基底对PDMS-碳纤维复合材料粘附性能的影响

主要介绍了PDMS(polydimethylsiloxane,聚二甲基硅氧烷)-碳纤维复合仿生粘附材料的制备工艺及其粘附性能的测试方法,并测试了该材料在几种不同基底下的法向和切向粘附力。实验结果显示,硅、钛、氧化硅、氮化硅基底中,粘附材料在氮化硅表面的法向粘附力最高(8.24N/cm~2),在硅表面的切向粘附力最高(2.22N/cm~2)。粘附力的大小受基底接触角、粗糙度等多种物理特性的共同影响。本文通过对粘附力与基底的接触角和粗糙度间关系的讨论,为PDMS-碳纤维复合材料今后的应用提供了理论依据。     

多组份硅橡胶基末端膨大二级结构粘附性能研究

本文在前期工作基础上,在仿生刚毛一级结构末端固化1层粘附层,制备出末端膨大二级结构,用UMT测试其粘附性能。结果表明：正向滑移单根阵列支杆产生的切向力为5.3 mN,5倍于一级结构的刚毛;末端膨大结构的粘附层因材料组份的不同,其粘附阵列产生的切向粘附力明显不同;倾斜的末端膨大二级结构具有各向异性的粘附特性,正向滑移产生的切向力是逆向滑移的切向力的3.5倍。     

细胞粘附的生物力学研究进展

介绍了细胞粘附的生物力学领域的进展和基本概念,对生物力学中这一新领域的研究进行了评价．同时对力学分析方法和试验方法给予评论,而这些方法示明：细胞粘附的生物力学研究趋势是从细胞力学至分子力学,而在不久将来将进入微观力学范畴     

纳米GeSb2Te4薄膜在大气环境中的摩擦性能研究

采用摩擦力显微镜考察了磁控溅射纳米GeSb2Te4薄膜在大气环境中的微观摩擦性能,利用JKRS理论分析了针尖同GeSb2Te4薄膜接触时的粘附力和表面能之间的关系.结果表明:当湿度较大时,粘附力较大;而当湿度较小时,粘附力较小;当针尖表面能一定时,粘附力的微小变化可以导致GeSb2Te4薄膜的表面能产生较明显变化;随着扫描范围逐渐减小,摩擦力变化趋于稳定;不同扫描速度下法向力和摩擦力保持较好线性关系,但不同扫描速度下的平均摩擦力随扫描速率变化而呈现非线性变化;为了更好地分析探针和样品表面的微观摩擦机制,宜选择扫描范围为0.1～0.5μm或更小.     

单颗金刚石磨削花岗石中力的离散单元分析及试验验证

对花岗石进行了单颗粒金刚石磨削试验.通过测量磨削力对单颗金刚石磨粒所承受的平均法向力和切向力进行了研究,讨论了主轴转速和单颗磨粒最大切削厚度与磨削力的关系.利用离散单元方法(DEM)构造了2种不同的花岗石数字模型,在此基础上对单颗磨粒磨削进行了模拟分析,分析结果与试验结果基本吻合.     

数字标记点识别方法及其在材料性能测试中的应用

基于相关理论，提出了一种非接触性测量面内位移的数字标记点识别方法。该方法能应用于物体变形前后标记点的识别。相对于其它光学测量方法而言，该技术实验过程简单，能够应用于小变形、大变形等不同的变形范围。本文还将这一方法应用于高分子薄膜材料的时间特性实验测试，结果表明，此方法可有效用于柔度较大材料的变形测量。     

一种由圆柱体试件的侧向压缩力-位移关系同时测量材料弹性模量和泊松比的新方法

材料的弹性模量和泊松比是材料表征的重要力学参数,传统的压缩试验需要同时测量荷载、压缩和横向变形,才能实现对弹性模量和泊松比的同时测量。本文从Hertz接触理论出发,推导出弹性圆柱体在侧向压缩下的位移-力关系公式,在该关系式中位移与力的关系除与试件的几何尺寸相关外,还取决于材料的弹性模量和泊松比。因此,可以通过对侧向压缩试验测得的力-位移关系进行非线性拟合,得到材料的弹性模量和泊松比。本文通过对硅胶材料开展轴向与侧向压缩试验,对比两种试验测量得到的弹性模量和泊松比,结果较为一致,验证了本文提出方法的可行性。对于模量较小的软物质,因加载过程的荷载常常较小,系统测量的位移可代表试件的变形位移,故本文提出的新测量方法特别适合应用于该类型材料的相关性能测量。     

