Papers by Author: Qing Fen Li

Abstract: Wear failure behavior of steel surface with palygorskite powders (Palys) as lubricant additives was investigated in this paper. Different content of Palys was added in different lubricating oils. The wear failure behavior of the steelsteel contact surfaces was studied by using an optimal SRV oscillating friction/wear tester. The elemental component and morphology on worn surface were analyzed by SEM and EDS. From the results of the friction/wear tests and analysis of the worn surfaces, we can see that specimens with Palys as lubricant additives exhibit excellent wear reducing properties and introduce a smooth and compact oxide layer on the worn surface. This may be attributed to the layer-chain fibrous crystal structure of palygorskite and the complex physicochemical nature in friction process.

Abstract: In this paper, the computational predictions of crack initial breakpoint and deflection angles under bend and torsion loading conditions are investigated in conjunction with the modified virtual crack closure integral (MVCCI)-method by using the all fracture modes (AFM) specimen and commercial software ANSYS. The separated strain energy release rates (SERRs) along the crack front are calculated and subsequently converted to the stress intensity factors (SIFs) by using Irwin´s equations. Based on the SIFs results, the crack initiation predictions are presented by the maximum principal stress σ₁^'-criterion. Results show that when the AFM-model under a series of combined proportional bend and torsion loading conditions, asymmetrical stress fields are produced along the crack front. The presented investigation also shows that the maximum principal stress σ₁^'-criterion in conjunction with the MVCCI-method provides a powerful numerical tool for general computational approach to the fracture analysis of complex loading conditions.

Abstract: The microbiological influenced corrosion (MIC) behavior of the low alloy steel with granular-Zn-epoxy and flaky-Zn-epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), X-rays diffraction (XRD), scanning electron microscope (SEM) etc. Results show that the protection effect of the flaky-Zn coating specimen is much better than the granular-Zn coating one. The dissolution of zinc is more severe in granular-Zn coating than in flaky-Zn coating when the specimen immersed in the SRB solution. The shielding property of flaky zinc is much higher than granular zinc in the coating. The flaky-Zn coating is much more compact than the granular-Zn coating and therefore the property of anti-infiltration is much better. We may conclude that the flaky-Zn coating exhibited more favorable corrosion resistance property than the granular one.

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 G_II and G_III appears complex due to the global deformation and Poisson’s ratio, although the distribution of SEERs G_I is symmetrical with respect to the middle point along the crack front. The total SERRs, G_Tn-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.

Abstract: The MIC behavior of the ship plate steel specimen with LaCl₃-Zn epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated in this paper. The variation of corrosion potential over time of different specimens in SRB solution show that the corrosion potential of the specimen with LaCl₃-Zn epoxy coating was obviously higher than the Zn-epoxy coating, suggesting that the LaCl₃-Zn epoxy coating may offer better protection. The variations of lgflg |Z|=4.5 and f_h with time show that the property of anti-infiltration and corrosion resistance of LaCl₃-Zn coating is much better than the ones of Zn-epoxy coating. Results also show that more sulfides and corrosion products of LaCl₃-Zn epoxy coating were produced which increased the shielding property of the coating. The experimental results of XRD and SEM are in good agreement with the ones of E_corr, and EIS, etc. They all show that the LaCl₃-Zn epoxy coating exhibits more favorable corrosion resistance property than the Zn-epoxy coating. It is obvious that coating the ship plate steel with LaCl₃-Zn epoxy is an effective and promising method against the attack of SRB in marine environment.

Abstract: In the present study, the rare earths element YbCl₃ was added into the Zn-epoxy coating, and the MIC behavior of the low alloy steel specimen with YbCl₃-Zn-epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated and compared with the specimen of Zn-epoxy coating. Experimental results show that both the YbCl₃-Zn-epoxy and Zn-epoxy coating may offer effective protection for the basic low alloy steel. However, the corrosion potential of the specimen with YbCl₃-Zn epoxy coating was obviously higher than the Zn-epoxy coating, suggesting that the YbCl₃-Zn-epoxy coating may offer more favorable protection. Results of X-rays diffraction (XRD) and surface micrographs of specimens show that more sulfides and corrosion products of YbCl₃-Zn-epoxy coating were produced which increased the shielding property of the coating. The mechanism about the effect of YbCl₃-Zn-epoxy coating on MIC behavior was further discussed.

Abstract: In this paper, considering the material properties of the composite flywheel and the characteristics of the pre-stressed structure, stresses and strains induced by rotor rotation and interference fit were calculated by finite element (FE) method based on the plane stress hypothesis, in the commercial software ANSYS. Based on the given material properties and the main dimension with a certain speed of rotation, three 2D FE-models of hybrid composite flywheel rotors with two-layer rotor structure were built with the unit property of plane stress, axisymmetric and plane strain respectively. Followed, the radial stress, circumferential stress and radial displacement of the rotor were obtained. The three simulation results are almost accordant with the present theoretical results. It shows that the numerical analyses are reliable. It can be shown that is advisable to design and optimize the flywheel rotor.

Abstract: Ti/(Ru,Ir)O_x, and Ti/(Ru,Ir,La)O_x oxide electrodes were prepared by using thermal decomposition of the metal chlorides in the precursor solution on the Ti base. Their apparent electrocatalytic activity investigated by cyclic voltammetry, polarization curve, scanning electron microscope and X-ray diffraction. These data show that Ti/(Ru,Ir,La)Ox oxide electrode exhibits considerably high voltammetric charges, apparent current density and low onset potential for the ClER and OER. The XRD results reveal the main formation of the La-containing oxide electrode in amorphous phase.

Abstract: The microbiological influenced corrosion (MIC) behavior of the low alloy steel with Zn-rich epoxy coating and micaceous iron oxide epoxy coating in the sterilized medium and sulfate-reducing bacteria (SRB) solution was investigated by using both full-coated and nicked-coated specimens. Results show that for steel coated with Zn-rich epoxy, the corrosion resistance of both full-coated and nicked-coated specimens was improved obviously. The Zn-rich epoxy coating protected the test steel effectively in the microbial environment with the cathodic protection in the earlier period and physical barrier protection in the later period. For steel coated with micaceous iron oxide epoxy coating, the corrosion resistance of full coated specimens was improved greatly. However, for nicked-coated specimens, corrosion was aggravated because the small anodic area around the nick accelerated the corrosion. It is concluded that the basic low alloy steel may be effectively protected by the micaceous iron oxide epoxy coating only when the steel is perfectly coated with the coating, breakage must be avoided.

Abstract: The self-oscillation device has many advantages and is therefore suggested to be used in the pipeline supercharger. Simulation and analysis on the pressure-increasing effect of the pipeline supercharging caused by self-oscillation cavity were carried out by finite element method. The cavity structure of self-oscillation device was designed using the fluid network theory, natural frequency calculation, resonance conditions and Large Eddy Simulation Theory. A series of flow field distribution chart of the self-oscillation cavity were obtained. Results validate that the self-oscillation device is effective to increase the pressure of the pipeline supercharger. The relation curves of pressure-increasing effect with different structure parameters of the cavity were further analyzed. Previous experimental results are accordant with the present simulation results. It shows that the numerical analyses are reliable.