This study investigates how Internet media in the mobile phone influence on the cognitive and behavioral aspects of human sexuality. Sex is being deviating from socially accepted behaviors; ranging from bisexuality to...This study investigates how Internet media in the mobile phone influence on the cognitive and behavioral aspects of human sexuality. Sex is being deviating from socially accepted behaviors; ranging from bisexuality to homosexuality. Based on the qualitative methodology using particular case studies and textual analysis as well as survey research leading to quantitative methodology, this assumes of a transition of cultures as a result of the thorough impact of Internet towards society. In conclusion, lnternet implicit practices in the Mobile Phone in youth and teen societies storms a big change in sexuality, is also affecting towards the human cognitive and behavioral phases of the social life in traditional Buddhist rural village setting in Sri Lanka.展开更多
Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an...Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.展开更多
The laser powder bed fusion(L-PBF)additively manufactured CoCrFeNi high-entropy alloy(HEA),with face-centered cubic(FCC)crystal structure,demonstrates better comprehensive mechanical properties in the building directi...The laser powder bed fusion(L-PBF)additively manufactured CoCrFeNi high-entropy alloy(HEA),with face-centered cubic(FCC)crystal structure,demonstrates better comprehensive mechanical properties in the building direction(BD).Loading quasi-static,dynamic fatigue,and dynamic separated Hopkinson press bar(SHPB)impact stress conditions along the BD of the L-PBF processed HEA exhibit intriguing mi-crostructural evolution characteristics.The L-PBF generates hierarchical dislocation grids containing nu-merous cell substructures within the HEA FCC grains,impeding dislocation motion during deformation and improving the strength.When subjected to dynamic fatigue loading,the dislocation grids restrict the mean free path of dislocations and thus trigger the activation of abundant stacking faults.Hence,nu-merous nanotwins form near the end of the fatigue life.Multiple twinning systems can also be activated under dynamic high-speed impact loading.Especially at a low temperature of 77 K,the stacking fault energy of the CoCrFeNi HEA decreases,resulting in increased activation of nanotwins,exhibiting excep-tional toughness and resistance to dynamic loads.Additional twin boundaries also impede dislocation movement for the strain hardening.These findings hold valuable implications for the study of additively manufactured HEA parts working in extreme environments.展开更多
This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casti...This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.展开更多
Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.Th...Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.展开更多
This research addresses the growing demand for high-performance protective materials against high-velocity projectile impacts.The performance of multi-layered steel fiber-reinforced mortar(SFRM)panels with varying thi...This research addresses the growing demand for high-performance protective materials against high-velocity projectile impacts.The performance of multi-layered steel fiber-reinforced mortar(SFRM)panels with varying thicknesses and air gaps,was experimentally investigated under single and repeated impacts of 7.62×51 mm bullets fired from a distance of 50 m.The impact events were recorded using a high-speed camera at 40000 fps.Panel performance was assessed in terms of failure modes,kinetic energy absorption,spalling diameter,and percentage of back-face damage area,and weight loss.Results showed that panel configuration significantly influenced performance.Panel P10,with 70 mm SFRM thickness and 20 mm air gaps,provided the highest resistance,dissipating 5223 J of kinetic energy and preventing back-face damage.In contrast,P7,which absorbed 4476 J,presented a back damage area percentage of 8.93%after three impacts.Weight loss analysis further confirmed durability improvements,with P10 showing only 1.53%cumulative loss compared to 3.26%in P7.The inclusion of wider air gaps enhanced energy dissipation and reduced damage.Comparison between single and repeated impacts demonstrated the sustained resistance of high-performance panels,with P10 maintaining minimal degradation across three consecutive impacts.These findings highlight the potential of multi-layer SFRM panels to enhance ballistic resistance,making them suitable for military,security,and civilian protective applications requiring long-term durability.展开更多
Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel t...Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel tank is a rectangular structure,welded by six pieces of 2024 aluminum plate with a thickness of 6 mm,and filled with RP-3 aviation kerosene.Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s,and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed.However,the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene.Based on the experimental results,the radial pressure field is considered to be the main reason for the shear failure of weld.For mechanism considerations,the chemical energy released by the RMP enhances the hydrodynamic ram(HRAM)effect and provides additional ignition sources inside the fuel tank,thereby enhancing both rupture and ignition effects.Moreover,to further understand the enhanced ignition effect of RMP,the reactive debris temperature inside the kerosene is analyzed theoretically.The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene,resulting in the enhanced ignition of the kerosene.展开更多
The methods of numerical simulation and test are combined to analyze the impact behavior of glass fiber reinforced aluminum alloy laminate(GLARE).A new failure criteria is proposed to obtain the impact failure of GLAR...The methods of numerical simulation and test are combined to analyze the impact behavior of glass fiber reinforced aluminum alloy laminate(GLARE).A new failure criteria is proposed to obtain the impact failure of GLARE,and combined with material progressive damage method by writing code of LS-DYNA.Low velocity impact test of GLARE is employed to validate the feasibility of the finite element model established.The simulation results have been shown that progressive damage finite element model established is reliable.Through the application of the finite element model established,the delamination of GLARE evolution progress is simulated,various failure modes of GLARE during impact are obtained,and the effects of stacking sequence and impactor diameter on the impact damage of GLARE are obtained.展开更多
The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top laye...The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.展开更多
In automobiles, the CFRP （carbon fiber reinforced plastics） has a possibility of weight reduction in automotive structures which can contribute to improve mileage and then reduce carbon dioxide. On the other hand, t...In automobiles, the CFRP （carbon fiber reinforced plastics） has a possibility of weight reduction in automotive structures which can contribute to improve mileage and then reduce carbon dioxide. On the other hand, the safety of collision should be also made clear in the case of employing the CFRP to automotive structures. In this paper, the CFRP guarder belt equipped in the automotive door is developed and examined by an experiment and a numerical analysis for replacing the conventional steel door guarder beam. As the experimental relation of impact load to displacement for CFRP guarder belt agreed well with that of numerical result, the numerical method developed here is quite useful for estimating impact behaviors of CFRP guarder belt.展开更多
High density alloys with enhanced deformability and strength are urgently required in energy,military and nuclear industries,etc.In this work,we present a new kind of NiCoFeCrMoW high entropy alloys(HEAs)which possess...High density alloys with enhanced deformability and strength are urgently required in energy,military and nuclear industries,etc.In this work,we present a new kind of NiCoFeCrMoW high entropy alloys(HEAs)which possess higher densities and sound velocities than copper.We systematically investigate the phase structure,quasi-static tensile,dynamic compression and related deformation mechanism of these HEAs.It is shown that single FCC or FCC+μdual phases were formed in the HEAs depending on Mo and W content and annealing temperature.Excellent quasi-static tensile and dynamic compression properties have been achieved for these HEAs,e.g.Ni_(30)Co_(30)Fe_(21)Cr_(10)W_(9)HEA annealed at 1573 K exhibited a yield and ultimate tensile strength and elongation of~364 MPa,~866 MPa and~32%,respectively,in quasi-static test;a yield strength of~710 MPa and no fracture under the dynamic strain rate of 4100 s^(-1).Superior strain rate sensitivity(SRS)of yield strength than that of previously reported FCC HEAs have been evidenced.The dynamic stress-strain constitutive relation can be described by the modified Johnson-Cook model.As for the dynamic deformation mechanism,it is envisaged that the regulation of stacking fault energy and Peierls barrier in current HEAs resulted in occurrences of abundant nanoscale deformation twins and microbands during high strain rate compression.The synergistic microbanding and twinning effectively contributes to the enhanced dynamic deformability and strengthening effect.Besides,the interactions of dislocations with precipitates,stacking faults(SFs)with twins,and between SFs also contribute to extraordinary work-hardening capacity.展开更多
