In this work,a computational modelling and analysis framework is developed to investigate the thermal buckling behavior of doubly-curved composite shells reinforced with graphene-origami(G-Ori)auxetic metamaterials.A ...In this work,a computational modelling and analysis framework is developed to investigate the thermal buckling behavior of doubly-curved composite shells reinforced with graphene-origami(G-Ori)auxetic metamaterials.A semi-analytical formulation based on the First-Order Shear Deformation Theory(FSDT)and the principle of virtual displacements is established,and closed-form solutions are derived via Navier’s method for simply supported boundary conditions.The G-Ori metamaterial reinforcements are treated as programmable constructs whose effective thermo-mechanical properties are obtained via micromechanical homogenization and incorporated into the shell model.A comprehensive parametric study examines the influence of folding geometry,dispersion arrangement,reinforcement weight fraction,curvature parameters,and elastic foundation support on the critical buckling temperature(CBT).The results reveal that,under optimal folding geometry and reinforcement alignment with principal stress trajectories,the CBT can increase by more than 150%.Furthermore,the combined effect of G-Ori reinforcement and elastic foundation substantially enhances thermal buckling resistance.These findings establish design guidelines for architected composite shells in applications such as aerospace thermal skins,morphing structures,and thermally-responsive systems,and illustrate the potential of auxetic graphene metamaterials for multifunctional,lightweight,and thermally robust structural components.展开更多
Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properti...Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.展开更多
This study presents a significant advancement in the vibration analysis of functionally graded sandwich plates with auxetic cores by introducing a general viscoelastic foundation model that more accurately reflects th...This study presents a significant advancement in the vibration analysis of functionally graded sandwich plates with auxetic cores by introducing a general viscoelastic foundation model that more accurately reflects the complex interactions between the plate and the foundation.The novelty of this study is that the proposed viscoelastic foundation model incorporates elastic and damping effects in both the Winkler and Pasternak layers.To develop the theoretical framework for this analysis,the higher-order shear deformation theory is employed,while Hamilton's principle is used to derive the governing equations of motion.The closed-form solution is used to determine the damped vibration behaviors of the sandwich plates.The precision and robustness of the proposed mathematical model are validated through several comparison studies with existing numerical results.A detailed parametric study is conducted to investigate the influence of various parameters,including the elastic and damping coefficients of the foundation,the material gradation,and the properties of the auxetic core on the vibration behavior of the plates.The numerical results provide new insights into the vibration characteristics of sandwich plates with auxetic cores resting on viscoelastic foundation,highlighting the significant role of the two damping coefficients and auxetic cores in the visco-vibration behavior of the plates.展开更多
The nonlinear post-buckling response of functionally graded(FG)copper matrix plates enforced by graphene origami auxetic metamaterials(GOAMs)is investigated in the currentwork.The auxeticmaterial properties of the pla...The nonlinear post-buckling response of functionally graded(FG)copper matrix plates enforced by graphene origami auxetic metamaterials(GOAMs)is investigated in the currentwork.The auxeticmaterial properties of the plate are controlled by graphene content and the degree of origami folding,which are graded across the thickness of the plate.Thematerial properties of the GOAM plate are evaluated using genetic micro-mechanicalmodels.Governing nonlinear eigenvalue problems for the post-buckling response of the GOAM composite plate are derived using the virtual work principle and a four-variable nonlinear shear deformation theory.A novel differential quadrature method(DQM)algorithm is developed to solve the nonlinear eigenvalue problem.Detailed parametric studies are presented to explore the effects of graphene content,folding degree,and GO distribution patterns on the post-buckling responses of GOAM plates.Results show that high tunability in post-buckling characteristics can be achieved by using GOAM.FunctionallyGradedGraphene OrigamiAuxeticMetamaterials(FG-GOAM)plates can be used in aerospace structures to improve their structural performance and response.展开更多
Auxetic metamaterials have attracted much attention due to their outstanding advantages over traditional materials in terms of shear capacity,fracture resistance,and energy absorption.However,there are lack of design ...Auxetic metamaterials have attracted much attention due to their outstanding advantages over traditional materials in terms of shear capacity,fracture resistance,and energy absorption.However,there are lack of design inspirations for novel auxetic structures.According to the materials databases of atomic lattice,some natural crystals possess negative Poisson’s ratio(NPR).In this paper,the mechanism of auxeticity in microscale Ti crystal is investigated through density functional theory simulation.Then we propose a macroscopic auxetic metamaterial by mimicking the microscopic atomic lattice structure of the bodycentered cubic Ti crystal.The NPR property of the macroscopic metamaterial is verified by theoretical,numerical and experimental methods.The auxeticity keeps effective when scaling up to macroscopic Ti crystal-mimic structure,with the similar deformation mechanism.Furthermore,from the geometric parameter investigation,the geometric parameters have great influence on the Poisson’s ratio and Young’s modulus of the macroscopic metamaterial.Importantly,an optimized structure is obtained,which exhibits 2 times enhancement in auxeticity and 25 times enhancement in normalized Young’s modulus,compared to the original architecture.This work establishes a link between the physical properties at micro-nanoscale and macroscale structures,which provides inspirations for high load-bearing auxetic metamaterials.展开更多