基于Harris角点检测的位移测量算法

在力学实验中,位移和应变的测量是最基本任务之一。本文提出了一种基于Harris角点检测的位移测量算法。通过检测变形前图像的角点,然后利用光流跟踪技术在变形图像中搜索其匹配点,最终计算得到位移值。算法对图像采用网格划分方式进行计算,达到了全场测量的目的。实验结果表明,该算法位移测量精度高、稳定性好,可作为基于图像处理的无损测量方法。     

桩柱水流作用力实验测量技术研究

桩柱的绕流水流作用力一直是工程设计中所关注的问题。为了精确地测量模型试验中竖直桩柱在不同来流夹角下的水流作用力,基于力的平衡原理,设计并制作了一种新的桩柱水流作用力试验测量装置,并采用标准砝码模拟水流作用力,验证了该测量装置在不同来流工况下的测量精度。结果表明:桩柱受不同来流夹角的水流作用力时,该装置都具有相当高的测量精度,可满足模型试验要求。因此,该测量方法可用于竖直桩柱在水平或斜向水流作用下模型试验中水流作用力的试验研究。     

基于自然增长的细胞群粘附数值模拟

细胞群通过表面的粘附分子不断聚集的过程称为细胞群粘附, 是生物学许多研究领域(早期的胚胎发育、组织的新陈代谢以及肿瘤生长等)的基础. 考虑细胞群的自由运动和细胞群互相之间的粘附力作用, 并引入Logistic模型来描述细胞群自身的自然增长, 从宏观的角度研究细胞群粘附现象, 构建出一个细胞群粘附模型; 其数值模拟结果与实验结果较吻合, 能定性地对不同种类细胞群粘附的最终形态做出预判.      

First mushroom-shaped adhesive microstructure: A review

This letter reviews the adhesive and frictional properties of the first mushroom-shaped adhesive microstructure (MSAMS), which has come a long way from inspiration by the attachment devices evolved in beetles to a large-scale industrial production. It was shown to have an that about twice higher pull-off force compared to a smooth control made from the same material measured on smooth substrates. Pull-off forces measured underwater are even higher than those in air. Moreover, it retained adhesive performance over thousands of attachment cycles and initial adhesive capability could be recovered by washing after being contaminated. In shearing, MSAMS exhibits reduced and stabilized friction in comparison with a smooth control, which demonstrated pronounced stick-slip motion, and shows zero pull-off force in a sheared state, allowing the adhesion to be switched on and off. The presence of a fluid in the contact zone showed adhesion enhancement on both smooth and rough substrates. All these features lead us to conclude that MSAMS may have practical potential in a variety of applications.     

Migration and deformation of leukocytes in pressure driven flows

Direct numerical simulations (DNS) are used to study the motion and deformation of leukocytes in pressure driven flows in parallel plate channels. The influence of the adhesion force between the leukocytes and the channel wall on such motion and deformation is also investigated. Leukocytes are represented by two composite fluid models, consisting of a membrane, a cytoplasm and a nucleus. The adhesion force is computed using two adhesion force models. In the first model, the adhesion force is given by a potential, and in the second one it is given by Dembo’s kinetic adhesion model. The numerical code is based on the finite element method and the level set technique is used to track the cell membrane position. In the absence of the adhesion force, the leukocyte moves away from the wall to an equilibrium location that depends on the ratio of the cell to plasma viscosities. In presence of the adhesion force, the leukocyte is attracted to the layer of endothelial cells and, as it gets closer, it flattens under the action of hydrodynamic forces. This deformation, in turn, further increases the adhesion force. The leukocyte, however, can be captured only when it is placed sufficiently close to the wall, which for the kinetic model is of the order of 30 nm. We also find that for the normal parameter values and flow rates the adhesive force given by the kinetic model is too small to capture the leukocyte.     

Identifying traction–separation behavior of self-adhesive polymeric films from in situ digital images under T-peeling

In this paper procedures are developed to identify traction–separation curves from digital images of the deformed flexible films during peeling. T-peel tests were performed for self-adhesive polymeric films. High quality photographs of the deformed shape within and outside the zone of adhesive interaction were made in situ by the digital light microscope. The deformed line is approximated by a power series with coefficients computed by minimizing a least squares functional. Two approaches to identify the traction–separation curve for the given deformation line are proposed. The first one is based on the energy integral of the non-linear theory of rods and allows the direct evaluation of the adhesion force potential. The second one utilizes the complementary energy type variational equation and the Ritz method to compute the adhesion force. The accuracy of both approaches is analyzed with respect to different approximations for the deformed line and the force of interaction. The obtained traction vs. axial coordinate and the traction–separation curves provide several properties of the adhesive system including the maximum adhesion force, the length of the adhesive zone and the equilibrium position, where the adhesive force is zero while the separation is positive.     

