Investigations into the strain rate sensitivity of magnesium(Mg)alloys represent a current research focus in materials science.However,most studies have examined strain rate sensitivity in single alloy,lacking systema...Investigations into the strain rate sensitivity of magnesium(Mg)alloys represent a current research focus in materials science.However,most studies have examined strain rate sensitivity in single alloy,lacking systematic comparisons between different alloys.In the present study,a series of ZK60-xCe(x=0,0.3,0.8,1.3)alloys were fabricated via hot extrusion deformation.The microstructure evolution and strain rate sensitivity of these alloys under dynamic compressive loading were systematically investigated.According to thermal activation theory calculations,the strain rate sensitivities of ZK60-xCe alloys are predominantly governed by their deformation mechanisms.The enhanced strain rate sensitivity observed in Ce-containing ZK60 alloys is primarily attributed to their high dislocation density.This correlation stems from two key factors:(1)Ce-containing alloys demonstrate significantly higher ΔE and ΔT values compared to the base ZK60 alloy,providing the necessary energy conditions for high-density dislocation generation;and(2)the Ce addition effectively promotes (c+a) slip activation and facilitates cross-slip behavior.It is hoped that this work can provide a new perspective for the study of strain rate sensitivity in Mg alloys and offer a methodology for comparing strain rate sensitivity among different alloys.展开更多
The cooling rate sensitivities of A1TiB, RE and A1TiB-RE refiners were investigated using laboratory experiments and the actual industrial applications of A356 automotive wheel via low pressure die casting technology....The cooling rate sensitivities of A1TiB, RE and A1TiB-RE refiners were investigated using laboratory experiments and the actual industrial applications of A356 automotive wheel via low pressure die casting technology. Their impact mechanisms on the microstructure and mechanical properties of the A356 alloy were discussed. The results demonstrated that the AITiB-RE refiner possessed most effective and synergetic refinement effects compared to the individual A1TiB or RE refiners. The A1TiB-RE refiner exhibited the least sensitivity to the cooling rate changes than the other refiners. The comprehensive properties of alloy wheel refined by the A1TiB-RE refiner were improved significantly. The tensile strength, yield strength, and elongation of wheel spoke improved by approximately 11.3%, 10.8% and 44.1%, respectively. The property difference values of the tensile strength, yield strength, and elongation in different positions of the wheel decreased from 14.8%, 31.2% and 47.7% to 8.6%, 27.1% and 30.9%, respectively.展开更多
Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1....Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1.It is proposed from the measured small activation volume that the yielding of the nanotwinned steel at higher strain rates is governed by the dislocation bowing out from the carbon atmosphere.At lower strain rates,however,the yielding is controlled by the continuous re-pinning of dislocations due to the fast diffused carbon atoms,which leads to the relative insensitivity of yield strength to the strain rate.展开更多
Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200℃ and constant strain rates of 0.001,0.01,0.1,and 1 s^(−1).Hot flow curves were used to det...Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200℃ and constant strain rates of 0.001,0.01,0.1,and 1 s^(−1).Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent,and to construct the processing maps.Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation.Four variations were distinguished reflecting the different microstructural changes.Based on the analysis of the strain hardening exponent versus strain curves,the microstructural evolutions were dynamic recovery,single and multiple peak dynamic recrystallization,and interactions between dynamic recrystallization and precipitation.The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s^(−1) were compared with the microstructural evolutions.The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures.Additionally,the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions.The microstructural evolutions strongly correlated to the power dissipation ratio,and dynamic recrystallization occurred completely at lower power dissipation ratios.展开更多
With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid ...With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress--strain behaviour at different strain rates ranging from 700 s^-1 to 1950 s^-1. The numerical model of split Hopkinson pressure bar （SHPB） was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress--strain curves wez＇e developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate.展开更多
An ultrafine-grained Cu sample with a high density of growth twins was synthesized by means of pulsed electrodeposition technique. The strain rate sensitivity of the Cu sample was measured by strain rate cycling tests...An ultrafine-grained Cu sample with a high density of growth twins was synthesized by means of pulsed electrodeposition technique. The strain rate sensitivity of the Cu sample was measured by strain rate cycling tests under tension. The effects of grain size as well as twin density on the strength and strain rate sensitivity were discussed.展开更多
