Effects of water and temperature variations on deformation of limestone aggregates,cement paste,mortar and High Performance Concrete (HPC)

The present paper deals with the dimensional variations of limestone aggregates, cement paste, mortar, and High Performance Concrete (HPC) made with these constituents, when subjected to temperature changes in drying and sealed conditions. Variable water contents are studied for each material. The overall experimental results were obtained using strain gauges and Digital Image Correlation technique (DIC) is also applied for one configuration test. A significant difference between coefficients of Thermal Expansion (CTE) of cement paste and aggregate is observed, which leads to a large differential thermal deformation, able to explain thermal damage for temperatures between 50 °C and 100 °C. Water content has a great influence on material thermal dilation, causing delayed deformations especially for temperatures above 60 °C and for initially saturated samples. These experimental data may allow Thermo-Hydro-Mechanical models to be improved so that the in-situ long term behaviour of concrete can finally be predicted. The results confirm the dilation coefficient contrast between paste and aggregate, and also show that this contrast is markedly affected by the drying conditions and the initial state of saturation.     

Photocatalytic activity and stability of TiO2/ZnAl layered double hydroxide based coatings on mortar substrates

The surface properties and photocatalytic activity of the cement and pozzolanic mortar samples coated with TiO₂/ZnAl layered double hydroxides were studied with the intention to design suitable protective, hydrophilic coatings. In order to underline the existing correlation between the water uptake characteristics and the surface features, the coated mortars were subjected to water absorption test by capillarity, to photo-induced surface water absorption test and to photo-induced hydrophilicity test by contact angle measurements. The self-cleaning behavior of the mortar systems was evaluated by monitoring the photocatalytic rhodamine B removal efficiency in correlation with the development of photo-induced surface hydrophilicity. The coating durability was assessed towards the weathering effect of rain (essential for the coating self-cleaning properties). The positive result of the coating deposition was the improvement of photocatalytic activity, photo-induced hydrophilicity and the decrease of mortar systems surface roughness. The study revealed that the developed coating promotes self-cleaning effect.     

Relation between carbonation resistance,mix design and exposure of mortar and concrete

When cement with mineral additions is employed, the carbonation resistance of mortar and concrete may be decreased. In this study, mortars containing mineral additions are exposed both to accelerated carbonation (1% and 4% CO₂) and to natural carbonation. Additionally, concrete mixtures produced with different cements, water-to-cement ratios and paste volumes are exposed to natural carbonation. The comparison of the carbonation coefficients determined in the different exposure conditions indicates that mortar and concrete containing slag and microsilica underperform in the accelerated carbonation test compared to field conditions. The carbonation resistance in mortar and concrete is mainly governed by the CO₂ buffer capacity per volume of cement paste. It can be expressed by the ratio between water added during production and the amount of reactive CaO present in the binder (w/CaO_reactive) resulting in a novel parameter to assess carbonation resistance of mortar and concrete containing mineral additions.     

Ternary blending of cement with fly ash microsphere and condensed silica fume to improve the performance of mortar

The addition of condensed silica fume (CSF) to fill into the voids between cement grains would release the water entrapped there to form water films for lubrication. However, the large surface area of CSF would thin down the water film thickness (WFT). By adding also a cementitious material that is finer than cement but not as fine as CSF, such as fly ash microsphere (FAM), the water entrapped in the voids could be released without excessively increasing the surface area. This may produce a larger WFT and better flowability than adding CSF alone. In this research, ternary blending of cement with FAM and CSF was studied by testing mortar mixes with different amounts of FAM and CSF added. It was found that the WFT is the key factor governing the properties of mortar and that ternary blending of cement with both FAM and CSF does offer some advantages.     

Interaction of TEOS with cementitious materials: Chemical and physical effects

This study explored the effectiveness of tetraethyl orthosilicate (TEOS) as a Portland cement mortar consolidant to verify whether it meets the requirements for use in cultural assets. TEOS was found to raise cement mortar strength, lower its porosity and permeability and occasion minimal alteration in its appearance, an indication of its suitability to conserve heritage mortar works.FTIR and ²⁹Si MAS NMR studies supported the notion that TEOS interacts with the hydrated phases of the cement, portlandite and C–S–H gel. The reaction product between portlandite and TEOS was C–S–H gel and between TEOS and C–S–H gel was a gel with longer chain.     

