Plastic Deformation Rate Research Articles

Classification of pressure welding methods depending on thermal deformation conditions

In this study, a classification of welding methods is proposed, based on the peculiarities of metal gripping under various heat-deformation conditions for the implementation of welding processes. The theoretical basis of the developed classification is the hypothesis of the critical sizes of active centers. The main approaches to the classification of welding methods are considered, and four groups of pressure welding methods are proposed, depending on the mechanism of formation of stable centres of gripping: mechanical welding methods with low plastic deformation rate; mechanical methods of welding with a high plastic deformation rate; thermo-mechanical welding methods, in which, in addition to heating by deformation, additional sources of thermal energy are used to increase the temperature in the zone of joint formation; thermal pressure welding methods that envisage only a thermal activation channel.

Dimensionless numbers to study cell wall deformation of stiff mutants of Phycomyces blakesleeanus.

The sporangiophores of Phycomyces blakesleeanus are large cylindrical aerial cells that elongate vertically at rates between 10 μm/min and 60 μm/min. Wild‐type sporangiophores grow toward light, opposed to gravitational acceleration and away from solid barriers (tropic responses). Sporangiophores of stiff mutants C149 and C216 exhibit diminished tropic (bending) responses. Originally, it was thought that the altered genes affect the “stiffness” (elastic wall deformation) of the cell wall. Subsequent investigations employing the pressure probe demonstrated that the irreversible (plastic) wall deformation was smaller for the stiff mutants compared to wild type and could account for the diminished tropic responses. However, it was not shown whether the elastic wall deformation was altered in these stiff mutants. Recent theoretical studies have identified dimensionless numbers that can be used to quantitate the magnitudes of biophysical processes involved in expansive growth of walled cells. In this study, dimensionless numbers are used to determine the magnitudes of elastic deformation rate, plastic deformation rate, and stress relaxation rate of the cell wall during expansive growth of the stiff mutant sporangiophores. It is found that the altered genes reduce stress relaxation rates and plastic deformation rates of the wall, but do not significantly alter the magnitude of the elastic deformation rates of the wall. These results indicate that the mutant genes reduce wall loosening chemistry in these sporangiophores and the genetic mutation is not expressed in a change in “wall stiffness,” but in “wall viscosity” or “wall extensibility.”

Nondislocational Mechanisms of Strain Localization in Nickel Nanocrystals During Deformation by High-Pressure Torsion in Bridgman Anvils

Using the methods of transmission electron microscopy, new aspects of formation of reorientation nanobands with partial involvement of nondislocational deformation mechanisms are investigated in nickel nanocrystals under the conditions of its severe plastic deformation by high-pressure torsion in Bridgman anvils: local reversible (FCC→BCC→FCC) transformations of the martensitic type and quasi-viscous mass transfer by the flows of nonequilibrium point defects in the fields of high local pressure gradients. The features of disclinational structure and elastically stressed state at the nanoband propagation front are studied. A theoretical analysis of the rate of plastic deformation via the mechanisms of quasi-viscous mass transfer by the flows of nonequilibrium point defects is performed. A possibility of simultaneous realization of the martensitic and quasi-viscous deformation modes at the front of nanoband propagation is established. An analysis of the conditions and mechanisms where these modes are involved is performed as a function of the type of point defects (vacancies and interstitial atoms), deformation temperature, and peculiarities of disclination structure and elastically stressed state.

Serial deformation maps and elasto-plastic continua

This paper deals with the kinematics of finite plastic deformation. The starting point is E.H. Lee’s multiplicative decomposition of the deformation gradient into its elastic and plastic parts. We diverge from Lee’s (and others’) derivation of the deformation rate and spin tensors and prove that the elastic and plastic deformation rate and spin tensors are additive. It is then shown that the elastic and plastic strains are also additive and equal to the total strain. A central result, and a major deviation from continuum mechanics, is that not one, but two deformation maps are necessary for the constitutive response in elasto-plasticity. The two-map decomposition is then extended to the n-th order, and additivity is shown there as well. Elastoplastic constitutive equations in large deformation are presented and discussed in the context of path-dependent (endochronic) plasticity.

