Plastic Work Research Articles

A constitutive model for poly-methyl-methacrylate over a wide range of strain rates and temperatures

This study proposes a three-dimensional elasto-viscoplastic constitutive model to depict the rate- and temperature-dependent behaviour of poly-methyl-methacrylate (PMMA) under a variety of strain rates and temperature ranges at finite deformations. Yield stress is described via incorporating an appropriate Young's modulus into the Argon's model. The effects of temperature and strain rate are incorporated into the Young's modulus. Subsequently, a new empirical equation has been suggested to describe the softening behaviour over a wide range of strain rates and temperatures. Further, the temperature dependence of the fraction of plastic work rate converted to heat (β factor) has been studied. In addition, the expressions of hardening parameters (Cr and N) under a changing temperature in the full network model that represents the strain-hardening characteristics of polymers have been proposed. Moreover, a method to calibrate the values of newly introduced parameters has been introduced as well. The experimental results demonstrate that the new softening model can predict softening behaviour at various strain rates (from 0.0003 s−1 to 4300 s−1) and temperatures (from 298 K to the glass transition temperature θg).

異なる塑性加工を供したMg合金における組織とひずみの関係

A relationship between microstructure and strain induced by different plastic working is investigated in AZ31 magnesium alloy. AZ31 magnesium alloy was processed by different plastic workings (forging, rolling, extrusion, equal-channel angular pressing (ECAP), caliber rolling) at 573 K with equivalent strain controlled to the similar value. The strain induced in the processes was computed by using the finite element method (FEM). The deformation texture of forging and rolling were intensive basal texture, but the texture of extrusion, ECAP and caliber rolling were relatively weak. The FEM calculation and deformed texture showed that in all five processes, the basal plane is oriented to the direction perpendicular to compression strain, and tendency that the more compression strain is induced, the more intensive basal texture is formed.

Numerical Modeling of Energy Dissipation during Fatigue Crack Propagation in Metals

It is well-known that mechanical work spent on inelastic deformation of metal converts into the heat. However, experimental studies have shown that process of plastic deformation is accompanied not only by extensive heat dissipation but also by energy storage. Therefore, precise calculation of the dissipated energy value should take into account the portion of energy which is accumulated in the material. In this work, we applied thermodynamic constitutive theory based on multiple dissipation potentials to obtain constitutive equations for structural parameter responsible for the stored energy and plastic strain causing plastic dissipation. Evolution equation for structural parameter is derived from phenomenological form of free energy function. Combined hardening model is used for plastic strain calculation. Value of the dissipated energy is calculated as difference between plastic work and stored energy. We have applied this model to calculate dependence of dissipated energy per cycle on crack length for two titanium alloys (Ti-5Al-2V and Grade-2). Simulation was carried out in finite-element package Comsol Multiphysics in plane stress formulation. A stationary crack approach was used for energy balance calculation at the crack tip. Results of the simulation were compared with experimental data on heat dissipation obtained by original heat flux sensor.

Measurement of the Amount of Scale Formed in the Process of Heating the Steel Charge in Industrial Conditions

The article presents methods for determining the amount of mill scale formed in the process of heating the steel charge before plastic working. Relationships allowing to calculate the amount of scale, its thickness and loss of steel were presented. Measurements and calculations were made for the selected method. The results and conclusions are presented.

On use of interlocking structures in plastic metal working

An effective method to increase the rigidity and reliability of materials and structures by choosing a rational geometry of structural elements and conditions for their interaction with each other is proposed. This method, associated with interlocking structures, has found application in the creation of new technical solutions in metallurgy.

