Nanorubber/epoxy composites containing 0,2,6 and 10 wt%nanorubber are subjected to uniaxial compression over a wide range of strain rate from 8×10^(-4) s^(-1) to~2×10^(4) s^(-1).Unexpectedly,their strain rat...Nanorubber/epoxy composites containing 0,2,6 and 10 wt%nanorubber are subjected to uniaxial compression over a wide range of strain rate from 8×10^(-4) s^(-1) to~2×10^(4) s^(-1).Unexpectedly,their strain rate sensitivity and strain hardening index increase with increasing nanorubber content.Potential mechanisms are proposed based on numerical simulations using a unit cell model.An increase in the strain rate sensitivity with increasing nanorubber content results from the fact that the nanorubber becomes less incompressible at high strain,generating a higher hydro-static pressure.Adiabatic shear localization starts to occur in the epoxy under a strain rate of 22,000 s^(-1) when the strain exceeds 0.35.The presence of nanorubber in the epoxy reduces adiabatic shear localization by preventing it from propagating.展开更多
The Earth’s surface kinematics and deformation are fundamental to understanding crustal evolution.An effective research approach is to estimate regional motion field and deformation fields based on modern geodetic ne...The Earth’s surface kinematics and deformation are fundamental to understanding crustal evolution.An effective research approach is to estimate regional motion field and deformation fields based on modern geodetic networks.If the discrete observed velocity field is obtained,the velocity related fields,such as dilatation rate and maximum shear strain rate,can be estimated by applying varied mathematical approaches.This study applied Akaike's Bayesian Information Criterion(ABIC)method to calculate strain rate fields constrained by GPS observations in the southeast Tibetan Plateau.Comparison with results derived from other three methods revealed that our ABIC-derived strain rate fields were more precise.The maximum shear strain rate highlighted the Xianshuihe–Xiaojiang fault system as the main boundary for the outward migration of material in southeastern Tibet,indicating rotation of eastern Tibet material around the eastern Himalaya rather than whole extrusion along a fixed channel.Additionally,distinct dilatation rate patterns in the northeast and southwest regions of the fault system were observed.The northeast region,represented by the Longmenshan area,exhibited negative dilatational anomalies;while the southwest region,represented by the Jinsha River area north of 29°N,displayed positive dilatational anomalies.This indicates compression in the former and extension in the latter.Combined with deep geophysical observations,we believe that the upper and lower crusts of the Jinsha River area north of 29°N are in an entire expanding state,probably caused by the escape-drag effect of material.The presence of a large,low-viscosity region south of 29°N may not enable the entire escape of the crust,but instead result in a differential escape of the lower crust faster than the upper crust.展开更多
The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with differen...The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.展开更多
Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry.To study the mechanical behavior of a typical ductile cast iron(GJS-450)with nodular graphite,u...Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry.To study the mechanical behavior of a typical ductile cast iron(GJS-450)with nodular graphite,uni-axial quasi-static and dynamic tensile tests at strain rates of 10^(-4),1,10,100,and 250 s^(-1)were carried out.In order to investigate the influence of stress state on the deformation and fracture parameters,specimens with various geometries were used in the experiments.Stress strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10^(-4)to 250 s^(-1)were obtained.A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate range.The available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture strains.Simulations with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture process.The results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 alloys.The predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results,which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain rates.The proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.展开更多
High-energy gas fracturing of shale is a novel,high efficacy and eco-friendly mining technique,which is a typical dynamic perturbing behavior.To effectively extract shale gas,it is important to understand the dynamic ...High-energy gas fracturing of shale is a novel,high efficacy and eco-friendly mining technique,which is a typical dynamic perturbing behavior.To effectively extract shale gas,it is important to understand the dynamic mechanical properties of shale.Dynamic experiments on shale subjected to true triaxial compression at different strain rates are first conducted in this research.The dynamic stress-strain curves,peak strain,peak stress and failure modes of shale are investigated.The results of the study indicate that the intermediate principal stress and the minor principal stress have the significant influence on the dynamic mechanical behaviors,although this effect decreases as the strain rate increases.The characteristics of compression-shear failure primarily occur in shale subjected to triaxial compression at high strain rates,which distinguishes it from the fragmentation characteristics observed in shale under dynamic uniaxial compression.Additionally,a numerical three-dimensional Split Hopkinson Pressure Bar(3D-SHPB),which is established by coupling PFC3D and FLAC3D methods,is validated to replicate the laboratory characteristics of shale.The dynamic mechanical characteristics of shale subjected to different confining stresses are systematically investigated by the coupling PFC3D and FLAC3D method.The numerical results are in good agreement with the experimental data.展开更多
