Hysteresis Curves Research Articles

Dynamic modelling and parametric analysis of a bolted joint rotor-bearing system considering stick-slip behavior at mating interface

Bolted joint structure is widely utilized in the aeroengine compress rotor systems with convenience in assembly and maintenance. Due to the inherent structure discontinuity and stick-slip behavior at the mating interface, stiffness softening and frictional energy dissipation would be generated at the mating interface, resulting in complex vibration features of the rotor system. In this work, to describe the stick-slip behavior at the mating interface of the rotor system, an Iwan-based model is introduced to describe the contact state of asperities at the multi-scale level. The corresponding model identification method is proposed based on the partial hysteresis curve of the bolted joint. After that, a dynamic model of the bolted joint rotor system is established, and its dynamic response is obtained using the Runge–Kutta method. The effect of preload and friction coefficient on the nonlinear vibration of the bolted joint rotor is evaluated in detail based on the dynamic model. The result indicates that the stiffness softening would lead to the critical speed decreasing and aggravating the vibration response of the rotor system, while the frictional energy dissipation would restrain the response amplitude and induce the self-excited vibration within the super-critical speed range. The higher preload or friction coefficient has little effect on the motion state of the rotor system within the sub-critical speed range and makes system vibration stable between the 1st- and 2nd-order critical speed while unstable at the super-critical speed range. This research helps understand the vibration features of bolted joint rotor systems under the condition of stick-slip behaviors at the mating interface.

Research on Nonlinear Behavior of Local High-Performance Concrete Beam-Column Connections.

The seismic performance index of prefabricated structures is generally obtained via experimental analysis. However, in experimental research, it is impossible that every influencing factor can be taken into account. Therefore, the finite element analysis method can be used as a supplementary method for experimental research to carry out parametric analysis of joints. Based on this test, a hysteretic model of steel bars is developed on the ABAQUS platform; meanwhile, the model is used to simulate the seismic analysis of the proposed local reinforced joints. The hysteresis curve obtained via simulation exhibits a high degree of coincidence with the experimental results. Based on the validated model, a detailed parameter analysis of prefabricated local reinforced concrete frame joints is carried out. The analysis results illustrate that the axial pressure ratio at the top of the column has a minimal impact on the joint's performance. Decreasing the stirrup ratio within the core region, enlarging the diameter of the PC steel bar, and increasing the concrete strength that is poured in the keyway and the core region can raise the cumulative energy consumption of the joints, thereby reducing the damage degree of other units and improving the maximum bearing capability of the joints.

Lateral performance of cold-formed steel framed shear walls using slitted sheathing with stiffeners

Cold-formed steel (CFS) framed shear walls with steel sheathing are promising lateral-force-resisting members of mid-rise buildings in seismic regions. Previous studies have demonstrated that steel sheathed CFS framed shear walls have high shear capacity but some shortcomings, such as the low ductility caused by the premature damage of the frame and the shear buckling of the sheathing. This paper presents an experimental study on a novel type of CFS framed shear wall with slitted steel sheathing (CFS-SSWs), which uses longitudinal slits to change the failure mode of the sheathing so that the ductility of the wall can be improved; Meanwhile, stiffeners are utilized to enhance the out-of-plane stability of the slitted sheathing and the integrity of the wall. Six full-scale CFS-SSW specimens were tested under monotonic and cyclic lateral loading. Three types of stiffening approaches (Type I, Type II and Type III) were adopted for the walls. Test results were analysed to investigate lateral performances of walls under different stiffener arrangements, including failure modes, load-displacement hysteresis curves, backbone curves, stiffness and strength degradation, and energy dissipation capacity. The measured strengths of the walls in the tests were assessed using theoretical indexes. It is found that peak loads and energy dissipation capacity of stiffened walls are noticeably higher than those of the unstiffened wall. Type II and Type III are effective stiffening approaches that could mitigate the buckling of the slitted sheathing and enable the links between the slits to reach the full plastic strength. By connecting the stiffeners and studs through stiffener connectors, Type III has the most significant enhancement on the stiffness, strength and ductility of the wall.

