采用曲面四边形单元分析张力膜结构内力

根据几何非线性有限元理论,采用8节点曲面四边形等参单元,分析了张力膜结构内力。对褶皱单元的处理,提出了平均主应力褶皱判断准则。对不同矢跨比、初始预应力、不同荷载类型等参数组合下的菱形马鞍面张力膜结构进行较为系统的内力性能比较。矢跨比和初始预应力的大小对该结构的内力和变形产生较大影响,而其他参数影响不大。程序经过算例验证,结论表明该方法的可靠性和有效性。     

Designing Zwitterionic SiO2NH2‐Au Particles with Tunable Patchiness using Wrinkles

A facile template‐based approach toward zwitterionic SiO₂NH₂‐Au patchy particles is presented. Therefore, wrinkle templates prepared by stress release in a bilayer system comprised of an elastic PDMS fundament and a thin SiO_x top layer are used. After aligning positively charged, amine‐functionalized silica particles in wrinkle grooves, their surfaces are partially modified with negatively charged gold nanoparticles in an electrostatic adsorption step. Patchiness is precisely controlled by the degree of immersion of the initial particles into wrinkles of varying dimensions. By ultrasonication or wetting with a water droplet, patchy particles are easily released from the substrate‐yielding particles with two oppositely charged hemispheres. Interfacial tension measurements prove the surface activity of the SiO₂NH₂‐Au particles in an oil/water system and are explained in the view of the Janus‐type surface charges of the particles and the charge of the oil/water interface.     

空间薄膜结构的褶皱研究进展

大型柔性薄膜结构是目前国际上十分关注的可满足多项空间任务需要的新型空间结构. 由于薄膜材料柔性且抵抗压缩应力作用的能力十分有限, 因此这些空间结构在轨时多处于带有褶皱的工作状态. 褶皱的存在会改变结构的力学性能且会影响结构表面形状, 因此开展薄膜褶皱研究对柔性结构的设计和力学性能评价等具有重要意义. 本文综述了空间薄膜结构褶皱研究的发展和现状, 重点介绍了薄膜褶皱的理论研究概况, 并讨论了其中存在的问题.根据褶皱研究的最新进展对其未来的发展趋势进行了展望.      

Dynamic laser prototyping for biomimetic nanofabrication

Micronanofabrication technologies developed so far pursue faithful conversion from digital models to matter structures. This is vital for microdevices in optics, mechanics, and electronics, where device shape and size matter. However, biotissues grow under rich environmental factor interactions, as demands novel manufacturing approaches for biomimetic and biological fabrication. Here, a concept of dynamic laser prototyping is reported, which is based on a new finding of a multilayered three‐dimensional (3D) wrinkling phenomenon. The 3D wrinkling started with formation of a photocrosslinked hydrogel sheet by femtosecond laser direct writing. It was followed by spontaneous self‐bending of the sheet, caused by a purposely designed sheet–substrate stress mismatch. The flower blooming process has been successfully mimicked, indicating broader usages of the technology in biotissue‐growth‐related manufacturing.     

Wrinkle-crease interaction behavior simulation of a rectangular membrane under shearing

Wrinkling analysis of a rectangular membrane with a single crease under shearing is performed to understand the wrinkle-crease interaction behaviors.The crease is considered by introducing the residual stresses from creasing and the effective modulus into the baseline configuration with assumed circular cross-sectional crease geometry.The wrinkling analysis of the creased membrane is then performed by using the direct perturb-force(DP) simulation technique which is based on our modified displacement components(MDC) method.Results reveal that the crease may influence the stress transfer path in the membrane and further change the wrinkling direction.The crease appears to improve the bending stiffness of the membrane which has an effective resistance on the wrinkling evolution.The effects of the crease orientation on wrinkle-crease interaction are studied toward the end of this paper.The results show that the wrinkling amplitude,wavelength,and direction increase as the crease orientation increases,and the wrinkling number decreases with the increasing crease orientation.These re-sults will be of great benefit to the analysis and the control of the wrinkles in the membrane structures.     

