The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At ...The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.展开更多
A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-...A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.展开更多
A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based ...A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.展开更多
In order to qualify shock resistance performance of shipboard equipments and simulate real underwater explosion environment,a novel dual-pulse shock test machine is proposed.The new machine will increase testing capab...In order to qualify shock resistance performance of shipboard equipments and simulate real underwater explosion environment,a novel dual-pulse shock test machine is proposed.The new machine will increase testing capability and meet special shock testing requirement.Two key parts of the machine,the velocity generator and the shock pulse regulator,play an important role in producing the positive acceleration pulse and the succeeding negative acceleration pulse,respectively.The generated dual-pulse shock for test articles is in conformity with an anti-shock test specification.Based on the impact theory,a nonlinear dynamic model of the hydraulically-actuated test machine is established with thorough analysis on its mechanism that involves conversion of gas potential energy and dissipation of kinetic energy.Simulation results have demonstrated that the proposed machine is able to produce a double-pulse acceleration shock in the time domain or a desired shock response spectrum in the frequency domain,which sets up a base for the construction of the machine.展开更多
AIM:To investigate whether electroacupuncture(EA)at Zusanli(ST36)prevents intestinal barrier and remote organ dysfunction following prolonged hemorrhagic shock through a vagus anti-inflammatory mechanism.METHODS:Sprag...AIM:To investigate whether electroacupuncture(EA)at Zusanli(ST36)prevents intestinal barrier and remote organ dysfunction following prolonged hemorrhagic shock through a vagus anti-inflammatory mechanism.METHODS:Sprague-Dawley rats were subjected to about 45%of total blood volume loss followed by delayed fluid replacement(DFR)with Ringer lactate 3h after hemorrhage.In a first study,rats were randomly divided into six groups:(1)EAN:EA at non-channel acupoints followed by DFR;(2)EA:EA at ST36 after hemorrhage followed by DFR;(3)VGX/EA:vagotomy(VGX)before EA at ST36 and DFR;(4)VGX/EAN:VGX before EAN and DFR;(5)α-bungarotoxin(α-BGT)/EA:intraperitoneal injection ofα-BGT before hemorrhage,followed by EA at ST36 and DFR;and(6)α-BGT/EAN group:α-BGT injection before hemorrhage followed by EAN and DFR.Survival and mean arterial pressure(MAP)were monitored over the next 12 h.In a second study,with the same grouping and treatment,cytokine levels in plasma and intestine,organ parameters,gut injury score,gut permeability to 4 kDa FITC-dextran,and expression and distribution of tight junction protein ZO-1 were evaluated.RESULTS:MAP was significantly lowered after blood loss;EA at ST36 improved the blood pressure at corresponding time points 3 and 12 h after hemorrhage.EA at ST36 reduced tumor necrosis factor-αand interleukin(IL)-6 levels in both plasma and intestine homogenates after blood loss and DFR,while vagotomy or intraperitoneal injection ofα-BGT before EA at ST36reversed its anti-inflammatory effects,and EA at ST36did not influence IL-10 levels in plasma and intestine.EA at ST36 alleviated the injury of intestinal villus,the gut injury score being significantly lower than that of EAN group(1.85±0.33 vs 3.78±0.59,P<0.05).EA at ST36 decreased intestinal permeability to FITCdextran compared with EAN group(856.95 ng/mL±90.65 ng/mL vs 2305.62 ng/mL±278.32 ng/mL,P<0.05).EA at ST36 significantly preserved ZO-1 protein expression and localization at 12 h after hemorrhage.However,EA at non-channel acupoints had no such effect,and abdominal vagotomy andα-BGT treatment could weaken or eliminate the effects of EA at ST36.Besides,EA at ST36 decreased blood aminotransferase,MB isoenzyme of creatine kinase and creatinine vs EAN group at corresponding time points.At the end of 12-h experiment,the survival rate of the EA group was significantly higher than that of the other groups.CONCLUSION:EA at ST36 attenuates the systemic inflammatory response,protects intestinal barrier integrity,improves organ function and survival rate after hemorrhagic shock via activating the cholinergic antiinflammatory mechanism.展开更多
