Plastic Deformation Rate Research Articles

Anisotropy of the yield strength and structural parameters of nanocrystalline titanium obtained by cryodeformation

Anisotropy of the yield strength of nanocrystalline VT1-0 technical-grade titanium with grain size ∼45 nm, obtained by the cryomechanical grain fragmentation method, was studied. The experiments were carried out using the uniaxial compression regime at a nominal plastic deformation rate of 3.5 × 10−4 s−1 in the temperature range 4.2–300 K. The temperature dependences of the macroscopic yield strength of the samples with the compression axis parallel and perpendicular to the cryorolling direction were obtained. The anisotropy coefficient of the yield strength was calculated, and its temperature dependence was established. The parameters of the deformation microstructure in mutually orthogonal planes were determined: the crystallite (coherent scattering region) sizes and the magnitudes of microdeformations. It was observed that the crystallites are morphologically anisotropic. The calculated and experimental values of the yield strength of the samples deformed parallel and perpendicular to the cryorolling direction were found to be in agreement with the Hall–Petch ratio and the observed crystallite sizes. It was established that the anisotropy of the yield strength of nanocrystalline titanium is related to the shape anisotropy of its structural elements, such as a grain/crystallite.

A fractional transient model for the viscoplastic response of polymers based on a micro-mechanism of free volume distribution

In the present work, the nonlinear viscoelastic/viscoplastic response of polymeric materials is described by introducing essential modifications on a model developed in previous works. A constitutive equation of viscoelasticity, based on the transient network theory, is introduced in a more generalized form, which takes into account volume changes during deformation. This time-dependent equation accounts for the nonlinearity and viscoplasticity at small elastic and finite plastic strain regime. The present description was proved to be more flexible, given that it contains a relaxation function that has been derived by considering instead of first order kinetics a fractional derivative that controls the rate of molecular chain detachment from their junctions. Therefore, the new equation has a more global character, appropriate for cases where heavy tails are expected. On the basis of the distributed nature of free volume, a new functional form of the rate of plastic deformation is developed, which is combined with a proper kinematic formulation and leads to the separation of the total strain into the elastic and plastic part. A three-dimensional constitutive equation is then derived for an isotropic, compressible medium. This analysis was proved to be capable of capturing the main aspects of inelastic response as well as the instability stage taking place at the tertiary creep, related to the creep failure.

A numerical investigation of the plastic deformation at the spall edge for a roller bearing

Abstract A clear understanding of dynamic contact characteristics in roller bearings (RBs) is a primary task for vibration analysis of the machineries, especially in the presence of spall failures. This work presents a new dynamic modelling method for a RB with a spall on the races to predict the time-varying plastic deformation at the spall edge. An improved two-degree-of-freedom dynamic model is used to calculate vibrations of the RB. Effects of the spall length, spall edge radius, external radial load, and rotor speed on the dynamic impact force between the spall edge and roller, maximum contact stress at the spall edge, total contact deformation between the spall edge and roller, plastic deformation at the spall edge, and spall edge propagation rate are analyzed. The proposed method is validated by a finite element (FE) method. The numerical results illustrate that the spall edge shape, external radial load, and rotor speed have a significant influence on the dynamic impact force, maximum contact stress, total contact deformation, plastic deformation, and spall edge propagation rate. This paper provides a greater understanding of the effects of the spall sizes and the spall edge shape on the contact characteristics and the vibrations for the RBs.

Numerical study of impact erosion of multiple solid particle

Material erosion caused by continuous particle impingement during hydraulic fracturing results in significant economic loss and increased production risks. The erosion process is complex and has not been clearly explained through physical experiments. To address this problem, a multiple particle model in a 3D configuration was proposed to investigate the dynamic erosion process. This approach can significantly reduce experiment costs. The numerical model considered material damping and elastic-plastic material behavior of target material. The effects of impact parameters on erosion characteristics, such as plastic deformation, contact time, and energy loss rate, were investigated. Based on comprehensive studies, the dynamic erosion mechanism and geometry evolution of eroded crater was obtained. These findings can provide a detailed erosion process of target material and insights into the material erosion caused by multiple particle impingement.

