Papers by Author: Yi Wang Bao

Abstract: Simulation analysis of thermal performance for vacuum glazing was conducted in this paper. The heat conduction through the support pillars and edge seal and the radiation between two glass sheets were considered. The heat conductance of residual gas in vacuum gap was ignored for a low pressure of less than 0.1Pa. Two pieces of vacuum glazing with sizes of 0.3 × 0.3 m and 1.0 × 1.0 m were simulated. In order to check the accuracy of simulations with specified mesh number, the thermal performance of a small central area (4mm×4mm) with a single pillar in the center was simulated using a graded mesh of 41×41×5 nodes. The heat transfer coefficients of this unit obtained from simulation and analytic prediction were 2.194Wm^-2K^-1 and 2.257Wm^-2K^-1 respectively, with a deviation of 2.79%. The three dimensional (3D) isotherms and two dimensional (2D) isotherms on the cold and hot surfaces of the specimens were also presented. For a validity of simulated results, a guarded hot box calorimeter was used to determine the experimental thermal performance of 1.0m×1.0m vacuum glazing. The overall heat transfer coefficients obtained from experiment and simulation were 2.55Wm^-2K-1 and 2.47Wm^-2K^-1 respectively, with a deviation of 3.14%.

Abstract: Laminated glass and photovoltaic laminated glass are widely used in architecture. The interfacial bonding strengths between poly(vinyl butyral) (PVB) and glass were investigated by the cross-bonding method from room temperature to -50 °C. The loading speed was 5 mm/min, and the cooling speed was about 0.5 °C/min. The testing sample was hold at each temperature for half an hour. It was revealed that the testing temperature had great effect on the bonding strength. At room temperature, the tensile bonding strength was 11.49 MPa and the shear bonding strength was 6.61 MPa. With the temperature decreased from RT to -50 °C, the tensile bonding strength was decreased by 66.81%, but the shear bonding strength was increased by 212.16%. From RT to -30 °C, the change rates of the tensile and shear bonding strength bonding strength were 65.57% and 172.68% respectively, only 3.61% and 14.48% from -30 °C to -50 °C. The mechanism for the bonding strength depended on testing temperatures from RT to -50 °C was also discussed.

Abstract: Spherical impact indentation tests with different impact angles (90°, 60°, 45°, and 30°) was carried out to understand the effect of impact angles on damage degree of cement clinker. A linear rail which can adjust angle to alter impact velocity was used to guide the slipping impact head to impact the sample. The different steel wedge was used to change the impact angle. It is found that the area of damage surface for cement clinker is most serious the peak impact force for surface damage decreases but the contact indentation becomes longer with decreasing impact angle when the impact angle is 45°. Under almost the same impact velocity, the smaller the impact angle, the higher the impulse, the longer contact time, and the peak impact force of 45° is maximum.

Abstract: Bi-layer all-ceramic dental crowns comprise an inner core made of alumina or zirconia and an outer porcelain shell. The veneer safe from damage is mainly depended on the properties of core materials due to the poor strength and toughness of porcelain. The fracture modes and crack transformation of zirconia/porcelain and alumina/porcelain bi-layer composites reveal the potential feasibilities of improving the fatigue life of all-ceramic restorations. The failure modes of bi-layer composites were confirmed under cyclic spherical fatigue loading by dynamic microcosmic observation. Crack modes and evolvement of bi-layered composites were explored inflecting with fatigue load, cycles, frequency and water environment. Microcosmic morphology of the samples was observed by high depth of field stereomicroscope to determine degree and modes of fatigue damage. The appearance of cone cracks of porcelain surface was almost consistent in both of zirconia and alumina bi-layer composites. However, the pattern and process of the damage are different under cycle fatigue load. Furthermore, process of fatigue damage of bi-layer composites were observed to failure rapidly under water environment in both of zirconia and alumina bi-layer composites.

Abstract: Building-integrated photovoltaics (BIPV) is a relatively recent new application of photovoltaic (PV) energy technologies whose energy output is affected by many design-related factors including PV module technologies, installation orientation, tilt and shadow range of solar panels. The shading analysis of a residential house’s PV roof in Beijing was conducted by using building analysis program Autodesk Ecotect 2010. Analysis result shows that there is no shadow on the PV roof from 9a.m to 4p.m in winter solstice when the solar altitude angle reaches minimum, which ensures almost no shading losses for the PV modules over the year. The differences in monthly energy output were compared in the case of different installation tilt of solar panels and PV module technologies. Finally, the contribution to the building energy of the PV roof was discussed. The results show that appropriate design and selection of PV modules can compensate for the energy requirements for building heating and cooling to some extent.

Abstract: It is revealed that the conventional reduced modulus used in depth-sensing indentation tests is invalid for a flat-ended cylindrical indenter due to the fact that the contact area during the loading is a constant irrelative to load. The load-displacement curve of flat punch is related to the length of the punch and the ratio of the elastic modulus of the indenter to the specimen (the modulus ratio Ei/E). Furthermore, theoretic analysis and finite element simulation demonstrated that, for conical indenter, the measured hardness from depth-sensing indentation tests would increase with increasing modulus ratio because the load increased with the ratio for the same displacement.

Abstract: Glass/ zirconia laminated material is the most commonly used material in the field of dental restoration, although the biocompatibility of such material has been subject to lots of research and the mechanical compatibility and durability have not been deeply researched. This paper, by the research on the contact stress of static and dynamic surfaces of the ceramic material, reveals the physical meaning of damage and fatigue at the interface of material; through contacting with the sphere indentation test and by the investigation of fatigue and damage of the surface and interface of such material in the corresponding time scale as well as by the use of acoustic emission monitoring for detecting the damage process and crack propagation process within the detection layer and the laminated ceramic surface, the time of occurrence and corresponding load can be obtained, which plays an importantly practical role in resolving the forecasting of the changes in material damage and the analysis of fatigue.

Abstract: Bond behavior plays an important role in developing load carrying capacity and ductility for concrete structures. Studies on bond behavior of single bars have been extensively conducted and whereas those on steel meshes are rather limited. This paper reports an experimental study on the bond behavior of concrete blocks with steel meshes. By varying the rib pattern and bar size of the steel mesh, their influence was examined.

Abstract: This paper describes the temperature effect on breakage behavior of cement clinker by single particle compression test. Portland cement clinker nodules, with mean diameter of 22 mm, were chosen as the test specimens. They were treated with heating to the temperatures of 300°C and 1000°C or cooling to -20°C and -88°C, respectively. The breakage behaviors were compared with the untreated nodules. The compression force-displacement profiles show that the treated nodules are easier to be broken because of the micro-cracks. Scanning electron microscope images illustrate that the clinker microstructures were changed after heating or cooling treatments. However, the main components are still the same according to the examination of X-ray diffraction. Comparing the heating with the cooling processes, it is more possible to use the waste heat of clinker sintering stage to reheat the clinker nodules, and these new reheating circuits may improve the energy efficiency of comminution.

Abstract: Initiation and propagation of Hertz crack in glass was investigated by combining sphere indentation test and optical microscope under a transparent testing platform. Thus, the process of the crack growth in glass and the critical indentation load and contact crack radius could be determined conveniently. Indentation fatigue tests were carried out to understand the contact damage resistance, the fatigue cycle number for cracking increase with decrease of the fatigue load. This simple testing method is demonstrated convenient and available for calculating the surface local strength of glass in situ via measurements of the critical load and contact crack size.