Effect of different configurations of end stirrups on the seismic performance of RC columns

To improve the seismic performance of reinforced concrete (RC) columns, this paper establishes the equations for the theoretical relationship of bending-shear resistance of RC columns based on the theory of truss and arch. Tests and finite element simulations are carried out on six groups of specimens with the same main reinforcement but different stirrup configurations and stirrup ratios. Based on theoretical calculations, test data, and simulation results, the hysteresis curves, failure modes, compressive deformations, main reinforcement deformations, and deformations at the ultimate limit state of carrying capacity of the RC columns are investigated. Moreover, the feasibility of adjusting the stirrup configurations and stirrup ratio for controlling the damage location at the end of the column is discussed. The comparison of the results shows that the hysteresis curves obtained from the tests and the finite element simulations are in general agreement, verifying the correctness of using the concrete plastic damage model for modeling. In addition, the theoretical results based on the theory of truss and arch are closer to the test results, which also proves the reliability of the theory. By analyzing the results, the relationship between the ratio of the test and theoretical values (Z) and the stirrup ratio (ρw) is summarized through fitting. Under the ultimate limit state of carrying capacity, it can be concluded that the encryption of the stirrup reinforcement at the end of the column can retard the crack development and reduce the shear deformation. Overall, the computational method proposed in this paper has high accuracy in predicting column cracks and detecting the ultimate load-carrying capacity.

Numerical analysis of a prefabricated concrete beam-to-column connection with bolted end plates

Precast concrete structures have been widely used in China in recent years because of the obvious advantages in construction speed, labor saving and quality control. Many experimental and numerical studies have been performed to investigate the seismic behavior of the precast concrete structures. However, the numerical analysis on prefabricated concrete beam-to-column connection with bolted end plates (PCC) under cyclic loading is still limited. Therefore, in this paper, the developed finite element models (FEM) were established to further study the seismic performance of the PCC specimens. The sensitivity analysis were conducted to ensure the reliability and validity of the FEM. Then, the FE models of the typical specimens were validated by test data such as failure modes, hysteresis curves and steel strain. Parametric analysis was carried out to investigate the effect of the end plate thickness, preload of bolt, concrete strength, etc. The key parameters affecting the seismic behavior of the connections were obtained. Eventually, based on the numerical simulation results, the law between the responses of the connections and the key parameters was determined quantitatively by response surface methodology. According to the yield line theory, the theoretical formula on the bending capacity of the connection with thin end plate was derived. Meanwhile, the formulas on the bending capacity of the unbonded prestressed concrete beam were also obtained. The results indicated that the bearing capacity and initial stiffness of the connection were improved with the increase of end plate thickness and bolt preload. The steel box significantly enhanced the shear capacity of joint region of the PCC specimens. Although the bending capacity of the beam can be improved by increasing the concrete strength, high strength concrete significantly reduced the ductility. The calculated value of the connection matched well with the test or simulation data which may provide a reference for predicting the bending capacity of specimens with different failure modes in subsequent studies.

Experimental and numerical study on the seismic behavior of groove grouting precast concrete shear walls with different joint types

A groove grouting precast concrete shear wall (GGPCSW) subjected to seismic performance tests was explored in this research. Four full-scale specimens were designed for use in quasi-static experiments. These specimens included three GGPCSWs with different joint types (i.e., a horizontal joint, a vertical joint, and a combination of horizontal and vertical joints) and one reference cast-in-place reinforced concrete shear wall (CIPRCSW). The failure modes, failure process, hysteresis curves, bearing capacity, stiffness degradation, and ductility of the GGPCSWs were clarified. The experimental results revealed that all shear wall specimens failed in the flexural-shear failure mode. The crack distribution, load capacity, energy consumption, and stiffness degradation of the GGPCSW with a horizontal joint were found to be basically the same as those of the CIPRCSW before the displacement angle reached 1/100. The positive load capacity of the GGPCSW with a vertical joint was 22.5% greater than that of the CIPRCSW under the same conditions. It is noteworthy that the peak load of the GGPCSW with a combination of horizontal and vertical joints was basically the same as that of the GGPCSW with a vertical joint, while the ultimate displacement was 14% less than that of the GGPCSW with a horizontal joint. Furthermore, the GGPCSWs demonstrated a comparable level of ductility to the CIPRCSW, meeting the necessary deformability criteria. Finally, a series of numerical analyses were completed to investigate the skeleton curves, the distribution of the concrete damage, and the stress distribution of the steel bars. The findings were basically consistent with the test results, and further parametric investigations of GGPCSWs were performed.

