Plastic Work Research Articles

A practical constitutive theory based on egg-shaped function in elasto-plastic modeling for soft clay

An exploratory discussion is presented on the application of egg-shaped function in elasto-plastic constitutive analysis for soft clay. Two main tasks of the paper are: 1) to propose a complete yield criterion based on egg-shaped function and supplement its definition in the deviatoric section, and then a yield criterion suitable for 3D stress conditions is obtained; 2) to elaborate its numerical implementation based on the drained triaxial tests. During the above discussion, a non-associated flow rule is proposed, in which the stress-dilatancy relationship in most classical theory is replaced by a linear dependence between the stress state parameter η and the rotation angle η of the plastic potential surface. Thereafter, isotropic and kinematic hardening behavior is considered by employing the hardening parameter H, which can be expressed as the function of plastic work Wp. Finally, comparisons between numerical results and test data on Taizhou soft clay are made to verify the effectiveness of the proposed model.

Phase Stress Measurement of Centrifugally Cast Duplex Stainless Steel by Neutron Diffraction

Residual stress can be easily generated during material processing and affect the performance of structural components. Phase stress distribution in austenitic-ferritic duplex stainless steels (DSSs) is complicated due to the different material properties between the two phases. In this study, residual phase stress distribution along the thickness direction of centrifugally cast DSS hollow cylinder was measured by pulsed neutron diffraction with the time-of-flight (TOF) method. The triaxial phase stress distribution along the thickness direction shows that the phase stress of austenitic phase is generally in tension and higher than that of ferrite phase. From the outer surface to the inner surface, the macro-stress distributes from −400 MPa to 200 MPa. The mechanism of macro-stress formation was deduced by taking into consideration the thermal shrinkage behavior during the cooling process of water quench after the solution heat treatment. Furthermore, the lattice strain and phase stress evolution under the uniaxial tensile loading was evaluated by in-situ neutron diffraction measurement. The results indicated that the magnitude of phase stress could be affected by plastic working as well. All these measurements were conducted at Japan Proton Accelerator Research Complex (J-PARC).

A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties**Supported by the Chongqing Research Program of Basic Research and Frontier Technology (Grant Nos. cstc2018jcyjAX0329 and cstc2018jcyjAX0444), and the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant No. KJZD-K201900501).

A new Cu-based bulk metallic glass composite of nominal composition (at.%) Cu41Ni27Ti25Al7 with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation, which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications.

Self-heating of rolled ZnCuTi sheets

Self-heating effect for thermomechanical forming processes turns out to be dramatically significant for material with a very low melting point, such as zinc alloys. Zinc low melting point temperature (419.54°C) accentuates metallurgical effects when it is formed in cold or warm manufacturing processes. During deformation, self-heating can therefore induce a relative softening in the behavior law (that could improve formability) which competes with the conventional plastic hardening of the material. Hence, the correct identification of zinc material behavior has to account for both softening and hardening phenomena. This paper studies the effect of plastic work energy in the material identified by means of tensile tests by combining digital image correlation and infrared thermography technique.

Forming Processes of Modern Metallic Materials

The plastic working of metallic materials is one of the most efficient and important manufacturing technologies used in industry today [...]

The Experimental and Numerical Research for Plastic Working of Nickel Matrix Composite Coatings.

In the machine, metallurgical, and shipbuilding industries, steel products with alloy and composite coatings based on nickel may be used. It is expedient to improve the physicochemical properties of the surface layer of products as they have a significant roughness value after thermal spraying. It is therefore important to finish the layers applied by flame spraying, where machining is used for this purpose. However, it causes a loss of coating material, which is quite expensive. Therefore, in order to reduce costs and improve the quality of the surface layer, the finishing treatment of nickel-based coatings by means of plastic working is used. Two types of plastic working were proposed: rolling and burnishing. Numerical and experimental tests of the plastic processing of alloy coatings were carried out. The roughness of the coatings after rolling decreased to 1/25 and 30% strengthening of the alloy coating matrix was determined. After burnishing, roughness was reduced to 1/12 and the alloy coatings were strengthened by 25%. Plastic working by rolling and burnishing has a beneficial effect on the surface quality of the workpiece, not only by significantly improving the roughness, but also by increasing the strength properties of the surface layers.