冻雨环境下润湿性表面覆冰黏附力测试方法

覆冰黏附力是仿生超疏水材料防结冰工程应用的关键技术指标之一. 根据覆冰样片降温过程中产生应变受冰层黏附力作用的原理, 提出利用电阻应变片传感器于模拟冻雨结冰环境下在线检测覆冰黏附力的方案. 应变片应变信号经数据采集、信号转换和软件处理, 实现了应变传感电压实时监测与在线显示, 结合受力分析对比计算出不同润湿性表面覆冰黏附力. 该方法可实时表征低温结冰环境下不同润湿性表面的结/融冰行为及覆冰黏附力变化趋势.     

MEASUREMENT OF ADHESION FORCES IN AIR WITH THE VIBRATION METHOD

The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally altemating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces. rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas.     

Observations of shear adhesive force and friction of Blatta orientalis on different surfaces

The shear adhesive force of four non-climbing cockroaches (Blatta orientalis Linnaeus, 1758) was investigated by the use of a centrifugal machine, evaluating the shear safety factor (adhesion force divided by body weight) on six surfaces (steel, aluminium, copper, two sandpapers and a common paper sheet) having different roughness. The adhesive system of Blatta orientalis was characterized by means of a field emission scanning electron microscope and the surface roughness was determined by an atomic force microscope. The cockroach maximum shear safety factor, or apparent friction coefficient, is determined to be 12.1 on the less rough of the two sandpapers, while its minimum value is equal to 1.9 on the steel surface. A two-sample Student t analysis has been conducted in order to evaluate the significance of the differences among the obtained shear safety factors due to both roughness and chemistry. An interesting correlation between cockroach shear adhesion and surface roughness emerges with a threshold mechanism dictated by the competition between claw tip radius and roughness, indicating that the best adhesion is obtained for roughness larger than the claw tip radius.     

Adhesive contact in the context of multi-asperity interaction

In order to analyse the scale effect of roughness and adhesion in contact between solids, we introduce in this work a 3D model of elastic contact combined with the adhesive theory. The model of roughness with different fractal dimension is introduced to study the adhesive contact in the elastic state at different length scales.The results of this study show that the scale of roughness modifies the distribution law of the contact pressure and stiffness. The introduction of the adhesive force and fractal property of roughness clearly shows the combined influence of roughness scale and adhesive force on contact stiffness.     

壁虎粘附微观力学机制的仿生研究进展

本文针对壁虎粘附系统最小单元的真实形状, 类似于有限尺寸纳米薄膜的铲状纤维, 综述了对其微观粘附力学机制主要影响因素的多个研究, 主要考虑了有限尺寸纳米薄膜长度、厚度、撕脱角等对撕脱力的影响; 物体表面粗糙度以及环境湿度等对粘附的影响因素; 包括实验、理论及数值模拟的研究及结果比较. 最后给出仿生粘附力学方向仍然存在的主要科学问题及进一步的研究展望.     

剪切载荷作用下植物细胞的力学特性分析

根据植物细胞的结构特点,以二维问题为研究对象,在已建立的植物单细胞力学模型的基础上,利用有限元方法和MATLAB计算软件研究了单细胞受到剪切载荷作用时,外力、应力、应变及内压间的相互关系,给出了关系曲线图。得出了在剪切情况下,外力、应力、应变及内压之间的关系是非线性的;细胞内压改变量随外力或细胞变形或细胞壁应力的增加而增加;细胞壁的应力随剪切力的增大而增大;细胞将在哪个方向破裂等6个结论。     

ADHESION STRENGTH AND MORPHOLOGIES OF r BMSCs DURING INITIAL ADHESION AND SPREADING

Cell adhesion plays an important role in cell physiology. A better understanding of this process could facilitate many clinical therapies. In this study, Rat bone marrow-derived mesenchymal stem cells(r BMSCs) were cultured on glass substrate, and the morphology and adhesion strength were characterized. The cell morphology was defined as spherical, adhesive,and spreading. The adhesion strengths of the different morphologies exhibited different distribution patterns. The spherical cells exhibited low adhesion strength; the adhesive cells exhibited rapidly increasing adhesion strength while their diameters remained relatively constant. The adhesion strength increased with the cell diameter in the spreading cells. These findings suggest that adhesion strength can be quickly assessed by examining the cell morphology.