The steel-epoxy-steel sandwich structures provide enhanced corrosion resistance and fatigue resistance,making them suitable for pipeline rehabilitation with effective repair and long-term durability.However,the repair...The steel-epoxy-steel sandwich structures provide enhanced corrosion resistance and fatigue resistance,making them suitable for pipeline rehabilitation with effective repair and long-term durability.However,the repair quality can be compromised by disbond between the steel and epoxy layers,whichmay result frominsufficient epoxy injection.Conventional ultrasonic testing faces challenges in accurately locating disbond defects due to aliased echo interference at interfaces.This paper proposes a signal processing algorithm for improving the accuracy of ultrasonic reflection method for detecting disbond defects between steel and epoxy layers.First,a coati optimization algorithmvariational mode decomposition(COA-VMD)is applied to adaptively decompose the ultrasonic signals and extract the intrinsic mode function components that show high correlation with the defect-related signals.Then,by calculating the relative reflectance at the interface and establishing a quantitative evaluation index based on acoustic impedance discontinuity,the locations of disbond defects are identified.Experimental results demonstrate that this method can effectively detect the locations of disbond defects between steel and epoxy layers.展开更多
Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate...Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.展开更多
The bipolar plate(BPP)is a crucial component of proton exchange membrane fuel cells(PEMFC).However,the weight of BPPs can account for around 80%of a PEMFC stack,posing a hindrance to the commercialization of PEMFCs.Th...The bipolar plate(BPP)is a crucial component of proton exchange membrane fuel cells(PEMFC).However,the weight of BPPs can account for around 80%of a PEMFC stack,posing a hindrance to the commercialization of PEMFCs.Therefore,the lightweight design of BPPs should be considered as a priority.Honeycomb sandwich structures meet some requirements for bipolar plates,such as high mechanical strength and lightweight.Animals and plants in nature provide many excellent structures with characteristics such as low density and high energy absorption capacity.In this work,inspired by the microstructures of the Cybister elytra,a novel bio-inspired vertical honeycomb sandwich(BVHS)structure was designed and manufactured by laser powder bed fusion(LPBF)for the application of lightweight BPPs.Compared with the conventional vertical honeycomb sandwich(CVHS)structure formed by LPBF under the same process parameters setting,the introduction of fractal thin walls enabled self-supporting and thus improved LPBF formability.In addition,the BVHS structure exhibited superior energy absorption(EA)capability and bending properties.It is worth noting that,compared with the CVHS structure,the specific energy absorption(SEA)and specific bending strength of the BVHS structure increased by 56.99%and 46.91%,respectively.Finite element analysis(FEA)was employed to study stress distributions in structures during bending and analyze the influence mechanism of the fractal feature on the mechanical properties of BVHS structures.The electrical conductivity of structures were also studied in this work,the BVHS structures were slightly lower than the CVHS structure.FEA was also conducted to analyze the current flow direction and current density distribution of BVHS structures under a constant voltage,illustrating the influence mechanism of fractal angles on electrical conductivity properties.Finally,in order to solve the problem of trapped powder inside the enclosed unit cells,a droplet-shaped powder outlet was designed for LPBF-processed components.The number of powder outlets was optimized based on bending properties.Results of this work could provide guidelines for the design of lightweight BPPs with high mechanical strength and high electrical conductivity.展开更多
In this paper,the numerical simulation method is used to study the ballistic performances of hourglass lattice sandwich structures with the same mass under the vertical incidence of fragments.Attention is paid to eluc...In this paper,the numerical simulation method is used to study the ballistic performances of hourglass lattice sandwich structures with the same mass under the vertical incidence of fragments.Attention is paid to elucidating the influences of rod cross-section dimensions,structure height,structure layer,and rod inclination angle on the deformation mode,ballistic performances,and ability to change the ballistic direction of fragments.The results show that the ballistic performances of hourglass lattice sandwich structures are mainly affected by their structural parameters.In this respect,structural parameters optimization of the hourglass lattice sandwich structures enable one to effectively improve their ballistic limit velocity and,consequently,ballistic performances.展开更多
In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to c...In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to create the hollow centers of the tapering tubes,with and without corrugations.The results demonstrate that the energy absorption(EA)and specific energy absorption(SEA)of the single corrugated tapered tube sandwich are 51.6% and 19.8% higher,respectively,than those of the conical tube sandwich.Furthermore,the results demonstrate that energy absorbers can benefit from corrugation in order to increase their efficiency.Additionally,the tapered corrugated tubes'resistance to oblique impacts was studied.Compared to a straight tube,the tapered tube is more resistant to oblique loads and has a lower initial peak crushing force(PCF),according to numerical simulations.After conducting a parametric study,it was discovered that the energy absorption performance of the sandwich construction is significantly affected by the amplitude,number of corrugations,and wall thickness.EA and SEA of DTS with corrugation number of 8 increased by 17.4%and 29.6%,respectively,while PCF decreased by 9.2% compared to DTS with corrugation number of 10.展开更多
The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding ...The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234.The out-of-plane compression and shear tests were conducted.Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures.Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.展开更多
Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight.This makes them very suitable for lightweight applications,where high stiffness to weight ratios are needed....Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight.This makes them very suitable for lightweight applications,where high stiffness to weight ratios are needed.Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets.However,adhesive bonding is prone to delamination,a failure mode that is often difficult to detect.This paper presents the results of delamination testing of fully additive manufactured(AM)AlSi10Mg sandwich structures with pyramidal lattice truss core using Laser Powder Bed Fusion(LPBF).The faces and struts are 0.5 mm thick,while the core is 2 mm thick.The inclination of the struts is 45°.To characterise the bonding strength,climbing drum peel tests and out-of-plane tensile tests are performed.Analytical formulas are derived to predict the expected failure loads and modes.The analytics and tests are supported by finite element(FE)calculations.From the analytic approach,design guidelines to avoid delamination in AM sandwich structures are derived.The study presents a critical face sheet thickness to strut diameter ratio for which the structure can delaminate.This ratio is mainly influenced by the inclination of the struts.The peel tests resulted in face yielding,which can also be inferred from the analytics and numerics.The out-of-plane tensile tests didn’t damage the structure.展开更多
Due to a viscoelastic damping middle layer,sandwich structures have the capacity of energy consumption.In this paper,we describe the frequency-dependent property of viscoelastic materials using complex modulus model,a...Due to a viscoelastic damping middle layer,sandwich structures have the capacity of energy consumption.In this paper,we describe the frequency-dependent property of viscoelastic materials using complex modulus model,and iterative modal strain energy method and iterative complex eigenvalue method are presented to obtain frequency and loss factor of sandwich structures.The two methods are effective and exact for the large-scale complex composite sandwich structures.Then an optimum analysis method is suggested to apply to sandwich structures.Finally,as an example,an optimum analysis of a clamped-clamped sandwich beams is conducted,theoretical closed-form solution and numerical predictions are studied comparatively,and the results agree well.展开更多
This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a freque...This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.展开更多
This paper is concerned with the decay of Saint-Venant end effects for plane deformations of piezoelectric （PE）-piezomagnetic （PM） sandwich structures, where a PM layer is located between two PE layers with the sa...This paper is concerned with the decay of Saint-Venant end effects for plane deformations of piezoelectric （PE）-piezomagnetic （PM） sandwich structures, where a PM layer is located between two PE layers with the same material properties or reversely. The end of the sandwich structure is subjected to a set of self-equilibrated magneto-electro-elastic loads. The upper and lower surfaces of the sandwich structure axe mechanically free, electrically open or shorted as well as magnetically open or shorted. Firstly the constitutive equations of PE mate- rials and PM materials for plane strain are given and normalized. Secondly, the simplified state space approach is employed to arrange the constitutive equations into differential equations in a matrix form. Finally, by using the transfer matrix method, the characteristic equations for eigen- values or decay rates axe derived. Based on the obtained characteristic equations, the decay rates for the PE-PM-PE and PM-PE-PM sandwich structures are calculated. The influences of the electromagnetic boundary conditions, material properties of PE layers and volume fraction on the decay rates are discussed in detail.展开更多
The so-called″X-cor sandwich structure″is a highly promising novel material as an alternative to honeycomb used in aircraft.Although much work has been conducted on the performance of the X-cor sandwich structure,th...The so-called″X-cor sandwich structure″is a highly promising novel material as an alternative to honeycomb used in aircraft.Although much work has been conducted on the performance of the X-cor sandwich structure,the gap is still hardly bridged between experimental results and theoretical analyses.Therefore,a method has been innovated to establish semi-empirical formula for the prediction of compressive and shear moduli of X-cor sandwich structure composites,by combining theoretical analyses and experimental data.In addition,aprediction software was first developed based on the proposed method,of which the accuracy was verified through confirmatory experiments.This software can offer a direct reference or guide for engineers in structural designing.展开更多
In the present study,experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores.The high velocity impact tests were carried out using a compressed air gu...In the present study,experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores.The high velocity impact tests were carried out using a compressed air gun.A sharp conical nosed projectile was impacted normally and with some offset distance(20 mm and 40 mm).The deformation,failure mode and energy dissipation characteristics were obtained for both kinds of loading.Moreover,the explicit solver was run in Abaqus to create the finite element model.The numerically obtained test results were compared with the experimental to check the accuracy of the modelling.The numerical result was further employed to obtain strain energy dissipation in each element by externally running user-defined code in Abaqus.Furthermore,the influence of inscribe circle diameter and cell wall and face sheet thickness on the energy dissipation,deformation and failure mode was examined.The result found that ballistic resistance and deformation were higher against offset impact compared to the normal impact loading.Sandwich panel impacted at 40 mm offset distance required 3 m/s and 1.9 m/s more velocity than 0 and 20 mm offset distance.Also,increasing the face sheet and wall thickness had a positive impact on the ballistic resistance in terms of a higher ballistic limit and energy absorption.However,inscribe circle diameter had a negative influence on the ballistic resistance.Also,the geometrical parameters of the sandwich structure had a significant influence on the energy dissipation in the different deformation directions.The energy dissipation in plastic work was highest for circumferential direction,regardless of impact condition followed by tangential,radial and axial directions.展开更多
Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic resp...Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic response and damage behavior of hybrid corrugated sandwich structures subjected to high velocity hail ice impact.The impact and breaking behavior of hail are described using the FE-smoothed particle hydrodynamics(FE-SPH)method.A rate-dependent progressive damage model is employed to capture the intra-laminar damage response;cohesive element and surface-based cohesive contact are implemented to predict the inter-laminar delamination and sheet/core debonding phenomena respectively.The transient processes of sandwich structure under different hail ice impact conditions are analyzed.Comparative analysis is conducted to address the influences of core shape and impact position on the impact performance of sandwich structures and the corresponding energy absorption characteristics are also revealed.展开更多
Inspired by nature's self-similar designs,novel honeycomb-spiderweb based self-similar hybrid cellular structures are proposed here for efficient energy absorption in impact applications.The energy absorption is e...Inspired by nature's self-similar designs,novel honeycomb-spiderweb based self-similar hybrid cellular structures are proposed here for efficient energy absorption in impact applications.The energy absorption is enhanced by optimizing the geometry and topology for a given mass.The proposed hybrid cellular structure is arrived after a thorough analysis of topologically enhanced self-similar structures.The optimized cell designs are rigorously tested considering dynamic loads involving crush and high-velocity bullet impact.Furthermore,the influence of thickness,radial connectivity,and order of patterning at the unit cell level are also investigated.The maximum crushing efficiency attained is found to be more than 95%,which is significantly higher than most existing traditional designs.Later on,the first and second-order hierarchical self-similar unit cell designs developed during crush analysis are used to prepare the cores for sandwich structures.Impact tests are performed on the developed sandwich structures using the standard 9-mm parabellum.The influence of multistaging on impact resistance is also investigated by maintaining a constant total thickness and mass of the sandwich structure.Moreover,in order to avoid layer-wise weak zones and hence,attain a uniform out-of-plane impact strength,off-setting the designs in each stage is proposed.The sandwich structures with first and second-order self-similar hybrid cores are observed to withstand impact velocities as high as 170 m/s and 270 m/s,respectively.展开更多
This work attempts to optimize Graphene nanoplatelets(GPLs)distribution in the face sheet of sandwich plates to pursue the minimum thermal deflection and transverse shear stresses at interfaces.Thus,an Improved Legend...This work attempts to optimize Graphene nanoplatelets(GPLs)distribution in the face sheet of sandwich plates to pursue the minimum thermal deflection and transverse shear stresses at interfaces.Thus,an Improved Legendre Higher-order plate Theory combined with Isogeometric Analysis(ILHT-IGA)is,first,proposed to accurately predict thermomechanical behaviors of GPLs-reinforced sandwich plates,which can ensure the reliability of the optimized results.Then,an accelerated multi-objective optimization approach is proposed to optimize thermomechanical behaviors.The trained machine learning algorithm based on ILHT-IGA is employed as a surrogate model to accelerate the optimization process.Finally,X-shaped GPLs distribution can provide the maximum stiffness to resist thermal expansion.However,X-shaped GPLs distribution on face sheets will result in large difference of stiffnesses at adjacent surfaces of face sheets and core layer.Thus,transverse shear stresses at interfaces are obviously increased.To avoid a sudden increase of transverse shear stresses at interfaces,an alternative optimized GPLs distribution has been obtained,where GPLs gradually increase toward the upper and lower surfaces of face sheets and suddenly decrease near the surface of face sheets.Such distributions can effectively enhance the stiffness of sandwich plates to resist thermal expansion behaviors and decrease transverse shear stresses at interfaces.展开更多
The high-temperature mechanical behaviors of Multi-Layer Composite Panels(MCP)and Corrugated Sandwich Panels(CSP)of Continuous Glass Fiber-Reinforced Polypropylene(CGFRPP)are critical for their application in aerospac...The high-temperature mechanical behaviors of Multi-Layer Composite Panels(MCP)and Corrugated Sandwich Panels(CSP)of Continuous Glass Fiber-Reinforced Polypropylene(CGFRPP)are critical for their application in aerospace fields,which have been rarely mentioned in previous studies.High-temperature quasi-static tensile and compression tests on CGFRPP MCP are conducted first.The results showed that the tensile and compression strength,stiffness,and tensile modulus of MCP decreased with increasing temperature.The Gibson model was found to be more suitable for predicting the high-temperature mechanical performance of MCP after comparing the calculated results of different theoretical models with experimental data.Secondly,hightemperature planar compression tests were conducted on the CGFRPP CSP,revealing that the main failure modes were corrugated core buckling and delamination between the face panel and core material,with delamination being intensified at higher temperatures.Therefore,we proposed a strength theoretical model that considers structural buckling failure and interface delamination failure,and introduced the influence factor to evaluate the effect of interface delamination on structural strength.展开更多
