Plastic Deformation Zone Research Articles

Plastic Deformation Zone Size during Indenter Scratch Tests of Materials

The plastic deformation zone sizes in various metallic materials (steel, copper, armco-iron) are studied during tests by scratching with a tetrahedral Vickers pyramid under the scratch formation conditions at a constant depth. The ratio of the plastic deformation zone depth under a scratch to the scratch depth is found to weakly depend on the scratch depth and to be 6.3–8.5 for the materials under study. Based on these results, we concluded that, when the mechanical properties of a metallic material are determined by scratching, the ratio of the material thickness to the scratch depth should be at least 8.5.

The influence of intrinsic size in amorphous CuxTa100-x/Cu crystalline nanolaminates using molecular dynamics simulation

Nanoindentation process is performed by molecular dynamics simulations to study the plastic deformation phenomena and mechanical properties of the amorphous/nanocrystalline Cu x Ta 100-x /Cu nanolaminates. The influences of the number of Cu layers, indenter velocity, temperature, and percentage of the Cu–Ta component are systematically assessed. By introducing the Cu nanocrystalline layer and controlling its thickness, the shear bands propagation and the expansion of plastic deformation are restricted. Further, the important factors of mechanical property such as indentation force, hardness, recovery ratio, von Mises stress are significantly affected by adding Cu nanocrystalline layers and changing the working conditions. Based on simulation results, dominant deformation mechanisms and phenomena of the amorphous/nanocrystalline Cu x Ta 100-x /Cu nanolaminates are propounded and deeply discussed. • The mechanical phenomena of the CuTa/Cu nanolaminates are studied by MD method. • The plastic deformation zone increases as the number of layers increases. • The hardness and the average von Mises increases at a higher velocity. • The recovery ratio and the average von Mises increase as the temperature rises. • The Cu 75 Ta 25 /Cu is more flexible, while the Cu 25 Ta 75 /Cu is more crunchy and harder.

Analysis of asymmetrical rolling of strip considering two deformation region types

Analytical models of two deformation region types considering the percentages of three regions in the plastic deformation zone are proposed for analyzing asymmetrical rolling of strip and used to calculate the critical speed ratio, three region percentages, roll force, and roll torque. The effective range of speed ratio on thickness reduction increases with increasing critical speed ratio. When the deformation region type is backward-slip zone + cross-shear zone + forward-slip zone (B+C+F), with increasing speed ratio, the thickness reduction in asymmetrical strip rolling increases evidently, but remains unchanged when the critical speed ratio is exceeded, where the deformation region type is backward-slip zone + cross-shear zone (B+C). It is achievable to increase thickness reduction by increasing the roll force and front tension, which can not only increase the reduction rate, but also increase the critical speed ratio. The effect of asymmetrical rolling on thickness reduction is enhanced with decreasing of the roll force and front and back tension because of the increasing cross-shear zone percentage.

The amplitude-sensitive eddy current method for investigation of the plastically deformed metal zone beneath the indent obtained by ball indentation

The paper presents the analysis of the results of plastic deformation zones obtained by the ball indentation into the surface of a non-magnetic metal plate using the amplitude-sensitive eddy current method. Calculation and experimental methods were used in the research. A two-dimensional finite-element model of an eddy current probe installed above a local plastically deformed zone on the metal plate surface was developed. The finite-element modelling of the electromagnetic field of eddy currents induced in the aluminium plate during multi-frequency excitation was made. It is found that the amplitude-sensitive eddy current method is appropriate not only to estimate the plastic deformation zone propagation depth, but also to detect a zone with the maximum stress values beneath the indent (hydrostatic core zone). An experimental verification of the proposed model was done. The specific zones in the deformed metal beneath the indent were detected by the eddy current method and the hydrostatic core size was evaluated.