This paper presents,for the first time,an effective numerical approach based on the isogeometric analysis(IGA)and the six-variable quasi-three dimensional(3D)higher-order shear deformation theory(HSDT)to study the fre...This paper presents,for the first time,an effective numerical approach based on the isogeometric analysis(IGA)and the six-variable quasi-three dimensional(3D)higher-order shear deformation theory(HSDT)to study the free vibration characteristics of functionally-graded(FG)graphene origami(GOri)-enabled auxetic metamaterial(GOEAM)plates submerged in a fluid medium.The plate theory incorporates the thickness stretching and the effects of transverse shear deformation without using any shear correction factors.The velocity potential function and Bernoulli's equation are used to derive the hydrodynamic pressure acting on the plate surface.Both horizontally and vertically immersed plate configurations are considered here in the form of inertia effects.The plates are composed of multilayer GOEAMs,with the GOri content varying through the plate's thickness in a layer-wise manner.This design results in graded auxetic growth.The material properties are evaluated by mixing rules and a genetic programming(GP)-assisted micromechanical model.The governing equations of motion for the FG-GOEAM plates immersed in a fluid medium are derived by Hamilton's principle.After validating the convergence and accuracy of the present model,a comprehensive parametric study is carried out to examine the effects of the GOri content,GOri distribution pattern,GOri folding degree,fluid level,immersed depth,and geometric parameter on the natural frequencies of the FG-GOEAM plates.The results show that the natural frequencies for the four GOri distribution patterns increase with the increase in the layer number when the lay number is fewer than 10,and then stabilize after the layer number reaches 10.Besides,in general,the natural frequency of the FG-GOEAM plate in a vacuum or fluid increases when the GOri content increases,while decreases when the GOri folding degree increases.Some additional findings related to the numerical results are presented in the conclusions.It is believed that the present results are useful for the precise design and optimization of FG-GOEAM plates immersed in a fluid medium.展开更多
Three new kinds of molecular networks are designed and predicted to exhibit negative Poisson ratios. Molecular mechanics calculations on these networks show that the magnitude of Poisson ratios depends on the relative...Three new kinds of molecular networks are designed and predicted to exhibit negative Poisson ratios. Molecular mechanics calculations on these networks show that the magnitude of Poisson ratios depends on the relative flexibility of beam and arm structures. Several new kinds of auxetic polymers, whose successful synthesis should be easier than that of the corresponding auxetic networks, are then proposed. It is found that the kabob-like polymers with auxegens lying vertically on the main chain can acquire auxeticity while those with auxegens lying horizontally on the main chain cannot. Besides, a half kabob-like or pseudo-ladder polymer with auxegens linked at the intersection of the beam and the arm does show auxeticity when adopting constrictive conformers. It is, however, worthwhile noting that the origins of auxeticity still await and strongly deserve further experimental and theoretical investigations.展开更多
Auxetic mechanical metamaterials are artificially architected materials that possess negative Poisson’s ratio,demonstrating transversal contracting deformation under external vertical compression loading.Their physic...Auxetic mechanical metamaterials are artificially architected materials that possess negative Poisson’s ratio,demonstrating transversal contracting deformation under external vertical compression loading.Their physical properties are mainly determined by spatial topological configurations.Traditionally,classical auxetic mechanical metamaterials exhibit relatively lower mechanical stiffness,compared to classic stretching dominated architectures.Nevertheless,in recent years,several novel auxetic mechanical metamaterials with high stiffness have been designed and proposed for energy absorption,load-bearing,and thermal-mechanical coupling applications.In this paper,mechanical design methods for designing auxetic structures with soft and stiff mechanical behavior are summarized and classified.For soft auxetic mechanical metamaterials,classic methods,such as using soft basic material,hierarchical design,tensile braided design,and curved ribs,are proposed.In comparison,for stiff auxetic mechanical metamaterials,design schemes,such as hard base material,hierarchical design,composite design,and adding additional load-bearing ribs,are proposed.Multi-functional applications of soft and stiff auxetic mechanical metamaterials are then reviewed.We hope this study could provide some guidelines for designing programmed auxetics with specified mechanical stiffness and deformation abilities according to demand.展开更多
Focusing on the structural optimization of auxetic materials using data-driven methods,a back-propagation neural network(BPNN)based design framework is developed for petal-shaped auxetics using isogeometric analysis.A...Focusing on the structural optimization of auxetic materials using data-driven methods,a back-propagation neural network(BPNN)based design framework is developed for petal-shaped auxetics using isogeometric analysis.Adopting a NURBSbased parametric modelling scheme with a small number of design variables,the highly nonlinear relation between the input geometry variables and the effective material properties is obtained using BPNN-based fitting method,and demonstrated in this work to give high accuracy and efficiency.Such BPNN-based fitting functions also enable an easy analytical sensitivity analysis,in contrast to the generally complex procedures of typical shape and size sensitivity approaches.展开更多
