Finite element simulations of static and sliding contact between a human fingertip and textured surfaces

This paper presents a mechanics study of the variations with position and time of stresses within the dermis and epidermis of a human fingertip when it is loaded and slid over textured surfaces. Its purpose is to examine how fingerprints interact with surface texture to cause stress variations in tune with the sensitivities of Meissner and Pacinian corpuscles through which humans in part interpret tactile sensations. A two-dimensional multilayer elastic finite element model of a fingertip has been created for this purpose. Results show that fingertip’s epidermal ridges have little effect on stress distribution within the fingertip in static loading but significantly increase stress oscillations during sliding over a textured surface. Oscillation frequencies from the sliding simulations are in ranges that should stimulate a fingertip’s Meissner and Pacinian corpuscle nerve endings.     

Rheological characterization of edible films made from collagen colloidal particle suspensions

A rheological characterization of collagen edible films is proposed through the experimental evaluation of shear elastic modulus, toughness, hydration capability and stress and stretch ratio at fracture. These properties are obtained from hydration, simple extension and compression tests and analyzed through the BST (Blatz, Sharda, & Tschoegl, 1974) hyperelastic model. Also precursor collagen particle suspensions, with solid concentrations in the range 0.5–4% w/w, are studied to evaluate their thixotropic responses in sudden imposed shear rates and shear loops. These responses are a consequence of particle aggregations leading to cluster formations. The particle size distribution function of suspensions is determined via scanning electron microscopy. Films are formed by casting and then fixed through either a coagulation process with a salt solution or a chemical process involving covalent cross-links with glutaraldehyde. Results indicate that these collagen films behave as colloidal particulate networks composed of particles and clusters. Also it is found that the fractal dimension of clusters is an intrinsic property of collagen particle suspensions, independently from the maturation time. Clusters in these suspensions are formed with a rather open architecture (low fractal value) due to rather large particle attractive forces. The evaluation of the BST rheological parameters allows one the estimation of the energy amount required to get film fracture for different collagen and cross-linker concentrations. Since the final films have to satisfy several quality requirements before using, the interplay between their stiffness and toughness is presented and discussed.     

浅谈低等级公路改建为一级公路的几点思考

针对目前国、省道等干线公路沿线集镇化严重的现状，探讨了低等级公路改建为一级公路的方法，提出应合理确定道路的设计速度，优化路基标准横断面布置，合理确定平交口的设置间距，以期实现“民生交通”“低碳交通”。     

Children's ideas about the environmental impact of cars: a cross age study

The ideas of children about the environmental impact of vehicle emissions have been explored using a precoded questionnaire. The children were from British National Curriculum Years 7 (age 11/12 years), 9 (age 13/14) and 11 (age 15/16). Even in the oldest group only about half of the children appreciated the advantages of smaller, well‐maintained cars; this could have practical implication if not corrected in the adult population. Children seemed well aware of the environmental problems, smog, Acid Rain and Global Warming, to which vehicle emissions contribute, but these are part of an over‐generalised model which children employ in which cars are envisaged as contributing to other problems such as Ozone Layer depletion. We suggest that the use of the generic term ‘pollution’ to describe a wide range of environmental insults and the use of the word ‘environment’ in a non‐defined way might hinder children's differentiation of the different causes of separate environmental problems. The gaps in children's knowledge of the different components of vehicle emissions may reflect and exacerbate this difficulty. Ironically, children have a regard for the environmental and an interest in cars, and a combination of these enthusiasms may provide an opportunity for environmental education and curriculum science teaching.     

