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A high strength and ductile Mg-Gd-Y-Zn-Zr alloy was designed and fabricated. The local strain evolution of the alloys during plastic deformation was analyzed using high-resolution digital image correlation (DIC). The results showed that the β particles, nano-sized γ' phases, and LPSO phases were distributed in the as-extruded alloy and a bimodal microstructure was exhibited, including elongated un-dynamic recrystallized grains and fine dynamic recrystallized grains. With increasing extrusion ratio, the grain size remained, with the volume fraction of dynamic recrystallization of the as-extruded alloy increasing from 30% to 75%, and the as-extruded alloy exhibited a high strength-ductility synergy, which is attributed to the grain refinement, extensive β particles, and elongated block-shaped LPSO phases. The strain evolution analysis showed that a strain-transfer from un-DRXed regions to adjacent DRXed regions and LPSO phases can promote uniform plastic deformation, which tends to improve the ductility of the alloy. [ABSTRACT FROM AUTHOR]

The addition of superelastic shape memory alloy fibers (SMAF) into engineering cementitious composites (ECC) can create a new type of SMAF-ECC composite material with good self-recovery and energy dissipation performance, which is very suitable for seismic structures. In this study, 10 groups of beam specimens with different volume contents of SMAF were fabricated, and the bending performance, deflection recovery and energy dissipation ability of these beams were studied through three-point bending cyclic loading tests. The failure mode, peak load, load–deflection curve, crack width and other indicators of the specimens were analyzed, and the relationship expression between fiber content and bending strength was established by fitting analysis. The results show that adding SMA fibers can significantly improve the peak load of ECC beams, with a maximum increase of 48.31%. The knotted SMA fibers can fully exert their superelasticity, providing the beam specimens with crack self-closing and deflection recovery ability. When the volume content of SMA fibers is 0–0.6%, the bending strength, energy dissipation ability and deflection recovery ability of the composite material beams increase with the increase in fiber content. When the volume content of SMA fibers is 0.6–1.0%, the above indicators decrease with the increase in fiber content. The suggested equations can well reflect the relationship between fiber content and beam bending strength. The research results of this paper provide theoretical support for the engineering application of SMAF-ECC composite materials. [ABSTRACT FROM AUTHOR]

Combining Engineered Cementitious Composites (ECC) with shape memory alloy (SMA) fibers can form SMA fiber reinforced ECC (SMAF-ECC) that has excellent deformation recovery and energy dissipation capabilities. Substituting some of the tensioned concrete with this new composite material, along with steel bars, is expected to significantly improve the seismic energy dissipation and self-recovery capabilities of traditional reinforced concrete components. However, a reliable bond between steel bars and SMAF-ECC is critical to ensure their synergistic performance. In this paper, the failure mode and bond strength of steel bars and SMAF-ECC were studied through direct tensile tests, and the influence factors such as steel bar diameter, bond length, and SMAF volume fraction were analyzed. A bond-slip constitutive model for steel bars and SMAF-ECC was proposed. The results show that the failure mode of the tensile test specimens is mainly steel bar pull-out failure; the incorporation of SMAF significantly enhances the bond strength between the steel bar and matrix; increasing the steel bar diameter and bond length both lead to a decrease in bond strength while increasing the SMAF volume fraction can significantly increase the bond strength. Among them, the specimen with a steel bar diameter of 12 mm, bond length of 70 mm, and SMAF volume fraction of 0.5% has the largest increase in bond strength, reaching 52.96%. The proposed improved bond-slip constitutive model is in good agreement with the bond-slip curve obtained in the experiments, with a determination coefficient of 0.99. The research results of this paper provide an important theoretical basis for promoting the engineering application of SMAF-ECC materials. [ABSTRACT FROM AUTHOR]

