Anisotropic Steel Research Articles

INTEGRATING NEURAL NETWORKS INTO SHEET METAL FORMING: A REVIEW OF RECENT ADVANCES AND APPLICATIONS

In order to predict defects, improve performance, and streamline operations, machine learning techniques are becoming ever more indispensable in manufacturing processes, mainly in sheet metal forming. Incorporating neural networks into the process of sheet metal forming is the subject of this article's exhaustive examination of recent developments and applications. Exploring datasets from a variety of sheet metal forming processes, numerous machine learning models, including ensemble and single learning techniques are investigated. The functionality of this method extends to various tasks, including the prediction of springback in cold-rolled anisotropic steel sheets. The review provides a conclusion section that presents the main implementation methodologies and how they address to some manufacturing issues.

CIVA as an Aid to Understanding Ultrasonic Anisotropy in Steel

Standard calibration blocks to assess beam paths and configure data displays using ultrasonic instruments use low carbon steel with isotropic acoustic properties. However, industry is trending towards the use of high tensile steels where the acoustic properties are anisotropic. When an ultrasonic system, calibrated on an isotropic steel reference block, is used on anisotropic steels, the beam can be bent, skewed and attenuated so that the reference setup is rendered useless. CIVA simulation software can be used to aid in understanding the effects on the data displays. As well, CIVA can help to demonstrate the degree of change that can occur when the acoustic velocities are established for the fast and slow shear modes in an anisotropic steel.

Technical solutions to reduce losses in magnetic cores and material consumption of three-phase transformer and reactor equipment

Purpose. The increase in energy costs and the need for further energy saving lead to an increase in requirements for reducing losses in the magnetic cores of transformers and reactors. Problem. The improvement of transformer and reactor equipment is traditionally carried out by applying the achievements of electrical materials science and new technologies to traditional designs and structures of electromagnetic systems. The basis of modern transformers is made up of laminated and twisted magnetic cores. The disadvantage of laminated magnetic cores is large additional losses in corner zones due to the texture of anisotropic steel. Disadvantage of twisted three-phase three-contour magnetic cores is large additional losses caused by the lack of magnetic coupling of three separate magnetic flux contours. The disadvantages of combined joint tape-plate magnetic cores are the unsatisfactory use of the active volume and increased losses, which are determined by the uneven distribution of the magnetic field and the negative impact of steel texture in the corner zones of the twisted parts. Aim. To determine the possibility of improving three-phase transformers and reactors. Methodology. The improvement is achieved by geometrical and structural transformations of the outer contours and elements of the varieties of magnetic cores. Results. The possibility of eliminating additional losses of a planar laminated magnetic core by a combination of anisotropic and isotropic steels at the appropriate location in the yoke-rod and corner sections is determined. With an octagonal outer contour of the combined magnetic core, a reduction in mass is achieved without an increase in losses. The mutually orthogonal position of the steel layers or the elements of the joint twisted and combined three-phase planar and spatial magnetic cores achieves magnetic coupling and elimination of additional losses of individual twisted contour sections. The hexagonal configurations of the inner contours of the twisted yoke-corner parts and the cross-sections of the laminated rods of the variants of the axial spatial joint magnetic core improve the magnetic flux density distribution and reduce the main losses of the yokes, as well as reduce the complexity of manufacturing rods from identical rectangular steel layers. Originality. The paper presents constructive and technological proposals and features of varieties of non-traditional planar and spatial, laminated, twisted and combined tape-plate joint magnetic cores, which differ in the combination of anisotropic, isotropic and amorphous steels, as well as the multifaceted geometric shape of contours and the spatial arrangement of elements. Based on the identity of the optimal geometric ratios of the variants of electromagnetic systems of transformers and reactors, with joint planar and spatial twisted and combined and tape-plate magnetic cores, the unification of the structure of transformer and reactor equipment with a capacity of I-III dimensions.

