Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most o...Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.展开更多
In this research, the effect of precipitation hardening on the tribological behavior of the ZK60Gd/SiC composite was studied. For this purpose, ZK60Gd alloy containing with 5 and 10 wt% SiC were produced with stir cas...In this research, the effect of precipitation hardening on the tribological behavior of the ZK60Gd/SiC composite was studied. For this purpose, ZK60Gd alloy containing with 5 and 10 wt% SiC were produced with stir casting method. The microstructure characterization of the samples showed the wide distributions of Mg_(7)Zn_(3) and Gd(Mg_(0.5)Zn_(0.5)) precipitates were formed during casting. The results of hardness measurement after precipitation hardening at different temperatures showed that the hardness peck was obtained at 175 ℃. The wear tests with different loads(10, 40, 60, 90, and 120 N) and velocities(0.1, 0.3, 0.6, and 0.9 m/s) were performed on the as-cast and heat treated sample at 125, 175, and 225 for 12 h. Between the different precipitation hardening conditions, the precipitation hardened samples at 175 ℃ had the highest hardness values and least wear rate. The sample containing 10% reinforcement had the least wear rate between the unreinforced alloy and the composites. The results showed that abrasive, adhesive, delamination, MML, and fatigue wear mechanisms were the dominant wear mechanisms for the composite samples. In contrast, the dominant wear mechanism for the unreinforced samples was abrasive, adhesive,delamination, MML, and plastic deformation.展开更多
Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microsc...Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microscopy,scanning electron microscopy,electron back scattered diffraction and transmission electron microscopy.The experimental results show that Mg-1Zn alloy exhibits conventional three-stage strain hardening curves,while Mg-1Y alloy exhibits novel six-stage strain hardening curves.For Mg-1Y alloy,rare earth texture leads to weak tensile twinning activity in compression and consequently results in a moderate evolution to<0001>texture.Moreover,inefficient tensile twinning activity and weak slip-twinning interaction give rise to excellent ductility and high hardening capacity but low strain hardening rate.For Mg-1Zn alloy,basal texture leads to pronounced tensile twinning activity in compression and consequently results in rapid evolution to<0001>texture.The intense tensile twinning activity and strong slip-twinning interaction lead to high strain hardening rate but poor ductility and low hardening capacity.展开更多
The interactions between a plate-like precipitate and two twin boundaries(TBs)({1012},{1121}) in magnesium alloys are studied using molecular dynamics(MD) simulations. The precipitate is not sheared by {1012} TB, but ...The interactions between a plate-like precipitate and two twin boundaries(TBs)({1012},{1121}) in magnesium alloys are studied using molecular dynamics(MD) simulations. The precipitate is not sheared by {1012} TB, but sheared by {1121} TB. Shearing on the(110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for {1121} twinning. All the precipitates show a blocking effect on {1121} twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length(in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the {1012} twinning(non-sheared precipitate), {1121} twinning(sheared precipitate) and basal dislocations(non-sheared precipitate) are compared together. Results show that the blocking effect on {1121} twinning is stronger than that on {1012} twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.展开更多
In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy...In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200℃, 250℃ and 300℃ are β’’(DO19) → β’(BCO) → β(FCC), β’’(DO19) → β’(BCO) → β_(1)(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200℃, 250℃ and 300℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200℃ and 250℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β’’ to β’ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β’ precipitate, the hardness of the alloy aged at 200℃ is higher than that aged at 250℃. For the alloy aged at 300℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.展开更多
The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 direct...The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress(CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening.Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.展开更多
In recent years, the place occupied by the various manifestations of cyber-crime in companies has been considerable. Indeed, due to the rapid evolution of telecommunications technologies, companies, regardless of thei...In recent years, the place occupied by the various manifestations of cyber-crime in companies has been considerable. Indeed, due to the rapid evolution of telecommunications technologies, companies, regardless of their size or sector of activity, are now the target of advanced persistent threats. The Work 2035 study also revealed that cyber crimes (such as critical infrastructure hacks) and massive data breaches are major sources of concern. Thus, it is important for organizations to guarantee a minimum level of security to avoid potential attacks that can cause paralysis of systems, loss of sensitive data, exposure