Hysteresis Curves Research Articles

Formation of magnetite within the droplet phase of immiscible glass

An immiscible glass system consisting of a continuous silica-rich phase and a discontinuous droplet phase enriched in phosphorus form the glassy framework for a novel magnetite glass-ceramic. Upon cooling from the molten state, the material phase separates into the droplet-in-matrix structure and magnetite precipitates spontaneously within the phosphorus-enriched droplet phase. Magnetic hysteresis curves of an exemplary magnetite glass-ceramic show a saturation magnetization of ∼20 emu/g and magnetic remanence of 2.6 emu/g for a maximum externally applied field of 30 kOe. This novel material space provides a simple and economical means to produce magnetite glass-ceramics with potential suitability for a variety of biomedical applications.

Study on seismic performance of RC columns strengthened with CFRP-steel tube self-compacting concrete

In order to study the seismic performance of Reinforced Concrete columns strengthened with Carbon Fiber Reinforced Polymer-steel tube self-compacting concrete, seven strengthened columns and one unstrengthened column were designed and manufactured with the main parameters of axial compression ratio, self-compact concrete strength, steel tube shape and steel tube thickness. The hysteresis curve, skeleton curve, ductility, energy dissipation capacity, stiffness, steel tube surface and steel bar strain variation of the specimens were analyzed. The test results show that the strengthened part of the specimen has good cooperative working ability with the RC column, and the failure process and failure mode of the specimen are similar to those of the concrete filled steel tube. Under the action of horizontal reciprocating load, the concrete at the bottom of the strengthened column is cracked; with the increase of horizontal displacement, the hysteresis curve becomes full and the energy dissipation capacity increases. The finite element software ABAQUS is used to model and analyze the specimens. The simulation results are in good agreement with the experimental results. It is proved that the simulation is reasonable and effective in unit selection, contact setting, meshing and material constitutive selection. The hysteresis curve, skeleton curve and failure mode of each specimen are obtained.

Experimental study of a novel prestressed precast concrete beam-to-column joint based on plastic hinge relocation

To avoid the difficulties and high costs associated with traditional prestressed dry joints in construction, a novel post-tensioned precast concrete frame based on plastic hinge relocation (PPFBP) beam-to-column joint is proposed in this study. The precast columns and beams were integrated solely through the application of post-tensioned (PT) strands. The combined use of the haunched beams and the vertical slots for plastic hinge relocation simplifies the connection of the joint and enhances assembly efficiency. The mechanism of the proposed joint is analyzed first, followed by the development of a complete design procedure that complies with the criteria for plastic hinge relocation and self-centering. Three full-scale interior beam-to-column joints were designed and tested under cyclic loading to investigate the seismic performance in hysteresis curves, ductility, energy dissipation capacity, and residual displacement. The results indicate that the bearing capacity and ductility of the proposed joint are similar to those of cast-in-place structures, with the advantage of minimal residual displacement, enabling rapid post-earthquake repairability. The hysteresis curve of PPFBP joint with plastic hinge relocation exhibits a flag shape, indicating significant self-centering capability and energy dissipation ability. The cumulative energy dissipation of PPFBP joint with plastic hinge relocation is much higher compared to that without it, achieving a maximum equivalent viscous damping coefficient of about 15 %, which is similar to that of hybrid dry joints. The insufficient strength of the prestressed grouting material led to bond slippage in the specimen with bonded PT strands, exhibiting a hysteresis response similar to that with partially bonded PT strands. Finally, the prediction of the bearing capacity in PPFBP joint is consistent with the experimental results, validating the effectiveness of the proposed design method.

