An evaluation method for nanoscale wrinkle

In this paper, a spectrum-based wrinkling analysis method via two-dimensional Fourier transformation is proposed aiming to solve the difficulty of nanoscale wrinkle evaluation. It evaluates the wrinkle characteristics including wrinkling wavelength and direction simply using a single wrinkling image. Based on this method, the evaluation results of nanoscale wrinkle characteristics show agreement with the open experimental results within an error of 6%. It is also verified to be appropriate for the macro wrinkle evaluation without scale limitations. The spectrum-based wrinkling analysis is an effective method for nanoscale evaluation, which contributes to reveal the mechanism of nanoscale wrinkling.     

Experiment and evaluation of wrinkling strain in a corner tensioned square membrane

Prediction of wrinkling characteristics is strongly correlated with the strain perpendicular to wrinkling direc- tion. In this paper, the strain field of wrinkled membrane is tested by VIC-3D system based on the digital image correlation technique. Experimental results are validated by the tension wrinkling simulation. The experimental strain perpendicular to wrinkling direction is analyzed in depth. The wrinkling strain of a square wrinkled membrane under corner tension is extracted from experimental strain perpendicular to wrinkling direction. A quantitative characterization format of the experimental wrinkling strain is proposed. A modified prediction method of wrinkling amplitude is presented based on the experimental wrinkling strain. The re- sults show that the precision of modified prediction model has improved 13.2% compared with the classical prediction model. The results reveal that the modified model can give an accurate prediction of the wrinkling amplitude.     

Stretch-induced wrinkling of polyethylene thin sheets: Experiments and modeling

This paper presents a study on stretch-induced wrinkling of thin polyethylene sheets when subjected to uniaxial stretch with two clamped ends. Three-dimensional digital image correlation was used to measure the wrinkling deformation. It was observed that the wrinkle amplitude increased as the nominal strain increased up to around 10%, but then decreased at larger strain levels. This behavior is consistent with results of finite element simulations for a hyperelastic thin sheet reported previously (Nayyar et al., 2011). However, wrinkles in the polyethylene sheet were not fully flattened out at large strains (>30%) as predicted for the hyperelastic sheet, but exhibited a residual wrinkle whose amplitude depended on the loading rate. This is attributed to the viscoelastic response of the material. Two different viscoelastic models were adopted in finite element simulations to study the effects of viscoelasticity on wrinkling and to improve the agreement with the experiments, including residual wrinkles and rate dependence. It is found that a parallel network model of nonlinear viscoelasticity is suitable for simulating the constitutive behavior and stretch-induced wrinkling of the polyethylene sheets.     

基于聚醚胺(PEA)动态交联网络的多重响应性表面褶皱图案

刺激响应性表面图案赋予了材料动态可调的表面性能,是智能材料领域研究的热点,然而如何通过简单有效的方法构建这类动态表面图案也是该领域的难点.本文将动态硼酸酯键和光可逆二聚基团引入到聚醚胺(PEA)交联网络中,通过双层褶皱体系构建一系列具有光和湿度刺激响应性表面褶皱图案.在365 nm紫外光照和加热的条件下,蒽基团(AN)的光二聚与硼酸键的形成使得上表层聚醚胺模量变大,产生微米级表面褶皱图案;在254 nm紫外光照射或水蒸气作用下,聚醚胺网络解交联,表面褶皱图案消失;利用光化学时空分辨的特性,通过光掩膜板光照还可以制备多层次动态表面褶皱图案.这种多重刺激响应性表面褶皱图案为构建智能聚合物表面提供了新思路,在传感和防伪等领域具有潜在的应用前景.     

弹性基底表面薄膜起皱的计算机模拟

本文设计了一种起皱模型用以研究起皱现象的动态过程.模拟表明整个起皱过程包括三个阶段.在孵化和起皱阶段,水平方向上软基底的应力在回缩过程中传递给硬膜.而在构象松弛平衡阶段,硬膜上的应力又缓慢地传回给软基底,整个起皱过程体系的总能量持续下降.研究发现起皱后软基底上的应力集中在上表层,尤其是在波谷处.而硬膜上的应力分布则取决于方向,在垂直方向,平衡位置的应力要大于波峰和波谷处,与此相反,在水平方向应力则更集中于波峰和波谷.我们的模型既能重现起皱现象,又能重现起皮现象,为材料应力释放导致的结构失稳机理研究提供了一个非常有利的工具.     