to blackmail, damage to reputation or even a commercial harm. To do this, among other means, hardening is used, the main objective of which is to reduce the attack surface within a company. The execution of the hardening configurations as well as the verification of these are carried out on the servers and network equipment with the aim of reducing the number of openings present by keeping only those which are necessary for proper operation. However, nowadays, in many companies, these tasks are done manually. As a result, the execution and verification of hardening configurations are very often subject to potential errors but also highly consuming human and financial resources. The problem is that it is essential for operators to maintain an optimal level of security while minimizing costs, hence the interest in automating hardening processes and verifying the hardening of servers and network equipment. It is in this logic that we propose within the framework of this work the reinforcement of the security of the information systems (IS) by the automation of the mechanisms of hardening. In our work, we have, on the one hand, set up a hardening procedure in accordance with international security standards for servers, routers and switches and, on the other hand, designed and produced a functional application which makes it possible to: 1) Realise the configuration of the hardening;2) Verify them;3) Correct the non conformities;4) Write and send by mail a verification report for the configurations;5) And finally update the procedures of hardening. Our web application thus created allows in less than fifteen (15) minutes actions that previously took at least five (5) hours of time. This allows supervised network operators to save time and money, but also to improve their security standards in line with international standards.展开更多
To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed u...To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy.展开更多
By defining the yield stress in a latent hardening test as the first deviation from the elas-tic straight line,the yielding and hardening behavior on a latent system in the positive and negative slipdirection was stud...By defining the yield stress in a latent hardening test as the first deviation from the elas-tic straight line,the yielding and hardening behavior on a latent system in the positive and negative slipdirection was studied in aluminium single crystals.It is shown that the yield stresses on both the posi-tive and negative latent systems are about equal to or a little lower than the maximum resolved shearstress in the primary test,but much higher than that of the active system.The influence of relativeorientation and prestrain on latent hardening and initial work-hardening in the secondary test was alsoinvestigated,and it was found that there is a considerable effect on initial work-hardening,but noneon latent hardening.With reasonable approximation,a hardening rule for single crystal could be pro-posed from the experimental results,that is,except for the yield stress on the system negative to theactive system that is very low,hardening on the other systems is nearly the same as self-hardening.展开更多
Locking nuts are widely used in industry and any defects from their manufacturing may cause loosening of the connection during their service life.In this study,simulations of the folding process of a nut’s flange mad...Locking nuts are widely used in industry and any defects from their manufacturing may cause loosening of the connection during their service life.In this study,simulations of the folding process of a nut’s flange made from AISI 1040 steel are performed.Besides the bilinear isotropic hardening rule,Chaboche’s nonlinear kinematic hardening rule is employed with associated flow rule and Hill48 yield criterion to set a plasticity model.The bilinear isotropic hardening rule’s parameters are determined by means of a monotonic tensile test.The Chaboche’s parameters are determined by using a low cycle tension/compression test by applying curve fitting methods on the low cycle fatigue loop.Furthermore,the parameter calibrations are performed in the finite element simulations by using an optimization approach based on the inverse analysis.Dimensional accuracy for the nut is of primary concern due to the tolerance constraints of the nut manufacturers.Experimental diameter and height measurements of the folded locking nut are compared with those obtained from the optimized model.The results reveal that the folding dimensions can be predicted more accurately when the model parameters are determined by using the combined hardening rule.The calibrated parameters are presented for the folding and cycling deformation processes.展开更多