Research on the loading method for lost motion testing of small-sized reducer

Lost motion is utilized to characterize the transmission accuracy of gear reducers and is commonly evaluated through the hysteresis curve method. In examinations of lost motion for large and medium-sized reducers, the default practice is the application of the equal torque gradient loading method. Nonetheless, for small-sized reducers, this approach is deemed inappropriate due to the constraints of the servo motor loading resolution. This study reveals that employing a larger unit torque for equal torque gradient loading can modify the shape of the hysteresis curve and influence the assessment of lost motion. As a result, this paper introduces two innovative loading techniques, namely equal position gradient loading and uniform speed loading, to address the limitations of equal torque gradient loading and reduce the demands on testing equipment. Subsequent experiments validate the issues associated with equal torque gradient loading, confirm the effectiveness of the two new loading techniques, and yield more comprehensive hysteresis curves. It is important to note that all three loading methods are influenced by the loading rate, but the two novel methods can mitigate the effects of loading rate dependency.

Green synthesis of emerging ZnO and Ca-doped ZnO nanoparticles towards optical, magnetic properties and its antibacterial application

A green synthesis method is adopted to prepare emerging low cost ZnO (ZNP) and Ca substitute ZnO nanoparticles (CZNP) using Psidium guajava fruit (PGF) extract as an effective reducing and capping agent. An X-ray diffraction study of the synthesized nanoparticles revealed that they have a hexagonal wurtzite structure. The elemental compositions and oxidation states of ZNP and CZNP surfaces are quantified. The HRSEM image shows the nano-flake like structure of the synthesized nanomaterials ZNP and CZNP samples. The elemental compositions were identified using EDAX spectra. From the Raman spectra, the low wavenumber region of 2nd order Raman modes at 341 and 346 cm-1 were ascribed to the difference E2 high-E2 low. Kubelka–Munk (K–M) method is used for estimating direct band gap and it is 3.3 eV and 3.04 eV for ZNP and CZNP respectively. Due to the zinc and oxygen vacancies, six different bands were observed in the photoluminescence spectra. The TG analysis was observed 5.6% of weight loss for ZNP and 5.8% of weight loss for CZNP sample. The Magnetization–Field (M–H) hysteresis curves revealed the appearance of diamagnetic behavior at room temperature. The asfabricated pure ZnO and Ca-doped ZnO nanoparticles were evaluated for the antibacterial activity. The Ca substituted ZnO sample showed higher antibacterial activity than pure ZnO sample.

Seismic Behavior of T-Shaped Concrete-Filled Steel Tubular Column to Steel Beam Joints with Side Plates

This study investigates the seismic behavior of the T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, aimed at expanding their applicability in areas with high-seismic fortification intensity. A construction form of T-shaped CFST column to steel beam joint with side plates is presented. The variables studied in these experiments include the side plate length, the axial compression ratio, the presence of side plates, and the presence of binding bars. The force mechanism, failure modes, load–displacement curves, strength, stiffness, ductility, and energy dissipation capacity of seven specimens were evaluated under low-cycle reciprocating load. The experimental results demonstrate that the joints of side plates show a full hysteresis curve, with the ductility coefficient ranging from 1.67 to 2.49, and the equivalent viscous damping coefficient between 0.147 and 0.234. The joint panel zone displays strong deformation and energy dissipation capacity. The inclusion of side plates and binding bars improves the seismic behavior of the joint. The setting of side plates enables the formation of a plastic hinge on the steel beam, creating a beam hinge failure mechanism and satisfying the seismic design principle of “strong column and weak beam, strong joint and weak member” as required by the building structures.