AIM: To investigate the effect of carbachol on gastrointestinal function in a dog model of oral resuscitation for burn shock. METHODS: Twenty Beagle dogs with intubation of the carotid artery, jugular vein and jejunum...AIM: To investigate the effect of carbachol on gastrointestinal function in a dog model of oral resuscitation for burn shock. METHODS: Twenty Beagle dogs with intubation of the carotid artery, jugular vein and jejunum for 24 h were subjected to 35% total body surface area fullthickness burns, and were divided into three groups: no fluid resuscitation (NR, n = 10), in which animals did not receive fluid by any means in the first 24 h postburn; oral fluid resuscitation (OR, n = 8), in which dogs were gavaged with glucose-electrolyte solution (GES) with volume and rate consistent with the Parkland formula; and oral fluid with carbachol group (OR/CAR, n = 8), in which dogs were gavaged with GES containing carbachol (20 μg/kg), with the same volume and rate as the OR group. Twenty-four hours after burns, all animals were given intravenous fluid replacement, and 72 h after injury, they received nutritional support. Hemodynamicand gastrointestinal parameters were measured serially with animals in conscious and cooperative state. RESULTS: The mean arterial pressure, cardiac output and plasma volume dropped markedly, and gastrointestinal tissue perfusion was reduced obviously after the burn injury in all the three groups. Hemodynamic parameters and gastrointestinal tissue perfusion in the OR and OR/CAR groups were promoted to pre-injury level at 48 and 72 h, respectively, while hemodynamic parameters in the NR group did not return to pre-injury level till 72 h, and gastrointestinal tissue perfusion remained lower than pre-injury level until 120 h post-burn. CO 2 of the gastric mucosa and intestinal mucosa blood flow of OR/CAR groups were 56.4 ± 4.7 mmHg and 157.7 ± 17.7 blood perfusion units (BPU) at 24 h postburn, respectively, which were significantly superior to those in the OR group (65.8 ± 5.8 mmHg and 127.7 ± 11.9 BPU, respectively, all P < 0.05). Gastric emptying and intestinal absorption rates of GES were significantly reduced to the lowest level (52.8% and 23.7% of pre-injury levels) in the OR group at about 2 and 4 h post-burn, and did not return to 80% of pre-injury level until 24 h. In the first 24 h postburn, the rate of gastric emptying and intestinal water absorption were elevated by a mean 15.7% and 11.5%, respectively, in the OR/CAR group compared with the OR group. At 5 days, the mortality in the NR group was 30% (3/10), 12.5% in the OR group (1/8), and none in the OR/CAR group. CONCLUSION: Carbachol had a beneficial effect on oral resuscitation of burn shock by promoting gastric emptying and intestinal absorption in our canine model.展开更多
Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing me...Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber. The fluid mesh distortion was controlled by the CEL language, and the fluid struc^tre interaction mathematical model was established. The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique. The local sensitive computational area was meshed by prismatic grid, which could reduce the negative volume problem during the simulation. The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads. Flow characteristic and dynamics characteristic were obtained. The pressure distribution and the displacement of circulation value were obtained, and the acceleration curve of circulation valve was simulated and analyzed. The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber, which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.展开更多
The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 b...The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analy- sis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pres- sure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction.展开更多
For qualifying the anti-shock performance of shipboard equipments and simulating actual underwater explosion environments, a novel dual-wave shock test machine is proposed to increase testing capability of shock test ...For qualifying the anti-shock performance of shipboard equipments and simulating actual underwater explosion environments, a novel dual-wave shock test machine is proposed to increase testing capability of shock test machines as well as to meet certain shock testing specification. The machine can generate a double-pulse acceleration shock for test articles according to specification defined in BV043/85. On the basis of the impact theory, a nonlinear dynamic model of the hydraulically-actuated test machine is established with thorough analysis on its mechanism which involves conversion of gas potential energy and dissipation of kinetic energy. Simulation results have demonstrated that the machine can produce a double-pulse acceleration shock in the time domain or a desired shock response spectrum in the frequency domain, which sets a theoretical base for the construction of the proposed machine.展开更多
Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85-131 GPa. The longitudinal sound speeds axe obtained from the time-resolved particle speed profiles of the specimen me...Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85-131 GPa. The longitudinal sound speeds axe obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector （VISAR） technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20-70 GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state （EOS）, shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of P/η^1/3 in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.展开更多
Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals.In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry ti...Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals.In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry tilt grain boundary(ATGB) under shock-loading is performed. We find that the shock response of asymmetric grain boundaries is quite different from that of symmetric grain boundaries. Especially, our simulation proves that shock can induce migration of asymmetric grain boundary in iron. We also find that the shape and local structure of grain boundary(GB) would not be changed during shock-induced migration of Σ3 [110] ATGB, while the phase transformation near the GB could affect migration of GB. The most important discovery is that the shock-induced shear stress difference between two sides of GB is the key factor leading to GB migration. Our simulation involves a variety of piston velocities, and the migration of GB seems to be less sensitive to the piston velocity. Finally, the kinetics of GB migration at lattice level is discussed. Our work firstly reports the simulation of shock-induced grain boundary migration in iron. It is of great significance to the theory of GB migration and material engineering.展开更多
Basically on the multi-body system dynamics,the virtual prototype of the hydraulic shock absorber for the bench test is developed in the ADAMS environment.Dynamic behaviors of the absorber are studied by both computer...Basically on the multi-body system dynamics,the virtual prototype of the hydraulic shock absorber for the bench test is developed in the ADAMS environment.Dynamic behaviors of the absorber are studied by both computer simulation and real test.Numerical predictions of dynamic responses are produced by the established virtual prototype of the absorber and compared with experimental results.It has been shown from the comparison that the vibration behaviors of the prototype with hysteretic damping characteristics are considered to be more identical with the bench test results than those of the same prototype with piecewise linear damping properties are.The current virtual prototype of the shock absorber is correct and can be a developing terrace for the optimizing design of the absorber and matching capability of the whole car.展开更多
The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide ...The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide spectrum and irreversible destructive nature of intense shock waves.This work proposes a novel approach for actively controlling intense shock waves in solids,inspired by the principles of optical and explosive lenses.Specifically,by designing a shock wave convex lens composed of a low-shock-impedance material embedded in a high-shock-impedance matrix,we prove the feasibility of transforming a planar shock into a spherically converging shock.This is based on oblique shock theory,according to which shock waves pass through an oblique interface and then undergo deflection.Both experimental and simulation results demonstrate that,as expected,the obtained local spherical shock wave has a wavefront that is nearly perfectly spherical and uniform in pressure.Thus,this work proves the possibility of generating spherical shock waves using plate-impact experiments and highlights the potential of further exploration of the manipulation of shock waves in solids.It also contributes an innovative perspective for both armor penetration technologies and shock wave mitigation strategies.展开更多
Failure wave generations on both impacted surface and internal surface inside the sample have been observed for K9 glass under planar shock wave loading,which demonstrates that formation of failure wave is a process r...Failure wave generations on both impacted surface and internal surface inside the sample have been observed for K9 glass under planar shock wave loading,which demonstrates that formation of failure wave is a process related to the surface microcracks nuclei developing.Based on these observations,a hypothesis is suggested that the large local strains resulting from the rearrangement of SiO4 tetrahedral within the permanent densification region behind the shock wave front and then strains releasing due to the surface microcracks developing could be responsible for the failure wave generation.展开更多
