Plastic Work Research Articles

Comparative Modeling of Power Hardening Micro-scale Metallic Plates Based on Lower and Higher-Order Strain Gradient Plasticity Theories

Present study investigates a comparative study of lower and higher-order strain gradient plasticity (SGP) theories involving the size-dependent micromechanically flexural behaviors of crystalline thin plates. The investigation includes the Mechanism-Based and the Chen–Wang SGP models established on the Taylor dislocation hardening by evoking the statistically stored dislocations and geometrically necessary dislocations. In addition, these models are conjugated with a multiple plastic work-hardening law proposed for the microstructural applications of the SGP. An analytical approach based on energy minimizing method is used for obtaining deflection values in terms of the length scale, exponent of the work-hardening and the tangential module. The obtained results indicate a meaningful dependence of the deflections to the length scale, plastic work hardening and other parameters as well.

Studies on applying hot-rolled coil to hull superstructure

Application of the hot-rolled steel sheet for the members of superstructure, where the strength requirement of these parts in ships is not severe, is expected as a solution to reduce the hull construction cost. Because the hot-rolled steel sheet is applied after recoiling by cold working to return it to a flat plate, the material properties is deteriorated due to excessive plastic working and the residual stress induced by the plastic work might affect for the thermal cutting and welding. There is a possibility that the hot-rolled steel sheet has poor properties comparing with the flat rolled steels applied for hull parts where the structural integrities are required by the classification societies’ rules. The difference of properties between the hot-rolled steel sheet and the flat rolled steel are investigated in this research.

Some principles of generating seismic input for calculating structures

In this paper different models of seismic input are analyzed. The most essential characteristics of seismic effects are peak ground acceleration, peak ground velocity, peak ground displacement, Arias intensity, cumulative absolute velocity, seismic energy density, harmonic coefficient κ, pseudo spectral kinematic characteristics, root-mean-square peak kinematic characteristics, plastic forces work and damage spectrum. The influence of seismic impulse on characteristics of seismic input is studied. A.A. Dolgaya’s and L.N. Dmitrovskaya’s models with seismic impulse are compared. L.N. Dmitrovskaya’s model allows to reach estimated values of energy characteristics of seismic input with the smallest deviation. When generating such processes, it is important to take into account both the properties of real actions and the limiting state of the calculated structure. The considered models of seismic inputs should be applied in the following cases: a) in case of designing mass construction projects when it is not possible to get a package of design accelerograms, b) in typical designing when the design object can be located on sites with different seismic and geological conditions, c) at early stages of designing important objects when the package of design accelerograms is not available yet but it is necessary to make technical solutions.

Application of 2XXX and 7XXX series alloys as input material for the new casting-forging hybrid process

The aim of the work has been to analyze the aluminum alloys for plastic working from the point of view of their usefulnessin the new hybrid manufacturing process which includes gravity casting and forging. The tests have been carried out onpopular aluminum alloys from the 2xxx and 7xxx series: 2017A, 2024, 7022, and 7075, respectively. The authors have focusedon the problem of using these materials at the casting stage. The analyses have included verification of the technologicalproperties of alloys, including fluidity and the tendency to create porosities. Next, the influence of the solidification rate(associated with the use of various molds) on the casting microstructure has been determined. Based on the conducted analyzes, thealloys with the best casting behavior have been indicated. At the same time, possible problems that may occur at the forging stagehave been discussed.

Hybrid Model of Mathematical and Neural Network Formulations for Rolling Force and Temperature Prediction in Hot Rolling Processes

Steelmaking requires precise calculation at several steps of the manufacturing processes. We focus on the hot rolling process using Steckel mills, almost the end step in steel coil manufacturing. The rolling process is a type of plastic working in which a slab passes between two rolls and is stretched to reach the target thickness. It is necessary to predetermine the exact rolling force to obtain a coil with an accurate thickness after the rolling process. First, we introduced a machine learning model for calculating the rolling force, which can be used in-line in real plants. However, a direct calculation of the rolling force can cause stability problems, because the model output directly affects the process. In order to avoid such a problem, we determined a special temperature of the coil by inverse calculation of the classical mechanical model of hot rolling and set it as the model output value. As learning models, deep neural networks (DNN) and gradient boosting-based decision tree models were used. We preprocessed the collected process history data and added artificial features to the model input by creating physical variables used in the classical models. Moreover, to supplement the black-box nature of DNN, feature importance was analyzed from the decision tree model, and utilization and interpretation of each feature in the process are presented. Thus, our methods take advantage of both the classical mathematical model and the deep neural network model.