Micromagnetic behavior of permalloy (Ni80Fe20) nanodots as a function of aspect ratio

We present the results of computational micromagnetic simulations at zero temperature under free boundary conditions for Permalloy nanodots. The nanodot’s diameter (D) was varied from 20 to 120 nm, and the thickness (t) ranged from 4 to 120 nm, which allows to obtain different aspect ratios t/D. Simulations were conducted using the Ubermag platform and the Object Oriented Micromagnetic Framework (OOMMF). The hysteresis loops exhibited a strong dependence on the aspect ratio (t/D), which was evident in the narrowing of the hysteresis curves as this ratio approached unity. This phenomenon led to the formation of nucleation and annihilation fields, resulting in the formation of vortex-type magnetic textures with a central core capable of moving within the basal plane. Furthermore, the time dynamics at each step of the magnetic field were addressed by solving the time-dependent Landau–Lifshitz–Gilbert differential equation, where the system’s Hamiltonian is defined in terms of magnetocrystalline anisotropy, demagnetization, exchange, and Zeeman contributions. Energy diagrams illustrate the competition among these energies, attempting to attain their equilibrium state, thereby creating a complex energy landscape. Moreover, they operate on different orders of magnitude, whence their relative importance is discussed. Final results are summarized in a proposal of phase diagrams.

Poly(dimethyldiallylammonium chloride)-modified magnetic bentonite for removal of polystyrene nanoplastics

Nanoplastics (NPs) can contaminate water sources and living organisms, posing significant challenges for removal due to their small size and complex surface properties. There is a need to develop efficient technologies for the removal of NPs. In this study, bentonite was magnetically modified and loaded with Poly(dimethyldiallylammonium chloride) (PDMDAC) to enhance the adsorption for NPs, and improve separation and recovery efficiency. The synthesized PDMDAC-modified magnetic bentonite (PDMMB) had a high specific surface area of 49.386 m2/g and a maximum adsorption capacity of 250.50 mg/g for polystyrene nanoplastics (PS-NPs). The incorporation of PDMDAC increased the surface charge of magnetic bentonite from −39.50 mV to +37.7 mV, generating strong electrostatic attraction to the negatively charged PS-NPs (-64.3 mV). The PDMMB exhibited a saturation magnetization of 17.619 emu/g and an S-type hysteresis curve, indicating strong superparamagnetism that facilitating magnetic separation and recovery. Characterization analysis revealed that the adsorption was driven by electrostatic attraction and the Fe-O functional group. Kinetics and adsorption model analyses indicated that the adsorption mechanism involved electrostatic attraction, complexation, and single/multilayer adsorption, the adsorption process was exothermic and thermodynamically favorable. The adsorption rate remained at 86.41 % after 5 adsorption-desorption cycles. PDMMB exhibited high removal efficiency over a wide range of pH (3−10), ionic strength (0.01–0.5 mol/L), and in the presence of various anion types, indicating its potential for flexible application. The high efficiency, easy operation and excellent regeneration of PDMMB demonstrate its potential for effective removal of NPs from wastewater.

Analysis of axial force variations and seismic performance of subway station columns under earthquake loading

Central column failure is a predominant seismic damage mode in subway station structures. During seismic events, the central columns’ vertical compressive force, as indicated by the axial compression ratio (ACR), undergoes continuous variations, significantly impacting both their failure modes and the seismic performance. This study involved establishing a finite element model of a subway station and conducting time history analyses to identify the distinct variation patterns of ACR in central columns for various seismic design scenarios. Based on these summarized patterns, appropriate ACR variations were designed for the columns, and the validity of the column model was confirmed using experimental data, enabling analyses of their failure modes and hysteresis characteristics under cyclic loads. Lastly, a sensitivity analysis of the parameters associated with the central columns was performed. The results demonstrated that the horizontal displacement and the ACR of the top of the central column were asynchronous, the frequency of the latter was 1.4–3.8 times that of the former, and the amplitude of the ACR was 0.08–0.68. When the frequency of the variable ACR was odd times, the damage and hysteresis curve of the column showed obvious asymmetry and harmfulness, and it exacerbated the damage to the core concrete of the column. Compared to applying a constant ACR, the bearing capacity and energy dissipation of the column were even reduced by about 50 % and 74 %, respectively. The specimens with the upper limit value of 0.95 of variable ACR had even more adverse effects on the damage and hysteresis behavior of the column than the scheme with a constant ACR of 0.95. In addition, the even multiple frequency of variable ACR had a limited effect on the seismic performance of the column, but the harm caused by the large amplitude variation of variable ACR could not be ignored. As to the impacts of structural parameters under cyclic loadings, elevating the longitudinal reinforcement ratio and decreasing the stirrup spacing within the central columns would substantially enhance energy dissipation capacity, with a maximum increase of about 69 %. Meanwhile, for columns with the same cross-sectional area, square columns exhibited superior hysteresis behavior compared to their circular counterparts. The findings of this study could provide guidance for the engineering design of the central columns.

