13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Effect of Loading Frequency in Fatigue Properties and Micro-Plasticity Behavior of JIS S15C Low Carbon Steel Benjamin Guennec1,*, Akira Ueno2, Tatsuo Sakai2, Masahiro Takanashi3, Yu Itabashi3 1 Student Member: Graduate School of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan 2 College of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan 3 Research Laboratory, Structural Strength Department, IHI Corporation, Yokohama, Kanagawa 235-8501, Japan * Corresponding author: gr0081rh@ed.ritsumei.ac.jp Abstract Ultrasonic testing method has allowed some impressive improvements in order to better grasp fatigue properties of various metallic materials the latest 20 years. It is particularly the case in the very high cycle regime since ultrasonic fatigue tests are conducted at very high stressing frequencies. However, the question of a potential difference of fatigue strengths due to huge frequency gap between ultrasonic method (usually carried out at 20 kHz) and servo-hydraulic one (usually in the range of 1~100 Hz) is still unclear and needs to be studied for a various kind of metallic materials. The case of low carbon steels presents a singularity, as fatigue properties are significantly different between these two fatigue tests methods. It seems particularly interesting to study this kind of materials in order to get a better overview of frequency effect in metallic materials fatigue. Aim of the present work, which consists of a general survey of JIS S15C steel (0.15% C) fatigue properties, is firstly to reconfirm such a frequency effect. Secondly, based on several experiments related to micro-plasticity behavior, some discussions will be held in order to explain this frequency effect in the case of low carbon steels. Keywords Frequency effect, Low carbon Steel, Ultrasonic test, Cyclic hardening, EBSD observations 1. Introduction The past 20 years in the field of fatigue test marks increase of ultrasonic testing method for various industrial uses. Since study of the very high cycle regime has become a topical issue, ultrasonic stressing frequency allowed by this fatigue testing method is essential to conduct fatigue test in a definite time. It is indeed almost impossible to reach 109~1010 cycles with a conventional fatigue testing machine. However, question of a potential influence of stressing frequency on fatigue test result, usually known as “frequency effect”, have been studied by numerous literatures and is still unclear, except for some particular materials. Low carbon steels reveal usually a clear difference of fatigue strength between usual fatigue testing (servo-hydraulic as instance) and ultrasonic testing method. As a consequence, it was decided to make a focus on the effect of loading frequency on low carbon steels. The present work discusses some phenomenon possibilities involved in frequency effect of low carbon steels. 2. Experimental Procedure In the present study, material tested is JIS S15C steel, extracted from as rolled material. Chemical composition and mechanical properties are indicated in Tables 1 and 2, respectively. Figure 1 shows the microstructure of this steel, with typical ferritic and pearlitic composition. One can see that grains are elongated in the rolling direction.
RkJQdWJsaXNoZXIy MjM0NDE=