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
The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains lar...The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.展开更多
In order to accommodate higher speeds,heavier axle weights,and vibration damping criteria,a new floating slab structure was proposed.The new type of floating slab track structure was composed of three prefabricated fl...In order to accommodate higher speeds,heavier axle weights,and vibration damping criteria,a new floating slab structure was proposed.The new type of floating slab track structure was composed of three prefabricated floating slabs longitudinally interconnected with magnesium ammonium phosphate concrete(MPC).This study investigated the dynamic performance of the structure.We constructd a full-scale indoor experimental model to scrutinize the disparities in the impact performance between a longitudinally connected floating slab track and its longitudinally disconnected counterpart.Additionally,a long-term fatigue experiment was conducted to assess the impact performance of longitudinally connected floating slab tracks under fatigue loading.The findings are described in the following.1)The new structure effectively suppresses ground vibrations,exhibiting a well-balanced energy distribution profile.However,the imposition of fatigue loading leads to a reduction in the damping performance of the steel spring damping system,thereby reducing its capacity to attenuate structural vibrations and leading to an increase in ground vibration energy;2)After 107 loading cycles,the attenuation rate of the vibration acceleration for the MPC increases by 171.9%.Conversely,at the corresponding disconnected location,the attenuation rate of ground vibration acceleration decreases by 65.6%.In conclusion,longitudinally connected floating slab tracks exhibit superior vibration reduction performance.While the vibration reduction performance of longitudinally connected floating slab tracks may diminish to some extent during long-term service,these tracks continue to meet specific vibration reduction requirements.展开更多
We have carried out an experimental study of liquid drop impact on superhydrophobic substrates covered by a carpet of chemically coated nano-wires.The micro-structure of the surface is similar to some biological ones(...We have carried out an experimental study of liquid drop impact on superhydrophobic substrates covered by a carpet of chemically coated nano-wires.The micro-structure of the surface is similar to some biological ones(Lotus leaf for example).In this situation the contact angle can then be considered as equal to 180 degrees,with no hysteresis.Due to its initial inertia,the drop experiences a flattening phase after it hits the surface,taking the shape of a pancake.Once it reaches its maximal lateral extension,the drop begins to retract and bounces back.We have extracted the lateral extension of the drop,and we propose a model that explains the trend.We find a limit initial velocity beyond which the drop protrudes into the nano-wire carpet.We discuss the relevance of practical issues in terms of self-cleaning surfaces or spray-cooling.展开更多
An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper(EWMD)and parallel springs are proposed in this work to enhance the reliability of engineering equipment.The impact res...An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper(EWMD)and parallel springs are proposed in this work to enhance the reliability of engineering equipment.The impact response and the energy dissipation mechanism of hat-shaped EWMD under different quasi-static compression deformations(2-7 mm)and impact heights(100-200 mm)are investigated using experimental and numerical methods.The results demonstrate distinct stages in the quasi-static mechanical characteristics of hat-shaped EWMD,including stiffness softening,negative stiffness,and stiffness hardening.The loss factor gradually increases with increasing compression deformation before entering the stiffness hardening stage.Under impact loads,the hat-shaped EWMD exhibits optimal impact energy absorption when it enters the negative stiffness stage(150 mm),resulting in the best impact isolation effect of metallic buffer.However,the impact energy absorption significantly decreases when hat-shaped EWMD enters the stiffness hardening stage.Interestingly,quasi-static compression analysis after experiencing different impact loads reveals the disappearance of the negative stiffness phenomenon.Moreover,with increasing impact loads,the stiffness hardening point progressively shifts to an earlier stage.展开更多
We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and p...We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.展开更多
