Analysis Of Hysteresis Loops Research Articles

Support vector machines for automated modelling of nonlinear structures using health monitoring results

Structural health monitoring (SHM) is backwards analysis of past to current state of damage, but cannot create a structure-specific nonlinear model for forward analysis of future response and damage. This paper aims to develop an automated modelling approach to translate proven hysteresis loop analysis (HLA) SHM results into nonlinear foundation models for response forecasting in subsequent events, particularly for steel structures with post-yielding behaviors. Support vector machine (SVM) is employed to identify the proposed nonlinear baseline model. Stiffness features are extracted from HLA to train the SVM model incorporating the constraints of SHM identification.A proof-of-concept case study validates the ability of the proposed method to accurately identify 12 model parameters with average error of 2.8% for a nonlinear numerical structure in the presence of 10% RMS measurement noise. Experimental validation from a full-scale 3-storey real building shows the predicted nonlinear responses match the measured response well with cross correlation coefficients Rcoeff = 0.94, 0.92 and 0.89 for the first, second and third floor, respectively. In addition, the predicted stiffness changes also match the SHM results very well with errors less than 2.1%. Finally, and most importantly, the identified model is able to predict the response of 2 further events with average of correlation coefficient Rcoeff = 0.91 and average error of 1.9% for stiffness changes across all cases. The overall results validate the ability of the created predictive model to accurately capture the essential dynamics and structural degradation, as well as predicting future possible response and risk.

Preparation and characterisation of Fe/Fe3O4 fibres based soft magnetic composites

Soft magnetic composites (FSMCs) have been prepared by using Fe fibres coated with a layer of Fe3O4, this layer playing the role of insulating material. The coating was made via blackening method by simply immersing the fibres in the blackening bath for 5, 10 and 15 min. The formation of the Fe3O4 coating on the surface of the fibres was confirmed by X-ray diffraction. The SEM investigation, used to evaluate the thickness of the coatings, has proved that increasing the coating duration leads to the increase of the coating thickness and complete coverage of the surface of the fibres. Differential scanning calorimetry and thermomagnetic measurements were used to investigate the thermal stability of the composite fibres. The fibres coated with Fe3O4 were compacted at a compaction pressure of 700 MPa to obtain toroidal magnetic cores. The obtained cores were characterised in DC and AC magnetisation regime. The analysis of the quasi-static hysteresis loops evidenced that increasing the thickness of the Fe3O4 leads to a slight deterioration of the compact's magnetic properties. However, as the thickness of the Fe3O4 layer increases, the development of eddy currents at a larger scale is hindered as proved by the AC magnetic investigations. A model for analytic separation of the core losses is proposed. By applying this model to the prepared samples, we are now able to discriminate between the occurring losses and adjust the preparation process of new samples to the targeted characteristics.

Synthesis and magnetic properties of chromium doped cobalt ferrite nanotubes

Chromium (Cr) doped cobalt ferrite (Co1−xCrxFe2O4:x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1, denoted as to CCFO) hollow nanotubes were synthesized by electrospinnig method followed by, calcining treatment at 700 °C in air. The samples exhibited a single phase cubic spinel phase. The lattice constant of the samples was found to initially decreased and thereafter increases with increased of Cr content. The morphology analysis indicated that the samples displayed a disordered arrangements of hollow structures and the relevant surfaces were rough and porous. Transmission electron microscopy (TEM) paragraph confirmed that the doped CCFO nanotubes had a polycrystalline nature and exhibited the changes in the corresponding crystal structure. X-ray photoelectron spectroscopy (XPS) confirmed that Cr doping affect the crystal structure and atomic-binding energy. The analysis of magnetic hysteresis loop indicated an obvious reduction in the saturation magnetization (Ms) of cobalt ferrite with increasing in Cr substitution. The remanent magnetization (Mr) and coercivity were increased at first and then decreased with increasing of Cr content, which was elucidated by the surface effect and magnetic moment direction. The switching field distribution analysis indicated the magnetically crystal soft phase and there were multiple-step processes to reach magnetic reversal.

