Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of sh...Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.展开更多
Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.Th...Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.展开更多
With the application of hypervelocity weapons in warfare,comprehensively evaluating their destructive effects is of particular interest for protective engineering.Existing studies mostly focused on the depth of penetr...With the application of hypervelocity weapons in warfare,comprehensively evaluating their destructive effects is of particular interest for protective engineering.Existing studies mostly focused on the depth of penetration by hypervelocity projectile,while investigation on stress waves associated with hypervelocity penetration was very limited.To clarify the generation and propagation of stress waves in concrete targets induced by hypervelocity projectile penetration,in the present study,six spherical projectile penetration tests on concrete targets were firstly conducted with projectile velocity ranged from 1875 m/s to 3940 m/s,in which the stress waves were carefully measured by the PVDF transducers.Then corresponding numerical models were developed and validated,and based on the validated numerical model the mechanisms of generation and propagation of stress waves were clarified.It was found that the stress waves observed during hypervelocity penetration are generated by the continuous interactions of projectile and target during penetration,and have unique characteristics such as the directionality and the"two peaks"phenomenon when compared with the stress waves generated by charge explosion.Finally,the effects of projectile velocity,projectile material,and target strength on the stress waves below the penetration depth we re numerically investigated,and two important indexes for evaluating the stress waves by hypervelocity penetration were proposed.展开更多
The motion characteristics of projectile during oblique penetration into concrete were studied using a three-dimensional meso-scale model.The finite element model validation and parameter chosen were conducted by comp...The motion characteristics of projectile during oblique penetration into concrete were studied using a three-dimensional meso-scale model.The finite element model validation and parameter chosen were conducted by comparing the experimental data,with computational efficiency enhanced through improved mesh refinement.Penetration simulations involving deformable projectiles at various incident angles analyzed the effects of aggregate volume fraction and particle size on ballistic trajectory and terminal deflection.Sensitivity analysis reveals a strong power-law relationship between aggregate content and the projectile's deflection angle.The increase in aggregate content will enhance the confinement effect,shorten the intrusion distance of the projectile,and lead to a decrease in the deflection angle of the projectile.The effect of aggregate particle size on the projectile deflection angle follows a Gaussian distribution.The maximum deflection angle occurs when the aggregate particle size is between 2.7 and 3.1 times the projectile diameter.An increase in particle size reduces the number of aggregate-mortar interfaces at the same aggregate volume fraction,leading to an enlargement of the damage zone in concrete,a decrease in the number of cracks,and an increase in crack length.These findings enhance the understanding of concrete penetration mechanisms and offers valuable insights for engineering structure protection.展开更多
The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced ...The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced by the EPWs, experimental and numerical investigations are carried out in this paper.Firstly, a series of sequential explosion tests are conducted to provide the basic data of the crater size.Then, a numerical model is established to simulate the damage effects of sequential explosions using the meshfree method of Smoothed particle Galerkin. The effectiveness of numerical model is verified by comparison with the experimental results. Finally, based on dimensional analysis, several empirical formulas for describing the crater size are presented, including the conical crater diameter and the conical crater depth of the single explosion, the conical crater area and the joint depth of the secondary explosion. The formula for the single explosion expresses the relationship between the aspect ratio of the charge ranging from 3 to 7, the dimensionless buried depth ranging from 2 to 14 and the crater size. The formula for the secondary explosion expresses the relationship between the relative position of the two explosions and the crater size. All of data can provide reference for the design of protective structures.展开更多
Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the ...Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.展开更多
Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.Thi...Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.This study investigates the blasting effects and underlying mechanisms of concrete frustums subjected to contact explosions,employing both numerical simulations and field tests.It focuses on the effects of top and side blasting,with particular emphasis on fracture modes,damage patterns,and fragment sizes,as well as the causes of different failure modes and the propagation of stress waves.The study also explores the blasting effects of detonating explosives at varying positions along the side and with different charge amounts.The results show that side-blasting leads to complete fragmentation,with tensile waves playing a significant role in creating extensive damage zones that propagate parallel to the frustum's outer surface,concentrating damage near the surface.During top-blasting,the upper half of the frustum undergoes fragmentation,while the lower half experiences cracking.Tensile waves propagate from the top to the bottom surface,forming larger blocks in regions with lower wave intensity.Three distinct damage zones within the frustum were identified,and a series of mathematical formulas were derived to describe the relationship between the maximum fragment size and charge mass.As the charge mass increased from 1.0 kg to 4.0 kg,the maximum fragment size decreased.Detonation at the center of the frustum's side resulted in the most severe fragmentation,with a 51.8%reduction in fragment size compared to other detonation positions.Finally,four broken modes were classified,each influenced by charge mass and explosive location.This study provides valuable insights for optimizing civil blasting operations and designing protective engineering structures.展开更多
Concrete material model plays an important role in numerical predictions of its dynamic responses subjected to projectile impact and charge explosion.Current concrete material models could be distinguished into two ki...Concrete material model plays an important role in numerical predictions of its dynamic responses subjected to projectile impact and charge explosion.Current concrete material models could be distinguished into two kinds,i.e.,the hydro-elastoplastic-damage model with independent equation of state and the cap-elastoplastic-damage model with continuous cap surface.The essential differences between the two kind models are vital for researchers to choose an appropriate kind of concrete material model for their concerned problems,while existing studies have contradictory conclusions.To resolve this issue,the constitutive theories of the two kinds of models are firstly overviewed.Then,the constitutive theories between the two kinds of models are comprehensively compared and the main similarities and differences are clarified,which are demonstrated by single element numerical examples.Finally,numerical predictions for projectile penetration and charge explosion experiments on concrete targets are compared to further demonstrate the conclusion made by constitutive comparison.It is found that both the two kind models could be used to simulate the dynamic responses of concrete under projectile impact and blast loadings,if the parameter needed in material models are well calibrated,although some discrepancies between them may exist.展开更多
With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure m...With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure modes are transformed.In order to reveal the failure mode and transformation rule of reinforced concrete slabs under impact loads,a dynamic impact response test was carried out using a drop hammer test device.The dynamic data pertaining to the impact force,support reaction force,structural displacement,and reinforcement strain were obtained through the use of digital image correlation technology(DIC),impact force measurement,and strain measurement.The analysis of the ultimate damage state of the reinforced concrete slab identified four distinct types of impact failure modes:local failure by stamping,overall failure by stamping,local-overall coupling failure,and local failure by punching.Additionally,the influence laws of hammerhead shape,hammer height,and reinforcement ratio on the dynamic response and failure mode transformation of the slab were revealed.The results indicate that:(1)The local damage to the slab by the plane hammer is readily apparent,while the overall damage by the spherical hammer is more pronounced.(2)In comparison to the high reinforcement ratio slabs,the overall bending resistance of the low reinforcement ratio slabs is significantly inferior,and the slab back exhibits further cracks.(3)As the hammer height increases,the slab failure mode undergoes a transformation,shifting from local failure by stamping and overall failure by stamping to local-overall coupling failure and local failure by punching.(4)Three failure mode thresholds have been established,and by comparing the peak impact force with the failure thresholds,the failure mode of the slab can be effectively determined.展开更多
Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since...Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since conventional OGFC mixes last typically less than ten years before major maintenance or rehabilitation is needed. This work investigates a new open-graded asphalt mixture that uses epoxy asphalt as binder to improve mix durability. One type of epoxy asphalt that has been successfully applied to dense-graded asphalt concrete for bridge deck paving was selected. A procedure of compacting the mix into slab specimens was developed and a series of laboratory tests were conducted to evaluate the performance of the new mix, including Cantabro loss, permeability, friction, shear strength, and wheel rutting tests. Results show superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix. There are also preliminary indications that the OGFC mix with 4.75-mm NMAS gradation can improve the resistance performance to raveling, while the OGFC mix with 9.5-mm NMAS gradation can improve the performance of surface friction at a high slip speed.展开更多
