Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate...Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.展开更多
This paper presents an actuator used for the trajectory correction fuze,which is subject to high impact loadings during launch.A simulation method is carried out to obtain the peak-peak stress value of each component,...This paper presents an actuator used for the trajectory correction fuze,which is subject to high impact loadings during launch.A simulation method is carried out to obtain the peak-peak stress value of each component,from which the ball bearings are possible failures according to the results.Subsequently,three schemes against impact loadings,full-element deep groove ball bearing and integrated raceway,needle roller thrust bearing assembly,and gaskets are utilized for redesigning the actuator to effectively reduce the bearings’stress.However,multi-objectives optimization still needs to be conducted for the gaskets to decrease the stress value further to the yield stress.Four gasket’s structure parameters and three bearings’peak-peak stress are served as the four optimization variables and three objectives,respectively.Optimized Latin hypercube design is used for generating sample points,and Kriging model selected according to estimation result can establish the relationship between the variables and objectives,representing the simulation which is time-consuming.Accordingly,two optimization algorithms work out the Pareto solutions,from which the best solutions are selected,and verified by the simulation to determine the gaskets optimized structure parameters.It can be concluded that the simulation and optimization method based on these components is effective and efficient.展开更多
Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure m...Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.展开更多
In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-ele...In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-electric surface layers(referred to as"FG-TPMS-MEE curved-doubly shells")subjected to low-velocity impact loads.This study presents low-velocity impact load model based on a single springmass(S-M)approach.The FG-TPMS-MEE curved-doubly shells are covered with two magneto-electric surface layers,while the core layer consists of three types:I-graph and Wrapped Package-graph(IWP),Gyroid(G),and Primitive(P),with various graded functions.These types are notable for their exceptional stiffness-to-weight ratios,enabling a wide range of potential applications.The Maxwell equations and electromagnetic boundary conditions are applied to compute the change in electric potentials and magnetic potentials.The equilibrium equations of the shell are derived from a refined higher-order shear deformation theory(HSDT),and the transient responses of the FG-TPMS-MEE curveddoubly shells are subsequently determined using Newmark's direct integration method.These results have applications in structural vibration control and the analysis of structures subjected to impact or explosive loads.Furthermore,this study provides a theoretical prediction of the low-velocity impact load and magneto-electric-elastic effects on the free vibration and transient response of FG-TPMS-MEE curved-doubly shells.展开更多
Reinforced concrete(RC)structures are generally designed to carry quasi-static gravity loads through almost indispensable components namely slab,however,it may be subjected to high intense loads induced from the impac...Reinforced concrete(RC)structures are generally designed to carry quasi-static gravity loads through almost indispensable components namely slab,however,it may be subjected to high intense loads induced from the impact of projectiles generated by the tornado,falling construction equipment,and also from accidental explosions during their construction and service lifespan.Impacts due to rock/boulder falls do occur on the structures located especially in hilly areas.Such loadings are not predictable but may cause severe damage to the slab/structure.It stimulates structural engineers and researchers to investigate and understand the dynamic response of RC structures under such impulsive loading.This research work first investigates the performance of 1000×1000×75 mm^(3)conventionally reinforced two-way spanning normal strength concrete slab with only tension reinforcement(0.88%)under the concentric impact load(1035 N)using the finite element method based computer code,ABAQUS/Explicit-v.6.15.The impact load is delivered to the centroid of the slab using a solid-steel cylindroconical impactor(drop weight)with a flat nose of diameter 40 mm,having a total mass of 105 kg released from a fixed height of 2500 mm.Two popular concrete constitutive models in ABAQUS namely;Holmquist-Johnson-Cook(HJC)and Concrete Damage Plasticity(CDP),with strain rate effects as per fib MODEL CODE 2010,are used to model the concrete material behavior to impact loading and to simulate the damage to the slab.The slab response using these two models is analyzed and compared with the impact test results.The strain rate effect on the reinforcing steel bars has been incorporated in the analysis using the Malvar and Crawford(1998)approach.A classical elastoplastic kinematic idealization is considered to model the steel impactor and support system.Results reveal that the HJC model gives a little overestimation of peak displacement,maximum acceleration,and damage of the slab while the predictions given by the CDP model are in reasonable agreement with the experimental test results/observations available in the open literature.Following the validation of the numerical model,analyses have been extended to further investigate the damage response of the slab under eccentric impact loadings.In addition to the concentric location(P1)of the impacting device,five locations on a quarter of the slab i.e.,two along the diagonal(P2&P3),the other two along the mid-span(P4&P5),and the last one(P6)between P3 and P5,covering the entire slab,are considered.Computational results have been discussed and compared,and the evaluation of the most damaging location(s)of the impact is investigated.It has been found that the most critical location of the impact is not the centroid of the slab but the eccentric one with the eccentricity of 1/6th of the span from the centroid along the mid-span section.展开更多