It is well documented that the strain rate sensitivity(m)increases at refined grain size for face-centered cubic(FCC)metals and alloys.Through a series of nanoindentation testing,however,we experimentally demonstrated...It is well documented that the strain rate sensitivity(m)increases at refined grain size for face-centered cubic(FCC)metals and alloys.Through a series of nanoindentation testing,however,we experimentally demonstrated a striking departure from conventional FCC metals that Co Cr Fe Mn Ni high entropy alloy(HEA)with FCC lattice structure exhibits monotonously decreased m as grain size reduced fromμ30.3m to 7.2 nm.Moreover,the apparent activation volume v*,which generally shows an opposite trend of m,exhibited the identical decreasing trend with reduced grain size as that of m.Such an unusual trend of m and its correlation with v*in the FCC HEA alloys can be understood by a distinct deformationmechanism-transitions and unique dislocation morphology evolution that differs from conventional FCC metals.展开更多
The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures a...The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures and properties of deformed samples under different strain rates were investigated comparatively.These results show that positive strain rate sensitivity was observed with the increase in strain rates and that there was a significant difference in strain rate sensitivity factor(m)between quasi-static compression(m=0.029)and dynamic impact deformation(m=0.190).Compared to the quasi-static compression,the dynamic impact deformation exhibited higher yield strength.Microstructural examination reveals that the primary twins were frequently found during the quasi-static compression process,and the secondary twins were rarely observed.However,the secondary and multi-fold deformation twins were florescent in the dynamic impact samples.At the initial stage of dynamic impact deformation,partial dislocations and staking faults on multiple conjugate{111}planes were simultaneously activated and produced a large number of Lomer-Cottrell dislocations,resulting in a large increase in yield strength during dynamic impact.展开更多
In this work,we prepare transformable HEA/Cu nanolaminates(NLs)with equal individual layer thick-ness(h)by the magnetron sputtering technique,i.e.,Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu and Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu,an...In this work,we prepare transformable HEA/Cu nanolaminates(NLs)with equal individual layer thick-ness(h)by the magnetron sputtering technique,i.e.,Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu and Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu,and comparatively study He-ion irradiation effects on their microstructure and mechanical properties.It ap-pears that the as-deposited HEA/Cu NLs manifest two size h-dependent hardness regimes(i.e.,increased hardness at small h and hardness plateau at large h),while the He-implanted ones exhibit monotonically increased hardness.Contrary to the fashion that smaller h renders less irradiation hardening in bimetal NLs,the Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs manifest the trend that smaller h leads to greater irradiation hard-ening.By contrast,the Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs exhibit the maximum irradiation hardening at a critical h=50 nm.Below this critical size,smaller h results in lower radiation hardening(similar to bimetal NLs),while above this size,smaller h results in greater radiation hardening(similar to Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs).Moreover,these transformable HEA/Cu NLs display inverse h-dependent strain rate sensitivity(SRS m)before and after He-ion irradiation.Nevertheless,compared with as-deposited samples,the irradi-ated Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs display reduced SRS,while the irradiated Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs dis-play enhanced SRS.Such unusual size-dependent irradiation strengthening and inverse h effect on SRS in irradiated samples were rationalized by considering the blocking effects of He bubbles on dislocation nucleation and motion,i.e.,dislocations shearing or bypassing He bubbles.展开更多
The mechanisms occurring when the switched temperature technique is applied,as an accelerated enhanced low dose rate sensitivity(ELDRS)test technique,are investigated in terms of a specially designed gate-controlled l...The mechanisms occurring when the switched temperature technique is applied,as an accelerated enhanced low dose rate sensitivity(ELDRS)test technique,are investigated in terms of a specially designed gate-controlled lateral PNP transistor(GLPNP)that used to extract the interface traps(Nit)and oxide trapped charges(Not).Electrical characteristics in GLPNP transistors induced by ^(60)Co gamma irradiation are measured in situ as a function of total dose,showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP.Based on the analysis of the variations of Nit and Not,with switching the temperature,the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation.Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup.In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP,which provides us with a new insight into the test technique for ELDRS.展开更多