Evaluation of interface structure and high-temperature tensile behavior in Cu/Al8011/Al5052 trilayered composite

This paper dealt with the combined processing of roll-casting and hot-rolling to fabricate high-performance Cu/Al8011/Al5052 composite with ultrathin copper thickness. It was shown that the intermetallic compounds formed at the Cu/Al interface include Al4Cu9, AlCu, and Al2Cu from the copper side, respectively, in which the CuAl phase has the lowest thickness due to its the high diffusion activation energy. Also, Al2Cu, due to having the lowest amount of Gibbs free energy, was initially formed at the interface, followed by the Al4Cu9 and AlCu phases. Although the room-temperature tensile strength of the trilayered composite is close to each other in both directions, the elongation to failure in the rolling direction is about 37% better than that of the transversal direction. Furthermore, no clear slip bands were observed in the uniform plastic deformation zone of the stress-strain curve during the high-temperature tensile tests compared to the room-temperature counterparts. Despite the decrease in tensile strength with increasing test temperature, this composite shows good tensile behavior at temperatures below 200 °C due to the pure shear fracture mode.

Microstructure, mechanical properties and wear resistance of an Al–Mg–Si alloy produced by equal channel angular pressing

Microstructure, mechanical properties and wear resistance in an ultrafine-grained Al–Mg–Si alloy fabricated utilizing a combination of equal channel angular pressing (ECAP) and dynamic aging were investigated in this paper. The results indicated that the grain size of the ECAP alloy was significantly refined, i.e., to ~239 nm after three ECAP passes. Meanwhile, the yield and tensile strength of the ECAPed material reached 340 MPa and 445 MPa, respectively, while maintaining a significant uniform elongation of 14%. Wear resistance results demonstrated that the wear rate, wear depth and width of the ECAPed material decreased in comparison with the solution-treated (SST) and peak-aged (T6) conditions under a load range of 5–25 N. The adhesive wear that occurs in the undeformed specimens at 10 N does not appear in the ECAPed specimen at the same load, indicating that the ECAPed specimen delay the appearance of more serious wear mechanisms under certain loads. The cooperative interaction of high density nano-scale β" precipitates and dislocations resulted in a combination of super-high strength and good work hardening ability which suppressed the extension of cracks between the friction layer and the plastic deformation zone. As a consequence, the combination of ECAP and dynamic aging brings a significant improvement for antifriction performance of the 6061 aluminum alloy.

STABILITY ANALYSIS OF A ROCKY SLOPE CONSIDERING EXCAVATION UNLOADING EFFECT

The rock mass encountered in actual geotechnical engineering usually undergoes long-term digenesis and geological tectonic action, and also subjected to repeated actions of loading and unloading repeatedly. This paper aims to study the influence of excavation unloading on the stability of a rocky slope, and the slope excavation process of Jinping Grade I Hydroelectric Station was selected as a case, and the 2D finite element software PLAXIS was used to evaluate the effect for the slope stability of without considering unloading and considering unloading, including stress, safety factor, plastic deformation zone and slip surface of the slope. The results show that the slope excavation unloading has a significant influence on the stress, stability safety factor, plastic deformation zone and slip surface, the stability of slope with considering unloading is far less than without considering unloading significantly. Therefore, the numerical method used to simulate the excavation of rocky slopes should consider the effect of unloading fully to service the engineering design and ensure the safety of engineering construction.