Particle swarm algorithm(PSO) and genetic algorithm(GA) were used to optimize the back propagation(BP) artificial neural network for predicting the dynamic responses of the through silicon via(TSV) based three-dimensi...Particle swarm algorithm(PSO) and genetic algorithm(GA) were used to optimize the back propagation(BP) artificial neural network for predicting the dynamic responses of the through silicon via(TSV) based three-dimensional packaging structures.A finite element model of the TSV packaging structure with a strain-rate dependent constitutive model for solder joints was created to simulate the drop impact due to a free fall of 0.8 m to the rigid ground to investigate the structural dynamic responses during the whole impact process.The spatial coordinates of the solder joints were used as the input parameters of the hybrid neural network model for the drop impact responses,while the maximum Von Mises stress and PEEQ(plastic strain) values are identified the output parameters.The correlation coefficient(R),the mean absolute percentage error(MAPE) and the training time were used as the measures to validate and compare the proposed PSO-BP and GA-BP neural networks.The results show that both the PSO-BP model and the GA-BP model can achieve high accuracy predictions with strong generalization capability.Apparently,both optimized algorithms outperform the original BP model,but the PSO-BP model is slightly more superior than the GA-BP model.It is also demonstrated that the proposed optimized algorithms efficiently predict the drop impact responses of TSV packaging structures by greatly saving the computational and experimental cost of drop impact tests.展开更多
In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the ...In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity.For the parameter range explored,we identify the regime where splashing occurs with corolla breaking into droplets,and the regime where no splashing is observed.Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity,if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached.Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity,in the term of Froude and Reynolds numbers.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
The ffects of different laying angles on impact resistance and damage types of woven carbon fibre-reinforced polymer(CFRP)laminates were studied.The drop harmmer impact test and simulation analysis of woven CFRP lamin...The ffects of different laying angles on impact resistance and damage types of woven carbon fibre-reinforced polymer(CFRP)laminates were studied.The drop harmmer impact test and simulation analysis of woven CFRP laminates at four different velocities were carried out by means of the combination of experiment and explicit finite element analysis.The effect of impact velocity on damage pattern and fracture of woven CFRP laminates with eight layers and four laying angles(0°,15°,30°,and 45°)was studied by drop weight impact test,and the damage area of woven CFRP larminates with different laying angles was measured by ultrasonic nondestructive testing method.A user-defined material model was developed based on LS-DYNA to simulate the impact behavior of woven CFRP laminates.A finite element simulation model was established to effectively predict the complex damage evolution of woven CFRP laminates under low-speed impact loading.Its effectiveness was verified by impact response and damage crack pattern.The energy absorption and impact force of the laminated plate increase gradually from 0°to 45°in the laying angle of woven fabric.With the increase of laying angle from 0°to 459,the length of fracture crack and the damage area increase.The developed model can accurately predict the impact properties of the composites.展开更多
A thorough understanding of drop-weight impacted responses for polymer-bonded explosives(PBXs)is significant to evaluate their impact sensitivity.The characteristics of the drop-weight impacted pressed PBXs including ...A thorough understanding of drop-weight impacted responses for polymer-bonded explosives(PBXs)is significant to evaluate their impact sensitivity.The characteristics of the drop-weight impacted pressed PBXs including deforming,fracturing,forming a local high-temperature region and igniting,were simulated using a coupled mechanical-thermo-chemical model integrating micro-defects evolution.A novel evaluation method for impact sensitivity is established using the relation between the input kinetic energy and the output energy due to deformation,crushing energy,local hot spot energy and ignition.The effects of impact velocity on sensitivity were analyzed and the critical local ignition impact velocity is determined as 4.0-4.5 m/s.The simulated results show that shear-crack friction heating is the dominant ignition mechanism.The region along the boundary of PBXs sample is the most hazardous regions where ignition first occur.The propagation of stress wave in PBXs causes shear-crack hotspot and bulk temperature exhibiting an approximate 45°direction evolution path,which is the main reason that dominated damage-ignition region transits from the boundary to the central of sample.展开更多
A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this proble...A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.展开更多
Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this...Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this work, and the drop impact on such a stiffness-patterned substrate consisting of soft spirals surrounded by a rigid region is systematically investigated. The results show that the splash behavior of a drop on a stiffness-patterned substrate exhibits distinct characteristics from those on a homogeneous substrate. Prompt splash is more likely to occur on the substrate with the greater heterogeneity of stiffness, which is reflected in the lower critical impact velocity. Moreover, the splash velocity of emitted droplet is significantly larger on the heterogeneous substrate than that on a corresponding homogeneous substrate,especially at a higher impact velocity of the drop, indicating a stronger splash intensity on the heterogeneous substrate.The difference in drop splashing between homogeneous substrate and heterogeneous substrate is largely due to the stiffness heterogeneity, rather than the variation of overall stiffness of the substrate. The use of spiral shape provides a feasible solution for introducing stiffness heterogeneity of substrate. This study is conducive to the understanding of drop impact research beyond uniform substrates, reveals the potential of using stiffness-patterned substrates to control splash, and may find useful applications in industries related to drop impact and splash.展开更多
Solder interconnects reliability during drop impact is important for portable electronic products. In this paper, board level drop impact tests were conducted according to the standard of the Joint Electronic Devices ...Solder interconnects reliability during drop impact is important for portable electronic products. In this paper, board level drop impact tests were conducted according to the standard of the Joint Electronic Devices Engineering Council （JEDEC）. Solder failure drop numbers were recorded and solder failure analyses were carried out. A high speed data acquisition system was constructed to measure the printed cireuit board （ PCt~ ） dynamic response during the impact. Measured response data were used to characterize the loading feature of the impact. The relatioT~~hip between solder failure features and PCB dynamic response was correlated. Solder failure mechanisms were discussed. The correlation of PCB strain data with the solder failure life indicates that the solder damage accumulated during drop impact is dependent on both strain amplitude and modes contribution of the PCB. Compared with high strain amplitude loading condition, lower strain amplitude with higher mode can even produce more severe damage to the solder interconnects. Repeated impact loadings to the solder induce the combination failure mechanism of both impact and fatigue. Failure analyses results provide convincing verification for the complexity of the failure mechanisms.展开更多
The distribution of material resulting from the impact of a freely falling drop with a target liquid has been studied by photo and video registration methods.Different cases have been investigated by considering drops...The distribution of material resulting from the impact of a freely falling drop with a target liquid has been studied by photo and video registration methods.Different cases have been investigated by considering drops made of aqueous solutions(ink,salt,acid)and including fine solid particles(i.e.,suspensions).New features have been observed in terms of flow dynamics and thin components produced as a result of the impact(such as banded elements,ligaments,and vortices at the surface of the liquid).In particular,the characteristics of emerging netlike structures have been found to depend on the size of the suspension clusters.For the case of acetic acid,a different patterning behavior has been obtained:sequences of concentric arcs are produced in that case.However,linear scaling laws and the discrete nature of the distribution of the droplet material seem to be features common to all the cases considered.展开更多
Pear fruit is susceptible to bruising from mechanical impact during field harvesting operations and at all stages of postharvest handling.The postharvest shelf life of bruised fruits were shorter,and they softened rap...Pear fruit is susceptible to bruising from mechanical impact during field harvesting operations and at all stages of postharvest handling.The postharvest shelf life of bruised fruits were shorter,and they softened rapidly under cold storage compared with non-bruised samples.Developing strategies for reducing bruising during the supply chain requires an understanding of fruit dynamic behavior to different enforced loadings.Finite Element Method(FEM)is among the best techniques,in terms of accuracy and cost-efficiency,for studying the factors effective in impact-induced bruising.In this research,the drop test of pear sample was simulated using FEM.The simulation was conducted on a 3D solid model of the pear that was created by using non-contact optical scanning technology.This computer-based study aimed to assess the stress and strain distribution patterns within pear generated by collision of the fruit with a flat surface made of different materials.The contact force between two colliding surfaces is also investigated.The simulations were conducted at two different drop orientations and four different impact surfaces.Results showed that,in both drop orientations,the largest and smallest stresses,strains and contact forces were developed in collision with the steel and rubber surfaces,respectively.In general,these parameters were smaller when fruit collided with the surfaces along its horizontal axis than when collided along its vertical axis.Finally,analyses of stress and strain magnitudes showed that simulation stress and strain values were compatible with experiments data.展开更多