The increasing threat of explosions on the battle field and the terrorist action requires the development of more effective blast resistance materials and structures.Curved structure can support the external loads eff...The increasing threat of explosions on the battle field and the terrorist action requires the development of more effective blast resistance materials and structures.Curved structure can support the external loads effectively by virtue of their spatial curvature.In review of the excellent energy absorption property of auxetic structure,employing auxetic structure as core material in curved sandwich shows the potential to improve the protection performance.In this study,a novel cylindrical sandwich panel with double arrow auxetic(DAA) core was designed and the numerical model was built by ABAQUS.Due to the complexity of the structure,systematic parameter study and optimal design are conducted.Two cases of optimal design were considered,case1 focuses on reducing the deflection and mass of the structure,while case2 focuses on reducing the deflection and increasing the energy absorption per unit mass.Parameter study and optimal design were conducted based on Latin Hypercube Sampling(LHD)method,artificial neural networks(ANN) metamodel and the nondominated sorting genetic algorithm(NSGA-Ⅱ).The Pareto front was obtained and the cylindrical DAA structure performed much better than its equal solid panel in both blast resistance and energy absorption capacity.Optimization results can be used as a reference for different applications.展开更多
Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially compressed (i.e., the materials exhibit...Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially compressed (i.e., the materials exhibit a negative Poisson's ratio). The current study focuses on assessing the potential of an auxetic material to enhance the buckling capacity of a rectangular plate under uniaxial compression. The in-plane translational restraint along the unloaded edges that was often neglected in open literature is taken into consideration in our buckling model proposed in this study. The closed-form expressions for the critical buckling coefficient of the rectangle are provided and the predicted results agree well with those determined by the finite element method. Furthermore, the results indicate that the buckling performance of a rectangular plate under uniaxial compression can be significantly improved by replacing the traditional material that has a positive Poisson's ratio with an auxetic material when there is in-plane translation restraint along the unloaded edges. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.展开更多
Auxetic honeycomb structures are promising metamaterials with outstanding mechanical properties,and can be potentially used in energy absorption applications.In this study,a novel modified re-entrant hybrid auxetic me...Auxetic honeycomb structures are promising metamaterials with outstanding mechanical properties,and can be potentially used in energy absorption applications.In this study,a novel modified re-entrant hybrid auxetic metamaterial inspired by Islamic motif art is designed by integrating four-pointed double re-entrant motifs with symmetric semi-hexagonal unit cells to achieve a high energy absorption capacity(EAC).Theoretical analyses and numerical simulations are performed to examine the dynamic crushing behavior of the four-pointed double re-entrant combined structure(FDRCS).The developed finite element models(FEMs)are validated by the experiments under quasi-static compression.The deformation mode and stress-strain curves are further studied under low,medium,and high crushing velocities.The theoretically predicted plateau stress of the FDRCS under different crushing velocities is consistent with the numerical simulation results.The crushing stress and the EAC of the FDRCS are influenced by the geometric parameters and crushing velocities.The FDRCS exhibits a negative Poisson's ratio(NPR),owing to the four-point re-entrant structure(RES).Moreover,the specific energy absorption(SEA)of these structures is higher than that of nonauxetic hexagonal and auxetic re-entrant structures,owing to the generation of more plastic hinges that dissipate more energy during dynamic crushing.展开更多
Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular character...Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular characteristics and mechanical behavior.Geometrical models have been developed to justify and artificiall reproduce such materials＇ auxetic behavior.The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters.It is shown that,even in the presence of protruding ribs,there may not be auxetic behavior,and this depends on the geometry of each reentrant structure.Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.展开更多
The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is studied.The shell is modeled utilizing th...The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is studied.The shell is modeled utilizing the first-order shear deformation theory(FSDT)incorporating the relative,centripetal,and Coriolis accelerations alongside the initial hoop tension created by the rotation.The governing equations,compatibility conditions,and boundary conditions are attained using Hamilton’s principle.Utilizing trigonometric functions,an analytical solution is derived in the circumferential direction,and a numerical one is presented in the meridional direction via the differential quadrature method(DQM).The effects of various factors on the critical rotational speeds and forward and backward frequencies of the shell are studied.The present work is the first theoretical work regarding the dynamic analysis of a rotating sandwich conical shell with an auxetic honeycomb core strengthened with a ring support.展开更多
The main objective of this research is to investigate the hygroelastic behavior of a non-homogeneous circular plate made up of porous metamaterial resting on an auxetic material plate.The mechanical properties of the ...The main objective of this research is to investigate the hygroelastic behavior of a non-homogeneous circular plate made up of porous metamaterial resting on an auxetic material plate.The mechanical properties of the main plate,as well as moisture concentration,vary as an exponential function in the transverse direction.Poisson’s ratio is constant.The elastic supporting medium is developed by considering the structurestructure coupling.Based on the linear hygroelasticity theory,the governing state equations in terms of displacements and moisture concentration are acquired.At first,the Fickian equation is solved to compute the nonlinear distribution of moisture through the plate thickness,and then the state equations are semi-analytically solved using the statespace(SS)method and the differential quadrature(DQ)rule to predict the elastic field quantities.A comprehensive parametric analysis is accomplished to elucidate the effects of key parameters on the steady-state response of the plate under the mechanical and hygral loads.展开更多