内嵌碟簧型自复位防屈曲支撑性能试验及其恢复力模型研究

提出了一种内芯与约束构件均为型钢的全钢装配式防屈曲支撑,该支撑具有全装配、内芯可更换、工艺简单、造价低廉和可用于既有构件加固等优点。钢内芯由2个角钢与加劲板组成T型截面,外约束构件由角钢和盖板通过螺栓连接形成。对6个该支撑试件进行拟静力试验,讨论其滞回性能、抗震性能及破坏机理,并分析内芯上设置填板、内芯与约束构件的间隙、内芯双角钢之间的间距以及限位方式对滞回性能的影响。结果表明,该支撑的实际性能与设计性能基本一致,具有稳定的滞回性能;在支撑中间设置填板对支撑的滞回性能基本没有影响;内芯与约束构件的间隙及内芯双角钢之间的间距过大会降低支撑的滞回性能;采用中部限位方式的支撑滞回性能优于端部限位方式。对试件的抗震性能分析表明,该支撑具有较好的延性和累积塑性变形能力,可作为阻尼器应用于结构中。通过分析破坏模式发现,加劲板末端的焊缝应力集中会造成支撑的断裂位置由屈服段转移至止焊处;设置中部限位卡可以减小摩擦力的不利影响。     

人工耳蜗非实时研究平台开发与验证

人工耳蜗帮助超过40万人恢复了部分听力,但其性能仍有较大提升空间,且电听觉机理仍有待进一步揭示。针对诺尔康人工耳蜗系统开发了非实时研究平台。为了验证平台的有效性,对成年植入者开展了电听觉基础心理物理实验(位置音高和包络音高)和噪声中的言语接受阈测量实验。心理物理结果显示,被试者可以按照电极位置从蜗尖到蜗底或按照幅度调制频率从50~200 Hz,产生音高上升的感觉。言语测试显示,基于该平台实现的策略,能提供与临床处理器相当水平的噪声中言语接受阈。该平台可以帮助研究者快速开展电听觉心理物理和信号处理策略方面的研究。     

Modeling of R-410A variable capacity compressor with Modelica and experimental validation

This paper presents an analysis of modeling methods for a short cycling, R-410A scroll compressor. Two parametric efficiency models of the short cycling scroll compressors are investigated, one with steady-state mean, and one with time varying efficiencies. Additionally, a dynamic model of a short cycling scroll compressor that incorporates scroll geometry, leakage, and a mathematical approximation of the digital capacity mechanism has been developed and verified against experimentally obtained data. Agreement with data for all methods was generally good, though in the dynamic model refrigerant mass flow was found to match observations when neglecting leakage. To validate the proposed models, a novel experimental testbed was developed by retrofitting a 15 ton nominal capacity rooftop heat pump with a short cycling scroll compressor. Unit operating conditions were varied in a parametric fashion using a large scale psychrometric chamber and the compressor transient performance was evaluated at full and part loads.     

Development and validation of an automated FEM-based design optimization tool for continuum compliant structures

International Journal of Mechanics and Materials in Design - This paper presents a design optimization method for continuum compliant structures. The developed optimization tool enables automated...     

Development and validation of an analytical method for tensile strength determination of fibrous bulk solids

The increasing significance of products consisting of elongated particles or fibres along with a lack of understanding flow properties of fibrous bulk solids in processes urge for appropriate test procedures.Therefore, a tensile tester was designed with respect to the special needs in terms of test techniques of those bulk solids. The procedure of tensile strength determination was tested with regard to several possible influencing factors. Following from that, the manner of filling and filling height were identified to have the greatest influence on results. Furthermore, it is shown that the developed load system is capable of improving the repeatability of test results for fibrous bulk solids.Based on the derived standard procedure, systematic tests were carried out on beech and spruce chips in three different fractions each as well as model materials such as polypropylene fibres and differently sized bunches of glass fibres. The biomass materials have been characterised by dynamic image analysis prior to and after experiments resulting in particle size and shape factor distributions. It is found that tensile strength is affected by particle shape, size, roughness and interparticle contact area.     