Polypropylene(PP) fibres have primarily used to control shrinkage cracks or mitigate explosive spalling in concrete structures exposed to fire or subjected to impact/blast loads, with limited investigations on capacit...Polypropylene(PP) fibres have primarily used to control shrinkage cracks or mitigate explosive spalling in concrete structures exposed to fire or subjected to impact/blast loads, with limited investigations on capacity improvement. This study unveils the possibility of using PP micro-fibres to improve the impact behaviour of fibre-reinforced ultra-high-performance concrete(FRUHPC) columns. Results show that the addition of fibres significantly improves the impact behaviour of FRUHPC columns by shifting the failure mechanism from brittle shear to favourable flexural failure. The addition of steel or PP fibres affected the impact responses differently. Steel fibres considerably increased the peak impact force(up to 18%) while PP micro-fibres slightly increased the peak(3%-4%). FRUHPC significantly reduced the maximum midheight displacement by up to 30%(under 20°impact) and substantially improved the displacement recovery by up to 100%(under 20° impact). FRUHPC with steel fibres significantly improved the energy absorption while those with PP micro-fibres reduced the energy absorption, which is different from the effect of PP-macro fibre reported in the literature. The optimal fibre content for micro-PP fibres is 1% due to its minimal fibre usage and low peak and residual displacement. This study highlights the potential of FRUHPC as a promising material for impact-resistant structures by creating a more favourable flexural failure mechanism, enhancing ductility and toughness under impact loading, and advancing the understanding of the role of fibres in structural performance.展开更多
According to the catastrophe model for impact buckling of static loading structures, a new catastrophe model for impact loading failure of a static loading rock system was established, and one dimension (1D) catastrop...According to the catastrophe model for impact buckling of static loading structures, a new catastrophe model for impact loading failure of a static loading rock system was established, and one dimension (1D) catastrophe model was analyzed. The analysis results indicate that the furcation collection where catastrophe may take place is not only decided by mechanical system itself but also relates to exterior loading, which is different from the results obtained under mono-static loading where the bifurcation collection is only determined by mechanics of the system itself and has nothing to do with exterior loading. In addition, the corresponding 1D coupled static-dynamic loading experiment is designed to verify the analysis results of catastrophe model. The test is done with Instron 1342 electro-servo controlled testing system, in which medium strain rate is caused by monotony rising dynamic load. The parameters are obtained combining theoretical model with experiment. The experimental and theoretical curves of critical dynamic load vs static load are rather coincided, thus the new model is proved to be correct.展开更多
Having an accurate understanding of concrete behavior under effects of high strain rate loading with the aim of reducing incurred damages is of great importance. Due to complexities and high costs of experimental rese...Having an accurate understanding of concrete behavior under effects of high strain rate loading with the aim of reducing incurred damages is of great importance. Due to complexities and high costs of experimental research, numerical studies can be an appropriate alternative for experimental methods. Therefore, in this research capability of the finite element method for predicting concrete behavior at various loading conditions is evaluated by LS-DYNA software. First, the proposed method is presented and then is validated in three stages under different conditions. Results of load-lnidspan displacement showed good agreement between experimental and finite element results. Capability of finite element method in analyses of beams under various rates of loading was also validated by low error of the results. In addition, the proposed method has reasonable ability to evaluate reinforced concrete beams under various loading rates and different conditions.展开更多
YAG (Y_(3)Al_(5)O_(12)) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding t...YAG (Y_(3)Al_(5)O_(12)) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding the fracture behavior and damage mechanism of YAG is necessary for armor design. To explore the damage characteristics of YAG under compression and tension, shock compression and shockless spalling experiments with soft recovery technique are conducted. The spall strength of YAG is obtained and the recovered samples are observed by CT and SEM. It is shown that the macroscopic damage characteristic of YAG under compression is vertical split cracks with oblique fine cracks distributed in the entire sample, while that under tension is horizontal transgranular cracks concentrated near the main spall surface. The cracks generated by macroscopic compression, tension and shear stress extend in similar tensile form at the microscale. The proportion of transgranular fractures on spall surfaces is higher than that of cracks induced by macroscopic compression. Meanwhile, higher loading rate and longer loading duration increase the transgranular fracture percentage.展开更多
To examine the similarities and differences in the evolution of cavity,wetting and dynamics of a highspeed,oblique water-entry projectile with different positive angles of attack,a comparative analysis has been conduc...To examine the similarities and differences in the evolution of cavity,wetting and dynamics of a highspeed,oblique water-entry projectile with different positive angles of attack,a comparative analysis has been conducted based on the numerical results of two mathematical models,the rigid-body model and fluid-structure interaction model.In addition,the applicable scope of the above two methods,and the structural response characteristics of the projectile have also been investigated.Our results demonstrate that:(1) The impact loads and angular motion of the projectile of the rigid-body method are more likely to exhibit periodic variations due to the periodic tail slap,its range of positive angles of attack is about α<2°.(2) When the projectile undergone significant wetting,a strong coupling effect is observed among wetting,structural deformation,and projectile motion.With the applied projectile shape,it is observed that,when the projectile bends,the final wetting position is that of Part B(cylinder of body).With the occu rrence of this phenomenon,the projectile ballistics beco me completely unstable.(3) The force exerted on the lower surface of the projectile induced by wetting is the primary reason of the destabilization of the projectile traj ectory and structu ral deformation failure.Bending deformation is most likely to appear at the junction of Part C(cone of body) and Part D(tail).The safe angles of attack of the projectile stability are found to be about α≤2°.展开更多
