Hysteretic Behavior Research Articles

Parametric excitations of coupled nanomagnets

We demonstrate that parametrically excited eigenmodes in nearby nanomagnets can be coupled to each other. Both positive (in-phase) and negative (anti-phase) couplings can be realized by a combination of appropriately chosen geometry and excitation field frequency. The oscillations are sufficiently stable against thermal fluctuations. The phase relation between field-coupled nanomagnets shows a hysteretic behavior with the phase relation being locked over a wide frequency range. We envision that this computational study lays the groundwork to use field-coupled nanomagnets parametrons as building blocks of logic devices, neuromorphic systems of Ising machines.

Manufacturing, development and control of a two-way 3D printed soft actuator actuated with SMAs

In this contribution, the development of a novel two-way 3D printed soft actuator actuated with shape memory alloys (SMAs) is presented, considering all the stages from the design, manufacturing, control, and implementation. The SMAs are integrated into the 3D printed composite using thermoplastic polyurethane (TPU). In order to measure the deflection of the soft actuator a computer vision system was implemented. With these measures and using system identification techniques, a mathematical model was developed, which describes the dynamics of the prototype and helps to design of a controller. However, precise control of deflection in systems actuated by SMAs is challenging due to their inherent nonlinearities and hysteretic behavior. To face this challenge, a proportional-integral (PI) controller was designed based on robust stability conditions. The effectiveness of the designed PI controller was validated through experimental results.

Cyclic behaviour of precast beam-column connections with shear key and hybrid rebar coupler: An experimental study

The current work attempts to examine the cyclic behaviour of the proposed shear key based precast beam-column wet connections. The configurations consist of shear keys, fiber reinforced composites and interface treatment between beam & column. The rebar continuity between the precast beam and column was established using hybrid rebar couplers. Six precast specimens and one monolithic joint were cast and tested under reversed cyclic loading. The seismic performance of the connections was assessed and discussed in terms of hysteretic behaviour, stiffness and strength degradation, damage tolerance, displacement ductility, energy dissipation characteristics, and joint principal tensile stresses. The strength enhancement, dissipated energy, stiffness retention of precast specimens was similar to monolithic specimen. The crack patterns revealed the influence of stiffness of coupler in the plastic hinge region with shifting of cracks next to coupler and joint region. Also, the presence of fiber reinforced composites, shear key and interface treatment in the connection region exhibited controlled cracking in the plastic hinge region and restricted the joint shear failure. The obtained results were validated through ACI 374.1–05 requirements criteria, which shows the acceptable seismic behaviour. The findings obtained from this study demonstrated the integrity of proposed beam-column connections against seismic forces and could achieve emulative design philosophy.

Role of time variant and invariant terms on soil moisture spatio‐temporal variability in a subhumid coastal wetland

AbstractThe knowledge of soil moisture spatio‐temporal variability is highly relevant for water resources management. This paper reports an analysis of the spatial–temporal variability of soil moisture data for a small to medium‐scale soil‐sensors network in a coastal wetland of southwestern Spain. Measurements were taken from five sites located in the Doñana National Park over the time‐period of one hydrological year from September 2017 to September 2018. The total area of the soil‐sensors network shows an extension about 25 × 3 km. Soil moisture data was separated into time invariant (the temporal mean of the whole period at each site) and time‐variant terms (the deviations of soil moisture from the mean, or anomalies). The time‐invariant component was generally the main contributor to the total spatial variance of soil moisture and it was mostly controlled by the groundwater levels in the area. Nevertheless, the time variant terms have a huge effect on soil moisture variability in very dry states. Characteristic convex time‐dependent patterns for this field site were found between spatially averaged soil moisture and its variability. This information could be used for the up and downscaling of soil moisture from satellite data. Those patterns of relation between spatial mean and variability of soil moisture were only affected by heavy rainfalls giving rise to hysteretic behaviour. This study shows that even though groundwater level is a time‐variant variable, it significantly affects soil moisture's time‐variant but also time‐invariant terms due to the different average groundwater level depths at the different sites.