The survival ability of insects can be limited with the changes in the levels of energy metabolites under stressful conditions but only a few studies have considered the plastic effects of heat and related climatic fa...The survival ability of insects can be limited with the changes in the levels of energy metabolites under stressful conditions but only a few studies have considered the plastic effects of heat and related climatic factors relevant to tropical habitats. The objectives of our study were to determine whether adults of <i><span style="font-family:Verdana;">Zaprionus</span></i> <i><span style="font-family:Verdana;">indianus</span></i><span style="font-family:Verdana;"> are capable of rapid heat hardening (RHH) and rapid desiccation hardening (RDH) and to compare its benefits with heat acclimation (HA) and desiccation acclimation (DA). Adult flies reared under season-specific simulated conditions were subjected to 38<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C for RHH and 32<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C for HA, while 5% relative humidity (RH) was maintained for RDH and 40% RH for DA. Stress-induced effects of heat and desiccation on the levels of five metabolites namely cuticular lipids (CL), total body lipids (TBL), protein, proline, and carbohydrates were then estimated by biochemical method. Different duration of heat hardening and acclimation led to more accumulation of CL whereas different durations of desiccation hardening and acclimation revealed less accumulation. In contrast, there was an accumulation of carbohydrates and protein under desiccation hardening and acclimation whereas there was the utilization of carbohydrates and protein under heat hardening and acclimation. However, mixed results were observed on the level of proline and TBL under both heat and desiccation stress. These stress-triggered changes in the levels of various metabolites suggest a possible link between heat and desiccation tolerance. Hence, these compensatory changes in the level of various metabolites also suggest possible energetic homeostasis in </span><i><span style="font-family:Verdana;">Z.</span></i> <i><span style="font-family:Verdana;">indianus</span></i><span style="font-family:Verdana;"> living under harsh climatic conditions of heat and drought in tropical regions.</span>展开更多
The microstructural changes in the machined surface layer of Ni-based super alloys essentially determine the final performance of the structural components of aerospace engines in which these alloys are used.In this w...The microstructural changes in the machined surface layer of Ni-based super alloys essentially determine the final performance of the structural components of aerospace engines in which these alloys are used.In this work,multiscale metallurgical observations using scanning electron microscopy,electron-backscatter diffraction microscopy,and transmission electron microscopy were conducted to quantitatively characterize the microstructure of the machined subsurface.Next,to elucidate the factors that affect the formation of the refinement microstructure,the distributions of the deformation parameters(strain,strain rate,and temperature) in the machined subsurface were analyzed.A dislocation–twin interaction dynamic recrystallization mechanism for grain refinement during machining of Inconel 718 is proposed.Furthermore,microhardness evolution induced by grain refinement in the machined surface is evaluated.The results suggest that the gradient microstructure and the work hardening can be optimized by controlling the cutting parameters during turning of Inconel 718.展开更多
The effects of microstructure and its evolution on the macroscopicsuperelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)arestudied by a microstructure-based constitutive model developed in this...The effects of microstructure and its evolution on the macroscopicsuperelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)arestudied by a microstructure-based constitutive model developed in this paper.Themodel is established on the following basis:(1)the transformation conditions of theunconstrained single crystal SMA microdomain(to be distinguished from the bulksingle crystal),which serve as the local criterion for the derivation of overall transfor-mation yield conditions of the polycrystal;(2)the micro-to macro-transition schemeby which the connection between the polycrystal aggregates and the single crystalmicrodomain is established and the macroscopic transformation conditions of thepolycrystal SMA are derived;(3)the quantitative incorporation of three microstruc-ture factors(i.e.,nucleation,growth and orientation distribution of martensite)intothe modeling.These microstructural factors are intrinsic of specific polycrystal SMAsystems and the role of each factor in the macroscopic constitutive response is quan-titatively modeled.It is demonstrated that the interplay of these factors will resultin different macroscopic transformation kinematics and kinetics which are responsiblefor the observed macroscopic stress-strain hardening or softening response,the latterwill lead to the localization and propagation of transformation bands in TiNi SMA.展开更多
A theoretical rigid-plastic analysis for the dynamic shear failure ofbeams under impulsive loading is presented when using a travelling plastic shear hingemodel which takes into account material strain hardening.The m...A theoretical rigid-plastic analysis for the dynamic shear failure ofbeams under impulsive loading is presented when using a travelling plastic shear hingemodel which takes into account material strain hardening.The maximum dynamicshear strain and shear strain-rate can be predicted in addition to the permanenttransverse deflections and other parameters.The conditions for the three modesof shear failure,i.e.,excess deflection failure,excess shear strain failure and adia-batic shear failure are analyzed.The special case of an infinitesimally small plasticzone is discussed and compared with Nonaka’s solution for a rigid,perfectly plasticmaterial.The results can also be generalized to examine the dynamic response offibre-reinforced beams.展开更多
