Papers by Author: Li Tian

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: Using the interactive software, this study was mainly focused on developing a 3-D joint shape after the as-reflowed soldering which is the one of chief factors affecting the reliability. From the results, the soldering process can be simulated and observed directly. By changing the various conditions and constraints, such as surface tension, wetting angle and specific gravity, it makes a comparison between the simulated result and the experimental one. The simulated parameters are based on those of the traditional eutectic Sn-Pb solder. After slicing and comparing the different profiles of the simulated shape, the 3-D simulated geometry fits well with the experimental one.

Abstract: The correlations between of lightness, chroma, Cr3+ and color index were studied to analyze the impact of all these three elements on ruby red color; and with the color difference research, the lightness difference is testified to be the key affecting color appearance. Based on the uniform color space CIE 1976L*a*b*, the ruby displays the best red color when the content of Cr3+ is within (1555, 5183ppm), L* (32.64, 44.25) and ho  (354.14, 0.7). With the help of partial correlation analysis of color difference, it is illustrated that the correlation between L* and E* (r=0.999) is relatively higher than that between L* and E* (r=0.948); and with high significance level ( = 0.129) of H* and E*, it shows that H* has little impact on E*. It is concluded that the color change of ruby from red to purple are mostly affected by lightness change; lightness difference should be considered as the most important factor when evaluating the red color of ruby, and then followed by the chroma and hue jointly.

Abstract: A simple and new method was introduced to measure the elastic modulus and strength of glass and brittle ceramic materials at different temperatures by compressing a notch ring specimen. For a notch ring specimen, the maximum tensile stress is generated in the outside of the testing sample at half of the height under an applied load. During the elastic deformation range, the elastic modulus can be calculated from the slope of loading curve and sample size. The fractured strength is derived by the critical load when the testing sample is failed. To verify the feasibility and reliability of this suggested method, typical brittle materials, including glass, coarse Al2O3 and fine ZrO2 ceramic, were used as the testing samples. The measured elastic modulus and strength obtained from this method at room temperature to 1300 oC agreed well with those from conventional testing methods.

Abstract: Micro-hardness measurements of thin coatings have to face the problem of the influence of the substrate. Based on relative method and the relationship between the composite hardness (the hardness of the coated sample) and the substrate hardness, a new model is proposed to evaluate the absolute hardness of ceramic coatings. Indentation tests with various load levels were carried out with specimens of (Ti,Al)xN1-x/SiyN1-y composite coating on SKH51 steel substrate. The results were analyzed by the new model and compared with those calculated by J-H (Jönsson and Hogmark) and L-C (Lesage and Chicot) models. The mean coating hardness obtained from this model shows similar results with the J-H model but a little higher than that from L-C model.