In this research, a series of hollow glass powder(HGP) reinforced magnetorheological plastomers(MRPs)were prepared to improve the impact resistance of the materials, and the dynamic compressive properties of MRPs unde...In this research, a series of hollow glass powder(HGP) reinforced magnetorheological plastomers(MRPs)were prepared to improve the impact resistance of the materials, and the dynamic compressive properties of MRPs under high strain rate were investigated by using a split Hopkinson pressure bar(SHPB)system equipped with a customized magnetic device. Experimental results showed the HGPs greatly enhanced the yield stresses of the MRPs. Especially, for MRPs with 9 vol.% carbonyl iron powders(CIPs), the magnetic-induced yield stress increased from 7.3 MPa to 17.1 MPa(134% increased) by adding 18 vol.%HGPs. The particle structures in MRPs were further simulated and the corresponding intergranular stress was calculated to study the enhancement effect of HGPs. The simulated results showed that more compact structures were formed with the excluded volume caused by secondary HGPs, so the yield stresses of the MRPs increased under a magnetic field. However, when the mass ratio of HGP to CIP was larger than 0.67, HGPs would hinder the formation of chain-like structures and reduce the magneto-mechanical properties. As a result, the replacing of CIPs by HGPs was proven to be an excellent strategy to improve the dynamic properties of MRPs.展开更多
The excellent mechanical properties of carbon nanotubes make them potential candidates for engineering application. In this paper, the impact and failure behaviors of single-walled carbon nanotubes （SWCNTs） are inve...The excellent mechanical properties of carbon nanotubes make them potential candidates for engineering application. In this paper, the impact and failure behaviors of single-walled carbon nanotubes （SWCNTs） are investigated. The effects of diameter, length, and chirality on their energy absorption characteristics under lateral impact and axial crush are studied. By integrating the principle of molecular structural mechanics （MSM） into finite element method （FEM）, the locations and directions of fracture process can be predicted. It is shown that the specific energy absorption （SEA） of SWCNTs is 1-2 order of magnitude higher than that of the ordinary metallic materials and composites in axial impact, indicating that carbon nanotubes are promising energy absorption materials for engineering applications.展开更多
A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied t...A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied through numerical simulation and experimental testing of a knife impacting a substrate,and an optimal structural design was obtained accordingly, with a tilted angle of 22.5and optimal thickness of 1.2 mm. It was shown that the triangular pyramidal structure generated twice the internal energy of the knife than the flat substrate due to the dispersing effect of the structure. The force parallel to the inclination caused a significant scratch on the substrate surface, while the force perpendicular caused obvious substrate deformation. A new riveting method was used to form the total layer, which passed the GA 68-2008 standard. The stab-resistant clothing coupled with the reduced wearing burden could provide effective protection and avoid fatal injuries on security personnel working in dangerous environments. The method provided may enlighten the future design and manufacturing of stabresistant clothing.展开更多
Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,ca...Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.展开更多
In order to study the three jump training and competition on knee joint impact damage degree,left knee joint of one healthy male athletes is used as the research object,a complete knee three-dimensional model was esta...In order to study the three jump training and competition on knee joint impact damage degree,left knee joint of one healthy male athletes is used as the research object,a complete knee three-dimensional model was established based on the jumper’s knee CT scan and magnetic resonance imaging(MRI),including the femur,tibia,fibula,patella and knee major cartilage,ligaments.The multi-body dynamics analysis(MDA)and finite element analysis(FEA)method are used to calculate the three jump,jump starting,landing process of athletes knee joint impact,the state should change the status of stress,strain and displacement.The results show that in the three jump process,the load on the lateral contact area of the knee joint is the largest,the displacement is the largest,and it increases with the impact of jump and landing.This exacerbated the degree of wear and tear of the tibia,it tends to induce knee injury in athletes.The results show that the combination of finite element and MDA can better study the knee joint’s shock and vibration during the three-level jump training and competition,and these open up a new research method for the knee joint injury.It also provides a certain reference for the prevention and treatment of knee joint injury.展开更多