Dimensionless number is central to stress relaxation and expansive growth of the cell wall

Experiments demonstrate that both plastic and elastic deformation of the cell wall are necessary for wall stress relaxation and expansive growth of walled cells. A biophysical equation (Augmented Growth Equation) was previously shown to accurately model the experimentally observed wall stress relaxation and expansive growth rate. Here, dimensional analysis is used to obtain a dimensionless Augmented Growth Equation with dimensionless coefficients (groups of variables, or Π parameters). It is shown that a single Π parameter controls the wall stress relaxation rate. The Π parameter represents the ratio of plastic and elastic deformation rates, and provides an explicit relationship between expansive growth rate and the wall’s mechanical properties. Values for Π are calculated for plant, algal, and fungal cells from previously reported experimental results. It is found that the Π values for each cell species are large and very different from each other. Expansive growth rates are calculated using the calculated Π values and are compared to those measured for plant and fungal cells during different growth conditions, after treatment with IAA, and in different developmental stages. The comparison shows good agreement and supports the claim that the Π parameter is central to expansive growth rate of walled cells.

Experimental study of SS304L cylindrical shell with/without cutout under cyclic combined and uniaxial loading

In this research, ratcheting behavior of SS304L cylindrical shells under cyclic combined and uniaxial loadings was studied. Experimental tests were carried outby a servo-hydraulic INSTRON 8802 machine and the shells were fixed normal and oblique at angle of 20° with respect to the longitudinal direction of the shell. Force-control loadings were applied and the effect of length, angle of cylindrical shell and loading history on ratcheting behavior were examined.It was shown as the angle of cylindrical shell increases, due to increase of bending moment, accumulation of plastic deformation increases.Also, linear relation was observed between plastic energy and rate of plastic deformation which shows the rigidity of fixtures used in tests. Cutout effect on cylindrical shells under these kinds of loading has been studied and it was observed that creating cutout increases the plastic deformation and its rate.

The effect of plastic deformation rate on the wear performance of hardfaced coatings

The objective of this study aimed to investigate the effect of plastic deformation rate and heat treatment routes on the wear performance of surfaced coatings obtained using submerged arc welding (SAW) and flux supplemented by additions of alloying powder. Powder of cemented tungsten carbide and high-speed tool steel has been selected as additives to the composition of shielding flux AMS1. Graphite powder was used as addition in two test batches in order to compensate carbon content, which burns out during welding. Results of spectrum analysis have revealed high concentration of alloying elements (Co 0.91–1.573%, W 2.5–9.5%, Mn 1.67–2.39%), which ensured low wear of tested coatings. Tempering at different temperatures showed formation of retained austenite; this fact was confirmed after X-ray diffraction analysis. Different extent of plastic deformation was accomplished to all test batches on the purpose of evaluation of influence on the wear performance of coatings. Wear results showed proportional dependence of rate of deformation and weight loss values. Addition of graphite helped to reach the lowest wear of coatings obtained using the flux alloyed with cemented tungsten carbide and high-speed tool steel (weight loss 0.12 and 0.148 g, respectively).

Laboratory evaluation of railroad ballast behavior under heavy axle load and high traffic conditions

Abstract Repeated loading of railroad track results in deformation of the track foundation materials. The degree of ballast fouling and the amount of moisture affect the rate and magnitude of both elastic and plastic deformation of the track. As train traffic accumulates, the track deforms to a point where maintenance is required. Studying the effects of fouled ballast in different moisture conditions under different loads leads to a better understanding of the risk factors and maintenance needs of the track. In this study, a large ballast testing box was used to simulate the degradation of fouled ballast at different moisture conditions under heavy axle loading and high traffic conditions. The ballast compression tests were conducted on ballast with different fouling and moisture conditions up to 2,500,000 cycles of repeated heavy loading. The ballast was also tested in saturated conditions that simulated heavy rainfall events. The laboratory results have been compared with an accepted settlement model and different measured field settlements. The ballast box test results show comparable results with field measurements and analytical modeling. This paper presents conclusions regarding the effects of various factors on the rate and magnitude of the plastic and elastic settlement.