Molecular dynamics modeling of nonlinear propagation of surface acoustic waves

A new computational setup suitable for the exploration of nonlinear effects in free propagation and dissipation of surface acoustic waves (SAWs) is developed based on the molecular dynamics (MD) simulation method. First applications of the computational model demonstrate the ability of atomistic simulations to reproduce the key features of the nonlinear SAW evolution, which are distinct from their well-known counterparts in bulk wave propagation. In particular, the MD simulations predict the increasing localization of the acoustic energy near the surface of the substrate during the nonlinear sharpening of the wave profile, which leads to the formation of a shock front with characteristic cusps in the horizontal strain and velocity profiles. The peak values of surface strain and velocity associated with the cusps can significantly exceed those of the initial wave. Some of the effects revealed in the MD simulations are outside the capabilities of continuum-level models and have not been explored so far. These include the observation of an unusual quadratic correction to the dispersion relation at short wavelengths defined by the frequency-dependent localization of SAWs near the surface of the substrate, the establishment of a new mechanism of the energy dissipation at the SAW shock front, where SAW harmonics generated at the limit of frequency up-conversion transform very effectively into clouds of phonon wave packets descending into the substrate bulk, and the generation of localized zones of plastic deformation at a substantial distance from the wave source. Overall, the MD methodology developed for atomistic modeling of free SAW propagation not only enables detailed analysis of the intrinsic properties of nonlinear SAWs and verification of theoretical models but also opens up a broad range of opportunities for investigation of acoustically induced surface processes, material modification by SAWs, and the interaction of SAWs with preexisting crystal defects and other material heterogeneities.

Setup for studying the kinetics of crack growth in cyclic bending tests

The goal of the study is analysis of the features of fatigue cyclic fracture of steels. An installation has been designed to induce fatigue cracks and to study the kinetics of fatigue crack development. Crack growth is recorded by the method of potential difference. The data on the crack growth kinetics were processed on a computer using LGraph2 programs and Excel spreadsheets. When studying the kinetics of the fatigue crack development, the electrodes were soldered to the edges of the initial notch of the sample and time dependence of the potential difference was recorded on a computer during crack growth. To interpret the experimental data, a calibration chart in the coordinates «potential difference (U) – the crack length (Lcr)» constructed on the basis of the millivoltmeter readings was used, with due regard for the size of the sample section, current flow and length of the fatigue crack. Cyclic loading of the sample resulted in a stepwise character of the crack growth: first occurred zone of plastic deformation of the metal is then followed by accumulation of stresses of a certain size, their relaxation in the form of a crack and sudden crack growth. An abrupt crack growth is clearly visible on a graph of the fatigue crack growth rate obtained upon computer processing of experimental data. Using a graphical editor KOMPAS, a graph was constructed which characterized the growth of the fatigue crack against the number of cycles of fatigue tests for bending. The experimental setup provides the possibility of fatigue crack formation for impact tests, determination of the work of crack propagation, as well as studying of the kinetics of crack development and computer processing of experimental data.

Contact Yield Initiation and Its Influence on Rolling Contact Fatigue of Case-Hardened Steels

AbstractStress distributions and plastic deformation zones are factors directly influencing the fatigue life of components under cyclic contact. An effective approach to improving the resistance of a steel to contact fatigue failure is surface hardening, which builds gradient yield strength from the surface of the steel to the bulk. When using the distortion energy theory as the criterion to identify failure initiation for a case-hardened steel, contact yield starts in the subsurface wherever the von Mises stress reaches the local material strength, rather than at the point of the maximum von Mises stress in the subsurface. If the yield strength changes from the surface to the bulk following a straight line, the location of yield initiation should occur at the tangency of the strength line and the von Mises stress curve. Analyses on circular, rectangular, and elliptical contacts are presented to reveal the locations of contact yield initiation for such case-hardened steels subjected to rolling contact stresses, for which the influence of friction can be ignored. A group of formulas relating contact yield initiation, in terms of the critical pressure, location of the first yield, and plasticity index (transition to plasticity) to case-hardening parameters, such as the case slope, the minimum case depth, and surface and bulk strengths, are derived to facilitate contact element designs using case-hardened materials. The results are applied to examine the rolling contact behaviors of several case-hardened steels, and the data correlation suggests that their rolling contact fatigue lives are related to a nondimensional case-hardening slope besides external loading.

