Papers by Author: Qing Fen Li

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Authors: Li Li, Qing Fen Li, Hui Min Zhou
Abstract: For most of the experiments and the practical problems about the non-equilibrium grain-boundary segregation (NGS), segregation will always occur during continuous cooling. The effective-time-method assumed that any continuous cooling curve for a sample can be replaced by a corresponding stepped curve. In this paper, the non-equilibrium grain-boundary segregation of phosphorus in step cooling process in an industrial steel12Cr1MoVis studied based on the effective-time-method and compared with that in isothermal holding process. Results show that the calculated result is in good accordance with the experimental observation. It provides a direct support for the effective-time-method of NGS. The step cooling process can speed-up the embrittlement of the steel. Based on the step cooling technique, a control method of grain-boundary brittleness is proposed.
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Authors: Yu Pu Ma, Xin Zhi Lin, Qing Fen Li, Zhen Li
Abstract: When stress is high, delaminate damage can be induced by transverse cracks. A complete parabolic shear-lag damage model containing delamination induced by transverse cracks is therefore proposed and applied to predict the stiffness reduction by transverse cracking in cross-ply laminated composite materials. The predictions of the complete parabolic shear-lag analysis model, the incomplete parabolic shear-lag analysis model, and the complete parabolic shear-lag damage model containing delamination proposed in this paper have been compared. Results show that the young’s modulus reduction values obtained by our analysis model are better agreement with the experimental ones than other models.
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Authors: Hui Min Zhou, Qing Fen Li, Li Li, Yu Feng Zheng
Abstract: Dental diamond bur is now a regular rotary tool, with its head made of diamond particles embedded into nickel coating, and its shank made of stainless steel. There are strong demands from the dentist on prolongation of usage life and avoiding of breakage. To solve this problem, on the one hand, since diamond is hard to be wetted under the condition of normal temperature and pressure due to the high interfacial energy between diamond and general metals and alloys. Diamond particles coated with titanium layer was used for the preparation of composite electroplating with the intention of improving the interfacial adhesion between diamond and metal matrix; on the other hand, superelastic biomedical NiTi alloy was used as the substrate to improve the flexibility and prevent the breakage. In this study, the optimal preparation parameters of Ni/surface-modified diamond electroplating were determined by orthogonal test, and the bonding conditions between the diamond particles and the NiTi alloy substrate were studied by scanning electron microscope. Further performance comparison of Ni/modified and Ni/un-modified diamond composite electroplating was conducted on a pin-on-disc wear machine under the dry sliding condition, and the material removal volume was used as the evaluating criterion of wear resistance. The results showed that the binding strength between diamond particles and NiTi alloy substrate could be enhanced, as well as the wear resistance, which may give direction on the future design of dental bur.
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Authors: Jeong Pyo Nam, Sung Ho Yoon, Young Eun Hwang, Hong Li, Qing Fen Li
Abstract: In this study, the effect of combined environmental factors such as ultraviolet ray, high temperature and high moisture on mechanical and thermal analysis properties of glass fabric and phenolic composites are evaluated through a 2.5KW accelerated environmental aging tester. The environmental factors such as temperature, moisture and ultraviolet ray applied of specimens. A xenon-arc lamp is utilized for ultraviolet light and exposure time of up to 3000 hours are applied. Several types of specimens - tensile, bending, and shear specimens that are warp direction and fill direction are used to investigate the effects of environmental factors on mechanical properties of the composites. Mechanical degradations for tensile, bending and shear properties are evaluated through a Universal Testing Machine (UTM). Also, storage shear modulus, loss shear modulus and tan δ are measured as a function of exposure time through a Dynamic Mechanical Analyzer (DMA). From the experimental results, changes in material properties of glass fabric and phenolic composites are shown to be slightly degraded due to combined environmental effects.
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Authors: Qing Fen Li, Chun Hui Li, Ping Long, Li Li Xue
Abstract: The microbiological influenced corrosion (MIC) behaviors of the ship plate steel directly exposed in different medias (the sterile seawater, the ferrous bacteria solution and the sulfate-reducing bacteria solution) were investigated with electrochemical impedance spectroscopy (EIS), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Corrosion potential, electrochemical impedance and micrographs of specimens under different experimental conditions were obtained. Results show that the FB and SRB in the marine environment affect the corrosion behavior of the ship plate steel greatly. The corrosion process in FB and SRB environment was controlled by both bacteria and corrosion products. The mechanism of MIC is discussed.