We completed the uniaxial tensile test of mortar in the range of strain rate from 10^(-6)to 10^(-4)s^(-1)in the section containing softening,and carried out acoustic emission monitoring(AE)simultaneously.A series of A...We completed the uniaxial tensile test of mortar in the range of strain rate from 10^(-6)to 10^(-4)s^(-1)in the section containing softening,and carried out acoustic emission monitoring(AE)simultaneously.A series of AE parameters and spectrum analysis methods were used to identify the damage evolution process and cracking mechanism of mortar at different strain rates.The results show that,with the increase of strain rate,the peak stress and tensile elastic modulus of mortar increase obviously,and the stress level corresponding to the starting point of AE activity increases significantly as well,which indicates that the mechanical properties and AE characteristics of mortar have obvious strain rate effect.With the increase of strain rate,the cumulative AE hit decreases gradually,while the average AE hit rate increases significantly,indicating that the increase of strain rate reduces the damage degree of internal microstructure of the specimen,but the crack propagation speed increases.In the pre-peak stress stage,the average of AE ringing count and signal energy decreases with the increase of strain rate,while the average of duration increases;in the post-peak stress stage(f_(t)-30%f_(t)),the average of the three AE parameters all increase with the increase of strain rate,indicating that the strain rate effect on the damage process of mortar is different before and after peak stress,and the damage mechanism represented by different parameters is also different.In the whole process of uniaxial tensile of mortar,with the increase of strain rate,the scatter distribution of AE frequency-amplitude becomes more discrete,and the b-value shows a decreasing trend.In addition,the average level of AE peak frequency decreases with the increase of strain rate,while that of ca8 band wavelet energy spectrum coefficient increases.It is indicated that the increase of strain rate enables the crack propagation state of mortar specimen to become unstable,and the width of macrocrack increases but the proportion decreases.展开更多
In order to evaluate the effects of triploidy induction on a selected strain‘Haida No.2’of the Pacific oyster Crassostrea gigas,which is characterized with golden shell color and high growth rate,the growth,survival...In order to evaluate the effects of triploidy induction on a selected strain‘Haida No.2’of the Pacific oyster Crassostrea gigas,which is characterized with golden shell color and high growth rate,the growth,survival rate and stability of triploid rate were analyzed at different development stages in the present study.Three different conditions inhibiting the release of polar body Ⅱ or polar body Ⅰ were tested:(A)Cytochalasin-B(CB),0.5mg L^(−1) at 10min post-insemination for 15 min;(B)CB,0.5mg L^(−1)at 15 min postinsemination for 20 min;and(C)CB,0.7mg L^(−1),at 15 min post-insemination for 20 min.The triploidy induction treatments significantly reduced the D-larvae and survival rates at the larvae stage but not at the juvenile and adult stages.Triploid rate dramatically decreased at the larval stage and did not significantly change at the juvenile and adult stages.Regarding the stability of the triploid rate,there was a significant difference between the three treatment groups.Larvae from the treatment A and control groups exhibited higher growth rates in shell height than those from the other two treatment groups at day 27.Triploid juveniles and adults from the treatment A group exhibited a higher wet weight than diploids from the control group and triploids from the other treatment groups.Triploidy induction did not affect the shell color of the progeny.The results obtained in the study demonstrate that triploidy induction has the potential to be used to increase the production of C.gigas variety‘Haida No.2’without modifying its golden shell color.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