With the rapid development of flexible equipment,high-energy/-power requirements have been proposed for energy storage devices.Nevertheless,the poor conductivities of metallic oxides and their low levels of transmissi...With the rapid development of flexible equipment,high-energy/-power requirements have been proposed for energy storage devices.Nevertheless,the poor conductivities of metallic oxides and their low levels of transmission of electrons/ions hinder their widespread application.Here,a sandwich-structured Co_(3)O_(4)-Fe_(3)O_(4)(CFO) composite with binder-free was synthesized on a carbon cloth substrate via co-precipitation and partial ion exchange.The appropriate substitution of Co_(3)O_(4)with Fe_(3)O_(4)is favorable in promoting the rapid transfer of electrolyte ions and alleviating changes in volume during the electrochemical studies.When the duration of the substitution reaction is 20 min,the obtained electrode delivers a maximum specific capacitance of 1196.2 Fg^(-1)at a current density of 1 A g^(-1)and a superior capacity retention of~71%when the current density varies from 1to 30 Ag^(-1).Furthermore,the fabricated CFO//activated carbon flexible all-solid-state supercapacitor exhibits arespective maximum energy and power density of 68.7Wh kg^(-1)and 16,000 W kg^(-1)and excellent flexibility.It also displays a specific capacity retention of 81.3%under four continuous bending states at a current density of 6A g^(-1)over 10,000 cycles.These remarkable electrochemical char ac teristics suggest that the sandwich-structured CFO composite displays considerable potential for application in flexible high-energy/-power supercapacitors.展开更多
To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,f...To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,flexibility,exceptional mechanical strength,and superior electrothermal and photothermal properties,particularly for flexible and wearable electronics.In this regard,we designed an absorption-based composite film comprising carbon nanotubes(CNT)and α-Fe_(2)O_(3),featuring a CNT layer sandwiched between twoα-Fe_(2)O_(3)layers on the upper and lower surfaces.This composite film was fabricated through an electrodeposition process followed by a thermal annealing procedure to achieve enhanced EMI shielding performance along with improved electrothermal and photothermal properties.The strategically designed sandwich structure allows the rough surface of the upper α-Fe_(2)O_(3)layer to not only improve the impedance mismatch between free space and the composite film,facilitating the penetration of incident electromagnetic(EM)waves into the film and promoting increased EM absorption rather than reflection,but also to enhance electrical conductivity,thereby improving electron mobility and density.Consequently,the average total shielding effectiveness(SE)of the CNT/Fe_(16)-300 composite demonstrates remarkable EMI shielding effectiveness(EMI SE:56.8 dB).Furthermore,the alteration in the absorption-to-reflection ratio(A/R)signifies a transition in the EMI shielding mechanism from reflection(0.69 for the pristine CNT film)to absorption(1.86 for the CNT/Fe_(16)-300)with the incremental deposition of α-Fe_(2)O_(3)nanoparticles.This work presents a feasible manufacturing approach for developing composite films with a sandwich structure that exhibits absorption-dominant EMI shielding capabilities,contributing to advancements in thermal management and multifunctional electromagnetic shielding applications.展开更多
The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and...The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and mold pressing,require multiple steps and complex tools,thus limiting the exploration of advanced sandwich structure designs.This study reports a novel multi-material additive manufacturing(AM)process that allows the single-step production of continuous fiber-reinforced polymer composite(CFRPC)sandwich structures with multiscale cellular cores.Specifically,the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs.The cellular core design spans three levels:microcellular,unit-cell,and graded structures.Sandwich structures with a diverse set of unit-cell designs,that is,rhombus,square,honeycomb,and re-entrant honeycomb,were fabricated and their flexural behaviors were studied experimentally.The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness,strength,and specific energy absorption.In addition,the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined.The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.展开更多
Carbon fiber reinforced polymer(CFRP)and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact.The mechanical characteristics of composite honeycomb sandwich structures under oblique ...Carbon fiber reinforced polymer(CFRP)and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact.The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment.The oblique impact model is established,and the reliability of the model is verified by the oblique impact test.To further analyze the influence of structural parameters on energy absorption under oblique impact,the influence of impact angle,face sheet thickness and wall thickness of the honeycomb is numerically studied.The results show that the impact angle has an important effect on energy distribution.The structural parameters also have an effect on the peak contact force,contact time,and energy absorption,and the effect is different from normal impact due to the presence of frictional dissipation energy.Compared with normal impact,the debonding of oblique impact will be reduced,but the buckling range of the honeycomb core will be expanded.展开更多
基金supported by the Research Funding of Hangzhou International Innovation Institute of Beihang University(Grant No.015731201-2024KQ126)National Key R&D Program of China(Grant No.2023YFF0716600)National Natural Science Foundation of China(Grant No.62271021).
文摘The steel-epoxy-steel sandwich structures provide enhanced corrosion resistance and fatigue resistance,making them suitable for pipeline rehabilitation with effective repair and long-term durability.However,the repair quality can be compromised by disbond between the steel and epoxy layers,whichmay result frominsufficient epoxy injection.Conventional ultrasonic testing faces challenges in accurately locating disbond defects due to aliased echo interference at interfaces.This paper proposes a signal processing algorithm for improving the accuracy of ultrasonic reflection method for detecting disbond defects between steel and epoxy layers.First,a coati optimization algorithmvariational mode decomposition(COA-VMD)is applied to adaptively decompose the ultrasonic signals and extract the intrinsic mode function components that show high correlation with the defect-related signals.Then,by calculating the relative reflectance at the interface and establishing a quantitative evaluation index based on acoustic impedance discontinuity,the locations of disbond defects are identified.Experimental results demonstrate that this method can effectively detect the locations of disbond defects between steel and epoxy layers.