A single-phase free surface tracking model based on the Lattice Boltzmann Method （LBM）, which has capability of simulating liquid-gas system with the assumption that the gas phase has only negligible influence on th...A single-phase free surface tracking model based on the Lattice Boltzmann Method （LBM）, which has capability of simulating liquid-gas system with the assumption that the gas phase has only negligible influence on the liquid phase, is utilized to simulate the flow of a drop impacting on a liquid film. Three typical outcomes in the flows, i.e., deposition, crown and splash, which have been observed in the previous experiments, are obtained in the present three dimensional numerical simulations. The numerical results are consistent with the experimental and analytical results available.展开更多
Numerical simulations using CLSVOF(coupled level set and volume of fluid)method are performed to investigate the coalescence and splashing regimes when a spherical water drop hits on the water surface with an impingem...Numerical simulations using CLSVOF(coupled level set and volume of fluid)method are performed to investigate the coalescence and splashing regimes when a spherical water drop hits on the water surface with an impingement angle.Impingement angle is the angle between the velocity vector of primary drop and the normal vector to water surface.The effect of impingement angle,impact velocity and the height of target liquid are carried out.The impingement angle is varied from 0o to 90o showing the gradual change in phenomena.The formation of ship pro like shape,liquid sheet,secondary drops and crater are seen.Crater height,crater displacement,crown height and crown angle are calculated and the change in the parameters with change in impingement angle is noted.展开更多
This paper describes the connection establishment of label switched paths (LSP) in IP/MPLS over optical networks. Our investigations on two typical network topologies show that the number of add/drop ports of OXCs has...This paper describes the connection establishment of label switched paths (LSP) in IP/MPLS over optical networks. Our investigations on two typical network topologies show that the number of add/drop ports of OXCs has a significant impact on the LSP blocking performance.展开更多
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support from the Natural Science Foundation of Jiangsu Province(Grant No.BK20242059)the Collaborative Innovation Center for Prevention and Control of Mountain Geological Hazards of Zhejiang Province(PCMGH-2023-02)the opening fund of State Key Laboratory of Coal Mine Disaster Dynamics and Control(2011DA105827-FW202209)are gratefully acknowledged.
文摘The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.
基金Project(2022-Major-14)supported by the Science and Technology Research and Development Program Project of China Railway Group Limited。
文摘In order to accommodate higher speeds,heavier axle weights,and vibration damping criteria,a new floating slab structure was proposed.The new type of floating slab track structure was composed of three prefabricated floating slabs longitudinally interconnected with magnesium ammonium phosphate concrete(MPC).This study investigated the dynamic performance of the structure.We constructd a full-scale indoor experimental model to scrutinize the disparities in the impact performance between a longitudinally connected floating slab track and its longitudinally disconnected counterpart.Additionally,a long-term fatigue experiment was conducted to assess the impact performance of longitudinally connected floating slab tracks under fatigue loading.The findings are described in the following.1)The new structure effectively suppresses ground vibrations,exhibiting a well-balanced energy distribution profile.However,the imposition of fatigue loading leads to a reduction in the damping performance of the steel spring damping system,thereby reducing its capacity to attenuate structural vibrations and leading to an increase in ground vibration energy;2)After 107 loading cycles,the attenuation rate of the vibration acceleration for the MPC increases by 171.9%.Conversely,at the corresponding disconnected location,the attenuation rate of ground vibration acceleration decreases by 65.6%.In conclusion,longitudinally connected floating slab tracks exhibit superior vibration reduction performance.While the vibration reduction performance of longitudinally connected floating slab tracks may diminish to some extent during long-term service,these tracks continue to meet specific vibration reduction requirements.
文摘We have carried out an experimental study of liquid drop impact on superhydrophobic substrates covered by a carpet of chemically coated nano-wires.The micro-structure of the surface is similar to some biological ones(Lotus leaf for example).In this situation the contact angle can then be considered as equal to 180 degrees,with no hysteresis.Due to its initial inertia,the drop experiences a flattening phase after it hits the surface,taking the shape of a pancake.Once it reaches its maximal lateral extension,the drop begins to retract and bounces back.We have extracted the lateral extension of the drop,and we propose a model that explains the trend.We find a limit initial velocity beyond which the drop protrudes into the nano-wire carpet.We discuss the relevance of practical issues in terms of self-cleaning surfaces or spray-cooling.
