The Analysis of Power of Hydraulic Fatigue Testing Machine under Pulsating Tension

Abstract

The fatigue tests of materials using objects in practical use as specimens are remarkably common in recent years.Larger amplitudes are required in the fatigue tests, therefore, both of stress and of strain.When there is large deflection of specimens in the test made by means of a hydraulic large-fatigue testing machine, it is necessary to reduce the load repetition cycle.In this kind of testing machine either electrical or mechanical, the prime mover that is in common use is capable of adjusting speed within the range about 1:4.The driving torque of these prime movers is almost constant at any speed.At low speed, therefore, both the power produced by this prime mover and the effect of the fly wheel are smaller than those at high speed.At low speed, moreover, the driving shaft of the machine receives shock due to the large reversed torque created by the reaction of the specimen.In the present paper, the author has worked out the analysis of the mean torque of the hysteresis loop of the specimen and the reversed torque caused on the driving shaft by the compressibility of oil in the hydraulic system.In order to keep uniformity against the varying torque, he installed an accelerative fly wheel capable of being switched to the driving shaft to change the gear ratio.For the purpose of increasing both the mean torque and the starting torque, he introduced an improvement on the mechanical gearing system particularly to prevent the shock of reversed torque effectively when the machine is operated at low speed.By adopting these new devices into the fatigue testing system, it is made possible now to enhance its capacity and to reduce the electric power consumption.