Dynamic response and damage evolution of Zr_(70)Cu_(13)Ni_(9.8)Al_(3.6)Nb_(3.4)Y_(0.2) bulk metallic glass(Zr-based BMG)under impact pressure ranging from 4.03 GPa to 27.22 GPa were studied.The Hugoniot Elastic Limit(...Dynamic response and damage evolution of Zr_(70)Cu_(13)Ni_(9.8)Al_(3.6)Nb_(3.4)Y_(0.2) bulk metallic glass(Zr-based BMG)under impact pressure ranging from 4.03 GPa to 27.22 GPa were studied.The Hugoniot Elastic Limit(HEL)and the spalling Strength(σ_(sp))were measured as 7.09 GPa and 2.28 GPa,and the curve of impact velocity(D)and particle velocity(u)were also obtained.Under the strain rate of~10^(5)s^(-1),local crystallization phenomenon was observed.As increasing the impact pressure,the failure mode of Zr-based BMG changed from spallation to fragmentation caused by the combination of spalling cracks and longitudinal cracks.Cone-cup structures were also observed in the internal spalling zone via nano-CT characterization.When increasing the impact pressure,the thickness of Zr-based BMG increased after impact and the remelting and cladding layers were also observed on the fracture surfaces.The fragments of the specimen were welded after impact due to the high temperature remelting,which causes plastic deformation of Zr-based BMG under shock loading.展开更多
Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at ...Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirm- ing the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.展开更多
Based on the theory and the practical experiences of linearity design of feasible design area and inverse solution of non linear outer characteristic of suspension shock absorber, in accordance with non linearity ou...Based on the theory and the practical experiences of linearity design of feasible design area and inverse solution of non linear outer characteristic of suspension shock absorber, in accordance with non linearity outer characteristic formed by open up damping coefficient, full open damping coefficient and smoothness to safety ratio of suspension shock absorber, a method and a research conclusion of the feasible design and inverse solution for the basic problems of designing and inverse solution of non linear outer characteristic of suspension damping components are provided.展开更多
A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater ex...A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater explosion environments in laboratory as well as increase the testing capability of shock test machine. In order to produce the required negative shock pulse in the given time duration, four hydraulic actuators are utilized. The model is then used to formulate an advanced feedforward controller for the system to produce the required negative waveform and to address the motion synchronization of the four cylinders. The model provides a safe and easily controllable way to perform a ＂virtual testing＂ before starting potentially destructive tests on specimen and to predict performance of the system. Simulation results have demonstrated the effectiveness of the controller.展开更多
Based on the concept of hydraulic dissipation of kinetic energy, a novel shock wave regulator, which is composed of a damper and an extemally triggered valve, is presented with thorough analyses on its working mechani...Based on the concept of hydraulic dissipation of kinetic energy, a novel shock wave regulator, which is composed of a damper and an extemally triggered valve, is presented with thorough analyses on its working mechanism. By establishing motion equations of each component of the regulator and simulating the dynamic behavior of the whole system, the shock wave regulator is demonstrated numerically to be able to change the width and amplitude of shock pulses. Prompt and easy adjustment can be achieved by changing the equivalent flow area of damping orifices and consequently the closing velocity of the flow area of a valve, which makes it applicable to different impact testing.展开更多
Metal matrix composites (MMCs) offer extra strength and high temperature capabilities in comparison with unrein-forced metals. Aluminum composites possess higher stiffness, strength, fatigue properties and low weight ...Metal matrix composites (MMCs) offer extra strength and high temperature capabilities in comparison with unrein-forced metals. Aluminum composites possess higher stiffness, strength, fatigue properties and low weight advantages. Carbon fiber reinforced Al composites (Al-Cf) and silicon carbide particulate reinforced Al composites (AI-SiCp) were shock densified using axisymmetric assemblies for underwater explosions. Unidirectional planar shock waves were applied to obtain uniform consolidation of the composites. The energy generator was a high explosive of 6.9 km/s detonation velocity. Irregular morphological powders of Al were the base material. The reinforcement ratio was 15 Vol. pet for Al-Cf composites and 30 Vol. pet for AI-SiCp composites. The microstructural and the strength characteristics of the shock consolidated Al composites are reported.展开更多
基金the National Natural Science Foundation of China(U2241245,91960202 and 52271012)the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(6142902220301)+2 种基金the Aeronautical Science Foundation of China(2022Z053092001)the Shanghai Engineering Research Center of High-Performance Medical Device Materials(20DZ2255500)the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics(2022JCJQLB05702).
