Indicators of HSLA steel behavior under low cycle fatigue loading

Abstract

In present paper, the experimental research of the behaviour of high-strength low-alloy steel (HSLA) exposed to low-cycle fatigue (LCF) with controlled and fully reversible strain (Δɛ/2 = const, Rɛ = ɛmin/ɛmax = -1) has been analysed. Low-cycle fatigue tests were performed on a series of smooth specimens made of steel Nionikral 70 (NN-70), with semi-amplitude of controlled strain, Δɛ/2=0.35, 0.45, 0.50, 0.60, 0.70 and 0.80. Characterization and description of the low-cycle elastoplastic behaviour of the material by construction of characteristic curves of low-cycle fatigue are made using the characteristic hysteresis, load -strain force for each level of controlled strain, selected from the areas of stabilization. For the selection of stabilized hysteresis and processing of the results of low-cycle fatigue tests the recommendations of the ISO 12106:2003 (E) and ASTM E 606-04 standards were used, which in this work means to compare the two results. For each strain level characteristic stabilized hysteresis were selected, determined in accordance with recommendations of the ISO 12106:2003 (E) and ASTM E 606-04 standards, from which the data necessary for further processing of the results and finally for the construction of characteristic curves of low-cycle fatigue were read. Constructed curves are compared, and the effect of selection of the recommendations from the standards on characterization of the behaviour of steel NN-70 estimated. The results of experimental investigation have given us important information on the understanding of fatigue behaviour of steel NN-70. In this work the results of static and dynamic, that is monotonous and fatigue behaviour of the material, were compared, which is a practical contribution to the assessment of the behaviour of steel NN-70 exposed to the effects of low- cycle fatigue, i.e. monotonous and fatigue behaviour of the material.