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SynopsisTo understand influences of various factors on dynamic durability of engineering plastics, effects of average molecular weights of samples, molding variables, preparing methods of specimens, and fillers on plane and rotational bending, torsional, and impacting fatigue and cavitation erosion and solvent cracking of polycarbonate were studied. From the experimental results, the following tendencies are observed as a whole in case of polycarbonate: The extent of influence of the factors on dynamic durability varies depending on the type of testing. Increase in molecular weight has a favorable effect on dynamic durabilities. Influence of molding conditions is remarkable: especially, deficient drying of resin pellets before molding decreases dynamic durability noticeably, and specimens prepared by injection molding have much better durabilities than those by machining from extruded sheet. Polyethylene blending has an unfavorable effect on durability, except for hod-type impact strength and solvent cracking. Reinforcement by glass fiber has a favorable effect on fatigue under constant load and solvent cracking, but has unfavorable effect on fatigue under constant deformation and cavitation erosion.