基金the financial support by the National Natural Science Foundation of China(No.12272094)the Natural Science Foundation of Fujian Province of China(No.2022J01541)Natural Science Foundation of Hubei Province of China(No.2022CFB441)。
文摘An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper(EWMD)and parallel springs are proposed in this work to enhance the reliability of engineering equipment.The impact response and the energy dissipation mechanism of hat-shaped EWMD under different quasi-static compression deformations(2-7 mm)and impact heights(100-200 mm)are investigated using experimental and numerical methods.The results demonstrate distinct stages in the quasi-static mechanical characteristics of hat-shaped EWMD,including stiffness softening,negative stiffness,and stiffness hardening.The loss factor gradually increases with increasing compression deformation before entering the stiffness hardening stage.Under impact loads,the hat-shaped EWMD exhibits optimal impact energy absorption when it enters the negative stiffness stage(150 mm),resulting in the best impact isolation effect of metallic buffer.However,the impact energy absorption significantly decreases when hat-shaped EWMD enters the stiffness hardening stage.Interestingly,quasi-static compression analysis after experiencing different impact loads reveals the disappearance of the negative stiffness phenomenon.Moreover,with increasing impact loads,the stiffness hardening point progressively shifts to an earlier stage.
基金supported by the National Natural Science Foundation of China(Grant No.51109178)the Science and Technology Innovation Foundation of Northwestern Polytechnical University,China(Grant No.JC20120218)
文摘We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.
基金supported by the National Natural Science Foundation of China (No. 52175148)the Natural Science Foundation of Shaanxi Province (No. 2021KW-25)the Astronautics Supporting Technology Foundation of China (No. 2019-HT-XG)。
文摘Particle swarm algorithm(PSO) and genetic algorithm(GA) were used to optimize the back propagation(BP) artificial neural network for predicting the dynamic responses of the through silicon via(TSV) based three-dimensional packaging structures.A finite element model of the TSV packaging structure with a strain-rate dependent constitutive model for solder joints was created to simulate the drop impact due to a free fall of 0.8 m to the rigid ground to investigate the structural dynamic responses during the whole impact process.The spatial coordinates of the solder joints were used as the input parameters of the hybrid neural network model for the drop impact responses,while the maximum Von Mises stress and PEEQ(plastic strain) values are identified the output parameters.The correlation coefficient(R),the mean absolute percentage error(MAPE) and the training time were used as the measures to validate and compare the proposed PSO-BP and GA-BP neural networks.The results show that both the PSO-BP model and the GA-BP model can achieve high accuracy predictions with strong generalization capability.Apparently,both optimized algorithms outperform the original BP model,but the PSO-BP model is slightly more superior than the GA-BP model.It is also demonstrated that the proposed optimized algorithms efficiently predict the drop impact responses of TSV packaging structures by greatly saving the computational and experimental cost of drop impact tests.
基金This work was supported by the National Natural Science Foundation of China(Grants 91848201,11988102,11521202,11872004,and 11802004)The authors also acknowledge the partial support from the Beijing Natural Science Foundation(Grants L172002)The numerical simulations were performed on Tianhe-1 A,the National Super Computing Center in Tianjin,China.Muhammad Mohasan would like to thank Chinese Scholarship Council for providing Chinese Government Scholarship.
文摘In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity.For the parameter range explored,we identify the regime where splashing occurs with corolla breaking into droplets,and the regime where no splashing is observed.Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity,if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached.Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity,in the term of Froude and Reynolds numbers.