In-situ observation of hardmetal deformation processes by transmission electron microscopy. Part II: Deformation caused by tensile loads

In the 1st part of this article, hardmetal deformation processes caused by bending loads were examined in-situ by transmission electron microscopy. The major objective of this work is to examine hardmetal deformation processes in special thin hardmetal samples as a result of applying tensile loads in-situ directly in a transmission electron microscope with the aid of the push-to-pull method. Applying tensile loads to the samples results in the plastic deformation of the Co-based binder phase leading to the formation of different crystal lattice defects in the binder. Force-time and displacement-time curves recorded when loading the samples and maintaining the loads provide evidence for continuous processes of the formation and movement of crystal lattice defects, presumably dislocations, in the WC phase and Co-based binder leading to a high rate of the binder plastic deformation. After increasing the tensile loads up to a certain level leading to the severe plastic deformation of the binder phase, the samples suddenly fail as a result of the crack initiation and propagation at WC-Co interfaces. Presence of cobalt on the WC surface after the cracking suggests that the cracks propagate through the binder region adjacent to the interface rather than through the interface itself.

In-situ observation of hardmetal deformation processes by transmission electron microscopy. Part I: Deformation caused by bending loads

WC-based hardmetals have a unique combination of different properties including high hardness, fracture toughness, abrasion resistance, strength, fatigue resistance, etc. Such properties are achieved due to extraordinary features of tungsten carbide, which is characterized by a certain degree of plastic deformation before failure when loading. The major objective of this work is to examine hardmetal deformation processes leading to the formation and movement of crystallographic defects in a hardmetal lamella as a result of its in-situ bending directly in a transmission electron microscope. The deformation is found to result in the formation of different crystal lattice defects in the Co-based binder and WC grains. Mainly dislocations form in the tungsten carbide grains. The dislocations start moving when increasing the applied bending load. The deformation of the binder phase is found to result in the formation of mainly lamellae and stacking faults in the Co crystal lattice. As a result of the formation, interaction and movement of the crystal lattice defects in the WC phase and binder phase a significant rate of plastic deformation of the hardmetal lamella was achieved under bending loads without its breakage.

Effect of Cyclic Load Amplitude on the Evolving Characteristics of Accumulative Deformation in Subgrade Bed

To investigate the evolving characteristics of plastic deformation for the angular gravels that are used to construct subgrade bed, a laboratory model test is performed with cyclic load applying. Vertical deformation is measured in real time by displacement transducers and further modified to analyze the plastic behavior of model fillings. It can be found that vertical plastic deformation shows quite different developing patterns under the effect of different cyclic amplitudes for a given model. A power function is adopted to describe the relationship between deformation rate and loading times. By analyzing the value of the power exponent and the corresponding developing features of plastic deformation rate, model filling status can be classified into four different zones, i.e., rapid stabilization, tardy stabilization, tardy failure, and rapid failure. Such a classification reveals different developing patterns of plastic deformation and satisfies the design of subgrade bed for ballasted and unballasted railway.

Beneficial effect of low plastic deformation rate on the flatness and residual stress of the magnesium alloy plate straightened at room temperature

Currently, magnesium alloys are extensively used owing to their excellent comprehensive mechanical properties. Rolling is a primary method used to produce magnesium alloy plates. However, so far, only few reports have been investigated about the straightening of rolled magnesium alloy plates. In this study, multi-roller straightening of the magnesium alloy plate is theoretically analyzed and simulated using the finite element method. Multi-roller straightening process of the magnesium alloy plate was performed as follows: the original bending curvature that exhibited large numerical differences in different directions was gradually reduced through reasonable distribution of the plastic deformation rate of each straightening roller system. Finite element simulation and experimental results are obtained for room-temperature magnesium alloy plate straightening at four different plastic deformation rates. However, the straightening effect is minimal when the micro plastic deformation rate is used for straightening the magnesium alloy plate with an initial curvature, this is because the reverse bending rate required for straightening is not attained. Straightening effect can be achieved with low, moderate, or high plastic deformation rates, and the flatness achieved after straightening at a low plastic deformation rate is relatively better than that obtained using moderate and high deformation rates. Both perpendicular to and along the straightening direction, the residual stress after straightening is less than that observed before straightening. Furthermore, the residual stress after straightening at a low plastic deformation rate is the lowest and uniformly distributed.

