Advanced Materials Research Vols. 194-196

Abstract: Steel trusses are often used in the railway bridges.It is known that fatigue cracks may occour in the welded joints under the long-term dynamic loading. If the cracks are not detected and repaired in time, which may endanger the safety of bridges. This paper presents a solid element modeling method by the commercial finite element software package ANSYS, which can be used to model three dimensional cracked joint of bridge structures. Based on this method, the stress intensity factors are calculated. The results show that the modeling method is efficient and has a high precision for the stress intensity factor, which can be used to predict the fatigue life of the bridge.

Abstract: Ceramic samples with the nominal composition (1-x) BaTiO₃ + x Ba₃Ti₂YO_8.5 (x = 0 - 0.4) were prepared by the solid-state reaction method. The X-ray diffraction (XRD) analysis and the lattice parameters determination indicate that the samples with x≤ 0.16 exhibit a single phase cubic perovskite structure. When x > 0.16, the system is of biphasic composites, which consist of Ba(Ti_0.911Y_0.089)O₃ and Ba₃Ti₂YO_8.5. The microstructure observation by Scanning Electron Microscopy (SEM) supports the XRD result. For the biphasic composites, the dielectric constant follows the Lichtenecker relation in a wide temperature range.

Abstract: Mg2Si particle reinforced hypereutectic Al-Si-Mg alloy composite is prepared by melt superheating, and the effects of the main processing parameters, such as superheating temperature and holding time, on the microstructure of the composite are studied. The results indicate that it is feasible to prepare Mg₂Si particle reinforced Al-18%Si-Mg alloy composite by melt superheating. The suitable preparing parameters of melt superheating on the alloy are obtained. When the superheating temperature is 860°C and holding time is 25 min, the average size of Mg₂Si particle in the alloy will be reduced to about 11μm compared with 34μm without melt superheating.

Abstract: In this paper, low-velocity impact characteristics and residual tensile strength of carbon fiber composite lattice core sandwich structures are investigated experimentally and numerically. Low-velocity impact tests and residual tensile strength tests are simulated by the FE (finite element) software, ABAQUS/Explicit and its subroutine (VUMAT). In order to give more detailed description about the impact damage of the structure and improve modeling accuracy, multi-steps analysis method is employed to simulate impact process and residual tensile strength test in one analysis model. The calculation results computed by the FE model have been compared to the value of experiments, the difference of impact process simulation is about 3.3% and that of tensile strength test simulation is about 12.9%. The calculation error of computation model is acceptable, since unavoidable damage could be introduced in the courses of manufacture, processing and transportation of composite materials, and these damages are determinated difficultly in the computation programs. Next, the degradation tendency chart of residual tensile strength and impact energy threshold U_o of carbon fiber composite lattice core sandwich structures are obtained by the computation value of residual tensile strength after impacted with different impact energy. Previously, this threshold can only be obtained by experiment tests. After the contact force which is bigger than the threshold U_o impact on the sandwich structures, the residual tensile strength of structures are degraded greatly. This conclusion is significant for the design and application of carbon fiber composite lattice core sandwich structures.

Abstract: In this paper, modeling, procedure and algorithm using Monte Carlo (MC) technology were investigated respectively to simulate grain size and microstructure . First, two different kinetic model were defined by both experimental and statistics method. Then the procedure and algorithm were worked out based on MC technology. Thirdly, the grain growth process in HAZ was simulated, which has great influence on grain growth in HAZ. The result of the simulation demonstrates the grain growth process dynamically. Good agreement between MC simulation results and the experimental results was obtained which can provide a reliable evidence for evaluating the welding craft and the weldability.

Abstract: Transformation Induced Plasicity (TRIP) steels have attracted a growing interest in recent years due to their high strength and ductility combination.An alternative alloy and processing concept has been studied to evaluate the feasibility of producing low-carbon medium-manganese TRIP Steels. Conventional hot-rolling, and batch annealing processes were simulated with three laboratory heats of varying manganese content. The steels were found to be fully hardenable with conventional hot-strip mill processing and subsequent batch annealing simulations produced significant retained austenite levels. The combination of the prior martensitic microstructure in the as-hot-rolled condition, and austenite created during annealing,resulted in remarkable combinations of strength and ductility. Optimum properties were found when samples were annealed at approximately 630°C. While this treatment maded the tensile strength to 800-1020 MPa, the total elongation increased to between 27 percent and 35 percent. UTS*TE products exceeding 30,000 MPa*% were observed, making these materials attractive for high strength, high ductility applications.

Abstract: The inhibition effects of sodium silicate, phytic acid and their mixtures in 5% NaCl solutions have been investigated using weight loss method and Tafel polarization techniques. The surface morphology of carbon steel was obtained using scanning electron microscopy (SEM). The results show that the co-addition of 70 mg∙1^-1 sodium silicate and 5 g∙1^-1 phytic acid has the optimum inhibition efficiency (84.15%) and the lowest corrosion rate (0.13 g∙m^-2∙h^-1). Compared with their individual inhibition effects, the optimum inhibition efficiency of sodium silicate is 62.17% at 90 mg∙1^-1 and phytic acid is 80.05% at 15 g∙1^-1, respectively. The results obtained from weight loss method and Tafel polarization curves are in good agreement. The results show the enhanced inhibition effect by the inhibitors mixtures.

Abstract: With development of theory on microalloy in steel, now there are trends of adding microalloy in many kinds of steels, making the production and application of microalloy-steel enlarge. The second phase in microalloy-steel is significant for quality of casting. During the periods of continuous casting, conveying and heating, different process may affect precipitation and dissolution behaviors of casting according to different heating profile, further affect state of precipitation and distribution of secondary phase. In this paper, secondary phase in micro-alloy steel J55 were studied. Results show that some secondary phase particulars in micro-alloy steel J55 steel distribute along the austenitic grain boundaries when the temperature of slab is below 805°C in roller conveying; The distribution of secondary phase particulars in different thermal history slab are comparatively similar after heating; Al, Ti, C and N elements which dissolute in J55 steel has the feature of austenitic grain boundary segregation.

Abstract: The as-rolled and enamel fired microstructure and mechanical properties of two low carbon steels with different compositions were analysed in the paper. The results show that the grains do not coarsen in lab firing process, and could be refined after industrial enamel firing process. The strength can keep stable in the firing process and the impact energy could be enhanced greatly under the industrial enamel firing process. The surface decarburized layer was occurred as a result of chemical reaction among the carbon in steel and water, oxides in the enamel frit.

Abstract: Hot-ductility tests of the microalloyed Q345B structural steel were performed in a tensile machine of Gleeble-1500D at different strain rates of 1.5•10^-3/s 、2.5•10^-3/s and 2•10^-2/s and at temperature range from 1300°C to 700°C(Δ T=100°C ), which are close to the continuous casting condition of steel. Fracture surfaces were examined using a scanning electron microscope; it was found that the hot decrease as strain rate decrease, because the void growth mechanism predominates over void nucleation, giving time for nucleation cracks to grow. The minimum ductility was found at about 800°C for the strain rates of 1.5•10^-3/s and 2.5•10^-3/s, and the fracture was intergranular. The steel has good plasticity in temperature range from 1200°C to 900°C which is suitable for straighten operation.