The aging process is a group of degenerative changes that physiologically occur in most of the people in the elderly. This affects one or more of the human body systems. The treatment of diseases related to the aging ...The aging process is a group of degenerative changes that physiologically occur in most of the people in the elderly. This affects one or more of the human body systems. The treatment of diseases related to the aging process has a huge impact on the economy of all nations. Aging of the skin comes on the top and despite that, the results of the already present lines of treatment are not always satisfactory. This acts as a stimulus for us to dig deeper to discover the root causes of the premature aging of the skin. This was simply caused by the accumulation of repeated minute damage to the internal structure skin. In other words, if the degree of minute damage is more than the capacity of the skin to repair, the repeated micro-damage is presented in the long run as a skin wrinkling. Moreover, the skin acts as a mirror that reflects the internal structures of the human body. Thus, the more degenerative changes in the human body systems, the more the skin could become wrinkled. Our strategy to prevent or at least slow down the aging process of the skin depends on 2 main steps;the 1<sup>st</sup> is to reduce the micro-damage as can as possible, and the 2<sup>nd</sup> is to enhance the capacity of tissue regeneration to be able to reverse the already present damaged skin. As the 2 processes are synchronized with each other, this strategy would be considered the ideal for prevention of skin wrinkling especially premature ones. This not only reverses premature skin wrinkling but also protects it from future wrinklings. This review sharply pointed out the role of the functional collagen of the dermal layer of the skin in the prevention of skin wrinklings. Therefore, it would be the target to study how collagen works in the complex machinery of the dermal layer of the skin. This concept deeply believes that the recovery of dermal collagen has a much better effect than simply ingesting collagen or receiving a topical collagen booster. .展开更多
Wrinkles in flat graded elastic layers have been recently described as a timevarying Hamiltonian system by the energy method.Cylindrical core/shell structures can also undergo surface instabilities under the external ...Wrinkles in flat graded elastic layers have been recently described as a timevarying Hamiltonian system by the energy method.Cylindrical core/shell structures can also undergo surface instabilities under the external pressure.In this study,we show that by treating the radial direction as a pseudo-time variable,the graded core/shell system with radially decaying elastic properties can also be described within the symplectic framework.In combination with the shell buckling equation,the present paper addresses the surface wrinkling of graded core/shell structures subjected to the uniform external pressure by solving a series of ordinary differential equations with varying coefficients.Three representative gradient distributions are showcased,and the predicted critical pressure and critical wave number are verified by finite element simulations.The symplectic framework provides an efficient and accurate approach to understand the surface instability and morphological evolution in curved biological tissues and engineered structures.展开更多
The surface wrinkling of biological tissues is ubiquitous in nature.Accumulating evidence suggests that the mechanical force plays a significant role in shaping the biological morphologies.Controlled wrinkling has bee...The surface wrinkling of biological tissues is ubiquitous in nature.Accumulating evidence suggests that the mechanical force plays a significant role in shaping the biological morphologies.Controlled wrinkling has been demonstrated to be able to spontaneously form rich multiscale patterns,on either planar or curved surfaces.The surface wrinkling on planar substrates has been investigated thoroughly during the past decades.However,most wrinkling morphologies in nature are based on the curved biological surfaces and the research of controllable patterning on curved substrates still remains weak.The study of wrinkling on curved substrates is critical for understanding the biological growth,developing threedimensional(3D)or four-dimensional(4D)fabrication techniques,and creating novel topographic patterns.In this review,fundamental wrinkling mechanics and recent advances in both fabrications and applications of the wrinkling patterns on curved substrates are summarized.The mechanics behind the wrinkles is compared between the planar and the curved cases.Beyond the film thickness,modulus ratio,and mismatch strain,the substrate curvature is one more significant parameter controlling the surface wrinkling.Curved substrates can be both solid and hollow with various 3D geometries across multiple length scales.Up to date,the wrinkling morphologies on solid/hollow core-shell spheres and cylinders have been simulated and selectively produced.Emerging applications of the curved topographic patterns have been found in smart wetting surfaces,cell culture interfaces,healthcare materials,and actuators,which may accelerate the development of artificial organs,stimuli-responsive devices,and micro/nano fabrications with higher dimensions.展开更多
In this paper,the quasi-static large deformation,wrinkling and fracture behaviors of bimodular structures and membranes are studied with an implicit bond-based peridynamic computational framework.Firstly,the constant ...In this paper,the quasi-static large deformation,wrinkling and fracture behaviors of bimodular structures and membranes are studied with an implicit bond-based peridynamic computational framework.Firstly,the constant and tangential stiffness matrices of the implicit peridynamic formulations for the nonlinear problems are derived,respectively.The former is con structed from the linearization of the bond strain on the basis of the geometric approximation while the latter is established according to the linearization of the pairwise force by using first-order Taylor’s expansion.Then,a bimodular material model in peridynamics is developed,in which the tensile or compressive behavior of the material at each point is conveniently described by the tensile or compressive states of the bonds in its neighborhood.Moreover,the bimodular material model is extended to deal with the wrinkling and fracture problems of membranes by setting the compressive micro-modulus to be zero.In addition,the incremental-iterative algorithm is adopted to obtain the convergent solutions of the nonlinear problems.Finally,several representative numerical examples are presented and the results demonstrate the accuracy and efficiency of the proposed method for the large deformation,wrinkling and fracture analyses of bimodular structures and membranes.展开更多
