Plastic deformation behavior of a Cu-10Ta alloy under strong impact loading

In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volume specific heat,are tested.Via the split Hopkinson pressure bar(SHPB)and flyerplate impact experiments,the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298-823 K and under strain rates of 1×10^(-3)-5.2×10^(3)s^(-1),and the Hugoniot relationship at impact pressures of 1.46-17.25 GPa and impact velocities of 108-942 m/s is obtained.Evolution of the Cu-10Ta microstructure that occurs during high-strain-rate impact is analyzed.Results indicate that the Cu-10Ta alloy possesses good thermal stability,and at ambient temperatures of up to 50%its melting point,stress softening of less than 15%of the initial strength is observed.A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate.Under strong impact,the copper phase is identified as the primary source of plastic deformation in the Cu-10Ta alloy,while significant deformation of the high-strength tantalum particles is less pronounced.Furthermore,the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact.Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.

Superplasticity of fine-grained Mg-10Li alloy prepared by severe plastic deformation and understanding its deformation mechanisms

The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαphase,were examined in a temperature range of 473 K to 623 K.The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling.The best superplasticity was achieved at 523 K and at strain rates of 10^(-4)-5×10^(-4)s^(-1),where tensile elongations of 550±600%were obtained.During the heating and holding stage of the tensile samples prior to tensile loading,a significant increase in grain size was observed at temperatures above 573 K.Therefore,it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms.In the investigated strain rate range,the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding,while at high strain rates,lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism.It was concluded that solute drag creep is unlikely to occur.During the late stages of deformation at 523 K,it was observed that grain boundary sliding led to the agglomeration of theαphase,resulting in significant strain hardening.Deformation mechanism maps were constructed forβ-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate,stress,temperature,and grain size,using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.

Study on creep deformation and energy development of underground surrounding rock under four‐dimensional support

There is an urgent need to develop optimal solutions for deformation control of deep high‐stress roadways,one of the critical problems in underground engineering.The previously proposed four‐dimensional support(hereinafter 4D support),as a new support technology,can set the roadway surrounding rock under three‐dimensional pressure in the new balanced structure,and prevent instability of surrounding rock in underground engineering.However,the influence of roadway depth and creep deformation on the surrounding rock supported by 4D support is still unknown.This study investigated the influence of roadway depth and creep deformation time on the instability of surrounding rock by analyzing the energy development.The elastic strain energy was analyzed using the program redeveloped in FLAC3D.The numerical simulation results indicate that the combined support mode of 4D roof supports and conventional side supports is highly applicable to the stability control of surrounding rock with a roadway depth exceeding 520 m.With the increase of roadway depth,4D support can effectively restrain the area and depth of plastic deformation in the surrounding rock.Further,4D support limits the accumulation range and rate of elastic strain energy as the creep deformation time increases.4D support can effectively reduce the plastic deformation of roadway surrounding rock and maintain the stability for a long deformation period of 6 months.As confirmed by in situ monitoring results,4D support is more effective for the long‐term stability control of surrounding rock than conventional support.

Electro-chemo-mechanical analysis of the effect of bending deformation on the interface of flexible solid-state battery

Flexible solid-state battery has several unique characteristics including high flexibility,easy portability,and high safety,which may have broad application prospects in new technology products such as rollup displays,power implantable medical devices,and wearable equipments.The interfacial mechanical and electrochemical problems caused by bending deformation,resulting in the battery damage and failure,are particularly interesting.Herein,a fully coupled electro-chemo-mechanical model is developed based on the actual solid-state battery structure.Concentration-dependent material parameters,stress-dependent diffusion,and potential shift are considered.According to four bending forms(k=8/mm,0/mm,-8/mm,and free),the results show that the negative curvature bending is beneficial to reducing the plastic strain during charging/discharging,while the positive curvature is detrimental.However,with respect to the electrochemical performance,the negative curvature bending creates a negative potential shift,which causes the battery to reach the cut-off voltage earlier and results in capacity loss.These results enlighten us that suitable electrode materials and charging strategy can be tailored to reduce plastic deformation and improve battery capacity for different forms of battery bending.

Revealing the grain size dependent hot workability and deformation mechanisms in a Mg-Zn-Y alloy

Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.

Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy

In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.

Revealing the role of pyramidal slip in the high ductility of Mg-Li alloy

The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal<c+a>slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.%Li plate,with a relative activity of approximately 18%.Although the limited activity of pyramidal<c+a>slip alone cannot accommodate a large plastic strain,it effectively reduces the number of{10.11}−{10.12}double twins,which are believed to be favorable sites for crack initiation.The evidently reduced activity of double twins leads to a lower cracking tendency,and therefore improves ductility.