Removal of arsenic contaminants using a novel porous nanoadsorbent with superior magnetic recovery

Novel porous and magnetic iron oxide nanoparticles (PMNPs) with good magnetic properties were synthesized through a simple sol–gel method and exhibited excellent adsorption performance for aqueous arsenic contaminants as well as magnetic recoverability. Hysteresis loop analysis confirmed that the PMNPs were typical superparamagnetic material with a ultrahigh magnetic saturation (Ms) of 94.77 emu/g, which allowed their quick and complete recovery even under magnetic fields less than 0.25 T. The kinetics and isotherms results confirmed that adsorption equilibrium could achieved in 30 min and the saturated adsorption capacities for As(III) and As(V) exceeded 0.64 and 0.76 mmol/g at 30 °C. The effects of initial pH and diverse co-existing ions demonstrated that the optimal conditions for arsenic removal were closely related to the PMNPs surface charge distribution and the electron density of As(III) and As(V). In addition, after 10 adsorption–desorption cycles, PMNPs still held more than 80% of the primal arsenic adsorption capacities.

On the strain-induced martensitic transformation process of the commercial AISI 304 stainless steel during cyclic loading

Low-cycle fatigue tests were performed on metastable austenitic steel at two initial material states, the as-received, with a high crystal defect density, and the solution treated one, with fewer crystal defects. Cyclic curves have shown different hardening behavior depending on the initial material states. To understand these differences, the back and friction stresses were studied from the hysteresis loop analysis. The correlation of these results with the volume fraction of induced martensite and the observed microstructure revealed that the cyclic hardening behavior strongly depends on the existence of potential martensite nucleation sites.

Demagnetization Processes in Multilayered Permalloy-Based Film Structures

By examples of multilayered film structure Cu/[FeNi/Cu]10 deposited by the method of ion-plasma sputtering, a comparative analysis of the magnetic hysteresis loops measured on a vibrating magnetometer, a magnetic measuring complex with primary converter on the basis of SQUID (SQUID magnetometer), and a magneto-optical Kerr microscope is carried out. The use of a SQUID magnetometer made it possible to detect the step-by-step nature of remagnetization of the film structure, the presence of which was confirmed by observations on the Kerr microscope in the quasi-static remagnetization mode.

Simulating the Hysteretic Characteristics of Hard Magnetic Materials Based on Nd2Fe14B and Ce2Fe14B Intermetallics

The Ce2Fe14B intermetallic, like Nd2Fe14B, has the tetragonal Nd2Fe14B-type structure (space group P42/mnm), in which Ce ions have a mixed-valence state characterized by the coexistence of trivalent 4f1 and tetravalent 4f0 electron states. Despite the fact that the saturation magnetization, magnetic anisotropy field, and Curie temperature of the Ce2Fe14B intermetallic are substantially lower than those of Nd2Fe14B and Pr2Fe14B, Ce2Fe14B retains the capacity of being able to be used in the manufacturing of rare-earth permanent magnets. Moreover, at low temperatures, the anisotropy field of Се2Fe14B is higher than that of Nd2Fe14B, and Се2Fe14B does not undergo the spin-reorientation transition. In this respect, studies of (Nd, Ce)-Fe-B alloys, which are intended for the improvement of the service characteristics-to-cost ratio, are very relevant. A model and algorithm for calculating the hysteresis loops of uniaxial hard magnetic materials with allowance for the K1 and K2 (K2 > 0 and K1 > 0 and K1 < 0) magnetic anisotropy constants were developed and allowed us to obtain data on their effect on the parameters of hysteresis loops for a wide temperature range (0–300 K). The simulation and analysis of hysteresis loops of the quasi-ternary intermetallics (Nd1−хСех)2Fe14B (х = 0–1) was performed. Results of the simulation indicate that the alloying of the Nd2Fe14B intermetallic with Ce to x = 0.94 (1) does not completely eliminate the negative effect of spin-reorientation phase transition on the residual magnetization of the (Nd1−хCeх)2Fe14B intermetallic and (2) slightly decreases the slope of magnetization reversal curve.