In this paper,the wrinkle-crease interaction behavior of a rectangular membrane under edge tension is simulated.The creased membrane is modeled by using a Modified Two-Parameter model.In this model,two crease paramete...In this paper,the wrinkle-crease interaction behavior of a rectangular membrane under edge tension is simulated.The creased membrane is modeled by using a Modified Two-Parameter model.In this model,two crease parameters,i.e.the effective modulus of creased membrane and the residual stress from creasing,are computed by using MacNeal's method that was firstly applied directly in a flat membrane with the local crease.We have proposed a method to solve the wrinkling computing issue of the creased membrane by using a Direct Perturb-Force technique in our previous work.Based on our method,the effects of crease location on the wrinkle-crease interaction behavior can be evaluated accurately.These results will be of great benefit to the analysis and the control of the wrinkles in the membrane structures.展开更多
The three-dimensional(3D)graphene-based materials have raised significant interest due to excellent catalytic performance and unique electronic properties,while the preparation of uniform and stable 3D graphene struct...The three-dimensional(3D)graphene-based materials have raised significant interest due to excellent catalytic performance and unique electronic properties,while the preparation of uniform and stable 3D graphene structures remains a challenge.In this paper,using molecular dynamics simulations,we found that the nanotwinned copper(nt-Cu)matrix with small twin spacing can induce the wave-shaped wrinkling and sawtooth-shaped buckling graphene structures under uniaxial compression.The nt-Cu matrix possesses a symmetrical lattice structure for the lattice rotation with the dislocation annihilation,resulting in the transition of sandwiched graphene from 2D to 3D structures with good uniformity.The newly formed twin boundaries(TBs)in the nt-Cu matrix improve the resistance of graphene against the out-of-plane deformation so that graphene can maintain a stable wrinkling or buckling morphology in a wide strain range.These 3D texturing structures show great flexibility and their micro parameters can be controlled by applying different compressive strains.Furthermore,we propose a simple sliding method for decoupling graphene from the nt-Cu matrix without any damage.This work provides a novel strategy to induce and transfer the uniform wrinkling and buckling of graphene,which may expand the application of graphene in energy storage and catalysts.展开更多
This work presents an approximate analytical study of the problem of dynamic wrinkling of a thin metal sheet under a specified time varying tension. The problem is investigated in the framework of the dynamic stabilit...This work presents an approximate analytical study of the problem of dynamic wrinkling of a thin metal sheet under a specified time varying tension. The problem is investigated in the framework of the dynamic stability of a nonlinear plate model on elastic foundation which namely takes into account the nonlinear mechanics of mid-plane stretching and the dependence of the membrane force on this mechanics. The plate is assumed to be a wide rectangular slab, hinged at two opposite ends and free at the long ends, which can be deformed in a cylindrical shape so that the governing in-plane bending equation of motion takes the same form as that of a beam (e.g. lateral strip) element. An approximate analytical analysis of the beam wrinkling behavior under sinusoidal parametric excitation is carried out by using the assumed single mode wrinkling motion to reduce the beam field nonlinear partial differential equation to that of a single degree of freedom non-linear oscillator. A first order stability analysis of an approximate analytical solution obtained using the Multi-Time-Scales (MMS) method is used to derive a criterion defining critical driving frequency in terms of system parameters for the initiation of wrinkling motion in the thin metal sheet. Results obtained using this criterion is presented for selected values of system parameters.展开更多
In this paper, the features of fabric wrinkle structure are analyzed, by image processing technique. The wrinkle images are processed and character parameters are extracted. The wrinkle side surface area ratio of imag...In this paper, the features of fabric wrinkle structure are analyzed, by image processing technique. The wrinkle images are processed and character parameters are extracted. The wrinkle side surface area ratio of image gray level intensity, the standard deviation of total pixels’ gray level intensity and the standard deviation of wrinkle block area are adopted to evaluate fabric wrinkling. The results show that these three character parameters can be served for ranking the wrinkling. It provides a feasible objective method for fabrics wrinkling degree assessing.展开更多
A stress extremum method is developed based on Von Karman equations for analysis of membrane wrinkles in this paper. A mechanical model is also established for analyzing shear membrane wrinkles. Expressions of wrinkli...A stress extremum method is developed based on Von Karman equations for analysis of membrane wrinkles in this paper. A mechanical model is also established for analyzing shear membrane wrinkles. Expressions of wrinkling wavelength,amplitude and angle are obtained in terms of the stress extremum method. A numerical analysis approach-directly disturbing method is proposed to analyze the configuration parameters of shear membrane wrinkles by introducing out-of-plane disturbing forces to trigger wrinkle formation,while it timely removes the applied forces in order to eliminate the effect of disturbing forces on analytical results. The simulation results agree well with analytical results,which demonstrate that the proposed approach is capable for analyzing the membrane wrinkles with good accuracy.展开更多