Tensile deformation behaviors of the electrodeposited 40 nm grain sized Ni,25 nm Ni-1.7 wt.%Co,and 13 nm Ni-8.6 wt.%Co alloys at various strain rates and room temperature were reviewed with emphasis on strain rate sen...Tensile deformation behaviors of the electrodeposited 40 nm grain sized Ni,25 nm Ni-1.7 wt.%Co,and 13 nm Ni-8.6 wt.%Co alloys at various strain rates and room temperature were reviewed with emphasis on strain rate sensitivity and activation volume,respectively.It is found that the strain rate sensitivity and activation volume were strongly grain size dependent.An analytic model based on the bow out of a single dislocation well predicted the relationship between the strain rate sensitivity and the activation volumes for these nanocrystaline metals.展开更多
Cu-Al/Al nanostructured metallic multilayers with Al layer thickness hAl varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The r...Cu-Al/Al nanostructured metallic multilayers with Al layer thickness hAl varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing hAl down to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu-Al monolithic thin films. The strain rate sensitivity （SRS, m）, however, decreased monotonically with reducing hAl. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu-Al nanolayers dominated at hAl≤ 20 nm, while the crystalline Al nanolayers dominated at hAl 〉 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with hAl. In addition, the hAFdependent hardness and SRS were quanti- tatively modeled in light of the strengthening mechanisms at different length scales.展开更多
The effects of strain rate on tensile properties and fracture behavior of HfNbTaTiZr refractory high-entropy alloy (RHEA) were investigated. With the increase of strain rate in the range from 0.0001 to 0.1 s^(−1), the...The effects of strain rate on tensile properties and fracture behavior of HfNbTaTiZr refractory high-entropy alloy (RHEA) were investigated. With the increase of strain rate in the range from 0.0001 to 0.1 s^(−1), the yield strength increases from 740 to 825 MPa, demonstrating a strain rate sensitivity coefficient of 0.0173. Notably, while the uniform elongation diminished with rising strain rates, the fracture elongation of the RHEA remained constant at ~ 43%, suggesting an enhanced non-uniform elongation and an improved resistance to tensile fracture. Single-edge notch tension test further proves that the notch toughness increases at elevated loading rates. The complete work-hardening rate curves were plotted, and the work-hardening ability of the RHEA was found not decreasing significantly after necking, especially at high strain rate. The fracture of tensile samples across all the strain rates was dominated by void growth and coalesce, with dimples on the fracture surface being smaller at higher strain rates. This work reveals an unconventional increase in fracture resistance at higher strain rates, further indicating that ductile RHEAs may possess superior potential for use in structural applications subjected to high strain rate loading.展开更多
Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in...Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.展开更多
This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incor...This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.展开更多
Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress,...Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress, strain hardening rate and strain rate sensitivity was investigated experimentally. The results show that both the effect of temperature on flow stress and its strain rate sensitivity of ECAPed Al is much larger than those of the coarse-grained Al. The temperature sensitivity of ultrafine-grained Al is comparatively weaker than that of the coarse-grained Al. Based on the experimental results, the apparent activation volume was estimated at different temperatures and strain rates. The forest dislocation interactions is the dominant thermally activated mechanism for ECAPed Al compressed at quasi-static strain rates, while the viscous drag plays an important role at high strain rates.展开更多
To overcome the limitation in formability at room temperature,manufacturers have developed magnesium alloys with remarkable properties by adding rare-earth elements.The rare-earth magnesium alloys behave differently f...To overcome the limitation in formability at room temperature,manufacturers have developed magnesium alloys with remarkable properties by adding rare-earth elements.The rare-earth magnesium alloys behave differently from the conventional alloys,especially with respect to their coupled anisotropic and strain rate sensitive behavior.In the current work,such behavior of the rare-earth Mg alloy ZEK100 sheet at room temperature is investigated with the aid of the elastic viscoplastic self-consistent polycrystal plasticity model.Different strain rate sensitivities(SRSs)for various deformation modes are employed by the model to simulate the strain rate sensitive behaviors under different loading directions and loading rates.Good agreement between the experiments and simulations reveals the importance and necessity of using different SRSs for each deformation mode in hexagonal close-packed metals.Furthermore,the relative activities of each deformation mode and the texture evolution during different loadings are discussed.The anisotropic and strain rate sensitive behavior is ascribed to the various operating deformation modes with different SRSs during loading along different directions.展开更多