A new pinched nonlinear hysteretic structural model for automated creation of digital clones in structural health monitoring

Optimizing risk treatment of structures in post-event decision-making is extremely difficult due to the lack of information on building damage/status after an event, particularly for nonlinear structures. This work develops an automated, no human intervention, modeling approach using structural health monitoring results to create accurate digital building clones of nonlinear structures for collapse prediction assessment and optimized decision-making. Model-free hysteresis loop analysis structural health monitoring method provides accurate structural health monitoring results from which model parameters of a nonlinear computational foundation model are identified. A new identifiable nonlinear smooth hysteretic model capturing essential structural dynamics and deterioration is developed to ensure robust parameter identification using support vector machines. Method performance is validated against both numerical and experimental data of a scaled 12-story reinforced concrete nonlinear structure. Results of numerical validation show an average error of 1.5% across 18 structural parameters from hysteresis loop analysis and an average error of 2.0% over 30 identified model parameters from support vector machines in the presence of 10% added root-mean-square noise. Validation using experimental data of the scale test reinforced concrete structure also shows a good match of identified hysteresis loop analysis and predicted nonlinear stiffness changes using the digital clones created with an average difference of 1.4%. More importantly, the predicted response using the digital clones for the highly nonlinear pinched hysteretic behavior matches the measured response well, with the average correlation coefficient Rcoeff = 0.92 and average root-mean-square error of 4.6% across all cases. The overall approach takes structural health monitoring from a tool providing retrospective damage data into automated prospective prediction analysis by “cloning” the structure using computational modeling, which in turn allows optimized decision-making using existing risk analyses and tools.

Parameter updating of a patient-specific lung mechanics model for optimising mechanical ventilation

Mechanical ventilation (MV) is the primary way to treat patients with acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU). Positive-end-expiratory-pressure (PEEP) is often applied in MV to maximise gas exchange and prevent further lung damage. However, optimal MV with patient-specific PEEP level is subjective, based on clinician experience, thus increasing the risk variability, and cost of care. In this study, a single compartment lung mechanics model is employed to predict pressure outcomes at higher PEEP levels using data from lower PEEP levels. Particularly, a hysteresis loop analysis (HLA) algorithm is applied to both the dynostatic curve and pressure-volume (PV) loop to identify the lung elastance at lower PEEP levels. Pulmonary resistance can then be calculated with measured airway pressure and identified elastance. Finally, the elastance and resistance at higher PEEP levels are predicted based on model fitting techniques to obtain the pressure with changes of PEEP. The result of pressure fitting and prediction show 95% of the airway pressure curve errors are within 3% across all the 8 data sets, while peak-inspiratory-pressure (PIP) prediction errors are within 1% for all data sets. The overall approach is readily automated, thus providing an initial critical information in determining optimal MV and PEEP settings. Such a model could also be used to validate the prediction accuracy of other more complex models and improve the confidence of their clinical application. Most importantly, the ability to predict PIP and overall pressure trajectories provide a means to safely titrate PEEP to optimal levels without the necessary to build an accurate enough mathematical model which could cost plenty of time and effort.