Effect of powder bed fusion laser melting process parameters, build orientation and strut thickness on porosity, accuracy and tensile properties of an auxetic structure in IN718 alloy

In this paper the geometry of an auxetic, re-entrant honeycomb structure made from Inconel 718 (IN718), was optimised with respect to the process parameters of laser melting process using a Renishaw AM250 after which the quasi static behaviour was analysed under tensile loading. Two different PBF process parameters were used with 2 different laser energy densities to manufacture the auxetic structures with 3 different strut thicknesses (0.3, 0.6 and 0.9 mm) in 2 building orientations (XY and ZX plane). A strut thickness of 0.6 mm was found to have the least porosity and the best dimensional accuracy. The latter geometry was then manufactured as part of a tensile test sample which were then tested at a strain rate of 0.001 s−1 after which the stress strain curve, yield stress, structural stiffness, plastic work and Poisson's Ratio were compared. The building directions XY, ZX and XZ of the auxetic structure were investigated, as well as the orientation of the individual cells with respect to the loading direction. XY was found to provide the best mechanical properties and the kinematics of deformation was found to be dependent on the loading direction with respect to the cells direction which resulted in a significant change in Poisson's ratio. Finite Element Analysis was also done in order to compare the stress strain curves and the deformation mode obtained from numerical modelling and experiment, and a good agreement was observed.

Design of a Laboratory Electro-hydraulic Installation for Water Disinfection

Electrohydraulic effect is used in various fields of industry and agriculture: for cleaning metal casting forms, cleaning pipes of power boilers, treatment of heating radiators, soil treatment and water disinfection. Existing technical means for water disinfection with high-voltage discharges are expensive, cumbersome and untransportable. Currently used installations use an operating voltage of 10-50 kilovolts, capacitors designed for a voltage of no more than 100 kilovolts, with a capacity of 0.025 microfarads. Water disinfection according to the conducted research can be carried out with a voltage of 10 kilovolts. (Research purpose) The research purpose is in developing and manufacturing a laboratory electrohydraulic installation for water disinfection, which has a technical novelty in terms of mobility and compactness for implementing a method of water disinfection at a voltage of no more than 10 kilovolts. (Materials and methods) During the research, next materials, equipment and devices were used: power supply; transformer; capacitor; forming gap; working body; shunt resistance. (Results and discussion) The principle of the electrohydraulic effect, which is a consequence of the occurrence of electrohydraulic shocks between high-voltage electrodes placed in a liquid, is the basis for the development and manufacture of the installation. Authors developed a structural diagram of a laboratory electrohydraulic unit for water disinfection. The article presents an experimental sample of a laboratory installation for water disinfection, which has a technical novelty in terms of mobility and compactness for implementing a method for water disinfection at a voltage of no more than 10 kilovolts. The installation consists of a power supply unit FA-5-1/300W, a high-voltage step-up transformer TDKS32-04, a capacitor K75-29A (16 kilovolts, 1 microfarad), forming a gap of metal balls with a diameter of 18 millimeters, a plastic working body made of ABS material, a shunt resistance of 1 kilohm. (Conclusions) They article shows the scientific and practical significance of the research results: a technical means for water disinfection, providing the possibility of conducting experimental laboratory studies of the electrohydraulic effect at a voltage of no more than 10 kilovolts.

Fatigue Properties and Microstructure of SnAgCu Bi-Based Solder Joint

Abstract The reliability of solder joints plays a critical role in electronic assemblies. SnAgCu solder alloys with doped elements such as Bi and Sb is one of the candidates for high reliability applications. However, the mechanical and fatigue properties of the actual solder joint structure have not been studied for these new alloys. In this paper, a cyclic fatigue test was conducted on individual real solder joints of different alloys, including SnAgCu, SnCu–Bi, SnAgCu–Bi, and SnAgCu–BiSb. The fatigue property of those solder joints was analyzed based on the characteristic fatigue life and stress–strain, hysteresis, loops. The results show that solder joints with both Ag and Bi content have a better fatigue resistance than the solder joints with Ag or Bi content only. The results of SnAgCu and SnCu–Bi solder alloys show similar fatigue performance. Also, the fatigue performance of SnAgCu–Bi is close to SnAgCu–BiSb in the accelerated test. But the SnAgCu–Bi alloy is estimated to have a longer characteristic life under low-stress amplitude cycling. The microstructure analysis shows a bismuth-rich phase formed around the Ag3Sn precipitates. Adding bismuth in the solder alloy can significantly improve the fatigue properties through solid solution hardenings. On another hand, the plastic strain range and work dissipation were measured from the hysteresis loops for all tests. The Morrow Energy and the Coffin–Manson models were developed from the fitted data to predict the fatigue life as a function of work dissipation and plastic strain range.

