Cyclic Response Curves Research Articles

Effect of strain level on the cyclic response and microstructure characteristics of selective laser melted 304L

Considering the relationship between austenite stability and strain level, the cyclic response curves are obtained for SLM 304L under different strain amplitude at R = 0.3. The results indicate that since the microstructure characteristics shift from stacking faults (SFs) at low strain amplitude to martensite and twins at high strain amplitude, the cyclic softening behavior transitions to cyclic hardening behavior. Besides, it also indicates that high strain levels can overcome the influence of initial microstructure on fatigue performance, presenting a new sight to understand the relationship between cyclic hardening and martensite transformation.

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

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.

Characterizations of Fatigue Deformation and Fracture Behavior of Commercially Pure Iron with Grain Boundary Micro-Voids

Fatigue deformation behavior of the commercially pure iron containing micro-voids at grain boundaries (GBs) were investigated under total strain amplitude control, and fatigue fractures were quantitatively characterized by fractal analyses. The cyclic response curves of the CP iron show an initial softening stage within early several cycles followed by a continuous cyclic hardening. No stress saturation phenomenon was found. Pre-existence of micro-voids at GBs spurs intergranular cracking to become a common damage mode besides transgranular cracking along slip bands. Quantitative analyses of fracture surface demonstrate that the value of fractal dimension D of the scanning profile in the crack growth zone is the largest as compared to those in the crack source zone and final rapid fracture area, almost regardless of the applied strain amplitude. This phenomenon was discussed in terms of the tortuosity of crack propagation path.

Cyclic response of RC continuous span bridges with irregular configuration in longitudinal direction

Cyclic response of a class of reinforced concrete bridges with different degrees of irregularity in longitudinal direction has been investigated. Eighteen bridge configurations have been identified from regular to the so-called highly irregular models. The geometric irregularity in this class of bridges is assumed to vary with the height of the piers. Using non-linear fibre-based analytical models, the cyclic response curves have been generated for theindividual piers of each of these 18 bridge models. Discussions have been made about the imposition of the displacement ductility demand of the piers versus the bridge regularity. Comparison of the cyclic response curves shows that the most vulnerable bridges are the irregular ones, and a high level of damage and ductility demand is expected for the short piers of this class of bridges.