This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic(T700/LY113)under compression.The test samples were manufactu...This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic(T700/LY113)under compression.The test samples were manufactured through the filament winding of flat plates.To establish the strain rate dependencies of the strength and elastic modulus of the material,dynamic tests were carried out using a drop tower,the Split Hopkinson Pressure Bar method,and standard static tests.The samples were loaded both along and perpendicular to the direction of the reinforcing fiber.The applicability of the obtained samples for static and dynamic tests was confirmed through finite elementmodeling and the high-speed imaging of the deformation and failure of samples during testing.As a result of the conducted experimental studies,static and dynamic stress-strain curves,time dependencies of deformation and the stress and strain rates of the samples during compression were obtained.Based on these results,the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001-6001/s are constructed.It is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under compression.An increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42%and 50%,respectively.Perpendicular loading resulted in a strength and elastic modulus increase by 58%and 50%,respectively.The average strength along the fibers at the largest studied strain rate was about 1000MPa.The obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads,as well as to build models of mechanical behavior and failure criteria of such materials,taking into account the strain rate effects.展开更多
The scaling-dependent behaviors of rocks are significant to the stability and safe operation of the structures built in or on rock masses for practical engineering.Currently,many size effect models are employed to con...The scaling-dependent behaviors of rocks are significant to the stability and safe operation of the structures built in or on rock masses for practical engineering.Currently,many size effect models are employed to connect laboratory measurements at small scales and engineering applications at large scales.However,limited works consider the strain rate effect.In this study,an fractal-statistical scaling model incorporating strain rate is proposed based on a weakest-link approach,fractal theory and dynamic fracture mechanics.The proposed scaling model consists of 8 model parameters with physical meaning,i.e.rate-dependent parameter,intrinsic material parameter,dynamic strain rate,quasi-static strain rate,quasi-static fracture toughness,micro-crack size,micro-crack intensity and fractal dimension,enabling the proposed scaling model to model the scaling behaviors under different external conditions.Theoretical predictions are consistent with experimental data on red sandstone,proving the reliability and effectiveness of the proposed scaling model.Thus,the scaling behaviors of rocks under dynamic loading conditions can be captured by the proposed fractal-statistical scaling model.The sensitivity analysis indicates that the nominal strength difference becomes more obvious with a higher strain rate,larger fractal dimension,smaller micro-crack size or lower micro-crack intensity.Therefore,the proposed scaling model has the potential to capture the scaling behaviors considering the thermal effect,weathering effect,anisotropic characteristic etc.,as the proposed scaling model incorporated model parameters with physical meaning.The findings of this study are of fundamental importance to understand the scaling behaviors of rock under dynamic loading condition,and thus would facilitate the appropriate design of rock engineering.展开更多
The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carrie...The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10<sup>-3</sup> s<sup>-1</sup>, 20.85 × 10<sup>-3</sup> s<sup>-1</sup>, and 208.5 × 10<sup>-3</sup> s<sup>-1</sup>. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.展开更多
This paper presents a mathematical model consisting of conservation and balance laws (CBL) of classical continuum mechanics (CCM) and ordered rate constitutive theories in Lagrangian description derived using entropy ...This paper presents a mathematical model consisting of conservation and balance laws (CBL) of classical continuum mechanics (CCM) and ordered rate constitutive theories in Lagrangian description derived using entropy inequality and the representation theorem for thermoviscoelastic solids (TVES) with rheology. The CBL and the constitutive theories take into account finite deformation and finite strain deformation physics and are based on contravariant deviatoric second Piola-Kirchhoff stress tensor and its work conjugate covariant Green’s strain tensor and their material derivatives of up to order m and n respectively. All published works on nonlinear dynamics of TVES with rheology are mostly based on phenomenological mathematical models. In rare instances, some aspects of CBL are used but are incorrectly altered to obtain mass, stiffness and damping matrices using space-time decoupled approaches. In the work presented in this paper, we show that this is not possible using CBL of CCM for TVES with rheology. Thus, the mathematical models used currently in the published works are not the correct description of the physics of nonlinear dynamics of TVES with rheology. The mathematical model used in the present work is strictly based on the CBL of CCM and is thermodynamically and mathematically consistent and the space-time coupled finite element methodology used in this work is unconditionally stable and provides solutions with desired accuracy and is ideally suited for nonlinear dynamics of TVES with memory. The work in this paper is the first presentation