The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytic...The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytical study of the evolution of the nose shape of larger hollow projectiles under hypersonic penetration.In the hypersonic penetration test,eight ogive-nose AerMet100 steel projectiles with a diameter of 40 mm were launched to hit concrete targets with impact velocities that ranged from 1351 to 1877 m/s.Severe erosion of the projectiles was observed during high-speed penetration of heterogeneous targets,and apparent localized mushrooming occurred in the front nose of recovered projectiles.By examining the damage to projectiles,a linear relationship was found between the relative length reduction rate and the initial kinetic energy of projectiles in different penetration tests.Furthermore,microscopic analysis revealed the forming mechanism of the localized mushrooming phenomenon for eroding penetration,i.e.,material spall erosion abrasion mechanism,material flow and redistribution abrasion mechanism and localized radial upsetting deformation mechanism.Finally,a model of highspeed penetration that included erosion was established on the basis of a model of the evolution of the projectile nose that considers radial upsetting;the model was validated by test data from the literature and the present study.Depending upon the impact velocity,v0,the projectile nose may behave as undistorted,radially distorted or hemispherical.Due to the effects of abrasion of the projectile and enhancement of radial upsetting on the duration and amplitude of the secondary rising segment in the pulse shape of projectile deceleration,the predicted DOP had an upper limit.展开更多
For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles...For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.展开更多
An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic traje...An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.展开更多
Al-Sc and Al-Ti semi-infinite targets were impacted by high-speed projectiles at velocities of 0.8, 1.0, 1.2 and 1.5 km/s, respectively. It is found that the Al-Sc targets demonstrate more excellent ability to resist ...Al-Sc and Al-Ti semi-infinite targets were impacted by high-speed projectiles at velocities of 0.8, 1.0, 1.2 and 1.5 km/s, respectively. It is found that the Al-Sc targets demonstrate more excellent ability to resist high-speed impact. It is concluded that different microstructures of Al-Sc and Al-Ti alloys, including different grain sizes and secondary particles precipitated in the matrix, result in their greatly different capabilities of resisting impact. Furthermore, the effect of the size range ofnanoscale A13Sc precipitate in A1-Sc alloy on the resistance of high-speed impact was investigated. In addition, computer simulations and validation of these simulations were developed which fairly accurately represented residual crater shapes/geometries. Validated computer simulations allowed representative extrapolations of impact craters well beyond the laboratory where melt and solidification occurred at the crater wall, especially for hypervelocity impact （〉5 km/s）.展开更多
The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the pe...The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0展开更多
The initial oblique and attacking angles as well as the asymmetrical nose abrasion may lead to bending or even fracture of a projectile,and the penetration efficiency decreases distinctly.The structural stability of a...The initial oblique and attacking angles as well as the asymmetrical nose abrasion may lead to bending or even fracture of a projectile,and the penetration efficiency decreases distinctly.The structural stability of a high-speed projectile non-normally penetrating into concrete and the parametric influences involved are analyzed with the mass abrasion taken into account.By considering the symmetrical or asymmetrical nose abrasion as well as the initial oblique and attacking angles,both the axial and the transverse drag forces acting on the projectile are derived.Based on the ideal elastic-plastic yield criterion,an approach is proposed for predicting the limit striking velocity（LSV）that is the highest velocity at which no yielding failure has occurred and the projectile can still maintain its integral structural stability.Furthermore,some particular penetration scenarios are separately discussed in detail.Based on the engineering model for the mass loss and nose-blunting of ogive-nose projectiles established in Part I of this study,the above approach is validated by several high-speed penetration tests.The analysis on parametric influences indicates that the LSV is reduced with an increase in the asymmetrical nose abrasion,thelength-diameter-ratio,and the concrete strength,as well as the oblique and attacking angles.Also,the LSV raises with an increase in the initial caliber-radius-head（CRH）and the dimensionless cartridge thickness of a projectile.展开更多
Environmental impact evaluation system boundary of high-speed railway was defined based on the total life cycle theory,and the index system to evaluate the environmental impact of high-speed railway was established wi...Environmental impact evaluation system boundary of high-speed railway was defined based on the total life cycle theory,and the index system to evaluate the environmental impact of high-speed railway was established with the fuzzy analytic hierarchy method,and the matter-element evaluation model was established on the basis of the extension theory.By calculating its comprehensive interrelatedness,the evaluation rank of environment impacts of high-speed railway was determined.The numerical example shows that the model has vast prospect,which can not only expand the application areas of extension theory,but also change the traditional evaluation methods and provide new ideas and means for environmental impact evaluation of high-speed railway.展开更多