Temperature effect on nanotwinned Ni under nanoindentation using molecular dynamic simulation

Temperature effect on atomic deformation of nanotwinned Ni (nt-Ni) under localized nanoindentation is investigated in comparison with nanocrystalline Ni (nc-Ni) through molecular simulation.The nt-Ni exhibits enhanced critical load and hardness compared to nc-Ni,where perfect,stair-rod and Shockley dislocations are activated at (111),(111) and (111) slip planes in nt-Ni compared to only SSockley dislocation nucleation at (111) and (111) slip planes of nc-Ni.The nt-Ni exhibits a less significant indentation size effect in comparison with nc-Ni due to the dislocation slips hindrance of the twin boundary.The atomic deformation associated with the indentation size effect is investigated during dislocation transmission.Different from the decreasing partial slips parallel to the indenter surface in nc-Ni with increasing temperature,the temperaturedependent atomic deformation of nt-Ni is closely related to the twin boundary:from the partial slips parallel to the twin boundary (~10 K),to increased confined layer slips and decreased twin migration(300 K–600 K),to decreased confined layer slips and increased dislocation interaction of dislocation pinning and dissociation (900 K–1200 K).Dislocation density and atomic structure types through quantitative analysis are implemented to further reveal the above-mentioned dislocation motion and atomic structure alteration.Our study is helpful for understanding the temperature-dependent plasticity of twin boundary in nanotwinned materials.

An Elastoplastic Fracture Model Based on Bond-Based Peridynamics

Fracture in ductile materials often occurs in conjunction with plastic deformation.However,in the bond-based peridynamic(BB-PD)theory,the classic mechanical stress is not defined inherently.This makes it difficult to describe plasticity directly using the classical plastic theory.To address the above issue,a unified bond-based peridynamics model was proposed as an effective tool to solve elastoplastic fracture problems.Compared to the existing models,the proposed model directly describes the elastoplastic theory at the bond level without the need for additional calculation means.The results obtained in the context of this model are shown to be consistent with FEM results in regard to force-displacement curves,displacement fields,stress fields,and plastic deformation regions.The model exhibits good capability of capturing crack propagation in ductile material failure problems.

Effects of ultrasonic vibration on plastic deformation of AZ31 during the tensile process

An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration（with a frequency of 15 kHz and a maximum output of 2 kW） during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects：the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.

Severe plastic deformation (SPD) of biodegradable magnesium alloys and composites: A review of developments and prospects

The use of magnesium in orthopedic and cardiovascular applications has been widely attracted by diminishing the risk of abnormal interaction of the implant with the body tissue and eliminating the second surgery to remove it from the body.Nevertheless,the fast degradation rate and generally inhomogeneous corrosion subsequently caused a decline in the mechanical strength of Mg during the healing period.Numerous researches have been conducted on the influences of various severe plastic deformation(SPD)processes on magnesium bioalloys and biocomposites.This paper strives to summarize the various SPD techniques used to achieve magnesium with an ultrafine-grained(UFG)structure.Moreover,the effects of various severe plastic deformation methods on magnesium microstructure,mechanical properties,and corrosion behavior have been discussed.Overall,this review intends to clarify the different potentials of applying SPD processes to the magnesium alloys and composites to augment their usage in biomedical applications.

Experimental and numerical studies of nonlinear ultrasonic responses on plastic deformation in weld joints

The experimental measurements and numerical simulations are performed to study ultrasonic nonlinear responses from the plastic deformation in weld joints. The ultrasonic nonlinear signals are measured in the plastic deformed30Cr2Ni4 Mo V specimens, and the results show that the nonlinear parameter monotonically increases with the plastic strain, and that the variation of nonlinear parameter in the weld region is maximal compared with those in the heat-affected zone and base regions. Microscopic images relating to the microstructure evolution of the weld region are studied to reveal that the change of nonlinear parameter is mainly attributed to dislocation evolutions in the process of plastic deformation loading. Meanwhile, the finite element model is developed to investigate nonlinear behaviors of ultrasonic waves propagating in a plastic deformed material based on the nonlinear stress–strain constitutive relationship in a medium. Moreover, a pinned string model is adopted to simulate dislocation evolution during plastic damages. The simulation and experimental results show that they are in good consistency with each other, and reveal a rising acoustic nonlinearity due to the variations of dislocation length and density and the resulting stress concentration.

Acoustic emission study of the plastic deformation of quenched and partitioned 35CrMnSiA steel

Acoustic emission （AE） monitored tensile tests were performed on 35CrMnSiA steel subjected to different heat treatments. The results showed that quenching and partitioning （Q-P） heat treatments enhanced the combined mechanical properties of high strength and high ductility for commercial 35CrMnSiA steel, as compared with traditional heat treatments such as quenching and tempering （Q-T） and austempering （AT）. AE signals with high amplitude and high energy were produced during the tensile deformation of 35CrMnSiA steel with retained austenite （RA） in the microstructure （obtained via Q-P and AT heat treatments） due to an austenite-to-martensite phase transformation. Moreover, additional AE signals would not appear again and the mechanical properties would degenerate to a lower level once RA degenerated by tempering for the Q-P treated steel.