Microstructure Evolution in Nano-sized Wiredrawing Process:

By using molecular dynamics (MD) simulation, the mechanism of nanometer-sized wiredrawing is studied. The possibility of nano-sized plastic working process and predictive microstructures are investigated. As a drawn material, pure iron (α-Fe) and magnesium (Mg) single crystals are compared. The MD models are constructed by utilizing many-body-type (FS or EAM) interatomic potentials with adequate modification for lubrication between wire and die. Dislocation slip is a principal mechanism of plastic deformation in the case of α-Fe in any drawing direction of single crystal. Besides, dislocation densities increases with increase of the wire diameter, where nucleation, annihilation and mutual behavior of dislocations are observed in detail. On the other hand, in Mg single crystal, mechanism of plastic deformation depends strongly on crystal orientation as to drawing direction. Twinning and twin boundaries can be identified by detecting a network of interface dislocations. When the c-axis of hcp lattice is inclined by 45 degrees from the drawing direction, dislocations on basal plane occur, but no twin, and therefore the minimum dislocation density is obtained.

Chapter 26 - The role of plasticity in the recovery of consciousness

Disorders of consciousness (DOCs), i.e., coma, vegetative state, and minimally conscious state are the consequences of a severe brain injury that disrupts the brain ability to generate consciousness. Recovery from DOCs requires functional and structural changes in the brain. The sites where these plastic changes take place vary according to the pathophysiology of the DOC. The ascending reticular activating system of the brainstem and its complex connections with the thalamus and cortex are involved in the pathophysiology of coma. Subcortical structures, such as the striatum and globus pallidus, together with thalamocortical and corticothalamic projections, the basal forebrain, and several networks among different cortical areas are probably involved in vegetative and minimally conscious states. Some mechanisms of plasticity that allegedly operate in each of these sites to promote recovery of consciousness will be discussed in this chapter. While some mechanisms of plasticity work at a local level, others produce functional changes in complex neuronal networks, for example by entraining neuronal oscillations. The specific mechanisms of brain plasticity represent potential targets for future treatments aiming to restore consciousness in patients with severe DOCs.

Design and Fabrication of Plastic Compressor Machine for Plastic Waste

This project work is on design and fabrication of a plastic compressor machine to compress plastic waste. The objective of this project is to help to reduce plastic waste mostly from domestically usage and turn into a paving brick that can be uses as decoration in a mini garden or walkway. This plastic compressor machine works using a modified old conventional oven to melt shredded plastic waste in a mould and let the melted plastic cooled and turned to a paving brick. The temperature to melt the shredded plastic waste of 450 grams is 250 degrees Celsius in 1 hour. The machine fabricated using recycled materials, which makes it cheap, easy to maintain and affordable.

Research on Mechanical and Electrical Properties of Cu-Ag Alloys Designed for the Construction of High Magnetic Field Generators

The individual sections, wiring and construction of electromagnet windings responsible for strong magnetic field impulses may be one application for hypoeutectic Cu-Ag alloys. High electrical properties and mechanical properties (tensile strength, yield strength, impact strength) as well as high heat, fatigue and rheological resistance are required for these kinds of applications due to the unique nature of such operations (strong vibrations of high frequency and amplitude resulting from Lorenz forces and the possibility of significant and rapid heating from Jule’s heat). The limited solubility of copper and silver in the solid state enables the effective modification of the alloys’ microstructure through heat treatment and further shaping of their high mechanical and electrical properties via cold plastic working. The article presents the manufacturing of Cu-Ag alloys with the weight percent of Ag between 3 and 7 using the continuous casting process along with research on the physicochemical, mechanical and electrical properties of the obtained casts. The research on the amount of plastic deformation and its influence on the wire drawing process and the mechanical and electrical properties of the wires is also discussed. The temperature coefficients of resistance were defined in order to determine the temperature influence on the electrical resistance changes dynamics. The microstructural analysis was carried out in the as-cast state. The preliminary research conducted indicates that the obtained Cu-Ag alloys in the as-cast state exhibit a set of high mechanical and electrical properties. The prospective next stage of research includes the selection of favourable heat treatment parameters which would provide optimally modified microstructure of the alloys, as well as determining the deformation coefficients allowing for further increases in the mechanical and electrical properties.