Effect of plastic deformation rate at room temperature on structure and mechanical properties of high-Mn austenitic Mn-Al-Si 25-3-3 type steel

Purpose: The aim of the paper is to determine influence of plastic deformation rate at room temperature on structure and mechanical properties of high-Mn austenitic Mn-Al-Si 25-3-3 type steel tested at room temperature. Design/methodology/approach: Mechanical properties of tested steel was determined using Zwick Z100 static testing machine for testing with the deformation speed equal 0.008 s-1, and RSO rotary hammer for testing with deformation speeds of 250, 500 and 1000s-1. The microstructure evolution samples tested in static and dynamic conditions was determined in metallographic investigations using light microscopy as well as X-ray diffraction. Findings: Based on X-ray phase analysis results, together with observation using metallographic microscope, it was concluded, that the investigated high-Mn X13MnAlSiNbTi25-3-3 steel demonstrates austenitic structure with numerous mechanical twins, what agrees with TWIP effect. It was demonstrated, that raise of plastic deformation rate produces higher tensile strength UTS and higher conventional yield point YS0.2. The UTS strength values for deformation rate 250, 500 and 1000 s-1 grew by: 35, 24 and 31%, appropriately, whereas in case of YS0.2 these were: 7, 74 and 130%, accordingly, in respect to the results for the investigated steel deformed under static conditions, where UTS and YS0.2 values are 1050 MPa and 700 MPa. Opposite tendency was observed for experimentally measured uniform and total relative elongation. Homogeneous austenitic structure was confirmed by X-ray diffractometer tests. Research limitations/implications: To fully describe influence of strain rates on structure and mechanical properties, further investigations specially with using transmission electron microscope are required. Practical implications: Knowledge about obtained microstructures and mechanical properties results of tested X13MnAlSiNbTi25-3-3 steel under static and dynamic conditions can be useful for the appropriate use of this type of engineering material in machines and equipment susceptible to static or dynamic loads. Originality/value: The influence of plastic deformation at room temperature under static and dynamic conditions of new-developed high-manganese austenitic X13MnAlSiNbTi25-3-3 steels were investigated.

Dimensionless Numbers to Analyze Expansive Growth Processes.

Cells of algae, fungi, and plants have walls and exhibit expansive growth which can increase their volume by as much as 10,000 times. Expansive growth is central to their morphogenesis, development, and sensory responses to environmental stimuli. Equations describing the biophysical processes of the water uptake rate and the wall deformation rate have been derived, validated, and established. A significant amount of research provides insight into the molecular underpinnings of these processes. What is less well known are the relative magnitudes of these processes and how they compare during expansive growth and with walled cells from other species. Here, dimensionless numbers (Π parameters) are used to determine the magnitudes of the biophysical processes involved in the expansive growth rate of cells from algae (Chara corallina), fungi (Phycomyces blakesleeanus), and plants (Pisum satinis L.). It is found for all three species that the cell’s capability for the water uptake rate is larger than the wall plastic deformation rate and much larger than the wall elastic deformation rate. Also, the wall plastic deformation rates of all three species are of similar magnitude as their expansive growth rate even though the stress relaxation rates of their walls are very different. It is envisioned that dimensionless numbers can assist in determining how these biophysical processes change during development, morphogenesis, sensory responses, environmental stress, climate change, and after genetic modification.