Effects of external loads-induced inclination damage on the seismic performance of traditional straight M-T joints

Under the earthquakes, wind, and other external loads, ancient timber structures have experienced various degrees of damages, in which the inclination damage of mortise and tenon (M-T) joints, induced by the external loads, has an adverse effect on the safety of the whole structure. To study the effect of various degrees of inclination damage on the seismic behavior of straight M-T joints, we fabricated four 1/3.2-scaled ancient straight M-T joint specimens, one without inclination and three with different degrees of inclination, and subjected them to the cyclic loading tests. The inclination of the joint was simulated artificially, i.e., pushing the intact joint to the predetermined inclination rotation and holding the loads, then unloading when the part of tenon entered a nonrecoverable plastic state. The failure modes, initial elastic stiffness, moment-resisting capacity, strength and stiffness degradation laws as well as energy dissipation and deformation capacities of the joints were investigated. The results showed that the plastic deformation of the tenon and mortise edge, tenon pull-out, and longitudinal splitting of the tenon were exhibited in the inclined joint specimens. Compared to the intact joint, the plastic deformation of the tenon and tenon pull-out for the inclined M-T joints were more apparent during the positive loading. The hysteretic curve of each joint exhibited an anti- "Z" shaped, and the greater the inclination degree, the more apparent the negative initial slipping and pinching effect. With an increase in the damage degree, the initial stiffness, ultimate moment-resisting capacity, and hysteretic energy dissipation behavior of the inclined M-T joint gradually degraded. When the damage degree was 3.89%, the positive yielding moment, peak moment, and initial stiffness of the inclined M-T joint degraded to 52.41%, 86.09%, and 67.19% of that of the intact joint. Based on the hysteretic characteristics and test results of the inclined M-T joints, the degradation formulas of the key parameters of seismic behavior for the inclined M-T joints were established, and an improved degraded hysteretic model, which can reflect the hysteretic behaviors of inclined M-T joint, was proposed. Good agreements between the model predictions and the test results were observed.

Experimental and analytical investigations on backbone curve models for RC shear keys under sequential seismic-tsunamic impacts

Reinforced concrete (RC) sacrificial shear keys play a crucial role in enhancing the structure resilience of coastal bridge against lateral impacts induced by seismic-tsunami scenarios. Existing researches have primarily focused on their performance under cyclic effects to simulate seismic impacts during earthquakes. However, their ability to withstand enduring forces under tsunami wave has been rarely studied yet. In this research, an experimental test was carried out to investigate the failure mechanism of RC shear keys under sequential cyclic-persistent effects, in which three typical failure modes of shear keys were considered. Various damage states were introduced to account for the possible damage levels after sustaining seismic impacts. The test results were analyzed by focusing on damage pattern, hysteretic behavior, peak capacity, and strain development, showing great distinctions with respect to different failure modes and corresponding damage stages. Furthermore, the analytical backbone curve models were developed based on the experimental test results. The presented models were validated using the typical strain-stress curve of reinforcement, and exhibited better applicability in characterizing the performance of shear keys under either cyclic or cyclic-persistent sequential effects, comparing to the other approaches that emphasizes on their seismic properties.

A Finite Element Modeling Approach for Analyzing the Cyclic Behavior of RC Frames

Numerous approaches and inputs for nonlinear finite element analysis used for modeling reinforced concrete systems under cyclic loads have been outlined. Practitioners usually take into account a number of significant factors when modeling, for example deciding upon the constitutive relations, the connection among concrete and steel reinforcement, and the mesh sensitivities, in order to accurately simulate the nonlinear response of reinforced concrete under cyclic loads. Therefore, it is essential to thoroughly assess popular modeling approaches and develop a reliable modeling approach with reliability, stability, and consistency. A modeling technique and practical guidelines for nonlinear finite element analysis of reinforced concrete frames subjected to cyclic loading are described in this study, taking into account the influence of parameters such as dilation angle, stiffness recovery, friction coefficient, and mesh sizes. The hysteretic force–displacement behavior and load-carrying capacity of reinforced concrete frames subjected to cyclic loading have been compared using numerical and experimental curves. Discrete fracture paths are specified in the model’s geometry to achieve an accurate depiction of the stress distribution and an adequate fit of the hysteretic behavior. The proposed modeling approach provides a precise representation of the stress distribution and hysteretic behavior while keeping computational costs reasonable.