The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitativel...The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.展开更多
In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness...In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness of 25 mm while increasing its impact by 2 J at each strike from 6 J to 16 J. The results show that the impact energies from 6 J to 12 J could not penetrate aluminum foam. However, the aluminum foam applied with the impact energy of 12 J incurred severe damages on its lower part. Finally, the aluminum foam applied with the impact energy of 14 J was penetrated. The striker having the impact energy of 6 J could penetrate aluminum foam around 10 mm. At this moment, aluminum foam could absorb the impact energy of around 9 J. When the impact energy of 14 J was applied on the aluminum foam, the aluminum foam was penetrated and it absorbed the impact energy of around 17.2 J. It is possible to create the safer structure against impact using the results of this work. The simulation results for the verification of the experimental results imply that the results for all the experiments in this work are reliable. It is possible to predict the structural safety of the aluminum foam for an impact if the impact behavior of aluminum foam performed in this work is utilized.展开更多
The transient response of an unlimited cylindrical cavity buried in the infinite elastic soil subjected to an anti-plane impact load along the cavern axis direction was studied.Using Laplace transform combining with c...The transient response of an unlimited cylindrical cavity buried in the infinite elastic soil subjected to an anti-plane impact load along the cavern axis direction was studied.Using Laplace transform combining with contour integral of the Laplace inverse transform specifically,the general analytical expressions of the soil displacement and stress are obtained in the time domain,respectively.And the numerical solutions of the problem computed by analytical expressions are presented.In the time domain,the dynamic responses of the infinite elastic soil are analyzed,and the calculation results are compared with those from numerical inversion proposed by Durbin and the static results.One observes good agreement between analytical and numerical inversion results,lending the further support to the method presented.Finally,some valuable shear wave propagation laws are gained: the displacement of the soil remains zero before the wave arrival,and after the shear wave arrival,the stress and the displacement at this point increase abruptly,then reduce and tend to the static value gradually at last.The wave attenuates along the radial,therefore the farther the wave is from the source,the smaller the stress and the displacement are,and the stress and the displacement are just functions of the radial distance from the axis.展开更多
This work presents a numerical simulation of ballistic penetration and high velocity impact behavior of plain and reinforced concrete panels.This paper is divided into two parts.The first part consists of numerical mo...This work presents a numerical simulation of ballistic penetration and high velocity impact behavior of plain and reinforced concrete panels.This paper is divided into two parts.The first part consists of numerical modeling of reinforced concrete panel penetrated with a spherical projectile using concrete damage plasticity(CDP)model,while the second part focuses on the comparison of CDP model and Johnson-Holmquist-2(JH-2)damage model and their ability to describe the behavior of concrete panel under impact loads.The first and second concrete panels have dimensions of 1500 mm1500 mm150 mm and 675 mm675 mm200 mm,respectively,and are meshed using 8-node hexahedron solid elements.The impact object used in the first part is a spherical projectile of 150 mm diameter,while in the second part steel projectile of a length of 152 mm is modeled as rigid element.Failure and scabbing characteristics are studied in the first part.In the second part,the comparison results are presented as damage contours,kinetic energy of projectile and internal energy of the concrete.The results revealed a severe fracture of the panel and high kinetic energy of the projectile using CDP model comparing to the JH-2 model.In addition,the internal energy of concrete using CDP model was found to be less comparing to the JH-2 model.展开更多
Aiming at the problems of demagnetization effect of electromagnetic buffer(EMB)caused by high velocity under intensive impact load and the difficulty and error of machining composite thin-walled long tube,a segmented ...Aiming at the problems of demagnetization effect of electromagnetic buffer(EMB)caused by high velocity under intensive impact load and the difficulty and error of machining composite thin-walled long tube,a segmented EMB is proposed.The inner tube and air-gap are divided into initial segments and the traversing segments.Through theoretical analysis,impact test and simulation,it can be found that the RRF curve has two peaks.Firstly,in order to reduce the resultant resistance force(RRF)peaks,the sensitivity analysis based on optimal Latin hypercube design(OLHD)and polynomial regression was performed.The results show that the smallest contribution ratio to the dynamic response is the seventh and ninth segments of the inner tube,which are less than 1%.Then,fully considering the uncertain factors,important parameters are selected for uncertain optimization after sensitivity analysis.The interval order and interval probability degree methods are used to establish interval uncertain optimization model of the RRF considering robustness.The model was solved using an interval nested optimization method based on radial basis function(RBF)neural network.Finally,the Pareto front is obtained and numerical simulation is performed to verify the optimal value.It indicates that the two kinds of RRF peak is obviously reduced,and the optimization object and strategy are effective.展开更多