Fatigue life and fracture evolution of small-hole specimens by laser shock processing

The fatigue life and fracture characteristics of aluminum alloy small-hole specimens by laser shock processing (LSP) at different external loads were investigated. When the maximum load was 165.8 MPa, 195 MPa and 275.4 MPa, the median fatigue life gain by LSP was 3.77–4.21 times, 2.68–3.02 times and 1.77–2.20 times, respectively. The plastic deformation zone and residual stress distribution produced by LSP can restrain or control the initiation and propagation direction of cracks. It has been observed that the resulting fracture evolution depends on the applied external load. The stress simulation method, fracture morphology analysis are also used to establish the residual stress distribution, the crack propagation mode and its corresponding relationship with fatigue gain.

Study on the plastic deformation zone of Q235 steel via hammering tight seam

The formation of pre-stressing layer with certain depth on the surface via hammering can effectively prolong the fatigue life of parts. It is necessary but difficult to accurately analyze the symmetry and synchronism of plastic deformation zone formed by hammering. In this work, we, herein, create an experimental method that tights the Q235 steel rods together via external force and study the plastic deformation zone near tight seam. Through morphology analysis, it is found that the cross profile of plastic deformation zone near tight seam is circular and radially symmetrical, indicating that the sharp of internal plastic deformation zone is spherical. Additionally, the result of dynamic strain experiment confirms that the result obtained by hammering the tight seam is reliable.

Microstructure and Mechanical Properties of Inertia‐Friction‐Welded Fe–Cr–Ni–Mo High‐Strength Steel

Inertia friction welding (IFW) is a solid‐state welding technology that avoids defects associated with molten weld processes; however, this process has rarely been used to weld ultrahigh‐strength steel (UHSS). Herein, 32CrMnSi2Ni6MoV UHSS is joined successfully via IFW. The mechanical properties after welding at different rotational speeds and the microstructure at 2800 rpm are studied in detail. The temperature distributions in the peripheral and central areas are modeled according to the temperature at the weld zone. The microstructural transformation is analyzed for different temperature intervals, and the microstructural characteristics of each interval correspond to the actual microstructure of the welded joint according to the temperature distribution model. High‐strength martensite forms at the weld zone, and the thermomechanical‐affected zone (TMAZ) in the peripheral region is divided into phase transformation zone, partial recrystallization zone, and plastic deformation zone, whereas the TMAZ in the central region includes only the partial recrystallization and pure plastic deformation zones. This difference is due to the higher frictional heat caused by the higher peripheral linear velocity during rotation. A tensile test shows that fracture occurs in the base metal (BM) region, and the yield strength, tensile strength, and elongation are 805 MPa, 1064 MPa, and 13.88%, respectively.

Rotary forging with multi-cone rolls

As equipment safety levels increase, the application of large-diameter discs in nuclear reaction vessels and other high-pressure vessels becomes increasingly important. At present, it is very difficult to form a large-diameter disc using the existing process. Therefore, a new metal plastic forming technology, which is named rotary forging with multi-cone rolls (MCRs), is presented for the integral forming of large-diameter and ultra-thin disc parts for the first time in this paper. Based on the reliable three-dimensional rigid-plastic FE model, the basic deformation characteristics of MCRs forming of disc parts are explored. The result shows that rotary forging with MCRs is also a process of gradual plastic deformation zone permeation, its axial plastic equivalent plastic strain is similar to that of conventional cold rotary forging. The effects of various parameters on rotary forging with MCRs, the main defects in the deformation process and the preventive measures were studied. The research results will help to better understand the metal plastic forming technology of rotary forging with MCRs and promote further development of rotary forging with MCRs.