Lotus-type porous copper was fabricated by unidirectional solidification, and compressive experiments were subsequently conducted in the strain rate range of 10-3-2400 s-1 with the compressive direction parallel to th...Lotus-type porous copper was fabricated by unidirectional solidification, and compressive experiments were subsequently conducted in the strain rate range of 10-3-2400 s-1 with the compressive direction parallel to the pores. A GLEEBLE-1500 thermal-mechanical simulation system and a split Hopkinson pressure bar （SHPB） were used to investigate the effect of strain rate on the compressive deforma-tion behaviors of lotus-type porous copper. The influence mechanism of strain rate was also analyzed by the strain-controlling method and by high-speed photography. The results indicated that the stress-strain curves of lotus-typed porous copper consist of a linear elastic stage, a plateau stage, and a densification stage at various strain rates. At low strain rate （〈1.0 s^-1）, the strain rate had little influence on the stress-strain curves; but when the strain rate exceeded 1.0 s^-1, it was observed to strongly affect the plateau stage, showing obvious strain-rate-hardening characteristics. Strain rate also influenced the densification initial strain. The densification initial strain at high strain rate was less than that at low strain rate. No visible inhomogeneous deformation caused by shockwaves was observed in lotus-type porous copper during high-strain-rate deformation. However, at high strain rate, the bending deformation characteristics of the pore walls obviously differed from those at low strain rate, which was the main mechanism by which the plateau stress exhibited strain-rate sensitivity when the strain rate exceeded a certain value and exhibited less densification initial strain at high strain rate.展开更多
The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation. Room temperature tensile tests were carried out at various...The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation. Room temperature tensile tests were carried out at various strain rates to investigate the effect on volume fraction of martensite, temperature increase and flow stress. The results show that with increasing strain rate, the local temperature increases, which suppresses the transformation of martensite. To take into account the dependence on strain level, strain rate sensitivity and thermal effects, a kinetic model of martensitic transformation was proposed and constitutive modeling on stress-strain response was conducted. The validity of the proposed model has been proved by comparisons between simulation results and experimental ones.展开更多
In order to analyze the stability of the underground rock structures,knowing the sensitivity of geomechanical parameters is important.To investigate the priority of these geomechanical properties in the stability of c...In order to analyze the stability of the underground rock structures,knowing the sensitivity of geomechanical parameters is important.To investigate the priority of these geomechanical properties in the stability of cavern,a sensitivity analysis has been performed on a single cavern in various rock mass qualities according to RMR using Phase 2.The stability of cavern has been studied by investigating the side wall deformation.Results showed that most sensitive properties are coefficient of lateral stress and modulus of deformation.Also parameters of Hoek-Brown criterion and r c have no sensitivity when cavern is in a perfect elastic state.But in an elasto-plastic state,parameters of Hoek-Brown criterion and r c affect the deformability;such effect becomes more remarkable with increasing plastic area.Other parameters have different sensitivities concerning rock mass quality(RMR).Results have been used to propose the best set of parameters for study on prediction of sidewall displacement.展开更多
基金financial supports from the General Project of Liaoning Provincial Department of Education[No.LJKMZ20220462]and[No.LJKMZ20220467]Liaoning Nature Fund Guidance Plan[No.2022-BS-179]。
文摘Investigations into the strain rate sensitivity of magnesium(Mg)alloys represent a current research focus in materials science.However,most studies have examined strain rate sensitivity in single alloy,lacking systematic comparisons between different alloys.In the present study,a series of ZK60-xCe(x=0,0.3,0.8,1.3)alloys were fabricated via hot extrusion deformation.The microstructure evolution and strain rate sensitivity of these alloys under dynamic compressive loading were systematically investigated.According to thermal activation theory calculations,the strain rate sensitivities of ZK60-xCe alloys are predominantly governed by their deformation mechanisms.The enhanced strain rate sensitivity observed in Ce-containing ZK60 alloys is primarily attributed to their high dislocation density.This correlation stems from two key factors:(1)Ce-containing alloys demonstrate significantly higher ΔE and ΔT values compared to the base ZK60 alloy,providing the necessary energy conditions for high-density dislocation generation;and(2)the Ce addition effectively promotes (c+a) slip activation and facilitates cross-slip behavior.It is hoped that this work can provide a new perspective for the study of strain rate sensitivity in Mg alloys and offer a methodology for comparing strain rate sensitivity among different alloys.