This study focuses on the effect of lateral mass impact on ring-stiffened thin-walled cylindrical shell.Cylindrical shells were fabricated to validate the numerical modeling and analytical techniques,and drop tests we...This study focuses on the effect of lateral mass impact on ring-stiffened thin-walled cylindrical shell.Cylindrical shells were fabricated to validate the numerical modeling and analytical techniques,and drop tests were performed using a rigid spherical indenter.Next,stiffened-ring cylindrical shells with various structural size parameters were simulated using ABAQUS software.The relationships between the impact force,deformation displacement,and rebound velocity were established,on the basis of impact mechanics theory and simulation results.It derived fitting functions to analyse the relationship between the maximum load and maximum displacement of ring-stiffened cylindrical shell under dynamic mass impact.Based on the validation of the simulation model,the fitting function data were compared with the simulation results,and the functions showed a good accuracy.Besides,the parameters,mass ratio and stiffened-ring mass ratio were used to reflect the effect of the mass change in the ring-stiffened cylindrical shell.Furthermore,parametric studies on ring-stiffened cylindrical shell models were conducted to analyse the progressive impact responses.展开更多
Ultra-high molecular weight polyethylene(UHMWPE)fiber composite has been extensively used to construct lightweight protective structures against ballistic impacts,yet little is known about its performance when subject...Ultra-high molecular weight polyethylene(UHMWPE)fiber composite has been extensively used to construct lightweight protective structures against ballistic impacts,yet little is known about its performance when subjected to combined blast and fragment impacts.Built upon a recently developed laboratory-scale experimental technique to generate simulated combined loading through the impact of a fragment-foam composite projectile launched from a light gas gun,the dynamic responses of fullyclamped UHMWPE plates subjected to combined loading were characterized experimentally,with corresponding deformation and failure modes compared with those measured with simulated blast loading alone.Subsequently,to explore the underlying physical mechanisms,three-dimensional(3D)numerical simulations with the method of finite elements(FE)were systematically carried out.Numerical predictions compared favorably well with experimental measurements,thus validating the feasibility of the established FE model.Relative to the case of blast loading alone,combined blast and fragment loading led to larger maximum deflections of clamped UHMWPE plates.The position of the FSP in the foam sabot affected significantly the performance of a UHMWPE target,either enhancing or decreasing its ballistic resistance.When the blast loading and fragment impact arrived simultaneously at the target,its ballistic resistance was superior to that achieved when subjected to fragment impact alone,and benefited from the accelerated movement of the target due to simultaneous blast loading.展开更多
To evaluate the operator health risk exposed to whole-body vibration(WBV) while the electric-shovel loads the ore on the truck body, the semi-truck mathematical model and 3-D virtual prototype were built to simulate t...To evaluate the operator health risk exposed to whole-body vibration(WBV) while the electric-shovel loads the ore on the truck body, the semi-truck mathematical model and 3-D virtual prototype were built to simulate the high shockwave of truck cab under the shovel loading. Discrete element method was utilized to accurately estimate the impacting force on the truck body. Based on the ISO 2631-5 criteria, the Sed is about 0.56 MPa in both models, which means that the dump operators have a high probability of adverse health effects over long-term exposure to these vibrations. The 4-DOF operator model was built to investigate the biodynamic response of seated-human body exposed to WBV in terms of the transmission of vibrations through the body. The results show that the response peak is in the frequency range of 4-6 Hz corresponding to the primary body resonant frequency.展开更多
In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests ...In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests were implemented in the drop plate impact device.Strain gauges were employed to measure impact loads and crack initiation time.The corresponding numerical model was established by using the dynamic finite difference program AUTODYN,and the experimental-numerical method and ABAQUS code were utilized to obtain the initial fracture toughness of the crack.Using experiments and numerical research,we concluded that the DCCP specimen is suitable for measuring the initial fracture toughness of pure mode Ⅰ and mode Ⅱ cracks at the same time;the dynamic initiation toughness increases with the increase of loading rate and the crack initiation time decreases with increasing loading rate;the initiation toughness of mode Ⅱ crack is 0.5 times that of mode Ⅰ crack when subjected to the same loading rate.For the pre-crack in the vicinity of the bottom of a sample,when its length increases from 20 to 100 mm,the dynamic initiation toughness of the pure mode Ⅰ crack gradually decreases,and the longer the lower crack length is,the easier the crack would initiate,but the dynamic initiation toughness of pure mode Ⅱ crack varies little.展开更多
This paper presents a new 3D mesoscopic model of ultra-high performance cement-based composite(UHPCC)to investigate its dynamic tensile behavior.In this model,the UHPCC is regarded as a two-phase material composed of ...This paper presents a new 3D mesoscopic model of ultra-high performance cement-based composite(UHPCC)to investigate its dynamic tensile behavior.In this model,the UHPCC is regarded as a two-phase material composed of cementitious matrix and randomly distributed fibers.The model is established using the commercial software LS-DYNA and involves generating the randomly distributed fiber elements with considerations of diameter,length,orientation and volume fraction,and then fully constraining them with the matrix.In particular,to capture the slipping effect between fibers and matrix that has a strong influence on the dynamic tensile behavior,the fibers are modelled by a fictitious material represented by the load-slip relation.The strain-rate effect of slipping force neglected in most of previous studies is considered by calibrating constitutive parameters of the fictitious material under different strain-rates based on the single fiber pullout tests.Finally,the 3D mesoscopic model is validated against three sets of tension-dominated experiments covered a wide range of loading intensity.Numerical predictions demonstrate that strain-rate effect of slipping force must be considered,and the neglect of it may lead to a great underestimation of the dynamic tensile strength of UHPCC material and would unavoidably underestimate the blast resistance of UHPCC components.展开更多
文摘Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.