of a mathematical model strictly based on CBL of CCM and the solution of the mathematical model is obtained using unconditionally stable space-time coupled computational methodology that provides control over the errors in the evolution. Both space-time coupled and space-time decoupled finite element formulations are considered for obtaining solutions of the IVPs described by the mathematical model and are presented in the paper. Factors or the physics influencing dynamic response and dynamic bifurcation for TVES with rheology are identified and are also demonstrated through model problem studies. A simple model problem consisting of a rod (1D) of TVES material with memory fixed at one end and subjected to harmonic excitation at the other end is considered to study nonlinear dynamics of TVES with rheology, frequency response as well as dynamic bifurcation phenomenon.展开更多
The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot...The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s?1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.展开更多
Variable 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 Ig (?). When (...Variable 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 Ig (?). When (?) < (?)cp, i.e. under quasi-static loading, n can be considered as a constant, but when (?)>(?)cp, n decreases rapidly till an ideal plastic state. n = 0. The characterizations and mechanisms of softening induced by high (?) are discussed.展开更多
The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture...The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.展开更多
The dynamic tensile test of 0.11C-0.62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transfor...The dynamic tensile test of 0.11C-0.62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transformation. At high strain rates, the uniform elongation decreases, whereas the total elongation and energy absorption increase. The tensile strength is less strain rate sensitive. With raising test temperature, the tensile strength is reduced and the mechanical properties generally deteriorate, especially at 110℃,However, excellent mechanical properties were obtained at 50℃ and 75℃.展开更多
The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K(0.67Tm-0.76Tm) and high strain rates ranging from 10^-3 to 1 s^...The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K(0.67Tm-0.76Tm) and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding(GBS),and the dislocation creep mechanism is considered as the main accommodation mechanism.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
A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with ...A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with a low extrusion ratio and rolling. The composites exhibite a total elongation of 220%~380% in the initial strain rates within 1.0×10 -2 ~1.0×10 -1 s -1 and at 893~903 K. According to differential thermal analysis(DTA) and microstructure observation, it is concluded that an appropriately small amount of liquid phase is necessary to cause a good high strain rate superplasticity in aluminum matrix composites in addition to fine and uniform microstructure.展开更多
The dynamic mechanical properties of Fe-30Mn-3Si-4A1 twinning induced plasticity (TWIP) steel were studied by the split-Hopkinson pressure bar (SHPB) at temperatures of 298-1073 K and strain rates of 700, 2500, an...The dynamic mechanical properties of Fe-30Mn-3Si-4A1 twinning induced plasticity (TWIP) steel were studied by the split-Hopkinson pressure bar (SHPB) at temperatures of 298-1073 K and strain rates of 700, 2500, and 5000 s-1. The TWIP steel indicates strain rate hardening effect between 700 and 2500 s-1, but it shows strain rate softening effect between 2500 and 5000 s-1. In addition, the strain rate softening effect enhances with an increase in deformation temperature. After deformation, the microstructures were studied by optical microscopy (OM). It is shown that the deformation bands become more convergence, a part of which become interwoven with an increase in strain rate, and the dynamic recovery and recrystallization are enhanced with an increase in both temperature and strain rate.展开更多
基金supported by the Key Research and Development Plan of Shaanxi Province (2023-GHZD-12)the Opening Fund of State Key Laboratory for Strength and Vibration of Mechanical Structures (SVL2021-KF-12)+1 种基金Fundamental Research Funds for the Central Universities (G2020KY05112)the 111 Project (BP0719007)
文摘Nanorubber/epoxy composites containing 0,2,6 and 10 wt%nanorubber are subjected to uniaxial compression over a wide range of strain rate from 8×10^(-4) s^(-1) to~2×10^(4) s^(-1).Unexpectedly,their strain rate sensitivity and strain hardening index increase with increasing nanorubber content.Potential mechanisms are proposed based on numerical simulations using a unit cell model.An increase in the strain rate sensitivity with increasing nanorubber content results from the fact that the nanorubber becomes less incompressible at high strain,generating a higher hydro-static pressure.Adiabatic shear localization starts to occur in the epoxy under a strain rate of 22,000 s^(-1) when the strain exceeds 0.35.The presence of nanorubber in the epoxy reduces adiabatic shear localization by preventing it from propagating.
