Papers by Keyword: Micro-Scale

Abstract: The purpose of this paper is to describe (at micro-scale) the geogrid-reinforced flexible pavement behaviour under a static loading. The finite element technique is used to analyse the mechanical interaction between granular particles, asphalt binder and geogrid. The geogrid is the most commonly used geosynthetic product for enhancing the stiffness and stability of traditional flexible pavement and it is beneficial for reducing the rutting damage in pavement. The geosynthetic performance is influenced by geometry, material and its placement inside the pavement layers. Whereas, the asphalt mixture performance is governed by properties of aggregate (shape, size distribution, etc.), properties of asphalt binder (grading, viscosity, asphalt modifiers, etc.) and asphalt-aggregate interactions (adhesion and absorption, etc.). Through FEM software (ABAQUS) the microstructure is modelled in 3D. This microstructure is made up of three different components: spherical particles (aggregates), asphalt binder and one strip of geogrid.

Abstract: Understanding matrix failure in LFRP composites is one of the main challenges when developing failure criteria for these materials. This work aims to study the influence of the secondary transverse load on the crack initiation at micro-scale. Four non-classical approaches of fracture mechanics are used to model the onset of fibre-matrix interface debonds: Linear Elastic Brittle Interface Model (LEBIM), an Energetic Approach for the Linear Elastic Brittle Interface Model (EA-LEBIM), an Energetic Approach for the bilinear Cohesive Zone Model (EA-CZM) and the Coupled Criterion of the Finite Fracture Mechanics (CC-FFM). Results obtained by these approaches predict that, for brittle fibre-matrix configurations, a secondary transverse compression reduces the critical value of the main transverse tension leading to the debond onset. This fact is not taken into account by the currently used failure criteria

Abstract: In this paper, the technology, equipment and method used to m easure the mechanical properties of micro-scale new-style intelligent shape memory alloy material were studied. First, two groups of small-scale shape memory alloy samples were made and the suitable micro load device was designed according to samples’ size and force range. Then the strain of the samples were observed with the video microscopy and calculated. Comparing with the corresponding force, the stress-strain curves of the two groups of samples were obtained respectively. After fitting these two curves, the stress-strain curve of the sample material was obtained. Finally, the basic mechanical properties of this shape memory alloy materials were discussed.

Abstract: Chiral sculptured thin films (STFs) Glancing-angle deposition (GLAD) thin films are nanoengineered to meet the requirements of a variety of applications such as micro filters, sensors, and waveguides due to their unique frequency characteristics which cannot be achieved by conventional solid materials. For the design, it is necessary to understand the elastic properties of STFs. To facilitate this, we report on our newly developed advanced micro-scale vibration testing process. In the testing, specially designed micro-specimens with surface areas of tens by tens of microns are excited using a piezoelectric (PZT) actuator and the resonance frequencies are detected by a laser device in the vertical or lateral directions successfully. The anisotropy elastic modulus of STFs composed of helical nanosprings are identified on the basis of vibration testing. The thin film shows strong characteristic anisotropy that the solid one hardly can attain. The micro-scale testing technique can be extended to other materials and microstructures.

Abstract: A micro scale model of a solid oxide fuel cell (SOFC) involving the mass transfer together with the electrochemical reaction, the electron and ion transports through respective cylindrical shaped electron-and ion-conducting particles inside the electrodes was mathematically developed. The predicted cell performance was showed according to the operating and design condition. The effects of micro-scale electrode geometry on the cell performance were also taken into account. This present study reveals the working mechanisms of SOFC at the micro-scale level, while demonstrating the use of micro-scale relations to enhance the SOFC performance. The accuracy of the presented model was validated by comparing to already existing experimental results from the available literatures.

Abstract: The intrinsic complexity of granular materials stems from the fact that the characterizing variables at the micro-scale and the macro-scale are of different nature. Macroscopically, tensorial variables (stress tensor, strain tensor, fabric tensor) are commonly used based on Representative Volume Element (RVE), while vectorial variables (contact force, contact displacement, contact normal) are adopted at particle-scale. This paper mainly discusses some basic characterizations for these two scales, as well as their correlations. Numerical simulations using Discrete Element Method (DEM) are then conducted to show the evolutions of both microscopic and macroscopic variables during monotonic loading. It is indicated that the particle reorientations in the dense sample are much more pronounced than that in the loose one during shearing.

Abstract: Catalytic combustion of hydrogen/air mixture inside micro-tube was numerically investigated with detailed gas phase and surface catalytic chemical reaction mechanisms. Combustion characteristics for different reaction models, inlet velocity, tube diameter on surface catalytic combustion reaction, and comparison of numerical and experimental studies were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The effect of the surface catalytic reaction on the gas phase reaction can be divided to three types. The existence of catalytic wall will help to reach complete reaction in the micro-tube. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.

Abstract: Catalytic combustion of hydrogen/air mixture inside micro-tube was numerically investigated with detailed gas phase and surface catalytic chemical reaction mechanisms. Combustion characteristics for different reaction models, the influence of wall thermal conductivity, inlet velocity, and tube diameter on surface catalytic combustion reaction were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The higher wall temperature gradient for low wall thermal conductivity will promote the gas phase combustion shift upstream and will result in a higher temperature distribution. The micro-tube can be divided into two regions. The upstream region is dominated by the surface catalytic reaction and the downstream region is dominated by the gas phase combustion. With increasing inlet velocity, the region dominated by surface catalytic reactions expanded downstream and finally occupied the whole tube. The temperature of the flame core decreases with the decrease of tube diameter. Decreasing the tube diameter will enhance the surface catalytic reactions. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.

Abstract: Catalytic combustion of hydrogen/air mixture inside micro-tube was numerically investigated with detailed gas phase and surface catalytic chemical reaction mechanisms. Combustion characteristics for different reaction models, the influence of wall thermal conductivity, and inlet velocity on surface catalytic combustion reaction were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The higher wall temperature gradient for low wall thermal conductivity will promote the gas phase combustion shift upstream and will result in a higher temperature distribution. The micro-tube can be divided into two regions. The upstream region is dominated by the surface catalytic reaction and the downstream region is dominated by the gas phase combustion. With increasing inlet velocity, the region dominated by surface catalytic reactions expanded downstream and finally occupied the whole tube. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.

Abstract: As one of the key devices of finishing line of medium & thick plate, pinch roll is mainly used for clamping, transferring and specialized lengths. Nowadays, there generally exist the off-tracking phenomena of pinch roll apparatus, the shearing and lengthening quality of steel plate are heavily influenced and the normal production of enterprise are disturbed. This paper introduces the micro-scale behaviors of pinch roll apparatus, deeply analyzes the reasons that result in off-tracking of pinch roll, and points out the corresponding solutions, which can provide theoretical guide to the design of new-type pinch roll.