In 2011-12,greenhouse gas emissions from the Australian residential sector were 101.6 Mt and are expected to grow by 38%by 2050.In order to reduce these emissions,much emphasis has been placed on increasing the energy...In 2011-12,greenhouse gas emissions from the Australian residential sector were 101.6 Mt and are expected to grow by 38%by 2050.In order to reduce these emissions,much emphasis has been placed on increasing the energy efficiency of buildings and appliances.Occupant behaviour,however,is probably the single most significant factor which determines energy use and emissions.This paper describes research undertaken to rank the most common occupant behaviours,based upon their impact on greenhouse gas emissions associated with residential energy use,in an architect-designed house in Australia.The occupant behaviours investigated were changing:the heating and cooling temperature set points,window openings,external blind use and lighting use.Simulations were carried out using Primero and EnergyPlus software.Based on the simulation results of greenhouse gas emissions,the following ranking of overall influence(from most influential to the least)has been determined:external blind use was one of the most effective measures to reduce emissions.Cooling set point temperature was similarly important with the magnitude of impact depending on the set point e.g.a 2℃ increase had an impact comparable to the use of external blinds.The impact of the heating set point temperature was also dependent on the set point and overall slightly lower compared to the cooling set point temperature.Lighting use was the least influential parameter in the context of this study.展开更多
A real-time intelligent fiber-optic perimeter intrusion detection system （PIDS） based on the fiber Bragg grating （FBG） sensor network is presented in this paper. To distinguish the effects of different intrusion e...A real-time intelligent fiber-optic perimeter intrusion detection system （PIDS） based on the fiber Bragg grating （FBG） sensor network is presented in this paper. To distinguish the effects of different intrusion events, a novel real-time behavior impact classification method is proposed based on the essential statistical characteristics of signal＇s profile in the time domain. The features are extracted by the principal component analysis （PCA）, which are then used to identify the event with a K-nearest neighbor classifier. Simulation and field tests are both carried out to validate its effectiveness. The average identification rate （IR） for five sample signals in the simulation test is as high as 96.67%, and the recognition rate for eight typical signals in the field test can also be achieved up to 96.52%, which includes both the fence-mounted and the ground-buried sensing signals. Besides, critically high detection rate （DR） and low false alarm rate （FAR） can be simultaneously obtained based on the autocorrelation characteristics analysis and a hierarchical detection and identification flow.展开更多
The impact region of the dactyl club of mantis shrimp features a rare sinusoidally helicoidal architecture,contributing to its efficient impact-resistant characteristics.This study aims to attain bioinspired sinusoida...The impact region of the dactyl club of mantis shrimp features a rare sinusoidally helicoidal architecture,contributing to its efficient impact-resistant characteristics.This study aims to attain bioinspired sinusoidally architected composites from a practical engineering way.Morphological features of plain-woven fabric were characterized,which demonstrated that the interweaving warp and weft yarns exhibited a sinusoidal architecture.Interconnected woven composites were thus employed and helicoidally stacked to achieve the desired structure.Quasi-static three-point bending and low-velocity impact tests were subsequently performed to evaluate their mechanical performance.Under three-point bending condi-tion,the dominant failure mode gradually changed from fiber breakage to delamination with the increase in the pitch angle.Failure displacement and energy absorption of the heli-coidal woven composites were,respectively,43.89%and 141.90%greater than the unidirectional ones.Under low-velo-city impact condition,the damage area of the helicoidal woven composites decreased by 49.66%while the residual strength increased by 10.10%compared with those of the unidirectional ones,exhibiting better damage resistance and tolerance.Also,effects of fiber architecture on mechanical properties were examined.This work will shed light on future design of the next-generation impact-resistant architected composites.展开更多
文摘This study investigates how Internet media in the mobile phone influence on the cognitive and behavioral aspects of human sexuality. Sex is being deviating from socially accepted behaviors; ranging from bisexuality to homosexuality. Based on the qualitative methodology using particular case studies and textual analysis as well as survey research leading to quantitative methodology, this assumes of a transition of cultures as a result of the thorough impact of Internet towards society. In conclusion, lnternet implicit practices in the Mobile Phone in youth and teen societies storms a big change in sexuality, is also affecting towards the human cognitive and behavioral phases of the social life in traditional Buddhist rural village setting in Sri Lanka.