تفعيل دور الطاقة الايجابية في معالجة التصميم الداخلي للحيزات السكنية للأسر بالمملكة العربية السعودية في منطقة الأحساء (تصور مقترح)

To continue in life despite the great pressure we are exposed to at home or in the workplace, we must find our own sources that provide us with positive energy that supports us a lot. These sources may be available around us while we are unaware of them. So the aim of the research is to reveal the relationship between the residential space in which the family lives and their positive energy. The design of the place in which he lives and the effect of the interior design elements of colors, light, shape, furniture, space, raw materials, plastic works and building materials in improving the psychological comfort of the individual and increasing his positive energy.

Anisotropic hardening and evolution of r-values for sheet metal based on evolving non-associated Hill48 model

The uniaxial tensile tests and biaxial tensile tests were carried out to investigate the deformation behavior and yield loci of DC06 steel sheet. The continuous evolution of r-values was calculated by the proposed inverse method, which has higher accuracy and simpler form compared with the previous methods. Based on the equivalent plastic work principle, the anisotropic hardening, the evolution of r-values and subsequent yield loci were investigated. Then, an evolving non-associated Hill48 anisotropic plasticity model was formulated. Where, based on the constructed stress cost-function and constraint conditions of r-values, the anisotropic parameters coupling the distortional hardening and evolution of r-values were developed to characterize the anisotropy evolution. Moreover, the relationship between the uniaxial tensile plastic strain and the equivalent plastic strain was derived. Based on this, the continuous variation curves of anisotropic parameters with real equivalent plastic strain were obtained. The comparison between the experimental and prediction results indicates that the developed model can accurately capture the distortional hardening, evolution of r-values and yield loci simultaneously. Furthermore, the effect of distortional hardening and evolution of r-values on the subsequent yield surfaces and plastic potential is analyzed.

3D zero-thickness interface model for fracture of cement-based materials with chemical degradation

In the framework of the Finite Element Method, zero-thickness interface elements have been widely used to model fracturing processes in quasi-brittle materials in a broad variety of problems. In particular, interface elements equipped with elastoplastic constitutive laws that account for the softening of the material strength parameters due to the fracturing mechanical work has been proved to accurately reproduce observed fracture propagation behaviour in concrete. Along this line, this paper presents the extension of an existing constitutive law of this kind to include the effect of chemical degradation of the material in the formation of fractures. The law is defined in terms of the normal and shear stresses on the average plane of the crack and the corresponding normal and shear relative displacements. A hyperbolic cracking (plastification) surface in the stress state determines the crack initiation. The softening of the cracking surface is governed by two history variables: an internal variable that accounts for the dissipated fracturing (plastic) work, and an external variable to be provided by a chemical degradation model that accounts for the effect of chemical degradation on the strength parameters. After a detailed discussion of the formulation, the main characteristics of the proposed law are illustrated with a number of academic examples for different combinations of mechanical loading and chemical degradation sequences. The model is finally validated against experimental results from the literature consisting of three-point bending tests performed on mortar samples previously exposed to an aggressive solution for different time periods.

Inverse Approach of Parameter Optimization for Nonlinear Meta-Model Using Finite Element Simulation

Accurate and efficient estimation and prediction of the nonlinear behavior of materials during plastic working is a major issue in academic and industrial settings. Studies on property meta-models are being conducted to estimate and predict plastic working results. However, accurately representing strong nonlinear properties using power-law and exponential models, which are typical meta-models, is difficult. The combination meta-model can be used to solve this problem, but the possible number of parameters increases. This causes a cost problem when using FE simulation. In this study, the accuracy of the nonlinear properties of materials and the number of iterations were compared for three typical meta-models and the proposed advanced meta-models considering stress–strain properties. A material property test was conducted using ASTM E8/E8M, and the meta-model was initialized using ASTM E646 and MATLAB Curve Fitting Toolbox. A finite element (FE) simulation was conducted for the meta-models, and the test and simulation results were compared in terms of the engineering stress–strain curve and the root-mean-square error (RMSE). In addition, an inverse method was applied for the FE simulation to estimate the true stress–strain properties, and the results were analyzed in terms of the RMSE and the number of iterations and simulations. Finally, the need for an advanced meta-model that exhibits strong nonlinearity was suggested.