A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the late...A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the latent heat of phase transformation and the temperature dependence of thermal properties of materials were considered. The heat source was considered as a moving Gaussian heat flux with a constant velocity. Three-dimension unequally spatial grid explicit finite difference equations, alternating direction implicit finite difference equations and implicit finite difference equations were deduced respectively. Three programs to calculate the temperature field were developed using Fortran language. The transient temperature fields of C22, 42CrMo, C60 steel samples during laser transformation hardening process were calculated using these programs, and the widths and depths of laser transformation hardening zones were also predicted. C22, 42CrMo, C60 steel samples were treated by CO2 laser,the widths and depths of laser transformation hardening zones of these samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.展开更多
Precipitation of Ni2Al in supersaturated NiAl containing Ta and corresponding hardening have been investigated by hardness measurements and by transmission electron microscope observations. Selected area electron diff...Precipitation of Ni2Al in supersaturated NiAl containing Ta and corresponding hardening have been investigated by hardness measurements and by transmission electron microscope observations. Selected area electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectrometer analysis have shown that the Ni2Al with a hexagonal structure precipitates coherently in the B2-NiAl matrix. Ni2Al is an ordered phase with a. unit cell parameter, aNi2All=aNiAl and CNi2Al= aNiAl. The orientation relationship between the Ni2Al precipitate and the B2-NiAl matrix is (0001)Ni2Al (111)NiAl and [1120]Ni2Al[110]NiAl. NiAlhardens appreciably by the precipitation of Ni2Al phase.展开更多
The strain hardening is an effective mode of enhancing mechanical properties in alloys.In this work,the strain hardening behaviors of Mg-xY(x=1,2,and 3 wt%)after extrusion process was investigated using uniaxial tensi...The strain hardening is an effective mode of enhancing mechanical properties in alloys.In this work,the strain hardening behaviors of Mg-xY(x=1,2,and 3 wt%)after extrusion process was investigated using uniaxial tensile tests.Results suggest that the Mg-xY alloys are composed ofα-Mg with a little amount of Mg24Y5 phase.The average grain size reduces from 19.8μm to 12.2μm as the Y content adds from 1 wt%to 2 wt%.Nevertheless,when Y content reaches 3 wt%,the grain size reaches to 12.9μm,which is close to that of Mg-2Y.The strain hardening rate decreases from 883 MPa to 798 MPa at(σ-σ0.2)=40 MPa,and Mg-2Y and Mg-3Y have the similar strain hardening response.Moreover,Mg-1Y shows an obvious ascending stage after the steep decreasing stage,which is mainly caused by the activation of twinning.The strain hardening behavior of Mg-xY is explained based on understanding the roles of the deformation mechanisms via deformation microstructure analysis and Visco-Plastic Self Consistent(VPSC)model.The variation of strain hardening characteristics with increasing Y content is related to the effects of grain size and texture.展开更多
Fariabh strain rate tension tests for 4 metallic materials show that as the strain rate in creases the strain hardening exponent n decreases.The trend follows a two stage linear relation between n and lg（?）.When （...Fariabh strain rate tension tests for 4 metallic materials show that as the strain rate in creases the strain hardening exponent n decreases.The trend follows a two stage linear relation between n and lg（?）.When （?）【（?）<sub>ep’</sub>i.e.under quasi-statie loading,n can be consideredas a constant,but when（?）】（?）<sub>ep’</sub>,n decreases rapidlv till an ideal plastic state,n=0.Thecharacteri=ations and mechanisms of so fiening induced by high （?）are discussed.展开更多
Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and...Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.展开更多
A Two-dimensional transient heat transfer model for laser transformation hardening process of cylindrical bodies has been developed. The surface heat loss of the sample, the latent heat of phase transformation, and th...A Two-dimensional transient heat transfer model for laser transformation hardening process of cylindrical bodies has been developed. The surface heat loss of the sample, the latent heat of phase transformation, and the temperature dependence of thermal properties of material were considered. The laser heat source was considered as a moving Gaussian heat flux with a constant velocity. Finite element method was used to calculate the transient temperature field. A program to calculate the temperature field was developed using FORTRAN language. The transient temperature field, the width and depth of laser transformation hardening zone of 42CrMo steel sample during laser transformation hardening process was calculated. The widths and depths of laser transformation hardening zones of 42CrMo steel samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.展开更多
基金funding support from the Israeli Ministry of Housing and Construction(Grant No.2028286).
