Forecasting Low-Cycle Fatigue Performance of Twinning-Induced Plasticity Steels: Difficulty and Attempt
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THE use of fatigue data in material design has increased over the years, considering most of engineering structures and components are served under cyclic loading condition. However, fatigue testing is a timeand money-consuming process; hence, it is highly desirable to estimate the fatigue property or fatigue life through relatively simple and labor-saving tests without performing a series of complete fatigue tests. Attempts have been made by the previous researchers to correlate the cyclic deformation properties to monotonic tensile data and/or hardness for many years.[1–5] It is wellknown that materials with a higher tensile strength usually display a higher fatigue strength[6] and a large monotonic ductility often corresponds to a long low-cycle fatigue (LCF) life.[7] For example, by adding Al
C.W. SHAO is with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China and also with the University of Chinese Academy of Sciences, Beijing 100049, P.R. China. P. ZHANG, Z.J. ZHANG, R. LIU, and Z.F. ZHANG are with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences. Contact e-mail: [email protected] Manuscript submitted February 8, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
element into Cu alloys, both the tensile strength and uniform elongation are simultaneously improved,[8] meanwhile, the fatigue properties, including the fatigue life in the LCF regime[9,10] and the fatigue strength in the high-cycle fatigue (HCF) regime,[10] are enhanced correspondingly. To improve the strength and ductility of metallic materials, so as to expect a better fatigue resistance, some significant developments have been achieved in the past decades.[11–14] For example, an excellent combination of high strength (tensile strength greater than 800 MPa) and ductility (uniform elongation 80 to 85 pct) can be achieved in high-Mn TWIP (twinning-induced plasticity) steel,[15,16] which has its origin from the dynamic Hall–Petch effect caused by deformation twinning during plastic deformation.[17,18] Unfortunately, the fatigue performances of Fe-18Mn-0.6C TWIP steel, especially the LCF properties, are not so great or even worse in comparison with other candidate steels, e.g., high-nitrogen steel and commercial Avesta Sheffield 654 SMO steel.[19–21] Still, this short slab has not been effectively improved, and research was seldom conducted on the mismatch between tensile and fatigue properties. In our previous work, the LCF properties were not only determined by material’s static toughness, but also influenced by its work-hardening ability.[9,22] Even so, it should be acknowledged that sometimes forecasting the
fatigue properties directly from monotonic mechanical properties is still difficult and lacks theoretical support, considering the essential differences between monotonic and cyclic deformation mechanisms. Specifically, some materials with similar tensile properties may have remarkable differ
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