High-Cycle, Low-Cycle, Extremely Low-Cycle Fatigue and Monotonic Fracture Behaviors of Low-Carbon Steel and Its Welded Joint

Abstract

Low-carbon steels are commonly used in welded steel structures and are exposed to various fatigue conditions, depending on the application. We demonstrate that the various transitions in the fracture mode during fatigue testing can be distinguished by their different cyclic response curves and microstructural features after fracture. Fractography, surface damage micrographs, and microstructural evolution clearly indicated the transition of the fracture modes from high-cycle to low-cycle, extremely low-cycle fatigue, and monotonic behavior. The high-cycle fatigue mode showed initial cyclic softening, followed by cyclic stabilization, and showed inclusion-induced crack initiation at fish-eyes, while the low-cycle fatigue mode showed initial cyclic hardening followed by cyclic stabilization, where fractography images showed obvious striations. In addition, the extremely low-cycle fatigue mode showed no cyclic stabilization after initial cyclic hardening, which was characterized by quasi-cleavage fractures with a few micro-dimples and transgranular cracking, while the monotonic fracture mode predominantly showed micro-dimples.

On the low-cycle fatigue behavior of thermo-mechanically processed high-strength aluminum alloys

“…3. It is well-accepted that the LCF regime considers tests up to about 10 5 cycles [47] and, thus, specimens exceeding 150,000 cycles without failure are reported as runouts in the present study. All specimen fatigued at the lowest total strain amplitude (Δε t /2 = 0.2%) except the AA6082 condition formed in the tool with a temperature of 350 °C could withstand more than 150,000 cycles.…”

Fatigue Analysis of the Microturbine Rotor Disc Made of 7075 Aluminium Alloy Using a New Hybrid Calculation Method

“…The above- The above σ-N diagram shows a curve that is typical of aluminium alloys, i.e., a group of materials commonly used, for example, in the aircraft industry. Such curves obtained for specific alloys are presented in the studies carried out by Zhao and Jiang [27] as well as by Yang et al [28,29]. Thanks to the study carried out by Yang et al [28], it was possible to create a diagram that was used for further analysis.…”

“…The diagram below (Figure 1) shows the division between low-and high-cycle fatigue. The limit between LCF and HCF can be set differently, but in this paper, it was adopted similarly to that in [27] by Kim and Hwang, which is about 10 4 cycles. systems.…”

“…The diagram below (Figure 1) shows the division between low-and high-cycle fatigue. The limit between LCF and HCF can be set differently, but in this paper, it was adopted similarly to that in [27] by Kim and Hwang, which is about 10 4 cycles. The above σ-N diagram shows a curve that is typical of aluminium alloys, i.e., a group of materials commonly used, for example, in the aircraft industry.…”

NDSHA - The New Paradigm for RSHA - An Updated Review

“…to which PSHA astrologers first looked (Cornell 1968) to foretell (they say) the most universally appropriate way to handle "the uncertainty in the number, sizes, and locations of future earthquakes"! Finally, it is important to point out that both wind-resistant and seismicresistant design considerations (although fundamentally different) identically share the same vulnerability to fatigue strength degradation of welded joints in steel frame buildings: due to low cycle fatigue phenomena (Kim and Hwang, 2019) The caveat: the tall building performance in the extreme wind event, or alternatively in the MCE earthquake (Parvez et al, 2011)… may not be per the design intent -but rather actual performance will reflect the integrated sum of all (both wind and seismic) low cycle events affecting degradation of the fatigue strength of welded joints -meaning that the building is now more realistically "what it is cracked-upto-be"!…”