基金The authors would like to acknowledge the support of the National Natural Science Foundation of China(No.52279097,No.51779264)Blue and Green Project of Jiangsu Province.
文摘Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.
基金sponsored by the National Natural Science Foundation of China(Grant No.52175140)National Key R&D Program of China(Grant No.2022YFB4602102)+2 种基金Fundamental Research Funds for the Central Universities in China(Grant No.JKG01231610)Pre research project of Civil Aerospace Technology(Grant No.D020301)Equipment Pre-research Sharing Technology Key Project(Grant No.JZX7Y20210422004601).
文摘The laser powder bed fusion(L-PBF)additively manufactured CoCrFeNi high-entropy alloy(HEA),with face-centered cubic(FCC)crystal structure,demonstrates better comprehensive mechanical properties in the building direction(BD).Loading quasi-static,dynamic fatigue,and dynamic separated Hopkinson press bar(SHPB)impact stress conditions along the BD of the L-PBF processed HEA exhibit intriguing mi-crostructural evolution characteristics.The L-PBF generates hierarchical dislocation grids containing nu-merous cell substructures within the HEA FCC grains,impeding dislocation motion during deformation and improving the strength.When subjected to dynamic fatigue loading,the dislocation grids restrict the mean free path of dislocations and thus trigger the activation of abundant stacking faults.Hence,nu-merous nanotwins form near the end of the fatigue life.Multiple twinning systems can also be activated under dynamic high-speed impact loading.Especially at a low temperature of 77 K,the stacking fault energy of the CoCrFeNi HEA decreases,resulting in increased activation of nanotwins,exhibiting excep-tional toughness and resistance to dynamic loads.Additional twin boundaries also impede dislocation movement for the strain hardening.These findings hold valuable implications for the study of additively manufactured HEA parts working in extreme environments.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.U1902220,51674166,51074106 and 50674067)the National Key Research and Development Program of China(Grant No.2016YFB0301001)。
文摘This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.
基金Supports from National Natural Science Foundation of China(U20A20286 and 12372135)。
文摘Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.
基金funded by Thailand Research Fund under Research and Researchers for Industries (contract no. MSD62I0063)
文摘This research addresses the growing demand for high-performance protective materials against high-velocity projectile impacts.The performance of multi-layered steel fiber-reinforced mortar(SFRM)panels with varying thicknesses and air gaps,was experimentally investigated under single and repeated impacts of 7.62×51 mm bullets fired from a distance of 50 m.The impact events were recorded using a high-speed camera at 40000 fps.Panel performance was assessed in terms of failure modes,kinetic energy absorption,spalling diameter,and percentage of back-face damage area,and weight loss.Results showed that panel configuration significantly influenced performance.Panel P10,with 70 mm SFRM thickness and 20 mm air gaps,provided the highest resistance,dissipating 5223 J of kinetic energy and preventing back-face damage.In contrast,P7,which absorbed 4476 J,presented a back damage area percentage of 8.93%after three impacts.Weight loss analysis further confirmed durability improvements,with P10 showing only 1.53%cumulative loss compared to 3.26%in P7.The inclusion of wider air gaps enhanced energy dissipation and reduced damage.Comparison between single and repeated impacts demonstrated the sustained resistance of high-performance panels,with P10 maintaining minimal degradation across three consecutive impacts.These findings highlight the potential of multi-layer SFRM panels to enhance ballistic resistance,making them suitable for military,security,and civilian protective applications requiring long-term durability.