Iron Loss Modelling of Electrical Traction Motors for Improved Prediction of Higher Harmonic Losses

A Finite Element (FE) modelling approach is presented to account for the core losses in electrical machines that are generated by higher harmonic frequencies, for example those caused by Pulse Width Modulation (PWM) switching or by space harmonics due to the machine geometry. The model builds further on a post-processing calculation tool that was recently developed to take into account the magnetic skin effect in electrical steel laminations at high frequencies, and extends this by a more detailed loss analysis of the minor hysteresis loops that are caused by the higher harmonics. Further, these tools for high-frequency loss analysis are integrated into a complete electrical machine model with separate consideration of the major and minor loops. The modelling approach relies strongly on extensive magnetic measurement data of the electrical steel, in order to accurately predict the different loss components for minor hysteresis loops as a function of the DC bias field, frequency and amplitude of the minor loop. Results from the model are shown for an automotive traction motor, illustrating the losses caused by PWM harmonics and demonstrating the relevance of including the skin effect in these calculations.

Development of Inelastic Deformation upon Electromechanical Treatment and Surface Plastic Deformation of Grade 45 Steel

The effect of combined surface hardening such as electromechanical treatment and surface plastic deformation exerted on inelastic deformation processes occurring in grade 45 steel has been studied. The results of tensile tests and the analysis of the mechanical hysteresis loops for samples of grade 45 steel subjected to combined surface hardening are presented. The characteristic features of the inelastic properties and microinhomogeneous deformation of steel samples are considered, depending on a regularly inhomogeneous structure of the hardened surface layer.

A Nonlinear Hysteretic Model for Automated Prediction of Lung Mechanics during Mechanical Ventilation.

Mechanical ventilation (MV) is core intensive care unit (ICU) therapy during the Covid-19 pandemic. Optimising MV care to a specific patient with respiratory failure is difficult due to inter- and intra- patient variability in lung mechanics and condition. The ability to accurately predict patient-specific lung response to a change in MV settings would enable semi-automated care and significantly improve the efficiency of MV monitoring and care. It has particular emphasis when considering MV care required to treat Covid-19 patients, who require longer MV care, where patient-specific care can reduce the time on MV required.This study develops a nonlinear smooth hysteresis loop model (HLM) able to capture the essential lung dynamics in a patient-specific fashion from measured ventilator data, particularly for changes of compliance and infection points of the pressure-volume loop. The automated (no human input) hysteresis loop analysis (HLA) method is applied to identify HLM model parameters, enabling automated digital cloning to create a virtual patient model to accurately predict lung response at a specified positive end expiratory pressure (PEEP) level, as well as in response to the changes of PEEP. The performance of this automated digital cloning approach is assessed using clinical data from 4 patients and 8 recruitment maneuver (RM) arms.Validation results show the HLM-based hysteresis loops identified using HLA match clinical pressure-volume loops very well with root-mean-square (RMS) errors less than 2% for all 8 data sets over 4 patients, validating the accuracy of the developed HLM in capturing the essential lung physiology and respiratory behaviours at different patient conditions. More importantly, the patient-specific digital clones at lower PEEP levels accurately predict lung response at higher PEEP levels with predicted peak inspiratory pressure (PIP) errors less than 2% in average. In addition, the resulted additional lung volume Vfrc obtained with PEEP changes are predicted with average absolute difference of 0.025L. The overall results validate the versatility and potential of the developed HLM for delineating changes of nonlinear lung dynamics, and its capability to create a predictive virtual patient with use of HLA for future treatment personalization and optimisation in MV therapy.

Monitoring the microstructural changes of heat treated medium carbon steel by Barkhausen noise and hysteresis loop techniques

Heat treatment plays an important role to improve the thermo-mechanical properties of different carbon steel. This paper focus on a study the effect of different heat treatment process i.e. annealing, normalising, and quenching on the microstructure of medium carbon steel using non-destructive techniques like Barkhausen Noise (BN) and Hysteresis Loop (HL). Microstructural behavior was evaluated in terms of phase transformation, BN-peak value, differential permeability, and core loss at different austenitizing temperature. BN and HL analysis indicated that higher BN-peak and differential permeability were obtained in annealed sample. Further, higher core loss was obtained in quenched sample.

