How to ensure the safety of occupants has become a challenge for protective design of armored vehicles against intensive blast loadings.In this study,for armored vehicles subjected to shallow-buried explosions,an anal...How to ensure the safety of occupants has become a challenge for protective design of armored vehicles against intensive blast loadings.In this study,for armored vehicles subjected to shallow-buried explosions,an analytical model was established to characterize the dynamic performance of an all-metallic sandwich floorboard attached with a double mass-spring-damping system(mimicking seat and occupant),with the former consisting of a front face,a core and a rear face.For validation,numerical simulations with the method of finite elements(FE)were performed.Good agreement between analytical predictions and numerical results was achieved.The analytical model was then employed to quantify the effects of explosive mass,yield stress of material make,configurational parameters of sandwich panel,spring stiffness,and damping coefficient on dynamic response of the sandwich panel and double mass-spring-damping system.With increasing explosive mass and decreasing yield stress of material make,the peak displacements of rear face,seat and occupant were all found to increase.As core relative density was increased,these peak displacements also increased when the ratio of face thickness to core height was relatively small.Increasing the ratio of face thickness to core height led to increased peak accelerations of seat and occupant.The peak displacement of rear face was insensitive to the increase of either spring stiffness or damping coefficient,while the peak acceleration of occupant increased with increasing spring stiffness.Upon increasing the damping coefficient between the rear face and seat or that between the seat and occupant or both,the peak acceleration of occupant increased.With occupant safety duly considered,the proposed analytical model provides useful guidance for designing high-performance protective structures for armored vehicles subjected to intensive blast loadings.展开更多
The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective str...The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective structures have been proposed as attachments to the thin plate. In the present study, a novel ultralight all-metallic sandwich panel with three-dimensional(3D) tube cellular cores mounted to the vehicle underbody was envisioned as such a protective system. A metallic substrate(mimicking vehicle bottom)was placed above the proposed sandwich panel to construct a sandwich-substrate combinative structure. A series of sandwich panels having 3D tube cellular cores were fabricated via argon protected welding and laser welding. Mechanical responses of the combinative structure subjected to the denotation of 6 kg TNT explosives shallow-buried in dry sand were experimentally measured. Full numerical simulations with the method of finite elements(FE) were subsequently carried out to explore the physical mechanisms underlying the observed dynamic performance and quantify the effects of key geometrical parameters and connection conditions of the protective system. The performance of the proposed sandwich panel under shallow-buried explosives was also compared with competing sandwich constructions having equal mass. Finally, a preliminary optimal design of the 3D tube cellular core was carried out.展开更多
The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was e...The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was established to analyze the protection ability and energy absorption by the foam under low velocity impact conditions.For validation,drop hammer experiments were carried out for high porosity closed-cell aluminum foam specimens subjected to low velocity impact loading.The dynamic deformation behavior of the specimen was observed and the velocity attenuation of the drop hammer was measured.The results demonstrated that the aluminum foam had excellent energy absorption capabilities,with its dynamic compressive behavior similar to that obtained under quasi-static loading conditions.Finite element method(FEM) was subsequently employed to obtain stress distributions in the foam specimen.As the propagating period of stress in the specimen was far less than the duration of attenuation,the evolution of the stress was similar to that under quasi-static loading conditions and no obvious stress wave effect was observed,which agreed with the experimental observation.Finally,the predicted velocity attenuation by the ODF-CM was compared with both the experimental measurements and FEM simulation,and good agreements were achieved when the stress distribution was considered to be uniform and the "quasi-static" compressive properties are employed.展开更多
The natural convective heat transfer performance and thermo-fluidic characteristics of honeycombs with/without chimney extensions are numerically investigated.The present numerical simulations are validated by the pur...The natural convective heat transfer performance and thermo-fluidic characteristics of honeycombs with/without chimney extensions are numerically investigated.The present numerical simulations are validated by the purposely-designed experimental measurements on honeycombs with/without chimney.Good agreement between numerical simulation and experimental measurement is obtained.The influences of inclination angle and geometric parameters such as cell shape,streamwise and spanwise length are also numerically quantified.With the increment in inclination angle,the overall heat transfer rate decreases for the honeycombs with/without chimney.For honeycombs with the same void volume fraction but different cell shapes,there is little difference on the overall heat transfer rate.To enhance the natural convective heat transfer of honeycombs,these techniques including increasing the length of honeycomb in the streamwise/spanwise direction,increasing the thermal conductivity of hon-eycomb structure or adding a chimney extension may be helpful.展开更多