文摘Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel tank is a rectangular structure,welded by six pieces of 2024 aluminum plate with a thickness of 6 mm,and filled with RP-3 aviation kerosene.Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s,and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed.However,the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene.Based on the experimental results,the radial pressure field is considered to be the main reason for the shear failure of weld.For mechanism considerations,the chemical energy released by the RMP enhances the hydrodynamic ram(HRAM)effect and provides additional ignition sources inside the fuel tank,thereby enhancing both rupture and ignition effects.Moreover,to further understand the enhanced ignition effect of RMP,the reactive debris temperature inside the kerosene is analyzed theoretically.The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene,resulting in the enhanced ignition of the kerosene.
文摘The methods of numerical simulation and test are combined to analyze the impact behavior of glass fiber reinforced aluminum alloy laminate(GLARE).A new failure criteria is proposed to obtain the impact failure of GLARE,and combined with material progressive damage method by writing code of LS-DYNA.Low velocity impact test of GLARE is employed to validate the feasibility of the finite element model established.The simulation results have been shown that progressive damage finite element model established is reliable.Through the application of the finite element model established,the delamination of GLARE evolution progress is simulated,various failure modes of GLARE during impact are obtained,and the effects of stacking sequence and impactor diameter on the impact damage of GLARE are obtained.
基金Funded by the National National Natural Science Foundation of China(No.51505189)Open Project of Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment&Technology(No.FM-2015-5)
文摘The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.
文摘In automobiles, the CFRP （carbon fiber reinforced plastics） has a possibility of weight reduction in automotive structures which can contribute to improve mileage and then reduce carbon dioxide. On the other hand, the safety of collision should be also made clear in the case of employing the CFRP to automotive structures. In this paper, the CFRP guarder belt equipped in the automotive door is developed and examined by an experiment and a numerical analysis for replacing the conventional steel door guarder beam. As the experimental relation of impact load to displacement for CFRP guarder belt agreed well with that of numerical result, the numerical method developed here is quite useful for estimating impact behaviors of CFRP guarder belt.
基金the National Science and Technology Major Project of China(No.J2019-Ⅵ-0004-0117)the National Natural Science Foundation of China(No.52001024)the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-19-037A1 and FRF-GF-19-027B)。
文摘High density alloys with enhanced deformability and strength are urgently required in energy,military and nuclear industries,etc.In this work,we present a new kind of NiCoFeCrMoW high entropy alloys(HEAs)which possess higher densities and sound velocities than copper.We systematically investigate the phase structure,quasi-static tensile,dynamic compression and related deformation mechanism of these HEAs.It is shown that single FCC or FCC+μdual phases were formed in the HEAs depending on Mo and W content and annealing temperature.Excellent quasi-static tensile and dynamic compression properties have been achieved for these HEAs,e.g.Ni_(30)Co_(30)Fe_(21)Cr_(10)W_(9)HEA annealed at 1573 K exhibited a yield and ultimate tensile strength and elongation of~364 MPa,~866 MPa and~32%,respectively,in quasi-static test;a yield strength of~710 MPa and no fracture under the dynamic strain rate of 4100 s^(-1).Superior strain rate sensitivity(SRS)of yield strength than that of previously reported FCC HEAs have been evidenced.The dynamic stress-strain constitutive relation can be described by the modified Johnson-Cook model.As for the dynamic deformation mechanism,it is envisaged that the regulation of stacking fault energy and Peierls barrier in current HEAs resulted in occurrences of abundant nanoscale deformation twins and microbands during high strain rate compression.The synergistic microbanding and twinning effectively contributes to the enhanced dynamic deformability and strengthening effect.Besides,the interactions of dislocations with precipitates,stacking faults(SFs)with twins,and between SFs also contribute to extraordinary work-hardening capacity.