Comprehensive structural, nanomechanical and tribological evaluation of silver doped DLC thin film coating with chromium interlayer (Ag-DLC/Cr) for biomedical application

Silver (Ag) doping in carbon matrix have shown promising results in anti-bacterial potency. Adhesion of diamond-like-coating (DLC) on steel substrates is inferior; however, this can be circumvented by employing interlayers to it. In the present study, Ag incorporated DLC coating with chromium interlayer (Ag-DLC/Cr) was deposited on surgical SS using cathodic arc deposition technique. The topographical, morphological and structural analysis of the coating was performed using AFM, XRD, Raman spectroscopy and FTIR studies. The nanomechanical and wear performance of the coating was evaluated using nanoindentation, nanoscratch, dry sliding simulated tribotest and Vickers microhardness tests. Depositing chromium interlayer to DLC film resulted in improved hardness, adhesion and elastic modulus of the substrate due to sp3 content and formation of transmittal chromium carbide in the coating. Moreover, Ag doping causes formation of ductile bridges in carbon matrix enabling it to absorb more energy during deformation. While the coating exhibited higher strain hardening exponent and lower plastic work contributing to higher scratch hardness, lower deformation and no pile-up; the coating simultaneously resulted in reduction of wear rate by four orders of magnitude. SEM micrographs suggest emanation of lubricious film during tribotests due to dispersion of soft Ag clusters on the top layer, resulting in lower friction coefficient. Also, the sticky nature of DLC particles on the counter-face acted as an anti-adhesive agent thereby preventing transfer of material from the counterbody during tribotest. Lastly, the friction dynamics during dry sliding and Vickers microhardness test post tribotests highlights enhanced durability of Ag-DLC/Cr coated substrates.

EFFECT OF THE PLASTIC STRAIN AND DRAWING QUALITY ON THE FRICTIONAL RESISTANCE OF STEEL SHEETS

The aim of the research presented in this article is to investigate the frictional resistance of steel sheets with different drawing quality. Friction tests have been carried out using the bending under tension (BUT) test which simulates the contact conditions at the rounded edges of the punch and die in sheet metal forming operations. The effect of sheet deformation and temper state on the value of the coefficient of friction has been studied. It was found that increasing the value of elongation of the sheet is associated with an increase in the value of the COF for both friction conditions analysed. The intensity of work hardening, by changing the mechanical properties of the sheet, is a factor that changes contact conditions. The lubricant which is typically used in plastic working provided a reduction of frictional resistance by approximately 3.6-14%, depending on the degree of sheet deformation.

A novel analytical model based on arc tangent velocity field for prediction of rolling force in strip rolling

Accurate prediction of rolling force is an effective method to improve strip quality in rolling process. To achieve this goal, a novel arc tangent velocity field model based on the upper bound method is proposed to evaluate the rolling force. The mathematical expression of rolling force is derived from the virtual work principle and maximum plastic work principle. Comparing the experimental results with the proposed analytical model prediction, it has been found that this model is good for estimation of rolling force. Meanwhile, the finite element method is also used to simulate the rolling process to verify the validity of the analytical model. It is shown that this model can be used for prediction of rolling force in practice.

New Multistage Sheet-Bulk Metal Forming Process Using Oscillating Tools

A new sheet-bulk metal forming process for the production of bulk components out of a flat sheet has been developed. Superimposed oscillation has been applied to the new process. By this means, process limits regarding better mould filling were expanded, and forming forces could be reduced. In order to investigate the effects of superimposed oscillation on material behaviour, plane strain and ring compression tests were carried out. The superimposed oscillated plane strain compression test showed a reduction in biaxial flow stress and thus in plastic work. Furthermore, reduced friction and roughness were verified in ring compression tests using superimposed oscillation.

Size effect on the subsequent yield and hardening behavior of metal foil

With the growing demand for miniaturized and integrated products, the metal foils have been extensively applied in the field of aerospace, electronics, medical equipment, and microsystem technology. However, the deformation process is usually under the complex stress status for the fabrication of the micropart. In addition, size effect dramatically impact the microforming process and therefore the well-developed metal forming theory established at macroscale is inapplicable at the grain level. To further investigate the size effect on the subsequent yield and hardening behavior, the biaxial tests of stainless-steel foils with diverse grain sizes and thicknesses were conducted under different stress states. The initial and subsequent yield loci are computed under various loading histories according to the plastic work per unit volume principle. It is found that the evolution of yield loci from initial to the subsequent state shows a remarkable difference for metal foils with different grain sizes. Based on Yld2000-2d yield criterion, the theoretical yield loci based on three different hardening models, including isotropic, kinetic, and isotropic-kinetic mixed hardening models, were acquired to explore and evaluate their applicability at microscale. Results indicated that the isotropic-kinetic mixed hardening model can better describe the evolution of subsequent yield locus than the individual hardening model. In addition, the back stress is shifted down with the increase of grain size for the foils with a certain thickness. Based on the Taylor-Bishop-Hill (TBH) polycrystal plasticity model, the evolution of subsequent yield surface is interpreted by the transformation of grain orientation.

