Applied Mechanics and Materials Vol. 889

Abstract: The compressive strength development always go along with the microstructure development in concrete through the process of cement hydration. In the hydrated products of cement, calcium silicate hydrate (C-S-H) forms a network of nanoparticles so C-S-H gel is the main compound giving compressive strength of concrete. As we know that C-S-H gel produced by the reactions with water of two main minerals in cement such as Tricalcium Silicate () and Dicalcium Silicate (). In addition, the increase of C-S-H content in concrete due to the pozzolanic reaction of the pozzolan with calcium hydroxide (CH). With the aim of this research is quantitative study of hydration of and in the Reactive Powder Concrete (RPC) together with its compressive strength development, three concrete formulas were estimated in this study which made from three different types of cement ownership different mineral compositions content were tested on compressive strength and on heat flux emitted from hydration process by isothermal calorimetry. The purpose of measuring heat flux emitted from chemical reaction process in concrete is to verify the hydration kinetic model for portland cement containing the silica fume. Basing on this simulation program, the amount of C-S-H gel in concrete is calculated. The research results showed that the the C-S-H content formed in binder paste of RPC is proportional to compressive strength development. The (Ordinary Portland Cement) OPC with higher content have compressive strength development earlier.

Abstract: Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydration products. By the process of hydration Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. The Therefore, the concrete properties always accompanies with the hydration degree of cement. This paper presents some experimental test results on how silica fume affects the cement hydration in cement pastes of the Reactive Powder Concrete as increasing levels of silica fume addition with the content from 0% to 30% of cement mass. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, rate of heat evolution, of binder pastes obtained by isothermal calorimetry (TAM-Air). In addition, the portlandite content, the hydration degree of pure cement, reaction degree of binder paste as well as reaction degree of silica fume were investigated. The quantitative assessment on these characteristics are due to the simulation of the hydration of Portland cement pastes containing silica fume.

Abstract: In recently years, Automotive industry in Vietnam is a fast growing sector, mainly reliant on domestic produces, assembly and sales. There are some details of cars that have been modeled, calculated to research and fabricate. Body vibration of the vehicles is one of the criteria to evaluate quality in the process of manufacturing and assembling automobiles. There are so many factors affecting on vibration of vehicles, in that body structure is one of the main causes. Up to now, automobiles manufactured and assembled in Vietnam have not yet had specific evaluations and standards on vibration. Determination of characteristic body vibration is a main part to reduce sound and vibration. In this paper, the modelling and calculating the body’s characteristic vibration of cars manufactured, assembled in Vietnam was researched. The body structure is designed by 3D model using commercial Catia Software. The model was transformed from Catia software to Hypermesh software, using finite element method to simulate. The calculation results of 25 measurement characteristic vibrations whose frequency is in range of 22.77 Hz to 97.21 Hz. The results are shown that, characteristic vibration of state 1 and 2 significantly influence the noise of the body. This is also the basis for optimal analysis of the body structure to control the vibration and noise of automobiles.

Abstract: Non-uniformly polarized piezoceramic materials can be used in effective energy harvesting devices. Axisymmetric and plane models of electro elastic bodies were studied using applied theory and finite element method (FEM). Applied theory for devices made of parts with longitudinal and transverse polarization was developed. It was based on bending of electro elastic plates models. Numerical experiments for FEM models were performed in ACELAN package. Comparison of applied theory and FEM results showed satisfactory accuracy. First model consists of three parts: transversally polarized part and two parts with opposite longitudinal polarization. It was compared with uniformly polarized model of the same size. Both electro-mechanical coupling coefficient and output voltage produced by forced oscillations were greater in case of non-uniform polarization. Geometrical parameters – such as relative size of parts, electrode positioning and thickness of the device - were varied in series of numerical experiments to determine range of applicability for developed models and to perform initial analyses of most effective set of parameters. Model was analyzed for different boundary conditions. Automation tools for applied theory computations were developed. Second model is a disk with transvers polarization in the central part and opposite longitudinal polarization in two layers of outer part. It also showed output voltage growth. Appling polarization to the device is an important part of manufacturing process. In some cases, parts can be polarized with imperfections as incomplete polarization of deviation of polarization direction. Polarization process for predefined model geometry and electrode scheme can be performed in ACELAN package. Vector field of the polarization were transferred to finite element meshes and used for solving problems with non-uniform polarization. Difference between simplified block model presented in applied theory and full model solved with FEM was estimated. Some problems can be reduced from full to simplified model without significant accuracy loss. Described programs, models and techniques are developed for advanced analysis of non-uniformly polarized energy storage devices.