Seismic performance of the ST-RC columns to RC beams exterior joint with assembled connection details

An innovative composite column type, the steel tube-reinforced concrete column (ST-RC), consists of a core of concrete-filled steel tube (CFST) and reinforced concrete (RC) encasement. This study aims to validate the reliability of two convenient and rapid assembly methods between RC beams and ST-RC columns. Four full-scale beam-column joint specimens were tested, comprising two prefabricated assembly joints of ST-RC column-RC beam frames, one integrally cast joint of ST-RC column-RC beam frames, and one traditional integrally cast joint of RC column-RC beam frames for comparison. The experiments were conducted based on the principles of a self-balanced system, and quasi-static tests under constant axial compression on the ST-RC columns were performed. Hysteresis curves, skeleton curves, failure modes, strength degradation, energy dissipation capacity, stiffness degradation, deformation capacity and the influence of connection method and joint form on mechanical performance were analyzed and obtained based on the test results. The results indicate that, compared to integral casting, the assembly surrounding method with steel sleeves reduces specimen energy dissipation by 19.8 % and damping ratio by 21 % at 4 % drift, with minimal impact on other mechanical properties. In contrast, reinforcement surrounded and connected by steel plates reduces initial stiffness and peak load-carrying capacity by 1.0 %, along with decreasing negative ductility. It also lowers total energy dissipation by 37.4 % and damping ratio by 45.4 % due to compressive effects from bottom steel plate connections. Despite these effects, its impact on negative ductility and load-carrying capacity remains minimal. Additionally, experimental observations and rebar strain data indicate higher stress on rebars at the base of steel plate connection beams, suggesting a need to strengthen transverse rebars at the beam’s base. The study confirms the feasibility of two convenient and rapid assembly methods for the joints of ST-RC column. Both methods meet current Chinese standards for MCE, with failure modes characterized by “strong columns and weak beams” in both cases.

Advanced cyclic constitutive model and parameter calibration method for austenitic stainless steel

Austenitic stainless steel is recognized for its potential in improving structural seismic resistance due to its exceptional ductility. This study seeks to analyse the material characteristics and cyclic constitutive model of austenitic stainless steel under cyclic loading using a combination of experiments and numerical studies. The primary goal is to enhance the precision of numerical simulations predicting the seismic performance of stainless steel and to minimize the costs associated with calibrating the parameters of the cyclic constitutive model. By conducting cyclic loading experiments on stainless steel with different plate thicknesses, the hysteresis curves under different loading protocols were obtained. The loading protocol significantly influences the cyclic hardening behaviour of stainless steel. To calibrate material parameters in the Chaboche model more effectively, a new parameter calibration method based on genetic algorithm optimization is proposed. Additionally, a method is proposed to calibrate the material parameters of the Hu model by utilizing the monotonic tensile stress-strain curve of austenitic stainless steel, which provides a new material model option for the numerical simulation of stainless steel seismic performance. The applicability of the Chaboche model and the Hu model in numerical simulations of stainless steel members is then verified and compared using existing seismic performance test results. The findings indicate that the Hu model offers more accurate numerical simulations of cyclic loading on austenitic stainless steel members compared to the Chaboche model.