Cyclic fracture simulation through element deletion in structural steel systems

This paper presents a finite element-based model for direct simulation of cyclic fracture in steel components and connections with application to predicting failure and collapse of steel structures. The formulation couples a plasticity model for large deformations that captures plastic work stagnation and the Bauschinger effect with a two-stage damage model to simulate fracture initiation, propagation, and failure through an element deletion strategy. The model includes the non-proportional loading and load-history effects in the fracture initiation and propagation process. Fracture initiation and propagation is controlled using new fracture initiation strain and fracture energy surfaces with stress triaxiality and Lode angle dependance that can represent different fracture behaviors. Model calibration is discussed for common grades of structural steel, weldments and bolts using typical material tests. The model capabilities are validated against experiments including ancillary material tests, components, and subassemblies of steel structures that experienced fracture subjected to monotonic and cyclic loading. A culminating validation is conducted on a four-story steel frame structure tested to collapse. The proposed model provides a robust and valuable tool for stability analysis and simulations of damage and collapse triggered by fracture in components and connections of three-dimensional steel structures subjected to extreme loads.

Post-Machining Deformations of Thin-Walled Elements Made of EN AW-2024 T351 Aluminum Alloy as Regards the Mechanical Properties of the Applied, Rolled Semi-Finished Products

The paper presents an evaluation of post-machining deformations of thin-walled elements as regards the mechanical properties of the applied, rolled semi-finished products. Nowadays, wrought aluminum alloys, supplied primarily in the form of rolled plates, are widely applied in the production of thin-walled integral parts. Considering the high requirements for materials, especially in the aviation sector, it is important to be aware of their mechanical properties and for semi-finished products delivered after plastic working to take into account the so-called “technological history” concerning, inter alia, the direction of rolling. The study focused on determining the influence of the ratio of the tension direction to the rolling direction on the selected mechanical properties of the EN AW-2024 T351 aluminum alloy depending on the sample thickness and its relation to the deformation of thin-walled parts. Based on the obtained results, it was found that the sample thickness and the ratio of the tension direction to the rolling direction affected the mechanical properties of the selected aluminum alloy, which in turn translated into post-machining deformations. Summarizing, the textured surface layer had a significant impact on the mentioned deformation. Greater deformations were noted for samples made of a semi-finished product with a thickness of 5 mm in comparison to 12 mm. It was the result of the influence of the surface layer, which at lower thickness had a higher percentage of contents than in thicker samples.

A micromechanically based model for dynamic damage evolution in unidirectional composites

This article addresses the micromechanically motivated, quasistatic to dynamic, failure response of fibre reinforced unidirectional composites at finite deformation. The model draws from computational homogenization, with a subscale represented by matrix and fibre constituents. Undamaged matrix response assumes isotropic viscoelasticity–viscoplasticity, whereas the fibre is transversely isotropic hyperelastic. Major novelties involve damage degradation of the matrix response, due to shear in compression based on a rate dependent damage evolution model, and the large deformation homogenization approach. The homogenized quasi-brittle damage induced failure is described by elastically stored isochoric energy and plastic work of the undamaged polymer, driving the evolution of damage. The developed model is implemented in ABAQUS/Explicit. Finite element validation is carried out for a set of off-axis experimental compression tests in the literature. Considering the unidirectional carbon–epoxy (IM7/8552) composite at different strain rates, it appears that the homogenized damage degraded response can represent the expected ductile failure of the composite at compressive loading with different off-axes. Favourable comparisons are made for the strain and fibre rotation distribution involving localized shear and fibre kinking.