5-Aminolevulinic acid (ALA) is a natural amino acid that is used as a raw material for the biosynthesis of red-blood-cell hemoglobin in humans and animals. ALA is the subject of research in a wide range of human healt...5-Aminolevulinic acid (ALA) is a natural amino acid that is used as a raw material for the biosynthesis of red-blood-cell hemoglobin in humans and animals. ALA is the subject of research in a wide range of human health care fields, including skin care and medicine. This study investigated whether and to what extent cosmetics containing ALA (skin lotions and creams) improved facial-skin condition in women. As such, a double-blind controlled experiment was conducted among 45 women aged 47.0 ± 1.72 years. Participants were divided into two intervention groups, including those who used cosmetics containing ALA (C-ALA, n = 22) and those who used cosmetics without ALA (W-ALA, n = 23). Specifically, participants were instructed to use their assigned cosmetics twice per day (morning and evening) after washing their faces before each application. Inner skin condition and skin-water content were evaluated via VISIA-Evolution and Multi Display Devices at baseline and after four and eight weeks of use. The experiment lasted for a total of eight weeks. A baseline comparison at week four showed that skin moisture content increased significantly for the C-ALA group (p = 0.021). Further, wrinkling significantly decreased at week four among participants in the C-ALA group who were evaluated as having many wrinkles at baseline (p = 0.034). These findings suggest that cosmetics containing ALA have moisturizing effects and reduce wrinkling caused by dryness.展开更多
Assembling two-dimensional(2D)sheets into macroscopic three-dimensional(3D)forms has created a promising material family with rich functionalities.Multiscale wrinkles are intrinsic features of 2D sheets in their 3D as...Assembling two-dimensional(2D)sheets into macroscopic three-dimensional(3D)forms has created a promising material family with rich functionalities.Multiscale wrinkles are intrinsic features of 2D sheets in their 3D assembles.Therefore,the precise wrinkling modulation optimizes the transition of outstanding properties of 2D sheets to expected performances of assembled materials and dominates their fabrication process.The wrinkling evolution of 2D sheets assembling onto flat surfaces has been extensively understood,however,the wrinkling behaviors on the more generally curved surface still remain unclear.Here,we investigate the wrinkling behaviors of graphene oxide sheets assembled onto curved surfaces and reveal the selection rule of wrinkling modes that determined by the curvature mismatch between 2D sheets and target surfaces.We uncover that three wrinkling modes including isotropic cracked land,labyrinth,and anisotropic curtain phases,respectively emerge on flat,spherical,and cylindrical surfaces.A favorable description paradigm is offered to quantitatively measure the complex wrinkling patterns and assess the curvature mismatch constraint underlying the wrinkling mode selection.This research provides a general and quantitative description framework of wrinkling modulation of 2D materials such as high performance graphene fibers,and guides the precise fabrication of particles and functional coatings.展开更多
We report the formation of antisymmetric wrinkling patterns in films on ridged substrates induced by the buckling instability of the substrates via finite element simulations and experiments.Our simulated results reve...We report the formation of antisymmetric wrinkling patterns in films on ridged substrates induced by the buckling instability of the substrates via finite element simulations and experiments.Our simulated results reveal that the uniaxial compression along the ridge can trigger both the wrinkling instability of the film and the lateral buckling instability of the ridge.The latter could change the wrinkles from a symmetric pattern to an antisymmetric pattern in a range of film-substrate modulus ratio and aspect ratio of the ridge profile,as validated by the experimental observations.A three-dimensional phase diagram with four buckling patterns,i.e.,sole ridge buckling pattern,antisymmetric wrinkling pattern with different wavelengths from ridge buckling,symmetric wrinkling pattern without ridge buckling,and antisymmetric wrinkling pattern with the same wavelength as ridge buckling,is built with respect to the uniaxial compression,modulus ratio,and aspect ratio.The results not only elucidate how and when the interplay between the wrinkling instability and the ridge instability results in the formation of the antisymmetric wrinkling pattern but also offer a way to generate controllable complex wrinkling patterns.展开更多
Sandwich structures have been widely applied in the wing and the horizontal tail of the aircraft,so face sheets of such structure might occur wrinkling deformation in the process of service,which will largely decrease...Sandwich structures have been widely applied in the wing and the horizontal tail of the aircraft,so face sheets of such structure might occur wrinkling deformation in the process of service,which will largely decrease capability of sustaining loads.As a result,this paper aims at proposing a reasonable strategy resisting wrinkling deformation of sandwich structures.To this end,an enhanced higher-order model has been proposed for wrinkling analysis of sandwich structures.Buckling behaviors of a five-layer sandwich plate are firstly analyzed,which is utilized to assess performance of the proposed model.Subsequently,wrinkling behaviors of four sandwich plates are further investigated by utilizing present model,which have been evaluated by using quasi threedimensional(3D)elasticity solutions,3D Finite Element Method(3D-FEM)results and experimental datum.Finally,the present model is utilized to study the buckling and the wrinkling behaviors of sandwich plates reinforced by Carbon Nano Tubes(CNTs).In addition,influence of distribution profile of CNTs on wrinkling behaviors has been analyzed,and a typical distribution profile of CNTs has been chosen to resist wrinkling deformation.Without increase of additional weight,the present strategy can effectively resist wrinkling deformation of sandwich plates,which is rarely reported in published literature.展开更多