Effect of prior plastic deformation and deformation rate on the corrosion resistance of AISI 321 austenitic stainless steel

In this work, the role of prior plastic deformation and rate of deformation on the corrosion behavior of plastically-deformed metastable AISI 321 austenitic stainless steel in 3.5 wt% NaCl solution was investigated. Samples were deformed under dynamic (έT = 8.8 × 103 s−1) and quasi-static (έT = 4.4 × 10−3 s−1) loading conditions to a common true strain of ~0.86 using a split Hopkinson pressure bar and Instron R5500 mechanical testing systems, respectively. While the specimen subjected to quasi-static compression experienced substantial deformation-induced martensitic transformation, phase transformation was significantly suppressed in the specimen subjected to dynamic loading due to temperature rise during impact. The yield strength of the specimen under dynamic impact loading is higher than that of the specimen compressed under quasi-static loading condition. However, the specimen deformed under quasi-static loading shows higher strain-hardening rate compared to the specimen subjected to dynamic impact load which is dominated by thermal softening at true strain beyond ~0.6. Using the Tafel polarization and impedance spectroscopic techniques, the deformed specimens were found to be more resistant to chloride-induced intergranular corrosion at room temperature compared to the undeformed ones. The specimen subjected to quasi-static loading exhibits significantly higher corrosion resistance in comparison with those subjected to dynamic loading. This could be attributed to the formation of a denser passive film on the specimen subjected to quasi-static loading on exposure to the test electrolyte over time. In addition to the role of particles on pitting formation in metals exposed to corrosive environment, the current work affirms the important role of prior plastic deformation on the corrosion behavior of the investigated alloy. Evolution of twins and stable-end orientation (preferred crystallographic orientation) in both parent (austenite) and product (martensite) phases nullified what would have been the negative effects of plastic deformation (due to the associated deformation-induced martensitic phase and stored defects) on the corrosion resistance of the investigated stainless steel.

Influence of Aging Treatments on the Structural and Mechanical Properties of AGS Alloy Wire Cold Drawn

The scope of this work is to study of microstructural changes and mechanical properties during natural and artificial ageing treatment of AGS Alloy wire cold drawn with different deformation at ENICAB in Biskra. And as well to know the phase formation during different deformation of aluminum alloys wires. as well as the combined influence of the plastic deformation rate and the aging temperature. Wire section reduction shows a change in microstructure and texture. The methods of characterization used in this work are: scanning electron microscope and X-ray diffraction, micro hardness (Hv).

Synthesis of Nono-Crystalline Aluminum Carbide Using Thermal Treatment of Mechanically Activated Al and Graphite Mixture

In this work, Nono-crystalline aluminum carbide particles were synthesized using both mechanical and thermal treatments. Frist, Al and graphite powders had been milled in a planetary ball mill. Then, milled mixtures have been annealed isothermally after the mechanical activation. The effects of two processes on the synthesized products were separately studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (STA) methods. Further, the grain size, lattice strain and dislocation density values were calculated according to XRD data. The results showed that mechanical alloying process can create an ultra-fine microstructure. The grain size was mostly reduced after 40 h milling as well as the heat treatment at 550 °c and 2 h. in fact, the high rate of plastic deformation of aluminum particle during milling process lead to rising the internal energy of particles, and finally, nanocrystals of Al4C3 formed with the size of 14 nm. However, thermal analysis indicated that the mechanical activation of aluminum and the presence of carbon can play key roles in synthesis of aluminum carbide. Key words: Mechanical alloying, annealing, Al and graphite powders, Solid state reaction, Nono-crystalline aluminum carbide.

Mechanism of Plastic Collapse of Nanosized Crystals with BCC Lattice under Uniaxial Compression

Within the dislocation–kinetic approach, based on the nonlinear kinetic equation for dislocation density, an attempt is made to consider the problem of a catastrophic plastic collapse of defect-free nanocrystals of metals with bcc lattice under their uniaxial compression with a constant deformation rate. Solutions of this equation were found in the form of moving waves, describing the dislocation multiplication process as the wave moves along the crystal from a local dislocation source. Comparison of the theory with the results of experiments on defect-free Mo nanocrystals showed that their ultrahigh strength at the initial stage of deformation is associated with a low rate of rise of crystal plastic deformation in comparison with the growth of its elastic component. The subsequent plastic collapse of crystal is caused by a sharp increasing the plastic component, ending with reaching the equality of elastic and plastic deformation rates.