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Authors: Qing Fen Li, Hong Bin Chen
Abstract: Characteristics of deformation-induced transformation (DIT) in the refractory low alloy steel 2.25Cr1Mo were experimentally studied. Effect of different controlled-rolling and controlled-cooling process on the steel microstructure and mechanical properties were investigated and the mechanism was discussed. Results show that the grain size and the ferrite volume fraction were obviously affected by the rolling and cooling processes. Proper DIT technique may significantly accelerate the transformation of austenite to ferrite in the steel and improve the steel strength.
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Authors: Qing Fen Li, Li Zhu, Sheng Yuan Yan, Xiao Nan Zhang
Abstract: The computational analysis of an all fracture modes (AFM) specimen on mixed-mode I+II+III fracture is presented in this paper. The separated energy release rates (SERRs) along the crack front of the AFM-model are calculated by the modified virtual crack closure integral (MVCCI)-method and the commercially available software ANSYS. A transition model is built by adopting several 3D elements of SOLID45 and one point element of MASS21 in the ANSYS program. Under the related constraint conditions, the separate force and moments are respectively applied on the point element of the transition model, so the corresponding desired reaction forces can be obtained. When the desired loads are superimposed and applied on the AFM-model, the mixed-mode I+II+III fracture can then be achieved. Thereby, the SERR results are calculated. The calculation results show that the facture behavior of GII and GIII appears complex due to the global deformation and Poisson’s ratio, although the distribution of SEERs GI is symmetrical with respect to the middle point along the crack front. The total SERRs, GTn-values increase along the crack front with the minim value at one corner and the maxim value at the other corner. It can therefore be predicted that the fracture will occur initially at one corner on the crack front of the AFM-specimen in this case.
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Authors: Qing Fen Li, Li Zhu, Friedrich G. Buchholz, Sheng Yuan Yan
Abstract: Some results of 3D finite element analyses of the all fracture modes (AFM) specimen on mixed-mode II and III fracture are presented in this paper. The computational fracture analysis is based on the calculation of separated strain energy release rates (SERRs) along the crack front by the modified virtual crack closure integral (MVCCI)-method and the commercially available FE-code ANSYS. Calculation results show that under pure in-plane shear loading (mode II), not only the mode II, but also the mode III loading conditions, are generated owing to the Poission’s ratio effects. Similarly, under pure out-of-plane shear loading (mode III), besides the mode III, the mode II loading conditions are induced due to the global deformation. Nevertheless, once in-plane and out-of-plane shear loadings are superimposed, the fracture behavior appears more complex. Further discussion is given associate with some previous study.
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Authors: Gui Ying Qi, Friedrich G. Buchholz, Sheng Yuan Yan, Qing Fen Li
Abstract: In this paper some results of 3D-finite element analyses of a modified CTS-specimen(MCTS) with an inclined crack front are presented. It will be shown, that through the inclination of the crack front, even under pure in-plane shear loading of the specimen, mixed-mode II and III loading conditions can be generated along the straight inclined crack front. Furthermore a superposition of all fracture modes I, II and III can be generated, if this MCTS-specimen is subject to an in-plane tension/shear loading. The computational fracture analysis is based on the calculation of separated energy release rates GI, GII and GIII along the crack front by the numerically highly effective modified virtual crack closure integral(MVCCI)-method and for the finite element(FE)-modelling the commercially available FE-code ANSYS is utilized.
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Authors: Qing Fen Li, Gui Ying Qi, Sheng Yuan Yan, Friedrich G. Buchholz
Abstract: In this paper some results of 3D-finite element analyses of a modified CTS-specimen with an inclined crack plane are presented. It will be shown, that through the inclination of the crack plane, even under pure tension loading of the specimen, a superposition of all fracture modes I, II and III can be generated along the straight crack front of the inclined crack plane. Furthermore, mixed-mode I, II and III loading conditions can also be generated if this modified CTS-specimen is subject to an in-plane tension/shear loading. The computational fracture analysis is based on the calculation of separated energy release rates GI, GII and GIII along the crack front by the numerically highly effective modified virtual crack closure integral(MVCCI)-method and for the finite element(FE)-modelling the commercially available FE-code ANSYS is utilized.
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