SMAF-ECC material composed of shape memory alloy fiber (SMAF) and engineered cementitious composite (ECC) has good bending and tensile properties, as well as good crack self-healing ability, energy consumption, and self-centering ability. The bond behavior between fiber and matrix is crucial to the effective utilization of the superelasticity of SMAF. The experimental study considered three variables: SMA fiber diameter, fiber end shape, and bond length. The pullout stress–strain curve of SMAF was obtained, and the maximum pullout stress, maximum bond stress, and fiber utilization rate were analyzed. Compared with the straight end and the hook end, the maximum pullout stress of the specimen using the knotted end SMAF is above 900 MPa, the fiber undergoes martensitic transformation, and the fiber utilization rate is above 80%, indicating that the setting of the knotted end can give full play to the superelasticity of the SMAF. Within the effective bond length range, increasing the bond length can increase the maximum anchorage force of the knotted end SMAF. Increasing the fiber diameter can increase the maximum pullout stress and maximum anchoring force of the knotted end SMAF but reduce the utilization rate of SMA fiber. This study provides a reliable theoretical basis for the bonding properties between SMAF and ECC. [ABSTRACT FROM AUTHOR]

Quantitative calculation and evaluation of seismic damage are very important for structural safety, performance-based structural analysis, and seismic reinforcement. However, the relevant research results for precast concrete structures are extremely limited. In this paper, the seismic damage evaluation of beam-column joints in monolithic precast concrete frames was studied through cyclic loading tests and damage index calculation. The seismic damage process, load-displacement relationship, stiffness degradation, and the influence of axial compression ratio were analyzed, then the damage indexes were calculated and analyzed, and the quantitative evaluation of joint damage was conducted last. The results show that the connection seams can significantly affect the mechanical properties of precast joints, easily causing damage concentration, resulting in a lower bearing capacity and faster stiffness degradation compared with a cast-in-situ joint. A larger axial compression ratio can bring higher bearing capacity for the precast joints, and the peak load can be increased by 42.9% when the axial compression ratio is increased from 0.2 to 0.4. In contrast, the stiffness degradation will be accelerated with the increase in the axial compression ratio. From yield load to peak load, the stiffness of the precast joint with the largest axial compression ratio decreases by 46.0%, while the joint with the smallest axial compression ratio is only 36.4%. The damage index model adopted in this paper can accurately reflect the damage characteristics of the precast joints. The presented damage states based on the damage index calculation can accurately reflect the joint's damage characteristics according to different stages. The paper realizes the quantitative damage evaluation for this kind of joint and provides a theoretical basis and method for further studies. [ABSTRACT FROM AUTHOR]

The incorporation of superelastic shape memory alloy (SMA) fibers into engineered cementitious composite (ECC) materials can provide high seismic energy dissipation and deformation self-centering capabilities for ECC materials. Whether the SMA fibers can be sufficiently bonded or anchored in the ECC matrix and whether the mechanical properties of the SMA fibers in the ECC matrix can be effectively utilized are the key scientific issues that urgently need to be studied. In order to study the mechanical behavior of SMA fiber embedded in ECC matrix, four groups of semi-dog-bone pullout specimens were fabricated, and the cyclic pullout tests were conducted in this paper. The pullout stress, displacement, and self-centering capability were analyzed, and different influencing factors were discussed. The results show that the knotted ends can provide sufficient anchorage force for SMA fibers, and the maximum pullout stress of SMA fiber can reach 1100 MPa, thus the superelasticity can be effectively stimulated. The SMA fibers show excellent self-centering capability in the test. The minimum residual deformation in the test is only 0.29 mm, and the maximum self-centering ratio can reach 0.93. Increasing bond length can increase the ultimate strain of SMA fibers with knotted ends, but reduce the maximum pullout stress. Increasing fiber diameter can increase both the ultimate strain and the maximum stress of knotted end SMA fibers. While neither bond length nor fiber diameter has significant effect on the self-centering ratio. This paper provides a theoretical basis for further study of the combination of SMA fibers and ECC materials. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of an antibacterial 50Cr15MoVCu tool steel were studied. The flow stress curves presented three typical characteristics: (i) a single peak dynamic recrystallization curve, (ii) a monotone incremental work-hardening curve, and (iii) the equilibrium dynamic recovery curve. The flow stress increased with the increase of the deformation rate at each deformation temperature and decreased with the increase of the deformation temperature at the same deformation rate. The thermal activation energy and material constants were Q of 461.6574 kJ/mol, A of 3.42 × 1017, and α of 0.00681 MPa−1, respectively. The high temperature constitutive equation was: Z = ε ˙ exp Q / RT = 3 . 42   ×   10 17 sinh 0. 0068   ×   σ 5. 6807 . Based on the processing maps and microstructure evolution, the best hot working process was a deformation temperature of 1050 °C and deformation rate of 0.001 s−1. [ABSTRACT FROM AUTHOR]