Split Hopkinson pressure bar(SHPB)tests were conducted on pre-rolled AZ31 magnesium alloy at 150–350℃ with strain rates of 2150s-1,3430s^(-1) and 4160s-1.The mechanical response,microstructural evolution and accommo...Split Hopkinson pressure bar(SHPB)tests were conducted on pre-rolled AZ31 magnesium alloy at 150–350℃ with strain rates of 2150s-1,3430s^(-1) and 4160s-1.The mechanical response,microstructural evolution and accommodation mechanism of the pre-rolled AZ31 magnesium alloy under high-speed impact loading were investigated.The twin and shear band are prevailing at low temperature,and the coexistence of twins and recrystallized grains is the dominant microstructure at medium temperature,while at high temperature,dynamic recrystallization(DRX)is almost complete.The increment of temperature reduces the critical condition difference between twinning and DRX,and the recrystallized temperature decreases with increasing strain rate.The mechanical response is related to the competition among the shear band strengthen,the twin strengthen and the fine grain strengthen and determined by the prevailing grain structure.The fine grain strengthen could compensate soften caused by the temperature increase and the reduction of twin and shear band.During high-speed deformation,different twin variants,introduced by pre-rolling,induce different deformation mechanism to accommodate plastic deformation and are in favor for non-basal slip.At low temperature,the high-speed deformation is achieved by twinning,dislocation slip and the following deformation shear band at different deformation stages.At high temperature,the high-speed deformation is realized by twinning and dislocation slip of early deformation stage,transition shear band of medium deformation stage and DRX of final deformation stage.展开更多
In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of sp...In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode(2003).However,these IF coefficient values neglect the effects of very high speeds(>200 km/h)and soil-structure interaction(SSI).In this work,a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported.Three different configurations,each for the three-dimensional(3D)continuous and integral bridge,are considered.Also,single-track(1-T)and two-track(2-T)“real train”loading cases for both these bridge types are considered.Subsequently,finite element analysis of the full-scale 3D bridge models,to identify their IF values,considering the effects of SSI for three different soil conditions,is conducted.The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode(2003).The results reveal that with a loss of soil stiffness,the IF value reduces;thus,it confirms the importance of SSI analysis.展开更多
This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of ol...This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of old architecture and public buildings.We carried out penetration experiments in which four clay-fired brick walls employing two different patterns were subjected to impact from small high-speed projectile,i.e.12.7 mm armor-piercing explosive incendiary projectile and material tests in which the static and dynamic compressive strengths of clay-fired brick and mortar were determined by quasi-static and SHPB(Split Hopkinson Pressure Bar)tests.The experimental data include hit and exit velocities,damage configuration of clay brick masonry and mechanical properties of material at low and high strain rates,though which influence of thickness and bonding patterns of wall on kinetic loss of bullet,the damage patterns of masonry observed experimentally and dynamic increase of material strengths are analyzed.To keep minimum boundary inconsistency with reality,full 3D detailed finite element model consisting of two different material is established.Sharing common nodes and employing automatic tiebreak contact are combined to reduce computational time usage of large-scale model.For description of clay-fired brick and mortar RiedeleHiermaiereThoma(RHT)material model is employed.Material parameter set is derived based on experimental data,available literature and engineering assumptions.The numerical simulations study the mesh resolution dependency of material model,reproduce the crucial phenomena of masonry in experiment acceptably and offer more time-resolved insight into motion of bullet in the process of penetration.The feasibility of means of constructing finite element model and applying RHT model to the masonry herein and analogous constructions is explored through numerical investigation.展开更多
Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different ...Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach–Based on large eddy simulation(LES)method and Kirchhoff–Ffowcs Williams and Hawkings(K-FWH)equations,the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings–The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train.The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train,the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car,and the quadrupole sources are mainly distributed in the wake area.When the train runs at three speed levels of 400,500 and 600 km$h1,respectively,the radiated energy of quadrupole source is 62.4%,63.3%and 71.7%,respectively,which exceeds that of dipole sources.Originality/value–This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.展开更多
