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A strategy resisting wrinkling of sandwich structures reinforced using functionally-graded carbon nanotubes

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中国航空学报:英文版 2023年第9期36卷 243-255页

作者： Xiaohui REN Senlin ZHANG Zhen WU School of Mechanical Engineering Xi’an Aeronautical UniversityXi’an 710065China School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China

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.

关键词： Buckling Carbon nano tube Functionally graded plate Higher-order model wrinkling

Deep Drawing Process Using a Tractrix Die for Manufacturing Liners for a CNG High-Pressure Vessel(Type Ⅱ)

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Chinese Journal of Mechanical Engineering 2022年第1期35卷 132-143页

作者： Gun‑Young Park Hyo‑Seo Kwak Hyo‑Seong Jang Chul Kim School of Mechanical Engineering Pusan National UniversityPusan 46241South Korea Department of Mechanical Engineering Dong-eui UniversityPusan 47340Korea.

The liner of a CNG pressure vessel is manufactured by a DDI(deep drawing and ironing)process for the cylinder part,which is a continuous process that includes a drawing process to reduce the diameter of the billet and a subsequent ironing process to reduce the thickness of the billet.A tractrix die used in the 1^(st) deep drawing allows the blank to flow smoothly by decreasing the punch load and radial tensile stress occurring in the workpiece.It also increases the draw ratio compared to conventional dies,but it causes forming defects.In this study,a shape coefficient(S_(c))is proposed for the tractrix die using the blank diameter(D_(0)),inflow diameter of the workpiece(d_(i)),and inflow angle of the workpiece(θ)for design of the tractrix die.The effects of the thickness and inflow angle of the workpiece on wrinkling and folding were investigated through FEA.Also,a discriminant is proposed for the relative radial stress(σ)generated during the deep drawing process using the tractirx die and used to predict fracture.Based on the results,the blank thickness,the draw ratio,and the inflow of the workpiece angle in the 1^(st) deep drawing process are suggested,and the number of operations in the DDI process was reduced from 6 to 4.This improves the productivity and reduces the manufacturing cost.

关键词： Tractrix die Deep drawing wrinkling Folding LDR(Limit draw ratio) FEM

Analytical study of wrinkling in thin-film-on-elastomer system with finite substrate thickness

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Applied Mathematics and Mechanics(English Edition) 2017年第4期38卷 469-478页

作者： Xianhong MENG Guanyu LIU Zihao WANG Shuodao WANG School of Aeronautic Science and Engineering Beihang University School of Mechanical and Aerospace Engineering Oklahoma State University

Surface wrinkling, a film bonded on a pre-strained elastomeric substrate can form periodic wrinkling patterns, is a common phenomenon in daily life. In existing theoretical models, the film is much thinner than the substrate so that the substrate can be considered to be elastomeric with infinite thickness. In this paper, the effect of finite substrate thickness is analyzed theoretically for free boundary condition cases. Based on the minimum potential energy principle, a theoretical model is established, and the wave length and amplitude of the wrinkling pattern are obtained. When the thickness of the substrate is more than 200 times larger than the thickness of the film, the results of this study agree well with the results obtained from the previous models for infinite substrate thickness. However, for thin substrates, the effect of finite substrate thickness becomes significant. The model given in this paper accurately describes the effect of finite substrate thickness, providing important design guidelines for future thin-film-on-substrate systems such as stretchable electronic devices.

关键词： wrinkling finite substrate thickness theoretical mechanics model

wrinkling analysis of creased rectangular membrane

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Journal of Harbin Institute of Technology(New Series) 2012年第3期19卷 88-94页

作者：王长国兰澜谭惠丰 School of Astronautics Harbin Institute of Technology

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.***.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.

关键词： membrane wrinkling creasing

Regulating wrinkling patterns by periodic surface stiffness in film-substrate structures

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Science China(Technological Sciences) 2019年第5期62卷 747-754页

作者： LI Bo ZENG ChongQing YIN SiFan FENG XiQiao Institute of Biomechanics and Medical Engineering AML Department of Engineering Mechanics Tsinghua University

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.