Effect of the Crystallographic Texture Type on the Anisotropy of the Magnetic Leakage Field Parameters of Steel Sheets

This paper examines the distribution of the tangential and normal components of the magnetic leakage fields in pole-magnetized sheet materials, such as cold-worked structural steels St3, 09G2S, and 08G2B, as well as electrical steel with different grain structure and coarse-grained magnetically soft alloy Alfer, which have different types of texture induced by rolling and uniaxial tension. It has been found that even minor changes in the preferential orientation of easy magnetization axes 〈100〉 strongly affect the distribution of the tangential Нτ and normalHn components of magnetic leakage fields. For all studied materials, the magnitude ofНτ significantly exceeds that ofHn. However, in most cases, the componentНn exhibits a larger anisotropy thanНτ. Cold plastic working by rolling and uniaxial tension changes the texture state of the studied structural steels with the formation of multicomponent textures, which causes changes in the angular dependences of the parametersНτ and Hn. This fact indicates that the onset of plastic flow in a ferromagnetic material can be detected by changes in the form of circle diagrams of the leakage field components. The circle diagrams of the parametersНτ and Hn of deformed structural steels have the form of figure-eight patterns that are approximately perpendicular to each other. The position of the maxima of Нτ andHn on these diagrams corresponds to the position of the projections of the easy magnetization axes closest to the rolling plane, i.e., the directions along which iron and its alloys have the lowest strength. Therefore, it may be effective to estimate the anisotropy of strength properties of steel products with different texture states by the anisotropy of their magnetic parameters. More reliable results of magnetic texture analysis can be obtained by constructing full circle diagrams of the magnetic leakage field parameters.

Modelling and simulation of dynamic recrystallisation based on multi-phase-field and dislocation-based crystal plasticity models

ABSTRACT The mechanical properties of metals used as structural materials are significantly affected by hot (or warm) plastic working. Therefore, it is industrially important to predict the microscopic behaviour of materials in the deformation process during heat treatment. In this process, a number of nuclei are generated in the vicinity of grain boundaries owing to thermal fluctuation or the coalescence of subgrains, and dynamic recrystallisation (DRX) occurs along with the deformation. In this paper, we develop a DRX model by coupling a dislocation-based crystal plasticity model and a multi-phase-field (MPF) model through the dislocation density. Then, the temperature dependence of the hardening tendency in the recrystallisation process is introduced into the DRX model. A multiphysics simulation for pure Ni is conducted, and then the validity of the DRX model is investigated by comparing the numerical results of microstructure formation and the nominal stress–strain curve during DRX with experimental results. The obtained results indicate that in the process of DRX, nucleation and grain growth occur mainly around grain boundaries with high dislocation density. As deformation progresses, new dislocations pile up and subsequent nucleation occurs in the recrystallised grains. The influence of such microstructural evolution appears as oscillation in the stress–strain curve. From the stress–strain curves, the temperature dependence in DRX is observed mainly in terms of the yield stress, the hardening ratio, and the change in the hardening tendency after nucleation occurs.

Evaluation of Structure and Corrosion Behavior of FeAl Alloy after Crystallization, Hot Extrusion and Hot Rolling.

The paper presents the results of tests on the corrosion resistance of Fe40Al5Cr0.2TiB alloy after casting, plastic working using extrusion and rolling methods. Examination of the microstructure of the Fe40Al5Cr0.2TiB alloy after casting and after plastic working was performed on an Olympus GX51 light microscope. The stereological relationships of the alloy microstructure in the state after crystallization and after plastic working were determined. The quantitative analysis of the structure was conducted after testing with the EBSD INCA HKL detector and the Nordlys II analysis system (Channel 5), which was equipped with the Hitachi S-3400N microscope. Structure tests and corrosion tests were performed on tests cut perpendicular to the ingot axis, extrusion direction, and rolling direction. As a result of the tests, it was found that the crystallized alloy has better corrosion resistance than plastically processed material. Plastic working increases the intensity of the electrochemical corrosion of the examined alloy. It was found that as-cast alloy is the most resistant to corrosion in a 5% NaCl compared with the alloys after hot extrusion and after hot rolling. The parameters in this study show the smallest value of the corrosion current density and corrosion rate as well as the more positive value of corrosion potential.