Meta-sandwich composites with three-dimensional(3D)printed architecture structure are characterized by their high ability to absorb energy.In this paper,static and fatigue 3-point bending tests are implemented on a 3D...Meta-sandwich composites with three-dimensional(3D)printed architecture structure are characterized by their high ability to absorb energy.In this paper,static and fatigue 3-point bending tests are implemented on a 3D printed sandwich composites with a re-entrant honeycomb core.The skins,core and whole sandwich are manufactured using the same bio-based material which is polylactic acid with flax fiber reinforcement.Experimental tests are performed in order to evaluate the durability and the ability of this material to dissipate energy.First,static tests are conducted to study the bending behaviour of the sandwich beams,as well as to determine the failure parameters and the characteristic used in fatigue tests.Then,fatigue analyses were carried out to determine the fatigue resistance of these structures.The effects of the core density on the stiffness,hysteresis loop,energy absorption and loss factor,for two loading level,are determined.Moreover,the behaviour of this sandwich composite with re-entrant honeycomb core is compared with that of sandwiches with different core topologies.The results show that sandwich with high core density dissipate more energy,which results higher loss factors.The determined properties offer the most sensitive indicators of sandwich composite damage during its lifetime.This work aims to determine the static and fatigue properties of this material,thus,study its potential applications in industry.展开更多
Based on Mindlin plate models and Kirchhoff plate models,this study was concerned with the wave propagation characteristics in thick conventional and auxetic cellular structures,with the objective to clarify the effec...Based on Mindlin plate models and Kirchhoff plate models,this study was concerned with the wave propagation characteristics in thick conventional and auxetic cellular structures,with the objective to clarify the effects of negative Poisson＇s ratio,shear factor and orthotropic mechanical properties on the dynamic behaviors of thick plates.Numerical results revealed that the predictions using variable shear factor in Mindlin plate models resulted in high wave frequencies,which were more significant for plates with negative values of Poisson＇s ratio.The present study can be useful for the design of critical applications by varying the values of Poisson＇s ratio.展开更多
This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fib...This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load.Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber.The exterior is supported by a Kerr elastic foundation with three characteristics.The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer.In contrast to previous first-order shear deformation theories,no shear correction factor is required.Navier's exact solution was used to treat the double-curved shell problem with a single title boundary,while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements.To ensure the accuracy of these results,a thorough comparison technique is employed in conjunction with credible statements.The problem model's edge cases allow for this kind of analysis.The study's findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads.In addition,this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.展开更多
Manufacturing of a macro-scale helix auxetic yarn(HAY)was described. Consequently areal woven fabric and three kinds of woven fabrics various in weaves were introduced respectively. Their expected auxetic effect( assu...Manufacturing of a macro-scale helix auxetic yarn(HAY)was described. Consequently areal woven fabric and three kinds of woven fabrics various in weaves were introduced respectively. Their expected auxetic effect( assured by double helix yarn) was tested through the Poisson's ratio value(for auxetic structure is negative).Other observed parameters talked about variation in woven fabric porosity and the pores' parameters during the sample straining.Setting of this non-standard test( connection between dynamometer and image analysis) was also introduced. The differences among observed parameters were evaluated and conclusions for three types of woven fabrics were determined. It was found that less auxetic behavior caused less porosity. Less auxetic structure( satin) with longer floating threads embodies bigger pores' size and less circularity. The plain pattern has the greatest porosity but the smallest pores; the satin pattern behaves by contraries.展开更多
Auxetic metamaterials,which exhibit the negative Poisson’s ratio(NPR)effect,have found wide applications in many engineering fields.However,their high porosity inevitably weakens their bearing capacity and impact res...Auxetic metamaterials,which exhibit the negative Poisson’s ratio(NPR)effect,have found wide applications in many engineering fields.However,their high porosity inevitably weakens their bearing capacity and impact resistance.To improve the energy absorption efficiency of auxetic honeycombs,a novel vertex-based hierarchical star-shaped honeycomb(VSH)is designed by replacing each vertex in the classical star-shaped honeycomb(SSH)with a newly added self-similar sub-cell.An analytical model is built to investigate the Young’s modulus of VSH,which shows good agreement with experimental results and numerical simulations.The in-plane dynamic crushing behaviors of VSH at three different crushing velocities are investigated,and empirical formulas for the densification strain and plateau stress are deduced.Numerical results reveal more stable deformation modes for VSH,attributed to the addition of self-similar star-shaped sub-cells.Moreover,compared with SSH under the same relative densities,VSH exhibits better specific energy absorption and higher plateau stresses.Therefore,VSH is verified to be a better candidate for energy absorption while maintaining the auxetic effect.This study is expected to provide a new design strategy for auxetic honeycombs.展开更多