The impact and penetration of a projectile in a particle-laden space, which are expected to have frequently occurred during the formation of the solar system and will occur in the case of an impact probe for future pl...The impact and penetration of a projectile in a particle-laden space, which are expected to have frequently occurred during the formation of the solar system and will occur in the case of an impact probe for future planetary exploration, were experimentally simulated by using the ballistic range. A two-dimensional sheet made from small glass beads or emery powder was formed by the free-falling device through a long slit in the test chamber evacuated down to about 35 Pa. A polycarbonate projectile of a hemi-sphere-cylinder or sphere shape with the mass and diameter about 4 g and 25 mm, respectively, was launched at the velocity up to 430 m/s, and the phenomena were observed by the high-speed camera at 20,000 fps. From a series of images, the bow-shock-wave-like laterally facing U-shaped pattern over the projectile and the absence of particles in the trail behind it were clearly seen. At the impact of the particles on the projectile surface, fine grains were formed due to the destructive collision and injected outward from the projectile. The images obtained by different lighting methods including the laser light sheet were compared. The effects of the particle diameter, its material and the impact velocity were also investigated.展开更多
PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure...PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres,tungsten spheres of various diameters(5 mm,8 mm,and 10 mm)were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm,9 mm,and 14 mm.The penetration performance of the spheres was analyzed for different velocities,and the ultimate penetration velocity of the plate was obtained.It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure.Using the dimensional analysis method,a relationship between the bulge height of the steel plate and the fragment velocity,an equation for the ultimate penetration velocity,and a relationship between the target penetration energy and the fragment velocity were obtained.Then,a projectile-target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates.The results suggested that under the same thickness of the target plate,a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment.The equations obtained through dimensional analysis predicted values that agreed well with experimental values,indicating that these equations can be applied to engineering applications.展开更多
The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high...The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high-speed railway respectively. The impact factor for high-speed railway is based on Eurocode. Since the impact factor criteria inKoreawere established by adopting those of the Eurocode and without dedicated investigation relying on research results reflecting the domestic circumstances, thorough examination should be implemented on these criteria. Therefore the evaluation of impact factor based on field tests is required. Both dynamic and static vertical displacements are necessary to compute the impact factor. The dynamic response can be obtained from the measurement of deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea Train eXpress) running at high-speed. The main difficulties encountered are in obtaining static response because static response corresponds to the response of the bridge when the train remains immobile on the bridge or crosses the bridge at speed slower than5 km/hr. This study introduces the static response derived by applying the moving average method on the dynamic response signal. To that goal, field measurements was conducted under train speeds of5 km/hr and ranging from100 km/hr to300 km/hr on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed Railway Line before its opening. The validity of the application of the moving average method is verified from comparison of measured static response and derived static response by moving average method. Moreover, evaluation is conducted on the impact factor computed for a bridge crossed by the KTX train running at operational speed.展开更多
Objective: To study the local inflammatory stress response and pain mediator secretion after impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator. Methods: Patients who receive...Objective: To study the local inflammatory stress response and pain mediator secretion after impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator. Methods: Patients who received impacted wisdom tooth extraction in the First People's Hospital ofYunnan Province between March 2014 and June 2017 were selected as the research objects and randomly divided into the observation group who accepted impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator and the control group who accepted impacted wisdom tooth extraction with traditional chisel. The contents of inflammatory mediators, stress mediators and pain mediators in gingival crevicular fluid were measured before surgery and 3 days after surgery. Results: Three days after surgery, PTX3, ICAM1, MPO, PGE2, PPARγ, ROS, MDA, 5-HT, CGRP, SP, Gal and ATP contents in gingival crevicular fluid of both groups were higher than those before surgery whereas GPx and T-AOC contents were significantly lower than those before surgery, and PTX3, ICAM1, MPO, PGE2, PPARγ, ROS, MDA, 5-HT, CGRP, SP, Gal and ATP contents in gingival crevicular fluid of observation group were lower than those of control group whereas GPx and T-AOC contents were significantly higher than those of control group. Conclusions: The impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator can reduce the local inflammatory stress response and inhibit the secretion of pain mediators.展开更多