Dynamic Flow Stress Behavior of Hypo-Eutectoid Ferrite-Pearlite Steels Under Rapid Heating

In the machining process, the workpiece undergoes large plastic deformation at high strain rate and is heated rapidly by plastic work and friction. Rapid temperature excursions brought about during this process may result in non-typical microstructures whose mechanical behavior differs from what has traditionally been observed and modeled. This paper presents dynamic stress-strain measurements on three hypo-eutectoid ferrite-pearlite carbon steels of increasing carbon content (AISI 1018, 1045 and 1075) under rapidly heated conditions, with total heating times less under 4 s, up to 1000 °C. The mechanical behavior of these steels is broken down into four regions: low temperature thermal softening, followed by dynamic strain aging, pearlite decomposition and, finally, ferrite-austenite thermal softening. The present rapidly heated high strain rate results are generally commensurate with literature data up through dynamic strain aging to about 700 °C, indicating limited effects of short heating times below the pearlite decomposition temperature (A1). Above A1, however, the results diverge significantly, owing to the limited time for diffusion processes that govern the transformation from ferrite-pearlite to ferrite-austenite and finally austenite. The divergence includes an inversion of the effect of carbon content on flow stress above A1 compared to previous studies with longer heating times.

Characterization of Nano-Mechanical, Surface and Thermal Properties of Hemp Fiber-Reinforced Polycaprolactone (HF/PCL) Biocomposites

The quest for sustainable, low-cost and environmental friendly engineering materials has increased the application of natural fiber-reinforced polymer (FRP) composite. This paper experimentally investigates the effects of variable mean hemp fiber (HF) aspect ratios (ARs) of 00 (neat), aspect ratios AR_19, AR_26, AR_30 and AR_38 on nano-mechanical (hardness, modulus, elasticity and plasticity), surface and thermal properties of hemp fiber/polycaprolactone (HF/PCL) biocomposites. These biocomposites were characterized by nanoindentation, contact angle, surface energy, thermogravimetric analysis (TGA), thermal conductivity and differential scanning calorimetry (DSC) techniques. After nanoindentation and thermal conductivity tests, the results obtained evidently show that the HF/PCL sample with aspect ratio (AR_26) recorded optimal values. These values include maximum hardness of approximately 0.107 GPa, elastic modulus of 1.094 GPa, and plastic and elastic works of 1.580 and 1.210 nJ, respectively as well as maximum thermal conductivity of 0.2957 W/mK, when compared with other samples. Similarly, the optimal sample exhibits highest main degradable temperature and degree of crystallinity of 432 ℃ and 60.6%, respectively. Further results obtained for the total surface energies and contact angles of these samples with glycerol and distilled water are significant for their materials selection, design, manufacturing and various applications.

A fully coupled thermomechanical dislocation model for explosive crystal (β-HMX) subjected to isentropic compression loading

A fully coupled thermomechanical dislocation model is developed to analyze the thermomechanical responses of explosive crystal β-cyclotetramethylene tetranitramine (β-HMX) subjected to isentropic compression loading. The volumetric thermoelastic deformation is considered by a complete equation of state (logarithmic EoS) and the dislocation-based plasticity includes the automatic transition from the low-rate thermally activated to the high-rate drag limited regime. The proposed model is applied for the first time to simulate isentropic compression experiments (ICE) on oriented HMX single crystals. The calculated results can well capture the isentropic elastic limit, stress relaxation and steeper plastic wave speed of the ICE wave profiles. Nonlinear thermoelasticity by both pressure-dependent elasticity tensor and the complete EoS is shown to be responsible for the obvious steepness in wave profiles. The anisotropic elastoviscoplastic response can be distinctly reflected by detailed dislocation activities on seven slip systems instead of phenomenological model just through empirical determination. Pure isentrope is decoupled from quasi-isentrope by subtracting the contribution from deviatoric strain and thermal effect, providing thermodynamically consistent data for complete EoS. Contributions of anisotropic temperature rises by pressure volume work and dislocation-based plasticity work are influenced by loading history. Results provide insights into understanding the transition from isentropic wave to shock wave and ignition behavior of explosives at the mesoscale under complex thermodynamic scenarios.