In this study, the blast performance of steel reinforced concrete(RC) beams was experimentally and analytically investigated. The experiment consists of a total of 10 one-half-scale beams subjected to different levels...In this study, the blast performance of steel reinforced concrete(RC) beams was experimentally and analytically investigated. The experiment consists of a total of 10 one-half-scale beams subjected to different levels of blast loading using live explosives. The reflected pressure-time histories were recorded and different damage levels and modes were observed. The blast resilience of the damaged beams was quantified by measuring the time-dependent displacements. Experiment results show that the damage in steel reinforced concrete beams with higher explosive mass is enhanced compared with that of the beams with smaller explosive mass at the same scaled distance. Based on the experiment data, an empirical expression is developed via dimensional analysis to correct the relationship between the midspan displacement and scaled distance. Besides, a complex single degree of freedom model(SDOF)incorporating complex features of the material behavior, high strain-rate effect and the column geometry was proposed and validated by test results.展开更多
This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at t...This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.展开更多
In order to apply the performance-based seismic design, an engineer must first find out whether the column is expected to fail in shear before or after flexural yielding. According to column failure characteristics an...In order to apply the performance-based seismic design, an engineer must first find out whether the column is expected to fail in shear before or after flexural yielding. According to column failure characteristics and failure mode of reinforced concrete column, the UW-PEER structure performance database was discussed and analyzed. In order to investigate the relevance of failure mode and factors such as longitudinal reinforcement ratio, transverse reinforcement ratio, hoop spacing to depth ratio, aspect ratio, shearing resistance demand to shear capacity ratio and axial load ratio, Fisher's discriminant analysis(FDA) of the above factors was carried out. A discriminant function was developed to identify column failure mode. Results show that three factors, i.e., Vp /Vn, hoop spacing to depth ratio and aspect ratio have important influence on the failure mode. The failure mode has less to do with longitudinal reinforcement ratio, transverse reinforcement ratio and axial load ratio. Through using these three factors and the model proposed, over 85.6% of the original grouped cases were correctly classified. The value of coefficient of Vp /Vn is the largest, which means that discriminant equation is most sensitive to the shearing resistance demand to shear capacity ratio.展开更多
Air content, spacing factor and specific surface of fresh concrete and hardened concrete with different air contents, slumps and mineral admixtures (fly ash, slag, fly ash + slag, fly ash + slag + silica fume composit...Air content, spacing factor and specific surface of fresh concrete and hardened concrete with different air contents, slumps and mineral admixtures (fly ash, slag, fly ash + slag, fly ash + slag + silica fume composite) were studied by the air-void analyzer (AVA) method and the microscopical method. The correlations between the test results obtained from different methods were analyzed. The results show that, there is a close correlation of air content and spacing factor between the fresh concrete and the hardened concrete, but the specific surface correlation is weak. The air content of concrete measured by the AVA method is smaller than that of the pressure method and the microscopical method, because AVA device captures only the air voids with the size smaller than 3 mm. Spacing factor of the fresh concrete measured by the AVA method is greater than that of the hardened concrete measured by the microscopical method, while the specific surface is smaller. When the criterion of 4%-7% air content measured by the pressure method and microscopical method is acceptable for concrete freezing-thawing (F-T) durability in cold weather, the air content measured by the AVA method should be 2.4%-4.6%. For the concrete F-T durability, when the criterion of the spacing factor measured by the microscopical method is 300 μm, the spacing factor measured by the AVA method should be 360 μm.展开更多
Autoclaved aerated concrete(AAC) panels have ultra-light weight,excellent thermal insulation and energy absorption,so it is an ideal building material for protective structures.To improve the blast resistance of the A...Autoclaved aerated concrete(AAC) panels have ultra-light weight,excellent thermal insulation and energy absorption,so it is an ideal building material for protective structures.To improve the blast resistance of the AAC panels,three schemes are applied to strengthen the AAC panels through spraying 4 mm thick polyurea coating from top,bottom and double-sides.In three-point bending tests,the polyurea-coated AAC panels have much higher ultimate loads than the un-coated panels,but slightly lower than those strengthened by the carbon fiber reinforced plastics(CEFRPs).Close-in explosion experiments reveal the dynamic strengthening effect of the polyurea coating.Critical scaled distances of the strengthened AAC panels are acquired,which are valuable for the engineering application of the AAC panels in the extreme loading conditions.Polyurea coatings efficiently enhance the blast resistance of the bottom and double-sided polyurea-coated AAC panels.It is interesting that the polyurea-coated AAC panels have much more excellent blast resistance than the CFRP reinforced AAC panels,although the latter have better static mechanical properties.展开更多