Mesoflowers: A new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials

A method for the synthesis of a new class of anisotropic mesostructured gold material, which we call “mesoflowers”, is demonstrated. The mesoflowers, unsymmetrical at the single particle level, resemble several natural objects and are made up of a large number of stems with unusual pentagonal symmetry. The mesostructured material has a high degree of structural purity with star-shaped, nano-structured stems. The mesoflowers were obtained in high yield, without any contaminating structures and their size could be tuned from nano- to meso-dimensions. The dependence of various properties of the mesoflowers on their conditions of formation was studied. The near-infrared-infrared (NIR-IR) absorption exhibited by the mesoflowers has been used for the development of infrared filters. Using a prototypical device, we demonstrated the utility of the gold mesoflowers in reducing the temperature rise in an enclosure exposed to daylight in peak summer. These structures showed a high degree of surface-enhanced Raman scattering (SERS) activity compared to spherical analogues. SERS-based imaging of a single mesoflower is demonstrated. The high SERS activity and NIR-IR absorption property open up a number of exciting applications in diverse areas. Electronic Supplementary Material  Supplementary material is available in the online version of this article at http://dx.doi.org/ and is accessible free of charge.     

大跨距十字滑板的结构优化设计

主要讨论了大跨距滑板的结构问题。由于滑板的运动直接影响着被加工零件的表面粗糙度和形状误差,所以大跨距滑板的变形问题尤为重要,为了使滑板结构简单、紧凑以及变形量小,对滑板结构进行了分析和讨论,采用软件ANSYS对滑板模型进行有限元静态分析,获得模型在载荷作用下结构的应力应变值和结构的其它一些参数,从而为滑板结构优化设计提供依据。通过对结构进行优化设计,实现滑板即合理又经济的目的。     

Quantifying changes in weak layer microstructure associated with artificial load changes

Researchers and practitioners have long utilized a variety of penetrometers to investigate the snowpack. Identifying definitive relationships between penetrometer-derived microstructural information and stability has been challenging. The purpose of this study is two-fold: 1. We propose a simple field test to establish relationships between load and penetrometer-derived microstructural estimates, 2. We utilize the SnowMicroPen (SMP) to quantify changes in weak layer residual strength and microstructural dimension associated with an artificial loading event. Our dataset is from Moonlight Basin, Montana and includes three modified loaded-column tests, each paired with 5 SMP profiles. Depth hoar comprised the targeted weak layer. Results indicate that loading caused the residual strength and rupture frequency to decrease significantly. Much like a compression test at a micro-scale, the force required for the SMP to rupture individual structures as well as the micro-scale strength decreased significantly when the slab stress was increased by artificially adding blocks of snow. A decrease in observed rupture frequency within the weak layer (or an increase in the distance between ruptured structures) also occurred after the loading event, probably because some structures within the weak layer had already failed or were so close to failing that the penetrometer could not detect their rupture. Due in part to the large difference in loads, microstructural differences between the natural and loaded columns were significant enough that only one profile would have been necessary to determine a significant difference in residual strength. Artificial removal of slab stress resulted in greater rupture forces and larger microstructures, likely due to elastic rebound.     

On the strength of polycrystalline tungsten monocarbide

The paper consists of analytical and applied parts. The mathematical means of mechanics of hexagonal polycrystals are used in the former. Here the correspondence of the published data on single crystal elastic constants of tungsten monocarbide to elasticity moduli of polycrystalline WC has been analyzed. The relationship between ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide has been established too. The dependence of ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide on mean grain diameter is considered in the applied part. Here the available experimental data are used.     

Microstructure–mechanical property relationship in an Al–Mg alloy processed by constrained groove pressing-cross route

The constrained groove pressing-cross route process was implemented on a commercially annealed AA5052 alloy at room temperature, with up to two passes (strain of ～4.64) along the rolling direction and transverse direction. The results showed the formation of an ultrafine-grained structure with an average sub-grain/cell size in the 300–500?nm range. The indentation hardness and tensile strength increased significantly, up to ～75 and 105%, respectively, and became more homogenous with a uniform and isotropic trend, as compared to the annealed alloy. According to the Hall–Petch and Taylor models used, grain refinement and increasing dislocation density were proposed as the main strengthening mechanisms. Fractographic studies revealed a ductile-fracture behaviour, with a dimpled structure proportional to the UFG structure.