Notch Fatigue Life Research Based on Critical Distance Theory

Orthotropic anisotropic steel bridge panels are widely used in civil engineering due to their advantages of light deadweight, high ultimate bearing capacity, and wide range of applications. However, their fatigue problem is serious, and the fatigue-resistant design of the steel box girder diaphragm curved cutout is still difficult. In order to effectively predict the fatigue life of this typical fatigue-susceptible detail, a fatigue test of the specimen with curved notched segments of the diaphragm was carried out. ABAQUS 2016 version finite element analysis software was used to establish three kinds of finite element simplified models of the fatigue specimens with curved notches, and the laws of the influence of different notch radii on the fatigue life of the specimens were studied. Through the finite element solution of the three arc notch specimen models with different radii under the tensile load of 50 kN their respective principal stress distributions were obtained. The critical distance theory was introduced to analyze the characteristic stresses in the stress concentration area of the arc notch, and the point method and line method were used to calculate the characteristic stresses. The fatigue life prediction models of three kinds of notched components were established by combining the material fatigue limit and FE-safe life results. The results show that the point method is more conservative than the line method; no matter if the point method or the line method is used, the characteristic stress and the notch radius are inversely proportional to each other, and it is beneficial for the fatigue life of the structure to appropriately increase the notch radius. The fatigue prediction model of steel box girder diaphragms with curved notches based on the critical distance theory is of high accuracy, which is basically consistent with the test results, verifying the feasibility of the critical distance theory in the fatigue life prediction of notched specimens, and providing a reference for the fatigue life assessment of similar steel structures.

An Experimental Study on the Flexural Performance of a Steel-ECC Composite Bridge Deck Sheet in the Negative Moment Zone

This paper seeks to solve the problem of orthotropic anisotropic steel deck pavement being prone to damage and fatigue, and to study the negative moment performance of steel-ECC concrete composite deck slabs. In this work, four groups of eight specimens were designed for the negative moment four-point bending test study, which included four variables of two ECC slab thicknesses and two bolt spacings. By analyzing the damage mode, crack distribution characteristics, bending load capacity, load-deflection curve, and load-strain curve, the effects of different ECC slab thicknesses and bolt spacings on the bending performance, deformation capacity, and cracking behavior of the steel-ECC composite bridge deck were investigated. The test showed that the combined structure of the ECC and steel plate showed good integrity and good ductility under a negative bending moment, and the damage mode of the member was pure bending of a section of the ECC with concrete cracking damage. When the thickness of the ECC plate increased from 50 mm to 75 mm, the ultimate flexural load capacity of the specimen increased by 92.6%, and when the distance between bolts was reduced from 200 mm to 150 mm, the ultimate flexural load capacity of the specimen increased by 13.4%. The increase in the ECC layer thickness increases the ultimate bearing capacity of the specimen significantly, and the decrease in the bolt spacing increases the ultimate bearing capacity of the specimen less.

Influence of the Variation of Mechanical Properties and Thickness in Hot-Rolled Strips of Electrical Anisotropic Steel to Stabilize Cold Rolling

Influence of the Variation of Mechanical Properties and Thickness in Hot-Rolled Strips of Electrical Anisotropic Steel to Stabilize Cold Rolling

Strengthening of duplex stainless steel processed by equal channel angular pressing (ECAP)

This manuscript presents the study of the microstructural evolution, plastic anisotropy, and mechanical behavior of a duplex stainless steel (DSS) processed by the equal channel angular pressing (ECAP) technique. The ECAP process produced shear bands affecting both phases, austenite and ferrite, which in turns act as preferential sites for the appearance of the new ultrafine grains. Microstructural observations indicated grain sizes smaller than 300 nm in both phases. However, marked differences in the grain boundary misorientations were observed. Most ferrite grain boundaries showed low misorientations (average misorientation of 30°). In contrast, the austenite grain boundaries were mainly dominated by high-angle grain boundaries (average misorientation of 39°). The ECAP processing allowed to reach a yield strength over 1.1 GPa after one ECAP pass. Dislocations formed walls in the ferrite, while they were distributed evenly in the austenite grains creating plastic gradients between the two phases. Through the visco-plastic self-consistent model, it was found that austenite and ferrite strain hardening at different rates, generating plastic instabilities at different strain magnitudes. In this way, it was shown that austenite is the phase that provides more hardening while ferrite provides ductility. Regarding the anisotropy of the steel, crystal plasticity simulations showed that during the first passes of ECAP, the Lankford coefficients increase notably due to the heterogeneous microstructure of sheared grains with a higher density of defects forming subgrains in ferrite than austenite. Moreover, the austenite was more responsible for the larger planar anisotropy (Delta r = 2.18) values than ferrite (Delta r = 1.67) after two ECAP passes.