A series of impact tests of sandwich samples were completed using a large-diameter split Hopkinson pressure bar (SHPB)device at different velocities. The interlayer is made of foam concrete, loess or sand. The stress ...A series of impact tests of sandwich samples were completed using a large-diameter split Hopkinson pressure bar (SHPB)device at different velocities. The interlayer is made of foam concrete, loess or sand. The stress peak value decay, energy decay and waveform dispersion characters are studied by comparing the incident waves with the transmission waves. The tests indicate that the foam concrete has the best capabilities of shock resistance and energy absorption, the loess comes second, and the sand takes third place.展开更多
The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition.Based on the in-site geological conditions of Longgu coal mine,this paper us...The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition.Based on the in-site geological conditions of Longgu coal mine,this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition.Results showed that under the static loading condition,the maximum vertical stress,deformation and failure range are large,where the stress concentration coefficient is 1.64.The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm,respectively.Then,under the dynamic and static combined loading condition:(1)The influence of dynamic load frequency on the two-sides is more obvious;(2)The dynamic load amplitude has the greatest influence on the stress concentration degree,and the plastic failure tends to develop to the deeper;(3)With the dynamic load source distance increase,the response of surrounding rock is gradually attenuated.On this basis,empirical equations for each dynamic load conditions were obtained by using regression analysis method,and all correlation coefficients are greater than 0.99.This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.展开更多
The friction on the projectile shank is usually excluded in the penetration analysis due to the difficulties to measure the pressure and frictional coefficient.In this article,the frictional force on projectile shank ...The friction on the projectile shank is usually excluded in the penetration analysis due to the difficulties to measure the pressure and frictional coefficient.In this article,the frictional force on projectile shank is discussed indirectly through the comparison between experimental data and empirical/analytical formulas of the penetration depth for both concrete and aluminium-alloy targets.It is found that the effect of the frictional force along the projectile shank can be further discussed by the afore comparison and discussion and cannot be ignored because of the relatively large effecting area,especially for deep penetration of concrete and aluminium-alloy targets,where the friction will account for more proportion of penetration resistance.展开更多
The elliptical cross-section ogive-nose projectile(ECOP) has recently attracted attention because it is well suited to the flattened shape of earth-penetrating weapons. However, the penetration performance of ECOPs ha...The elliptical cross-section ogive-nose projectile(ECOP) has recently attracted attention because it is well suited to the flattened shape of earth-penetrating weapons. However, the penetration performance of ECOPs has not been completely understood. The objective of this study was to investigate the penetration performance of ECOPs into concrete targets using a theoretical method. A general geometric model of ECOPs was introduced, and closed-form penetration equations were derived according to the dynamic cavity-expansion theory. The model was validated by comparing the predicted penetration depths with test data, and the maximum deviation was 15.8%. The increment in the penetration depth of the ECOP was evaluated using the proposed model, and the effect of the majoreminor axis ratio on the increment was examined. Additionally, the mechanism of the penetration-depth increment was investigated with respect to the caliber radius head, axial stress, and resistance.展开更多
The influence of concrete components on projectile penetration is significant.To study the relationship between the equivalent mechanical properties and components of concrete under a penetration load,concrete is simp...The influence of concrete components on projectile penetration is significant.To study the relationship between the equivalent mechanical properties and components of concrete under a penetration load,concrete is simplified as a two-phase composite of coarse aggregate and mortar,and a meso-mechanical model is established,including the equivalent equation of state model,the equivalent confining pressure strength model and the equivalent dynamic tensile strength model,considering shear stress,large deformation and pore compression.Tests of the mechanical properties of mortar,concrete and limestone were conducted;the results show that the equivalent mechanical properties of concrete calculated by the meso-mechanical model are consistent with the test results,and the equivalent mechanical properties of concrete with different volume fractions of coarse aggregate are obtained.Meso-scale and macro-scale numerical simulations of a projectile penetrating into concrete are carried out,the penetration depths obtained by meso-scale and macro-scale numerical simulations are consistent for different volume fractions of coarse aggregate and different velocities of the projectile,which verifies the rationality of the meso-mechanical model.展开更多
基金supported by the National Science Foundation of China(Grant Nos.12372361,12102427,12372335 and 12102202)the Fundamental Research Funds for the Central Universities(Grant No.30923010908)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_0520).
文摘Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.
基金Supports from National Natural Science Foundation of China(U20A20286 and 12372135)。
文摘Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.
