Abstract
Fatigue failure mechanism in polymers was examined by using a fatigue testing machine of constant deflection type. The fatigue tests were carried out both on polycarbonate and polyamid, and the effect of the difference of their structure on fatigue behaviors was investigated. Moreover, the effect of temperature on a fatigue crack propagation was also investigated.
The state of stress in the specimen during crack propagation was theoretically analyzed and compared with the experimental value. From the relation between the rate of fatigue crack propagation and the applied stress the fatigue life of polymers was discussed.
The following results have been obtained:
(1) The results obtained from the stress analysis are qualitatively consistent with the experimental value. The rate of fatigue crack propagation is found to be proportional to 2-3 power of applied stress in polycarbonate, and it has decreased with an increase of the testing temperature.
(2) It has been found from fractographic examination that: (a) the fatigue crack in polycarbonate has initially propagated, forming striation markings on the fracture surface, but this marking of striation has not necessarily corresponded to each cycle, (b) the spherulite structure in polyamid seems to have had great influence on the failure mechanism.