基金financially supported by the National High Technology Research and Development Program(No.2013AA031002)
文摘The cooling rate sensitivities of A1TiB, RE and A1TiB-RE refiners were investigated using laboratory experiments and the actual industrial applications of A356 automotive wheel via low pressure die casting technology. Their impact mechanisms on the microstructure and mechanical properties of the A356 alloy were discussed. The results demonstrated that the AITiB-RE refiner possessed most effective and synergetic refinement effects compared to the individual A1TiB or RE refiners. The A1TiB-RE refiner exhibited the least sensitivity to the cooling rate changes than the other refiners. The comprehensive properties of alloy wheel refined by the A1TiB-RE refiner were improved significantly. The tensile strength, yield strength, and elongation of wheel spoke improved by approximately 11.3%, 10.8% and 44.1%, respectively. The property difference values of the tensile strength, yield strength, and elongation in different positions of the wheel decreased from 14.8%, 31.2% and 47.7% to 8.6%, 27.1% and 30.9%, respectively.
文摘Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1.It is proposed from the measured small activation volume that the yielding of the nanotwinned steel at higher strain rates is governed by the dislocation bowing out from the carbon atmosphere.At lower strain rates,however,the yielding is controlled by the continuous re-pinning of dislocations due to the fast diffused carbon atoms,which leads to the relative insensitivity of yield strength to the strain rate.
文摘Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200℃ and constant strain rates of 0.001,0.01,0.1,and 1 s^(−1).Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent,and to construct the processing maps.Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation.Four variations were distinguished reflecting the different microstructural changes.Based on the analysis of the strain hardening exponent versus strain curves,the microstructural evolutions were dynamic recovery,single and multiple peak dynamic recrystallization,and interactions between dynamic recrystallization and precipitation.The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s^(−1) were compared with the microstructural evolutions.The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures.Additionally,the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions.The microstructural evolutions strongly correlated to the power dissipation ratio,and dynamic recrystallization occurred completely at lower power dissipation ratios.
文摘With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress--strain behaviour at different strain rates ranging from 700 s^-1 to 1950 s^-1. The numerical model of split Hopkinson pressure bar （SHPB） was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress--strain curves wez＇e developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate.
基金This work was supported by the National Natural Science Foundation of China(No.50571096 50021101,50431010)the Ministry of Science and Technology(M0ST)of China(No 2005CB623604).
文摘An ultrafine-grained Cu sample with a high density of growth twins was synthesized by means of pulsed electrodeposition technique. The strain rate sensitivity of the Cu sample was measured by strain rate cycling tests under tension. The effects of grain size as well as twin density on the strength and strain rate sensitivity were discussed.