基金financially supported by the National Natural Science Foundation of China (Nos. 12102424, 12132016, 11972343, and 11822209)the National Key R&D Program of China (No. 2018YFB1201703)+1 种基金the Anhui’s Key R&D Program of China (No. 202104a05020009)the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB22040502)。
文摘In this research, a series of hollow glass powder(HGP) reinforced magnetorheological plastomers(MRPs)were prepared to improve the impact resistance of the materials, and the dynamic compressive properties of MRPs under high strain rate were investigated by using a split Hopkinson pressure bar(SHPB)system equipped with a customized magnetic device. Experimental results showed the HGPs greatly enhanced the yield stresses of the MRPs. Especially, for MRPs with 9 vol.% carbonyl iron powders(CIPs), the magnetic-induced yield stress increased from 7.3 MPa to 17.1 MPa(134% increased) by adding 18 vol.%HGPs. The particle structures in MRPs were further simulated and the corresponding intergranular stress was calculated to study the enhancement effect of HGPs. The simulated results showed that more compact structures were formed with the excluded volume caused by secondary HGPs, so the yield stresses of the MRPs increased under a magnetic field. However, when the mass ratio of HGP to CIP was larger than 0.67, HGPs would hinder the formation of chain-like structures and reduce the magneto-mechanical properties. As a result, the replacing of CIPs by HGPs was proven to be an excellent strategy to improve the dynamic properties of MRPs.
基金Funded by the National Natural Science Foundation of China(No.50975011)
文摘The excellent mechanical properties of carbon nanotubes make them potential candidates for engineering application. In this paper, the impact and failure behaviors of single-walled carbon nanotubes （SWCNTs） are investigated. The effects of diameter, length, and chirality on their energy absorption characteristics under lateral impact and axial crush are studied. By integrating the principle of molecular structural mechanics （MSM） into finite element method （FEM）, the locations and directions of fracture process can be predicted. It is shown that the specific energy absorption （SEA） of SWCNTs is 1-2 order of magnitude higher than that of the ordinary metallic materials and composites in axial impact, indicating that carbon nanotubes are promising energy absorption materials for engineering applications.
基金supported by the National Natural Science Foundation of China [51874041 and 71861167002]。
文摘A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied through numerical simulation and experimental testing of a knife impacting a substrate,and an optimal structural design was obtained accordingly, with a tilted angle of 22.5and optimal thickness of 1.2 mm. It was shown that the triangular pyramidal structure generated twice the internal energy of the knife than the flat substrate due to the dispersing effect of the structure. The force parallel to the inclination caused a significant scratch on the substrate surface, while the force perpendicular caused obvious substrate deformation. A new riveting method was used to form the total layer, which passed the GA 68-2008 standard. The stab-resistant clothing coupled with the reduced wearing burden could provide effective protection and avoid fatal injuries on security personnel working in dangerous environments. The method provided may enlighten the future design and manufacturing of stabresistant clothing.
基金supported by the National Natural Science Foundation of China(Grant No.11902295).
文摘Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.
基金This study is sponsored by the National Natural Science Foundation project(51304076)of Chinait is supported by Hunan Provincial Department of Education Scientific Research Project(17C0863).
文摘In order to study the three jump training and competition on knee joint impact damage degree,left knee joint of one healthy male athletes is used as the research object,a complete knee three-dimensional model was established based on the jumper’s knee CT scan and magnetic resonance imaging(MRI),including the femur,tibia,fibula,patella and knee major cartilage,ligaments.The multi-body dynamics analysis(MDA)and finite element analysis(FEA)method are used to calculate the three jump,jump starting,landing process of athletes knee joint impact,the state should change the status of stress,strain and displacement.The results show that in the three jump process,the load on the lateral contact area of the knee joint is the largest,the displacement is the largest,and it increases with the impact of jump and landing.This exacerbated the degree of wear and tear of the tibia,it tends to induce knee injury in athletes.The results show that the combination of finite element and MDA can better study the knee joint’s shock and vibration during the three-level jump training and competition,and these open up a new research method for the knee joint injury.It also provides a certain reference for the prevention and treatment of knee joint injury.
