Papers by Author: Yan Qiu

Abstract: The residual stress on the surface of tempered glass is very important for its safe service and the quality control. In this study, the sphere indentation and grazing angle surface polarimetry are compared to evaluate the surface residual stress of tempered glass. The test results showed that the measured results are similar, but the data dispersion of the sphere indentation method is little larger. The main reason is stemmed from the different tested area, of which residual stress is a mean value measured by the grazing angle polarization method. Yet for the indentation method, the residual stress in the micro region of glass is more susceptible to the inhomogeneity of material itself. However, it is difficult to select the right multiple optical path difference for the grazing angle polarization method, and it is only applicable when inspecting the tin surface of tempered glass, as well as the tin surface examination instrument. Thus, as a nondestructive testing method, indentation method can be widely used to measure the surface residual stress of glass without being influenced by other factors.

Abstract: The purpose of this paper is to study the durability and performance of photovoltaic glass components in salt spray environments. So it can be founed that a reasonable solution to increase the life of PV glass and to ensure the continuity of its performance. The PVB film was used for the comparison and performance analysis of the salt spray treatment of salt water at one week and two weeks. The PVB film was tested for the light transmission performance and other mechanical properties changes of PVB film. It was shown that the strength of the PV module sample after one week of salt spray treatment is 26.48508MPa, and the strength of the sample after two weeks of salt spray treatment of the PV module is 13.35496MPa. The direct sunlight transmittance ratio of A groups (300 ~ 2500nm) is 94.50. Direct sunlight transmission ratio of B groups (300 ~ 2500nm) is 92.30. The results show that the light transmission performance of the PV module after salt spray cycle is reduced by 2.3%, and the strength is obviously decreased by 49.57%.

Abstract: Tensile bond strength is one of the most significant properties for structural silicone sealants used in the glass curtain walls. During the service process, aging of the silicone sealants shall be involved in comprehensive actions of environment factors, e.g. temperature, humidity, and ultraviolet light etc. In this study, artificial accelerated aging test was conducted to make clear the development of tensile bond strength, Shore hardness and elongation. The test results show that: (i) the specimens under damp-heat test have more degeneration than specimens under humidity-freeze test; (ii) the environment of high temperature and high humidity leads to the change of tensile bond, Shore hardness, elongation, and results in interfacial failure of samples.

Abstract: Surface stress measurement is the key factor of the quality control for tempered glass. The nondestructive test of glass surface stress is based on the character of stress birefringence in glass. The basic principle of the measurement and test methods are introduced. The optical waveguide effect of tin-diffused layers plays a key role in prevalent surface stress measurements. The apparatus are compared for optimizing the testing devices. A portable digitalized surface stress meter based on optical waveguide effect is developed, which can work in severe optical conditions and reduce operation difficulty. The calibration record shows good linearity.

Abstract: The elastic modulus and fracture strength at ultrahigh temperatures over 1500°C is very important for Ultrahigh temperature ceramics (UHTCs), but no available method can be used so far because of the limitation of the testing equipments. In this work, a novel testing equipment was developed to determine the elastic modulus and fracture strength (bending, tensile and shear strength) of ceramics from 1500 °C to 2200 °C. To check the availability and reliability of this equipment, several typical UHTCs including C, C/C fiber woven composite and C/SiC ceramic composite, were used as the testing samples. The results indicate that this new designed testing equipment is a good and feasible for evaluating the ultrahigh temperature mechanical properties of ceramics over 1500 °C in vacuum or in air.

Abstract: Temperature and humidity cycles test of photovoltaic glass modules are carried out by different cycling time. The change of transmittance, interface and strength of photovoltaic glass modules are compared by different experiment time. With the increasing of temperature humidity cycle time of photovoltaic glass modules, the light transmittance of influence is more serious, and stress strength of the longest cycle is weakened 32.84% than one cycle. Therefore, the influence of photovoltaic glass modules under different temperatures and humidity conditions is more serious. So it is very necessary to study durability and safety under temperature and humidity cycles of photovoltaic glass, related to power generation efficiency of the photovoltaic glass modules.