文摘Polymethacrylimide(PMI)foam has the highest specific stiffness and strength among polymer foams,with excellent radar-absorbing capabilities,which provide it with broad prospects in underwater ap-plications.To evaluate the impact resistance of PMI foam sandwich structures,the dynamic response and energy absorption characteristics of PMI foam sandwich structures with different core layers under various water impact loads were investigated using combined experimental and numerical methods.A fluid-structure interaction device with a diffusion angle was used for water impact testing of the PMI foam sandwich structures.The 3D-DIC technique was employed to process the deformation images of the sandwich-structure back panel captured by the high-speed cameras.Numerical simulations were performed to analyze the dynamic deformation process of the PMI foam core.The results indicated that the maximum deformation of the back panel exhibited a nonlinear relationship with the impulse.Below the critical impulse,the maximum deformation of the back panel plateaued,which was determined by the core density.Beyond the critical impulse,the rate of deformation increased with the impulse was governed by the core thickness.Compared with different sandwich panels,PMI foam sandwich struc-tures demonstrate significant advantages in terms of impact resistance under high-impulse conditions.
基金Supported by Defense Industrial Technology Development Program of China(Grant No.JCKY2020605C007)Key Research and Development Program of Jiangsu Province of China(Grant Nos.BE2022069,BE2022069-1,BE2022069-3)Aeronautical Science Foundation of China(Grant No.2020Z049052001).
文摘The bipolar plate(BPP)is a crucial component of proton exchange membrane fuel cells(PEMFC).However,the weight of BPPs can account for around 80%of a PEMFC stack,posing a hindrance to the commercialization of PEMFCs.Therefore,the lightweight design of BPPs should be considered as a priority.Honeycomb sandwich structures meet some requirements for bipolar plates,such as high mechanical strength and lightweight.Animals and plants in nature provide many excellent structures with characteristics such as low density and high energy absorption capacity.In this work,inspired by the microstructures of the Cybister elytra,a novel bio-inspired vertical honeycomb sandwich(BVHS)structure was designed and manufactured by laser powder bed fusion(LPBF)for the application of lightweight BPPs.Compared with the conventional vertical honeycomb sandwich(CVHS)structure formed by LPBF under the same process parameters setting,the introduction of fractal thin walls enabled self-supporting and thus improved LPBF formability.In addition,the BVHS structure exhibited superior energy absorption(EA)capability and bending properties.It is worth noting that,compared with the CVHS structure,the specific energy absorption(SEA)and specific bending strength of the BVHS structure increased by 56.99%and 46.91%,respectively.Finite element analysis(FEA)was employed to study stress distributions in structures during bending and analyze the influence mechanism of the fractal feature on the mechanical properties of BVHS structures.The electrical conductivity of structures were also studied in this work,the BVHS structures were slightly lower than the CVHS structure.FEA was also conducted to analyze the current flow direction and current density distribution of BVHS structures under a constant voltage,illustrating the influence mechanism of fractal angles on electrical conductivity properties.Finally,in order to solve the problem of trapped powder inside the enclosed unit cells,a droplet-shaped powder outlet was designed for LPBF-processed components.The number of powder outlets was optimized based on bending properties.Results of this work could provide guidelines for the design of lightweight BPPs with high mechanical strength and high electrical conductivity.
基金supported by the Defense Industrial Technology Development Program(Grant No.JCKY2018604B004)the National Natural Science Foundation of China(Grant No.11972007)。
文摘In this paper,the numerical simulation method is used to study the ballistic performances of hourglass lattice sandwich structures with the same mass under the vertical incidence of fragments.Attention is paid to elucidating the influences of rod cross-section dimensions,structure height,structure layer,and rod inclination angle on the deformation mode,ballistic performances,and ability to change the ballistic direction of fragments.The results show that the ballistic performances of hourglass lattice sandwich structures are mainly affected by their structural parameters.In this respect,structural parameters optimization of the hourglass lattice sandwich structures enable one to effectively improve their ballistic limit velocity and,consequently,ballistic performances.
基金the grants from the National Natural Science Foundation of China(Nos.52078152 and 12002095)Guangzhou Government-University Union Fund(No.202201020532)。
文摘In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to create the hollow centers of the tapering tubes,with and without corrugations.The results demonstrate that the energy absorption(EA)and specific energy absorption(SEA)of the single corrugated tapered tube sandwich are 51.6% and 19.8% higher,respectively,than those of the conical tube sandwich.Furthermore,the results demonstrate that energy absorbers can benefit from corrugation in order to increase their efficiency.Additionally,the tapered corrugated tubes'resistance to oblique impacts was studied.Compared to a straight tube,the tapered tube is more resistant to oblique loads and has a lower initial peak crushing force(PCF),according to numerical simulations.After conducting a parametric study,it was discovered that the energy absorption performance of the sandwich construction is significantly affected by the amplitude,number of corrugations,and wall thickness.EA and SEA of DTS with corrugation number of 8 increased by 17.4%and 29.6%,respectively,while PCF decreased by 9.2% compared to DTS with corrugation number of 10.