Material Modeling in High Strain Range and Forming Limit Analysis for 6000 Series Aluminum Alloy Sheet

This study investigates the effects of material modeling in high strain range on the forming limit analysis of a 6000-series alloy sheet 6016-T4. A servo-controlled tension-internal pressure testing machine was used to measure the multiaxial plastic deformation behavior in a strain range from initial yield to fracture. Tubular specimens were fabricated with a weld line thicker than the sheet thickness to prevent fracture from occurring in the weld zone. Proportional loading in the first quadrant of the principal stress space was applied to the specimens to measure the forming limit curve (FLC) and forming limit stress curve (FLSC), in addition to the contours of plastic work and the directions of plastic strain rates. Moreover, forming limit strains were measured using a flat-headed punch stretching test (PST). From the multiaxial tube expansion test (MTET) data, although a differential hardening effect was observed, appropriate coefficients including the exponent of the Yld2000-2d yield function (Barlat et al, 2003) were determined and employed in the Marcińiak-Kuczyski (1967) forming limit analysis (M-K analysis). The calculated forming limit strains in the vicinity of equibiaxial tension were smaller than the measured ones. The M-K analysis predicted that the forming limit strain in the vicinity of equibiaxial tension becomes minimum when the inclination angle of the localized neck from the rolling direction (RD) is 45° (diagonal direction; DD) while the experimental fracture direction was the RD. With the additional MTET, the plastic deformation behavior in the DD was measured and compared with that calculated from the material model. The reason of the discrepancy in the fracture direction between the experiment and the M-K approach is discussed.

In-plane Biaxial Compression Test on 780MPa Cold Rolled Sheet Steel

Accuracy in finite element simulation (FE-simulation) of press-forming has improved through sophisticated material modelling partly by using data of various experiments such as uniaxial compression test, biaxial tension test, and in-plane cyclic loading test. However, biaxial compression test on sheet material has never been reported due to difficulty in buckling suppression, and difference between material behavior under biaxial tension and that under compression has not been discussed yet. In this paper, biaxial compression test on sheet material with special tools suppressing buckling and a specimen shape to achieve uniform deformation in measurement area is proposed mainly based on FE-simulation. The special tool has a urethane plate at the place where the tool contact with the measurement area of a specimen to prevent damage of strain gauges. Absolute values of compressive stress at a plastic work measured by the biaxial compression test were larger than tensile stresses at the same plastic work measured by biaxial tension test: the similar results observed in uniaxial tension and compression tests known as stress differential (SD) effect.

Failure Prediction Capability of Generalized Plastic Work Criterion

In this study, failure prediction capability of the generalized plastic work criterion was evaluated. Criterion was applied to the uniaxial tensile and Nakajima stretch forming tests to predict the forming limits of an advanced high strength steel sheet. Firstly, critical damage value of the material was calculated for two different cases. Energy value till uniform elongation range was considered for in the first case, while total energy value was considered in the second case. Finite element simulations of the uniaxial tensile and Nakajima stretch forming tests were performed for both cases. The fracture strain in the uniaxial tensile test and limit strains of each Nakajima sample were predicted and the predicted results were compared with the experimental results. Comparisons showed that the onset of the diffuse necking and the fracture strain were predicted successfully in the uniaxial tensile test. However, it was observed from Nakajima tests that limit strains at the left side of the forming limit diagram (FLD) were predicted successfully by the criterion, while they weren’t accurately predicted at the right side of the FLD.

Образы античности в творчестве Ф. Г. Гордеева

This article deals with some features of the creative way of the outstanding Russian sculptor of the18th century, Fedor Gordeev. The issue of the antique heritage in F. G. Gordeev’s as well as his contemporaries’ works originates and is solved at different levels. Reference to classical antiquity appeared in the direct use of classical subjects, in studying works of art, copying, the use of compositional techniques, in making creative pieces of work on different subjects including those from the Russian history. Works of classical art take a special place in Gordeev’s legacy. Contemplating the artist’s works, one can notice that it is predominated by classical motifs, the techniques of friso-based design of reliefs — processions — are widely used, the principles of classical proportioning and planned configuration are followed. A deeper, intermediated perception of classical antiquity appeared in Gordeev’s memorial plastic works. The Golitsyns family’s gravestones allow to trace the evolution of his creative method which reflects the general evolution of the style. The classical antiquity for Gordeev always remained the canon of beauty that he knew better than any of his contemporaries owing to many years’ of teaching experience at the Academy, continuous work in the workshop casting classical statues, and probably mainly due to the peculiarities of his creative talent fully expressing the features and stages of the evolution of the style of that era.