A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat i...A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat is totally absorbed by the projectile. Extrapolating this formula to predict the mass loss of local area of projectile, the receding displacement on projectile surface is obtained, which is vertical to the symmetry axis of projectile. Thereby, a finite difference method model is constructed to simulate the variation of projectile shape. The shape of residual projectile, depth of penetration of projectile and its mass loss obtained by calculation are found in good consistency with respective experimental data.展开更多
The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different...The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.展开更多
In order to develop a rotary percussive bit with diamond enhanced cutters assisted by high pressure water jets, it is necessary to study the damage mechanism and the penetration properties of PDC cutters subject to di...In order to develop a rotary percussive bit with diamond enhanced cutters assisted by high pressure water jets, it is necessary to study the damage mechanism and the penetration properties of PDC cutters subject to different impact load level and rock types. Therefore the impact experiments of the single PDC cutters with different attack angles in four rocks: black basalt, Missouri red granite, Halston limestone, and a very soft (Roubidoux) sandstone were carried out, and the effects of rake angles of PDC cutters on both the penetration and impact resistance of PDC cutters have been discussed in detail. Test results show that a PDC insert can withstand a very strong impact in compression but is easily damaged by impact shearing, the PDC cutters are more easily damaged by shearing if the attack angles are relatively small, the 45? PDC cutters have the least penetration resistance among the cutters tested. Thus it is suggested that the attack angles of PDC cutters should be larger than 30? for bits which must withstand impact from a hammer.展开更多
In this study,the anti-penetration performance of polyurea/ASTM1405-steel composite plate subjected to high velocity projectile was analyzed.Two kinds of modified polyurea material(AMMT-053 and AMMT-055)were selected ...In this study,the anti-penetration performance of polyurea/ASTM1405-steel composite plate subjected to high velocity projectile was analyzed.Two kinds of modified polyurea material(AMMT-053 and AMMT-055)were selected and a ballistic impact testing system including speed measuring target system and high-speed camera was designed.This experiment was conducted with a rifle and 5.8 mm projectile to explore the effects by the polyurea coating thickness,the polyurea coating position and the glass-fiber cloth on the anti-penetration performance of polyurea/ASTM1405-steel composite plate.The result showed that the effects of polyurea coating position were different between two types of polyurea,and that the effects of glass-fiber position were disparate between two types of polyurea as well.For AMMT-053 polyurea material,it was better to be on front face than on rear face;whereas for AMMT-055 polyurea,it was better to be on rear surface although the difference was very subtle.Additionally,formulas had been given to describe the relationship between the effectiveness of polyurea and the thickness of polyurea coating.In general,AMMT-055 had better anti-penetration performance than AMMT-053.Furthermore,five typical damage modes including self-healing,crack,local bulge,spallation and local fragmentation were defined and the failure mechanism was analyzed with the results of SHPB test.Additionally,the bonding strength played an important role in the anti-penetration performance of polyurea/steel composite plate.展开更多
This works presents the first fully validated and predictive capability to model the V_0-V_(100) probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V_0-V_(100) cur...This works presents the first fully validated and predictive capability to model the V_0-V_(100) probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V_0-V_(100) curve describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this paper comprises of a single-layer, fully-clamped, plain-weave Kevlar fabric impacted at the center by a 17-gr, 0.22 cal FSP or fragment-simulating projectile. Each warp and fill yarn in the fabric is individually modeled using 3 D finite elements and the virtual fabric microstructure is validated in detail against the experimental fabric microstructure. Material and testing sources of statistical variability including yarn strength and modulus, inter-yarn friction, precise projectile impact location, and projectile rotation are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, with each model comprising unique mappings. The impact velocities together with the outcomes(penetration, nonpenetration) are used to generate the numerical V_0-V_(100) curve which is then validated against the experimental V_0-V_(100) curve. The numerical Vi-Vrdata(impact, residual velocities) is also validated against the experimental Vi-Vrdata. For completeness, this paper also reports the experimental characterization data and its statistical analysis used for model input, viz. the Kevlar yarn tensile strengths, moduli, and inter-yarn friction, and the experimental ballistic test data used for model validation.展开更多
基金the National Natural Science Foundation of China(Grant No.12102050)the Open Fund of State Key Laboratory of Explosion Science and Technology(Grant No.SKLEST-ZZ-21-18).
