•A new shear panel damper with different out-of-plane stiffeners is proposed.•A weakened shape of flange stiffeners is investigated to postpone the plate boundary failure.•Three full-scale specimens ...are designed and tested.•A plasticity analysis of LYP225 steel concerning cyclic hardening is conducted.•A simplified calibration method for a combined hardening constitutive model with memory effects is proposed.•The cyclic response of shear panel dampers is well simulated.
Shear panel dampers are considered as a type of reliable passive energy dissipation device for seismic resistant structures with a damage-controlling concept. It has been revealed that the shear bulking of core plates and the premature failure of boundary plates are the main concerns for a shear panel damper that result in insufficient energy dissipation and undesirable ultra-low cycle fatigue performance. This study utilizes square steel tubes serving as out-of-plane stiffeners for the core plates made of a low-yield-point steel with a nominal yield stress of 225 MPa (named LYP225 steel). Meanwhile, a reduced flange plate section is adopted to mitigate the end fracture. An experimental study is carried out on three full-scale damper specimens with different flange plates and loading protocols. The test results show that the square tubes well prevent the bulking of the core plates and all the specimens exhibit plump hysteretic response and satisfactory energy dissipation capacity. The reduced plate sections reduce the likelihood of crack propagation occurring at the flange end, and thereby improve the ultra-low cycle fatigue performance. In order to develop the numerical model of shear panel dampers, a combined-hardening constitutive model with a memory surface is applied to represent the plasticity of LYP225 steel. Based on a plasticity analysis, a simplified calibration procedure is proposed associated with the three-dimensional constitutive model, where the plasticity parameters of LYP225 steel are determined using only the monotonic tensile test data. Eventually, the numerical results of uniaxial specimens and damper specimens are in good agreement with the test results, which validates the effectiveness of the constitutive model and the proposed calibration method.
Higher fatigue and creep resistance at high temperatures are the essential properties for materials such as those used in gas turbines for power generation and aircraft turbines. Therefore, the ...nickel-based superalloy CMSX-4 was developed through single-crystal casting to satisfy these requirements. In this study, the CMSX-4 creep test results reported by previous researchers were used to mathematically derive an equation to estimate the amount of creep damage occurring under variable load conditions. In addition, low-cycle fatigue tests were performed, and the effect of creep damage occurring during fatigue on material failure was described.
Under strong earthquakes, steel structures are prone to undergoing ultra-low cycle fatigue (ULCF) fracture after sustaining cyclic large-strain loading, leading to severe earthquake-induced damage. ...Thus, establishing a prediction method for ULCF plays a significant role in the seismic design of steel structures. However, a simple and feasible model for predicting the ULCF life of steel structures has not been recognized yet. Among existing models, the ductile fracture model based on ductility capacity consumption has the advantage of strong adaptability, while the loading history effect in the damage process can also be considered. Nevertheless, such models have too many parameters and are inconvenient for calibration and application. To this end, focusing on the prediction methods for ULCF damage in steel structures, with the fragile parts being in moderate and high stress triaxiality, this paper proposes a simplified uncoupled prediction model that considers the effect of stress triaxiality on damage and introduces a new historical-effect related variable function reducing the calibration work of model parameters. Finally, cyclic loading test results of circular notched specimens verify that the proposed model has the advantages of a small dispersion of parameters for calibration, being handy for application, and possessing reliable results, providing a prediction method for ULCF damage of structural steels.
•The maximum principal strain critical plane is more effective under both IP and OP loading.•FS model and KBM-P model can be applied to both IP and OP loading in a general form.•MLCF life prediction ...model based on newly defined αNf and α are established.
Non-proportional multiaxial low-cycle fatigue (MLCF) tests were performed on CP-Ti at different multiaxial strain ratios. The optical microscopy observations and life prediction models verified that the critical plane of CP-Ti was the maximum principal strain plane and that it was effective under non-proportional loading. A non-proportional life coefficient and strain energy density coefficient are proposed. Typical MLCF life prediction models, such as the ESN, FS, KBM, and KBM-P models, are discussed under non-proportional loading. Finally, by associating the newly defined non-proportional life coefficient with the non-proportional hardening factor, two comprehensive non-proportional MLCF life prediction models are established, which have higher accuracies than those of previous models.
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.
The drive for increasing fuel efficiency and decreasing anthropogenic greenhouse effect via lightweighting leads to the development of several new Al alloys. The effect of Mn and Fe addition on the ...microstructure of Al‐Mg‐Si alloy in as‐cast condition was investigated. The mechanical properties including strain‐controlled low‐cycle fatigue characteristics were evaluated. The microstructure of the as‐cast alloy consisted of globular primary α‐Al phase and characteristic Mg2Si‐containing eutectic structure, along with Al8(Fe,Mn)2Si particles randomly distributed in the matrix. Relative to several commercial alloys including A319 cast alloy, the present alloy exhibited superior tensile properties without trade‐off in elongation and improved fatigue life due to the unique microstructure with fine grains and random textures. The as‐cast alloy possessed yield stress, ultimate tensile strength, and elongation of about 185 MPa, 304 MPa, and 6.3%, respectively. The stress‐strain hysteresis loops were symmetrical and approximately followed Masing behavior. The fatigue life of the as‐cast alloy was attained to be higher than that of several commercial cast and wrought Al alloys. Cyclic hardening occurred at higher strain amplitudes from 0.3% to 0.8%, while cyclic stabilization sustained at lower strain amplitudes of ≤0.2%. Examination of fractured surfaces revealed that fatigue crack initiated from the specimen surface/near‐surface, and crack propagation occurred mainly in the formation of fatigue striations.