Abstract: Most of types of laser distance measuring instrument cost hundreds of thousand dollars such as Atos scanner or Depth Camera that gives depth maps of space very fast. However, the handling is too complicated for non-professional users and the utilization of 3D reconstruction is very limited. This paper introduces a workflow of 3D reconstruction using a new cheaper instrument, the Microsoft Kinect. The first experiences with Microsoft Kinect v2 sensor are presented, and the ability of 3D modelling for mechanical parts is investigated. For this purpose, the point cloud on output data as well as a calibration approach are demonstrated.

Abstract: Flexure hinges have been used in many precision mechanisms where repeatable, friction free motion and high precision are required. Many kinds of flexure profiles have been proposed during the past decade. This paper presents a new type of flexure hinge which combines circular longitudinal axis beams to form hollow joint. This novel design will help to improve the range of motion, reduce stress level and increase the maximum load before yielding. Due to its special design, the cavity inside the hinge can also be filled with an elastomeric filler material to provide vibration damping. In order to synthesis this hinge, shape optimization integrating genetic algorithm and response surface methodology is used. The optimization procedure is programmed in MATLAB whereas finite element analysis in ANSYS is also embedded into the codes to enhance the calculation process. The new flexure hollow hinge is compared to the conventional straight-axis solid hinges (circular, elliptical and corner-filleted flexure hinges) in terms of stiffness, rotational precision and stress levels. It is also supposed that this new design would increase the precision of the mechanism due to reducing the parasitic motion. Finite element analysis in ANSYS is used to verify for the viability of the design before it can be fabricated and tested.

Abstract: In this study, a dual-disc magneto-rheological brake (MRB) with two coils placed on each side housing is proposed for a cycling training system. The cycling training system is integrated a positioning system to simulate the cycling process in different slope ranging from 0 to 15⁰. By adjusting position of the bicycle, braking torque of the brake, a cyclist can experience different riding condition such as riding on flat road or steep road with the slope up to 15^o.

Abstract: As known, the aim of this paper is to present the field hysteresis behavior of a BMR actuator via identifying the hysteresis model. In order to realize this purpose, firstly, a BMR actuator is manufactured. The feature of this actuator has two disks which are rotated in opposite direction at the same speed and two coils are placed directly on each side of the housing. The two input signals consisting of velocity and current are applied to the BMR actuator to investigate the characteristic of this actuator. Secondly, a proper Preisach hysteresis model is built with two inputs and one output to estimate the torque of the actuator. Finally, the accuracy and the effectiveness of the model are demonstrated by the errors comparison between the constructed hysteretic curves and the experimental ones

Abstract: In this research, a shear-mode MR damper that can replace conventional passive damper of a front-loaded washing machine is designed, manufactured and an experiment based model is employed to characterize hysteresis behavior of the damper. Firstly, an optimized MR damper for front loaded washing machine is manufactured and an experimental system is set up for testing hysteresis behaviour of the damper. The experimental test is then conducted and presented. From experiential results, hysteresis of the damper is investigated and a suitable hysteresis model is proposed for the damper. The proposed hysteresis model of damper is then evaluated through experimental results.

Abstract: In the summer, the cars are exposed to strong sun when it is parked outdoor without the sunscreen, it has had accelerated the auto parts, interior aging and damage. In order to prevent that exposure, the solutions showed such as car awning, car sunshade and car sunscreen etc…, the above devices showed low effectivity for car sun protection. This paper will study effects of cooling system for outdoor sparking car using solar panels cover. A new covering car with multi-layers structure attaching flexible solar panels were designed to increase effectively sun protection, the nitrile rubber foam divided the light and heat radiation of the sun, the flexible solar panel converted solar energy into electric energy and supplied for the air conditioner to regulate inside car temperature. The results showed that, at nitrile rubber foam layer thickness of 4mm, the car maximum temperature of 41.5°C was observed for solar panel-awning-nitrile rubber cover which is much lower than it is exposed directly by sun radiation and commercial cover. The six solar panels (100W) were adapted on car cover, the solar electric energy supplied enough for a mini air conditioner of 340W. Performance of cooling system using solar panels was also investigated and it showed that the temperature inside car could be down to 24°C.