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the Jilin Scientific and Technological Development Program(No.20170101130JC)the National Natural Science Foundation of China(Nos.51775227 and 51375201)。
文摘The ffects of different laying angles on impact resistance and damage types of woven carbon fibre-reinforced polymer(CFRP)laminates were studied.The drop harmmer impact test and simulation analysis of woven CFRP laminates at four different velocities were carried out by means of the combination of experiment and explicit finite element analysis.The effect of impact velocity on damage pattern and fracture of woven CFRP laminates with eight layers and four laying angles(0°,15°,30°,and 45°)was studied by drop weight impact test,and the damage area of woven CFRP larminates with different laying angles was measured by ultrasonic nondestructive testing method.A user-defined material model was developed based on LS-DYNA to simulate the impact behavior of woven CFRP laminates.A finite element simulation model was established to effectively predict the complex damage evolution of woven CFRP laminates under low-speed impact loading.Its effectiveness was verified by impact response and damage crack pattern.The energy absorption and impact force of the laminated plate increase gradually from 0°to 45°in the laying angle of woven fabric.With the increase of laying angle from 0°to 459,the length of fracture crack and the damage area increase.The developed model can accurately predict the impact properties of the composites.
基金China National Nature Science Foundation(Grant No.11872119)Foundation Strengthening Project(Grant No.2020-JCJQ-GFJQ2126-007)+1 种基金Pre-research Program of Armament(Grant No.6142A03202002)China Postdoctoral Science Foundation(Grant No.BX20200046)for supporting this project。
文摘A thorough understanding of drop-weight impacted responses for polymer-bonded explosives(PBXs)is significant to evaluate their impact sensitivity.The characteristics of the drop-weight impacted pressed PBXs including deforming,fracturing,forming a local high-temperature region and igniting,were simulated using a coupled mechanical-thermo-chemical model integrating micro-defects evolution.A novel evaluation method for impact sensitivity is established using the relation between the input kinetic energy and the output energy due to deformation,crushing energy,local hot spot energy and ignition.The effects of impact velocity on sensitivity were analyzed and the critical local ignition impact velocity is determined as 4.0-4.5 m/s.The simulated results show that shear-crack friction heating is the dominant ignition mechanism.The region along the boundary of PBXs sample is the most hazardous regions where ignition first occur.The propagation of stress wave in PBXs causes shear-crack hotspot and bulk temperature exhibiting an approximate 45°direction evolution path,which is the main reason that dominated damage-ignition region transits from the boundary to the central of sample.
基金Project supported by the National Natural Science Foundation of China(Nos.11672310 and 11372326)the National Basic Research Program of China(No.2014CB04680202)
文摘A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.
基金Project supported by the Natural Science Foundation Project of Chongqing,China(Grant No.CSTC2020jcyjmsxmX0106)the Fundamental Research Funds for the Central Universities,China(Grant No.2020CDJ-LHSS-002)。
文摘Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this work, and the drop impact on such a stiffness-patterned substrate consisting of soft spirals surrounded by a rigid region is systematically investigated. The results show that the splash behavior of a drop on a stiffness-patterned substrate exhibits distinct characteristics from those on a homogeneous substrate. Prompt splash is more likely to occur on the substrate with the greater heterogeneity of stiffness, which is reflected in the lower critical impact velocity. Moreover, the splash velocity of emitted droplet is significantly larger on the heterogeneous substrate than that on a corresponding homogeneous substrate,especially at a higher impact velocity of the drop, indicating a stronger splash intensity on the heterogeneous substrate.The difference in drop splashing between homogeneous substrate and heterogeneous substrate is largely due to the stiffness heterogeneity, rather than the variation of overall stiffness of the substrate. The use of spiral shape provides a feasible solution for introducing stiffness heterogeneity of substrate. This study is conducive to the understanding of drop impact research beyond uniform substrates, reveals the potential of using stiffness-patterned substrates to control splash, and may find useful applications in industries related to drop impact and splash.
基金Supported by National Natural Science Foundation of China （No. 51075107 No. 51174069） and Key Project of Natural Science Foundation of Heilongjiang Province （No. ZD200910）.