Simultaneous Determination of Enantiomeric Purity and Organic Impurities of Dexketoprofen Using Reversed-Phase Liquid Chromatography-Enhancing Enantioselectivity through Hysteretic Behavior and Temperature-Dependent Enantiomer Elution Order Reversal on Polysaccharide Chiral Stationary Phases.

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of the potential impurities of dexketoprofen, including the distomer R-ketoprofen. After screening the separation capability of four polysaccharide columns (Lux Amylose-1, Lux Amylose-2, Lux Cellulose-1 and Lux Cellulose-2) in polar organic and in reversed-phase modes, appropriate enantioseparation was observed only on the Lux Amylose-2 column in an acidified acetonitrile/water mixture. A detailed investigation of the mobile phase composition and temperature for enantio- and chemoselectivity showed many unexpected observations. It was observed that both the resolution and the enantiomer elution order can be fine-tuned by varying the temperature and mobile phase composition. Moreover, hysteresis of the retention times and enantioselectivity was also observed in reversed-phase mode using methanol/water mixtures on amylose-type columns. This could indicate that the three-dimensional structure of the amylose column can change by transitioning from a polar organic to a reversed-phase mode, which affects the enantioseparation process. Temperature-dependent enantiomer elution order and rare enthalpic/entropic controlled enantioseparation in the operative temperature range were also observed in reversed-phase mode. To find the best methodological conditions for the determination of dexketoprofen impurities, a full factorial optimization design was performed. Using the optimized parameters (Lux Amylose-2 column with water/acetonitrile/acetic acid 50/50/0.1 (v/v/v) at a 1 mL/min flow rate at 20 °C), baseline separations were achieved between all compounds within 15 min. Our newly developed HPLC method was validated according to the current guidelines, and its application was tested on commercially available pharmaceutical formulations. According to the authors' knowledge, this is the first study to report hysteretic behavior on polysaccharide columns in reversed-phase mode.

Dissipation and recovery in collagen fibrils under cyclic loading: A molecular dynamics study.

The hysteretic behavior exhibited by collagen fibrils, when subjected to cyclic loading, is known to result in both dissipation as well as accumulation of residual strain. On subsequent relaxation, partial recovery has also been reported. Cross-links have been considered to play a key role in overall mechanical properties. Here, we modify an existing coarse-grained molecular dynamics model for collagen fibril with initially cross-linked collagen molecules, which is known to reproduce the response to uniaxial strain, by incorporating reformation of cross-links to allow for possible recovery of the fibril. Using molecular dynamics simulations, we show that our model successfully replicates the key features observed in experimental data, including the movement of hysteresis loops, the time evolution of residual strains and energy dissipation, as well as the recovery observed during relaxation. We also show that the characteristic cycle number, describing the approach toward steady state, has a value similar to that in experiments. We also emphasize the vital role of the degree of cross-linking on the key features of the macroscopic response to cyclic loading.

