Abstract
A new fatigue test apparatus with a small disk-type specimen, in which a cyclic oil pressure could be alternatively applied to both specimen surfaces at the frequency of 10 Hz was developed in this study. This testing technique was termed “Small Bulge Fatigue (SBF) Test”. Unlike the conventional small punch test, a hydraulic bulging method was adopted for avoiding problems attributable to the contact and/or the friction between ball and specimen. Additionally, in order to prevent cracking at the edge of specimen, the specimen thickness of central region was relatively reduced, and the small disk-type specimen with flat and concave surfaces was employed considering machinability and/or handleability. After some verification tests for the displacement and strain measurements, austenitic stainless steel SUS316 was subjected to the preliminary test using this newly developed testing technique. Experimental results revealed that crack was initiated on the vicinity of center of flat surface as expected by finite element analysis, and the oil pressure was abruptly dropped when a part of gauge area was broken. The SBF test result was in good agreement with those of conventional fatigue tests by defining a fatigue life as the number of cycles to sudden drop in pressure due to fracture.