A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fa...A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density.展开更多
Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of j...Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of jet flow structures with impinging distance is characterized using the technique of particle image velocimetry (PIV). Correspondingly, the distributions of wall pressure and heat transfer on the plate are measured. At sufficiently large impinging distances, without swirling flow, the obtained flow and wall pressure/heat transfer data are consistent with the classical observation for a conventional annular impinging jet, showing the transition from annular impinging jet flow to single circular impinging jet-like flow. In contrast, no such transition occurs in the presence of flow turning by short guide vanes. At short and intermediate impinging distances, flow turning causes more non-uniform distributions of wall pressure and heat transfer on the target plate and the local heat transfer rates higher than those of the conventional annular jet. This is attributed to the vortical flow structures shed and convected downstream from the short guide vanes. In sharp contrast, at large impinging distances, the larger momentum loss due to flow turning results in lower heat transfer rates on the plate.展开更多
Novel ultralight sandwich panels, which are comprised of corrugated channel cores and are faced with two identical solid sheets,subjected to generalized bending are optimally designed for minimum mass. A combined anal...Novel ultralight sandwich panels, which are comprised of corrugated channel cores and are faced with two identical solid sheets,subjected to generalized bending are optimally designed for minimum mass. A combined analytical and numerical(finite element) investigation is carried out. Relevant failure mechanisms such as face yielding, face buckling, core yielding and core buckling are identified, the load for each failure mode derived, and the corresponding failure mechanism maps constructed. The analytically predicted failure loads and failure modes are validated against direct finite element simulations, with good agreement achieved. The optimized corrugated channel core is compared with competing topologies for sandwich construction including corrugations, honeycombs and lattice trusses, and the superiority of the proposed structure is demonstrated. Corrugated-channel-core sandwich panels hold great potential for multifunctional applications, i.e., simultaneous load bearing and active cooling.展开更多
This work presents a theoretical study of the propagation behavior of Bleustein-Gulyaev waves in a layered structure consisting of a functionally graded piezoelectric material(FGPM) layer and a transversely isotropic ...This work presents a theoretical study of the propagation behavior of Bleustein-Gulyaev waves in a layered structure consisting of a functionally graded piezoelectric material(FGPM) layer and a transversely isotropic piezoelectric substrate. The influence of the graded variation of FGPM coefficients on the dispersion relations of Bleustein-Gulyaev waves in the layered structure is investigated. It is demonstrated that,for a certain frequency range of Bleustein-Gulyaev waves,the mechanical perturbations of the particles are restricted in the FPGM layer and the phase velocity is independent of the electrical boundary conditions at the free surface. Results presented in this study can not only provide further insight on the electromechanical coupling behavior of surface waves in FGPM layered structures,but also lend a theoretical basis for the design of high-performance surface acoustic wave(SAW) devices.展开更多
The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel f...The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel fibers specified by two basic physical parameters:fiber diameter and porosity.A self-consistent Brinkman approach is applied to the calculation of the dynamic resistivity of flow perpendicular to the cylindrical fibers.Based on the solved flow resistivity,the sound absorption of single layer fibrous material can be obtained by adopting the available empirical equations.Moreover,the recursion formulas of surface impedance are applied to the calculation of the sound absorption coefficient of multi-layer fibrous materials.Experimental measurements are conducted to validate the proposed model,with good agreement achieved between model predictions and tested data.Numerical calculations with the proposed model are subsequently performed to quantify the influences of fiber diameter,porosity and backed air gap on sound absorption of uniform(single-layer)fibrous materials.Results show that the sound absorption increases with porosity at higher frequencies but decreases with porosity at lower frequencies.The sound absorption also decreases with fiber diameter at higher frequencies but increases at lower frequencies.The sound absorption resonance is shifted to lower frequencies with air gap.For multi-layer fibrous materials,gradient distributions of both fiber diameter and porosity are introduced and their effects on sound absorption are assessed.It is found that increasing the porosity and fiber diameter variation improves sound absorption in the low frequency range.The model provides the possibility to tailor the sound absorption capability of the sintered fibrous materials by optimizing the gradient distributions of key physical parameters.展开更多