基金The authors would like to acknowledge National Defense Pre-Research Foundation of China(Grant No.41419030102)to provide fund for conducting experiments.
文摘This paper presents an actuator used for the trajectory correction fuze,which is subject to high impact loadings during launch.A simulation method is carried out to obtain the peak-peak stress value of each component,from which the ball bearings are possible failures according to the results.Subsequently,three schemes against impact loadings,full-element deep groove ball bearing and integrated raceway,needle roller thrust bearing assembly,and gaskets are utilized for redesigning the actuator to effectively reduce the bearings’stress.However,multi-objectives optimization still needs to be conducted for the gaskets to decrease the stress value further to the yield stress.Four gasket’s structure parameters and three bearings’peak-peak stress are served as the four optimization variables and three objectives,respectively.Optimized Latin hypercube design is used for generating sample points,and Kriging model selected according to estimation result can establish the relationship between the variables and objectives,representing the simulation which is time-consuming.Accordingly,two optimization algorithms work out the Pareto solutions,from which the best solutions are selected,and verified by the simulation to determine the gaskets optimized structure parameters.It can be concluded that the simulation and optimization method based on these components is effective and efficient.
基金Projects(51274254,51322403)supported by the National Natural Science Foundation of ChinaProject(NCET-11-0528)supported by theProgram for New Century Excellent Talents in University,ChinaProject(2013SK2011)supported by Hunan Province Science andTechnology Plan,China
文摘Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.
文摘In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-electric surface layers(referred to as"FG-TPMS-MEE curved-doubly shells")subjected to low-velocity impact loads.This study presents low-velocity impact load model based on a single springmass(S-M)approach.The FG-TPMS-MEE curved-doubly shells are covered with two magneto-electric surface layers,while the core layer consists of three types:I-graph and Wrapped Package-graph(IWP),Gyroid(G),and Primitive(P),with various graded functions.These types are notable for their exceptional stiffness-to-weight ratios,enabling a wide range of potential applications.The Maxwell equations and electromagnetic boundary conditions are applied to compute the change in electric potentials and magnetic potentials.The equilibrium equations of the shell are derived from a refined higher-order shear deformation theory(HSDT),and the transient responses of the FG-TPMS-MEE curveddoubly shells are subsequently determined using Newmark's direct integration method.These results have applications in structural vibration control and the analysis of structures subjected to impact or explosive loads.Furthermore,this study provides a theoretical prediction of the low-velocity impact load and magneto-electric-elastic effects on the free vibration and transient response of FG-TPMS-MEE curved-doubly shells.
文摘Reinforced concrete(RC)structures are generally designed to carry quasi-static gravity loads through almost indispensable components namely slab,however,it may be subjected to high intense loads induced from the impact of projectiles generated by the tornado,falling construction equipment,and also from accidental explosions during their construction and service lifespan.Impacts due to rock/boulder falls do occur on the structures located especially in hilly areas.Such loadings are not predictable but may cause severe damage to the slab/structure.It stimulates structural engineers and researchers to investigate and understand the dynamic response of RC structures under such impulsive loading.This research work first investigates the performance of 1000×1000×75 mm^(3)conventionally reinforced two-way spanning normal strength concrete slab with only tension reinforcement(0.88%)under the concentric impact load(1035 N)using the finite element method based computer code,ABAQUS/Explicit-v.6.15.The impact load is delivered to the centroid of the slab using a solid-steel cylindroconical impactor(drop weight)with a flat nose of diameter 40 mm,having a total mass of 105 kg released from a fixed height of 2500 mm.Two popular concrete constitutive models in ABAQUS namely;Holmquist-Johnson-Cook(HJC)and Concrete Damage Plasticity(CDP),with strain rate effects as per fib MODEL CODE 2010,are used to model the concrete material behavior to impact loading and to simulate the damage to the slab.The slab response using these two models is analyzed and compared with the impact test results.The strain rate effect on the reinforcing steel bars has been incorporated in the analysis using the Malvar and Crawford(1998)approach.A classical elastoplastic kinematic idealization is considered to model the steel impactor and support system.Results reveal that the HJC model gives a little overestimation of peak displacement,maximum acceleration,and damage of the slab while the predictions given by the CDP model are in reasonable agreement with the experimental test results/observations available in the open literature.Following the validation of the numerical model,analyses have been extended to further investigate the damage response of the slab under eccentric impact loadings.In addition to the concentric location(P1)of the impacting device,five locations on a quarter of the slab i.e.,two along the diagonal(P2&P3),the other two along the mid-span(P4&P5),and the last one(P6)between P3 and P5,covering the entire slab,are considered.Computational results have been discussed and compared,and the evaluation of the most damaging location(s)of the impact is investigated.It has been found that the most critical location of the impact is not the centroid of the slab but the eccentric one with the eccentricity of 1/6th of the span from the centroid along the mid-span section.
基金the financial support from Australian Research Council(ARC)(Grant No.DP220100307).