The combination of superelastic shape memory alloy fibers and ECC materials can form a new SMA fiber reinforced ECC composite material (SMAF-ECC) with good self-centering performance. In order to study the self-centering performance of the new composite material, 6 groups of pre-notch beam specimens were made for three-point bending cyclic loading tests, and the failure phenomenon, hysteresis curve, self-centering effect and influencing factors of the specimens were analyzed. The research results show that when the SMA fibers are effectively anchored in the ECC matrix, the SMA fibers can exert the superelastic properties to provide the ECC beams with recoverying force, and realize the crack self-closure and deflection self-recovery function for the beams, with the minimum residual crack width and deflection is only 0.9 mm and 1.3 mm respectively. Increasing fiber content can cause a small increase in the self-centering ability of the beams. However, only when the fiber diameter is appropriate, better self-centering effect can be achieved, but the difference caused by fiber diameter in the test was only 5%. SMA Fiber end forms have significant influence on self-centering performance. The knotted end beam can get a more than 70% self-centering ratio, while the straight end beams and bended end beams have no self-centering ability. The research results provide important reference for the research and application of this new self-centering materials and their structures. [ABSTRACT FROM AUTHOR]

The influence of Si, Cu, B, and trace alloying elements on the conductivity of aluminum die cast 12 (ADC12) alloy was investigated. The conductivity decreased linearly with increasing volume fraction of the Si phase attributed to a linear decrease of the volume of the more conductive Al phase through a rule of mixtures. The conductivity also decreased with increasing Cu content, between 0~3%. The conductivity increased with increasing B content, reached the peak at 0.02% B and thereafter decreased somewhat. The mechanism was that B reacted with the transition element in the Al phase to form boride, decreasing the transition element concentration in the Al lattice, and decreasing the lattice constant. The thermal conductivity, λ, was related to the electrical conductivity, σ , by means of λ = LT σ + λ g , where L is the apparent Lorentz constant, 1.86 × 10−8; T is the absolute temperature, 293 K; λg is the lattice conductivity, 42.3 W/(m·K). [ABSTRACT FROM AUTHOR]

The oxidation behavior of body-centered cubic (bcc) structure Cr20Mn17Fe18Ta23W22 refractory high-entropy alloy (RHEA) and the microdefects induced by hydrogen ions before and after oxidation were investigated. The results revealed that compared with oxidizing Cr20Mn17Fe18Ta23W22 at 800 °C (6.7 °C/min) for 4 h (ST3, Ar:O2 = 3:1), the heating procedure of oxidizing Cr20Mn17Fe18Ta23W22 at 300 °C (6 °C/min) for 2 h and then increased to 800 °C (5 °C/min) for 4 h is more conducive to the production of oxides without spalling on the surface, i.e., HT1 (Ar:O2 = 1:1), HT2 (Ar:O2 = 2:1) and HT3 (Ar:O2 = 3:1) samples. The oxidation of Cr20Mn17Fe18Ta23W22 RHEA is mainly controlled by the diffusion of cations instead of affinities with O. Additionally, HT1 and HT3 samples irradiated with a fluence of 3.9 × 1022 cm−2 hydrogen ions (60 eV) were found to have a better hydrogen irradiation resistance than Cr20Mn17Fe18Ta23W22 RHEA. The microdefects in irradiated Cr20Mn17Fe18Ta23W22 mainly existed as hydrogen bubbles, hydrogen-vacancy (H-V) complexes and vacancy/vacancy clusters. The microdefects in irradiated HT3 were mainly vacancies and H-V complexes, while the microdefects in irradiated HT1 mainly existed as vacancies and vacancy clusters, as large amounts of hydrogen were consumed to react with oxides on the HT1 surface. The oxides on the surface of the HT3 sample were more stable than those on HT1 under hydrogen irradiation. [ABSTRACT FROM AUTHOR]