The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to ...The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to calculate the radiated sound pressure level(SPL) versus frequency curves with reference to sound radiation of a bare plate immersed in a steady fluid.The flexural and rotational motions of the rib stiffeners are described by applying the Euler-Bernoulli beam theory and torsional wave equation,respectively.Therefore,the coupling forces and moments between the ribs and the face-panel,caused separately by flexural and rotational motion of the ribs,are both taken into account.Given the periodicity of the structure,the Fourier transform technique is employed to solve panel vibration equations and acoustic equations.Systematic parametric investigation demonstrates that the presence of mean flow as well as rib spacings play significant roles in the sound radiation behavior of parallelly rib-stiffened plates.The proposed model provides a convenient and efficient tool for the factual engineering design of this kind of periodic structures with acoustic requirements.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11972185 and 12002156)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-I-0222K01)+1 种基金the Fund of Prospective Layout of Scientific Research for NUAAthe Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)。
文摘How to ensure the safety of occupants has become a challenge for protective design of armored vehicles against intensive blast loadings.In this study,for armored vehicles subjected to shallow-buried explosions,an analytical model was established to characterize the dynamic performance of an all-metallic sandwich floorboard attached with a double mass-spring-damping system(mimicking seat and occupant),with the former consisting of a front face,a core and a rear face.For validation,numerical simulations with the method of finite elements(FE)were performed.Good agreement between analytical predictions and numerical results was achieved.The analytical model was then employed to quantify the effects of explosive mass,yield stress of material make,configurational parameters of sandwich panel,spring stiffness,and damping coefficient on dynamic response of the sandwich panel and double mass-spring-damping system.With increasing explosive mass and decreasing yield stress of material make,the peak displacements of rear face,seat and occupant were all found to increase.As core relative density was increased,these peak displacements also increased when the ratio of face thickness to core height was relatively small.Increasing the ratio of face thickness to core height led to increased peak accelerations of seat and occupant.The peak displacement of rear face was insensitive to the increase of either spring stiffness or damping coefficient,while the peak acceleration of occupant increased with increasing spring stiffness.Upon increasing the damping coefficient between the rear face and seat or that between the seat and occupant or both,the peak acceleration of occupant increased.With occupant safety duly considered,the proposed analytical model provides useful guidance for designing high-performance protective structures for armored vehicles subjected to intensive blast loadings.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11972185, 12002156 and 11902148)China Postdoctoral Science Foundation (Grant No. 2020M671473)+3 种基金State Key Laboratory of Smart Manufacturing for Special Vehicles and Transmission System (Grant No. GZ2019KF015)Natural Science Fund Project in Jiangsu Province (Grant Nos. BK20190392 and BK20190424)Open Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant Nos. MCMS-E-0219K02 and MCMS-I-0219K01)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)。
文摘The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective structures have been proposed as attachments to the thin plate. In the present study, a novel ultralight all-metallic sandwich panel with three-dimensional(3D) tube cellular cores mounted to the vehicle underbody was envisioned as such a protective system. A metallic substrate(mimicking vehicle bottom)was placed above the proposed sandwich panel to construct a sandwich-substrate combinative structure. A series of sandwich panels having 3D tube cellular cores were fabricated via argon protected welding and laser welding. Mechanical responses of the combinative structure subjected to the denotation of 6 kg TNT explosives shallow-buried in dry sand were experimentally measured. Full numerical simulations with the method of finite elements(FE) were subsequently carried out to explore the physical mechanisms underlying the observed dynamic performance and quantify the effects of key geometrical parameters and connection conditions of the protective system. The performance of the proposed sandwich panel under shallow-buried explosives was also compared with competing sandwich constructions having equal mass. Finally, a preliminary optimal design of the 3D tube cellular core was carried out.