文摘The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytical study of the evolution of the nose shape of larger hollow projectiles under hypersonic penetration.In the hypersonic penetration test,eight ogive-nose AerMet100 steel projectiles with a diameter of 40 mm were launched to hit concrete targets with impact velocities that ranged from 1351 to 1877 m/s.Severe erosion of the projectiles was observed during high-speed penetration of heterogeneous targets,and apparent localized mushrooming occurred in the front nose of recovered projectiles.By examining the damage to projectiles,a linear relationship was found between the relative length reduction rate and the initial kinetic energy of projectiles in different penetration tests.Furthermore,microscopic analysis revealed the forming mechanism of the localized mushrooming phenomenon for eroding penetration,i.e.,material spall erosion abrasion mechanism,material flow and redistribution abrasion mechanism and localized radial upsetting deformation mechanism.Finally,a model of highspeed penetration that included erosion was established on the basis of a model of the evolution of the projectile nose that considers radial upsetting;the model was validated by test data from the literature and the present study.Depending upon the impact velocity,v0,the projectile nose may behave as undistorted,radially distorted or hemispherical.Due to the effects of abrasion of the projectile and enhancement of radial upsetting on the duration and amplitude of the secondary rising segment in the pulse shape of projectile deceleration,the predicted DOP had an upper limit.
文摘For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.
基金supported by the National Natural Science Foundation of China (Grant No.62103432)supported by Young Talent fund of University Association for Science and Technology in Shaanxi, China(Grant No.20210108)。
文摘An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.
文摘Al-Sc and Al-Ti semi-infinite targets were impacted by high-speed projectiles at velocities of 0.8, 1.0, 1.2 and 1.5 km/s, respectively. It is found that the Al-Sc targets demonstrate more excellent ability to resist high-speed impact. It is concluded that different microstructures of Al-Sc and Al-Ti alloys, including different grain sizes and secondary particles precipitated in the matrix, result in their greatly different capabilities of resisting impact. Furthermore, the effect of the size range ofnanoscale A13Sc precipitate in A1-Sc alloy on the resistance of high-speed impact was investigated. In addition, computer simulations and validation of these simulations were developed which fairly accurately represented residual crater shapes/geometries. Validated computer simulations allowed representative extrapolations of impact craters well beyond the laboratory where melt and solidification occurred at the crater wall, especially for hypervelocity impact （〉5 km/s）.
基金supported by the National Outstanding Young Scientists Foundation of China(11225213)the Funds for Creative Research Groups of China(51321064)the National Natural Science Foundation of China(11172282 and 51378015)
文摘The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0
基金supported by the National Outstanding Young Scientists Foundation of China(11225213)the Funds for Creative Research Groups of China(51321064)the National Natural Science Foundation of China(11172282 and 51378015)
文摘The initial oblique and attacking angles as well as the asymmetrical nose abrasion may lead to bending or even fracture of a projectile,and the penetration efficiency decreases distinctly.The structural stability of a high-speed projectile non-normally penetrating into concrete and the parametric influences involved are analyzed with the mass abrasion taken into account.By considering the symmetrical or asymmetrical nose abrasion as well as the initial oblique and attacking angles,both the axial and the transverse drag forces acting on the projectile are derived.Based on the ideal elastic-plastic yield criterion,an approach is proposed for predicting the limit striking velocity（LSV）that is the highest velocity at which no yielding failure has occurred and the projectile can still maintain its integral structural stability.Furthermore,some particular penetration scenarios are separately discussed in detail.Based on the engineering model for the mass loss and nose-blunting of ogive-nose projectiles established in Part I of this study,the above approach is validated by several high-speed penetration tests.The analysis on parametric influences indicates that the LSV is reduced with an increase in the asymmetrical nose abrasion,thelength-diameter-ratio,and the concrete strength,as well as the oblique and attacking angles.Also,the LSV raises with an increase in the initial caliber-radius-head（CRH）and the dimensionless cartridge thickness of a projectile.