基金supported by the National Natural Science Foundation of China(Grant Nos.52178515 and 12472399)。
文摘With the application of hypervelocity weapons in warfare,comprehensively evaluating their destructive effects is of particular interest for protective engineering.Existing studies mostly focused on the depth of penetration by hypervelocity projectile,while investigation on stress waves associated with hypervelocity penetration was very limited.To clarify the generation and propagation of stress waves in concrete targets induced by hypervelocity projectile penetration,in the present study,six spherical projectile penetration tests on concrete targets were firstly conducted with projectile velocity ranged from 1875 m/s to 3940 m/s,in which the stress waves were carefully measured by the PVDF transducers.Then corresponding numerical models were developed and validated,and based on the validated numerical model the mechanisms of generation and propagation of stress waves were clarified.It was found that the stress waves observed during hypervelocity penetration are generated by the continuous interactions of projectile and target during penetration,and have unique characteristics such as the directionality and the"two peaks"phenomenon when compared with the stress waves generated by charge explosion.Finally,the effects of projectile velocity,projectile material,and target strength on the stress waves below the penetration depth we re numerically investigated,and two important indexes for evaluating the stress waves by hypervelocity penetration were proposed.
基金funded by the National Natural Science Foundation of China(Grant Nos.12472390 and 12102292)the special fund for Science and Technology Innovation Teams of Shanxi Province(Grant No.202204051002006)。
文摘The motion characteristics of projectile during oblique penetration into concrete were studied using a three-dimensional meso-scale model.The finite element model validation and parameter chosen were conducted by comparing the experimental data,with computational efficiency enhanced through improved mesh refinement.Penetration simulations involving deformable projectiles at various incident angles analyzed the effects of aggregate volume fraction and particle size on ballistic trajectory and terminal deflection.Sensitivity analysis reveals a strong power-law relationship between aggregate content and the projectile's deflection angle.The increase in aggregate content will enhance the confinement effect,shorten the intrusion distance of the projectile,and lead to a decrease in the deflection angle of the projectile.The effect of aggregate particle size on the projectile deflection angle follows a Gaussian distribution.The maximum deflection angle occurs when the aggregate particle size is between 2.7 and 3.1 times the projectile diameter.An increase in particle size reduces the number of aggregate-mortar interfaces at the same aggregate volume fraction,leading to an enlargement of the damage zone in concrete,a decrease in the number of cracks,and an increase in crack length.These findings enhance the understanding of concrete penetration mechanisms and offers valuable insights for engineering structure protection.
文摘The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced by the EPWs, experimental and numerical investigations are carried out in this paper.Firstly, a series of sequential explosion tests are conducted to provide the basic data of the crater size.Then, a numerical model is established to simulate the damage effects of sequential explosions using the meshfree method of Smoothed particle Galerkin. The effectiveness of numerical model is verified by comparison with the experimental results. Finally, based on dimensional analysis, several empirical formulas for describing the crater size are presented, including the conical crater diameter and the conical crater depth of the single explosion, the conical crater area and the joint depth of the secondary explosion. The formula for the single explosion expresses the relationship between the aspect ratio of the charge ranging from 3 to 7, the dimensionless buried depth ranging from 2 to 14 and the crater size. The formula for the secondary explosion expresses the relationship between the relative position of the two explosions and the crater size. All of data can provide reference for the design of protective structures.
文摘Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.
基金the support provided by the Technology Innovation Project (Grant No. KYGYZB002201) for the research work
文摘Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.This study investigates the blasting effects and underlying mechanisms of concrete frustums subjected to contact explosions,employing both numerical simulations and field tests.It focuses on the effects of top and side blasting,with particular emphasis on fracture modes,damage patterns,and fragment sizes,as well as the causes of different failure modes and the propagation of stress waves.The study also explores the blasting effects of detonating explosives at varying positions along the side and with different charge amounts.The results show that side-blasting leads to complete fragmentation,with tensile waves playing a significant role in creating extensive damage zones that propagate parallel to the frustum's outer surface,concentrating damage near the surface.During top-blasting,the upper half of the frustum undergoes fragmentation,while the lower half experiences cracking.Tensile waves propagate from the top to the bottom surface,forming larger blocks in regions with lower wave intensity.Three distinct damage zones within the frustum were identified,and a series of mathematical formulas were derived to describe the relationship between the maximum fragment size and charge mass.As the charge mass increased from 1.0 kg to 4.0 kg,the maximum fragment size decreased.Detonation at the center of the frustum's side resulted in the most severe fragmentation,with a 51.8%reduction in fragment size compared to other detonation positions.Finally,four broken modes were classified,each influenced by charge mass and explosive location.This study provides valuable insights for optimizing civil blasting operations and designing protective engineering structures.