Pengaruh Parameter Pemesinan terhadap Kualitas Hasil Potong Mesin Bubut Maximat V13 pada Benda Kerja Poros PVC

Metal cutting process (cutting process) is to cut metal to get the shape and size and quality of the planned cutting surface. The metal cutting process is carried out with special tools, according to the type of cutting process. So the tools for one process cannot be used in another process, even for similar processes, the tools cannot be exchanged if the cutting plans are not the same. Lathe process is a machining process to produce cylindrical machine parts which are carried out using a Lathe. Its basic form can be defined as the machining process of the outer surface of cylindrical or flat lathe objects. Polyvinyl Chloride, commonly abbreviated as PVC, is the third-order thermoplastic polymer in terms of total usage in the world, after Polyethylene (PE) and Polypropylene (PP). Worldwide, more than 50% of PVC produced is used in construction. PVC is produced by polymerizing vinyl chloride monomers (CH2 = CHCl). Because 57% of its mass is chlorine, PVC is the polymer that uses the lowest petroleum feedstock among other polymers. This research follows up the selection of configuration of the lathe machining process using plastic work pieces. In this study, Maximat V13 lathe and PVC type plastic were used. The variation of machining processes are spindle rotation (320, 540, and 900 rpm), feeding speed (0.07, 0.14, and 0.28), the use of tool types (carbide and HSS) and cooling (without cooling, coolant, and oil). So, with this research, it is expected that the optimal parameters in determining the configuration of the lathe machining process on a PVC work piece to produce a good turning surface can be achieved

High-strength ultrafine-grained titanium 99.99 manufactured by large strain plastic working

In this research, high-purity titanium (hp-Ti, 99.99 wt%) was subjected to a large strain via a cold plastic working process. To accumulate a relatively large plastic deformation in the workpiece, the hydrostatic extrusion (HE) technique was applied. The initial rod with a diameter of ∅50 mm was subjected to a multi-pass extrusion process, and, this way, rods with a diameter of ∅8 mm and ∅7 mm were obtained. In this paper, the results of an investigation of the structure and mechanical properties of the hp-Ti are presented. The size and shape of the grains of the as-received and extruded samples were examined, and an effective way of refining grain and strengthening hp-Ti using plastic working was demonstrated. Thanks to the process applied, an ultrafine-grained structure was obtained. In the transverse section, the average grain size determined by transmission electron microscopy was 117 nm on average. As a result of the extrusion, a significant increase in yield stress, tensile strength and microhardness was observed. Moreover, in this paper the overall potential of the HE technique was demonstrated. The results of this work confirm that it is possible to manufacture high-strength, ultrafine-grained high-purity titanium via cold plastic working.

Deep learning predicts path-dependent plasticity

Plasticity theory aims at describing the yield loci and work hardening of a material under general deformation states. Most of its complexity arises from the nontrivial dependence of the yield loci on the complete strain history of a material and its microstructure. This motivated 3 ingenious simplifications that underpinned a century of developments in this field: 1) yield criteria describing yield loci location; 2) associative or nonassociative flow rules defining the direction of plastic flow; and 3) effective stress-strain laws consistent with the plastic work equivalence principle. However, 2 key complications arise from these simplifications. First, finding equations that describe these 3 assumptions for materials with complex microstructures is not trivial. Second, yield surface evolution needs to be traced iteratively, i.e., through a return mapping algorithm. Here, we show that these assumptions are not needed in the context of sequence learning when using recurrent neural networks, diverting the above-mentioned complications. This work offers an alternative to currently established plasticity formulations by providing the foundations for finding history- and microstructure-dependent constitutive models through deep learning.

Modeling material behavior of AA5083 aluminum alloy sheet using biaxial tensile tests and its application in numerical simulation of deep drawing

Improvement in accuracy of the predicted results from numerical simulation results into a reduction of cost and time involved in tool design and experimental trials. However, the predicted results from finite element simulations are significantly affected by the chosen yield criterion and work hardening law. The selection of yield criterion and work hardening law depends on the characterization methods used for defining the material behavior. In this work, the mechanical behavior of AA5083-O aluminum alloy sheet is modeled by performing biaxial tensile tests using cruciform specimen and hydraulic bulging experiments in addition to uniaxial tensile tests. Biaxial to uniaxial yield stress ratios are determined using the equal plastic work principle from the flow curves obtained from these tests. The obtained ratios are used to find the coefficients of Yld2000-2d and Hill48 yield criteria which is then used in the numerical simulations of cylindrical cup deep drawing. Numerical simulations are also carried out using uniaxial and biaxial flow curves fitted with different isotropic hardening laws. Thickness distributions and the load-displacement curves are predicted and validated by performing cylindrical cup deep drawing experiments.