文摘The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.
基金supported by the National Natural Science Foundation of China (Grant No.12072331)the Science Challenge Project (Grant No.TZ2018001)+2 种基金the Japan Society for the Promotion of Science (Grant Nos.17H04820 and 21H01677)the Foundation of the United Laboratory of High-Pressure Physics and Earthquake Scienceperformed under the approval of the Photon Factory Program Advisory Committee (Proposal Nos.2016S2-006 and 2020G680)。
文摘A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.
基金Chinese Navy Warship Research Center(No.05131-1046)
文摘A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.
文摘In order to qualify shock resistance performance of shipboard equipments and simulate real underwater explosion environment,a novel dual-pulse shock test machine is proposed.The new machine will increase testing capability and meet special shock testing requirement.Two key parts of the machine,the velocity generator and the shock pulse regulator,play an important role in producing the positive acceleration pulse and the succeeding negative acceleration pulse,respectively.The generated dual-pulse shock for test articles is in conformity with an anti-shock test specification.Based on the impact theory,a nonlinear dynamic model of the hydraulically-actuated test machine is established with thorough analysis on its mechanism that involves conversion of gas potential energy and dissipation of kinetic energy.Simulation results have demonstrated that the proposed machine is able to produce a double-pulse acceleration shock in the time domain or a desired shock response spectrum in the frequency domain,which sets up a base for the construction of the machine.
基金Supported by The National Basic Research Program of China,973 Program,Grant No.2012CB518101
文摘AIM:To investigate whether electroacupuncture(EA)at Zusanli(ST36)prevents intestinal barrier and remote organ dysfunction following prolonged hemorrhagic shock through a vagus anti-inflammatory mechanism.METHODS:Sprague-Dawley rats were subjected to about 45%of total blood volume loss followed by delayed fluid replacement(DFR)with Ringer lactate 3h after hemorrhage.In a first study,rats were randomly divided into six groups:(1)EAN:EA at non-channel acupoints followed by DFR;(2)EA:EA at ST36 after hemorrhage followed by DFR;(3)VGX/EA:vagotomy(VGX)before EA at ST36 and DFR;(4)VGX/EAN:VGX before EAN and DFR;(5)α-bungarotoxin(α-BGT)/EA:intraperitoneal injection ofα-BGT before hemorrhage,followed by EA at ST36 and DFR;and(6)α-BGT/EAN group:α-BGT injection before hemorrhage followed by EAN and DFR.Survival and mean arterial pressure(MAP)were monitored over the next 12 h.In a second study,with the same grouping and treatment,cytokine levels in plasma and intestine,organ parameters,gut injury score,gut permeability to 4 kDa FITC-dextran,and expression and distribution of tight junction protein ZO-1 were evaluated.RESULTS:MAP was significantly lowered after blood loss;EA at ST36 improved the blood pressure at corresponding time points 3 and 12 h after hemorrhage.EA at ST36 reduced tumor necrosis factor-αand interleukin(IL)-6 levels in both plasma and intestine homogenates after blood loss and DFR,while vagotomy or intraperitoneal injection ofα-BGT before EA at ST36reversed its anti-inflammatory effects,and EA at ST36did not influence IL-10 levels in plasma and intestine.EA at ST36 alleviated the injury of intestinal villus,the gut injury score being significantly lower than that of EAN group(1.85±0.33 vs 3.78±0.59,P<0.05).EA at ST36 decreased intestinal permeability to FITCdextran compared with EAN group(856.95 ng/mL±90.65 ng/mL vs 2305.62 ng/mL±278.32 ng/mL,P<0.05).EA at ST36 significantly preserved ZO-1 protein expression and localization at 12 h after hemorrhage.However,EA at non-channel acupoints had no such effect,and abdominal vagotomy andα-BGT treatment could weaken or eliminate the effects of EA at ST36.Besides,EA at ST36 decreased blood aminotransferase,MB isoenzyme of creatine kinase and creatinine vs EAN group at corresponding time points.At the end of 12-h experiment,the survival rate of the EA group was significantly higher than that of the other groups.CONCLUSION:EA at ST36 attenuates the systemic inflammatory response,protects intestinal barrier integrity,improves organ function and survival rate after hemorrhagic shock via activating the cholinergic antiinflammatory mechanism.