Experimental study on seismic performance of two-segment replaceable link with separated splicing plates

Traditional I-beam sections connected with end plates face challenges related to end bolts and excessive residual deformation. In response to these challenges, this study introduces an innovative concept: two-segment replaceable links with separated splicing plates. Two variations of replaceable links have been designed - one with separated splicing plates featuring standard bolt holes, and another with short slotted bolt holes. Cyclic loading tests has been conducted to study their seismic performance. The test results reveal that the failure modes of the links include flange buckling and tearing at the welds connecting the flange and end plate. The hysteresis curves of the specimens are complete and stable. The average overstrength coefficient of the links is 1.75, meeting the specified limit requirement for an overstrength coefficient greater than 1.5 for the link. The ultimate plastic rotation reaches up to 0.19 rad. Notably, specimens with short slotted bolt holes exhibit a relatively significant energy dissipation ratio due to bolts slip during test and they demonstrate optimal replaceability in terms of minimized replacement time and residual shear rotation. Furthermore, the two-stage design method for high-strength bolts in splicing plate is proposed considering bolts slip.

Cyclic testing of two-level control system using friction-yielding top plates in beam-to-column rigid connections

The use of two-level control systems in structures is one of those having attracted the attention of researchers in the last decade. The design idea of the mentioned systems is to combine two separate control systems with different stiffness and strength in series, which creates dual seismic behaviors due to appropriate energy dissipation at different levels of earthquakes. In this study, at the first stage a two-level passive control system using friction-yielding top plate in beam-to-column rigid connections is presented and its cyclic behavior is evaluated with nonlinear static and dynamic analyses using finite element method by ABAQUS software. In the next stage, the hysteresis curves are investigated, which indicates a very ductile behavior for the proposed damping system in the rigid connection. In addition, the obtained hysteresis curves show that the system can reliably dissipate energy at different earthquake levels, as expected, satisfying the seismic criteria for the special moment resisting frames. In this system, maximum base shear decreased by 20% compared to traditional rigid connections in a single-story moment frame under dynamic time-history analysis.

Experimental study on out-of-plane seismic performance of precast composite sidewalls of utility tunnel with grouting-sleeve joints

The precast composite reinforced concrete wall with the advantages of fewer joints, superior impermeability and rapid construction provides an efficient and environmental friendly alternative in the construction of underground utility tunnels in the last few years. To investigate the seismic performance of precast concrete composite walls of utility tunnels with grouting-sleeve connection under out-of-plane loads, a series of quasi-static cyclic tests were performed on the full-scale sidewall specimens with different axial compression ratios in this study. The experimental results including the failure modes, crack distributions, and the influence of different connections on the out-of-plane seismic performance of precast concrete composite wall were carefully examined and compared with those from the cyclic tests of the cast-in-place sidewalls of the utility tunnel. The test results show that the seismic performance of the precast concrete composite sidewall specimen, such as the hysteresis curves, the ultimate bearing capacity, stiffness degradation pattern and the ductility ratio, is basically the same as that of the cast-in-place specimen, indicating that the seismic performance of the prefabricated structure is equivalent to that of the cast-in-place structure. Moreover, the grouting-sleeves of the joints can effectively transfer the reinforcement stress until the failure of the precast concrete composite sidewall specimens, which exhibits excellent out-of-plane ductility and serviceability.

Magnetization and exchange-bias effect in powders of the Heusler Ni2MnSn-based alloys

Experimentalinvestigation of properties of powders of the Heusler Ni2MnSn-based alloys revealed the extreme suppression of both, the magnetization and the exchange-bias and exchange spring effects in powders of the alloys. Furthermore, the structural transformation between austenite and martensite phases of the alloys is hindered in the powders, hysteresis curves do not exhibit saturation and observed cluster-glass behavior of the powders at low temperature is almost independent on magnetic field and on composition of the alloys. A complex conjunction of exchange-bias effect and frozen magnetization contribution has been revealed in the case of the powders. All the mentioned phenomena are strongly dependent on the size and the shape of particles of the powders prepared either in an agate mortar or in a ball mill. Temperature treatment of the powders and the compressed pellets at temperature 1173 K under argon led to a recovery of the applicable properties that are characteristic for the bulk alloys. Results of the earlier quantum mechanical calculations of effects of different arrangement of Mn and Sn atoms in crystal structure of the alloys have been used to discuss the observed properties of the powders and to assess a formation of clusters in magneto-crystalline structure of the alloys.