Seismic behavior and shear capacity prediction of coupled concrete‐filled multicellular steel tube composite shear walls

AbstractIn this paper, a coupled concrete‐filled multicellular steel tube composite shear walls structure (CCSSW) is proposed. A finite element model (FEM) is developed to investigate the seismic behavior of CCSSW, and the model was validated by the tests. The effects of four parameters including axial compression ratio (ACR) on the hysteretic behavior of the CCSSW were studied. Then, a theoretical model for predicting the ultimate shear capacity (USC) of CCSSW was established. The results show that the failure mode of coupled walls exchanged from flexural failure to flexural‐shear failure with increasing the ACR, and it is recommended that the ACR should less than 0.6 to ensure the ductility requirement. To better realize the function of the first line of defense of steel coupling beam (SCB), following recommendations are concluded: the span‐to‐depth ratio range of SCB is 4.0–6.0, the wall stiffness ratio is 2.4–4.7, and low yield strength material should be used for SCB. The maximum error on USC between FEM results and theoretical results is 12.8%, and most of them are less than 10%, indicating the effectiveness of the proposed theoretical model.

Frequency-response curves for rate-independent hysteretic mechanical responses of complex shape

We illustrate the performances of a brand new hysteretic model, recently proposed and denominated VRM+D, to characterize the nonlinear response of mechanical systems endowed with quite complex hysteretic behaviors. To this end, we combine the VRM+D with a continuation procedure based on Poincaré maps developed by Lacarbonara et al. in 1999. In this way, the steady-state response, as well as stability and bifurcation, of a large class of mechanical systems can be analyzed. In particular, we show the effectiveness of the VRM+D, in conjunction with the Poincaré map-based continuation procedure, in accurately predicting periodic solutions of the above-mentioned systems independently of the form of the hysteresis loop shapes. Furthermore, we draw some general considerations on the potential applications of the proposed approach in different fields of engineering to get an improved understanding of the dynamics of hysteretic mechanical systems subjected to cyclic loading.

Simulating the hysteretic behaviour of thin-walled H-Section steel members using the geometrically exact beam theory

Based on Gonçalves's geometrically exact beam theory considering cross-section deformation, the warping and distortional deformation of thin-walled members are described in this paper by means of a combination of section deformation modes. By integrating with the J2 elastic‒plasticity theory for the steel, a numerical model is established for the hysteretic behaviour of thin-walled steel members. Four classes of H-section members are selected on account of the design codes, and the influence of section warping and distortion deformation modes on the calculation of the hysteretic behaviour of components with different section types is analysed. The crucial aspect lies in the bending hysteresis behaviour around the strong and weak axes of the cross-section for H-beam steel members subjected to typical thin-walled members with relatively large widths and thicknesses. Test results on the hysteretic behaviour of H-section steel members are compared with those calculated from the proposed model in terms of the hysteric behaviour of components, strength degradation, energy-dissipating capacity, etc. These findings validate the correctness and feasibility of the established non-linear analysis model for thin-walled members.

Foam Generation Through a Single Pore with Rectangular Cross-Section: Hysteretic Behavior and Geometric Limitation of the Volume Fraction of Bubbles.

We study foam production and destabilization through a flow-focusing geometry, namely a single pore of rectangular cross-section, by coinjecting gas and liquid at constant pressure, Pg, and constant flow rate, Qw. We observe that bubble production results from a Rayleigh-Plateau destabilization of the internal gas thread that occurs at the pore neck when its width becomes comparable to the height of the rectangular-section channel. Using a simple model and numerical approach, we (i) predict the shape of the gas jet and its stability range as a function of flow parameters and device geometry, which we successfully compare with our experimental results, and (ii) demonstrate the existence of a critical local pressure drop at the pore neck that determines whether or not a stable gas flow can form. We thus show that bubble foam generation exhibits hysteretic behavior due to hydrodynamic feedback and demonstrate that there is a maximum bubble volume fraction that the generated foam cannot exceed, the value of which is fixed by the geometry. Our results suggest that the foam collapse observed in porous media when the fractional gas flow becomes too large may result from hydrodynamic feedback inhibiting foam generation and not necessarily from coalescence between bubbles, as is usually claimed.

Manufacture and Deformation Angle Control of a Two-Direction Soft Actuator Integrated with SMAs.