Studying of accumulation damages regularities under low cycle loading and cycle variable parameters conditions

The aim of the work is to study the possibilities of predicting cyclic durability in low-cycle fatigue and variable cycle parameters conditions, which combination describes the change complex nature in the stress-strain state over time of aircraft engine parts, based on linear and nonlinear models of damage accumulation. To do this, low-cycle fatigue tests of cylindrical samples were carried out for various loading forms, consisting of several simple-shape cycles. On the results of the tests carried out, fatigue life was predicted based on the nonlinear hypothesis of the Marco-Starkey damage accumulation. An analysis of the mechanical hysteresis loops was carried out to estimate the reasons for the increase of life during tests with a large number of groups in blocks.

Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F- and Cl- in phosphorus-rich solutions.

The magnetic nano-adsorbent Fe3O4@Mg/Al-CO3-LDH (Mg/Al-type layered double hydroxide) with a CO32− interlayer anion has been synthesized successfully on Fe3O4 nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO43− rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F− and Cl−, even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO43− in phosphorus-rich solutions, and especially can be utilized to determine trace F− and Cl− anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO43− for trace determinations. Herein, the hydrothermally synthesized Fe3O4@Mg/Al-CO3-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe3O4@Mg/Al-CO3-LDH was utilized successfully to adsorb PO43− in real samples and determine trace F− and Cl− accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO43− in phosphorus-rich samples, leaving F− and Cl− even if in a trace content.

Magnetic hysteresis loop behaviour of welded ferritic stainless steel 409L with the variation of magnetic field intensity

Hysteresis loop analysis technique, being a non-destructive testing technique is more beneficial than the destructive testing techniques to characterise the welded plate. In this study, the ferritic stainless steel AISI 409L plate was butt welded by gas metal arc welding process. Hysteresis loop analysis technique was used to study the microstructures and microhardness of the base metal region, heat affected zone and weldmetal zone. This study has been carried out at four different values of magnetic field intensity 250, 500, 750 and 1000 Oe. The effect of variation of magnetic field intensity on the hysteresis loop characteristics (average maximum flux density and core loss) has been investigated for base metal, heat affected zone and weldmetal zone. It was found that for each region, the average maximum flux density as well as core loss increases on increasing magnetic field intensity. Also, the variation of average maximum flux density is inversely proportional to the microhardness of the region at each value of magnetic field intensity.

Investigating the co-substitution impact of yttrium–nickel cations on lattice, morphological and magnetic parameters of SrM based ceramics

This study details the impact of the co-substitution of Y3+-Ni3+ ions for the Fe3+ ions on the structural, morphological and, magnetic parameters of SrM based SrYxFe12-2xNixO19 (0.00 ≤ x ≥ 0.25) (SrYFeNiO) ceramic magnets synthesized by the ceramic route. Rietveld refinement of XRD confirmed the hexagonal (P63/mmc (194), z = 2) SrFe12O19 phase for all and an additional rhombohedral (R-3c (167), z = 6) hematite Fe2O3 phase for x = 0.2, x = 0.25 doping levels. The experimental and theoretical measurements abstracted the stretch of lattice parameters, i.e., the crystallographic axis and the lattice cell volume, and the dislocation of the crystallographic plane (1 1 4) for the hexagonal system, certified the heavy Y3+-Ni3+ ions substitution. To examine the morphological parameters, FESEM presented the regular hexagonal platelets of sizes ~ 1–2 μm, and EDX revealed the presence of constituent elements with their atomic and weight percentages in SrFeYNiO products. The extraction of vibrational frequencies of Fe–O bonds at tetrahedral and octahedral sites of iron through FT-IR spectroscopy authenticates the formation of the SrM phase. XPS correlated the doped elements, i.e., nickel in Ni+2 and Ni+3 and yttrium in Y+3, whereas parent element, i.e., iron in Fe+3 and Fe+2 chemical states, enlightened their impact on the magnetic parameters. Hysteresis loop analysis deduced a linear decline in magnetic parameters such as saturation magnetization (Ms) and remnant magnetization (Mr) due to non-magnetic Y3+ and less magnetic Ni3+ ions installment in 4f1 and 2b polyhedral sites of Fe3+ ions. However, high coercivity (Hc) up to 2.92 kOe ∈ x = 0.15 and extended magnetocrystalline anisotropy (MCA) up to 5.790× 106 Erg/g ∈ x = 0.15 of our obtained ceramic magnets affirmed their application in permanent magnetic industry. M(T) curves also demonstrated the decrease in Ms and displayed an SPM at TB, which is shifting towards lower temperatures with increasing Y3+-Ni3+ contents approved the expansion of lattice parameters.