Effect of loading sequence on the ultra-low-cycle fatigue performance of all-steel BRBs

Buckling-restrained braces (BRBs) are intended to protect the primary structure of buildings by absorbing most earthquake input energy through the plastic deformation of the steel cores. The ultra-low-cycle fatigue performance of BRBs is crucial for their seismic performance as energy dissipators. Despite the plenty of research on the ultra-low-cycle fatigue behavior of steel members, it remains susceptible if arbitrary loading paths have a major effect on the ultra-low-cycle fatigue life or cumulative plastic deformation (CPD) capacity of BRBs. This paper introduces an experimental campaign of nine supposedly identical BRB specimens subjected to three different loading protocols of similar average strain amplitudes. For each loading protocol, the test was repeated for three times to account for possible uncertainty. The results show that the effect of loading protocol is trivial given the similar average strain amplitudes throughout the loading. The Miner's assumption that the loading sequence has no effect on the fatigue life of BRBs is supported by the test results, however, the proper choice of the Coffin-Masson model's parameters is crucial. The skeleton ratio, which is derived from decomposing the hysteresis curve into a skeleton part and a Bauschinger part and has been used to account for the loading path effects, is shown to be insensitive to varied loading protocols by the test results.

Seismic Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube Flanges and Honeycomb Steel Webs Subjected to Freeze-Thaw Cycles

To investigate the seismic behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycomb steel webs (STHHC) after being subjected to freeze-thaw cycles, 36 full-scale STHHCs were designed with the following main parameters: the shear span ratio (λs), the axial compression ratio (n0), the number of freeze-thaw cycles (Nc), the concrete cubic compression strength (fcu), and the steel ratio of the section (αs). Compared with existing experimental data, the validity of the finite element modeling method was verified. Parameter analysis was conducted on 36 full-scale STHHCs to obtain the hysteresis curve of the composite columns and to clarify the impact of the different parameters on the skeleton curve, the energy dissipation capacity, the stiffness degradation, and the ductility of the composite columns. The results showed that the hysteresis curves of all specimens after freeze-thaw cycles exhibited an ideal shuttle shape, reflecting that this kind of composite column has good energy dissipation ability and freeze-thaw resistance. The specimens’ maximum bulging deformation and maximum stress both occurred at the column base. Finally, the restoring force model of this kind of composite column is therefore established, and design recommendations based on these results are proposed.

Seismic performance of an innovative self-centering and repairable connection with SMA bolts in modular steel construction

Modular steel construction (MSC) is widely noticed and adopted in the building industry for its benefits of short construction period, low carbon emission, and great flexibility. The performance of inter-module connections, including the strength, toughness and ductility, is the focus of maintaining the load transfer mechanism and overall stability of modular structures. The structure with favorably designed connections can dissipate expected energy under cyclic loading with reduced structural damage. A self-centering and repairable connection (SRC) is herein proposed, with the benefits of a distinct load transmission path and easy assembly. Four full-size specimens were fabricated and tested under low-cycle loading, and the tested specimens were subsequently repaired by replacing angle cleats. The failure mode and bearing capacity of both SRC and repaired SRC specimens were investigated. Several seismic performance indices of the specimens, including hysteresis curves, strength and stiffness degradation, energy dissipation capacity, self-centering and repairable ability, were obtained. Furthermore, the performance of the SRC was comprehensively assessed according to Eurocode 3 Part 1–8, Chinese code GB 50011-2010, and American code AISC 341-16. In addition, an accurate finite element model (FEM) of the SRC was created and verified using experimental results. The developed FEM was used to investigate the effects of critical parameters, including angle cleat thickness and grade, vertical bolt diameter, and SMA bolt number and diameter, on the seismic performance of SRCs. Both experimental and FEM results show that only the replaceable angle cleats experienced the noticed plastic deformation for SRC specimens under cyclic loading, and SMA bolts provided the required self-centering force. It can be hence concluded that the proposed SRC can achieve the expected self-centering and recovery function.

Hydrophobic modification enhances the microstructure stability of the catalyst layer in alkaline polymer electrolyte fuel cells.