基金supported by the National Natural Science Foundations of China (Grant Nos. 52178515, 52078133)
文摘Concrete material model plays an important role in numerical predictions of its dynamic responses subjected to projectile impact and charge explosion.Current concrete material models could be distinguished into two kinds,i.e.,the hydro-elastoplastic-damage model with independent equation of state and the cap-elastoplastic-damage model with continuous cap surface.The essential differences between the two kind models are vital for researchers to choose an appropriate kind of concrete material model for their concerned problems,while existing studies have contradictory conclusions.To resolve this issue,the constitutive theories of the two kinds of models are firstly overviewed.Then,the constitutive theories between the two kinds of models are comprehensively compared and the main similarities and differences are clarified,which are demonstrated by single element numerical examples.Finally,numerical predictions for projectile penetration and charge explosion experiments on concrete targets are compared to further demonstrate the conclusion made by constitutive comparison.It is found that both the two kind models could be used to simulate the dynamic responses of concrete under projectile impact and blast loadings,if the parameter needed in material models are well calibrated,although some discrepancies between them may exist.
基金Supported by the National Natural Science Foundation of China(Grant No.52078283)Shandong Provincial Natural Science Foundation(Project No.ZR2024MA094)。
文摘With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure modes are transformed.In order to reveal the failure mode and transformation rule of reinforced concrete slabs under impact loads,a dynamic impact response test was carried out using a drop hammer test device.The dynamic data pertaining to the impact force,support reaction force,structural displacement,and reinforcement strain were obtained through the use of digital image correlation technology(DIC),impact force measurement,and strain measurement.The analysis of the ultimate damage state of the reinforced concrete slab identified four distinct types of impact failure modes:local failure by stamping,overall failure by stamping,local-overall coupling failure,and local failure by punching.Additionally,the influence laws of hammerhead shape,hammer height,and reinforcement ratio on the dynamic response and failure mode transformation of the slab were revealed.The results indicate that:(1)The local damage to the slab by the plane hammer is readily apparent,while the overall damage by the spherical hammer is more pronounced.(2)In comparison to the high reinforcement ratio slabs,the overall bending resistance of the low reinforcement ratio slabs is significantly inferior,and the slab back exhibits further cracks.(3)As the hammer height increases,the slab failure mode undergoes a transformation,shifting from local failure by stamping and overall failure by stamping to local-overall coupling failure and local failure by punching.(4)Three failure mode thresholds have been established,and by comparing the peak impact force with the failure thresholds,the failure mode of the slab can be effectively determined.
基金Project(51408125)supported by the National Natural Science Foundation of ChinaProject(2242015R30029)supported by the Fundamental Research Funds for the Central UniversitiesChina
文摘Open-graded friction course(OGFC) is applied to pavement surfaces to increase driving safety under wet conditions, and recently, to reduce tire/pavement noise. The durability of OGFC, however, has been a concern since conventional OGFC mixes last typically less than ten years before major maintenance or rehabilitation is needed. This work investigates a new open-graded asphalt mixture that uses epoxy asphalt as binder to improve mix durability. One type of epoxy asphalt that has been successfully applied to dense-graded asphalt concrete for bridge deck paving was selected. A procedure of compacting the mix into slab specimens was developed and a series of laboratory tests were conducted to evaluate the performance of the new mix, including Cantabro loss, permeability, friction, shear strength, and wheel rutting tests. Results show superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix. There are also preliminary indications that the OGFC mix with 4.75-mm NMAS gradation can improve the resistance performance to raveling, while the OGFC mix with 9.5-mm NMAS gradation can improve the performance of surface friction at a high slip speed.