Analysis and Synthesis of Hysteresis Loops in an Oscillator Frequency Characteristic

A methodology for the analysis and synthesis of multiple hysteresis loops in the frequency characteristic of a voltage-controlled oscillator (VCO) is presented. This is achieved through the coupling of an oscillator inductance to multiple external (passive) resonators with resonant frequencies in the tuning range of the VCO. A possible application to the implementation of a compact chipless radio frequency identification (RFID) system is explored, using the oscillator as a reader and placing the external resonators in the tag. The system takes advantage of the high sensitivity to the tag resonances in the presence of hysteresis, which leads to vertical jumps in frequency versus the tuning voltage. A desired bit pattern would be encoded in the tag by enabling or disabling passive resonances at a sequence of frequencies. In the practical realization, the inductors in the oscillator and the external board are implemented through spiral inductors so that the resonators in the VCO and the tag have strong broadside coupling. The coupling effect is modeled through electromagnetic simulations, from which a linear admittance, representing the coupled subnetwork, is extracted. The multihysteresis oscillator characteristic can also be obtained experimentally through a new methodology able to stabilize the physically unstable sections without altering their steady-state values. Different demodulation methods for reading the tag are discussed.

Magnetic properties of fired clay (bricks) possibly containing epsilon iron (III) oxide

We investigated bricks with ages from modern to late 19th century. The experimental and theoretical analysis of hysteresis loops and magnetization (ARM, IRM) acquisition curves show presence of two magnetic phases with high and low coercivity, respectively, which might be related to nanoparticles of oxidized and/or cation-substituted magnetite and epsilon iron (III) oxide. The fired clay (bricks) thus can be viewed as a model system in which epsilon iron (III) oxide forms readily.

A combined SHM/IDA method for assessing collapse capacity and risk in subsequent ground motions

Prediction of building collapse due to significant seismic motion is a principle objective of earthquake engineers, particularly after a major seismic event when the structure is damaged and decisions may need to be made rapidly concerning the safe occupation of a building or surrounding areas. Traditional model-based pushover analyses are effective, but only if the structural properties are well understood, which is not the case after an event when that information is most useful. This paper combines hysteresis loop analysis (HLA) structural health monitoring (SHM) and incremental dynamic analysis (IDA) methods to identify and then analyse collapse capacity and the probability of collapse for a specific structure, at any time, a range of earthquake excitations to ensure robustness. This nonlinear dynamic analysis enables constant updating of building performance predictions following a given and subsequent earthquake events, which can result in difficult to identify deterioration of structural components and their resulting capacity, all of which is far more difficult using static pushover analysis. The combined methods and analysis provide near real-time updating of the collapse fragility curves as events progress, thus quantifying the change of collapse probability or seismic induced losses very soon after an earthquake for decision-making. Thus, this combination of methods enables a novel, higher-resolution analysis of risk that was not previously available. The methods are not computationally expensive and there is no requirement for a validated numerical model, thus providing a relatively simpler means of assessing collapse probability immediately post-event when such speed can provide better information for critical decision-making. Finally, the results also show a clear need to extend the area of SHM toward creating improved predictive models for analysis of subsequent events, where the Christchurch series of 2010–2011 had significant post-event aftershocks.