| Abstract: | ![]()
It is shown that if the frequency of cyclic loading is varied, the total heat-up is small, and relaxation processes do not play a role (proceed too fast or too slowly), the loading times are additive. It is shown that deviations from this additivity rule manifest themselves in a disproportionally slow increase or even in a decrease of the strength with rising frequency; these deviations may be caused by relaxation factors, i.e., by structural changes and local warming up. It is established that the degree of deviation depends on various factors determining the rate of relaxation, i.e., on the temperature, plastification, and orientation, which is in accordance with ideas on the role of relaxation phenomena in fatigue rupturing but conflicts with the view that the number of load cycles should be the decisive factor. The phenomenon of fatigue rupturing of plastics exposed to repeated impacts is discussed; specific features of impacts are the high loading rate and the rest between the impacts. It is shown that, in spite of the much shorter action time of the load, the strength under repeated impacts is lower than that under harmonic loading, owing to the stronger effect of local excess stresses and disorientation during unloading.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 165–168, January–February, 1972. |