INFLUENCE OF DIFFERENT STATE PARAMETERS ON THE BEHAVIOR OF FATIGUE CURVES

The behavior of materials in different areas of cyclic loading is very different and can depend on both their state and the test conditions. As the criteria for damage during cyclic loading, width of the hysteresis loop, parameters of the dislocation theory, magnitude of the stresses and their intensity, relation with the grain size, etc. can serve. Meanwhile, there is still no general complex mathematical equation reflecting the effect on metal damage during fatigue of such important characteristics of polycrystals as the density or defectiveness, the stress relaxation rate, loading rate, structural and energy state of the material, namely, strength and hardness, and the applied emerging stress-strain state. In the present work, the influence of cyclic loading on failure from the point of view of competition of the loading and relaxation rates of internal stresses with allowance for the spectrum of plastic deformation waves is considered. Depending on the type and loading conditions, a different spectrum of the waves of plastic deformation and fracture is formed under different kinds and loading conditions. It is shown that as the frequency of cyclic loading (strain rate) increases, the voltage rise time decreases, and the voltage corresponding to a certain plastic deformation increases. The intensity of reducing the resistance to material destruction is related to the intensity of damage accumulation. General analytical equations for describing the behavior of the fatigue curves of polycrystalline metals and alloys are obtained, which allow one to represent the influence of the factors of their state in dependence on the influence of the external conditions of cyclic loading. The equation allows to simulate various situations of behavior of polycrystals with fatigue in metals, as well as to analyze the fatigue curves of materials in different states. Since the relaxation rate in polycrystals is the vectorial value = pl.d + p , representing the sum of the vectors of the plastic deformation rate ( pl.d ) and the actual fracture rate p is the nucleation and growth of cracks, then taking this into account, with increasing pl.d with constant total relaxation rate, the rate of destruction will decrease, the fatigue curve will go lower (position). Fatigue curves are constructed for various parameters of the structuralenergy state (Brinell hardness) and density-dependent coefficients.

Wear Resistance Improvement by Nanostructured Surface Layer Produced by Burnishing

Burnishing, which is one of the most powerful processes for microstructural evolution, was performed by a cemented carbide ball (6 mm in diameter) that was loaded and fed on the flat surface of a rotating disk specimen of carbon steel using a lathe machine. The effects of burnishing process parameters such as force and rotation speed on the surface roughness, microstructure and hardness were investigated. In addition the dry sliding wear properties of the burnished surface layers were studied using a ball-on-disk friction method. It was found that the burnished surface was much smoother than as-turned surface (before burnishing) owing to the plastic flow of the surface asperities through the rubbing motion of the burnishing ball. Nanostructure in the 30 - 50 nm grain size range was formed in the burnished sub-surface layer, and the hardness significantly increased due to the grain refinement. The nanocrystalline microstructure was observed at high burnishing forces and speeds owing to the high strain and strain rate of the friction-induced plastic deformation. Moreover the burnishing process reduced the specific wear rates by a factor of six. Thus we concluded that the wear resistance of carbon steel can be significantly improved by burnishing due to the smooth surface and nanostructured sub-surface layers.

Microstructure evolution in the conventional single side and bobbin tool friction stir welding of thick rolled 7085-T7452 aluminum alloy

The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction results reveal that a significant grain refinement and a larger percentage of high angle grain boundaries (HAGBs) exist in the weld nugget zone (WNZ) and the thermal-mechanical affected zone (TMAZ) compared with the base material. Meanwhile, more obviously inhomogeneous refined grains and HAGBs in WNZ along the thickness direction and a larger percentage of low angle grain boundaries (LAGBs) were observed in SS-FSW joint than that in BB-FSW joint. The change of the average grain size is the result of friction heat and strain rate of plastic deformation combined with a certain degree of recrystallization. Moreover, the recrystallization is mainly controlled by the strain rate during the FSW process. The presence of Cube and Cube ND after welding shows that the discontinuously dynamic recrystallization (DDRX) is a major factor in the final microstructural response. The research and findings help the understanding of the mechanism of microstructure homogenization and further optimizing the welding process for application.