Simulation and experimental validation of acoustic properties of hollow sphere structures

Customers nowadays regard the noise and vibration behavior as an essential product property. Cellular character materials, in particular hollow sphere structures, are predestined to absorb sound in a very efficient manner due to their cellular character. Depending on the constituent material, the geometric parameters like the diameter of the spheres, the thickness of the walls and the assembling schema of single spheres, the absorption coefficient can be reduced to very low levels. In contrast to other cellular materials, the frequency and bandwidth can actively be influenced by the variation of the above mentioned parameters. In order to predict the acoustic behavior of a structure, FE or CFD analyses are used as standard tools. In addition, there exist some parameter based models, e.g. the BIOT theory, which characterizes the absorption, transmission and reflection coefficients using a few macroscopic parameters. Within this contribution, the acoustic properties of hollow sphere structures are investigated by a so‐called virtual material laboratory GeoDict (by Math2Market GmbH, originally by the Fraunhofer Institute for Industrial Mathematics). The results for the absorption and reflection coefficients are compared to those gained by classical analysis methods and experiments based on Kundt's tube.     

Numerical modelling of tidal flows in complex estuaries including turbulence: an unstructured finite volume solver and experimental validation

In this paper an unstructured finite volume model for quasi‐2D tidal flow with wet–dry fronts and turbulence modelling is presented, and applied to the Crouch–Roach estuarine system (Essex, U.K.). Two depth averaged turbulence models, a mixing length model and a k–ε model, are used in the numerical computations. An additional limiter to the production of turbulence due to bed friction is introduced in order to improve the performance and numerical stability of the model near wet–dry fronts. In addition to a first‐order and a second‐order schemes, an hybrid second‐order/first‐order upwind scheme which improves the accuracy of the first‐order scheme while maintaining a good numerical stability is used to discretize the convective flux. Numerical results are compared with observed current speed and water level data, with particular reference to the ability of the model to reproduce shallow water tidal harmonics. Copyright © 2006 John Wiley & Sons, Ltd.     

Structural-modelling and experimental validation of percolation threshold for nanotube-polyurethane shape memory system

This paper presents a comprehensive structural orientation model to facilitate a hypothesis for the percolation threshold of nanotube-polyurethane systems, utilising Monte Carlo simulations. It considers a representative volume for nanotubes of diverse sizes and aspect ratios, uniformly dispersed at random positions and orientations. Continuous conductive networks formulated with the representative elements were identified for various filler contents, modelled and predicted percolation threshold of 0.19%. Experimental percolation threshold obtained was 0.21%, which determines the reliability of the model and furthermore, the model is broad and can, therefore, be extended to any nanocomposite, to predict the percolation threshold. The shape memory effect of the nanotube-polyurethane nanocomposite was evaluated for thermal and electrical stimuli, and the recovery efficiencies arrived to 95 and 98% respectively.     

Microstructure and composition evolution of a single-crystal superalloy caused by elements interdiffusion with an overlay NiCrAlY coating on oxidation

MCrAlY(M=Ni and/or Co) overlay coating is widely used as a protective coating against high temperature oxidation and corrosion. However, due to its big difference in chemical composition with the underlying superalloy, elements interdiffusion occurs inevitably. One of the direct results is the formation of interdiffusion zone(IDZ) and secondary reaction zone(SRZ) with a high density of fine topological closed-packed phases(TCPs), weakening dramatically the mechanical properties of the alloy substrate. It is by now the main problem of modern high-temperature metallic coatings, but there are still hardly any reports studying the formation, growth and transformation of IDZ and SRZ in deep, as well as the precipitation of TCPs.In this work, a typical NiCrAlY coating is deposited by arc ion plating on a single-crystal superalloy N5.Elements interdiffusion between them and its relationship on microstructure were clarified. Cr rather than Al from the coating diffuses into the alloy at high temperatures and segregates immediately beneath their interface, contributing largely to the formation of IDZ. Simultaneously, diffusion of Ni from the deep alloy to IDZ leads to the formation and continuous expansion of SRZ.     