Comportamento termomecânico na microusinagem do aço AISI 4140: Simulação numérica com validação experimental

In the last decade, various researches has shown how the finite element software can be used to predict the chip formation, cutting forces, temperature, tool wear, residual stresses in workpiece and other important parameters in machining. This article presents simulation using FEM (Finite Element Method) with experimental validation in orthogonal microturning of AISI 4140 steel. Machining simulation using FEM AdvantEdge® were applied to predict the cutting and thrust forces, von Mises stress, maximum cutting stress, plastic deformation, deformation rate and cutting temperature distribution. The work aims to evaluate the evolution of these variables as a function of feed rate using uncoated carbide tools. The orthogonal cutting was validated by comparing the cutting forces obtained experimentally with simulated results. Predictions of cutting temperature, plastic deformation and deformation rate during the machining of AISI 4140 steel were also obtained. The combination of finite element technique with actual measurements of cutting test allows to improve and to optimize the machining conditions. Experimental and simulated results showed close values as regards the cutting force. Keywords: AISI 4140; Finite Element Method; Machining simulation; Cutting temperature; Micromachining.

Study of plastic deformation and interface friction process for ultrasonic welding

Ultrasonic spot welding (USW) is attracting increasing attentions in joining of dissimilar metals. Previous experimental results show that material plastic deformation and interface friction plays key role for joint formation process. In the present study, experimental and theoretical analysis was carried out to study USW of copper and aluminium. Evolution of interface friction and surface deformation was obtained quantitatively. Meanwhile, theoretical analysis was proposed to research material flow and contact behaviour between faying interfaces of specimens. Conclusions can be made that interface friction resulted in tremendous plastic deformation, which was beneficial for joint formation. Growth rate of plastic deformation decreased as welding proceeds. Compression stress and cyclical shear stress induced by ultrasonic vibration determined direction and degree of material flow.

Mathematical plastic flow modeling for equal–channel angular pressing of bismuth chalcogenide base solid solution

In this work, mathematical modeling was used to optimize the geometry of the composite mold for developing the technology of equal−channel angular pressing with three channels for thermoelectric materials. To obtain the maximum degree of deformation in this work, we used a three−channel scheme. Taking into consideration the material characteristics (low resistance to tensile stresses), we proposed a tapering profile (along the length) of the third channel. To analyze the plastic flow in the proposed scheme of equal−channel angular pressing with three channels, we performed mathematical modeling of plastic flow, stress and deformation rates along the rod, deformation homogeneity along the cross−section and absence of stagnant zones in the extruder. The methodical approach is based on the combined use of the elastic and plastic solid state approximations according to the fundamentals of the elasticity and plasticity theory. Critical points are identified having the maximum stored energy accumulation without discontinuity of the material. Calculation of the flow velocity in planes perpendicular and parallel to the deformation axis showed a slight difference in the flow rate of the material for the section plane parallel to the deformation axis. This produces a bend with a large curvature radius but does not cause cracking of the material. Calculation of deformations along the flow axis allowed us to detect deformation inhomogeneity. This resulted in the appearance of small tensile stresses in the longitudinal section of the third channel. We show that the plastic deformation inhomogeneity revealed by modeling can be eliminated by using an equipment design with a greater output channel length. Mathematical modeling shows the suitability of the suggested unconventional design of equal−channel angular pressing equipment for bismuth chalcogenide base solid solutions.

Plastic deformation mechanisms of ultrafine-grained copper in the temperature range of 4.2–300 K

Main microstructural features of ultrafine-grained (UFG) polycrystalline oxygen-free copper (Cu–OF) obtained by direct and equal-channel angular hydrostatic extrusion were studied by EBSD and XRD methods. The effect of microstructure on the temperature dependences of the yield stress and strain rate sensitivity of the deforming stress was investigated using tensile and stress relaxation tests in the insufficiently studied temperature range of 4.2–300 K. Using thermal activation analysis it was established that in the range 77–200 K the rate of plastic deformation is controlled by the thermally activated mechanism of crossing the forest dislocations and its empirical parameters were obtained. The experimental anomalies below 77 K unaccountable by the forest crossing mechanism were explained by the inertial properties of dislocations revealed under conditions of high effective stress and low dynamic friction. The inversion of the temperature dependences of the activation volume observed above 200 K was attributed to the thermally activated detachment of dislocations from local pinning centers within the grain boundaries.