Coexistence of strain glass transition and martensitic transformation in highly nickel-rich ferroelastic alloy with large elastocaloric effect

Strain glass transition attracts increasing attention in ferroelastic alloys in the context that martensitic transformation serves as the dominant mechanism for shape memory alloys. However, observing the coexistence of strain glass transition and martensitic transformation has not been reported. In this work, we introduce the strain glass transition by doping element to form highly nickel-rich Ni55Ti45 at.% alloys and in the meantime attain the characteristics of martensitic transformation in the alloys. We confirm the existence of strain glass transition by 1) no exothermic/endothermic peaks in heat flow curves, 2) two deviations in electric resistivity curves, 3) two frequency-dependent dips of storage modulus, and 4) successive formation and constrained growth of nanodomains over a wide temperature range. We observe the martensitic transformation characterized by 1) two pronounced exothermic peaks upon cooling and one endothermic peak upon heating in heat flow curves, 2) thermal hysteresis in electric resistivity curves, and 3) macroscopic martensitic twins in transmission electron microscopy images. With these two phase transformations, the quasilinear superelasticity, high strength, and large elastocaloric ΔTad of up to 9.7 K are achieved. By designing the strain maps and microstructural evolution pathways, we have provided a temperature-composition transformation path diagram to offer mechanistic insights and tuning strategies for the development of advanced alloys.

A multi‐layer thermo‐mechanical coupling hysteretic model for high damping rubber bearings at low temperature

AbstractHigh damping rubber (HDR) bearings have been widely applied in seismic isolation of structures. However, the complex behavior of HDR bearings is influenced by thermal mechanism coupled with the seismic response of the structure, particularly at low ambient temperatures. In order to express the hysteretic restoring force behavior of HDR bearings involving temperature dependence, heating effect, and heat transfer with an improved accuracy, a multi‐layer thermo‐mechanical coupling model was developed. The thermal mechanism was illustrated by considering the heating effect and heat transfer in the multi‐layer thermal‐coupled model. A nonlinear hysteretic model including the temperature dependence of the stress‐strain relationship of rubber was incorporated. Quasi‐static cyclic loading was conducted for parameter identification and real‐time hybrid simulation tests were carried out for model validation. The model accurately represented the time‐dependent thermal mechanism within the bearing, considering the non‐uniform distribution of internal temperature. Numerical results exhibited good agreement with the experimental results, including the hysteresis curve, temperature history, and temperature distribution. The model demonstrated improved accuracy in computing the hysteretic behavior compared with an existing simple model.

Seismic performance of high-strength steel plate-concrete composite shear walls

The application of high-strength steel plate-concrete composite shear walls in super high-rise frame-core tube structure can significantly increase the bearing capacity, reduce the dimensions of the core tube and the frame part, and harmonize the stiffness ratio of frame and core tube, therefore improve the economic efficiency. In order to study the seismic performance of the high-strength steel plate-concrete composite shear walls, pseudo-static tests on three composite shear wall specimens with an aspect ratio of 1.43 were conducted, the failure mechanism, strength, ductility and energy dissipation capacity of specimens with Q355B, Q460B, Q550B steel were studied. Experimental results showed that the crushing of concrete and the failure of vertical reinforcement at the corner leaded to the flexural failure of specimens; hysteresis curves of specimens showed good energy dissipating capacities without pinching phenomena; with the increase of the steel strength, the yield strength, yield displacement, peak strength and ultimate displacement of specimens increased, while ductility decreased. Finite element analysis was conducted using OpenSees, the modeling method had been proven accurately simulate the performance of the specimens, and was subsequently used for parametric study to investigate the impact of axial compression ratio, thickness of the embedded steel plate, and aspect ratio (height to width) on the performance of high-strength steel plate-concrete composite shear walls.

Seismic performance of precast multi-segment columns with grouted sleeves: Experimental and numerical investigations

This research explores the seismic performance of multi-segment columns, which are gaining attention due to their segmented prefabrication and assembly that address transportation and installation challenges. The main objective is to investigate the effective use of grouted sleeves as connections, both between column segments and to the foundation, in order to achieve satisfactory seismic behavior. To achieve this objective, an experimental program involving reversed cyclic tests was conducted on three precast specimens, which were compared to a reference conventional cast-in-place (CIP) column. The precast specimens featured grouted sleeve connections, with variations in the number of column segments and the connection types. The test results showed higher peak strength but reduced ductility in the grouted sleeve specimens compared to the CIP column. Moreover, multi-segment columns displayed significant improvements in ductility (12.8%), deformation capacity (27.0%), and energy dissipation (14.8%) compared to the single-segment column. Transferring grouted sleeves to the foundation further improved ductility by 18.0%. In parallel, a finite element (FE) modeling method was developed, with simplified representations of cushions and grouted sleeves. The FE results exhibited satisfactory agreement with the experimental findings, validating the accuracy of the developed FE models in terms of hysteresis curves, residual displacement, peak strength, and energy dissipation.