基金supported by the National Natural Science Foundation of China under Grant Nos.90816024 and 10872059the Major State Basic Research Development Program of China under Grant No. 2011CB610303+2 种基金the Fundamental Research Funds for the central Universities grant No. HIT. NSRIF. 2010069the Program of Excellent Team in Harbin Institute of Technologythe Program for New Century Excellent Talents in University under Grant No.NCET-08-0152
文摘The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234.The out-of-plane compression and shear tests were conducted.Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures.Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.
基金Part of this work was supported by the German Federal Ministry for Economic Affairs and Energy(BMWi)(Grant No.20E1713B).
文摘Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight.This makes them very suitable for lightweight applications,where high stiffness to weight ratios are needed.Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets.However,adhesive bonding is prone to delamination,a failure mode that is often difficult to detect.This paper presents the results of delamination testing of fully additive manufactured(AM)AlSi10Mg sandwich structures with pyramidal lattice truss core using Laser Powder Bed Fusion(LPBF).The faces and struts are 0.5 mm thick,while the core is 2 mm thick.The inclination of the struts is 45°.To characterise the bonding strength,climbing drum peel tests and out-of-plane tensile tests are performed.Analytical formulas are derived to predict the expected failure loads and modes.The analytics and tests are supported by finite element(FE)calculations.From the analytic approach,design guidelines to avoid delamination in AM sandwich structures are derived.The study presents a critical face sheet thickness to strut diameter ratio for which the structure can delaminate.This ratio is mainly influenced by the inclination of the struts.The peel tests resulted in face yielding,which can also be inferred from the analytics and numerics.The out-of-plane tensile tests didn’t damage the structure.
文摘Due to a viscoelastic damping middle layer,sandwich structures have the capacity of energy consumption.In this paper,we describe the frequency-dependent property of viscoelastic materials using complex modulus model,and iterative modal strain energy method and iterative complex eigenvalue method are presented to obtain frequency and loss factor of sandwich structures.The two methods are effective and exact for the large-scale complex composite sandwich structures.Then an optimum analysis method is suggested to apply to sandwich structures.Finally,as an example,an optimum analysis of a clamped-clamped sandwich beams is conducted,theoretical closed-form solution and numerical predictions are studied comparatively,and the results agree well.
文摘This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.
基金Project supported by the National Natural Science Foundation of China (No. 10972147)
文摘This paper is concerned with the decay of Saint-Venant end effects for plane deformations of piezoelectric （PE）-piezomagnetic （PM） sandwich structures, where a PM layer is located between two PE layers with the same material properties or reversely. The end of the sandwich structure is subjected to a set of self-equilibrated magneto-electro-elastic loads. The upper and lower surfaces of the sandwich structure axe mechanically free, electrically open or shorted as well as magnetically open or shorted. Firstly the constitutive equations of PE mate- rials and PM materials for plane strain are given and normalized. Secondly, the simplified state space approach is employed to arrange the constitutive equations into differential equations in a matrix form. Finally, by using the transfer matrix method, the characteristic equations for eigen- values or decay rates axe derived. Based on the obtained characteristic equations, the decay rates for the PE-PM-PE and PM-PE-PM sandwich structures are calculated. The influences of the electromagnetic boundary conditions, material properties of PE layers and volume fraction on the decay rates are discussed in detail.
基金supported by the Aviation Science Fund of China(Nos.2015ZE52049,2015ZE521049)
文摘The so-called″X-cor sandwich structure″is a highly promising novel material as an alternative to honeycomb used in aircraft.Although much work has been conducted on the performance of the X-cor sandwich structure,the gap is still hardly bridged between experimental results and theoretical analyses.Therefore,a method has been innovated to establish semi-empirical formula for the prediction of compressive and shear moduli of X-cor sandwich structure composites,by combining theoretical analyses and experimental data.In addition,aprediction software was first developed based on the proposed method,of which the accuracy was verified through confirmatory experiments.This software can offer a direct reference or guide for engineers in structural designing.
文摘In the present study,experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores.The high velocity impact tests were carried out using a compressed air gun.A sharp conical nosed projectile was impacted normally and with some offset distance(20 mm and 40 mm).The deformation,failure mode and energy dissipation characteristics were obtained for both kinds of loading.Moreover,the explicit solver was run in Abaqus to create the finite element model.The numerically obtained test results were compared with the experimental to check the accuracy of the modelling.The numerical result was further employed to obtain strain energy dissipation in each element by externally running user-defined code in Abaqus.Furthermore,the influence of inscribe circle diameter and cell wall and face sheet thickness on the energy dissipation,deformation and failure mode was examined.The result found that ballistic resistance and deformation were higher against offset impact compared to the normal impact loading.Sandwich panel impacted at 40 mm offset distance required 3 m/s and 1.9 m/s more velocity than 0 and 20 mm offset distance.Also,increasing the face sheet and wall thickness had a positive impact on the ballistic resistance in terms of a higher ballistic limit and energy absorption.However,inscribe circle diameter had a negative influence on the ballistic resistance.Also,the geometrical parameters of the sandwich structure had a significant influence on the energy dissipation in the different deformation directions.The energy dissipation in plastic work was highest for circumferential direction,regardless of impact condition followed by tangential,radial and axial directions.