基金Project(2011QNZT062)supported by the Fundamental Research Funds for Central Universities of China
文摘Environmental impact evaluation system boundary of high-speed railway was defined based on the total life cycle theory,and the index system to evaluate the environmental impact of high-speed railway was established with the fuzzy analytic hierarchy method,and the matter-element evaluation model was established on the basis of the extension theory.By calculating its comprehensive interrelatedness,the evaluation rank of environment impacts of high-speed railway was determined.The numerical example shows that the model has vast prospect,which can not only expand the application areas of extension theory,but also change the traditional evaluation methods and provide new ideas and means for environmental impact evaluation of high-speed railway.
基金supported by the National Natural Science Foundation of China(Nos.52071139,51905166,52075167)well as from the Natural Science Foundation of Hunan Province(2020JJ5198)the Open Platform Fund of Hunan Institute of Technology(KFA20014).
文摘Split Hopkinson pressure bar(SHPB)tests were conducted on pre-rolled AZ31 magnesium alloy at 150–350℃ with strain rates of 2150s-1,3430s^(-1) and 4160s-1.The mechanical response,microstructural evolution and accommodation mechanism of the pre-rolled AZ31 magnesium alloy under high-speed impact loading were investigated.The twin and shear band are prevailing at low temperature,and the coexistence of twins and recrystallized grains is the dominant microstructure at medium temperature,while at high temperature,dynamic recrystallization(DRX)is almost complete.The increment of temperature reduces the critical condition difference between twinning and DRX,and the recrystallized temperature decreases with increasing strain rate.The mechanical response is related to the competition among the shear band strengthen,the twin strengthen and the fine grain strengthen and determined by the prevailing grain structure.The fine grain strengthen could compensate soften caused by the temperature increase and the reduction of twin and shear band.During high-speed deformation,different twin variants,introduced by pre-rolling,induce different deformation mechanism to accommodate plastic deformation and are in favor for non-basal slip.At low temperature,the high-speed deformation is achieved by twinning,dislocation slip and the following deformation shear band at different deformation stages.At high temperature,the high-speed deformation is realized by twinning and dislocation slip of early deformation stage,transition shear band of medium deformation stage and DRX of final deformation stage.
文摘In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode(2003).However,these IF coefficient values neglect the effects of very high speeds(>200 km/h)and soil-structure interaction(SSI).In this work,a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported.Three different configurations,each for the three-dimensional(3D)continuous and integral bridge,are considered.Also,single-track(1-T)and two-track(2-T)“real train”loading cases for both these bridge types are considered.Subsequently,finite element analysis of the full-scale 3D bridge models,to identify their IF values,considering the effects of SSI for three different soil conditions,is conducted.The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode(2003).The results reveal that with a loss of soil stiffness,the IF value reduces;thus,it confirms the importance of SSI analysis.
基金The work presented in this paper is funded by Opening Project of Science and Technology on Transient Impact Laboratory(Grant No.614260601010517).
文摘This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of old architecture and public buildings.We carried out penetration experiments in which four clay-fired brick walls employing two different patterns were subjected to impact from small high-speed projectile,i.e.12.7 mm armor-piercing explosive incendiary projectile and material tests in which the static and dynamic compressive strengths of clay-fired brick and mortar were determined by quasi-static and SHPB(Split Hopkinson Pressure Bar)tests.The experimental data include hit and exit velocities,damage configuration of clay brick masonry and mechanical properties of material at low and high strain rates,though which influence of thickness and bonding patterns of wall on kinetic loss of bullet,the damage patterns of masonry observed experimentally and dynamic increase of material strengths are analyzed.To keep minimum boundary inconsistency with reality,full 3D detailed finite element model consisting of two different material is established.Sharing common nodes and employing automatic tiebreak contact are combined to reduce computational time usage of large-scale model.For description of clay-fired brick and mortar RiedeleHiermaiereThoma(RHT)material model is employed.Material parameter set is derived based on experimental data,available literature and engineering assumptions.The numerical simulations study the mesh resolution dependency of material model,reproduce the crucial phenomena of masonry in experiment acceptably and offer more time-resolved insight into motion of bullet in the process of penetration.The feasibility of means of constructing finite element model and applying RHT model to the masonry herein and analogous constructions is explored through numerical investigation.
基金The research was supported by the National Key Research and Development Program(Grant No.2020YFA0710903)the Financial Funding Project for Central Colleges and Universities(Grant No.202045014)the Science and Technology Research and Development Program of China State Railway Group Co.,Ltd.(Grant No.P2019J008).
