We developed a uniaxial tension hydraulic servo fatigue-testing machine optimized for obtaining gigacycle fatigue data. Main development goals of this machine were as follows: (1) to assure high accuracy of each cyclic loading, (2) to minimize a bending stress generated in a specimen without alignment before the test, (3) to bear high durability enough for a number of gigacycle fatigue tests, (4) to have good user-friendliness for changing testing conditions freely including stress ratio and frequency, (5) to get twice or three-fold higher response compared with a conventional fatigue testing machine. To accomplish these goals, we introduced a miniaturization of the hardware, an alignment free mechanism, fluid lubrication bearings without a sealing system, and a digital controller. As a result, this machine achieved the following performance: (a) high accuracy with loading errors less than ±0.1%, (b) good alignment with bending stress in the specimen less than 3%, (d) high response with 150Hz of ±9.8kN loading, and (e) friendly user interface for setting testing conditions.