基金Supported by The Special Foundation of the 11th five-yearPlan for Military Medical Projects, No. 06Z055
文摘AIM: To investigate the effect of carbachol on gastrointestinal function in a dog model of oral resuscitation for burn shock. METHODS: Twenty Beagle dogs with intubation of the carotid artery, jugular vein and jejunum for 24 h were subjected to 35% total body surface area fullthickness burns, and were divided into three groups: no fluid resuscitation (NR, n = 10), in which animals did not receive fluid by any means in the first 24 h postburn; oral fluid resuscitation (OR, n = 8), in which dogs were gavaged with glucose-electrolyte solution (GES) with volume and rate consistent with the Parkland formula; and oral fluid with carbachol group (OR/CAR, n = 8), in which dogs were gavaged with GES containing carbachol (20 μg/kg), with the same volume and rate as the OR group. Twenty-four hours after burns, all animals were given intravenous fluid replacement, and 72 h after injury, they received nutritional support. Hemodynamicand gastrointestinal parameters were measured serially with animals in conscious and cooperative state. RESULTS: The mean arterial pressure, cardiac output and plasma volume dropped markedly, and gastrointestinal tissue perfusion was reduced obviously after the burn injury in all the three groups. Hemodynamic parameters and gastrointestinal tissue perfusion in the OR and OR/CAR groups were promoted to pre-injury level at 48 and 72 h, respectively, while hemodynamic parameters in the NR group did not return to pre-injury level till 72 h, and gastrointestinal tissue perfusion remained lower than pre-injury level until 120 h post-burn. CO 2 of the gastric mucosa and intestinal mucosa blood flow of OR/CAR groups were 56.4 ± 4.7 mmHg and 157.7 ± 17.7 blood perfusion units (BPU) at 24 h postburn, respectively, which were significantly superior to those in the OR group (65.8 ± 5.8 mmHg and 127.7 ± 11.9 BPU, respectively, all P < 0.05). Gastric emptying and intestinal absorption rates of GES were significantly reduced to the lowest level (52.8% and 23.7% of pre-injury levels) in the OR group at about 2 and 4 h post-burn, and did not return to 80% of pre-injury level until 24 h. In the first 24 h postburn, the rate of gastric emptying and intestinal water absorption were elevated by a mean 15.7% and 11.5%, respectively, in the OR/CAR group compared with the OR group. At 5 days, the mortality in the NR group was 30% (3/10), 12.5% in the OR group (1/8), and none in the OR/CAR group. CONCLUSION: Carbachol had a beneficial effect on oral resuscitation of burn shock by promoting gastric emptying and intestinal absorption in our canine model.
基金Project(51275542) supported by the National Natural Science Foundation of Chinaproject(CDJXS12110010) supported by the Fundamental Research Funds for the Central Universities of China
文摘Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber. The fluid mesh distortion was controlled by the CEL language, and the fluid struc^tre interaction mathematical model was established. The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique. The local sensitive computational area was meshed by prismatic grid, which could reduce the negative volume problem during the simulation. The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads. Flow characteristic and dynamics characteristic were obtained. The pressure distribution and the displacement of circulation value were obtained, and the acceleration curve of circulation valve was simulated and analyzed. The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber, which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.
基金supported by the National Natural Science Foundation of China (10972214 and 11172278)the Fundamental Research Funds for the Central Universities (WK2090050014)
文摘The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analy- sis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pres- sure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction.
基金supported by China Naval Armament Department (No. 05131/1046).
