Determination of Fatigue Properties Using Miniaturized Specimens

It is very important to determine Paris' power law constants to know the fatigue crack growth rate (FCGR) of a structure containing crack. These constants are generally determined by FCGR test using conventional specimens as specified by ASTM-E647 standard. This standard FCGR test procedure has placed strict size requirements on the conventional specimens and hence a large amount of material is needed to fabricate the specimens. However, sometimes, like in the case of testing of irradiated materials or nuclear pressure vessel surveillance, the material available for testing is not sufficient to make standard size specimens. Therefore, miniature specimens should be used to minimize the amount of material. In this work, constant load amplitude FCGR behavior of nuclear pressure vessel steel (20MnMoNi55) has been studied using miniature Single Edge Notched Tensile (SENT) specimens. The fatigue tests have been performed according to the procedure described in ASTM-E647 standard. The Paris' power law coefficient and exponent obtained by FCGR test of miniature SENT specimens are in the range of 10(-12) to 10(-13) and 2.8-3.5 respectively, when the FCGR (da/dN) is expressed in m/cycle and stress intensity range (Delta K) in MPaaem. These values of Paris' power law constants of miniature specimens are nearly of same order as that of the standard specimens where the results of standard specimens are taken from the literature.