Tension-shear multiaxial fatigue damage behavior of high-speed railway wheel rim steel

This work addresses the tension-shear multiaxial fatigue behavior of ER8 medium carbon steel, commonly used for the high-speed railway wheel. Making use of high-frequency fatigue tests with different applied loading angles, namely 0° (uniaxial), 30° and 45° (both multi-axial), the fatigue limit and its corresponding S-N curves were calculated. The results showed that as the loading angle increased, both the fatigue life and von Mises stress fatigue limit were dramatically reduced (more than 65% with respect to uniaxial loading). Temperature measurements were performed in the sample surface during the tests and the micro-structure of fatigue fractures were characterized. The surface temperature evolution tendency of the specimen in the multiaxial fatigue tests was similar to that in the uniaxial fatigue tests. Moreover, the surface temperature evolution can be divided into three stages: Rapid Increase Stage (RIS), Stability Stage (SS) and Mutation Stage (MS), corresponding to rapid plastic work, cyclic micro-plastic deformation and crack initiation, and crack growth, respectively. Although all tests showed brittle and ductile fractures, multiaxial fatigue lead to significant changes in the mode of cyclic micro-plastic strain and fatigue damage behavior. There was a change from the dislocation slip of the uniaxial fatigue, to deformation twinning of the multiaxial fatigue, owing to the larger shear stresses. We conclude that such large shear stresses induce profound changes in the fracture mode and deeply influences the fatigue behavior.

Grain Refinement Mechanism and Texture Evolution of Polycrystalline Cu Sheets during the Electromagnetic Forming Process

The grain refinement mechanism and texture evolution of electromagnetically formed polycrystalline Cu sheets were investigated using the electron back-scattered diffraction (EBSD) technique. It is found that the average grain size decreases from 35.88 μm to 8.77 μm. The grain refinement was mainly attributed to dynamic recrystallization (DRX) at the grain boundary regions of bulged Cu samples where the inhomogeneous dislocation density and the large lattice misorientation were observed. The DRX mechanisms at the grain boundaries were discussed with respect to the strain-induced grain boundary migration nucleation. Moreover, the orientation distribution function (ODF) of the sample with the strain of 50% demonstrated a strong {110} texture and a relatively weak {001} texture. The texture evolution was discussed using the plastic work values of the grains with various orientations, which were calculated according to the Taylor model and the virtual work principle. The experimental results show that the expended plastic work of the grains with {110} orientation is 9.69 MPa, which is distinctly higher than those of the grains with the {001} and {111} orientations. This indicates that the formation of the {110} orientated texture would be preferred with increasing strain in good agreement with the experimental result.

Peculiarities of Alloying Effect on the Eutectic Cementite Behavior Under Hot Rolling

Abstract Currently, cast iron remains one of the major modern casting materials in metallurgy and machine-building industry and is sure to take the lead in the future. Chilled cast iron has high hardness and wear resistance due to a large number of carbide phases in its structure. However, low ductility and impact hardness essentially limit its applicability in terms of processing. Hot plastic working, under which the eutectic net crushing is observed, appears to be one of the most effective means of the eutectic alloy products shape and microstructure transformation. Chilled cast iron properties fundamentally improve after hot plastic working: ductility, strength and impact hardness increase by 2-3 times on retention of the high hardness factor. Chilled cast iron ductility increase can be attained when using phase transformations in eutectic cementite under lean alloying with carbide forming elements. The purpose of the paper is to study alloying effect on the chilled cast iron ductility as well as eutectic cementite behavior under hot rolling. In the paper hardening and softening of the structural components in chilled cast iron under hot working have been studied. The deformation texture forming in eutectic cementite under hot rolling has been revealed, which is connected with the dynamic softening and depends on the degree and the nature of its alloying. The mechanism and regularities of the phase transformation effect in cementite on its behavior under plastic deformation and on the alloys ductility in general have been studied. In cementite chromium alloying initiates processes, that can be characterized as the pre-precipitation stage of the new phases, and this way it contributes to the cast iron ductility reduction and embrittles cementite. Carbide transformation, that occurs in eutectic cementite under alloying with vanadium, stimulates softening of the alloy and increases its ductility level. Moreover, the multiple glide planes {130},{011},{112} in cementite have been determined. It has been found out, that in supersaturated cementite vanadium carbides precipitation stimulates the extra glide plane {111} occurrence under hot rolling. The essence of the carbide transformation phenomenon is that under hot working there occurs the lubricating effect at the transition of the metastable iron carbide condition, which is strengthened with vanadium supersaturation and mechanical hardening, to a more stable condition due to precipitation of the proeutectoid constituents on the one hand, and because of the dynamic softening processes on the other hand. At that, the autocatalyticity effect is observed: there is precipitation of carbides with hardening and softening, similar to the processes that arise as a result of the superplastic effect induced by phase transformations.