基金supported by grants from the Ministry of Science and Technology(Grant Nos.2021FY100101,2019QZKK0901)the National Natural Science Foundation of China(Grant Nos.41941016,42230312,42020104007)China Geological Survey(Grant No.DD20221630).
文摘The Earth’s surface kinematics and deformation are fundamental to understanding crustal evolution.An effective research approach is to estimate regional motion field and deformation fields based on modern geodetic networks.If the discrete observed velocity field is obtained,the velocity related fields,such as dilatation rate and maximum shear strain rate,can be estimated by applying varied mathematical approaches.This study applied Akaike's Bayesian Information Criterion(ABIC)method to calculate strain rate fields constrained by GPS observations in the southeast Tibetan Plateau.Comparison with results derived from other three methods revealed that our ABIC-derived strain rate fields were more precise.The maximum shear strain rate highlighted the Xianshuihe–Xiaojiang fault system as the main boundary for the outward migration of material in southeastern Tibet,indicating rotation of eastern Tibet material around the eastern Himalaya rather than whole extrusion along a fixed channel.Additionally,distinct dilatation rate patterns in the northeast and southwest regions of the fault system were observed.The northeast region,represented by the Longmenshan area,exhibited negative dilatational anomalies;while the southwest region,represented by the Jinsha River area north of 29°N,displayed positive dilatational anomalies.This indicates compression in the former and extension in the latter.Combined with deep geophysical observations,we believe that the upper and lower crusts of the Jinsha River area north of 29°N are in an entire expanding state,probably caused by the escape-drag effect of material.The presence of a large,low-viscosity region south of 29°N may not enable the entire escape of the crust,but instead result in a differential escape of the lower crust faster than the upper crust.
基金supported by the Beijing Natural Science Foundation,China(Grant No.JQ20039)National Natural Science Foundation of China(Grant No.12172019).
文摘The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.
基金Supported by National Natural Science Foundation of China (Grant Nos.12202205,U1730101)the Federal Ministry of Economic Affairs and Energy (BMWi)via the German Federation of Industrial Research Associations‘Otto von Guericke’e.V. (AiF) (IGF-Nr.19567N)Forschungsvereinigung Automobiltechnik e.V. (FAT)。
文摘Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry.To study the mechanical behavior of a typical ductile cast iron(GJS-450)with nodular graphite,uni-axial quasi-static and dynamic tensile tests at strain rates of 10^(-4),1,10,100,and 250 s^(-1)were carried out.In order to investigate the influence of stress state on the deformation and fracture parameters,specimens with various geometries were used in the experiments.Stress strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10^(-4)to 250 s^(-1)were obtained.A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate range.The available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture strains.Simulations with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture process.The results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 alloys.The predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results,which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain rates.The proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.
基金supported by the National Natural Science Foundation of China(Nos.51839009 and 52027814)the Natural Science Foundation of Hubei Province(No.2023AFB589).