文摘In this work,a computational modelling and analysis framework is developed to investigate the thermal buckling behavior of doubly-curved composite shells reinforced with graphene-origami(G-Ori)auxetic metamaterials.A semi-analytical formulation based on the First-Order Shear Deformation Theory(FSDT)and the principle of virtual displacements is established,and closed-form solutions are derived via Navier’s method for simply supported boundary conditions.The G-Ori metamaterial reinforcements are treated as programmable constructs whose effective thermo-mechanical properties are obtained via micromechanical homogenization and incorporated into the shell model.A comprehensive parametric study examines the influence of folding geometry,dispersion arrangement,reinforcement weight fraction,curvature parameters,and elastic foundation support on the critical buckling temperature(CBT).The results reveal that,under optimal folding geometry and reinforcement alignment with principal stress trajectories,the CBT can increase by more than 150%.Furthermore,the combined effect of G-Ori reinforcement and elastic foundation substantially enhances thermal buckling resistance.These findings establish design guidelines for architected composite shells in applications such as aerospace thermal skins,morphing structures,and thermally-responsive systems,and illustrate the potential of auxetic graphene metamaterials for multifunctional,lightweight,and thermally robust structural components.
文摘Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.
基金the funding of the Deanship of Graduate Studies and Scientific Research,Jazan University,Saudi Arabia,through project number:RG24-M027.
文摘This study presents a significant advancement in the vibration analysis of functionally graded sandwich plates with auxetic cores by introducing a general viscoelastic foundation model that more accurately reflects the complex interactions between the plate and the foundation.The novelty of this study is that the proposed viscoelastic foundation model incorporates elastic and damping effects in both the Winkler and Pasternak layers.To develop the theoretical framework for this analysis,the higher-order shear deformation theory is employed,while Hamilton's principle is used to derive the governing equations of motion.The closed-form solution is used to determine the damped vibration behaviors of the sandwich plates.The precision and robustness of the proposed mathematical model are validated through several comparison studies with existing numerical results.A detailed parametric study is conducted to investigate the influence of various parameters,including the elastic and damping coefficients of the foundation,the material gradation,and the properties of the auxetic core on the vibration behavior of the plates.The numerical results provide new insights into the vibration characteristics of sandwich plates with auxetic cores resting on viscoelastic foundation,highlighting the significant role of the two damping coefficients and auxetic cores in the visco-vibration behavior of the plates.
文摘The nonlinear post-buckling response of functionally graded(FG)copper matrix plates enforced by graphene origami auxetic metamaterials(GOAMs)is investigated in the currentwork.The auxeticmaterial properties of the plate are controlled by graphene content and the degree of origami folding,which are graded across the thickness of the plate.Thematerial properties of the GOAM plate are evaluated using genetic micro-mechanicalmodels.Governing nonlinear eigenvalue problems for the post-buckling response of the GOAM composite plate are derived using the virtual work principle and a four-variable nonlinear shear deformation theory.A novel differential quadrature method(DQM)algorithm is developed to solve the nonlinear eigenvalue problem.Detailed parametric studies are presented to explore the effects of graphene content,folding degree,and GO distribution patterns on the post-buckling responses of GOAM plates.Results show that high tunability in post-buckling characteristics can be achieved by using GOAM.FunctionallyGradedGraphene OrigamiAuxeticMetamaterials(FG-GOAM)plates can be used in aerospace structures to improve their structural performance and response.
基金supported by the National Key R&D Program of China(Grant No.2021YFA1400300)the National Natural Science Foundation of China(Grant Nos.12172047,12372177,and 12102007)+1 种基金Beijing Natural Science Foundation(Grant Nos.1244057 and Z190011)Beijing Institute of Technology Research Fund Program for Young Scholars.
文摘Auxetic metamaterials have attracted much attention due to their outstanding advantages over traditional materials in terms of shear capacity,fracture resistance,and energy absorption.However,there are lack of design inspirations for novel auxetic structures.According to the materials databases of atomic lattice,some natural crystals possess negative Poisson’s ratio(NPR).In this paper,the mechanism of auxeticity in microscale Ti crystal is investigated through density functional theory simulation.Then we propose a macroscopic auxetic metamaterial by mimicking the microscopic atomic lattice structure of the bodycentered cubic Ti crystal.The NPR property of the macroscopic metamaterial is verified by theoretical,numerical and experimental methods.The auxeticity keeps effective when scaling up to macroscopic Ti crystal-mimic structure,with the similar deformation mechanism.Furthermore,from the geometric parameter investigation,the geometric parameters have great influence on the Poisson’s ratio and Young’s modulus of the macroscopic metamaterial.Importantly,an optimized structure is obtained,which exhibits 2 times enhancement in auxeticity and 25 times enhancement in normalized Young’s modulus,compared to the original architecture.This work establishes a link between the physical properties at micro-nanoscale and macroscale structures,which provides inspirations for high load-bearing auxetic metamaterials.