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20180855)Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-E-0219Y01)Research and Practice Innovation Program of postgraduates in Jiangsu Province(Grant No.KYCX20-3076)。
文摘Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic response and damage behavior of hybrid corrugated sandwich structures subjected to high velocity hail ice impact.The impact and breaking behavior of hail are described using the FE-smoothed particle hydrodynamics(FE-SPH)method.A rate-dependent progressive damage model is employed to capture the intra-laminar damage response;cohesive element and surface-based cohesive contact are implemented to predict the inter-laminar delamination and sheet/core debonding phenomena respectively.The transient processes of sandwich structure under different hail ice impact conditions are analyzed.Comparative analysis is conducted to address the influences of core shape and impact position on the impact performance of sandwich structures and the corresponding energy absorption characteristics are also revealed.
基金the Science and Engineering Research Board(SERB),Department of Science and Technology,India,for funding this research through grant number SRG/2019/001581。
文摘Inspired by nature's self-similar designs,novel honeycomb-spiderweb based self-similar hybrid cellular structures are proposed here for efficient energy absorption in impact applications.The energy absorption is enhanced by optimizing the geometry and topology for a given mass.The proposed hybrid cellular structure is arrived after a thorough analysis of topologically enhanced self-similar structures.The optimized cell designs are rigorously tested considering dynamic loads involving crush and high-velocity bullet impact.Furthermore,the influence of thickness,radial connectivity,and order of patterning at the unit cell level are also investigated.The maximum crushing efficiency attained is found to be more than 95%,which is significantly higher than most existing traditional designs.Later on,the first and second-order hierarchical self-similar unit cell designs developed during crush analysis are used to prepare the cores for sandwich structures.Impact tests are performed on the developed sandwich structures using the standard 9-mm parabellum.The influence of multistaging on impact resistance is also investigated by maintaining a constant total thickness and mass of the sandwich structure.Moreover,in order to avoid layer-wise weak zones and hence,attain a uniform out-of-plane impact strength,off-setting the designs in each stage is proposed.The sandwich structures with first and second-order self-similar hybrid cores are observed to withstand impact velocities as high as 170 m/s and 270 m/s,respectively.
基金supported by the National Natural Sciences Foundation of China(No.12172295)。
文摘This work attempts to optimize Graphene nanoplatelets(GPLs)distribution in the face sheet of sandwich plates to pursue the minimum thermal deflection and transverse shear stresses at interfaces.Thus,an Improved Legendre Higher-order plate Theory combined with Isogeometric Analysis(ILHT-IGA)is,first,proposed to accurately predict thermomechanical behaviors of GPLs-reinforced sandwich plates,which can ensure the reliability of the optimized results.Then,an accelerated multi-objective optimization approach is proposed to optimize thermomechanical behaviors.The trained machine learning algorithm based on ILHT-IGA is employed as a surrogate model to accelerate the optimization process.Finally,X-shaped GPLs distribution can provide the maximum stiffness to resist thermal expansion.However,X-shaped GPLs distribution on face sheets will result in large difference of stiffnesses at adjacent surfaces of face sheets and core layer.Thus,transverse shear stresses at interfaces are obviously increased.To avoid a sudden increase of transverse shear stresses at interfaces,an alternative optimized GPLs distribution has been obtained,where GPLs gradually increase toward the upper and lower surfaces of face sheets and suddenly decrease near the surface of face sheets.Such distributions can effectively enhance the stiffness of sandwich plates to resist thermal expansion behaviors and decrease transverse shear stresses at interfaces.
基金co-supported by the National Natural Science Foundation of China(Nos.12372127,12202085,12302464)the Fundamental Research Funds for the Central Universities,China(No.2024CDJXY009)+1 种基金the Chongqing Outstanding Youth Fund,China(No.CSTB2024NSCQ-JQX0028)the Chongqing Natural Science Foundation,China(Nos.cstc2021ycjh-bgzxm0117,CSTB2022NSCQ-MSX0608)。
文摘The high-temperature mechanical behaviors of Multi-Layer Composite Panels(MCP)and Corrugated Sandwich Panels(CSP)of Continuous Glass Fiber-Reinforced Polypropylene(CGFRPP)are critical for their application in aerospace fields,which have been rarely mentioned in previous studies.High-temperature quasi-static tensile and compression tests on CGFRPP MCP are conducted first.The results showed that the tensile and compression strength,stiffness,and tensile modulus of MCP decreased with increasing temperature.The Gibson model was found to be more suitable for predicting the high-temperature mechanical performance of MCP after comparing the calculated results of different theoretical models with experimental data.Secondly,hightemperature planar compression tests were conducted on the CGFRPP CSP,revealing that the main failure modes were corrugated core buckling and delamination between the face panel and core material,with delamination being intensified at higher temperatures.Therefore,we proposed a strength theoretical model that considers structural buckling failure and interface delamination failure,and introduced the influence factor to evaluate the effect of interface delamination on structural strength.