Generation of Shakedown Boundaries of Thin-Walled 90-Deg Scheduled Pipe Bends Determined Via Large and Small Displacement Finite Element Models

Abstract The present research investigates the effect of employing large displacement in finite element modeling on the generated shakedown (SD) boundaries of thin-walled 90-deg scheduled pipe bends. A recently developed methodology termed: shakedown limit—plastic work dissipation (SDLimit−PWD) method generates the SD boundaries via employing the large displacement in the finite element (FE) simulations. Additionally, a well-established direct noncyclic technique termed: shakedown direct noncyclic technique (SD_DNT) generates the SD boundaries via employing the small displacement formulation in the FE simulations. Comparing the SD boundaries generated via both methods illustrated a marked increase in the generated SD domains due to employing large displacement.

Atomistic investigation on the conversion of plastic work to heat in high-rate shear deformation

The conversion of work into heat is one of the most significant characteristics of plastic deformation, especially in a high strain rate regime. The quantitative characterization of the fraction of plastic work converted into heat plays a crucial role in understanding the deformation process and mechanism and establishing an accurate and reasonable thermomechanical constitutive model. However, the fraction of plastic work converted into heat is experimentally found to span over a wide range of values between 0.1 and 1. In this paper, the conversion of plastic work into heat in high-rate shear deformation is systematically investigated through the relations between temperatures, stresses, elastic and plastic strains using molecular dynamics simulation. The results show that the temperature rise in the shear deformation is caused by the heat dissipation of the plastic work rather than the thermo-elastic coupling effect due to invariance of the volume. Dislocation nucleation and glide are the main mechanisms of shear deformation and are also the origins of heat generation. The continuous slip of dislocations also results in the formation of deformation twins. Interestingly, the work-to-heat conversion coefficient is revealed to be independent of crystal orientation, in contrast to the plastic deformation itself. From the present study, we conclude that almost all the plastic work in shear deformation is converted into heat dissipation for all studied samples.

Analysis of Interference-Fit Joints

Interference fit joints have been widely used in many engineering constructions, in particular in electric motors. It is of particular importance to calculate the load capacity of press-fit joints, especially in the overload ranges of construction to estimate the safety factor. The article presents a FEM numerical simulation of pressing the shaft into the hub, taking into account various types of fits. The results of numerical simulations presented in the article were positively verified with the MTS measuring device, which confirmed the correctness of the numerical model. So far, the load-bearing capacity of press-fit joints has been calculated from Lame’s formulas. The results of the load capacity of the joints obtained by the FEM simulation were compared with the results obtained from Lame’s formula. The comparison shows that when designing interference fit joints, attention should be paid to the fact that the press-in process, depending on the type of fit, may be elastic-plastic. Plastic deformations in the contact zone of the joint affect its load-bearing capacity. Therefore, the design of press-fit joints should not be based on Lame’s formulas, which do not take into account the range of plastic work of the material.

The Analysis of Erosive Wear Resistance of WC-Co Carbides Obtained by Spark Plasma Sintering Method.

WC-Co (tungsten carbide-cobalt) composites are widely used in industry, wear-resistant parts, and cutting tools. As successful tool materials, WC-Co carbides are widely applied in metal cutting, wear applications, chipless forming, stoneworking, wood, and plastic working. These materials are exposed to severe solid particle erosion by sand particles, such as in the wood industry. During the production of furniture with HDF (High Density Fibreboard), MDF (Medium Density Fibreboard), or OSB (Oriented Strand Board), there are observed problems with tool erosion. Contamination, mainly of the HDF by sand, is quite often, which is why all tools used for the machining of such materials are exposed to erosion by sand particles. Although many studies have been performed on the erosion of various metals, and erosion models exist to predict their erosion behavior, the issue is still relevant. The aim of the study was to determine the effect of grain size (submicron, ultrafine) and the manufacturing technology (SPS—Spark Plasma Sintering, conventional) used on the erosive properties of WC-Co sintered carbides. Sinters produced by the SPS method with different sizes of WC grains and commercial samples were used for the tests. Ten two-hour cycles were carried out under medium conditions of quartz sand and quartz sand with 10% SiC added. Used samples were characterised using scanning electron microscopy (SEM) and roughness was determined. Furthermore, erosion studies allowed individuating a wear mechanism as well as the possibility to foresee cutting performance in prospective application.