•The low-cycle fatigue property of the nickel-based powder metallurgy alloy is improved by compound shot peening compared with turning.•The diffraction ring produced by the nanostructured grains on ...the outermost surface after compound shot peening was observed.•The anti-fatigue effect of compound shot peening is analyzed from relieving surface stress concentration and strengthening surface material.
In this study, a nickel-based powder metallurgy alloy was processed via turning, ceramic bead peening, and shot peening by high-intensity cast-iron shots and low-intensity ceramic beads (denoted as compound shot peening). We investigated the surface morphology (surface stress concentration factor, Kst), the surface residual stress profile, microstructure, and the hardness gradient of three surface states and compared the high-temperature low-cycle fatigue lives. The results showed that the surface stress concentration coefficients after turning, ceramic bead peening, and compound shot peening were 2.39, 1.98, and 2.12, respectively. The average surface roughness, Sa, after turning was low, but the bottom of the tool mark was sharp, so the Kst value was higher than that after shot peening, which formed a round bottom by bead blasting. Compared with ceramic bead peening, a surface structure with a deeper compressive residual stress profile and a higher hardness gradient was formed after compound shot peening, and nanostructured features appeared on the outermost surface. The estimated low-cycle fatigue lives after the ceramic bead peening and compound shot peening were 0.99 and 3.13 times longer than after the turning process respectively with strain amplitude 0.5% at 538℃. Moreover the gain of compound shot peening on low cycle fatigue performance gradually decreases with the increase of the strain amplitude.
•Both LTA and HTA leads to a homogeneous, non-textured, fine-grained martensitic microstructure.•Tensile tests reveal a noticeable high strength-ductility product (30,000 MPa-%) for LTA and HTA.•CDRs ...show a good reproducibility of LCF experiments without pronounced hardening or softening.•The influence of mean stress during LCF was assessed by the Smith-Watson-Topper damage parameter.•Energy-/cost-intensive HTA treatment can be avoided (no pronounced loss of performance)
Mold steels, usually being used for dies in low-temperature die casting or in molds for plastic injection, can additionally be considered as material of choice in precision optomechatronics. In any case, these steels will suffer from cyclic loading during their service life. Thus, despite of the envisaged application, the fatigue behavior must be studied comprehensively. In the present study, microstructure and mechanical properties, especially the low-cycle fatigue behavior, of a novel high-strength mold steel were investigated focusing on two different heat treatment conditions, i.e., low- and high-temperature annealing (LTA and HTA). The mechanical behavior being elaborated by tensile tests and strain controlled fatigue tests is discussed based on microstructural insights revealed by electron backscatter diffraction and fracture surface analysis. The results obtained indicate, that a more energy- and cost-intensive HTA treatment can be avoided without pronounced loss of mechanical performance.
•There is a lack of guidance with respect to the appropriate size of a stop hole that is usually determined based on the judgment of the attending surveyor/inspector.•In the present paper, a method ...is proposed for determining the appropriate size of a stop hole for cracked marine and offshore structures.•In addition to the traditional concerns over the size and nature of the crack, the proposed method incorporates high-cycle and low-cycle fatigue analyses into remain service life prediction taking into account both long-term and short term wave-induced loading.
Stop holes have been widely used as temporary repair means in marine and offshore engineering to extend the service life of cracked structural components that cannot be immediately replaced. However, there is a lack of guidance with respect to the appropriate size of a stop hole that is usually determined based on the judgment of the attending surveyor/inspector. In the present paper, a method is proposed for determining the appropriate size of a stop hole for cracked marine and offshore structures. In addition to the traditional concerns over the size and nature of the crack, the proposed method incorporates high-cycle and low-cycle fatigue analyses into remain service life prediction taking into account both long-term and short term wave-induced loading. The effects of the return period of the potential severest sea condition, the crack length, and the environmental severity factor on the remaining service life of a stop hole are investigated.
In this study, we report the effect of cerium (Ce) addition on the tension-compression yield and cyclic asymmetry in commercially pure magnesium (Cp-Mg) and Mg–Al alloy at room temperature (RT). The ...investigated materials Cp-Mg, Mg-0.5Ce, and Mg–3Al-0.5Ce were extruded at 400 °C, followed by annealing at the same temperature for 1 h. Incorporating 0.5 wt% Ce in pure Mg results in the weakening of its basal texture, uniform distribution of Mg12Ce precipitates, and grain size refinement. Consequently, the tensile yield strength and ductility of pure Mg increased, and tension-compression yield asymmetry was eliminated. However, the presence of 3 wt% Al in Mg suppresses the beneficial effects of Ce addition. The formation of non-uniformly distributed complex precipitates, such as Mg–Al–Ce and Al11Ce3, limits the weakening of the basal texture, reduction in grain size, improvement in ductility, and elimination of tension-compression yield asymmetry observed in Mg-0.5Ce. Nevertheless, Al contributes to the solid solution strengthening in Mg and possibly lowers the critical stress required for twinning in Mg, resulting in the highest tensile strength of Mg–3Al-0.5Ce. Finally, the addition of 0.5 wt% Ce enhances the cyclic strength, stabilizes cyclic stress response, reduces inelastic strain, and minimizes cyclic asymmetry in both pure Mg and Mg–Al alloy while maintaining a comparable fatigue life. Overall, Ce addition positively impacts the microstructure and mechanical behavior of pure Mg and its investigated alloy. The reasons for these improvements are discussed in detail.
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