A study on wrinkling characteristics and dynamic mechanical behavior of membrane

An eigenvalue method considering the membrane vibration of wrinkling out-of-plane deformation is introduced, and the stress distributing rule in membrane wrinkled area is analyzed. A dynamic analytical model of rectangular shear wrinkled membrane and its numerical analysis approach are also developed. Results indicate that the stress in wrinkled area is not uniform, i.e. it is larger in wrinkling wave peaks along wrinkles and two ends of wrinkle in vertical direction. Vibration modes of wrinkled membrane are strongly correlated with the wrinkling configurations. The rigidity is larger due to the heavier stress in the part of wrinkling wave peaks. Therefore, wave peaks are always located at the node lines of vibration mode. The vibration frequency obviously increases with the vibration of wave peaks.     

Computer Simulation of Thin Film Wrinkling on Elastic Substrate

Numerous theoretical and experimental efforts have been made to explain the dependence of the static wrinkling morphology on the materials' physical properties, whereas the dynamic wrinkling process remains elusive. In the present work, we design a wrinkling model consisting of a soft substrate and a graphene-like rigid thin film to investigate this dynamic process. The simulation shows that the whole wrinkling process includes three stages. At the incubation and wrinkling stages, the stress along the horizon direction of the soft substrate transfers to the stiff film. However, at the equilibrium stage, the stress of the rigid film slowly transfers back to the substrate although the total energy still decreases. It is found that the stress of the substrate concentrates at the top surface, especially at the trough, whereas the stress distribution of the film depends on direction. In the perpendicular direction, the stress at the wave's equilibrium position surpasses that at the crest and trough and, oppositely, the stress concentrates at the crest and trough in the horizon direction. Present model reproduces both wrinkling and delamination patterns and can be a powerful tool to deeply understand the structure deformation of material induced by stress release.     

灰色关联分析方法在板料抗皱性影响因素研究中的应用

应用灰色关联分析方法进行板料参数对抗皱性的综合影响研究，得到较为满意的结果。与通常的统计回归方法相比，这种方法具有计算简单、客观真实等优点．     

Symmetry breaking in biological systems. From molecules to tissues

Chirality of biomolecules is one of the major characteristics of living systems. Molecular asymmetry can be detected in the earliest prokaryotes and stereoselective synthesis of proteins and polysaccharides was recognized since Pasteur’s time. More recently much attention was paid to the molecular origin of asymmetric development of organs. This asymmetry can be followed up to the cellular and tissue levels. We compared the periorbital wrinkle pattern (crow’s feet) around the left and right eyes, as well as the microdepressional skin surface relief on the left and right arms. The pattern of these reliefs was shown to change with age in a typical manner. Apparently this age-dependent modification of the skin surface micro-relief as well as wrinkle formation is largely determined by the progressive modifications of the dermal extracellular matrix (ECM) and especially of the elastic fiber network as the result of the oriented (vectorial) biosynthetic activity of dermal fibroblasts. These cells do not form a homogeneous population as shown by their proliferation pattern. The reaction of these cells to receptor-mediated stimuli—by growth factors, cytokines, and hormones also exhibit microheterogeneity. Cell–cell interactions, especially between the keratinocyte layers of the epidermis and dermal fibroblasts might also play an important role in the regulation of cell-patterning. These mechanisms might well explain the asymmetry detected by our semi-automated image analysis program on left–right microdepressionary skin surface relief, as well as periorbital wrinkle formation.     

Synthesis of wrinkle silica nanospheres by solvent evaporation-induced self-assembly method for hydrogenation reaction

Wrinkle silica nanoparticles (WSNs) possess the typical characteristics in their short diffusion path and central-radial pore structure, which are favorable to use in a wide range of practical application. In this research, a solvent evaporation-induced self-assembly strategy was adopted for the preparation of WSN materials to give an insight into the formation mechanism of the WSNs. Through one-step temperature-controlled method, it was found that the WSNs could be successfully synthesized under the temperature of 60 °C, while the pore sizes and particle sizes were both gradually decreased as the synthesis temperature continued to increase. Comparably, a two-step temperature-controlled method was employed through modulating the stirring time length in order to synthesize silica nanospheres with large pore size and small particle size. The results showed that Ni₂P/WSNs-8+16 catalyst performed the highest naphthalene hydrogenation activity (almost 100% conversion at 300 °C) when the stirring time in the first stage and the second stage was 8 h and 16 h, respectively.