Alkaline polymer electrolyte fuel cells (APEFCs) have achieved notable advancements in peak power density, yet their durability during long-term operation remains a significant challenge. It has been recognized that increasing the hydrophobicity of the catalyst layer can effectively alleviate the performance degradation. However, a microscopic view of how hydrophobicity contributes to the stability of the catalyst layer microstructure is not clear. Here, we construct a membrane electrode assembly (MEA) with enhanced structural stability and durability by incorporating polytetrafluoroethylene (PTFE) particles into the catalyst layer. MEAs modified by this approach exhibit stabilized voltage platforms in current step tests and reduced hysteresis in current-voltage polarization curves during operation, indicating the critical role of PTFE in the removal of the excess water within the catalyst layer. Fuel cells with PTFE modification show more than 45% increase in electrochemical durability. By characterizing with field-emission scanning electron microscopy (FE-SEM) the surface and the internal microstructures of MEAs after durability tests, we find that the catalyst layers modified by PTFE experience much less reduction in porosity and less agglomeration of the solid components. These findings elucidate the microscopic mechanisms by which hydrophobicity promotes a more stable catalyst layer structure, thereby enhancing the durability of APEFCs. This research advances our understanding of hydrophobicity's impact on catalyst layer stability and offers a practical method to enhance the durability of APEFCs.

Wind-induced vibration and control of truss string structures subjected to thunderstorm downbursts

This study investigates the wind-induced vibration response of TSSs under thunderstorm downbursts and introduces self-centering braces to analyze the vibration control. The study reveals that the vertical peak displacement of the upper chord nodes exhibits a “V” shaped distribution along the span direction, while the vertical residual displacement follows an “S” shaped distribution. The wind-induced vibration response at the cantilevered end is much stronger, and after the introduction of self-centering braces, the wind-induced vibration response significantly decreases, indicating that the self-centering braces play a noticeable role in controlling wind vibration. Additionally, the cable forces of the TSS significantly decrease under thunderstorm downbursts, with a loss of about 68%. The residual cable forces are uniformly distributed for the original structure and show a minor correlation with cable locations, whereas the residual cable forces of the structure with self-centering braces have a higher correlation with the cable locations. The residual cable force is significantly reduced after installing the self-centering braces, with a maximum reduction of 57.22%. Furthermore, the self-centering braces have a full hysteresis curve under thunderstorm downbursts, which indicates that it has high energy dissipation capacity and a good self-centering effect, which is conducive to controlling the wind vibration response of the structure under thunderstorm downbursts.

Experimental Study on a Damage-Control and Repairable Fully Precast Beam-Column Joint

ABSTRACT A novel joint with a splice lap was proposed, which was damage-control and repairable fully precast beam-column joint (DRBJ) connected by energy-dissipating connecting steel plates to remarkably diminish the residual displacement of an RC frame under strong earthquakes and ensure the rapid rehabilitation of the structure. Four one-half scale beam-column-joint specimens were designed and fabricated in different connection forms and lap lengths, and one of the specimens was loaded again under the same conditions after repair. Low cyclic loading tests on DRBJ were conducted to investigate their hysteresis curves and energy-dissipation capacities. The test results revealed that the plastic deformation of DRBJ was concentrated on connecting steel plates, while the residual displacement was small. The deformation and bearing capacities of the short-lap joint were higher than those of the long-lap junction, and the bearing, energy consumption, and deformation capacities of the DRBJ connected by strip plates were still superior to those of the DRBJ connected by the rectangular plates. The DRBJ showed satisfactory repairability and energy-dissipation capacity with the help of the strip plates. A simplified force–displacement model was established based on the analysis of the functioning mechanism of DRBJ. The calculated results of the rotational stiffness and the test results agree well, which can provide a reference for the design of this type of splice joint.