文摘Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.
文摘In this research, the effect of precipitation hardening on the tribological behavior of the ZK60Gd/SiC composite was studied. For this purpose, ZK60Gd alloy containing with 5 and 10 wt% SiC were produced with stir casting method. The microstructure characterization of the samples showed the wide distributions of Mg_(7)Zn_(3) and Gd(Mg_(0.5)Zn_(0.5)) precipitates were formed during casting. The results of hardness measurement after precipitation hardening at different temperatures showed that the hardness peck was obtained at 175 ℃. The wear tests with different loads(10, 40, 60, 90, and 120 N) and velocities(0.1, 0.3, 0.6, and 0.9 m/s) were performed on the as-cast and heat treated sample at 125, 175, and 225 for 12 h. Between the different precipitation hardening conditions, the precipitation hardened samples at 175 ℃ had the highest hardness values and least wear rate. The sample containing 10% reinforcement had the least wear rate between the unreinforced alloy and the composites. The results showed that abrasive, adhesive, delamination, MML, and fatigue wear mechanisms were the dominant wear mechanisms for the composite samples. In contrast, the dominant wear mechanism for the unreinforced samples was abrasive, adhesive,delamination, MML, and plastic deformation.
基金Funded by the Beijing Municipal Natural Science Foundation (No.2202004)the National Natural Science Foundation of China (No.51801048)the Basic Research Fund for Newly Enrolled Teachers and the Fund for Distinguished Young Scholars of China Academy of Space Technology。
文摘Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microscopy,scanning electron microscopy,electron back scattered diffraction and transmission electron microscopy.The experimental results show that Mg-1Zn alloy exhibits conventional three-stage strain hardening curves,while Mg-1Y alloy exhibits novel six-stage strain hardening curves.For Mg-1Y alloy,rare earth texture leads to weak tensile twinning activity in compression and consequently results in a moderate evolution to<0001>texture.Moreover,inefficient tensile twinning activity and weak slip-twinning interaction give rise to excellent ductility and high hardening capacity but low strain hardening rate.For Mg-1Zn alloy,basal texture leads to pronounced tensile twinning activity in compression and consequently results in rapid evolution to<0001>texture.The intense tensile twinning activity and strong slip-twinning interaction lead to high strain hardening rate but poor ductility and low hardening capacity.
基金financial support from National Natural Science Foundation of China (12072211)Sichuan Province Science and Technology Project (2020JDJQ0029)。
文摘The interactions between a plate-like precipitate and two twin boundaries(TBs)({1012},{1121}) in magnesium alloys are studied using molecular dynamics(MD) simulations. The precipitate is not sheared by {1012} TB, but sheared by {1121} TB. Shearing on the(110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for {1121} twinning. All the precipitates show a blocking effect on {1121} twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length(in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the {1012} twinning(non-sheared precipitate), {1121} twinning(sheared precipitate) and basal dislocations(non-sheared precipitate) are compared together. Results show that the blocking effect on {1121} twinning is stronger than that on {1012} twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.
基金financially supported by the Key R&D program of Shanxi Province (International Cooperation) (No.201903D421036)the Natural Science Foundation of Shanxi Province (No.201901D111176)+5 种基金the Joint Funds of the National Natural Science Foundation of China (Grant No.U20A20230)the Bureau of Science,Technology and Industry for National Defense of China (No.WDZC2019JJ006)the National Natural Science Foundation of China (Grant No.52075501)Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (No.201802072)the National Defense Basic Scientific Research Program (No.JCKY2018408B003)the XX Supporting Scientific Research Project (No.xxxx-2019-021)。
文摘In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200℃, 250℃ and 300℃ are β’’(DO19) → β’(BCO) → β(FCC), β’’(DO19) → β’(BCO) → β_(1)(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200℃, 250℃ and 300℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200℃ and 250℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β’’ to β’ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β’ precipitate, the hardness of the alloy aged at 200℃ is higher than that aged at 250℃. For the alloy aged at 300℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.