Development and validation of an instrument to evaluate the content effectiveness of video games: a pilot study

Storytelling is the key design element in game design. Content preparation, which examines ‘what information users want’, yielded valuable data concerning the necessary attributes of storytelling in a web-based interface. After identifying 17 basic components of video games, the authors of this paper were able to categorise the components based on guidelines reported from the literature review into four major factors: game play; game setup; game control; and game help. In order to evaluate these factors, an experiment was conducted that required participants to evaluate three PC games selected for their distinctiveness and popularity: Need for Speed VII: Most Wanted; StarCraft; and Diablo II. Twelve highly skilled video game players were selected as participants. After playing each game, participants were asked to complete a 56-question survey and the results of a multiple regression analysis revealed that all items of development and content preparation are not of equal importance. Fantasy, pressure, reward/bonus, next step, pressure, status, menu, goal, character, hints and instruction are the components that have the most significant impact on user satisfaction.     

A simple but effective FE model with plastic shot for evaluation of peening residual stress and its experimental validation

We propose a practical finite element (FE) model for evaluation of peening residual stress. The model aims to produce a solution approaching the endeavored 3D FE solution. We investigate the effect of physical factors including material damping, dynamic friction and strain rate. The kinematical factors including shot diameter and impact velocity are also considered. Integrating those factors and plastic shots, we set up an effective FE model. Based on the arc height and coverage matching with the Almen saturation curve, impact velocity needed for FE analysis is determined. The model is found to provide the solution comparable with the 3D multi-impact FE solution and the experimental XRD result.     

CFD simulation and experimental validation of a GM type double inlet pulse tube refrigerator

Pulse tube refrigerator has the advantages of long life and low vibration over the conventional cryocoolers, such as GM and stirling coolers because of the absence of moving parts in low temperature. This paper performs a three-dimensional computational fluid dynamic (CFD) simulation of a GM type double inlet pulse tube refrigerator (DIPTR) vertically aligned, operating under a variety of thermal boundary conditions. A commercial computational fluid dynamics (CFD) software package, Fluent 6.1 is used to model the oscillating flow inside a pulse tube refrigerator. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary conditions are sinusoidal pressure inlet by user defined function at one end of the tube and constant temperature or heat flux boundaries at the external walls of the cold-end heat exchangers. The experimental method to evaluate the optimum parameters of DIPTR is difficult. On the other hand, developing a computer code for CFD analysis is equally complex. The objectives of the present investigations are to ascertain the suitability of CFD based commercial package, Fluent for study of energy and fluid flow in DIPTR and to validate the CFD simulation results with available experimental data. The general results, such as the cool down behaviours of the system, phase relation between mass flow rate and pressure at cold end, the temperature profile along the wall of the cooler and refrigeration load are presented for different boundary conditions of the system. The results confirm that CFD based Fluent simulations are capable of elucidating complex periodic processes in DIPTR. The results also show that there is an excellent agreement between CFD simulation results and experimental results.     

Development and validation of NIR-chemometric methods for chemical and pharmaceutical characterization of meloxicam tablets

Context: Near-Infrared (NIR) spectroscopy is an important component of a Process Analytical Technology (PAT) toolbox and is a key technology for enabling the rapid analysis of pharmaceutical tablets.

Objective: The aim of this research work was to develop and validate NIR-chemometric methods not only for the determination of active pharmaceutical ingredients content but also pharmaceutical properties (crushing strength, disintegration time) of meloxicam tablets.

Materials and methods: The development of the method for active content assay was performed on samples corresponding to 80%, 90%, 100%, 110% and 120% of meloxicam content and the development of the methods for pharmaceutical characterization was performed on samples prepared at seven different compression forces (ranging from 7 to 45?kN) using NIR transmission spectra of intact tablets and PLS as a regression method.

Results: The results show that the developed methods have good trueness, precision and accuracy and are appropriate for direct active content assay in tablets (ranging from 12 to 18 mg/tablet) and also for predicting crushing strength and disintegration time of intact meloxicam tablets.

Discussion: The comparative data show that the proposed methods are in good agreement with the reference methods currently used for the characterization of meloxicam tablets (HPLC-UV methods for the assay and European Pharmacopeia methods for determining the crushing strength and disintegration time).

Conclusion: The results show the possibility to predict both chemical properties (active content) and physical/pharmaceutical properties (crushing strength and disintegration time) directly, without any sample preparation, from the same NIR transmission spectrum of meloxicam tablets.