基金financially supported by the Natural Science Foundation of Shaanxi Province(No.2019TD-020)the Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2020JM-41 and 2020JM-33)the National Natural Science Foundation of China(No.51471131)。
文摘It is well documented that the strain rate sensitivity(m)increases at refined grain size for face-centered cubic(FCC)metals and alloys.Through a series of nanoindentation testing,however,we experimentally demonstrated a striking departure from conventional FCC metals that Co Cr Fe Mn Ni high entropy alloy(HEA)with FCC lattice structure exhibits monotonously decreased m as grain size reduced fromμ30.3m to 7.2 nm.Moreover,the apparent activation volume v*,which generally shows an opposite trend of m,exhibited the identical decreasing trend with reduced grain size as that of m.Such an unusual trend of m and its correlation with v*in the FCC HEA alloys can be understood by a distinct deformationmechanism-transitions and unique dislocation morphology evolution that differs from conventional FCC metals.
基金financially supported by the National Natural Science Foundation of China(Nos.51801060,51831004 and 52171006)。
文摘The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures and properties of deformed samples under different strain rates were investigated comparatively.These results show that positive strain rate sensitivity was observed with the increase in strain rates and that there was a significant difference in strain rate sensitivity factor(m)between quasi-static compression(m=0.029)and dynamic impact deformation(m=0.190).Compared to the quasi-static compression,the dynamic impact deformation exhibited higher yield strength.Microstructural examination reveals that the primary twins were frequently found during the quasi-static compression process,and the secondary twins were rarely observed.However,the secondary and multi-fold deformation twins were florescent in the dynamic impact samples.At the initial stage of dynamic impact deformation,partial dislocations and staking faults on multiple conjugate{111}planes were simultaneously activated and produced a large number of Lomer-Cottrell dislocations,resulting in a large increase in yield strength during dynamic impact.
基金financially supported by the National Natural Science Foundation of China(Nos.U2067219,51722104,51790482,51761135031 and 92163201)the National Key Research and Development Program of China(No.2017YFA0700701)+1 种基金the 111 Project 2.0 of China(No.BP2018008)the Fundamental Research Funds for the Central Universities(No.xtr022019004)。
文摘In this work,we prepare transformable HEA/Cu nanolaminates(NLs)with equal individual layer thick-ness(h)by the magnetron sputtering technique,i.e.,Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu and Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu,and comparatively study He-ion irradiation effects on their microstructure and mechanical properties.It ap-pears that the as-deposited HEA/Cu NLs manifest two size h-dependent hardness regimes(i.e.,increased hardness at small h and hardness plateau at large h),while the He-implanted ones exhibit monotonically increased hardness.Contrary to the fashion that smaller h renders less irradiation hardening in bimetal NLs,the Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs manifest the trend that smaller h leads to greater irradiation hard-ening.By contrast,the Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs exhibit the maximum irradiation hardening at a critical h=50 nm.Below this critical size,smaller h results in lower radiation hardening(similar to bimetal NLs),while above this size,smaller h results in greater radiation hardening(similar to Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs).Moreover,these transformable HEA/Cu NLs display inverse h-dependent strain rate sensitivity(SRS m)before and after He-ion irradiation.Nevertheless,compared with as-deposited samples,the irradi-ated Fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs display reduced SRS,while the irradiated Fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs dis-play enhanced SRS.Such unusual size-dependent irradiation strengthening and inverse h effect on SRS in irradiated samples were rationalized by considering the blocking effects of He bubbles on dislocation nucleation and motion,i.e.,dislocations shearing or bypassing He bubbles.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1532261 and 1630141)
文摘The mechanisms occurring when the switched temperature technique is applied,as an accelerated enhanced low dose rate sensitivity(ELDRS)test technique,are investigated in terms of a specially designed gate-controlled lateral PNP transistor(GLPNP)that used to extract the interface traps(Nit)and oxide trapped charges(Not).Electrical characteristics in GLPNP transistors induced by ^(60)Co gamma irradiation are measured in situ as a function of total dose,showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP.Based on the analysis of the variations of Nit and Not,with switching the temperature,the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation.Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup.In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP,which provides us with a new insight into the test technique for ELDRS.
基金The work is financially supported by the Foundation of National Key Basic Research and Development Program(No 2004CB619301)the Project 985-Automotive Engineering of Jilin University
文摘Tensile deformation behaviors of the electrodeposited 40 nm grain sized Ni,25 nm Ni-1.7 wt.%Co,and 13 nm Ni-8.6 wt.%Co alloys at various strain rates and room temperature were reviewed with emphasis on strain rate sensitivity and activation volume,respectively.It is found that the strain rate sensitivity and activation volume were strongly grain size dependent.An analytic model based on the bow out of a single dislocation well predicted the relationship between the strain rate sensitivity and the activation volumes for these nanocrystaline metals.
