent deterministic derivation for the creep rupture behavior ofpolymers is taken as the basis for the present work. The formulation isthat for the prediction of the lifetime of viscoelastic materials underconstant load, based upon kinetic crack growth from initial flaws. Thestatistical generalization involves using a Weibull type distributionfor the instantaneous static strengths. Then the resulting fullstatistical character for the lifetimes as a function of stress level isfound. The lifetime distributions are determined to be much broader thanare the static strength distributions. An unusual statisticalcharacteristic emerges from the derivation. When the lifetimes areviewed on log stress versus log lifetime scales the envelopes for thevarious probability levels of failure are found to have a common shape,as in a single master curve, but they are shifted relative to each otheralong the log stress axis. This shifting property could haveconsiderable utility in reducing the number of tests required to obtaina complete, statistical database. Finally, similar implications forfatigue characterization are considered.
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