Evaluation of Wood and Plastic Formworks in Building Construction Industry for Sustainable Development

This research work assessed wood and plastic in building construction. The study was a descriptive survey design and as such made use of questionnaire with 42 items. The Population of the study was 110 respondent which include 40 building professional and 70 non-building professional. The data were analyzed using mean and standard deviation. T-test was used to test the null hypothesis at 0.05 level of significant. The finding of the study shows that plastic work form can be used for casting slab, concrete wall among others. The finding also revealed some factors that determines the selection of form work such as climatic condition, labour efficiency and that plastic formwork saves cost as a result of long reuse period. It is therefore recommended that; plastic and wooden formwork should be integrated often in the casting of slabs, beam and columns without discrimination, proper adherence to standards and specifications for use of any type of formwork, there should be large scale production of plastic formwork to conserve forest and wood, factors to be considered in the selection of formwork should not be ignored, there should be proper weighing of the advantages and disadvantages of each type of formwork relating to the scale of construction before the choice of any formwork.

An improved plastically dilatant unified viscoplastic constitutive formulation for multiscale analysis of polymer matrix composites under high strain rate loading

Polymer matrix composites are commonly used to fabricate energy-absorbing structures expected to experience impact loading. As such, a detailed understanding of the dynamic response of the constituent materials is necessary. Since the rate, temperature, and pressure dependence of carbon fiber reinforced polymer matrix composites are primarily manifestations of the rate, temperature, and pressure dependence of the polymer matrix, it is crucial that the constitutive behavior of the matrix be accurately characterized. In this work, an existing unified viscoplastic constitutive formulation is extended to ensure thermodynamic consistency and to more accurately account for the tension-compression asymmetry observed in the response of polymeric materials. A new plastic potential function is proposed, and elementary loading conditions are utilized to determine relations between model constants to ensure nonnegative plastic dissipation, a necessary thermodynamic requirement. Expressions for plastic Poisson's ratios are derived and are bounded by enforcing nonnegative plastic dissipation. The model is calibrated against available experimental data from tests conducted over a range of strain rates, temperatures, and loading cases on a representative thermoset epoxy; good correlation between simulations and experimental data is obtained. Temperature rises due to the conversion of plastic work to heat are computed via the adiabatic heat energy equation. The viscoplastic polymer model is then used as a constitutive model in the generalized method of cells micromechanics framework to investigate the effects of matrix adiabatic heating on the high strain rate response of a unidirectional composite. The thermodynamic consistency of the model ensures plastic dissipation can only cause an increase in temperature. Simulation results indicate significant thermal softening due to the conversion of plastic work to heat in the composite for matrix dominated deformation modes.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

Nanomechanical characterization of nanostructured La2(Zr0.75Ce0.25)2O7 thermal barrier coatings by nanoindentation

Nanostructured rare-earth zirconates materials have a great potential in next generation ultra high temperature thermal barrier coatings. In this work, the nanostructured La2(Zr0.75Ce0.25)2O7 coatings were fabricated by atmospheric plasma spraying using as-prepared nanostructured La2(Zr0.75Ce0.25)2O7 spherical feedstocks and nanomechanical properties of coatings were characterized by nanoindentation in detail. Results indicate that the grain growth of nanostructured coating is not obvious compared with feedstocks. The elastic modulus and nano-hardness of coatings, which are sensitive to non-molten zones, are 116.483 ± 19.236 GPa and 5.715 ± 1.656 GPa, respectively. The elastic indentation work is 11.465 ± 0.750 nJ and the plastic indentation work is 23.981 ± 5.035 nJ. The parameter of energy dissipation during plastic deformation (microhardness dissipation parameter, MDP) is 0.672 ± 0.042, indicating that outstanding properties under wear conditions for nanostructured La2(Zr0.75Ce0.25)2O7 coatings.