The Analysis of Power of Hydraulic Fatigue Testing Machine under Completely Reversed Tension and Compression

Abstract

In the previous paper the author made an analysis of the power of hydraulic fatigue testing machine under pulsating tension and described the method to reduce the power.
This paper treats the analysis of power under completely reversed tension and compression by applying the results of the previous paper.
In this case, the power required to afford the tensile stress to the specimen is transmitted directly by the pulsator and the power to afford the compressive stress to specimen is transmitted by discharging the energy stored in the accumulator which utilizes the compressibility of hydraulic oil.
In other words, in the case of pulsating tension the twisting moment of the driving shaft is approximately zero in the range 5/6π∼7/6π of rotating angle of the shaft and reverses slowly in the neighborhood of both the end points, and reverses rapidly at 2π.
However, in the case of completely reversed tension and compression the moment reverses rapidly at π and 2π.
Accordingly, the torque in the case of tension and compression fluctuates rapidly compared with pulsating tension, and large energy fluctuation occurs.
Consequently, under the same load amplitude, the larger power is needed in the case of tension and compression than the pulsating tension, and results in the decrease of energy efficiency.
This paper carried out the analysis of the energy of hysterisis loop of the specimen in the case of tension and compression, and clarified the basis to design the fly wheel in order to raise the efficiency of energy of the fatigue testing machine.
The energy losses of the testing machine, excepting the true energy to afford the stress to specimen are as follows.
(1) The resistance of hydraulic system.
(2) The energy losses caused by the hydraulic pressure expansion of several parts.
(3) The oil leakage between the ram and cylinder, etc.
(4) Mechanical losses.
By calculating the above values (1∼4) the author could get the ratio of these values to the total consumption of power, and applying these values, he obtained the nomograph which shows the relation between the dynamic load, deflection of the specimen, the oil volume in hydraulic system, and the pulsator capacity which will afford the convenience in calculating the power.