基金supported by The National Natural Science Foundation of China under Grant No.11390362 and No.11221202
文摘In this study, the blast performance of steel reinforced concrete(RC) beams was experimentally and analytically investigated. The experiment consists of a total of 10 one-half-scale beams subjected to different levels of blast loading using live explosives. The reflected pressure-time histories were recorded and different damage levels and modes were observed. The blast resilience of the damaged beams was quantified by measuring the time-dependent displacements. Experiment results show that the damage in steel reinforced concrete beams with higher explosive mass is enhanced compared with that of the beams with smaller explosive mass at the same scaled distance. Based on the experiment data, an empirical expression is developed via dimensional analysis to correct the relationship between the midspan displacement and scaled distance. Besides, a complex single degree of freedom model(SDOF)incorporating complex features of the material behavior, high strain-rate effect and the column geometry was proposed and validated by test results.
基金supported by The National Natural Science Foundation of China under Grant No.11390362 and No. 11221202
文摘This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.
基金Project(2011ZA05) supported by the State Key Laboratory’s Autonomous Project of Subtropical Building Science in South China University of Technology
文摘In order to apply the performance-based seismic design, an engineer must first find out whether the column is expected to fail in shear before or after flexural yielding. According to column failure characteristics and failure mode of reinforced concrete column, the UW-PEER structure performance database was discussed and analyzed. In order to investigate the relevance of failure mode and factors such as longitudinal reinforcement ratio, transverse reinforcement ratio, hoop spacing to depth ratio, aspect ratio, shearing resistance demand to shear capacity ratio and axial load ratio, Fisher's discriminant analysis(FDA) of the above factors was carried out. A discriminant function was developed to identify column failure mode. Results show that three factors, i.e., Vp /Vn, hoop spacing to depth ratio and aspect ratio have important influence on the failure mode. The failure mode has less to do with longitudinal reinforcement ratio, transverse reinforcement ratio and axial load ratio. Through using these three factors and the model proposed, over 85.6% of the original grouped cases were correctly classified. The value of coefficient of Vp /Vn is the largest, which means that discriminant equation is most sensitive to the shearing resistance demand to shear capacity ratio.
基金Project(50908229) supported by the National Natural Science Foundation of ChinaProjects(2008G031-N, 50908229, 10125C131) supported by Technological Research and Development Programs of the Ministry of Railways, China
文摘Air content, spacing factor and specific surface of fresh concrete and hardened concrete with different air contents, slumps and mineral admixtures (fly ash, slag, fly ash + slag, fly ash + slag + silica fume composite) were studied by the air-void analyzer (AVA) method and the microscopical method. The correlations between the test results obtained from different methods were analyzed. The results show that, there is a close correlation of air content and spacing factor between the fresh concrete and the hardened concrete, but the specific surface correlation is weak. The air content of concrete measured by the AVA method is smaller than that of the pressure method and the microscopical method, because AVA device captures only the air voids with the size smaller than 3 mm. Spacing factor of the fresh concrete measured by the AVA method is greater than that of the hardened concrete measured by the microscopical method, while the specific surface is smaller. When the criterion of 4%-7% air content measured by the pressure method and microscopical method is acceptable for concrete freezing-thawing (F-T) durability in cold weather, the air content measured by the AVA method should be 2.4%-4.6%. For the concrete F-T durability, when the criterion of the spacing factor measured by the microscopical method is 300 μm, the spacing factor measured by the AVA method should be 360 μm.
基金Supports from the National Natural Science Foundation of China(11672130,51508567,51478465,and 51308544)the State Key Laboratory of Mechanics and Control of Mechanical Structures(MCMS-0217G03)the State Key Laboratory for Disaster Reduction in Civil Engineering(SLDRCE16-01)。
文摘Autoclaved aerated concrete(AAC) panels have ultra-light weight,excellent thermal insulation and energy absorption,so it is an ideal building material for protective structures.To improve the blast resistance of the AAC panels,three schemes are applied to strengthen the AAC panels through spraying 4 mm thick polyurea coating from top,bottom and double-sides.In three-point bending tests,the polyurea-coated AAC panels have much higher ultimate loads than the un-coated panels,but slightly lower than those strengthened by the carbon fiber reinforced plastics(CEFRPs).Close-in explosion experiments reveal the dynamic strengthening effect of the polyurea coating.Critical scaled distances of the strengthened AAC panels are acquired,which are valuable for the engineering application of the AAC panels in the extreme loading conditions.Polyurea coatings efficiently enhance the blast resistance of the bottom and double-sided polyurea-coated AAC panels.It is interesting that the polyurea-coated AAC panels have much more excellent blast resistance than the CFRP reinforced AAC panels,although the latter have better static mechanical properties.