Strain engineering has been leveraged to tune the thermal properties of materials by introducing stress and manipulating local atomic vibrations,which poses a detrimental threat to the mechanical integrity of material...Strain engineering has been leveraged to tune the thermal properties of materials by introducing stress and manipulating local atomic vibrations,which poses a detrimental threat to the mechanical integrity of materials and structures and limits the capability to regulate thermal transport.Here,we report that the interfacial thermal conductance of graphene on a soft substrate can be regulated by harnessing wrinkling and folding morphologies of graphene,which could be well controlled by managing the prestrain applied to the substrate.These obtained graphene structures are free of significant in-plane mechanical strain and only have infinitesimal distortion to the intrinsic thermal properties of graphene.The subsequent thermal transport studies with pumpprobe non-equilibrium molecular dynamics(MD)simulation show that the thermal conductance between graphene structures and the substrate is uniquely determined by the morphological features of graphene.The atomic density of interfacial interactions,energy dissipation,and temperature distribution are elucidated to understand the thermal transport across each graphene structure and substrate.We further demonstrate that the normalized thermal conductance decreases monotonically with the increase of the equivalent mechanical strain,showing the capability of mechanically programmable interfacial thermal conductance in a broad range of strains.Application demonstrations in search of on-demand thermal conductance are conducted by controlling the geometric morphologies of graphene.This study lays a foundation for regulating interfacial thermal conductance through mechanical loading-induced geometric deformation of materials on a soft substrate,potentially useful in the design of flexible and stretchable structures and devices with tunable thermal management performance.展开更多
Surface wrinkling of materials holds promise for important applications in diverse fields such as multifunctional surfaces and biomedical engineering. For these applications, it is of interest to attain various surfac...Surface wrinkling of materials holds promise for important applications in diverse fields such as multifunctional surfaces and biomedical engineering. For these applications, it is of interest to attain various surface wrinkles with tunable wavelengths and amplitudes. Through a combination of experiments and numerical simulations, we here propose a method to regulate the wrinkling patterns in a film-substrate system by introducing periodic surface stiffness, which is generated through sequential specified ultraviolet-ozone(UVO) treatments. Both experiments and numerical simulations demonstrate that the proposed technique can produce various patterns with wide, tunable geometrical features and anisotropy. The effects of surface stiffness distribution, the exposure durations of UVO-treatments, and the loading biaxiality are examined on the generated surface patterns.展开更多
The deformation patterns of elastic membranes under tension is called wrinkling.Wrinkling,which is caused by capillary surface tension,is called capillary wrinkling(Figure 1).In recent years wrinkling patterns have dr...The deformation patterns of elastic membranes under tension is called wrinkling.Wrinkling,which is caused by capillary surface tension,is called capillary wrinkling(Figure 1).In recent years wrinkling patterns have drawn particular attention[1-11],since it can be an useful tool to infer material parameters that might otherwise be inaccessible.For example,the commonly observed tearing instability of an展开更多
Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices.However,when flexible graphene nanosheets are assembled into macros...Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices.However,when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites,capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying,which greatly reduces the thermal conductivity of the composites.Herein,graphene nanosheets/aramid nanofiber(GNS/ANF)composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds andπ-πinteractions.The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets,thereby creating a fast in-plane heat transfer channel.The composite films(GNS/ANF-60 wt%)with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity(146 W m^(−1)K^(−1))and tensile strength(207 MPa).The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones,showing promising applications in the thermal management of high-power electronic devices.展开更多
Ⅰ. INTRODUCTIONThin circular plates, a kind of the basic structural element widely used in engineering,are of the simplest plane-stress mechanical model with double curvatures. Hence, the investigation on the fundame...Ⅰ. INTRODUCTIONThin circular plates, a kind of the basic structural element widely used in engineering,are of the simplest plane-stress mechanical model with double curvatures. Hence, the investigation on the fundamental mechanical properties of the thin circular plates has been attracting great attention and brought about many results. Due to the difficulties展开更多
Plastic wrinkling predictions and shear enforced wrinkling characteristics of Ti-alloy thin-walled tubes under combination die constraints have become key problems urgently in need of solutions in order to improve for...Plastic wrinkling predictions and shear enforced wrinkling characteristics of Ti-alloy thin-walled tubes under combination die constraints have become key problems urgently in need of solutions in order to improve forming quality in their shear bending processes under differential temperature fields. To address this, a wrinkling wave function was developed by considering their shear bend deformation characteristics. Based on this wave function and the thin shell theory, an energy prediction model for this type of wrinkling was established. This model enables consideration of the effects of shear deformation zone ranges, material parameters, loading modes, and friction coefficients between tube and dies on the minimum wrinkling energy. Tube wrinkling sensitive zones(WSZs) can be revealed by combining this wrinkling prediction model with a thermalmechanical coupled finite element model for simulating these bending processes. The reliability of this wrinkling prediction model was verified, and an investigation into the tube wrinkling characteristics was carried out based on the experimental conditions. This found that the WSZs are located on either a single side or both sides of the maximum shear stress zone. When the friction coefficients between the tube and the various dies coincide, the WSZs are located on both sides.The larger the value of the tube inner corner radius and/or the smaller the value of the outer cornerradius, the smaller the wrinkling probability. With an increase in the value of the moving die displacement, the wrinkling probability increases at first, and then decreases.展开更多
