The effect of temperature on compressive fatigue of polystyrene

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Abstract
Compressive fatigue experiments have been designed to compare this long term mechanical life property with shorter term stress‐strain behavior. Fatigue lifetime curves can be represented by three distinct regions. The fatigue failure curves shift to shorter lifetimes and lower stresses as temperature is increased. The results are discussed in terms of the Zhurkov model of static fatigue failure. Using a Coulomb‐Navier yield criterion modified rate expression, it is clear that activation energy and activation volume are functions of temperature. A change in temperature dependence of activation energy and endurance limiting stress occurs near the β transition suggesting that this molecular process is related to the fatigue process. The nearly identical dependence of fatigue and stress‐strain activation energies and activation volumes with temperature suggest that both deformation processes may be controlled by a similar mechanism, i.e., localized plastic deformation. Utilizing these concepts, a simple model of fatigue allows correlation of the endurance limiting stress and the number of stress cycles at the endurance limiting stress with measures of resistance to plastic flow as determined from stress‐strain data for this polystyrene. These data are used to project the longest and shortest mechanical fatigue lifetimes for these deformation conditions.