A new fatigue testing technique, the small bulge fatigue (SBF) test using a small disk‐type specimen with flat and concave surfaces, was developed in this study. In the technique, a cyclic oil pressure could be alternatively applied to both specimen surfaces at the frequency of 10 Hz. After some verification tests for the displacement and strain measurements, type 316 austenitic stainless steel specimens were subjected to a preliminary test using this newly developed testing technique. As a result, the SBF test results (S‐N curve) were in good agreement with those of conventional fatigue tests by defining fatigue life as the number of cycles to the sudden drop in oil pressure because of fracture.

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For developing the high temperature fatigue life evaluation method using small specimen, the effect of specimen size and test environment on the high temperature fatigue life of the reduced activation ferritic/martensitic steel, F82H-IEA, was investigated at 550• C under the total strain range of 0.5 -1.2 % using a new high temperature low cycle fatigue testing machine for the small round-bar specimen. No significant effect of the test environment (oxidation) on the fatigue life was observed in the standard-size specimen, whereas the slight reduction of the fatigue life due to that was indicated in the small-size specimen, especially at the final fracture stage of the test. It could be concluded that the new high temperature low cycle fatigue testing machine of the present study could satisfy the minimum requirements for the high temperature low cycle fatigue life evaluation using small specimen because the fatigue life data obtained using this testing machine could be acceptable based on the comparison with the previous studies data. To improve the reliability and the applicability of this test technology, further evaluations under the wider test temperature and strain conditions are expected in future.

This paper describes the development of a fatigue testing machine for small sized specimens in liquid environment. Since this type of testing machine is not available commercially, it has been designed, developed and built without any reference machine. The machine can operate tests on specimens with the shape of a solid cylinder with a diameter of 2 mm, a gage length of 4 mm and a total length of 34 mm. The testing machine consists of a testing stand, an environment vessel, a liquid cooling system and a test control system. Since the machine operates with combustible liquids, some safety devices have been also installed to prevent the machine from fire and explosion. The tests made for measuring the performance of the machine have been conducted on a specimen made by 440 stainless steel. The maximum applicable frequency by the testing machine is 100 Hz but only in a range of applied stress amplitude from 0 to 800 MPa. In 800 – 1200 MPa, the maximum frequency decreases down to 50 Hz with increase in the stress amplitude.

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