文摘For qualifying the anti-shock performance of shipboard equipments and simulating actual underwater explosion environments, a novel dual-wave shock test machine is proposed to increase testing capability of shock test machines as well as to meet certain shock testing specification. The machine can generate a double-pulse acceleration shock for test articles according to specification defined in BV043/85. On the basis of the impact theory, a nonlinear dynamic model of the hydraulically-actuated test machine is established with thorough analysis on its mechanism which involves conversion of gas potential energy and dissipation of kinetic energy. Simulation results have demonstrated that the machine can produce a double-pulse acceleration shock in the time domain or a desired shock response spectrum in the frequency domain, which sets a theoretical base for the construction of the proposed machine.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10232040 and 10672149)the foundation of Laboratory for Shock Wave and Detonation Physics Research, China Academy of Engineering Physics (Grant No 9140C6702020603)
文摘Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85-131 GPa. The longitudinal sound speeds axe obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector （VISAR） technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20-70 GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state （EOS）, shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of P/η^1/3 in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.
基金Project supported by the Fundamental Research for the Central Universities of Chinathe National Key Laboratory Project of Shock Wave and Detonation Physics of China+4 种基金the Science and Technology Foundation of National Key Laboratory of Shock Wave and Detonation Physics of Chinathe National Key R&D Program of China(Grant No.2017YFB0202303)the National Natural Science Foundation of China(Grant Nos.51871094,51871095,51571088,NSFC-NSAF U1530151,and U1830138)the Natural Science Foundation of Hunan Province of China(Grant No.2018JJ2036)the Science Challenge Project of China(Grant No.TZ2016001)
文摘Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals.In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry tilt grain boundary(ATGB) under shock-loading is performed. We find that the shock response of asymmetric grain boundaries is quite different from that of symmetric grain boundaries. Especially, our simulation proves that shock can induce migration of asymmetric grain boundary in iron. We also find that the shape and local structure of grain boundary(GB) would not be changed during shock-induced migration of Σ3 [110] ATGB, while the phase transformation near the GB could affect migration of GB. The most important discovery is that the shock-induced shear stress difference between two sides of GB is the key factor leading to GB migration. Our simulation involves a variety of piston velocities, and the migration of GB seems to be less sensitive to the piston velocity. Finally, the kinetics of GB migration at lattice level is discussed. Our work firstly reports the simulation of shock-induced grain boundary migration in iron. It is of great significance to the theory of GB migration and material engineering.
基金the Shanghai Administration of Education under Shanghai Key Disciplines Development Fund ProjectShanghai Automotive Technology Development Foundation under Contract NO.1 325 A
文摘Basically on the multi-body system dynamics,the virtual prototype of the hydraulic shock absorber for the bench test is developed in the ADAMS environment.Dynamic behaviors of the absorber are studied by both computer simulation and real test.Numerical predictions of dynamic responses are produced by the established virtual prototype of the absorber and compared with experimental results.It has been shown from the comparison that the vibration behaviors of the prototype with hysteretic damping characteristics are considered to be more identical with the bench test results than those of the same prototype with piecewise linear damping properties are.The current virtual prototype of the shock absorber is correct and can be a developing terrace for the optimizing design of the absorber and matching capability of the whole car.
基金supported by the National Key R&D Program of China(Grant No.2021YFB3802303)the National Natural Science Foundation of China(Grant Nos.12302493 and 12525211).
文摘The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide spectrum and irreversible destructive nature of intense shock waves.This work proposes a novel approach for actively controlling intense shock waves in solids,inspired by the principles of optical and explosive lenses.Specifically,by designing a shock wave convex lens composed of a low-shock-impedance material embedded in a high-shock-impedance matrix,we prove the feasibility of transforming a planar shock into a spherically converging shock.This is based on oblique shock theory,according to which shock waves pass through an oblique interface and then undergo deflection.Both experimental and simulation results demonstrate that,as expected,the obtained local spherical shock wave has a wavefront that is nearly perfectly spherical and uniform in pressure.Thus,this work proves the possibility of generating spherical shock waves using plate-impact experiments and highlights the potential of further exploration of the manipulation of shock waves in solids.It also contributes an innovative perspective for both armor penetration technologies and shock wave mitigation strategies.