文摘High-energy gas fracturing of shale is a novel,high efficacy and eco-friendly mining technique,which is a typical dynamic perturbing behavior.To effectively extract shale gas,it is important to understand the dynamic mechanical properties of shale.Dynamic experiments on shale subjected to true triaxial compression at different strain rates are first conducted in this research.The dynamic stress-strain curves,peak strain,peak stress and failure modes of shale are investigated.The results of the study indicate that the intermediate principal stress and the minor principal stress have the significant influence on the dynamic mechanical behaviors,although this effect decreases as the strain rate increases.The characteristics of compression-shear failure primarily occur in shale subjected to triaxial compression at high strain rates,which distinguishes it from the fragmentation characteristics observed in shale under dynamic uniaxial compression.Additionally,a numerical three-dimensional Split Hopkinson Pressure Bar(3D-SHPB),which is established by coupling PFC3D and FLAC3D methods,is validated to replicate the laboratory characteristics of shale.The dynamic mechanical characteristics of shale subjected to different confining stresses are systematically investigated by the coupling PFC3D and FLAC3D method.The numerical results are in good agreement with the experimental data.
基金Funded by the National Natural Science Foundation of China(No.51878245)Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX22_0622)。
文摘We completed the uniaxial tensile test of mortar in the range of strain rate from 10^(-6)to 10^(-4)s^(-1)in the section containing softening,and carried out acoustic emission monitoring(AE)simultaneously.A series of AE parameters and spectrum analysis methods were used to identify the damage evolution process and cracking mechanism of mortar at different strain rates.The results show that,with the increase of strain rate,the peak stress and tensile elastic modulus of mortar increase obviously,and the stress level corresponding to the starting point of AE activity increases significantly as well,which indicates that the mechanical properties and AE characteristics of mortar have obvious strain rate effect.With the increase of strain rate,the cumulative AE hit decreases gradually,while the average AE hit rate increases significantly,indicating that the increase of strain rate reduces the damage degree of internal microstructure of the specimen,but the crack propagation speed increases.In the pre-peak stress stage,the average of AE ringing count and signal energy decreases with the increase of strain rate,while the average of duration increases;in the post-peak stress stage(f_(t)-30%f_(t)),the average of the three AE parameters all increase with the increase of strain rate,indicating that the strain rate effect on the damage process of mortar is different before and after peak stress,and the damage mechanism represented by different parameters is also different.In the whole process of uniaxial tensile of mortar,with the increase of strain rate,the scatter distribution of AE frequency-amplitude becomes more discrete,and the b-value shows a decreasing trend.In addition,the average level of AE peak frequency decreases with the increase of strain rate,while that of ca8 band wavelet energy spectrum coefficient increases.It is indicated that the increase of strain rate enables the crack propagation state of mortar specimen to become unstable,and the width of macrocrack increases but the proportion decreases.
基金supported by the grants from the China Agriculture Research System Project(No.CARS-49)the Earmarked Fund for Agriculture Seed Improvement Project of Shandong Province(Nos.2020LZGC016,2021 LZGC027).
文摘In order to evaluate the effects of triploidy induction on a selected strain‘Haida No.2’of the Pacific oyster Crassostrea gigas,which is characterized with golden shell color and high growth rate,the growth,survival rate and stability of triploid rate were analyzed at different development stages in the present study.Three different conditions inhibiting the release of polar body Ⅱ or polar body Ⅰ were tested:(A)Cytochalasin-B(CB),0.5mg L^(−1) at 10min post-insemination for 15 min;(B)CB,0.5mg L^(−1)at 15 min postinsemination for 20 min;and(C)CB,0.7mg L^(−1),at 15 min post-insemination for 20 min.The triploidy induction treatments significantly reduced the D-larvae and survival rates at the larvae stage but not at the juvenile and adult stages.Triploid rate dramatically decreased at the larval stage and did not significantly change at the juvenile and adult stages.Regarding the stability of the triploid rate,there was a significant difference between the three treatment groups.Larvae from the treatment A and control groups exhibited higher growth rates in shell height than those from the other two treatment groups at day 27.Triploid juveniles and adults from the treatment A group exhibited a higher wet weight than diploids from the control group and triploids from the other treatment groups.Triploidy induction did not affect the shell color of the progeny.The results obtained in the study demonstrate that triploidy induction has the potential to be used to increase the production of C.gigas variety‘Haida No.2’without modifying its golden shell color.