基金Project supported by the National Natural Science Foundation of China(Nos.12162004 and 11562001)the Doctoral Research Start-up Fund Project at University of South China(No.Y00043-13)。
文摘This paper presents,for the first time,an effective numerical approach based on the isogeometric analysis(IGA)and the six-variable quasi-three dimensional(3D)higher-order shear deformation theory(HSDT)to study the free vibration characteristics of functionally-graded(FG)graphene origami(GOri)-enabled auxetic metamaterial(GOEAM)plates submerged in a fluid medium.The plate theory incorporates the thickness stretching and the effects of transverse shear deformation without using any shear correction factors.The velocity potential function and Bernoulli's equation are used to derive the hydrodynamic pressure acting on the plate surface.Both horizontally and vertically immersed plate configurations are considered here in the form of inertia effects.The plates are composed of multilayer GOEAMs,with the GOri content varying through the plate's thickness in a layer-wise manner.This design results in graded auxetic growth.The material properties are evaluated by mixing rules and a genetic programming(GP)-assisted micromechanical model.The governing equations of motion for the FG-GOEAM plates immersed in a fluid medium are derived by Hamilton's principle.After validating the convergence and accuracy of the present model,a comprehensive parametric study is carried out to examine the effects of the GOri content,GOri distribution pattern,GOri folding degree,fluid level,immersed depth,and geometric parameter on the natural frequencies of the FG-GOEAM plates.The results show that the natural frequencies for the four GOri distribution patterns increase with the increase in the layer number when the lay number is fewer than 10,and then stabilize after the layer number reaches 10.Besides,in general,the natural frequency of the FG-GOEAM plate in a vacuum or fluid increases when the GOri content increases,while decreases when the GOri folding degree increases.Some additional findings related to the numerical results are presented in the conclusions.It is believed that the present results are useful for the precise design and optimization of FG-GOEAM plates immersed in a fluid medium.
基金The financial support of the NSFC (20274004) and P&G is gratefully acknowledged.
文摘Three new kinds of molecular networks are designed and predicted to exhibit negative Poisson ratios. Molecular mechanics calculations on these networks show that the magnitude of Poisson ratios depends on the relative flexibility of beam and arm structures. Several new kinds of auxetic polymers, whose successful synthesis should be easier than that of the corresponding auxetic networks, are then proposed. It is found that the kabob-like polymers with auxegens lying vertically on the main chain can acquire auxeticity while those with auxegens lying horizontally on the main chain cannot. Besides, a half kabob-like or pseudo-ladder polymer with auxegens linked at the intersection of the beam and the arm does show auxeticity when adopting constrictive conformers. It is, however, worthwhile noting that the origins of auxeticity still await and strongly deserve further experimental and theoretical investigations.
基金support from the National Natural Science Foundation of China(Grant No.12102193)Shenzhen-Hong KongMacao Science and Technology Program(Category C)(SGDX2020110309300301)+1 种基金Key R&D Program from the Science and Technology Department of Sichuan Province(Key Science&Technology Project)(No.2022YFSY0001)Changsha Municipal Science and Technology Bureau under the Grant kh2201035.
文摘Auxetic mechanical metamaterials are artificially architected materials that possess negative Poisson’s ratio,demonstrating transversal contracting deformation under external vertical compression loading.Their physical properties are mainly determined by spatial topological configurations.Traditionally,classical auxetic mechanical metamaterials exhibit relatively lower mechanical stiffness,compared to classic stretching dominated architectures.Nevertheless,in recent years,several novel auxetic mechanical metamaterials with high stiffness have been designed and proposed for energy absorption,load-bearing,and thermal-mechanical coupling applications.In this paper,mechanical design methods for designing auxetic structures with soft and stiff mechanical behavior are summarized and classified.For soft auxetic mechanical metamaterials,classic methods,such as using soft basic material,hierarchical design,tensile braided design,and curved ribs,are proposed.In comparison,for stiff auxetic mechanical metamaterials,design schemes,such as hard base material,hierarchical design,composite design,and adding additional load-bearing ribs,are proposed.Multi-functional applications of soft and stiff auxetic mechanical metamaterials are then reviewed.We hope this study could provide some guidelines for designing programmed auxetics with specified mechanical stiffness and deformation abilities according to demand.
基金National Natural Science Foundation of China(Grant Nos.51705158 and 51805174)the Fundamental Research Funds for the Central Universities(Grant Nos.2018MS45 and 2019MS059)。
文摘Focusing on the structural optimization of auxetic materials using data-driven methods,a back-propagation neural network(BPNN)based design framework is developed for petal-shaped auxetics using isogeometric analysis.Adopting a NURBSbased parametric modelling scheme with a small number of design variables,the highly nonlinear relation between the input geometry variables and the effective material properties is obtained using BPNN-based fitting method,and demonstrated in this work to give high accuracy and efficiency.Such BPNN-based fitting functions also enable an easy analytical sensitivity analysis,in contrast to the generally complex procedures of typical shape and size sensitivity approaches.