HSC-RSW with laterally installed XADAS dampers: Seismic performance

This study investigates the seismic behavior of high-strength concrete (HSC) rocking shear walls (RSW) equipped with X-shape Adding Damping and Stiffness (XADAS) dampers installed perpendicular to the wall via brackets. Unlike previous studies where dampers are integrated along the wall length, this research leverages the advantages of HSC to minimize sectional dimensions while employing laterally installed XADAS dampers to enhance the cyclic response, yielding flag-shaped hysteresis curves. The alignment angle of the XADAS dampers is also considered a crucial variable in assessing the overall seismic performance of the proposed HSC-RSW system. A novel constructional approach using brackets to install lateral XADAS dampers is implemented. Post-tensioning (PT) forces are applied as consistent axial strains in cables, achieved through predefined cable support displacements. A macro-FEM model is developed to validate the chosen experimental reference test and is subsequently used for further parametric studies. The parametric studies indicate that increasing concrete compressive strength (CCS) enhances the self-centering capability by reducing RSW strains and facilitating rocking. Additionally, incorporating XADAS dampers into the system improves energy dissipation, with a zero-degree alignment angle identified as optimal. Notably, the modeled HSC-RSW systems exhibit limited drift capacity (less than 2 %) compared to normal strength concrete (NSC)-RSW systems, where wall toes are conventionally prone to crushing.

Out‐of‐plane response of prefabricated concrete shear walls connected via grouted sleeves

AbstractThe out‐of‐plane response of prefabricated (precast) concrete shear walls (PWs) are usually neglected in the structural designs. However, because of the relatively low stiffness and inevitable deformation of slabs, the out‐of‐plane behavior of PWs could influence the in‐plane response by causing premature failure or stability problems and affect the overall structural performance. This issue becomes significant when single‐row connections are employed because the neutral axial is shifted toward the compression side and the out‐of‐plane capacity is altered accordingly. In this study, PWs with grouted steel sleeve splices were tested under reciprocating cyclic loading. Both single‐row and paired connections were considered in test program. It was shown that all PWs suffered bending failure dominated by yielding of reinforcement at the bottom, and their load‐carrying capacity, stiffness degeneration trends were similar to the monolithic (cast‐in‐place) reference walls. Under the normalized compression of 0.12, the ductility of the prefabricated walls was 2.62 and 3.07, which was comparable to that of the reference cast‐in‐place wall (2.72). For the case that axial compression was not applied, the hysteresis curve of the PW with single‐row connection exhibited significant pinching. Nonetheless, the load‐carrying capacity of these walls did not exhibit significant drop at the end of the tests due to the lower axial compression, exhibiting high level of deformability. For both load cases, PWs with paired connection exhibited higher energy dissipation than the single‐row connected specimens.

Experimental and numerical study on seismic behavior of shear wall with cast‐in situ concrete infilled walls

AbstractThe shear wall system with cast‐in situ concrete infilled walls has been widely used in high‐rise buildings due to its significant advantages in construction. In this paper, quasi‐static tests were conducted on the shear walls with and without cast‐in situ concrete infilled walls to analyze their failure modes, load‐bearing capacity, stiffness, energy dissipation capacity, and ductility. A simplified model of the shear wall with cast‐in situ concrete infilled walls was proposed based on the fiber element model in OpenSees. The test results showed that the shear wall specimens with cast‐in situ concrete infilled walls exhibited full‐section compression or tension failure, and the cast‐in situ concrete infilled walls did not show obvious damage. Compared with the shear wall without infilled walls, the overall stiffness, load bearing capacity, and energy dissipation capacity of the shear wall specimens with cast‐in situ concrete infilled walls improved, indicating better seismic performance than those without infilled walls. Comparison between the hysteresis and skeleton curves derived from the tests and those simulated by the proposed simplified model revealed errors within 15% for stiffness, yield bearing capacity, and ultimate bearing capacity for shear walls with cast‐in situ concrete infill walls, affirming the effectiveness and accuracy of the model.