Liner wrinkling and collapse of bi-material pipe under bending

Lining internally a carbon steel pipe with a thin layer of corrosion resistant material is an economical method for protecting offshore tubulars from the corrosive ingredients of hydrocarbons. In applications involving severe plastic bending, such as in the reeling installation process, the liner can detach from the outer pipe and develop large amplitude buckles that compromise the flow. This paper outlines a numerical framework for establishing the extent to which lined pipe can be bent before liner collapse. The modeling starts with the simulation of the inflation process through which the two tubes develop interference contact pressure. Bending the composite structure leads to differential ovalization and eventually separation of part of the liner from the outer pipe. The unsupported strip of the liner on the compressed side first wrinkles and at higher curvature buckles and collapses in a diamond shaped mode. The sensitivity of the collapse curvature to the various parameters of the problem is studied, and amongst other findings the onset of collapse is shown to be very sensitive to small geometric imperfections in the liner. It is also demonstrated that bending the pipe under modest amounts of internal pressure can delay liner collapse to curvatures that make it reelable.     

Topographical and Electrical Stimulation of Neuronal Cells through Microwrinkled Conducting Polymer Biointerfaces

The development of smart biointerfaces combining multiple functions is crucial for triggering a variety of cellular responses. In this work, wrinkled organic interfaces based on the conducting polymer poly(3,4‐ethylene dioxythiophene) doped with poly(styrene sulfonate) are developed with the aim to simultaneously convey electrical and topographical stimuli to cultured cells. The surface wrinkling of thin films on heat‐shrink polymer sheets allows for rapid patterning of self‐assembled anisotropic topographies characterized by micro/sub‐microscale aligned wrinkles. The developed interfaces prove to support the growth and differentiation of neural cells (SH‐SY5Y, human neuroblastoma) and are remarkably effective in promoting axonal guidance, by guiding and stimulating the neurite growth in differentiating cells. Electrical stimulation with biphasic pulses delivered through the conductive wrinkled interface is found to further promote the neurite growth, demonstrating the suitability of such interfaces as platforms for conveying multiple stimuli to cells and tissues.     

Exact analytical solutions for the local and global buckling of sandwich beam-columns under various loadings

Sandwich structures are widely used in many industrial applications, due to the attractive combination of a lightweight and strong mechanical properties. This compromise is realized thanks to the presence of different parts in the composite material, namely the skins and possibly core reinforcements or thin-walled core structure which are both thin/slender and stiff relative to the other parts, namely the homogeneous core material, if any. The buckling phenomenon thus becomes mainly responsible for the final collapse of such sandwiches. In this paper, classical sandwich beam-columns (with homogeneous core materials) are considered and elastic buckling analyses are performed in order to derive the critical values and the associated bifurcation modes under various loadings (compression and pure bending). The two faces are represented by Euler–Bernoulli beams, whereas the core material is considered as a 2D continuous solid. A set of partial differential equations is first obtained from a general bifurcation analysis, using the above assumptions. Original closed-form analytical solutions of the critical loading and mode of a sandwich beam-column are then derived for various loading conditions. Finally, the proposed analytical formulae are validated using 2D linearized buckling finite element computations, and parametric analyses are performed.     

基于不同板理论的嵌于柔性层中薄膜的皱曲分析

论文对于柔性层-薄膜-柔性层三层结构系统,基于经典板理论、一阶剪切变形理论和高阶剪切变形理论,分别推导给出薄膜皱曲的控制方程.对于两个柔性层,则把它们处理成具有有限厚度的平面应变弹性体.针对上下柔性层固支边界或自由边界条件,利用线性扰动方法得到柔性层对薄膜的横向压力差,最终获得确定薄膜具有周期性正弦型皱曲的临界载荷方程...     

模内压板与成形复合工艺及杆系柔性成形模具

分析了板料在曲面成形过程中的应力分布情况和板料的受压屈曲与起皱机理,提出了一种新颖的板料成形方法———模内压板与成形复合工艺,板料在成形过程中板面法向受压板力的约束,可抑制板料受压屈曲,这种工艺方法可以显著地减少板料在成形过程中的起皱现象.杆系柔性成形模具由若干个可调节杆组成,若干个杆组合成一个阵列,各杆端冲压头可以更换,选用与被冲压板件局部成形面近似形状的冲压头组成一定尺寸的模具冲压面,以适应加工件的表面形状,从而构成冲压成形模具.模内压板技术与杆系柔性成形模具相结合,实现模内多点压板与成形,从而可以有效地抑制板料的起皱.