基金National Natural Science Foundation of China (51871032, 52071039 and 51671040)the 111 Project (B16007) of the Ministry of Education。
文摘The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress(CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening.Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.
文摘In recent years, the place occupied by the various manifestations of cyber-crime in companies has been considerable. Indeed, due to the rapid evolution of telecommunications technologies, companies, regardless of their size or sector of activity, are now the target of advanced persistent threats. The Work 2035 study also revealed that cyber crimes (such as critical infrastructure hacks) and massive data breaches are major sources of concern. Thus, it is important for organizations to guarantee a minimum level of security to avoid potential attacks that can cause paralysis of systems, loss of sensitive data, exposure to blackmail, damage to reputation or even a commercial harm. To do this, among other means, hardening is used, the main objective of which is to reduce the attack surface within a company. The execution of the hardening configurations as well as the verification of these are carried out on the servers and network equipment with the aim of reducing the number of openings present by keeping only those which are necessary for proper operation. However, nowadays, in many companies, these tasks are done manually. As a result, the execution and verification of hardening configurations are very often subject to potential errors but also highly consuming human and financial resources. The problem is that it is essential for operators to maintain an optimal level of security while minimizing costs, hence the interest in automating hardening processes and verifying the hardening of servers and network equipment. It is in this logic that we propose within the framework of this work the reinforcement of the security of the information systems (IS) by the automation of the mechanisms of hardening. In our work, we have, on the one hand, set up a hardening procedure in accordance with international security standards for servers, routers and switches and, on the other hand, designed and produced a functional application which makes it possible to: 1) Realise the configuration of the hardening;2) Verify them;3) Correct the non conformities;4) Write and send by mail a verification report for the configurations;5) And finally update the procedures of hardening. Our web application thus created allows in less than fifteen (15) minutes actions that previously took at least five (5) hours of time. This allows supervised network operators to save time and money, but also to improve their security standards in line with international standards.
基金supported by the Special Foundation for Introducing and Selecting Talent in Hefei University of Technology, China (No. 2004000197)
文摘To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy.
文摘By defining the yield stress in a latent hardening test as the first deviation from the elas-tic straight line,the yielding and hardening behavior on a latent system in the positive and negative slipdirection was studied in aluminium single crystals.It is shown that the yield stresses on both the posi-tive and negative latent systems are about equal to or a little lower than the maximum resolved shearstress in the primary test,but much higher than that of the active system.The influence of relativeorientation and prestrain on latent hardening and initial work-hardening in the secondary test was alsoinvestigated,and it was found that there is a considerable effect on initial work-hardening,but noneon latent hardening.With reasonable approximation,a hardening rule for single crystal could be pro-posed from the experimental results,that is,except for the yield stress on the system negative to theactive system that is very low,hardening on the other systems is nearly the same as self-hardening.
文摘Locking nuts are widely used in industry and any defects from their manufacturing may cause loosening of the connection during their service life.In this study,simulations of the folding process of a nut’s flange made from AISI 1040 steel are performed.Besides the bilinear isotropic hardening rule,Chaboche’s nonlinear kinematic hardening rule is employed with associated flow rule and Hill48 yield criterion to set a plasticity model.The bilinear isotropic hardening rule’s parameters are determined by means of a monotonic tensile test.The Chaboche’s parameters are determined by using a low cycle tension/compression test by applying curve fitting methods on the low cycle fatigue loop.Furthermore,the parameter calibrations are performed in the finite element simulations by using an optimization approach based on the inverse analysis.Dimensional accuracy for the nut is of primary concern due to the tolerance constraints of the nut manufacturers.Experimental diameter and height measurements of the folded locking nut are compared with those obtained from the optimized model.The results reveal that the folding dimensions can be predicted more accurately when the model parameters are determined by using the combined hardening rule.The calibrated parameters are presented for the folding and cycling deformation processes.