Seismic reduction principle and response analysis of variable damping viscous damper system

PurposeA new type of variable damping viscous damper is developed to meet the settings of different damping parameter values at different working stages. Its main principle and design structure are introduced, and the two-stage and multi-stage controllable damping methods are proposed.Design/methodology/approachThe theoretical calculation formulas of the damping force of power-law fluid variable damping viscous damper at elongated holes are derived, aiming to provide a theoretical basis for the development and application of variable damping viscous dampers. For the newly developed variable damping viscous damper, the dynamic equations for the seismic reduction system with variable damping viscous dampers under a multi-degree-of-freedom system are established. A feasible calculation and analysis method is proposed to derive the solution process of time history analysis. At the same time, a program is also developed using Matlab. The dynamic full-scale test of a two-stage variable damping viscous damper was conducted, demonstrating that the hysteresis curve is complete and the working condition is stable.FindingsThrough the calculation and analysis of examples, the results show that the seismic reduction effect of high and flexible buildings using the seismic reduction system with variable damping viscous dampers is significant. The program developed is used to analyze the seismic response of a broadcasting tower using a variable damping TMD system under large earthquakes. The results indicate that the installation of variable damping viscous dampers can effectively control the maximum inter-story displacement response of TMD water tanks and can effectively consume seismic energy.Originality/valueThis method can provide a guarantee for the safe and effective operation of TMD in wind and vibration control.

High electrical characteristics through graphene oxide doping process on physicochemically reformed inorganic thin films.

This study investigated the improvement of the electro-optical properties of a liquid crystal (LC) cell fabricated through brush coating using graphene oxide (GO) doping. The physical deformation of the surface was analyzed using atomic force microscopy. The size of the groove increased as the GO dopant concentration increased, but the direction of the groove along the brush direction was maintained. X-ray photoelectron spectroscopy analysis confirmed that the number of C-C and O-Sn bonds increased as the GO concentration increased. Since the van der Waals force on the surface increases as the number of O-metal bonds increases, we were able to determine why the anchoring energy of the LC alignment layer increased. This was confirmed by residual DC voltage and anchoring energy measurements that were later performed. As the GO concentration increased, the width of the hysteresis curve decreased, indicating that the residual DC voltage decreased. Additionally, the 15% GO-doped sample exhibited a significant increase in its anchoring energy up to 1.34 × 10-3J/m2, which is similar to that of rubbed polyimide. It also secured a high level of electro-optical properties and demonstrated potential as a next-generation thin-film display despite being produced via a simple brush-coating process.

Experimental and numerical studies of the multi-tube assembled buckling-restrained braces

In this paper, the multi-tube assembled bolt-connected buckling-restrained brace (MT-BRB) with four internally restrained rectangular steel tubes and one externally restrained square steel tube is experimentally analyzed. This study conducted cyclic loading tests on five specimens with different parameters to investigate the effects of different loading directions of the core plate, the presence or absence of unbonded materials, the gap-to-width ratio and the width-to-thickness ratio on the mechanical properties, seismic performance and failure mode of MT-BRB. The experimental results indicated that the MT-BRB specimens made of unbonded materials had stable cyclic performance and energy dissipation capacity. Subsequently, the same numerical model as the experimental specimen was established, and the hysteresis and stress curves extracted from the finite element model were compared with the experimental results. The simulation had ideal agreement with the experiment result, demonstrating that the model was effective for performance predictions. Based on this, the working mechanism of MT-BRB was further explored through finite element analysis. Finally, parameter analysis was conducted on the constraint ratio and constraint length ratio to further investigate the energy dissipation performance of MT-BRB. This study is beneficial for promoting the application of MT-BRB in energy dissipation and vibration reduction engineering.