基金supported by the National Natural Science Foundation of China(Grant Nos.5132100351322104and 51201123)+5 种基金the National Basic Research Program of China(Grant No.2010CB631003)the 111 Project of China(Grant No.B06025)the support from the Fundamental Research Funds for the Central Universitiesthe Tengfei Scholar projectthe Natural Science Basic Research Plan in Shaanxi Province of China(Program No.2015JM5158)the Shaanxi Province Postdoctoral Scientific Research Project for partial financial support
文摘Cu-Al/Al nanostructured metallic multilayers with Al layer thickness hAl varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing hAl down to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu-Al monolithic thin films. The strain rate sensitivity （SRS, m）, however, decreased monotonically with reducing hAl. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu-Al nanolayers dominated at hAl≤ 20 nm, while the crystalline Al nanolayers dominated at hAl 〉 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with hAl. In addition, the hAFdependent hardness and SRS were quanti- tatively modeled in light of the strengthening mechanisms at different length scales.
基金supported by the National Natural Science Foundation of China(Nos.52271072,52431002 and 52130110)the Research Fund of the State Key Laboratory of Solidification Processing(No.2021-TS-10)the Fundamental Research Funds for the Central Universities.
文摘The effects of strain rate on tensile properties and fracture behavior of HfNbTaTiZr refractory high-entropy alloy (RHEA) were investigated. With the increase of strain rate in the range from 0.0001 to 0.1 s^(−1), the yield strength increases from 740 to 825 MPa, demonstrating a strain rate sensitivity coefficient of 0.0173. Notably, while the uniform elongation diminished with rising strain rates, the fracture elongation of the RHEA remained constant at ~ 43%, suggesting an enhanced non-uniform elongation and an improved resistance to tensile fracture. Single-edge notch tension test further proves that the notch toughness increases at elevated loading rates. The complete work-hardening rate curves were plotted, and the work-hardening ability of the RHEA was found not decreasing significantly after necking, especially at high strain rate. The fracture of tensile samples across all the strain rates was dominated by void growth and coalesce, with dimples on the fracture surface being smaller at higher strain rates. This work reveals an unconventional increase in fracture resistance at higher strain rates, further indicating that ductile RHEAs may possess superior potential for use in structural applications subjected to high strain rate loading.
基金the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 101034425 for the project titled A2M2TECHThe Scientific and Technological Research Council of Türkiye (TUBITAK) with grant No 120C158 for the same A2M2TECH project under the TUBITAK's 2236/B program
文摘Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.
基金supported by the China Scholarship Council(Grant No.202007865002)the National Natural Science Foundation of China(Grant Nos.51865027,52065036,and 52065037)+2 种基金the Educational Unveiling Leadership Project of Gansu Province of China(Grant No.2021jyjbgs01)the support by JSPS KAKENHI(Grant No.JP23K20037)MEXT Programs(Grant Nos.JPMXP1122684766,JPMXP1020230325,and JPMXP1020230327).
文摘This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.
基金Projects(11272267,11102168,10932008)supported by the National Natural Science Foundation of ChinaProject(B07050)supported by Northwestern Polytechnical University
文摘Uniaxial compressive experiments of ultrafine-grained Al fabricated by equal channel angular pressing(ECAP) method were performed at wide temperature and strain rate range. The influence of temperature on flow stress, strain hardening rate and strain rate sensitivity was investigated experimentally. The results show that both the effect of temperature on flow stress and its strain rate sensitivity of ECAPed Al is much larger than those of the coarse-grained Al. The temperature sensitivity of ultrafine-grained Al is comparatively weaker than that of the coarse-grained Al. Based on the experimental results, the apparent activation volume was estimated at different temperatures and strain rates. The forest dislocation interactions is the dominant thermally activated mechanism for ECAPed Al compressed at quasi-static strain rates, while the viscous drag plays an important role at high strain rates.