文摘Polypropylene(PP) fibres have primarily used to control shrinkage cracks or mitigate explosive spalling in concrete structures exposed to fire or subjected to impact/blast loads, with limited investigations on capacity improvement. This study unveils the possibility of using PP micro-fibres to improve the impact behaviour of fibre-reinforced ultra-high-performance concrete(FRUHPC) columns. Results show that the addition of fibres significantly improves the impact behaviour of FRUHPC columns by shifting the failure mechanism from brittle shear to favourable flexural failure. The addition of steel or PP fibres affected the impact responses differently. Steel fibres considerably increased the peak impact force(up to 18%) while PP micro-fibres slightly increased the peak(3%-4%). FRUHPC significantly reduced the maximum midheight displacement by up to 30%(under 20°impact) and substantially improved the displacement recovery by up to 100%(under 20° impact). FRUHPC with steel fibres significantly improved the energy absorption while those with PP micro-fibres reduced the energy absorption, which is different from the effect of PP-macro fibre reported in the literature. The optimal fibre content for micro-PP fibres is 1% due to its minimal fibre usage and low peak and residual displacement. This study highlights the potential of FRUHPC as a promising material for impact-resistant structures by creating a more favourable flexural failure mechanism, enhancing ductility and toughness under impact loading, and advancing the understanding of the role of fibres in structural performance.
基金Project(50490272 ,50490274 ,10472134) supported by the Natural Science Foundation of China project(2005038250)supported by the China Postdoctoral Foundation
文摘According to the catastrophe model for impact buckling of static loading structures, a new catastrophe model for impact loading failure of a static loading rock system was established, and one dimension (1D) catastrophe model was analyzed. The analysis results indicate that the furcation collection where catastrophe may take place is not only decided by mechanical system itself but also relates to exterior loading, which is different from the results obtained under mono-static loading where the bifurcation collection is only determined by mechanics of the system itself and has nothing to do with exterior loading. In addition, the corresponding 1D coupled static-dynamic loading experiment is designed to verify the analysis results of catastrophe model. The test is done with Instron 1342 electro-servo controlled testing system, in which medium strain rate is caused by monotony rising dynamic load. The parameters are obtained combining theoretical model with experiment. The experimental and theoretical curves of critical dynamic load vs static load are rather coincided, thus the new model is proved to be correct.
文摘Having an accurate understanding of concrete behavior under effects of high strain rate loading with the aim of reducing incurred damages is of great importance. Due to complexities and high costs of experimental research, numerical studies can be an appropriate alternative for experimental methods. Therefore, in this research capability of the finite element method for predicting concrete behavior at various loading conditions is evaluated by LS-DYNA software. First, the proposed method is presented and then is validated in three stages under different conditions. Results of load-lnidspan displacement showed good agreement between experimental and finite element results. Capability of finite element method in analyses of beams under various rates of loading was also validated by low error of the results. In addition, the proposed method has reasonable ability to evaluate reinforced concrete beams under various loading rates and different conditions.
基金This work is funded by the National Natural Science Foundation of China(No.11772159)the NSAF Joint Fund(No.U1730101)the Fundamental Research Funds for the Central Universities(No.30917011104).
文摘YAG (Y_(3)Al_(5)O_(12)) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding the fracture behavior and damage mechanism of YAG is necessary for armor design. To explore the damage characteristics of YAG under compression and tension, shock compression and shockless spalling experiments with soft recovery technique are conducted. The spall strength of YAG is obtained and the recovered samples are observed by CT and SEM. It is shown that the macroscopic damage characteristic of YAG under compression is vertical split cracks with oblique fine cracks distributed in the entire sample, while that under tension is horizontal transgranular cracks concentrated near the main spall surface. The cracks generated by macroscopic compression, tension and shear stress extend in similar tensile form at the microscale. The proportion of transgranular fractures on spall surfaces is higher than that of cracks induced by macroscopic compression. Meanwhile, higher loading rate and longer loading duration increase the transgranular fracture percentage.
基金supported by the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX24_0714).
文摘To examine the similarities and differences in the evolution of cavity,wetting and dynamics of a highspeed,oblique water-entry projectile with different positive angles of attack,a comparative analysis has been conducted based on the numerical results of two mathematical models,the rigid-body model and fluid-structure interaction model.In addition,the applicable scope of the above two methods,and the structural response characteristics of the projectile have also been investigated.Our results demonstrate that:(1) The impact loads and angular motion of the projectile of the rigid-body method are more likely to exhibit periodic variations due to the periodic tail slap,its range of positive angles of attack is about α<2°.(2) When the projectile undergone significant wetting,a strong coupling effect is observed among wetting,structural deformation,and projectile motion.With the applied projectile shape,it is observed that,when the projectile bends,the final wetting position is that of Part B(cylinder of body).With the occu rrence of this phenomenon,the projectile ballistics beco me completely unstable.(3) The force exerted on the lower surface of the projectile induced by wetting is the primary reason of the destabilization of the projectile traj ectory and structu ral deformation failure.Bending deformation is most likely to appear at the junction of Part C(cone of body) and Part D(tail).The safe angles of attack of the projectile stability are found to be about α≤2°.
基金Projects(51822403,51827901)supported by the National Natural Science Foundation of ChinaProject(2019ZT08G315)supported by the Department of Science and Technology of Guangdong Province,China。
文摘The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.