文摘Solder interconnects reliability during drop impact is important for portable electronic products. In this paper, board level drop impact tests were conducted according to the standard of the Joint Electronic Devices Engineering Council （JEDEC）. Solder failure drop numbers were recorded and solder failure analyses were carried out. A high speed data acquisition system was constructed to measure the printed cireuit board （ PCt~ ） dynamic response during the impact. Measured response data were used to characterize the loading feature of the impact. The relatioT~~hip between solder failure features and PCB dynamic response was correlated. Solder failure mechanisms were discussed. The correlation of PCB strain data with the solder failure life indicates that the solder damage accumulated during drop impact is dependent on both strain amplitude and modes contribution of the PCB. Compared with high strain amplitude loading condition, lower strain amplitude with higher mode can even produce more severe damage to the solder interconnects. Repeated impact loadings to the solder induce the combination failure mechanism of both impact and fatigue. Failure analyses results provide convincing verification for the complexity of the failure mechanisms.
基金supported by the Russian Science Foundation(Project 19-19-00598“Hydrodynamics and energetics of drops and droplet jets:formation,motion,break-up,interaction with the contact surface,”).
文摘The distribution of material resulting from the impact of a freely falling drop with a target liquid has been studied by photo and video registration methods.Different cases have been investigated by considering drops made of aqueous solutions(ink,salt,acid)and including fine solid particles(i.e.,suspensions).New features have been observed in terms of flow dynamics and thin components produced as a result of the impact(such as banded elements,ligaments,and vortices at the surface of the liquid).In particular,the characteristics of emerging netlike structures have been found to depend on the size of the suspension clusters.For the case of acetic acid,a different patterning behavior has been obtained:sequences of concentric arcs are produced in that case.However,linear scaling laws and the discrete nature of the distribution of the droplet material seem to be features common to all the cases considered.
文摘Pear fruit is susceptible to bruising from mechanical impact during field harvesting operations and at all stages of postharvest handling.The postharvest shelf life of bruised fruits were shorter,and they softened rapidly under cold storage compared with non-bruised samples.Developing strategies for reducing bruising during the supply chain requires an understanding of fruit dynamic behavior to different enforced loadings.Finite Element Method(FEM)is among the best techniques,in terms of accuracy and cost-efficiency,for studying the factors effective in impact-induced bruising.In this research,the drop test of pear sample was simulated using FEM.The simulation was conducted on a 3D solid model of the pear that was created by using non-contact optical scanning technology.This computer-based study aimed to assess the stress and strain distribution patterns within pear generated by collision of the fruit with a flat surface made of different materials.The contact force between two colliding surfaces is also investigated.The simulations were conducted at two different drop orientations and four different impact surfaces.Results showed that,in both drop orientations,the largest and smallest stresses,strains and contact forces were developed in collision with the steel and rubber surfaces,respectively.In general,these parameters were smaller when fruit collided with the surfaces along its horizontal axis than when collided along its vertical axis.Finally,analyses of stress and strain magnitudes showed that simulation stress and strain values were compatible with experiments data.
基金the National Natural Science Foundation of China (Grant No. 10472062)the Special Scientific Foundation for Selection and Cultivation of Excellent Young Scholars in Shanghai and the Shanghai Leading Academic Discipline Project (Grant No.Y0103)
文摘A single-phase free surface tracking model based on the Lattice Boltzmann Method （LBM）, which has capability of simulating liquid-gas system with the assumption that the gas phase has only negligible influence on the liquid phase, is utilized to simulate the flow of a drop impacting on a liquid film. Three typical outcomes in the flows, i.e., deposition, crown and splash, which have been observed in the previous experiments, are obtained in the present three dimensional numerical simulations. The numerical results are consistent with the experimental and analytical results available.
文摘Numerical simulations using CLSVOF(coupled level set and volume of fluid)method are performed to investigate the coalescence and splashing regimes when a spherical water drop hits on the water surface with an impingement angle.Impingement angle is the angle between the velocity vector of primary drop and the normal vector to water surface.The effect of impingement angle,impact velocity and the height of target liquid are carried out.The impingement angle is varied from 0o to 90o showing the gradual change in phenomena.The formation of ship pro like shape,liquid sheet,secondary drops and crater are seen.Crater height,crater displacement,crown height and crown angle are calculated and the change in the parameters with change in impingement angle is noted.
文摘This paper describes the connection establishment of label switched paths (LSP) in IP/MPLS over optical networks. Our investigations on two typical network topologies show that the number of add/drop ports of OXCs has a significant impact on the LSP blocking performance.