Influence of the Peculiarities of Artificial Fragmentation of Domain Structure in a Fe–3% Si Anisotropic Electrical Steel on the Efficiency of Reducing the Magnetic Losses

Influence of the Peculiarities of Artificial Fragmentation of Domain Structure in a Fe–3% Si Anisotropic Electrical Steel on the Efficiency of Reducing the Magnetic Losses

Physical Modification of Products Made of Soft Magnetic Materials under Texturing Effects

The results of improving physical properties of different types of magnetic cores made of soft magnetic crystalline and amorphous alloys based on siliceous iron are presented. Methods and modes of controlling orientational, dimensional and dynamic parameters of magnetic domains by means of a uniaxially textured complex of thermomagnetic, locally laser, and plane deformation effects have been developed. As a result, in electrical magnetic cores made of anisotropic iron-silicon steels of 3407, 3408 grades a decrease in eddy-current magnetic losses by 25–35% and an increase in magnetic permeability by 1.5–2 times have been achieved.

Method for determining of the optimal thickness of sheets of magnetic cores of electrical machines by the wattmeter method

The problem of reducing magnetic losses (no-load losses) in the steel of the magnetic cores of electrical machines is investigated. The tasc of determining the optimal thickness of steel sheets of the magnetic circuit of an electric machine is considered. The criterion for optimality is the minimum power of magnetic losses in steel. Currently, this problem does not have an exact solution due to the fact that the exact ratio of the hysteresis and eddy current components of magnetic losses in steel is unknown. Analyzed the power of magnetic losses in modern electrical machines and devices, depending on the thickness of the sheets of electrical steel. A method is proposed for determining the optimal thickness of steel sheets of the magnetic circuit of an electric machine based on the wattmeter method. In the course of the experiment, two identical magnetic circuits were selected from steel sheets of different thicknesses, for which the losses in steel were measured at different frequencies of magnetization reversal and the optimal thickness of the sheets was calculated. The proposed formula for calculating the thickness of the sheets is valid for both isotropic and anisotropic steel. The proposed technique can be used for both transformers and electric motors and generators.

Forming defects prediction in cup drawing and embossing of a thick steel sheet

The accurate prediction of forming defects is fundamental for the virtual try-out of metallic sheet components. However, the constitutive model can have a strong impact on the numerical predictions, namely the cup earing, the occurrence of wrinkles and the tearing failure. The process conditions considered in this work are the ones established for the “Benchmark 2 – Cup Drawing of Anisotropic Thick Steel Sheet”, proposed under the Numisheet 2018 international conference. The axisymmetric cups are obtained from a steel sheet with 2.8 mm of thickness, resorting to different process conditions to induce different defects. The advanced yield criterion proposed by Cazacu and Barlat is used to define the anisotropic behavior of the blank. The calibration of the material parameters is carried out by fitting the following experimental data from: (i) uniaxial tensile tests performed in every 15º to the rolling direction; (ii) biaxial tension tests to evaluate the directions of the plastic strain rates in the first quadrant of the yield loci. The numerical predictions are compared with the experimental measurements, allowing to assess the accuracy of the finite element model to predict each type of forming defect. The cup earing and the strain localization are accurately predicted, while the wrinkles amplitude is clearly underestimated.

