The strain and breaking life of polycarbonate under loading of trapezoidal wave shape were investigated for analysing the behavior of polymers under the co-action of cyclic and constant loadings It was found that the fatigue/creep curves under trapezoidal loading are similar to the pure creep curves under constant loading．A strain platform was observed before the break of the samples With increasing the time length of maximum load in each cycle the platform strain value increases

and the break life decreases Under trapezoidal loading the break life of polycarbonate was not simply determined by the contributions of pure creep and pure fatigue

and a term reflecting the co-action of the two demage types should be considered The co-action term is more evident at low temperature A decrease of breaking life of the samples was observed with raising temperature and was explained as the result of increase of individual effects of pure creep or pure fatigue.