文摘The survival ability of insects can be limited with the changes in the levels of energy metabolites under stressful conditions but only a few studies have considered the plastic effects of heat and related climatic factors relevant to tropical habitats. The objectives of our study were to determine whether adults of <i><span style="font-family:Verdana;">Zaprionus</span></i> <i><span style="font-family:Verdana;">indianus</span></i><span style="font-family:Verdana;"> are capable of rapid heat hardening (RHH) and rapid desiccation hardening (RDH) and to compare its benefits with heat acclimation (HA) and desiccation acclimation (DA). Adult flies reared under season-specific simulated conditions were subjected to 38<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C for RHH and 32<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C for HA, while 5% relative humidity (RH) was maintained for RDH and 40% RH for DA. Stress-induced effects of heat and desiccation on the levels of five metabolites namely cuticular lipids (CL), total body lipids (TBL), protein, proline, and carbohydrates were then estimated by biochemical method. Different duration of heat hardening and acclimation led to more accumulation of CL whereas different durations of desiccation hardening and acclimation revealed less accumulation. In contrast, there was an accumulation of carbohydrates and protein under desiccation hardening and acclimation whereas there was the utilization of carbohydrates and protein under heat hardening and acclimation. However, mixed results were observed on the level of proline and TBL under both heat and desiccation stress. These stress-triggered changes in the levels of various metabolites suggest a possible link between heat and desiccation tolerance. Hence, these compensatory changes in the level of various metabolites also suggest possible energetic homeostasis in </span><i><span style="font-family:Verdana;">Z.</span></i> <i><span style="font-family:Verdana;">indianus</span></i><span style="font-family:Verdana;"> living under harsh climatic conditions of heat and drought in tropical regions.</span>
基金financial support from the National Natural Science Foundation of China (No.51425503)the Major Science and Technology Program of High-end CNC Machine Tools and Basic Manufacturing Equipment of China (No.2014ZX04012014)supported by a grant from the Taishan Scholar Foundation of Shandong province (No.TS20130922)
文摘The microstructural changes in the machined surface layer of Ni-based super alloys essentially determine the final performance of the structural components of aerospace engines in which these alloys are used.In this work,multiscale metallurgical observations using scanning electron microscopy,electron-backscatter diffraction microscopy,and transmission electron microscopy were conducted to quantitatively characterize the microstructure of the machined subsurface.Next,to elucidate the factors that affect the formation of the refinement microstructure,the distributions of the deformation parameters(strain,strain rate,and temperature) in the machined subsurface were analyzed.A dislocation–twin interaction dynamic recrystallization mechanism for grain refinement during machining of Inconel 718 is proposed.Furthermore,microhardness evolution induced by grain refinement in the machined surface is evaluated.The results suggest that the gradient microstructure and the work hardening can be optimized by controlling the cutting parameters during turning of Inconel 718.
基金The project supported by the Research Grant Committee(RGC)of Hong Kong SARthe National Natural Science Foundation of China and the Provincial Natural Foundation of Jiangxi Province of China
文摘The effects of microstructure and its evolution on the macroscopicsuperelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)arestudied by a microstructure-based constitutive model developed in this paper.Themodel is established on the following basis:(1)the transformation conditions of theunconstrained single crystal SMA microdomain(to be distinguished from the bulksingle crystal),which serve as the local criterion for the derivation of overall transfor-mation yield conditions of the polycrystal;(2)the micro-to macro-transition schemeby which the connection between the polycrystal aggregates and the single crystalmicrodomain is established and the macroscopic transformation conditions of thepolycrystal SMA are derived;(3)the quantitative incorporation of three microstruc-ture factors(i.e.,nucleation,growth and orientation distribution of martensite)intothe modeling.These microstructural factors are intrinsic of specific polycrystal SMAsystems and the role of each factor in the macroscopic constitutive response is quan-titatively modeled.It is demonstrated that the interplay of these factors will resultin different macroscopic transformation kinematics and kinetics which are responsiblefor the observed macroscopic stress-strain hardening or softening response,the latterwill lead to the localization and propagation of transformation bands in TiNi SMA.
文摘A theoretical rigid-plastic analysis for the dynamic shear failure ofbeams under impulsive loading is presented when using a travelling plastic shear hingemodel which takes into account material strain hardening.The maximum dynamicshear strain and shear strain-rate can be predicted in addition to the permanenttransverse deflections and other parameters.The conditions for the three modesof shear failure,i.e.,excess deflection failure,excess shear strain failure and adia-batic shear failure are analyzed.The special case of an infinitesimally small plasticzone is discussed and compared with Nonaka’s solution for a rigid,perfectly plasticmaterial.The results can also be generalized to examine the dynamic response offibre-reinforced beams.