The self-assembly of surface-order structures based on the surface wrinkling of stiff film-compliant substrate structures(SFCS)is potentially useful in the fabrication of functional devices,the manufacture of superhyd...The self-assembly of surface-order structures based on the surface wrinkling of stiff film-compliant substrate structures(SFCS)is potentially useful in the fabrication of functional devices,the manufacture of superhydrophobic or self-cleaning surfaces,and so on.Due to the influence of the intrinsic characteristic length(g),the surface wrinkling behavior of SFCS at the micro scale is different from that at the macro scale.In this work,based on the strain gradient theory,a trans-scale surface wrinkling model for SFCS is established.First,the effectiveness of this model is verified by previous experiments.Then,based on the model and dimensional analysis,the effect of g on the surface wrinkling behavior is investigated,and the scaling relationship of surface wrinkling of SFCS at different scales is analyzed.The results show that the influence of g cannot be neglected when the film thickness decreases to the one comparable to g.At the micro scale,g will lead to the increase of the critical wrinkling wavelength and load.In addition,the scaling relationship of surface wrinkling at the micro scale will not follow the traditional one.Our study explains the underlying mechanism of the dissimilarity of surface wrinkling behaviors of SFCS at different scales and lays a theoretical foundation for the precise control of surface-order structures.展开更多
文摘The aging process is a group of degenerative changes that physiologically occur in most of the people in the elderly. This affects one or more of the human body systems. The treatment of diseases related to the aging process has a huge impact on the economy of all nations. Aging of the skin comes on the top and despite that, the results of the already present lines of treatment are not always satisfactory. This acts as a stimulus for us to dig deeper to discover the root causes of the premature aging of the skin. This was simply caused by the accumulation of repeated minute damage to the internal structure skin. In other words, if the degree of minute damage is more than the capacity of the skin to repair, the repeated micro-damage is presented in the long run as a skin wrinkling. Moreover, the skin acts as a mirror that reflects the internal structures of the human body. Thus, the more degenerative changes in the human body systems, the more the skin could become wrinkled. Our strategy to prevent or at least slow down the aging process of the skin depends on 2 main steps;the 1<sup>st</sup> is to reduce the micro-damage as can as possible, and the 2<sup>nd</sup> is to enhance the capacity of tissue regeneration to be able to reverse the already present damaged skin. As the 2 processes are synchronized with each other, this strategy would be considered the ideal for prevention of skin wrinkling especially premature ones. This not only reverses premature skin wrinkling but also protects it from future wrinklings. This review sharply pointed out the role of the functional collagen of the dermal layer of the skin in the prevention of skin wrinklings. Therefore, it would be the target to study how collagen works in the complex machinery of the dermal layer of the skin. This concept deeply believes that the recovery of dermal collagen has a much better effect than simply ingesting collagen or receiving a topical collagen booster. .
基金Project supported by the National Natural Science Foundation of China(No.11972259)。
文摘Wrinkles in flat graded elastic layers have been recently described as a timevarying Hamiltonian system by the energy method.Cylindrical core/shell structures can also undergo surface instabilities under the external pressure.In this study,we show that by treating the radial direction as a pseudo-time variable,the graded core/shell system with radially decaying elastic properties can also be described within the symplectic framework.In combination with the shell buckling equation,the present paper addresses the surface wrinkling of graded core/shell structures subjected to the uniform external pressure by solving a series of ordinary differential equations with varying coefficients.Three representative gradient distributions are showcased,and the predicted critical pressure and critical wave number are verified by finite element simulations.The symplectic framework provides an efficient and accurate approach to understand the surface instability and morphological evolution in curved biological tissues and engineered structures.
基金financially supported by National Natural Science Foundation of China(Nos.61574172 and 31971291)Hunan Provincial Natural Science Foundation for Distinguished Young Scholars(No.14JJ1001).
文摘The surface wrinkling of biological tissues is ubiquitous in nature.Accumulating evidence suggests that the mechanical force plays a significant role in shaping the biological morphologies.Controlled wrinkling has been demonstrated to be able to spontaneously form rich multiscale patterns,on either planar or curved surfaces.The surface wrinkling on planar substrates has been investigated thoroughly during the past decades.However,most wrinkling morphologies in nature are based on the curved biological surfaces and the research of controllable patterning on curved substrates still remains weak.The study of wrinkling on curved substrates is critical for understanding the biological growth,developing threedimensional(3D)or four-dimensional(4D)fabrication techniques,and creating novel topographic patterns.In this review,fundamental wrinkling mechanics and recent advances in both fabrications and applications of the wrinkling patterns on curved substrates are summarized.The mechanics behind the wrinkles is compared between the planar and the curved cases.Beyond the film thickness,modulus ratio,and mismatch strain,the substrate curvature is one more significant parameter controlling the surface wrinkling.Curved substrates can be both solid and hollow with various 3D geometries across multiple length scales.Up to date,the wrinkling morphologies on solid/hollow core-shell spheres and cylinders have been simulated and selectively produced.Emerging applications of the curved topographic patterns have been found in smart wetting surfaces,cell culture interfaces,healthcare materials,and actuators,which may accelerate the development of artificial organs,stimuli-responsive devices,and micro/nano fabrications with higher dimensions.
基金The work was supported by the National Natural Science Foundation of China(Grants 11672062,11772082,and 11672063)the 111 Project(Grant B08014)the Fundamental Research Funds for the Central Universities.