基金supported by the National Basic Research Program of China ("973" Project)(Grant No. 2011CB610305)the National "111" Project of China (Grant No. B06024)the National Natural Science Foundation of China (Grant Nos. 10825210,11072188)
文摘The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was established to analyze the protection ability and energy absorption by the foam under low velocity impact conditions.For validation,drop hammer experiments were carried out for high porosity closed-cell aluminum foam specimens subjected to low velocity impact loading.The dynamic deformation behavior of the specimen was observed and the velocity attenuation of the drop hammer was measured.The results demonstrated that the aluminum foam had excellent energy absorption capabilities,with its dynamic compressive behavior similar to that obtained under quasi-static loading conditions.Finite element method(FEM) was subsequently employed to obtain stress distributions in the foam specimen.As the propagating period of stress in the specimen was far less than the duration of attenuation,the evolution of the stress was similar to that under quasi-static loading conditions and no obvious stress wave effect was observed,which agreed with the experimental observation.Finally,the predicted velocity attenuation by the ODF-CM was compared with both the experimental measurements and FEM simulation,and good agreements were achieved when the stress distribution was considered to be uniform and the "quasi-static" compressive properties are employed.
基金supported by the National 111 Project of China(Grant No.B06024)the National Basic Research Program of China("973"Project)(Grant No.2011CB610305)the National Natural Science Foundation of China(Grant No.51206128)
文摘The natural convective heat transfer performance and thermo-fluidic characteristics of honeycombs with/without chimney extensions are numerically investigated.The present numerical simulations are validated by the purposely-designed experimental measurements on honeycombs with/without chimney.Good agreement between numerical simulation and experimental measurement is obtained.The influences of inclination angle and geometric parameters such as cell shape,streamwise and spanwise length are also numerically quantified.With the increment in inclination angle,the overall heat transfer rate decreases for the honeycombs with/without chimney.For honeycombs with the same void volume fraction but different cell shapes,there is little difference on the overall heat transfer rate.To enhance the natural convective heat transfer of honeycombs,these techniques including increasing the length of honeycomb in the streamwise/spanwise direction,increasing the thermal conductivity of hon-eycomb structure or adding a chimney extension may be helpful.
基金Supported by the National Basic Research Program of China ("973" Project) (Grant No. 2006CB601202)the National Natural Science Foundation of China (Grant Nos. 10632060,10825210)+1 种基金the National "111" Project of China (Grant No. B06024)the National High-Tech Research and Development Program of China ("863" Project) (Grant No. 2006AA03Z519)
文摘A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2011CB610305)the National "111" Project of China (Grant No. B06024)the National Natural Science Foundation of China (Grant Nos. 10825210, 11072188)
文摘Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of jet flow structures with impinging distance is characterized using the technique of particle image velocimetry (PIV). Correspondingly, the distributions of wall pressure and heat transfer on the plate are measured. At sufficiently large impinging distances, without swirling flow, the obtained flow and wall pressure/heat transfer data are consistent with the classical observation for a conventional annular impinging jet, showing the transition from annular impinging jet flow to single circular impinging jet-like flow. In contrast, no such transition occurs in the presence of flow turning by short guide vanes. At short and intermediate impinging distances, flow turning causes more non-uniform distributions of wall pressure and heat transfer on the target plate and the local heat transfer rates higher than those of the conventional annular jet. This is attributed to the vortical flow structures shed and convected downstream from the short guide vanes. In sharp contrast, at large impinging distances, the larger momentum loss due to flow turning results in lower heat transfer rates on the plate.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11472209, 11472208)the China Postdoctoral Science Foundation (Grant No. 2016M600782)+2 种基金the Postdoctoral Scientific Research Project of Shaanxi Province (Grant No. 2016BSHYDZZ18)the Fundamental Research Funds for Xi’an Jiaotong University (Grant No. xjj2015102)the Jiangsu Province Key Laboratory of High-end Structural Materials (Grant No. hsm1305)
文摘Novel ultralight sandwich panels, which are comprised of corrugated channel cores and are faced with two identical solid sheets,subjected to generalized bending are optimally designed for minimum mass. A combined analytical and numerical(finite element) investigation is carried out. Relevant failure mechanisms such as face yielding, face buckling, core yielding and core buckling are identified, the load for each failure mode derived, and the corresponding failure mechanism maps constructed. The analytically predicted failure loads and failure modes are validated against direct finite element simulations, with good agreement achieved. The optimized corrugated channel core is compared with competing topologies for sandwich construction including corrugations, honeycombs and lattice trusses, and the superiority of the proposed structure is demonstrated. Corrugated-channel-core sandwich panels hold great potential for multifunctional applications, i.e., simultaneous load bearing and active cooling.