EFFECT OF UNEQUAL DEFORMATION IN DEVELOPMENT OF ADVANCED PLASTIC PROCESSING TECHNOLOGIES

An effect of unequal deformation in development of advanced plasticprocessing technologies is researched by studying an in-plane bending process of strip metal underunequal compressing. The research results show the following: If appropriately controlled, unequalplastic deformation can play an important role not only in the improvement of quality of partsobtained by plastic processing technologies, but also in the development of new processes foradvanced plastic working technologies. A coordinated growth of unequal plastic deformation candevelop the deformation potentiality of material to the fall. The degree of unequal plasticdeformation can be used as bases for optimization design of processes and dies of plastic forming.

Influence of Transverse Normal Pressure on Deformation Behavior of Sheet Metal

To investigate the influence of magnitude and distribution of the transverse normal pressure on deformation behavior of sheet metal,viscous pressure bulge test (VPB) of overlapping sheet metals is proposed,where the overlapped sheet metal is deformed under the dual-sided normal pressure provided by viscous medium and the overlapping sheet.The transverse normal pressure loading features provided by overlapping sheet metals are first simulated by DEFORM-2D.It shows that the magnitude and space distribution of transverse normal pressure are dependent on strain hardening exponent n-,strength coefficient K-and thickness t-values of the overlapping sheet metal.Based on the stress,deviator stress and strain distribution resulted from the finite element simulation,it indicated that the uniform transverse normal pressure has no effect on deviator stress,the figure and strain distribution of bulge specimens have no change.The non-uniform transverse normal pressure can remarkably change the figure and metal flow of specimens,and the formability of sheet metal can be improved by controlling the transverse normal pressure distribution.

A Model of Dynamic Recrystallization in Alloys during High Strain Plastic Deformation

Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization

Plastic Deformation Mechanism in Double-Roller Clamping Spinning of Flanged Thin-Walled Cylinder

Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.

Research on deformation mechanism of AZ31 magnesium alloy sheet with non-basal texture during uniaxial tension at room temperature:A visco-plastic self-consistent analysis

The relationship between activities of involved deformation mechanisms and the evolution of microstructure and texture during uniaxial tension of AZ31 magnesium alloy with a rare non-basal texture has been thoroughly investigated in the present study by means of electron backscattered diffraction(EBSD) measurement and visco-plastic self-consistent(VPSC) modeling. These results show that except basal slip and prismatic slip, {10■2} extension twin(ET) also plays a significant role during plastic deformation. With the increasing tilted angle between loading direction and rolling direction(RD) of sheet, the activity of {10■2} ET possesses a decreasing tendency and its role in plastic deformation changes from the one mainly sustaining plastic strain to the one mainly accommodating local strain between individual grains. When {10■2} ET serves as a carrier of plastic strain, it mainly results in the formation of basal texture component(c-axis//ND, normal direction). By comparison, when the role of {10■2} ET is to accommodate local strain, it mainly brings about the formation of prismatic texture component(c-axis//TD, transverse direction). At large plastic deformation, the competition between basal slip and pyramidal<c+a> slip is responsible for the concentration of tilted basal poles towards ND within all deformed samples. The larger difference is between the activities of basal slip and pyramidal <c+a> slip, the smaller separation is between these two tilted basal poles. Besides,VPSC modeling overesttmates volume fractions of {10■2} ET in samples with angle of 0 to 30° between loading direction and RD of sheet because interactions between twin variants are not included in VPSC modeling procedure at the present form. In addition, as compatible deformation between individual grains cannot be considered in VPSC modeling, the predicted volume fractions of {10■2} ET in samples with angle of 45 to 90° between loading direction and RD of sheet are smaller than the correspondingly measured results.

Corrosion-Facilitating Local Plastic Deformation for α-Ti in Methanol

The effect of corrosion process on facilitating local plastic deformation for α-Ti in methanol has been investigated with the micro-multiplicative moire interferometer technique. The size of plastic zone and the plastic strain ahead of loaded notch have been measured. The results show that the anodic dissolution, or corrosion process itself can enhance the plastic zone and the plastic strain ahead of a loaded notch during stress corrosion of α-Ti in methanol solution

Numerical analysis of joint temperature evolution during friction stir welding based on plastic deformation heat

3D numerical model for friction stir welding （FSW） was developed by using ABAQUS software considering the plastic deformation heat. Effects of the rotation and welding speeds on the temperature field of FSW 2024-73 aluminum alloy were systematicaUy investigated. The temperature measurement was performed to validate the reliability of the model. The simulation results are in good agreement with the experiments. Results show that changing the rotation speed has no influence on the time for reaching the peak temperature at certain point in the workpiece at a constant welding speed. While increasing the welding speed has significant effect on the time for reaching the peak temperature but the value of peak temperature changes little.