Study on hole quality and surface quality of micro-drilling nickel-based single-crystal superalloy

Nickel-based single-crystal superalloy has no grain boundary. This makes the traditional cutting mechanism of shearing and slipping along grain boundary of polycrystalline material based on the theory of elastic–plastic deformation not suitable for drilling single-crystal parts. To achieve high-quality and low-damage micro-drilling of nickel-based single-crystal superalloy, the micro-drilling surface/subsurface quality of the (001) crystal plane of nickel-based single-crystal superalloy was studied in this paper. Firstly, the influence rules of the cutting speed (vs) and the feed rate (vw) on the micro-drilling hole size, surface morphology, surface roughness and subsurface damage depth were studied. Then, the micro-hardness on micro-drilling subsurface was analyzed. Finally, the subsurface recrystallization was explored. The results show that with the increase in vs, the hole diameter error and the surface roughness decrease, and the depth of subsurface plastic deformation layer decreases first and then increases; with the increase in vw, the error of hole diameter and the surface roughness increase, and the depth of the deformation layer decreases first and then increases. When vw > 0.33 μm/r, there are severe scratches on the surface of the hole wall, and the hole wall appears undulating stripes; white layer structure and severe plastic deformation layer appeared on the micro-drilling subsurface; the γ and γ’ phases' deformation is severe; the micro-hardness at the subsurface white layer is small, and the micro-hardness value at the plastic deformation zone is large; after the high-temperature treatment, γ phase dissolves on the subsurface of micro-drilling parts, and the cellular recrystallization and the complete recrystallization occur. The minimum thickness of recrystallization layer obtained is 1.43 μm at vs = 141 m/min and vw = 0.105 μm/r. This study provides a good guidance and reference for the machining of nickel-based single-crystal superalloy micro-hole parts.

Atomistic simulation of hydrogen-induced plastic zone compression during cyclic loading

To investigate the effect of hydrogen atoms on the size of the plastic deformation zone, molecular dynamics (MD) simulations were performed on a single crack model. The model uses pre-charged hydrogen to quantify the compression effect of hydrogen atoms on the plastic zone during cyclic loading. The results show that stress release at the crack tip occurs mainly in the form of plastic deformation, and the degree of compression in the plastic zone increases with increasing hydrogen concentration. A compression factor, which considers hydrogen concentration, is found with the help of the simulation results. A modified fatigue crack growth rate (FCGR) model, combined with the compression factor, was then used to predict the hydrogen-assisted fatigue crack growth rate. The proposed model shows excellent agreement with the experimental data for X100 steel, and it provides a new framework to describe hydrogen-assisted cracking.

Microstructure characterization and tensile properties of processed TC17 via high energy shot peening

The microstructure and tensile properties of the processed TC17 via high energy shot peening (HESP) were investigated, in which special attention was paid to reveal the fracture behaviour of the HESP processed surface layer. The results indicated that the severe plastic deformation (SPD) zone with the nanograins appeared in the HESP processed surface layer of TC17, in which the SPD thickness increased with the increasing of air pressure while it increased firstly and then decreased with the prolonging of peening duration, and the finer nanograins could be obtained at the higher air pressure and longer peening duration. Due to the generation of the gradient structure layer, the HESP processed TC17 had ruptured in a hybrid fracture. The fracture features corresponding to nanograined structure, ultrafine-grained structure and coarse-grained structure were the brittle fracture, the mixed fracture and the ductile fracture respectively. Comparing with the properties of the annealed TC17, the HESP processed TC17 possessed a better strength-ductility balance owing to combined effects of grain refinement, high-density dislocations, work hardening and compressive residual stress (CRS), in which the yield strength (YS) and the ultimate tensile strength (UTS) were increased by 10.1% and 13.9%, respectively.