DESIGN AND TECHNOLOGICAL PROPOSALS FOR IMPROVING A SINGLE-PHASE TRANSFORMER WITH LAMINATED MAGNETIC CORE

Goal. The purpose of the work is to analyze the features and substantiate the advantages of the spatial radial electromagnetic system of a single-phase transformer with rectangular sections of the rods of a charged magnetic circuit. Methodology. Improvement of single-phase transformers is possible by structural-geometric transformations of active elements. The justification of the advantages of such transformations is achieved by the method of invariant objective functions with dimensionless optimization components and universal relative controlled variables. Results. Replacing the rectangular contours of the variants of a planar magnetic circuit with a hexagonal circuit leads to a decrease in the volume of steel and the loss of three angular zones of changes in the direction of the magnetic flux relative to the texture compared to planar counterparts. The separation of the windings into sections with an arrangement on three rods leads to a decrease in the average length of the coil. Originality. A three-core magnetic core can consist of rod and jugular-angular parallelogram plates of anisotropic and isotropic electrical steel. It is advisable to combine a combination of steels by integral welding of billets with subsequent separation into chevron jugular-rod elements. The method called on has developed mathematical models of the mass, cost, and active power losses of variants of a single-phase electromagnetic system of a transformer with rod and armor planar and spatial radial three-core magnetic cores. Practical significance. It was found that the decrease in the extrema of the mass and cost indicators, as well as the calculated decrease, under the condition that the coefficients of additional losses are identical, the extrema of the losses of the single-phase radial three-rod system of the transformer relative to the planar analogue with a bar stocked magnetic wire from anisotropic steel, respectively 13,0-12,3 %, 15,3-10,1 % and 15,1-18,1 % with copper windings and 10,8-10,2 %, 12,8-13,7 % and 12,6-12,3 % with aluminum windings. The main indicators of traditional single-phase systems with rod and armored magnetic circuits differ insignificantly, which is consistent with early known optimization and calculation data of transformers.

Topical Issues of the Technological Development of Advanced Electrical Steel Grade Production in Russia

The growing competition in the global steel market in the field of rolled products potentially implies an efficient, economical and environmentally friendly approach to the production of electrical steel. The following key elements of advanced strip steel casting are discussed: innovations in the use of cast strips for the production of the initial hot-rolled billet and cold-rolled steel from electrical anisotropic and isotropic steel, as well as amorphous steel strips for magnetic cores of electrical machines, which have been commercially applied in world practice.

Optimization algorithms for ultrasonic array imaging in homogeneous anisotropic steel components with unknown properties

In this paper, we investigate the ability of an adaptive ultrasonic method to image point-like reflectors inside anisotropic and homogeneous nuclear steels with unknown properties, such as V-shape welds or cladded components. The optimization scheme combines the Total Focusing Method (TFM) imaging algorithm with a customized gradient ascent method to improve both the quality and the reliability of ultrasound images. A statistical analysis of its robustness is performed with simulated echoes and using a surrogate model to speed up the computation times of the TFM images. Then, the optimization procedure is evaluated with several experimental cases and provides highly enhanced images with a 5 MHz array. The positioning of the artificial defects of 2.0 mm diameter is estimated with less than 1 mm error with respect to their actual position, and the signal-to-noise ratio is increased by up to 10 dB. The elastic properties are also estimated with less than 10% error when compared to their actual values.

Use of Time-Frequency Representation of Magnetic Barkhausen Noise for Evaluation of Easy Magnetization Axis of Grain-Oriented Steel.

The paper presents a new approach to non-destructive evaluation of easy/hard magnetization axis in grain-oriented SiFe electrical steels based on the Barkhausen phenomenon and its time-frequency (TF) characteristics. Anisotropy in steels is influenced by a number of factors that formulate the global relationship and affect the Barkhausen effect. Due to the observed high variability in the dynamics of magnetic Barkhausen noise (MBN) over time, obtained for various directions in grain-oriented steel, it becomes justified to conduct MBN signal analyses in the time-frequency domain. This representation allows not only global information from MBN signal over entire period to be expressed, but also detailed relationships between properties in time and in frequency to be observed as well. This creates the opportunity to supplement the information obtained. The main aspect considered in the work is to present a procedure that allows an assessment of the resultant angular characteristics in steel. For this purpose, a sample of a conventional grain-oriented SiFe sheet was used. Measurements were made for several angular settings towards the rolling and transverse directions. A data transformation procedure based on short-time Fourier transform (STFT) as well as quantitative analysis and synthesis of information contained in the TF space was presented. Angular characteristics of selected TF parameters were shown and discussed. In addition, an analysis of the repeatability of information obtained using the proposed procedure under various measurement conditions was carried out. The relationship between the selection of calculation parameters used during transformation and the repeatability of the obtained TF distributions were demonstrated. Then the selection of the final values of the calculation parameters was commented upon. Finally, the conclusions of the work carried out were discussed.