文摘Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach–Based on large eddy simulation(LES)method and Kirchhoff–Ffowcs Williams and Hawkings(K-FWH)equations,the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings–The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train.The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train,the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car,and the quadrupole sources are mainly distributed in the wake area.When the train runs at three speed levels of 400,500 and 600 km$h1,respectively,the radiated energy of quadrupole source is 62.4%,63.3%and 71.7%,respectively,which exceeds that of dipole sources.Originality/value–This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.
文摘The impact and penetration of a projectile in a particle-laden space, which are expected to have frequently occurred during the formation of the solar system and will occur in the case of an impact probe for future planetary exploration, were experimentally simulated by using the ballistic range. A two-dimensional sheet made from small glass beads or emery powder was formed by the free-falling device through a long slit in the test chamber evacuated down to about 35 Pa. A polycarbonate projectile of a hemi-sphere-cylinder or sphere shape with the mass and diameter about 4 g and 25 mm, respectively, was launched at the velocity up to 430 m/s, and the phenomena were observed by the high-speed camera at 20,000 fps. From a series of images, the bow-shock-wave-like laterally facing U-shaped pattern over the projectile and the absence of particles in the trail behind it were clearly seen. At the impact of the particles on the projectile surface, fine grains were formed due to the destructive collision and injected outward from the projectile. The images obtained by different lighting methods including the laser light sheet were compared. The effects of the particle diameter, its material and the impact velocity were also investigated.
文摘PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres,tungsten spheres of various diameters(5 mm,8 mm,and 10 mm)were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm,9 mm,and 14 mm.The penetration performance of the spheres was analyzed for different velocities,and the ultimate penetration velocity of the plate was obtained.It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure.Using the dimensional analysis method,a relationship between the bulge height of the steel plate and the fragment velocity,an equation for the ultimate penetration velocity,and a relationship between the target penetration energy and the fragment velocity were obtained.Then,a projectile-target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates.The results suggested that under the same thickness of the target plate,a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment.The equations obtained through dimensional analysis predicted values that agreed well with experimental values,indicating that these equations can be applied to engineering applications.
文摘The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high-speed railway respectively. The impact factor for high-speed railway is based on Eurocode. Since the impact factor criteria inKoreawere established by adopting those of the Eurocode and without dedicated investigation relying on research results reflecting the domestic circumstances, thorough examination should be implemented on these criteria. Therefore the evaluation of impact factor based on field tests is required. Both dynamic and static vertical displacements are necessary to compute the impact factor. The dynamic response can be obtained from the measurement of deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea Train eXpress) running at high-speed. The main difficulties encountered are in obtaining static response because static response corresponds to the response of the bridge when the train remains immobile on the bridge or crosses the bridge at speed slower than5 km/hr. This study introduces the static response derived by applying the moving average method on the dynamic response signal. To that goal, field measurements was conducted under train speeds of5 km/hr and ranging from100 km/hr to300 km/hr on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed Railway Line before its opening. The validity of the application of the moving average method is verified from comparison of measured static response and derived static response by moving average method. Moreover, evaluation is conducted on the impact factor computed for a bridge crossed by the KTX train running at operational speed.
文摘Objective: To study the local inflammatory stress response and pain mediator secretion after impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator. Methods: Patients who received impacted wisdom tooth extraction in the First People's Hospital ofYunnan Province between March 2014 and June 2017 were selected as the research objects and randomly divided into the observation group who accepted impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator and the control group who accepted impacted wisdom tooth extraction with traditional chisel. The contents of inflammatory mediators, stress mediators and pain mediators in gingival crevicular fluid were measured before surgery and 3 days after surgery. Results: Three days after surgery, PTX3, ICAM1, MPO, PGE2, PPARγ, ROS, MDA, 5-HT, CGRP, SP, Gal and ATP contents in gingival crevicular fluid of both groups were higher than those before surgery whereas GPx and T-AOC contents were significantly lower than those before surgery, and PTX3, ICAM1, MPO, PGE2, PPARγ, ROS, MDA, 5-HT, CGRP, SP, Gal and ATP contents in gingival crevicular fluid of observation group were lower than those of control group whereas GPx and T-AOC contents were significantly higher than those of control group. Conclusions: The impacted wisdom tooth extraction with high-speed turbine drill combined with original luxator can reduce the local inflammatory stress response and inhibit the secretion of pain mediators.