文摘A series of impact tests of sandwich samples were completed using a large-diameter split Hopkinson pressure bar (SHPB)device at different velocities. The interlayer is made of foam concrete, loess or sand. The stress peak value decay, energy decay and waveform dispersion characters are studied by comparing the incident waves with the transmission waves. The tests indicate that the foam concrete has the best capabilities of shock resistance and energy absorption, the loess comes second, and the sand takes third place.
基金Project(2018YFC0604703)supported by the National Key R&D Program of ChinaProjects(51804181,51874190)supported by the National Natural Science Foundation of China+3 种基金Project(ZR2018QEE002)supported by the Shandong Province Natural Science Fund,ChinaProject(ZR2018ZA0603)supported by the Major Program of Shandong Province Natural Science Foundation,ChinaProject(2019GSF116003)supported by the Key R&D Project of Shandong Province,ChinaProject(SDKDYC190234)supported by the Shandong University of Science and Technology,Graduate Student Technology Innovation Project,China。
文摘The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition.Based on the in-site geological conditions of Longgu coal mine,this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition.Results showed that under the static loading condition,the maximum vertical stress,deformation and failure range are large,where the stress concentration coefficient is 1.64.The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm,respectively.Then,under the dynamic and static combined loading condition:(1)The influence of dynamic load frequency on the two-sides is more obvious;(2)The dynamic load amplitude has the greatest influence on the stress concentration degree,and the plastic failure tends to develop to the deeper;(3)With the dynamic load source distance increase,the response of surrounding rock is gradually attenuated.On this basis,empirical equations for each dynamic load conditions were obtained by using regression analysis method,and all correlation coefficients are greater than 0.99.This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.
基金the scholarship granted by the China Scholarship Councilthe support from the Institute of Chemical Materials,CAEP
文摘The friction on the projectile shank is usually excluded in the penetration analysis due to the difficulties to measure the pressure and frictional coefficient.In this article,the frictional force on projectile shank is discussed indirectly through the comparison between experimental data and empirical/analytical formulas of the penetration depth for both concrete and aluminium-alloy targets.It is found that the effect of the frictional force along the projectile shank can be further discussed by the afore comparison and discussion and cannot be ignored because of the relatively large effecting area,especially for deep penetration of concrete and aluminium-alloy targets,where the friction will account for more proportion of penetration resistance.
基金supported by the National Natural Science Foundation of China (Nos. 11772269, 11802248, and 11872318)。
文摘The elliptical cross-section ogive-nose projectile(ECOP) has recently attracted attention because it is well suited to the flattened shape of earth-penetrating weapons. However, the penetration performance of ECOPs has not been completely understood. The objective of this study was to investigate the penetration performance of ECOPs into concrete targets using a theoretical method. A general geometric model of ECOPs was introduced, and closed-form penetration equations were derived according to the dynamic cavity-expansion theory. The model was validated by comparing the predicted penetration depths with test data, and the maximum deviation was 15.8%. The increment in the penetration depth of the ECOP was evaluated using the proposed model, and the effect of the majoreminor axis ratio on the increment was examined. Additionally, the mechanism of the penetration-depth increment was investigated with respect to the caliber radius head, axial stress, and resistance.
基金supported by the National Natural Science Foundation of China [grant number 51278250]
文摘The influence of concrete components on projectile penetration is significant.To study the relationship between the equivalent mechanical properties and components of concrete under a penetration load,concrete is simplified as a two-phase composite of coarse aggregate and mortar,and a meso-mechanical model is established,including the equivalent equation of state model,the equivalent confining pressure strength model and the equivalent dynamic tensile strength model,considering shear stress,large deformation and pore compression.Tests of the mechanical properties of mortar,concrete and limestone were conducted;the results show that the equivalent mechanical properties of concrete calculated by the meso-mechanical model are consistent with the test results,and the equivalent mechanical properties of concrete with different volume fractions of coarse aggregate are obtained.Meso-scale and macro-scale numerical simulations of a projectile penetrating into concrete are carried out,the penetration depths obtained by meso-scale and macro-scale numerical simulations are consistent for different volume fractions of coarse aggregate and different velocities of the projectile,which verifies the rationality of the meso-mechanical model.