Improving Prediction of Springback in Sheet Metal Forming Using Multilayer Perceptron-Based Genetic Algorithm.

This paper presents the results of predictions of springback of cold-rolled anisotropic steel sheets using an approach based on a multilayer perceptron-based artificial neural network (ANN) coupled with a genetic algorithm (GA). A GA was used to optimise the number of input parameters of the multilayer perceptron that was trained using different algorithms. In the investigations, the mechanical parameters of sheet material determined in uniaxial tensile tests were used as input parameters to train the ANN. The springback coefficient, determined experimentally in the V-die air bending test, was used as an output variable. It was found that specimens cut along the rolling direction exhibit higher values of springback coefficient than specimens cut transverse to the rolling direction. An increase in the bending angle leads to an increase in the springback coefficient. A GA-based analysis has shown that Young’s modulus and ultimate tensile stress are variables having no significant effect on the coefficient of springback. Multilayer perceptrons trained by back propagation, conjugate gradients and Lavenberg–Marquardt algorithms definitely favour punch bend depth under load as the most important variables affecting the springback coefficient.

Time-Frequency Analysis of Barkhausen Noise for the Needs of Anisotropy Evaluation of Grain-Oriented Steels.

The paper presents a new approach to obtain information on magnetic anisotropy in Si–Fe grain oriented ferromagnetic steel based on the observation of the magnetic Barkhausen noise (MBN). Until now, in the literature one can only notice the MBN study of magnetic anisotropy in steels carried out in a single time or frequency domain. However, due to the observed high variability of the dynamics of the MBN phenomenon over its occurrence period, depending on the steel properties, the idea of utilization of combined time and frequency representations to obtain new or supplementary information arises. For this purpose, the MBN phenomenon was observed in various directions for steels with oriented magnetic properties. Then, using the short-time Fourier transform, time-frequency (TF) distributions were determined and features vectors enabling the quantification of crucial information were determined. Before performing the final experiments, a series of tests were carried out for different measuring conditions. As a result, it was possible to adjust the conditions enabling us to obtain the highest possible sensitivity for MBN and discrimination level between directional properties in the material. Then, an algorithm of detailed analysis and division of the TF representation into subranges was proposed, enabling the extraction of more detailed information about the phenomena occurring during the magnetization process. This allowed us to clearly indicate and then separate three areas of MBN main activity. Finally, the obtained angular distributions of selected features were presented and discussed, and further conclusions were given.

Texture Formation in Hot Rolling of Electrical Anisotropic Steel

Processes of structure and texture formation in hot rolling of electrical anisotropic steel are studied. It is shown that the structure of the surface layers of hot-rolled strips forms as a result of the joint action of γ → α phase transformation and dynamic recrystallization. The structure of the central layers forms as a result of recovery of deformed grains.

Finite element prediction of the forming limit curve for anisotropic high-strength steel

Finite element prediction of the forming limit curve for anisotropic high-strength steel

Correlation of acoustoelasticity with hydrogen saturation during destruction

The surface effect of acoustic anisotropy in steel and aluminum industrial alloys was experimentally detected. Changes in the integral value of acoustic anisotropy in 10–15 times were observed after removing the surface layer with a thickness of 100 microns in steel specimens and 250 microns in aluminum specimens. The correlation between distributions of acoustic anisotropy and hydrogen concentrations in surface layer of specimens was found. It was suggested that the surface effect of acoustic anisotropy occurs due to the influence of microcrack systems localized in a surface layer of metal. This result can be used to improve existing approaches to estimating of corrosion damage, fatigue, mechanical stresses and plastic deformations of technical structures by using acoustic anisotropy.