基金supported by the National Natural Science Foundation of China (11172282)the Science Foundation of China Academy of Engineering Physics(2009A0201009)
文摘A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat is totally absorbed by the projectile. Extrapolating this formula to predict the mass loss of local area of projectile, the receding displacement on projectile surface is obtained, which is vertical to the symmetry axis of projectile. Thereby, a finite difference method model is constructed to simulate the variation of projectile shape. The shape of residual projectile, depth of penetration of projectile and its mass loss obtained by calculation are found in good consistency with respective experimental data.
基金Project supported by"863"Project (2006AA03Z532)the National Natural Science Foundation of China (NSFC 50341050)
文摘The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.
文摘In order to develop a rotary percussive bit with diamond enhanced cutters assisted by high pressure water jets, it is necessary to study the damage mechanism and the penetration properties of PDC cutters subject to different impact load level and rock types. Therefore the impact experiments of the single PDC cutters with different attack angles in four rocks: black basalt, Missouri red granite, Halston limestone, and a very soft (Roubidoux) sandstone were carried out, and the effects of rake angles of PDC cutters on both the penetration and impact resistance of PDC cutters have been discussed in detail. Test results show that a PDC insert can withstand a very strong impact in compression but is easily damaged by impact shearing, the PDC cutters are more easily damaged by shearing if the attack angles are relatively small, the 45? PDC cutters have the least penetration resistance among the cutters tested. Thus it is suggested that the attack angles of PDC cutters should be larger than 30? for bits which must withstand impact from a hammer.
基金This research was supported by the National Natural Science Foundation of China(Nos.51978660).
文摘In this study,the anti-penetration performance of polyurea/ASTM1405-steel composite plate subjected to high velocity projectile was analyzed.Two kinds of modified polyurea material(AMMT-053 and AMMT-055)were selected and a ballistic impact testing system including speed measuring target system and high-speed camera was designed.This experiment was conducted with a rifle and 5.8 mm projectile to explore the effects by the polyurea coating thickness,the polyurea coating position and the glass-fiber cloth on the anti-penetration performance of polyurea/ASTM1405-steel composite plate.The result showed that the effects of polyurea coating position were different between two types of polyurea,and that the effects of glass-fiber position were disparate between two types of polyurea as well.For AMMT-053 polyurea material,it was better to be on front face than on rear face;whereas for AMMT-055 polyurea,it was better to be on rear surface although the difference was very subtle.Additionally,formulas had been given to describe the relationship between the effectiveness of polyurea and the thickness of polyurea coating.In general,AMMT-055 had better anti-penetration performance than AMMT-053.Furthermore,five typical damage modes including self-healing,crack,local bulge,spallation and local fragmentation were defined and the failure mechanism was analyzed with the results of SHPB test.Additionally,the bonding strength played an important role in the anti-penetration performance of polyurea/steel composite plate.
基金supported by Teledyne Scientific&Imaging(TS&I),Internal Research and Development(IR&D)and approved for public release under TSI-PP-17-08
文摘This works presents the first fully validated and predictive capability to model the V_0-V_(100) probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V_0-V_(100) curve describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this paper comprises of a single-layer, fully-clamped, plain-weave Kevlar fabric impacted at the center by a 17-gr, 0.22 cal FSP or fragment-simulating projectile. Each warp and fill yarn in the fabric is individually modeled using 3 D finite elements and the virtual fabric microstructure is validated in detail against the experimental fabric microstructure. Material and testing sources of statistical variability including yarn strength and modulus, inter-yarn friction, precise projectile impact location, and projectile rotation are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, with each model comprising unique mappings. The impact velocities together with the outcomes(penetration, nonpenetration) are used to generate the numerical V_0-V_(100) curve which is then validated against the experimental V_0-V_(100) curve. The numerical Vi-Vrdata(impact, residual velocities) is also validated against the experimental Vi-Vrdata. For completeness, this paper also reports the experimental characterization data and its statistical analysis used for model input, viz. the Kevlar yarn tensile strengths, moduli, and inter-yarn friction, and the experimental ballistic test data used for model validation.
