Qing Fen Li

Improvement of MIC Behavior of Low Alloy Steel with Zn-Rich Epoxy Coating

The microbiological influenced corrosion (MIC) behavior of the low alloy steel with or without Zn-rich epoxy coating in the sterilized medium and sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and X-rays diffraction (XRD). Results show that the bacteria in the marine environment affect the corrosion behavior of the ship plate steel and the corrosion resistance of specimen coated with Zn-rich epoxy was improved greatly. The 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.

Effect of Niobium Film on Corrosion Resistance of AZ91D Magnesium Alloy

The niobium film is prepared by magnetron sputtering on the surface of the AZ91D magnesium alloy. The morphology, phase structure, roughness, nanohardness and elastic modulus of the niobium films were studied by filed emission scanning electron microscope, X-ray diffraction, atomic force microscope and nanoindentation respectively. The influences of film deposition parameters, such as substrate temperature, negative bias and power on the properties of films were investigated. The corrosion resistance of niobium films on magnesium alloy was investigated by electrochemical system. Results show that the microstructure, phase structure, roughness, nanohardness and elastic modulus of the niobium films are determined by power, negative bias and substrate temperature. And the corrosion resistance of magnesium alloy improved obviously when coated with the niobium films.

Numerical Simulation of Automotive Crash-Box Subjected to Low Velocity Frontal Impact

Thin walled tubes, particularly those of square or circular cross-section, are the common types of automobile crash-box, which equipped at the front end of a car, is one of the most important automotive parts for crash energy absorption. In the present work, energy absorption characters of square and circular cross-section thin walled tubes at low-velocity frontal impact are investigated respectively by using finite element (FE) method. The numerical simulations were carried out using the software LS-DYNA. The tubes were modeled using shell element of designation Belytschko-Tsay, which is suitable for large strain analyses. The FE model of the tube was validated by comparing the theoretical calculation results, experimental results and FE model results. Results show that on average the difference of these results was within 10%. The good correlation of results obtained show that the numerical analyses are reliable.

Fracture Behaviour and Temper Embrittlement Induced by NGS of Phosphorus

The non-equilibrium grain-boundary segregation (NGS) isotherms and its kinetics serve to provide a more complete understanding of inter-granular segregation behavior in relation to mechanical properties, not only for the engineering steels but also for a wide range of structural alloys. The NGS of phosphorus and temper embrittlement dynamics on the same heat treatment condition at the same isothermal holding time in two Cr-Mo steels, 12Cr1MoV and 2.25Cr1Mo, was experimentally studied. The fracture behaviour was also observed by tensile tests in situ in a scanning electron microscope (SEM). Results show that both the concentration of phosphorus atoms in grain boundaries and the degree of embrittlement reaches a maximum at the critical time. It can be satisfactorily elucidated by the temper embrittlement mechanism of NGS caused by cooling from solution temperature to isothermal holding temperature.

Study on Temper Embrittlement of Phosphorus in Steel 12Cr1MoV

According to the non-equilibrium grain-boundary segregation (NGS) kinetics curve of phosphorus, a series of Charpy impact tests was performed in an industrial steel 12Cr1MoV, at solution temperature 1050oC, with isothermal holding temperature 540oC, on specimens of different holding time (at the segregation process, the critical time, and the desegregation process respectively). The DBTT values were measured and a temper embrittlement kinetics curve was given. The reverse temper embrittlement NGS mechanism for steel 12Cr1MoV was proposed.

On the Effect of Plastic Constraint on Ductile Tearing

The effect of plastic constraint on the initiation of ductile te ars has been studied by measuring the J-integral and COD at initiation in three-point bend s pecimens with deep and shallow notches. Experimental results of 30 groups of steels show that both i δ and i J values increase with decreasing a/W when a/W0.3 and that shallow crack specimens which have les s constrained flow field give markedly higher values of toughness than deeply notched specimens. However, for a/W 0.3, the toughness was found to be independent of a /W. Slip-line-field analysis explains the result and the theoretical development of Two Param eter Fracture Mechanics also rationalized our experimental results. The advantage of enhanced tou ghness for specimens with low levels of constraint should be taken into account for defect assessment, and a modified reasonable result should be taken for engineering applications. Introduction In design practice, the critical value at initiatio n, i δ and i J , are normally measured on three-point-bend specimens where the crack depth is approximately half the depth of the beam and the plastic flow is confined to the ligament. Since th plastic flow is constrained, the hydrostatic component of stress in these specimens is high. How ever, in practice many defects are shallow and the plastic flow associated with them reaches the s urface of the component. In this case, the hydrostatic component of stress is smaller and the constraint is lower. As a consequence, the assessment for many shallow defects, the normal met hod is unduly conservative. Experimental and theoretical study on the effect of the ratio of not ch depth to specimen depth (a/W) on i δ and i J is therefore necessary. Although many previous work [1 -7] have pointed out that shallow crack Key Engineering Materials Online: 2003-10-15 ISSN: 1662-9795, Vols. 251-252, pp 197-202 doi:10.4028/www.scientific.net/KEM.251-252.197

Grain-Boundary Segregation of Phosphorus and Inter-Granular Fracture Behavior under Low Tensile Stresses

The present work is an effort to provide experimental results focusing on segregation behavior of phosphorus at grain boundary and the intergranular fracture behavio under low tensile stresses. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of intergranular fracture in Auger specimens in 12Cr1MoV steel were carried out in this paper. The variation of phosphorus segregation level in grain boundary under different low tensile stresses and at different temperature were obtained. Results show that NGS of phosphorus occurred in the experimental steel while subjected to low tensile stresses. Maximum values of phosphorus segregation level were obtained at the critical times. SEM photos of intergranular fracture in Auger specimens of the test steel show that the intergranular fracture rate increased with increasing concentration of phosphorus. The intergranular fracture behavior is accordant with the segregation behavior of phosphorus at grain boundary.

MIC Behavior of the Low Alloy Steel with Different Zn-Epoxy Coating in SRB Solution

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.

Computational Analysis of the AFM Specimen on Mixed-Mode I+II+III Fracture

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.

Optimum Design and Numerical Simulation of Automotive Front Side-Door Impact Beam

In the present work, the structure optimum design and simulation analysis of automobile side-door impact beam was carried out by using Finite Element (FE) method. The model of the side-door impact beam impacting with the rigid pole was set up according to the requirement of the Federal Motor Vehicle Safety Standards intensity test of side door (FMVSS214). The numerical simulations were carried out using the software LS-DYNA. Attention was focused upon finding an optimum cross- section shape of the beam in order to improve the energy absorption character. Several types of impact beams were studied and compared. Results show that the energy absorption characters of the beam improved obviously when square cross section with the wall slope 10° and a 9 mm long curled edge was adopted.