Abstract: Evaluation of the mechanical properties at ultra-high temperatures for ceramic composites is necessary and important for the safety of designing the ceramic components. In this work, a new and novel test method named as local ultra-high temperature together with applied load method (LUHTAL), was developed to determine the tensile, compressive, bending strength and fracture toughness of ceramic composites. The four point bending load was conducted to measure the bending strength and fracture toughness of ceramic composites after the center of the sample was heated up to about 1500-2000°C by oxygen-assisted spray combustion. To check the availability and reliability for this method, typical ceramic materials including ZrB₂/SiC and C/SiC fiber reinforced composite coated with Si, were used as the testing samples. It is indicated that this method is good and feasible for evaluating the mechanical properties of the ceramic composite at ultra-high temperatures in air.

Abstract: It is significant to explore the fatigue contact damage of bi-layer ceramic composites in order to improve the long-time mechanical reliability of bi-layer structured dental restorations. In this study, Hertz contact test was used to compare the fracture modes and the ability of anti-fatigue damage of zirconia and alumina bi-layer composites, to analyze the effect of loading rate and other factors on the damage mechanisms of bi-layer ceramic composites. Cyclic spherical fatigue loading was put on the bi-layer alumina and zirconia composites with different substrates. The samples were observed by high depth of field stereomicroscope and digital optical microscope after test. The results showed that the fatigue contact damage mode of zirconia bi-layer composite was the porcelain fracture from radial cracks without the damage of zirconia core. The fatigue contact damage mode of alumina bi-layer composite was the alumina core failure from radial cracks as the function of contact load. For both of zirconia and alumina bi-layer samples, the number of cycles to the sample failure as the function of same maximum contact load with high loading rate was obviously smaller than low loading rate. The mechanical properties of the substrate materials had limited effects on the number of cycles to the failure of both zirconia and alumina bi-layer samples from contact-induced radial cracks as maximum contact load with low loading rate. The ability of the zirconia bi-layer composites to resist fatigue damage was much higher than that of the alumina bi-layer composites.

Abstract: The residual strength of dental porcelain discs were test after cycling fatigue compressive load in this study. Moreover, the effects of stress intensity and cycle frequency to the damage of porcelain were explored. The porcelain specimens were bonded to the epoxy resin blocks, with 12.5mm height. The cycling fatigue contact loads were subjected on the porcelain surfaces of the bi-layer composites with silicon nitride spheres of radius 2.5mm. The crosshead speed was 6mm/min. The top load value was varied from 10N-20N in every load cycles. The cycling number was from 50-300. After cycling test, the residual strength of all porcelain samples was measured by bi-axial bending test. Fractured pieces of the specimens were collected and examined with optical microscope and SEM. On the fracture surfaces of porcelain discs after bi-axial bending test, Hertz cone cracks were presented due to cycling fatigue load. The result showed that the residual strength of dental porcelain had negative correlation with the fatigue load values and cycles. When the fatigue load cycles were lower than 100, the residual strength of porcelain presented no significant different under 10 or 20N fatigue load. In contrary, when the fatigue load cycles were over 100, the residual strength of porcelain was much lower under 20N fatigue load than 10N fatigue load. Based on the limited results of this study, the conclusion could be drawn that the residual strength of porcelain under fatigue compressive stress was main determined by load cycles in the range of small load values. The porcelain could be destroyed after very few cycles if the load is up to a critical value.

Abstract: The conventional method of producing porcelain standard disc specimens is based on the dental lab method for bilayer ceramic crowns, in order to reflect the clinical using condition. However heavy task is facing to the researchers, which is producing a large amount of the specimens efficiently. The press molding method is used to produce dental porcelain disc specimens in this study. Then, the basic mechanical properties of two groups of porcelain specimens were tested respectively, comparing with handmade and press molding method. The density was measured by Archimedes' method, the flexural strength was tested by biaxial bending test, and the hardness was checked by microhardness tester. The micro features of the specimens before and after bending test were observed under optical microscope and SEM. The results showed that there was no significant difference in the flexural strength, microhardness and density of porcelain discs made by two methods. Air pores were found in all specimens with size between 5-50 micrometers. The size and distribution of pores in the specimens by press molding method are more homogeneous than handmade method. Producing dental porcelain discs for laboratory testing specimens by press molding method was much easy than handmade method. Furthermore, the mechanical properties and microstructures of the specimens made by handmade method and press molding method were almost same.