文摘The increasing threat of explosions on the battle field and the terrorist action requires the development of more effective blast resistance materials and structures.Curved structure can support the external loads effectively by virtue of their spatial curvature.In review of the excellent energy absorption property of auxetic structure,employing auxetic structure as core material in curved sandwich shows the potential to improve the protection performance.In this study,a novel cylindrical sandwich panel with double arrow auxetic(DAA) core was designed and the numerical model was built by ABAQUS.Due to the complexity of the structure,systematic parameter study and optimal design are conducted.Two cases of optimal design were considered,case1 focuses on reducing the deflection and mass of the structure,while case2 focuses on reducing the deflection and increasing the energy absorption per unit mass.Parameter study and optimal design were conducted based on Latin Hypercube Sampling(LHD)method,artificial neural networks(ANN) metamodel and the nondominated sorting genetic algorithm(NSGA-Ⅱ).The Pareto front was obtained and the cylindrical DAA structure performed much better than its equal solid panel in both blast resistance and energy absorption capacity.Optimization results can be used as a reference for different applications.
基金supported by the National Natural Science Foundation of China (Nos. 11572071, 11332004,)the National Basic Research Program of China (No. 2011CB610304)+1 种基金the Program of Introducing Talents of Discipline to Universities (No. B14013)the China Scholarship Council (No. 201308210038)
文摘Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially compressed (i.e., the materials exhibit a negative Poisson's ratio). The current study focuses on assessing the potential of an auxetic material to enhance the buckling capacity of a rectangular plate under uniaxial compression. The in-plane translational restraint along the unloaded edges that was often neglected in open literature is taken into consideration in our buckling model proposed in this study. The closed-form expressions for the critical buckling coefficient of the rectangle are provided and the predicted results agree well with those determined by the finite element method. Furthermore, the results indicate that the buckling performance of a rectangular plate under uniaxial compression can be significantly improved by replacing the traditional material that has a positive Poisson's ratio with an auxetic material when there is in-plane translation restraint along the unloaded edges. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.
基金the National Natural Science Foundation of China(Nos.12102274,1207220311872253)+1 种基金the Natural Science Foundation of Hebei Province of China(No.A2022210005)the Central Guidance on Local Science and Technology Development Fund of Hebei Province of China(No.226Z4901G)。
文摘Auxetic honeycomb structures are promising metamaterials with outstanding mechanical properties,and can be potentially used in energy absorption applications.In this study,a novel modified re-entrant hybrid auxetic metamaterial inspired by Islamic motif art is designed by integrating four-pointed double re-entrant motifs with symmetric semi-hexagonal unit cells to achieve a high energy absorption capacity(EAC).Theoretical analyses and numerical simulations are performed to examine the dynamic crushing behavior of the four-pointed double re-entrant combined structure(FDRCS).The developed finite element models(FEMs)are validated by the experiments under quasi-static compression.The deformation mode and stress-strain curves are further studied under low,medium,and high crushing velocities.The theoretically predicted plateau stress of the FDRCS under different crushing velocities is consistent with the numerical simulation results.The crushing stress and the EAC of the FDRCS are influenced by the geometric parameters and crushing velocities.The FDRCS exhibits a negative Poisson's ratio(NPR),owing to the four-point re-entrant structure(RES).Moreover,the specific energy absorption(SEA)of these structures is higher than that of nonauxetic hexagonal and auxetic re-entrant structures,owing to the generation of more plastic hinges that dissipate more energy during dynamic crushing.
文摘Materials with a negative Poisson＇s ratio（PR）are called auxetics;they are characterized by expansion/contraction when tensioned/compressed.Given this counterintuitive behavior,they present very particular characteristics and mechanical behavior.Geometrical models have been developed to justify and artificiall reproduce such materials＇ auxetic behavior.The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters.It is shown that,even in the presence of protruding ribs,there may not be auxetic behavior,and this depends on the geometry of each reentrant structure.Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.
文摘The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is studied.The shell is modeled utilizing the first-order shear deformation theory(FSDT)incorporating the relative,centripetal,and Coriolis accelerations alongside the initial hoop tension created by the rotation.The governing equations,compatibility conditions,and boundary conditions are attained using Hamilton’s principle.Utilizing trigonometric functions,an analytical solution is derived in the circumferential direction,and a numerical one is presented in the meridional direction via the differential quadrature method(DQM).The effects of various factors on the critical rotational speeds and forward and backward frequencies of the shell are studied.The present work is the first theoretical work regarding the dynamic analysis of a rotating sandwich conical shell with an auxetic honeycomb core strengthened with a ring support.