基金supported by the National Natural Science Foundation of China(No.51975365)the Shanghai Pujiang Program(18PJ1405000)+1 种基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)the Province of Ontario
文摘To overcome the limitation in formability at room temperature,manufacturers have developed magnesium alloys with remarkable properties by adding rare-earth elements.The rare-earth magnesium alloys behave differently from the conventional alloys,especially with respect to their coupled anisotropic and strain rate sensitive behavior.In the current work,such behavior of the rare-earth Mg alloy ZEK100 sheet at room temperature is investigated with the aid of the elastic viscoplastic self-consistent polycrystal plasticity model.Different strain rate sensitivities(SRSs)for various deformation modes are employed by the model to simulate the strain rate sensitive behaviors under different loading directions and loading rates.Good agreement between the experiments and simulations reveals the importance and necessity of using different SRSs for each deformation mode in hexagonal close-packed metals.Furthermore,the relative activities of each deformation mode and the texture evolution during different loadings are discussed.The anisotropic and strain rate sensitive behavior is ascribed to the various operating deformation modes with different SRSs during loading along different directions.
基金financially supported by the National Natural Science Foundation(No.50904004)
文摘Lotus-type porous copper was fabricated by unidirectional solidification, and compressive experiments were subsequently conducted in the strain rate range of 10-3-2400 s-1 with the compressive direction parallel to the pores. A GLEEBLE-1500 thermal-mechanical simulation system and a split Hopkinson pressure bar （SHPB） were used to investigate the effect of strain rate on the compressive deforma-tion behaviors of lotus-type porous copper. The influence mechanism of strain rate was also analyzed by the strain-controlling method and by high-speed photography. The results indicated that the stress-strain curves of lotus-typed porous copper consist of a linear elastic stage, a plateau stage, and a densification stage at various strain rates. At low strain rate （〈1.0 s^-1）, the strain rate had little influence on the stress-strain curves; but when the strain rate exceeded 1.0 s^-1, it was observed to strongly affect the plateau stage, showing obvious strain-rate-hardening characteristics. Strain rate also influenced the densification initial strain. The densification initial strain at high strain rate was less than that at low strain rate. No visible inhomogeneous deformation caused by shockwaves was observed in lotus-type porous copper during high-strain-rate deformation. However, at high strain rate, the bending deformation characteristics of the pore walls obviously differed from those at low strain rate, which was the main mechanism by which the plateau stress exhibited strain-rate sensitivity when the strain rate exceeded a certain value and exhibited less densification initial strain at high strain rate.
基金Item Sponsored by National Natural Science Foundation of China(51275297)Doctor Subject Foundation of the Education Ministry of China(20100073110044)
文摘The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation. Room temperature tensile tests were carried out at various strain rates to investigate the effect on volume fraction of martensite, temperature increase and flow stress. The results show that with increasing strain rate, the local temperature increases, which suppresses the transformation of martensite. To take into account the dependence on strain level, strain rate sensitivity and thermal effects, a kinetic model of martensitic transformation was proposed and constitutive modeling on stress-strain response was conducted. The validity of the proposed model has been proved by comparisons between simulation results and experimental ones.
文摘In order to analyze the stability of the underground rock structures,knowing the sensitivity of geomechanical parameters is important.To investigate the priority of these geomechanical properties in the stability of cavern,a sensitivity analysis has been performed on a single cavern in various rock mass qualities according to RMR using Phase 2.The stability of cavern has been studied by investigating the side wall deformation.Results showed that most sensitive properties are coefficient of lateral stress and modulus of deformation.Also parameters of Hoek-Brown criterion and r c have no sensitivity when cavern is in a perfect elastic state.But in an elasto-plastic state,parameters of Hoek-Brown criterion and r c affect the deformability;such effect becomes more remarkable with increasing plastic area.Other parameters have different sensitivities concerning rock mass quality(RMR).Results have been used to propose the best set of parameters for study on prediction of sidewall displacement.