文摘In this paper,the quasi-static large deformation,wrinkling and fracture behaviors of bimodular structures and membranes are studied with an implicit bond-based peridynamic computational framework.Firstly,the constant and tangential stiffness matrices of the implicit peridynamic formulations for the nonlinear problems are derived,respectively.The former is con structed from the linearization of the bond strain on the basis of the geometric approximation while the latter is established according to the linearization of the pairwise force by using first-order Taylor’s expansion.Then,a bimodular material model in peridynamics is developed,in which the tensile or compressive behavior of the material at each point is conveniently described by the tensile or compressive states of the bonds in its neighborhood.Moreover,the bimodular material model is extended to deal with the wrinkling and fracture problems of membranes by setting the compressive micro-modulus to be zero.In addition,the incremental-iterative algorithm is adopted to obtain the convergent solutions of the nonlinear problems.Finally,several representative numerical examples are presented and the results demonstrate the accuracy and efficiency of the proposed method for the large deformation,wrinkling and fracture analyses of bimodular structures and membranes.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 10902027 and 11172079)Program for New Century Excellent Talents in University(Grant NoNCET-11-0807)+1 种基金Aeronautical Science Foundation of China(Grant No. 2010ZA77001)the Fundamental Research Funds for theCentral Universities (Grant No. HIT. NSRIF. 201156)
文摘In this paper,the wrinkle-crease interaction behavior of a rectangular membrane under edge tension is simulated.The creased membrane is modeled by using a Modified Two-Parameter model.In this model,two crease parameters,i.e.the effective modulus of creased membrane and the residual stress from creasing,are computed by using MacNeal's method that was firstly applied directly in a flat membrane with the local crease.We have proposed a method to solve the wrinkling computing issue of the creased membrane by using a Direct Perturb-Force technique in our previous work.Based on our method,the effects of crease location on the wrinkle-crease interaction behavior can be evaluated accurately.These results will be of great benefit to the analysis and the control of the wrinkles in the membrane structures.
基金Australia Research Council Discovery Project(DP170103092)National Natural Science Foundation of China(NSFC51701030).
文摘The three-dimensional(3D)graphene-based materials have raised significant interest due to excellent catalytic performance and unique electronic properties,while the preparation of uniform and stable 3D graphene structures remains a challenge.In this paper,using molecular dynamics simulations,we found that the nanotwinned copper(nt-Cu)matrix with small twin spacing can induce the wave-shaped wrinkling and sawtooth-shaped buckling graphene structures under uniaxial compression.The nt-Cu matrix possesses a symmetrical lattice structure for the lattice rotation with the dislocation annihilation,resulting in the transition of sandwiched graphene from 2D to 3D structures with good uniformity.The newly formed twin boundaries(TBs)in the nt-Cu matrix improve the resistance of graphene against the out-of-plane deformation so that graphene can maintain a stable wrinkling or buckling morphology in a wide strain range.These 3D texturing structures show great flexibility and their micro parameters can be controlled by applying different compressive strains.Furthermore,we propose a simple sliding method for decoupling graphene from the nt-Cu matrix without any damage.This work provides a novel strategy to induce and transfer the uniform wrinkling and buckling of graphene,which may expand the application of graphene in energy storage and catalysts.
文摘This work presents an approximate analytical study of the problem of dynamic wrinkling of a thin metal sheet under a specified time varying tension. The problem is investigated in the framework of the dynamic stability of a nonlinear plate model on elastic foundation which namely takes into account the nonlinear mechanics of mid-plane stretching and the dependence of the membrane force on this mechanics. The plate is assumed to be a wide rectangular slab, hinged at two opposite ends and free at the long ends, which can be deformed in a cylindrical shape so that the governing in-plane bending equation of motion takes the same form as that of a beam (e.g. lateral strip) element. An approximate analytical analysis of the beam wrinkling behavior under sinusoidal parametric excitation is carried out by using the assumed single mode wrinkling motion to reduce the beam field nonlinear partial differential equation to that of a single degree of freedom non-linear oscillator. A first order stability analysis of an approximate analytical solution obtained using the Multi-Time-Scales (MMS) method is used to derive a criterion defining critical driving frequency in terms of system parameters for the initiation of wrinkling motion in the thin metal sheet. Results obtained using this criterion is presented for selected values of system parameters.
文摘In this paper, the features of fabric wrinkle structure are analyzed, by image processing technique. The wrinkle images are processed and character parameters are extracted. The wrinkle side surface area ratio of image gray level intensity, the standard deviation of total pixels’ gray level intensity and the standard deviation of wrinkle block area are adopted to evaluate fabric wrinkling. The results show that these three character parameters can be served for ranking the wrinkling. It provides a feasible objective method for fabrics wrinkling degree assessing.
基金Sponsored by the National Natural Science Foundation of China (Grant No.51078114)the Doctoral Program of Higher Education of China (Grant No.2012302120058)
文摘A stress extremum method is developed based on Von Karman equations for analysis of membrane wrinkles in this paper. A mechanical model is also established for analyzing shear membrane wrinkles. Expressions of wrinkling wavelength,amplitude and angle are obtained in terms of the stress extremum method. A numerical analysis approach-directly disturbing method is proposed to analyze the configuration parameters of shear membrane wrinkles by introducing out-of-plane disturbing forces to trigger wrinkle formation,while it timely removes the applied forces in order to eliminate the effect of disturbing forces on analytical results. The simulation results agree well with analytical results,which demonstrate that the proposed approach is capable for analyzing the membrane wrinkles with good accuracy.
文摘5-Aminolevulinic acid (ALA) is a natural amino acid that is used as a raw material for the biosynthesis of red-blood-cell hemoglobin in humans and animals. ALA is the subject of research in a wide range of human health care fields, including skin care and medicine. This study investigated whether and to what extent cosmetics containing ALA (skin lotions and creams) improved facial-skin condition in women. As such, a double-blind controlled experiment was conducted among 45 women aged 47.0 ± 1.72 years. Participants were divided into two intervention groups, including those who used cosmetics containing ALA (C-ALA, n = 22) and those who used cosmetics without ALA (W-ALA, n = 23). Specifically, participants were instructed to use their assigned cosmetics twice per day (morning and evening) after washing their faces before each application. Inner skin condition and skin-water content were evaluated via VISIA-Evolution and Multi Display Devices at baseline and after four and eight weeks of use. The experiment lasted for a total of eight weeks. A baseline comparison at week four showed that skin moisture content increased significantly for the C-ALA group (p = 0.021). Further, wrinkling significantly decreased at week four among participants in the C-ALA group who were evaluated as having many wrinkles at baseline (p = 0.034). These findings suggest that cosmetics containing ALA have moisturizing effects and reduce wrinkling caused by dryness.