Numerical analysis of wellbore instability in gas hydrate formation during deep-water drilling

Gas hydrate formation may be encountered during deep-water drilling because of the large amount and wide distribution of gas hydrates under the shallow seabed of the South China Sea. Hydrates are extremely sensitive to temperature and pressure changes, and drilling through gas hydrate formation may cause dissociation of hydrates, accompanied by changes in wellbore temperatures, pore pressures, and stress states, thereby leading to wellbore plastic yield and wellbore instability. Considering the coupling effect of seepage of drilling fluid into gas hydrate formation, heat conduction between drilling fluid and formation, hydrate dissociation, and transformation of the formation framework, this study established a multi-field coupling mathematical model of the wellbore in the hydrate formation. Furthermore, the influences of drilling fluid temperatures, densities, and soaking time on the instability of hydrate formation were calculated and analyzed. Results show that the greater the temperature difference between the drilling fluid and hydrate formation is, the faster the hydrate dissociates, the wider the plastic dissociation range is, and the greater the failure width becomes. When the temperature difference is greater than 7°C, the maximum rate of plastic deformation around the wellbore is more than 10%, which is along the direction of the minimum horizontal in-situ stress and associated with instability and damage on the surrounding rock. The hydrate dissociation is insensitive to the variation of drilling fluid density, thereby implying that the change of the density of drilling fluids has a minimal effect on the hydrate dissociation. Drilling fluids that are absorbed into the hydrate formation result in fast dissociation at the initial stage. As time elapses, the hydrate dissociation slows down, but the risk of wellbore instability is aggravated due to the prolonged submersion in drilling fluids. For the sake of the stability of the wellbore in deep-water drilling through hydrate formation, the drilling fluid with low temperatures should be given priority. The drilling process should be kept under balanced pressures, and the drilling time should be shortened.

Механизм пластического коллапса наноразмерных кристаллов с ОЦК-решеткой при одноосном сжатии

AbstractWithin the dislocation–kinetic approach, based on the nonlinear kinetic equation for dislocation density, an attempt is made to consider the problem of a catastrophic plastic collapse of defect-free nanocrystals of metals with bcc lattice under their uniaxial compression with a constant deformation rate. Solutions of this equation were found in the form of moving waves, describing the dislocation multiplication process as the wave moves along the crystal from a local dislocation source. Comparison of the theory with the results of experiments on defect-free Mo nanocrystals showed that their ultrahigh strength at the initial stage of deformation is associated with a low rate of rise of crystal plastic deformation in comparison with the growth of its elastic component. The subsequent plastic collapse of crystal is caused by a sharp increasing the plastic component, ending with reaching the equality of elastic and plastic deformation rates.

Development of a new three-directional distractor system for the correction of maxillary transverse and sagittal deficiency

PurposeClass 3 malocclusions with maxillary deficiency, which are treated surgically and/or ordonotically, are common among adult patients. The aim of this study was to develop a three-directional bone-borne distractor that would allow the transverse expansion and sagittal advancement of the maxilla simultaneously. Materials and methodsComputed tomography images of a patient with maxillary deficiency were transmitted to a software program, and a distractor was designed with different sizes (D1, D2, D3) and manufactured from titanium alloy. Y-shape segmental osteotomies were performed on the model, and vertical bite forces were applied. The biomechanical properties were evaluated by using the finite element method. ResultsThe highest von Mises stress value on the body of the distractor was seen in D2 (D2>D3>D1), with 234 N bite forces. D2 had maximum stress distribution on maxillary bone under 234 N and 93 N (D2>D1>D3). No difference was found among the plastic deformation rates according to biomechanical test results. ConclusionA three-directional bone-borne palatal distractor was produced, and this distractor system can be used for the treatment of skeletal class 3 patients with maxillary hypoplasia for its advantages of shortening the overall treatment time and reducing the scar formation. However, further animal and clinical studies are essential to determine the biological response of soft and hard tissues.