Mechanical Response of Shape Memory Alloys Under a Rapid Heating Pulse - Part II

We report on a new experimental system for exploring the thermo-mechanical response of shape memory wires under a rapid heating pulse. The new setup enables the force and displacement generated by the phase transforming wire to be measured with a μs time resolution. In addition, part of the tests incorporated high-speed infrared and visible light photography. The experimental system enables exploring several unique dynamic effects. In particular, stress levels of 1.6 GPa with negligible plastic deformation and elastic strain rates of 103 s−1 are observed. Force measurements reveal a dead time of ~20 μs between the end of the electric pulse and the onset of the stress rise in the SMA wire. The high strain rate, generated by the phase transformation, induces string-like vibrations of the SMA wire that result in strong stress vibrations. The developed experimental system opens the way for studying the kinetics of the phase transformation.

Formation of ultrafine-grain structure in carbon steel by high-temperature high-speed compression

Increasing the rate of plastic deformation considerably changes the microstructure of metals. The structure and properties of metals are determined by factors such as the pressure (or pulse), the strain rate (or duration of the process), and the temperature. The influence of high-speed deformation on the microstructure of materials is studied. After high-speed deformation of steel 20 samples by means of the Gleeble 3500 system, at 800, 900, 1000, and 1200°C, their microstructure and microhardness are determined. In principle, the grain size in low-carbon steel 20 may be reduced to around 400 nm by fast deformation at 800–1000°C, as in profound plastic deformation with little or no heating of the metal (not exceeding the recrystallization temperature).

Complementary Machining – Machining Strategy for Surface Modification

In metal production mechanical surface treatments are used to optimize workpiece characteristics like fatigue strength. Complementary Machining is a new machining strategy which is characterized by the combination of cutting and mechanical surface treatment. After cutting the insert is used reversely acting as a tool for mechanical surface treatment. This paper shows the effect of high plastic deformation rates in the surface layer reducing surface roughness and increasing strain hardening. Furthermore, it is supposed that the process induces grain refinement in the surface layer. The process strategy Complementary Machining is investigated during machining Armco-Iron and AISI 4140.

Surface Modification of Oilfield Alloys by Ultrasonic Impact Peening: UNS N07718, N07716, G41400, and S17400

Ultrasonic impact peening (UIP) is a severe plastic deformation process to induce localized surface hardening combined with compressive residual stresses which therefore extends the useful life of mechanical parts. In this investigation, UIP has been applied to four widespread alloys in use in the oilfields. These include two premium NiCrMo alloys, UNS N07718 (718) and UNS N07716 (625 Plus®), both characterized by satisfactory oilfield performance but lacking hardness and abrasive wear resistance, and two relatively low-cost alloys, UNS G41400 (4140) and UNS S17400 (17-4PH), both limited by their corrosion fatigue. To promote comparisons and determine important alloy parameters for successful UIP, all four alloys were carefully selected so that their respective yield strengths were within relative proximity (~780 to ~910 MPa), and then ultrasonically impact peened under identical conditions. Among major findings from microstructural examinations, micro-hardness indentations, and residual stress measurements, surface topological changes (roughness), alloy microstructural evolution (depth and extent of strain hardening, including mechanical twinning in the NiCrMo alloys), and compressive residual stresses were found to be well correlated. Among all four alloys, the NiCrMo alloys, in particular UNS N07716 was found to be best suited for UIP. This is explained by its FCC austenitic microstructure, relatively low stacking-fault energy (prone to mechanical twinning), and in practical terms high yield strength and high tensile-to-yield strength ratio, both related to its excellent plastic flow behavior under ultrasonic rates of plastic deformation.