基金supported by the National Natural Science Foundation of China(Nos.52122301,51973191,52090030,and 51533008)Hundred Talents Program of Zhejiang University(No.188020*194231701/113)+2 种基金Key Research and Development Plan of Zhejiang Province(No.2018C01049)Shanxi-Zheda Institute of New Materials and Chemical Engineering(No.2012SZ-FR004)the Fundamental Research Funds for the Central Universities(Nos.K20200060,2017QNA4036,and 2017XZZX001-04).
文摘Assembling two-dimensional(2D)sheets into macroscopic three-dimensional(3D)forms has created a promising material family with rich functionalities.Multiscale wrinkles are intrinsic features of 2D sheets in their 3D assembles.Therefore,the precise wrinkling modulation optimizes the transition of outstanding properties of 2D sheets to expected performances of assembled materials and dominates their fabrication process.The wrinkling evolution of 2D sheets assembling onto flat surfaces has been extensively understood,however,the wrinkling behaviors on the more generally curved surface still remain unclear.Here,we investigate the wrinkling behaviors of graphene oxide sheets assembled onto curved surfaces and reveal the selection rule of wrinkling modes that determined by the curvature mismatch between 2D sheets and target surfaces.We uncover that three wrinkling modes including isotropic cracked land,labyrinth,and anisotropic curtain phases,respectively emerge on flat,spherical,and cylindrical surfaces.A favorable description paradigm is offered to quantitatively measure the complex wrinkling patterns and assess the curvature mismatch constraint underlying the wrinkling mode selection.This research provides a general and quantitative description framework of wrinkling modulation of 2D materials such as high performance graphene fibers,and guides the precise fabrication of particles and functional coatings.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1203602)the National Natural Science Foundation of China(Grant Nos.12025206,12072337,and 11872335)the Fundamental Research Funds for the Central Universities(Grant No.WK2090000020)。
文摘We report the formation of antisymmetric wrinkling patterns in films on ridged substrates induced by the buckling instability of the substrates via finite element simulations and experiments.Our simulated results reveal that the uniaxial compression along the ridge can trigger both the wrinkling instability of the film and the lateral buckling instability of the ridge.The latter could change the wrinkles from a symmetric pattern to an antisymmetric pattern in a range of film-substrate modulus ratio and aspect ratio of the ridge profile,as validated by the experimental observations.A three-dimensional phase diagram with four buckling patterns,i.e.,sole ridge buckling pattern,antisymmetric wrinkling pattern with different wavelengths from ridge buckling,symmetric wrinkling pattern without ridge buckling,and antisymmetric wrinkling pattern with the same wavelength as ridge buckling,is built with respect to the uniaxial compression,modulus ratio,and aspect ratio.The results not only elucidate how and when the interplay between the wrinkling instability and the ridge instability results in the formation of the antisymmetric wrinkling pattern but also offer a way to generate controllable complex wrinkling patterns.
基金supported by the National Natural Sciences Foundation of China(No.12172295)SKLLIM1902,China.
文摘Sandwich structures have been widely applied in the wing and the horizontal tail of the aircraft,so face sheets of such structure might occur wrinkling deformation in the process of service,which will largely decrease capability of sustaining loads.As a result,this paper aims at proposing a reasonable strategy resisting wrinkling deformation of sandwich structures.To this end,an enhanced higher-order model has been proposed for wrinkling analysis of sandwich structures.Buckling behaviors of a five-layer sandwich plate are firstly analyzed,which is utilized to assess performance of the proposed model.Subsequently,wrinkling behaviors of four sandwich plates are further investigated by utilizing present model,which have been evaluated by using quasi threedimensional(3D)elasticity solutions,3D Finite Element Method(3D-FEM)results and experimental datum.Finally,the present model is utilized to study the buckling and the wrinkling behaviors of sandwich plates reinforced by Carbon Nano Tubes(CNTs).In addition,influence of distribution profile of CNTs on wrinkling behaviors has been analyzed,and a typical distribution profile of CNTs has been chosen to resist wrinkling deformation.Without increase of additional weight,the present strategy can effectively resist wrinkling deformation of sandwich plates,which is rarely reported in published literature.
基金This work was supported by the Office of Naval Research Young Investigator Program(No.N00014-20-1-2611)This work in part used the Extreme Science and Engineering Discovery Environment(XSEDE)through allocation TGMCH210002which was supported by the National Science Foundation(No.ACI-1548562).