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This research was supported by the Russian Science Foundation(Grant No.21-19-00563,https://rscf.ru/en/project/21-19-00563/)H.M.Sedighi is grateful to the Research Council of Shahid Chamran University of Ahvaz for its financial support(Grant No.SCU.EM1401.98)。
文摘This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic(T700/LY113)under compression.The test samples were manufactured through the filament winding of flat plates.To establish the strain rate dependencies of the strength and elastic modulus of the material,dynamic tests were carried out using a drop tower,the Split Hopkinson Pressure Bar method,and standard static tests.The samples were loaded both along and perpendicular to the direction of the reinforcing fiber.The applicability of the obtained samples for static and dynamic tests was confirmed through finite elementmodeling and the high-speed imaging of the deformation and failure of samples during testing.As a result of the conducted experimental studies,static and dynamic stress-strain curves,time dependencies of deformation and the stress and strain rates of the samples during compression were obtained.Based on these results,the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001-6001/s are constructed.It is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under compression.An increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42%and 50%,respectively.Perpendicular loading resulted in a strength and elastic modulus increase by 58%and 50%,respectively.The average strength along the fibers at the largest studied strain rate was about 1000MPa.The obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads,as well as to build models of mechanical behavior and failure criteria of such materials,taking into account the strain rate effects.
基金supported by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(Grant No.2019ZT08G315)Shenzhen Fundamental Research Program(Grant No.JCYJ20220818095605012)Shenzhen Fundamental Research Program(Grant.No.JCYJ20210324093402006).
文摘The scaling-dependent behaviors of rocks are significant to the stability and safe operation of the structures built in or on rock masses for practical engineering.Currently,many size effect models are employed to connect laboratory measurements at small scales and engineering applications at large scales.However,limited works consider the strain rate effect.In this study,an fractal-statistical scaling model incorporating strain rate is proposed based on a weakest-link approach,fractal theory and dynamic fracture mechanics.The proposed scaling model consists of 8 model parameters with physical meaning,i.e.rate-dependent parameter,intrinsic material parameter,dynamic strain rate,quasi-static strain rate,quasi-static fracture toughness,micro-crack size,micro-crack intensity and fractal dimension,enabling the proposed scaling model to model the scaling behaviors under different external conditions.Theoretical predictions are consistent with experimental data on red sandstone,proving the reliability and effectiveness of the proposed scaling model.Thus,the scaling behaviors of rocks under dynamic loading conditions can be captured by the proposed fractal-statistical scaling model.The sensitivity analysis indicates that the nominal strength difference becomes more obvious with a higher strain rate,larger fractal dimension,smaller micro-crack size or lower micro-crack intensity.Therefore,the proposed scaling model has the potential to capture the scaling behaviors considering the thermal effect,weathering effect,anisotropic characteristic etc.,as the proposed scaling model incorporated model parameters with physical meaning.The findings of this study are of fundamental importance to understand the scaling behaviors of rock under dynamic loading condition,and thus would facilitate the appropriate design of rock engineering.
文摘The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10<sup>-3</sup> s<sup>-1</sup>, 20.85 × 10<sup>-3</sup> s<sup>-1</sup>, and 208.5 × 10<sup>-3</sup> s<sup>-1</sup>. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.