In this contribution, the development of a 3D-printed soft actuator integrated with shape memory alloys (SMA) wires capable of bending in two directions is presented. This work discusses the design, manufacturing, modeling, simulation, and feedback control of the actuator. The SMA wires are encased in Polytetrafluoroethylene (PTFE) tubes and then integrated into the 3D-printed matrix made of thermoplastic polyurethane (TPU). To measure and control the deformation angle of the soft actuator, a computer vision system was implemented. Based on the experimental results, a mathematical model was developed using the system identification method and simulated to describe the dynamics of the actuator, contributing to the design of a controller. However, achieving precise control of the deformation angle in systems actuated by SMA wires is challenging due to their inherent nonlinearities and hysteretic behavior. A proportional-integral (PI) controller was designed to address this challenge, and its effectiveness was validated through real experiments.

Deep learning enabled seismic fragility evaluation of structures subjected to mainshock-aftershock earthquakes

Mainshock-aftershock earthquakes have gained significant attention since accumulated damages induced by multiple shocks are likely to cause failure of structures. This paper presents a deep learning approach based on a Gated Recurrent Unit (GRU) network for assessing the seismic fragility of structures under mainshock-aftershock scenarios. The GRU network is utilized to create a surrogate model that captures the nonlinear relationship between seismic responses and mainshock-aftershock earthquakes. Subsequently, seismic fragility analysis is conducted based on double incremental dynamic analysis, employing the trained GRU network. A single-degree-of-freedom system with Bouc-Wen hysteretic behavior was investigated to demonstrate the proposed approach. The results indicate that the approach shows a substantial reduction in computational costs and holds promising potential for evaluating the seismic fragility of structures exposed to mainshock-aftershock earthquakes.

Hysteretic behavior and moment-rotation model of self-centering beam-column connection with angle steel

The objective of this study is to develop a moment-rotation model (M-θ) to evaluate the hysteresis behavior of self-centering beam-column connection with replaceable angle steel. Based on the previous pseudo-static test results of 13 groups of 22 beam-column joint specimens, the hysteretic behavior of the joint and the prestress loss of the post-tensioned (PT) strand are further studied. According to the phased hysteretic characteristic of the beam-column joint and the connection characteristic of two interfaces, the M-θ model for beam-column connection is established, which is divided by four key points: opening point, yield point, peak point and ultimate point. The proposed M-θ model includes the bilinear moment-rotation (M-θs) model of the endplate-bolt interface based on the component method, and the trilinear moment-rotation (M-θr) model of the self-centering interface considering the prestress loss of PT strand and the phased mechanical behavior of each component. The accuracy of the proposed M-θ model is verified by the comparisons of theoretical calculation results and experimental skeleton curves, which provides a theoretical basis for the engineering design of this kind self-centering beam-column connection.

Anomalies in the magnetostrictive modulation of love surface acoustic waves

A magnetic surface acoustic wave (SAW) sensor is built by growing a 100 nm galfenol (Fe72Ga28) film by sputtering between the interdigitated transducers of a SAW delay line. Love waves are produced when the shear waves excited on the piezoelectric substrate are guided by a 3.1 μm layer of amorphous SiO2. Due to the magnetostrictive nature of galfenol deposited on top, the application of magnetic fields modulates the propagation of the mechanical excitations along the sensor by the strain coupling. By introducing the delay line in a feedback loop circuit, these changes are studied as resonant frequency variations. Magnetic field cycles of ±40 mT are applied to the sample and the resonant frequency shift is tracked simultaneously. The sensor exhibited hysteretic frequency behavior that depends on the orientation of the applied magnetic field relative to the direction of Love wave propagation. In the configuration in which the wave vector and the applied field form an angle of 45°, the resonant frequency seems to increase with the magnetization induced by the external field. When the wave vector propagation is parallel to the field, two positive peaks appear close to the coercive field of the film, which has not been reported before. This is probably due to a more complex relationship between the acoustic wave and the magnetic state of the film which could be exploited to give rise to new models of magnetic sensors.