文摘Strain engineering has been leveraged to tune the thermal properties of materials by introducing stress and manipulating local atomic vibrations,which poses a detrimental threat to the mechanical integrity of materials and structures and limits the capability to regulate thermal transport.Here,we report that the interfacial thermal conductance of graphene on a soft substrate can be regulated by harnessing wrinkling and folding morphologies of graphene,which could be well controlled by managing the prestrain applied to the substrate.These obtained graphene structures are free of significant in-plane mechanical strain and only have infinitesimal distortion to the intrinsic thermal properties of graphene.The subsequent thermal transport studies with pumpprobe non-equilibrium molecular dynamics(MD)simulation show that the thermal conductance between graphene structures and the substrate is uniquely determined by the morphological features of graphene.The atomic density of interfacial interactions,energy dissipation,and temperature distribution are elucidated to understand the thermal transport across each graphene structure and substrate.We further demonstrate that the normalized thermal conductance decreases monotonically with the increase of the equivalent mechanical strain,showing the capability of mechanically programmable interfacial thermal conductance in a broad range of strains.Application demonstrations in search of on-demand thermal conductance are conducted by controlling the geometric morphologies of graphene.This study lays a foundation for regulating interfacial thermal conductance through mechanical loading-induced geometric deformation of materials on a soft substrate,potentially useful in the design of flexible and stretchable structures and devices with tunable thermal management performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672161,11432008)
文摘Surface wrinkling of materials holds promise for important applications in diverse fields such as multifunctional surfaces and biomedical engineering. For these applications, it is of interest to attain various surface wrinkles with tunable wavelengths and amplitudes. Through a combination of experiments and numerical simulations, we here propose a method to regulate the wrinkling patterns in a film-substrate system by introducing periodic surface stiffness, which is generated through sequential specified ultraviolet-ozone(UVO) treatments. Both experiments and numerical simulations demonstrate that the proposed technique can produce various patterns with wide, tunable geometrical features and anisotropy. The effects of surface stiffness distribution, the exposure durations of UVO-treatments, and the loading biaxiality are examined on the generated surface patterns.
文摘The deformation patterns of elastic membranes under tension is called wrinkling.Wrinkling,which is caused by capillary surface tension,is called capillary wrinkling(Figure 1).In recent years wrinkling patterns have drawn particular attention[1-11],since it can be an useful tool to infer material parameters that might otherwise be inaccessible.For example,the commonly observed tearing instability of an
基金the National Natural Science Foundation of China(No.51972162).
文摘Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices.However,when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites,capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying,which greatly reduces the thermal conductivity of the composites.Herein,graphene nanosheets/aramid nanofiber(GNS/ANF)composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds andπ-πinteractions.The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets,thereby creating a fast in-plane heat transfer channel.The composite films(GNS/ANF-60 wt%)with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity(146 W m^(−1)K^(−1))and tensile strength(207 MPa).The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones,showing promising applications in the thermal management of high-power electronic devices.
基金Project supported by the National Natural Science Foundation of China.
文摘Ⅰ. INTRODUCTIONThin circular plates, a kind of the basic structural element widely used in engineering,are of the simplest plane-stress mechanical model with double curvatures. Hence, the investigation on the fundamental mechanical properties of the thin circular plates has been attracting great attention and brought about many results. Due to the difficulties
基金support of National Natural Science Foundation of China (No. 51305415)
文摘Plastic wrinkling predictions and shear enforced wrinkling characteristics of Ti-alloy thin-walled tubes under combination die constraints have become key problems urgently in need of solutions in order to improve forming quality in their shear bending processes under differential temperature fields. To address this, a wrinkling wave function was developed by considering their shear bend deformation characteristics. Based on this wave function and the thin shell theory, an energy prediction model for this type of wrinkling was established. This model enables consideration of the effects of shear deformation zone ranges, material parameters, loading modes, and friction coefficients between tube and dies on the minimum wrinkling energy. Tube wrinkling sensitive zones(WSZs) can be revealed by combining this wrinkling prediction model with a thermalmechanical coupled finite element model for simulating these bending processes. The reliability of this wrinkling prediction model was verified, and an investigation into the tube wrinkling characteristics was carried out based on the experimental conditions. This found that the WSZs are located on either a single side or both sides of the maximum shear stress zone. When the friction coefficients between the tube and the various dies coincide, the WSZs are located on both sides.The larger the value of the tube inner corner radius and/or the smaller the value of the outer cornerradius, the smaller the wrinkling probability. With an increase in the value of the moving die displacement, the wrinkling probability increases at first, and then decreases.
基金supported by the Postdoctoral Science Foundation of China for Innovative Talents(Grant No.BX2022008)the National Natural Science Foundation of China(Grant Nos.12202007,11890681,12032001 and 11521202)。
文摘The self-assembly of surface-order structures based on the surface wrinkling of stiff film-compliant substrate structures(SFCS)is potentially useful in the fabrication of functional devices,the manufacture of superhydrophobic or self-cleaning surfaces,and so on.Due to the influence of the intrinsic characteristic length(g),the surface wrinkling behavior of SFCS at the micro scale is different from that at the macro scale.In this work,based on the strain gradient theory,a trans-scale surface wrinkling model for SFCS is established.First,the effectiveness of this model is verified by previous experiments.Then,based on the model and dimensional analysis,the effect of g on the surface wrinkling behavior is investigated,and the scaling relationship of surface wrinkling of SFCS at different scales is analyzed.The results show that the influence of g cannot be neglected when the film thickness decreases to the one comparable to g.At the micro scale,g will lead to the increase of the critical wrinkling wavelength and load.In addition,the scaling relationship of surface wrinkling at the micro scale will not follow the traditional one.Our study explains the underlying mechanism of the dissimilarity of surface wrinkling behaviors of SFCS at different scales and lays a theoretical foundation for the precise control of surface-order structures.