关键词： film-substrate system wrinkling surface patterns stiffness modification

The wrinkling and buckling of graphene induced by nanotwinned copper matrix:A molecular dynamics study

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Nano Materials Science 2021年第1期3卷 95-103页

作者： Che Zhang Cheng Lu Linqing Pei Jiaqing Li Rui Wang School of Mechanical MaterialsMechatronic and Biomedical EngineeringUniversity of WollongongWollongongNSW2522Australia College of Mechanical Engineering Chongqing UniversityChongqing400044China

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.

关键词： Molecular Dynamics Nanotwinned Copper 3D Graphene Structures wrinkling Twin boundaries

Plastic wrinkling model and characteristics of shear enforced Ti-alloy thin-walled tubes under combination die constraints and differential temperature fields

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Chinese Journal of Aeronautics 2016年第6期29卷 1815-1829页

作者： Yan Jing Aeronautical Key Laboratory for Plastic Forming Technology Beijing 100024China Beijing Key Laboratory of Digital Plastic Forming Technology and Equipment Beijing 100024China Beijing Aeronautical Manufacturing Technology Research Institute Beijing 100024China

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.

关键词： Combination die constraint Differential temperature field Energy method Finite element Shear bending Ti-alloy thin-walled tube wrinkling

Inner wrinkling control in hydrodynamic deep drawing of an irregular surface part using drawbeads

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Chinese Journal of Aeronautics 2014年第3期27卷 697-707页

作者： Meng Bao Wan Min Wu Xiangdong Yuan Sheng Xu Xudong Liu Jie School of Mechanical Engineering and Automation Beihang University Department of Manufacturing Engineering Chengdu Aircraft Industrial Corporation Sheet Metal Manufacturing Plant Chengdu Aircraft Industrial Corporation

Inner wrinkling phenomenon is more likely to develop during hydrodynamic deep drawing （HDD） of complicated component-forms due to the higher demand for controlling deformation sequences. Aiming at the problems in control of inner wrinkling for an irregular surface part featured with both concavity and convex, this research proposes an optimal design method of drawbead parameters to change the material flow. According to theoretical analysis of the mechanism of inner wrinkling, optimizing cavity pressure only is unreasonable to form a wrinkle-free deep-drawn part, so semi-circular drawbeads are employed. The effects of layout and height of drawbeads on forming results are discussed, and a process window is established based on evaluation indicators including the anti-wrinkle coefficient and the minimum wall thickness. Experiments are carried out to validate the process window, and the wall thickness and the wrinkle height are measured and compared with numerical findings. The results show that the anti-wrinkle ability of drawbeads weakens with increasing oblique angle and distance from the die center, while the wall thickness increases with increasing oblique angle and distance, and the inner wrinkling can be completely suppressed by drawbeads arranged in zones I and II with optimum penetration.

关键词： Aircraft part manufacturing Drawbead Hydrodynamic deep drawing Irregular surface part Numerical simulation Sheet metal wrinkling

Plastic wrinkling prediction in thin-walled part forming process: A review

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Chinese Journal of Aeronautics 2016年第1期29卷 1-14页

作者： Liu Nan Yang He Li Heng Yan Siliang State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical University

The precision forming of thin-walled components has been urgently needed in aviation and aerospace field. However, the wrinkling induced by the compressive instability is one of the major defects in thin-walled part forming. The initiation and growth of the wrinkles are interac- tively affected by many factors such as stress states, mechanical properties of the material, geometry of the workpiece and boundary conditions. Especially when the forming process involves compli- cated boundary conditions such as multi-dies constrains, the perturbation of clearances between workpiece and dies and the contact conditions changing in time and space, etc., the predication of the wrinkling is further complicated. In this paper, the cu.rent prediction methods were summa- rized including the static equilibrium method, the energy method, the initial imperfection method, the eigenvalue buckling analysis method, the static-implicit finite element method and the dynamic- explicit finite element method. Then, a systematical comparison and summary of these methods in terms of their advantages and limitations are presented. By using a combination of explicit FE method, initial imperfection and energy conservation, a hybrid method is recommended to predict plastic wrinkling in thin-walled part forming. Finally, considering the urgent requirements of com- plex thin-walled structures＇ part in aviation and aerospace field, the trends and challenges in wrin- kling prediction under complicated boundary conditions are presented.

关键词： Explicit algorithm Hybrid method Imperfections Implicit algorithm Thin-walled part forming wrinkling