基金Supported by the Science Foundation of China Academy of Engineering Physics,Contract No.9401001.
文摘Failure wave generations on both impacted surface and internal surface inside the sample have been observed for K9 glass under planar shock wave loading,which demonstrates that formation of failure wave is a process related to the surface microcracks nuclei developing.Based on these observations,a hypothesis is suggested that the large local strains resulting from the rearrangement of SiO4 tetrahedral within the permanent densification region behind the shock wave front and then strains releasing due to the surface microcracks developing could be responsible for the failure wave generation.
文摘Dynamic response and damage evolution of Zr_(70)Cu_(13)Ni_(9.8)Al_(3.6)Nb_(3.4)Y_(0.2) bulk metallic glass(Zr-based BMG)under impact pressure ranging from 4.03 GPa to 27.22 GPa were studied.The Hugoniot Elastic Limit(HEL)and the spalling Strength(σ_(sp))were measured as 7.09 GPa and 2.28 GPa,and the curve of impact velocity(D)and particle velocity(u)were also obtained.Under the strain rate of~10^(5)s^(-1),local crystallization phenomenon was observed.As increasing the impact pressure,the failure mode of Zr-based BMG changed from spallation to fragmentation caused by the combination of spalling cracks and longitudinal cracks.Cone-cup structures were also observed in the internal spalling zone via nano-CT characterization.When increasing the impact pressure,the thickness of Zr-based BMG increased after impact and the remelting and cladding layers were also observed on the fracture surfaces.The fragments of the specimen were welded after impact due to the high temperature remelting,which causes plastic deformation of Zr-based BMG under shock loading.
基金Project supported by the National Natural Science Foundation of China(Grant No.11172281)
文摘Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirm- ing the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.
文摘Based on the theory and the practical experiences of linearity design of feasible design area and inverse solution of non linear outer characteristic of suspension shock absorber, in accordance with non linearity outer characteristic formed by open up damping coefficient, full open damping coefficient and smoothness to safety ratio of suspension shock absorber, a method and a research conclusion of the feasible design and inverse solution for the basic problems of designing and inverse solution of non linear outer characteristic of suspension damping components are provided.
文摘A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater explosion environments in laboratory as well as increase the testing capability of shock test machine. In order to produce the required negative shock pulse in the given time duration, four hydraulic actuators are utilized. The model is then used to formulate an advanced feedforward controller for the system to produce the required negative waveform and to address the motion synchronization of the four cylinders. The model provides a safe and easily controllable way to perform a ＂virtual testing＂ before starting potentially destructive tests on specimen and to predict performance of the system. Simulation results have demonstrated the effectiveness of the controller.
基金the Naval Warship Research Department of Defense(No05131/1046)
文摘Based on the concept of hydraulic dissipation of kinetic energy, a novel shock wave regulator, which is composed of a damper and an extemally triggered valve, is presented with thorough analyses on its working mechanism. By establishing motion equations of each component of the regulator and simulating the dynamic behavior of the whole system, the shock wave regulator is demonstrated numerically to be able to change the width and amplitude of shock pulses. Prompt and easy adjustment can be achieved by changing the equivalent flow area of damping orifices and consequently the closing velocity of the flow area of a valve, which makes it applicable to different impact testing.
文摘Metal matrix composites (MMCs) offer extra strength and high temperature capabilities in comparison with unrein-forced metals. Aluminum composites possess higher stiffness, strength, fatigue properties and low weight advantages. Carbon fiber reinforced Al composites (Al-Cf) and silicon carbide particulate reinforced Al composites (AI-SiCp) were shock densified using axisymmetric assemblies for underwater explosions. Unidirectional planar shock waves were applied to obtain uniform consolidation of the composites. The energy generator was a high explosive of 6.9 km/s detonation velocity. Irregular morphological powders of Al were the base material. The reinforcement ratio was 15 Vol. pet for Al-Cf composites and 30 Vol. pet for AI-SiCp composites. The microstructural and the strength characteristics of the shock consolidated Al composites are reported.