基金Project(2011-0006548)supported by the Basic Research Program through the National Research Foundation of Korea
文摘In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness of 25 mm while increasing its impact by 2 J at each strike from 6 J to 16 J. The results show that the impact energies from 6 J to 12 J could not penetrate aluminum foam. However, the aluminum foam applied with the impact energy of 12 J incurred severe damages on its lower part. Finally, the aluminum foam applied with the impact energy of 14 J was penetrated. The striker having the impact energy of 6 J could penetrate aluminum foam around 10 mm. At this moment, aluminum foam could absorb the impact energy of around 9 J. When the impact energy of 14 J was applied on the aluminum foam, the aluminum foam was penetrated and it absorbed the impact energy of around 17.2 J. It is possible to create the safer structure against impact using the results of this work. The simulation results for the verification of the experimental results imply that the results for all the experiments in this work are reliable. It is possible to predict the structural safety of the aluminum foam for an impact if the impact behavior of aluminum foam performed in this work is utilized.
文摘The transient response of an unlimited cylindrical cavity buried in the infinite elastic soil subjected to an anti-plane impact load along the cavern axis direction was studied.Using Laplace transform combining with contour integral of the Laplace inverse transform specifically,the general analytical expressions of the soil displacement and stress are obtained in the time domain,respectively.And the numerical solutions of the problem computed by analytical expressions are presented.In the time domain,the dynamic responses of the infinite elastic soil are analyzed,and the calculation results are compared with those from numerical inversion proposed by Durbin and the static results.One observes good agreement between analytical and numerical inversion results,lending the further support to the method presented.Finally,some valuable shear wave propagation laws are gained: the displacement of the soil remains zero before the wave arrival,and after the shear wave arrival,the stress and the displacement at this point increase abruptly,then reduce and tend to the static value gradually at last.The wave attenuates along the radial,therefore the farther the wave is from the source,the smaller the stress and the displacement are,and the stress and the displacement are just functions of the radial distance from the axis.
文摘This work presents a numerical simulation of ballistic penetration and high velocity impact behavior of plain and reinforced concrete panels.This paper is divided into two parts.The first part consists of numerical modeling of reinforced concrete panel penetrated with a spherical projectile using concrete damage plasticity(CDP)model,while the second part focuses on the comparison of CDP model and Johnson-Holmquist-2(JH-2)damage model and their ability to describe the behavior of concrete panel under impact loads.The first and second concrete panels have dimensions of 1500 mm1500 mm150 mm and 675 mm675 mm200 mm,respectively,and are meshed using 8-node hexahedron solid elements.The impact object used in the first part is a spherical projectile of 150 mm diameter,while in the second part steel projectile of a length of 152 mm is modeled as rigid element.Failure and scabbing characteristics are studied in the first part.In the second part,the comparison results are presented as damage contours,kinetic energy of projectile and internal energy of the concrete.The results revealed a severe fracture of the panel and high kinetic energy of the projectile using CDP model comparing to the JH-2 model.In addition,the internal energy of concrete using CDP model was found to be less comparing to the JH-2 model.
基金the National Natural Science Foundation of China(grant number 301070603)。
文摘Aiming at the problems of demagnetization effect of electromagnetic buffer(EMB)caused by high velocity under intensive impact load and the difficulty and error of machining composite thin-walled long tube,a segmented EMB is proposed.The inner tube and air-gap are divided into initial segments and the traversing segments.Through theoretical analysis,impact test and simulation,it can be found that the RRF curve has two peaks.Firstly,in order to reduce the resultant resistance force(RRF)peaks,the sensitivity analysis based on optimal Latin hypercube design(OLHD)and polynomial regression was performed.The results show that the smallest contribution ratio to the dynamic response is the seventh and ninth segments of the inner tube,which are less than 1%.Then,fully considering the uncertain factors,important parameters are selected for uncertain optimization after sensitivity analysis.The interval order and interval probability degree methods are used to establish interval uncertain optimization model of the RRF considering robustness.The model was solved using an interval nested optimization method based on radial basis function(RBF)neural network.Finally,the Pareto front is obtained and numerical simulation is performed to verify the optimal value.It indicates that the two kinds of RRF peak is obviously reduced,and the optimization object and strategy are effective.
基金supported by the National Natural Science Foundation of China(Grant No.51508123,named“Study on blast response of floating roof storage tank in material point method”)Natural Science Foundation of Heilongjiang Province,China(LH2019A008)to provide fund for conducting experiments and research.The authors would like to acknowledge Professor Wei Wang in Harbin Institute of Technology for instructions and help in experiment design.
文摘This study focuses on the effect of lateral mass impact on ring-stiffened thin-walled cylindrical shell.Cylindrical shells were fabricated to validate the numerical modeling and analytical techniques,and drop tests were performed using a rigid spherical indenter.Next,stiffened-ring cylindrical shells with various structural size parameters were simulated using ABAQUS software.The relationships between the impact force,deformation displacement,and rebound velocity were established,on the basis of impact mechanics theory and simulation results.It derived fitting functions to analyse the relationship between the maximum load and maximum displacement of ring-stiffened cylindrical shell under dynamic mass impact.Based on the validation of the simulation model,the fitting function data were compared with the simulation results,and the functions showed a good accuracy.Besides,the parameters,mass ratio and stiffened-ring mass ratio were used to reflect the effect of the mass change in the ring-stiffened cylindrical shell.Furthermore,parametric studies on ring-stiffened cylindrical shell models were conducted to analyse the progressive impact responses.