文摘In 2011-12,greenhouse gas emissions from the Australian residential sector were 101.6 Mt and are expected to grow by 38%by 2050.In order to reduce these emissions,much emphasis has been placed on increasing the energy efficiency of buildings and appliances.Occupant behaviour,however,is probably the single most significant factor which determines energy use and emissions.This paper describes research undertaken to rank the most common occupant behaviours,based upon their impact on greenhouse gas emissions associated with residential energy use,in an architect-designed house in Australia.The occupant behaviours investigated were changing:the heating and cooling temperature set points,window openings,external blind use and lighting use.Simulations were carried out using Primero and EnergyPlus software.Based on the simulation results of greenhouse gas emissions,the following ranking of overall influence(from most influential to the least)has been determined:external blind use was one of the most effective measures to reduce emissions.Cooling set point temperature was similarly important with the magnitude of impact depending on the set point e.g.a 2℃ increase had an impact comparable to the use of external blinds.The impact of the heating set point temperature was also dependent on the set point and overall slightly lower compared to the cooling set point temperature.Lighting use was the least influential parameter in the context of this study.
基金National High Technology Research and Development Program of China （863 Program, Grant No. 2007AA01Z245）, the supports provided for this research by the Major Program （Grant No. 61290312） and Youth Foundation （Grant No. 61301275） of the National Natural Science Foundation of China （NSFC）, and the Fundamental Research Funds for the Central Universities （Grant No. ZYGX2011J010）. This work is also supported by Program for Changjiang Scholars and Innovative Research Team in University （PCSIRT, IRT1218）, and the 111 Project （B14039）.
文摘A real-time intelligent fiber-optic perimeter intrusion detection system （PIDS） based on the fiber Bragg grating （FBG） sensor network is presented in this paper. To distinguish the effects of different intrusion events, a novel real-time behavior impact classification method is proposed based on the essential statistical characteristics of signal＇s profile in the time domain. The features are extracted by the principal component analysis （PCA）, which are then used to identify the event with a K-nearest neighbor classifier. Simulation and field tests are both carried out to validate its effectiveness. The average identification rate （IR） for five sample signals in the simulation test is as high as 96.67%, and the recognition rate for eight typical signals in the field test can also be achieved up to 96.52%, which includes both the fence-mounted and the ground-buried sensing signals. Besides, critically high detection rate （DR） and low false alarm rate （FAR） can be simultaneously obtained based on the autocorrelation characteristics analysis and a hierarchical detection and identification flow.
基金National Natural Science Foundation of China[No.12172025]Science Foundation of National Key Laboratory of Science and Technology on Advanced Composites in Special Environments[No.6142905222707].
文摘The impact region of the dactyl club of mantis shrimp features a rare sinusoidally helicoidal architecture,contributing to its efficient impact-resistant characteristics.This study aims to attain bioinspired sinusoidally architected composites from a practical engineering way.Morphological features of plain-woven fabric were characterized,which demonstrated that the interweaving warp and weft yarns exhibited a sinusoidal architecture.Interconnected woven composites were thus employed and helicoidally stacked to achieve the desired structure.Quasi-static three-point bending and low-velocity impact tests were subsequently performed to evaluate their mechanical performance.Under three-point bending condi-tion,the dominant failure mode gradually changed from fiber breakage to delamination with the increase in the pitch angle.Failure displacement and energy absorption of the heli-coidal woven composites were,respectively,43.89%and 141.90%greater than the unidirectional ones.Under low-velo-city impact condition,the damage area of the helicoidal woven composites decreased by 49.66%while the residual strength increased by 10.10%compared with those of the unidirectional ones,exhibiting better damage resistance and tolerance.Also,effects of fiber architecture on mechanical properties were examined.This work will shed light on future design of the next-generation impact-resistant architected composites.