Modeling and identification of hysteresis of marine damper considering shock environment based on evolutionary sparrow search algorithm

The mechanical properties of marine dampers are usually highly nonlinear in order to adapt to dynamic and shock environments. The dampers are subjected to dynamic and shock tests and the hysteresis curves are found to be rate-dependent and asymmetric. To be able to describe the dynamic hysteresis and shock hysteresis, a rate-dependent generalized Prandtl-Ishlinskii (RDGPI) model is proposed based on the generalized Prandtl-Ishlinskii (GPI) model, which is a hybrid of the GPI model and the radial basis function (RBF) neural network. Due to the large number of parameters in the model, thus aiming to improve the effect of parameter identification, an evolutionary sparrow search algorithm mixed with sparrow search algorithm and differential evolutionary algorithm is proposed. Compared with other algorithms, sparrow search algorithm is verified to have ideal optimization effect and convergence speed, and it is not easy to fall into the local optimum. Finally, the RDGPI model is experimentally verified, and the results show that the prediction error of the RDGPI model for dynamic hysteresis is within 0.06 kN, and the prediction error for shock hysteresis is within 0.8 kN, which is capable of describing the rate-dependent characteristics of the damper hysteresis. And it has a very good generalization ability, which makes it very suitable to be used in the modeling of the mechanical characteristics of the marine damper.

Small polaron hopping and tunneling mechanisms in Ba0.9La0.1Fe12O19 hexaferrite ceramic at low temperatures

The correlation between dielectric relaxation and conduction mechanisms in the Ba0.9La0.1Fe12O19 ceramic hexaferrite, at temperatures below 100 K was investigated. The sample was prepared using the conventional solid-state reaction method. X-ray diffraction analysis indicated that the sample is composed of a hexagonal BaFe12O19 phase (lattice parameters a = 5.8778(6) Å and c = 23.170(3) Å) and a small proportion of hematite (α-Fe2O3). The average grain size is 1.48 ± 0.4 μm, with irregular hexagonal and agglomerated grains. The magnetic hysteresis curve shows characteristics typical of ferro and ferrimagnetic materials, with an effective magnetic anisotropy coefficient of 0.960×106 emu/cm3 and an anisotropy field of 1.587×104 Oe. A dielectric relaxation process is observed between 50 and 100 K, with an activation energy of 60.4 ± 0.4 meV and a characteristic relaxation time of 2.09 ×10−10 s, mainly attributed to the electrical behavior of the grains. Two conduction mechanisms were identified: small polaron tunneling (high temperatures and low frequencies) and correlated barrier hopping of electrons (low temperatures and high frequencies). The activation energy for free polaron formation, according to the Komine-Iguchi hopping polarization model, was 7.12 ± 0.02 meV. In the dielectric modulus relaxation process between 30 and 54 K, the activation energy was 40.8 ± 0.9 meV, with a characteristic relaxation time of 2.41×10−10 s. The small polaron conductivity in the grain region was 67.52 meV and 54.0 meV in the grain boundary region. The results highlight that the polarization and conduction mechanisms in this ceramic at low temperatures are dominated by small polaron hopping and tunneling, and emphasize the influence of La3+ doping on the structural, magnetic, and electrical properties of barium hexaferrite.

Experimental study on seismic performance of two-story two-bay. Precast concrete frame with UHPC-based connections

The UHPC-based connections, utilizing Ultra-high performance concrete (UHPC) to connect rebars within precast concrete structures, present the advantages of short splice length, simplified construction, and low cost due to the excellent bond property between UHPC and rebars. This investigation focuses on seismic performance of precast concrete frame (PCF) with UHPC-based connections. The UHPC-based connections were arranged strategically to the beam-column joints and column bases in PCF to connect longitudinal rebars of beams and columns, respectively. Two half-scale, two-story, two-bay reinforced concrete frames, including PCF and a monolithic concrete frame (MCF) for reference, were tested under cycle loading with axial compression ratios of 0.33 in the middle columns and 0.22 in the side columns. The results revealed that PCF exhibited a beam sway mechanism, with all beam hinges developed prior to column hinges, while MCF displayed a mixed sway mechanism, with part of beam hinges developed prior to column hinges. The hysteresis curves of the two frames were globally stable with minimal pinching, and PCF displayed greater energy dissipation compared to MCF. The load-carrying capacity of PCF was 9 % higher than that of MCF. The displacement ductility of PCF was 4.14, exceeding that of MCF by 10 %. The two frames showed similar laws of stiffness degradation. Overall, the precast concrete frame with the UHPC-based connections exhibited better seismic performance in comparison with the monolithic counterpart.