文摘A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the latent heat of phase transformation and the temperature dependence of thermal properties of materials were considered. The heat source was considered as a moving Gaussian heat flux with a constant velocity. Three-dimension unequally spatial grid explicit finite difference equations, alternating direction implicit finite difference equations and implicit finite difference equations were deduced respectively. Three programs to calculate the temperature field were developed using Fortran language. The transient temperature fields of C22, 42CrMo, C60 steel samples during laser transformation hardening process were calculated using these programs, and the widths and depths of laser transformation hardening zones were also predicted. C22, 42CrMo, C60 steel samples were treated by CO2 laser,the widths and depths of laser transformation hardening zones of these samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.
文摘Precipitation of Ni2Al in supersaturated NiAl containing Ta and corresponding hardening have been investigated by hardness measurements and by transmission electron microscope observations. Selected area electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectrometer analysis have shown that the Ni2Al with a hexagonal structure precipitates coherently in the B2-NiAl matrix. Ni2Al is an ordered phase with a. unit cell parameter, aNi2All=aNiAl and CNi2Al= aNiAl. The orientation relationship between the Ni2Al precipitate and the B2-NiAl matrix is (0001)Ni2Al (111)NiAl and [1120]Ni2Al[110]NiAl. NiAlhardens appreciably by the precipitation of Ni2Al phase.
基金The authors thank the National Key R&D Program of China(2016YFB0301100)National Natural Science Foundation of China(51571043)+1 种基金Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYB18004)Fundamental Research Funds for the Central Universities(Nos.2018CDJDCL0019,cqu2018CDHB1A08 and 2018CDGFCL0005).
文摘The strain hardening is an effective mode of enhancing mechanical properties in alloys.In this work,the strain hardening behaviors of Mg-xY(x=1,2,and 3 wt%)after extrusion process was investigated using uniaxial tensile tests.Results suggest that the Mg-xY alloys are composed ofα-Mg with a little amount of Mg24Y5 phase.The average grain size reduces from 19.8μm to 12.2μm as the Y content adds from 1 wt%to 2 wt%.Nevertheless,when Y content reaches 3 wt%,the grain size reaches to 12.9μm,which is close to that of Mg-2Y.The strain hardening rate decreases from 883 MPa to 798 MPa at(σ-σ0.2)=40 MPa,and Mg-2Y and Mg-3Y have the similar strain hardening response.Moreover,Mg-1Y shows an obvious ascending stage after the steep decreasing stage,which is mainly caused by the activation of twinning.The strain hardening behavior of Mg-xY is explained based on understanding the roles of the deformation mechanisms via deformation microstructure analysis and Visco-Plastic Self Consistent(VPSC)model.The variation of strain hardening characteristics with increasing Y content is related to the effects of grain size and texture.
文摘Fariabh strain rate tension tests for 4 metallic materials show that as the strain rate in creases the strain hardening exponent n decreases.The trend follows a two stage linear relation between n and lg（?）.When （?）【（?）<sub>ep’</sub>i.e.under quasi-statie loading,n can be consideredas a constant,but when（?）】（?）<sub>ep’</sub>,n decreases rapidlv till an ideal plastic state,n=0.Thecharacteri=ations and mechanisms of so fiening induced by high （?）are discussed.
基金Project(U1460101)supported by the National Natural Science Foundation of ChinaProject(20120006120002)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.
文摘A Two-dimensional transient heat transfer model for laser transformation hardening process of cylindrical bodies has been developed. The surface heat loss of the sample, the latent heat of phase transformation, and the temperature dependence of thermal properties of material were considered. The laser heat source was considered as a moving Gaussian heat flux with a constant velocity. Finite element method was used to calculate the transient temperature field. A program to calculate the temperature field was developed using FORTRAN language. The transient temperature field, the width and depth of laser transformation hardening zone of 42CrMo steel sample during laser transformation hardening process was calculated. The widths and depths of laser transformation hardening zones of 42CrMo steel samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.
