Papers by Author: Qin Zhi Fang

Abstract: Residual thermal stress, which has a strong effect on the coating performance, is generated during the fabrication of TBC. In this paper, the residual thermal stress in TBC (92%ZrO2-8%Y2O3) with two different thicknesses (0.38 mm and 0.90 mm) is analyzed with a bi-material model. TBC specimens were sprayed by an Air Plasma Spray (APS). In addition, a chemical material removal method was used to obtain TBC specimens after it cooling down to the room temperature. Before and after the coating removed from the substrate, the deformation of the TBC was measured. Then the bi-material model was used to calculate the residual thermal stress in the TBC. The experiment result shows that, the residual thermal stress in thin TBC is smaller than that in thick TBC (the average residual thermal stress in thin and thick specimens are 145.5 MPa and 225.13 MPa respectively). The micro-structures in thin and thick TBC are also observed and discussed.

Abstract: As a direct and simple method, essential work of fracture has been widely used for fracture measurement of ductile polymers. In this paper, fracture toughness of PC and PC/ABS alloy is experimentally investigated. A series of double edge-notched tension (DENT) specimens and essential work method are employed to measure the fracture toughness of PC and PC/ABS alloy. By the way, the critical crack tip opening displacement is obtained. Moreover, the fracture surfaces of DENT specimens are examined by using a scanning electron microscope (SEM).

Abstract: Large deformation performances of polycarbonate (PC) and PC/ABS (Acrylonitrile Butadiene Styrene) have been investigated experimentally in this paper. The displacement fields of these polymers are measured with a system based on digital image correlation (DIC) method. The variations of strains during tension are measured and the true stress-strain curves are presented. For these materials, it is observed that the contraction in thickness is larger than that in width during tension. No obvious stress softening is observed in the true stress-strain curves. The true stress-strain curves can be fitted well with three-stage model.

Abstract: The tensile property of PC/ABS was investigated with an optical image analysis method in the paper. With the consideration of polymer micro mechanism, a three-stage phenomenon based model is used to describe the true stress-strain curves. The regression constants obtained with the method could be described with definite physical meanings. It is shown that two lateral contractions are not identical at the later necking stages. The fracture strain could be used as a criterion to describe uniaxial tensile fracture.

Abstract: An automatic fatigue crack growth measurement system was developed, in which a special four-channel A-D acquisition board that could collect data in phase was used. The data collecting frequency is in the range of 4×(2~25600)Hz. The system is suitable for fatigue tests with the frequencies not higher than 250Hz. Eddy current transducers and standard load cell were used to measure displacement and load, respectively. The system can instantly calculate fatigue crack lengths, stress intensity factors and fatigue crack growth rates. As an application of the system, fatigue crack growth rates (FCG) and the thresholds of steels 42CrV and IR3Mo were presented.