基金financially supported by the Fundamental Research Funds for the Central Universities,North Minzu University(No.2020KYQD18)the Key Research and Development Program(Talents Introduction Project)of Ningxia(No.2021BEB04027)+1 种基金the Fundamental Research Funds for the Central Universities,North Minzu University(No.2021KJCX04)the Natural Science Foundation of Ningxia Province(No.2022AAC05033)
文摘With the rapid development of flexible equipment,high-energy/-power requirements have been proposed for energy storage devices.Nevertheless,the poor conductivities of metallic oxides and their low levels of transmission of electrons/ions hinder their widespread application.Here,a sandwich-structured Co_(3)O_(4)-Fe_(3)O_(4)(CFO) composite with binder-free was synthesized on a carbon cloth substrate via co-precipitation and partial ion exchange.The appropriate substitution of Co_(3)O_(4)with Fe_(3)O_(4)is favorable in promoting the rapid transfer of electrolyte ions and alleviating changes in volume during the electrochemical studies.When the duration of the substitution reaction is 20 min,the obtained electrode delivers a maximum specific capacitance of 1196.2 Fg^(-1)at a current density of 1 A g^(-1)and a superior capacity retention of~71%when the current density varies from 1to 30 Ag^(-1).Furthermore,the fabricated CFO//activated carbon flexible all-solid-state supercapacitor exhibits arespective maximum energy and power density of 68.7Wh kg^(-1)and 16,000 W kg^(-1)and excellent flexibility.It also displays a specific capacity retention of 81.3%under four continuous bending states at a current density of 6A g^(-1)over 10,000 cycles.These remarkable electrochemical char ac teristics suggest that the sandwich-structured CFO composite displays considerable potential for application in flexible high-energy/-power supercapacitors.
基金financially supported by the National Natural Science Foundation of China(Nos.52222202 and 51772310)Chinese Academy of Sciences Key Research Program of Frontier Sciences(No.QYZDY-SSWJSC031)Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(No.JCYJ-SHFY-2021-001).
文摘To mitigate secondary electromagnetic pollution,there is an urgent need to develop absorption-dominant electromagnetic interference(EMI)shielding materials with low density,reduced thickness,lightweight construction,flexibility,exceptional mechanical strength,and superior electrothermal and photothermal properties,particularly for flexible and wearable electronics.In this regard,we designed an absorption-based composite film comprising carbon nanotubes(CNT)and α-Fe_(2)O_(3),featuring a CNT layer sandwiched between twoα-Fe_(2)O_(3)layers on the upper and lower surfaces.This composite film was fabricated through an electrodeposition process followed by a thermal annealing procedure to achieve enhanced EMI shielding performance along with improved electrothermal and photothermal properties.The strategically designed sandwich structure allows the rough surface of the upper α-Fe_(2)O_(3)layer to not only improve the impedance mismatch between free space and the composite film,facilitating the penetration of incident electromagnetic(EM)waves into the film and promoting increased EM absorption rather than reflection,but also to enhance electrical conductivity,thereby improving electron mobility and density.Consequently,the average total shielding effectiveness(SE)of the CNT/Fe_(16)-300 composite demonstrates remarkable EMI shielding effectiveness(EMI SE:56.8 dB).Furthermore,the alteration in the absorption-to-reflection ratio(A/R)signifies a transition in the EMI shielding mechanism from reflection(0.69 for the pristine CNT film)to absorption(1.86 for the CNT/Fe_(16)-300)with the incremental deposition of α-Fe_(2)O_(3)nanoparticles.This work presents a feasible manufacturing approach for developing composite films with a sandwich structure that exhibits absorption-dominant EMI shielding capabilities,contributing to advancements in thermal management and multifunctional electromagnetic shielding applications.
基金supported by National Natural Science Foundation of China(Grant No.52105261)Shenzhen Science and Technology Inno-vation Committee of China(Grant No.JCYJ20210324104610028)Department of Education of Guangdong Province of China(Grant No.2022ZDZX3020).
文摘The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities.However,current manufacturing processes,such as hot-press molding and mold pressing,require multiple steps and complex tools,thus limiting the exploration of advanced sandwich structure designs.This study reports a novel multi-material additive manufacturing(AM)process that allows the single-step production of continuous fiber-reinforced polymer composite(CFRPC)sandwich structures with multiscale cellular cores.Specifically,the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs.The cellular core design spans three levels:microcellular,unit-cell,and graded structures.Sandwich structures with a diverse set of unit-cell designs,that is,rhombus,square,honeycomb,and re-entrant honeycomb,were fabricated and their flexural behaviors were studied experimentally.The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness,strength,and specific energy absorption.In addition,the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined.The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.
基金This research was supported by the National Natural Science Foundations of China(Nos.52175153,U1833116,51705468 and 11402234)the China Scholarship Council(CSC).
文摘Carbon fiber reinforced polymer(CFRP)and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact.The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment.The oblique impact model is established,and the reliability of the model is verified by the oblique impact test.To further analyze the influence of structural parameters on energy absorption under oblique impact,the influence of impact angle,face sheet thickness and wall thickness of the honeycomb is numerically studied.The results show that the impact angle has an important effect on energy distribution.The structural parameters also have an effect on the peak contact force,contact time,and energy absorption,and the effect is different from normal impact due to the presence of frictional dissipation energy.Compared with normal impact,the debonding of oblique impact will be reduced,but the buckling range of the honeycomb core will be expanded.