Machine learning-based prediction of hysteretic behaviors of two-side clamped steel shear walls

This study proposes a methodology that can construct the hysteretic curves of two-side clamped steel shear walls (TCSSWs) using a machine learning technology to address the inherent deficiencies of multivariable regression analysis which has been typically used for developing the hysteretic model of a common structural element. A deep neural network (DNN) is adopted for this study and a new architecture is proposed by modifying numbers of neurons and hidden layers to well capture the cyclic response of TCSSWs. Using a training datasets DNN architectures with several combinations of input parameters and configurations relating to numbers of neurons and hidden layers had been trained. This study considers a total of 70 DNN architectures and selects the best-fitting DNN architecture which produces the minimum mean-square-error value. Estimates from the proposed DNN architecture are evaluated with a test dataset and their accuracy is acceptable. Finally, the selected DNN architecture is further verified with a validation dataset consisting of TCSSWs with different material properties of steel. The modeling parameters for the hysteretic curves of TCSSWs can be properly captured by the proposed DNN architecture.

Hysteretic Behavior of Full-Scale Precast U-Shaped Composite Beam–Column Connections with Large-Diameter Reinforcements under High Axial Compression

This study introduces precast concrete beam–column connections comprised of composite beams, precast columns, and a monolithic joint core. The composite beams consist of U-shaped beams and floor slabs, leveraging the U-shaped beams for their lightweight nature, acceptable stiffness, and reduced demand for on-site support systems. To mitigate reinforcement congestion in the joint core, the precast connections incorporate large-diameter rebars (greater than 25 mm). This study conducted cyclic loading tests on four full-scale beam–column connections under 0.3 normalized compression, encompassing precast interior and exterior connections, along with two monolithic reference specimens, to investigate their behavior under seismic actions. The results revealed that all specimens exhibited bending failure at the beam ends, with minimal concrete deterioration observed in the joint core areas and columns. The hysteresis curves of the precast specimens and the monolithic connections exhibited a slight pinching effect. The strengths of the interior and exterior precast specimens were 13.3% and 7.8% lower than those of the reference monolithic connections, respectively. The ductility of interior precast connections and monolithic specimens stood at 2.36 and 2.23, respectively, indicating a negligible difference of less than 5%. Meanwhile, the positive and negative ductility of exterior precast connections were 3.06 and 2.34, which was approximately 8% lower than that of the reference connections. Furthermore, the stiffness degradation and energy dissipation capacity of the precast specimens aligned closely with the performance of the reference monolithic ones.

Improvement effects of knee-bracing friction dampers on cyclic behavior of steel joints in antique buildings

To inherit the unique characteristics of historical timber architecture, the steel antique building (SAB) imitating ancient Chinese timber structures has been constructed using contemporary steel materials and fabrication techniques. These buildings typically exhibit premature yielding cracks and weak energy dissipation at the beam ends under seismic loads. To improve the seismic performance of SABs, two different types of friction dampers were deployed at the knee-bracing region around beam-column joints in SABs. First, cyclic loading tests on dampers indicate that both shear friction dampers and rotational friction dampers exhibit full hysteretic behavior, demonstrating an excellent and stable energy dissipation capacity. The friction coefficient of dampers with brass pads was theoretically calculated to be 0.35. Second, the quasi-static test showed that failure of steel joint specimens with knee-bracing dampers primarily occurred at replaceable angles in the beam-column connection region, which demonstrates that the repairability of steel joints in SABs can be greatly improved without overcomplicated labor. Adding knee-bracing dampers effectively postpones damage to the replaceable angles, which improves the strength, stiffness, and energy dissipation capacity of the steel joints significantly. The shear damper exhibits a more pronounced improvement in the overall structural seismic performance compared to the rotational damper with the same frictional sliding force. Moreover, numerical simulations showed that the strength of the proposed joints with knee-bracing friction dampers decreases with an increase in the axial compression ratio, while increasing the thickness of angles or the sliding force of dampers can effectively improve the seismic performance of the steel joints in SABs.