文摘The main objective of this research is to investigate the hygroelastic behavior of a non-homogeneous circular plate made up of porous metamaterial resting on an auxetic material plate.The mechanical properties of the main plate,as well as moisture concentration,vary as an exponential function in the transverse direction.Poisson’s ratio is constant.The elastic supporting medium is developed by considering the structurestructure coupling.Based on the linear hygroelasticity theory,the governing state equations in terms of displacements and moisture concentration are acquired.At first,the Fickian equation is solved to compute the nonlinear distribution of moisture through the plate thickness,and then the state equations are semi-analytically solved using the statespace(SS)method and the differential quadrature(DQ)rule to predict the elastic field quantities.A comprehensive parametric analysis is accomplished to elucidate the effects of key parameters on the steady-state response of the plate under the mechanical and hygral loads.
文摘Meta-sandwich composites with three-dimensional(3D)printed architecture structure are characterized by their high ability to absorb energy.In this paper,static and fatigue 3-point bending tests are implemented on a 3D printed sandwich composites with a re-entrant honeycomb core.The skins,core and whole sandwich are manufactured using the same bio-based material which is polylactic acid with flax fiber reinforcement.Experimental tests are performed in order to evaluate the durability and the ability of this material to dissipate energy.First,static tests are conducted to study the bending behaviour of the sandwich beams,as well as to determine the failure parameters and the characteristic used in fatigue tests.Then,fatigue analyses were carried out to determine the fatigue resistance of these structures.The effects of the core density on the stiffness,hysteresis loop,energy absorption and loss factor,for two loading level,are determined.Moreover,the behaviour of this sandwich composite with re-entrant honeycomb core is compared with that of sandwiches with different core topologies.The results show that sandwich with high core density dissipate more energy,which results higher loss factors.The determined properties offer the most sensitive indicators of sandwich composite damage during its lifetime.This work aims to determine the static and fatigue properties of this material,thus,study its potential applications in industry.
基金Project supported by the National Natural Science Foundation of China(No.11172239)the 111 project(No.B07050)the Doctoral Program Foundation of Education Ministry of China(20126102110023)
文摘Based on Mindlin plate models and Kirchhoff plate models,this study was concerned with the wave propagation characteristics in thick conventional and auxetic cellular structures,with the objective to clarify the effects of negative Poisson＇s ratio,shear factor and orthotropic mechanical properties on the dynamic behaviors of thick plates.Numerical results revealed that the predictions using variable shear factor in Mindlin plate models resulted in high wave frequencies,which were more significant for plates with negative values of Poisson＇s ratio.The present study can be useful for the design of critical applications by varying the values of Poisson＇s ratio.
文摘This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load.Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber.The exterior is supported by a Kerr elastic foundation with three characteristics.The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer.In contrast to previous first-order shear deformation theories,no shear correction factor is required.Navier's exact solution was used to treat the double-curved shell problem with a single title boundary,while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements.To ensure the accuracy of these results,a thorough comparison technique is employed in conjunction with credible statements.The problem model's edge cases allow for this kind of analysis.The study's findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads.In addition,this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.
文摘Manufacturing of a macro-scale helix auxetic yarn(HAY)was described. Consequently areal woven fabric and three kinds of woven fabrics various in weaves were introduced respectively. Their expected auxetic effect( assured by double helix yarn) was tested through the Poisson's ratio value(for auxetic structure is negative).Other observed parameters talked about variation in woven fabric porosity and the pores' parameters during the sample straining.Setting of this non-standard test( connection between dynamometer and image analysis) was also introduced. The differences among observed parameters were evaluated and conclusions for three types of woven fabrics were determined. It was found that less auxetic behavior caused less porosity. Less auxetic structure( satin) with longer floating threads embodies bigger pores' size and less circularity. The plain pattern has the greatest porosity but the smallest pores; the satin pattern behaves by contraries.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972287,12072266)the Fundamental Research Funds for the Central Universities.
文摘Auxetic metamaterials,which exhibit the negative Poisson’s ratio(NPR)effect,have found wide applications in many engineering fields.However,their high porosity inevitably weakens their bearing capacity and impact resistance.To improve the energy absorption efficiency of auxetic honeycombs,a novel vertex-based hierarchical star-shaped honeycomb(VSH)is designed by replacing each vertex in the classical star-shaped honeycomb(SSH)with a newly added self-similar sub-cell.An analytical model is built to investigate the Young’s modulus of VSH,which shows good agreement with experimental results and numerical simulations.The in-plane dynamic crushing behaviors of VSH at three different crushing velocities are investigated,and empirical formulas for the densification strain and plateau stress are deduced.Numerical results reveal more stable deformation modes for VSH,attributed to the addition of self-similar star-shaped sub-cells.Moreover,compared with SSH under the same relative densities,VSH exhibits better specific energy absorption and higher plateau stresses.Therefore,VSH is verified to be a better candidate for energy absorption while maintaining the auxetic effect.This study is expected to provide a new design strategy for auxetic honeycombs.