Flow rules for rigid-plastic strain kinematic hardening solids

Abstract The associated flow rule is commonly supposed to be one of the cornerstones of classical plasticity theory for metals though some experimental results do not accord with it. This paper investigates the flow rule of plastic deformation rate for von Mises materials exhibiting kinematic hardening. It is found that the associated flow rule is not valid in rigid-plastic deformations. The associated flow rule for von Mises materials exhibiting kinematic hardening is modified. The modified associated flow rule implies that the vector of plastic deformation rate need not be perpendicular to the yield surface in nine-dimensional stress space. Finally, the principle of maximum plastic dissipation is modified as well.

A Uniform Viscoelastic-Plastic Constitutive Model for MD-PMMA at a Wide Temperature Range

The deformation characteristics of MD-PMMA vary greatly at different temperatures. In the paper, whether a uniform model could be used to describe these complex characteristics was discussed. Tensile properties of MD-PMMA at the temperatures of -50˚C, -25˚C, 20˚C, 60˚C, 90˚C were experimentally investigated. The entire deformation processes of PMMA were divided into four stages: elastic stage, viscoelastic stage, yielding stage and post-yielding stage. Strain softening and strain hardening phenomenon occurred in the yielding and post-yielding stage, it was the results of the competition between loading rate and plastic strain rate. A nonlinear model of activation dashpot was constructed, in the model, the evolution rate of plastic deformation was defined by Eyring’s theory, and the actual stress was the difference between external applied stress and internal resistance stress caused by plastic strain. The above activation dashpot serially connected with the standard linear model (SLM) to identify elastic and viscoelastic characteristics. A two iterations integral algorithm was proposed to simplify the inter-coupling between the internal stress and the plastic strain, and the unknown parameters in the model could be easily fitted by the experimental data. This uniform viscoelastic-plastic model was demonstrated that could predict different deformation behaviors at a wide temperature range.

The Influence of Sample Preparation on the Quantitative Analysis of the Volume Fraction of Martensite Formed in a 304l Trip Steel

The metastable 304L austenitic stainless steels are susceptible to phase transformation induced by plastic deformation. The traditional metallographic preparation, via mechanical methods, introduces superficial plastic deformation from grinding and polishing. It is important to evaluate this effect on the results of quantitative analysis of martensite formed in 304L steels and similar alloys. In this work, phase transformation was induced by a tensile test at room temperature with two different plastic deformation rates in order to provide distinct structural conditions for the proposed analysis. X-ray Diffraction (XRD) and Ferritescopy were used to determine the volume fraction of martensite in samples with and without metallographic preparation. The results show that the analyses quantitative were not affected by metallographic preparation.

Strain gradient plasticity: energetic or dissipative?

For an infinite slab of strain gradient sensitive material subjected to plane-strain tensile loading, computation established and analysis confirmed that passivation of the lateral boundaries at some stage of loading inhibits plastic deformation upon further loading. This result is not surprising in itself except that, remarkably, if the gradient terms contribute to the dissipation, the plastic deformation is switched off completely and only resumes at a clearly defined higher load, corresponding to a total strain \(\varepsilon _c\), say. The analysis presented in this paper confirms the delay of plastic deformation following passivation and determines the exact manner in which the plastic flow resumes. The plastic strain rate is continuous at the exact point \(\varepsilon _c\) of resumption of plastic flow and, for the first small increment \(\Delta \varepsilon =\varepsilon -\varepsilon _c\) in the imposed total strain, the corresponding increment in plastic strain, \(\Delta \varepsilon ^\mathrm{p}\), is proportional to \((\Delta \varepsilon )^2\). The constant A in the relation \(\Delta \varepsilon ^\mathrm{p}(0) = A(\Delta \varepsilon )^2\), where \(\Delta \varepsilon ^\mathrm{p}(0)\) denotes the plastic strain increment at the centre of the slab, has been determined explicitly; it depends on the hardening modulus of the material. The presence of energetic gradient terms has no effect on the value of \(\varepsilon _c\) unless the dissipative terms are absent, in which case passivation reduces the rate of plastic deformation but introduces no delay. This qualitative effect of dissipative gradient terms opens the possibility of experimental discrimination of their presence or absence. The analysis employs an incremental variational formulation that is likely to find use in other problems.