文摘This paper presents a mathematical model consisting of conservation and balance laws (CBL) of classical continuum mechanics (CCM) and ordered rate constitutive theories in Lagrangian description derived using entropy inequality and the representation theorem for thermoviscoelastic solids (TVES) with rheology. The CBL and the constitutive theories take into account finite deformation and finite strain deformation physics and are based on contravariant deviatoric second Piola-Kirchhoff stress tensor and its work conjugate covariant Green’s strain tensor and their material derivatives of up to order m and n respectively. All published works on nonlinear dynamics of TVES with rheology are mostly based on phenomenological mathematical models. In rare instances, some aspects of CBL are used but are incorrectly altered to obtain mass, stiffness and damping matrices using space-time decoupled approaches. In the work presented in this paper, we show that this is not possible using CBL of CCM for TVES with rheology. Thus, the mathematical models used currently in the published works are not the correct description of the physics of nonlinear dynamics of TVES with rheology. The mathematical model used in the present work is strictly based on the CBL of CCM and is thermodynamically and mathematically consistent and the space-time coupled finite element methodology used in this work is unconditionally stable and provides solutions with desired accuracy and is ideally suited for nonlinear dynamics of TVES with memory. The work in this paper is the first presentation of a mathematical model strictly based on CBL of CCM and the solution of the mathematical model is obtained using unconditionally stable space-time coupled computational methodology that provides control over the errors in the evolution. Both space-time coupled and space-time decoupled finite element formulations are considered for obtaining solutions of the IVPs described by the mathematical model and are presented in the paper. Factors or the physics influencing dynamic response and dynamic bifurcation for TVES with rheology are identified and are also demonstrated through model problem studies. A simple model problem consisting of a rod (1D) of TVES material with memory fixed at one end and subjected to harmonic excitation at the other end is considered to study nonlinear dynamics of TVES with rheology, frequency response as well as dynamic bifurcation phenomenon.
基金co-funded by the National Natural Science Foundation of China and Baoshan Iron & Steel Co., Ltd. (No. 50834008)
文摘The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s?1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.
文摘Variable 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 Ig (?). When (?) < (?)cp, i.e. under quasi-static loading, n can be considered as a constant, but when (?)>(?)cp, n decreases rapidly till an ideal plastic state. n = 0. The characterizations and mechanisms of softening induced by high (?) are discussed.
文摘The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.
基金Item Sponsored by China-Belgium Bilateral Project BIL01
文摘The dynamic tensile test of 0.11C-0.62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transformation. At high strain rates, the uniform elongation decreases, whereas the total elongation and energy absorption increase. The tensile strength is less strain rate sensitive. With raising test temperature, the tensile strength is reduced and the mechanical properties generally deteriorate, especially at 110℃,However, excellent mechanical properties were obtained at 50℃ and 75℃.
基金supported by the National Natural Science Foundation of China(No.50674067).
文摘The high strain rate superplastic deformation properties and characteristics of a rolled AZ91 magnesium alloy at temperatures ranging from 623 to 698 K(0.67Tm-0.76Tm) and high strain rates ranging from 10^-3 to 1 s^-1 were investigated.The rolled AZ91 magnesium alloy possesses excellent superplasticity with the maximum elongation of 455% at 623 K and a strain rate of 10-3 s-1,and its strain rate sensitivity m is high up to 0.64.The dominant deformation mechanism responsible for the high strain rate superplasticity is still grain boundary sliding(GBS),and the dislocation creep mechanism is considered as the main accommodation mechanism.
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.
文摘A β SiC whisker reinforced pure aluminum composites expected to exhibit high strain rate superplasticity has been successfully fabricated by a new processing route consisting of pressure infiltration, extrusion with a low extrusion ratio and rolling. The composites exhibite a total elongation of 220%~380% in the initial strain rates within 1.0×10 -2 ~1.0×10 -1 s -1 and at 893~903 K. According to differential thermal analysis(DTA) and microstructure observation, it is concluded that an appropriately small amount of liquid phase is necessary to cause a good high strain rate superplasticity in aluminum matrix composites in addition to fine and uniform microstructure.
文摘The dynamic mechanical properties of Fe-30Mn-3Si-4A1 twinning induced plasticity (TWIP) steel were studied by the split-Hopkinson pressure bar (SHPB) at temperatures of 298-1073 K and strain rates of 700, 2500, and 5000 s-1. The TWIP steel indicates strain rate hardening effect between 700 and 2500 s-1, but it shows strain rate softening effect between 2500 and 5000 s-1. In addition, the strain rate softening effect enhances with an increase in deformation temperature. After deformation, the microstructures were studied by optical microscopy (OM). It is shown that the deformation bands become more convergence, a part of which become interwoven with an increase in strain rate, and the dynamic recovery and recrystallization are enhanced with an increase in both temperature and strain rate.