基金Supported by the National Natural Science Foundation of China (Grant No. 10632060)the National Basic Research Program of China (Grant No. 2006CB601202)+1 种基金the National 111 Project of China (Grant No. B06024)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070698064)
文摘This work presents a theoretical study of the propagation behavior of Bleustein-Gulyaev waves in a layered structure consisting of a functionally graded piezoelectric material(FGPM) layer and a transversely isotropic piezoelectric substrate. The influence of the graded variation of FGPM coefficients on the dispersion relations of Bleustein-Gulyaev waves in the layered structure is investigated. It is demonstrated that,for a certain frequency range of Bleustein-Gulyaev waves,the mechanical perturbations of the particles are restricted in the FPGM layer and the phase velocity is independent of the electrical boundary conditions at the free surface. Results presented in this study can not only provide further insight on the electromechanical coupling behavior of surface waves in FGPM layered structures,but also lend a theoretical basis for the design of high-performance surface acoustic wave(SAW) devices.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2011CB610300)the National Natural Science Foundation of China(Grant Nos.11102148,11321062 and 51134003)the Fundamental Research Funds for Central Universities of China(Grant No.xjj2011005)
文摘The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel fibers specified by two basic physical parameters:fiber diameter and porosity.A self-consistent Brinkman approach is applied to the calculation of the dynamic resistivity of flow perpendicular to the cylindrical fibers.Based on the solved flow resistivity,the sound absorption of single layer fibrous material can be obtained by adopting the available empirical equations.Moreover,the recursion formulas of surface impedance are applied to the calculation of the sound absorption coefficient of multi-layer fibrous materials.Experimental measurements are conducted to validate the proposed model,with good agreement achieved between model predictions and tested data.Numerical calculations with the proposed model are subsequently performed to quantify the influences of fiber diameter,porosity and backed air gap on sound absorption of uniform(single-layer)fibrous materials.Results show that the sound absorption increases with porosity at higher frequencies but decreases with porosity at lower frequencies.The sound absorption also decreases with fiber diameter at higher frequencies but increases at lower frequencies.The sound absorption resonance is shifted to lower frequencies with air gap.For multi-layer fibrous materials,gradient distributions of both fiber diameter and porosity are introduced and their effects on sound absorption are assessed.It is found that increasing the porosity and fiber diameter variation improves sound absorption in the low frequency range.The model provides the possibility to tailor the sound absorption capability of the sintered fibrous materials by optimizing the gradient distributions of key physical parameters.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2011CB610300)the National Natural Science Foundation of China (Grant Nos. 11102148,11072188,11021202 and 10825210)the Fundamental Research Funds for the Central Universities
文摘The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to calculate the radiated sound pressure level(SPL) versus frequency curves with reference to sound radiation of a bare plate immersed in a steady fluid.The flexural and rotational motions of the rib stiffeners are described by applying the Euler-Bernoulli beam theory and torsional wave equation,respectively.Therefore,the coupling forces and moments between the ribs and the face-panel,caused separately by flexural and rotational motion of the ribs,are both taken into account.Given the periodicity of the structure,the Fourier transform technique is employed to solve panel vibration equations and acoustic equations.Systematic parametric investigation demonstrates that the presence of mean flow as well as rib spacings play significant roles in the sound radiation behavior of parallelly rib-stiffened plates.The proposed model provides a convenient and efficient tool for the factual engineering design of this kind of periodic structures with acoustic requirements.
