Development of multi-type fatigue testing machine in axial loading and verification of its fundamental performance

Fatigue behavior of metallic materials in very high cycle regime has become an impotant subject to guarantee the safety of mechanical structures during the long term service. In order to perform fatigue tests in very high cycle regime of N=109, a long period such as 230 days is required at the testing fiequency of 50 Hz. The multi-type fatigue testing machine which can give cyclic loadings to a number of specimens simultaneously is valuable to obtain fatigue test data within the specified period. From this point of view, a multi-type fatigue testing machine for axial loading was developed by using a special hydraulic system with a rotary valve to distribute high pressure oil into the respective actuators. By means of this testing machine, fatigue tests for four different specimens can be perfermed simultaneously at the frequency of 80 Hz. The loading capacity for each specimen is ±10kN and the applied load can be given independently to the individual specimen. Thus. one can perform the fatigue tests in the long life regime for many specimens within the specified period even in the usual frequency where the temperature rise does not take place on the specimens. The fundamental structure and its performance are presented here together with the fundamental experimental results on the bearing steel of SUJ 2.