Research of nonlinear dynamic deformation of spatial bodies with cracks

The object of research is the process of dynamic interaction of a complex system of cyclically symmetric parts of the support joint, taking into account the presence of stationary cracks. A significant number of structural elements and parts operated under dynamic loads are characterized by the occurrence and propagation of cracks in areas of significant plastic deformation. In particular, for the supporting device, it is a cyclically symmetric body with a limiting case of heterogeneity, under the action of pulsed loads, plastic flow zones arise at the boundaries of the joints of the cylindrical part with projections. If there are cracks in these areas, it becomes necessary to reliably determine the fracture parameters and predict the crack growth over time.To build models of this class of objects, one of the most universal and reliable numerical methods is the semi-analytical finite element method.In this paper, the results of calculating of the parameters of fracture mechanics on the basis of the semi-analytical method of finite elements are presented for an object with inhomogeneous physical and mechanical properties in the presence of stationary cracks under conditions of pulsed loading and plastic deformations. The numerical study is performed in two stages. At the first stage, the laws of the elastic-plastic dynamic deformation of the system are established. The most probable zones of damage accumulation and cracking are determined, which is the reason for the failure of structural elements. At the second stage, a model with a crack located in the zone of plastic deformations is considered, the calculated values of the dynamic stress intensity factors are studied, and their evolution over time is investigated.The obtained research results can be used in numerous calculations of inhomogeneous bodies with damage such as cracks in the conditions of elastic-plastic dynamic deformations.

Dynamic Response Analysis of Large Arch-Roof Oil Tank Subjected to the Coupling Impact of Two-Source Blast Waves Based on Finite Element Method

Research on failure law of target oil storage tank subjected to the coupling impact of multiple blast waves is one of the theoretical bases for domino effect accident prevention and control of chemical industrial parks. Taking the coupling impact of two-source blast waves as an example, the propagation law of blast waves in air and the distribution law of peak overpressure on the surface of tank wall are analyzed, and the dynamic response laws of displacement, stress, strain and energy for a 5000 m3 atmospheric steel arch-roof oil tank are studied by using ANSYS/LS-DYNA. The results are compared with those subjected to single blast wave and show that the maximum overpressure peak value is formed near the ground in 0° direction on the surface of tank wall, which is 79.6% larger than that subjected to single blast wave. The peak values of displacement, stress and strain for the tank wall subjected to the coupling impact of two-source blast waves are 114.9%, 39.6%, 134.9% larger than those subjected to single blast wave, respectively. The failure mode of arch-roof tank subjected to two-source blast waves is to form multiple concave plastic deformation zones on the explosion face, which extend to the surrounding area and produce plastic hinge lines and form irreversible residual deformation and cracking finally. The analysis results can provide reference for explosion-resistant design of tank structure and reasonable layout of tank area scene.

A calculation model to predict the impact stress field and depth of plastic deformation zone of additive manufactured parts in the process of ultrasonic impact treatment

Considering some inherent characteristics such as obvious mechanical anisotropy and high residual stress existing in additive manufactured parts, a novel fabrication method by combining additive manufacturing (AM) and ultrasonic impact treatment (UIT) techniques was further investigated to eliminate those adverse effects of as-deposited parts. To obtain the processing parameters of the hybrid fabrication method easily and conveniently, a calculation model was presented in this paper to predict the impact stress field and depth of plastic deformation zone of additive manufactured parts in the process of UIT. Derivation process of the calculation model can be divided into two parts. Firstly, theoretical analysis was carried out based on impact dynamics and stress wave theory. The pin velocity, material response under repeated impacts, indentation model and yield criteria were discussed to obtain the calculation model. Semi-analytical method by combining analytical and numerical methods was adopted to correct the model. Secondly, specific experiments were conducted to verify the calculation model. 304 stainless steel (SS) and 316 L SS samples were prepared by laser metal deposition (LMD) and then treated by UIT. The parameters such as Poisson’s ratio, elastic modulus, density and kinematic hardening material mode were measured. Different UIT parameters were selected to further validate the applicable conditions of the model. Obvious plastic deformation in the near surface zone was observed by the EBSD data, and the depth of plastic deformation zone was quantitatively obtained by the microhardness measurement. Theoretically calculated and experimentally measured depths of the plastic deformation zone were compared, and acceptable deviations confirm the correctness of the calculation model. The calculation model can be used as a reference to determine the hybrid processing parameters of AM and UIT, such as the thickness of each deposited layer and linear energy density input in the AM process, ultrasonic frequency and amplitude in the UIT process.