基金supported by the National Natural Science Foundation of China(Grant No.12032010,11902155 and 12072250)by the Natural Science Foundation of Jiangsu Province(Grant No.BK20190382)+2 种基金by the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-I-0222K01)by the Fund of Prospective Layout of Scientific Research for NUAAby the Foundation for the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Ultra-high molecular weight polyethylene(UHMWPE)fiber composite has been extensively used to construct lightweight protective structures against ballistic impacts,yet little is known about its performance when subjected to combined blast and fragment impacts.Built upon a recently developed laboratory-scale experimental technique to generate simulated combined loading through the impact of a fragment-foam composite projectile launched from a light gas gun,the dynamic responses of fullyclamped UHMWPE plates subjected to combined loading were characterized experimentally,with corresponding deformation and failure modes compared with those measured with simulated blast loading alone.Subsequently,to explore the underlying physical mechanisms,three-dimensional(3D)numerical simulations with the method of finite elements(FE)were systematically carried out.Numerical predictions compared favorably well with experimental measurements,thus validating the feasibility of the established FE model.Relative to the case of blast loading alone,combined blast and fragment loading led to larger maximum deflections of clamped UHMWPE plates.The position of the FSP in the foam sabot affected significantly the performance of a UHMWPE target,either enhancing or decreasing its ballistic resistance.When the blast loading and fragment impact arrived simultaneously at the target,its ballistic resistance was superior to that achieved when subjected to fragment impact alone,and benefited from the accelerated movement of the target due to simultaneous blast loading.
基金Project(2006BAB11B03)supported by the National Key Technology Research and Development Program of ChinaProject(Z1011030055010004)supported by Beijing Municipal Science Program of China
文摘To evaluate the operator health risk exposed to whole-body vibration(WBV) while the electric-shovel loads the ore on the truck body, the semi-truck mathematical model and 3-D virtual prototype were built to simulate the high shockwave of truck cab under the shovel loading. Discrete element method was utilized to accurately estimate the impacting force on the truck body. Based on the ISO 2631-5 criteria, the Sed is about 0.56 MPa in both models, which means that the dump operators have a high probability of adverse health effects over long-term exposure to these vibrations. The 4-DOF operator model was built to investigate the biodynamic response of seated-human body exposed to WBV in terms of the transmission of vibrations through the body. The results show that the response peak is in the frequency range of 4-6 Hz corresponding to the primary body resonant frequency.
基金Projects(U19A2098,1210021843)supported by the National Natural Science Foundation of ChinaProject(2021SCU12130)supported by Fundamental Research Funds for the Central Universities,China+1 种基金Project(2021YJ0511)supported by the Sichuan Science and Technology Program,ChinaProjects(DESEYU202205,DESE202005)supported by the Open Fund of Key Laboratory of Deep Earth Science and Engineering,China。
文摘In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests were implemented in the drop plate impact device.Strain gauges were employed to measure impact loads and crack initiation time.The corresponding numerical model was established by using the dynamic finite difference program AUTODYN,and the experimental-numerical method and ABAQUS code were utilized to obtain the initial fracture toughness of the crack.Using experiments and numerical research,we concluded that the DCCP specimen is suitable for measuring the initial fracture toughness of pure mode Ⅰ and mode Ⅱ cracks at the same time;the dynamic initiation toughness increases with the increase of loading rate and the crack initiation time decreases with increasing loading rate;the initiation toughness of mode Ⅱ crack is 0.5 times that of mode Ⅰ crack when subjected to the same loading rate.For the pre-crack in the vicinity of the bottom of a sample,when its length increases from 20 to 100 mm,the dynamic initiation toughness of the pure mode Ⅰ crack gradually decreases,and the longer the lower crack length is,the easier the crack would initiate,but the dynamic initiation toughness of pure mode Ⅱ crack varies little.
基金supported by the National Natural Science Foundations of China(No.52178515,No.51808550 and No.51738011).
文摘This paper presents a new 3D mesoscopic model of ultra-high performance cement-based composite(UHPCC)to investigate its dynamic tensile behavior.In this model,the UHPCC is regarded as a two-phase material composed of cementitious matrix and randomly distributed fibers.The model is established using the commercial software LS-DYNA and involves generating the randomly distributed fiber elements with considerations of diameter,length,orientation and volume fraction,and then fully constraining them with the matrix.In particular,to capture the slipping effect between fibers and matrix that has a strong influence on the dynamic tensile behavior,the fibers are modelled by a fictitious material represented by the load-slip relation.The strain-rate effect of slipping force neglected in most of previous studies is considered by calibrating constitutive parameters of the fictitious material under different strain-rates based on the single fiber pullout tests.Finally,the 3D mesoscopic model is validated against three sets of tension-dominated experiments covered a wide range of loading intensity.Numerical predictions demonstrate that strain-rate effect of slipping force must be considered,and the neglect of it may lead to a great underestimation of the dynamic tensile strength of UHPCC material and would unavoidably underestimate the blast resistance of UHPCC components.
