Abstract: Electrochemical material characterization method was applied to the creep specimens of 12%Cr ferritic steel to evaluate the changes in precipitates during creep. Experimental results revealed that the peak current densities “Ip1” and “Ip2” appeared at specific potentials during anodic polarization curve measurement in 1M-KOH solution. These peak current densities corresponded to the selective dissolution of several kinds of precipitates, respectively. The Ip2, which reflected the amount of M23C6 and Laves phase, increased more siginificantly with creep than thermal aging. On the other hand, the effect of applied stress was not reflected on the change in Ip1, although it increased with thermal aging and creep as well as the Ip2.
Abstract: The paper deals with the problem of the determination of the in-plane behavior of periodic masonry material. The masonry is considered as a composite material obtained as a regular distribution of blocks connected by horizontal and vertical mortar joints. The macromechanical equivalent Cosserat medium is derived by a rational homogenization procedure based on the Transformation Field Analysis. The micromechanical analysis is developed considering a Cauchy model for the masonry components. In particular, linear elastic constitutive relationship is considered for the blocks, while nonlinear constitutive law is adopted for the mortar joints, accounting for the damage and friction phenomena occurring during the loading history. Numerical applications are performed in order to assess the performances of the proposed procedure in reproducing the mechanical behavior of the masonry material.
Abstract: In this paper, the effects of the average size of nanometric particles (ASNP) from submicron scale (less than 1 µm) to nanometric scale (less than 10 nm) have been studied on the properties of nanocomposite layers which usually have not been studied or rarely studied. These properties consist of corrosion current density after long time immersion, roughness of obtained layer and distribution of nanometric particles. All of the other effective factors for fabrication of nanocomposite coatings have been fixed for better studying the effect of the ASNP. It has been seen that decreasing the ASNP will lead to lower corrosion current densities however in some cases pitting phenomena has been observed. The roughness illustrated a minimum level while the distribution of nanometric particles will be more uniform by decreasing the ASNP.
Abstract: It is well known that controlling the microstructure of most industrial materials is the key to control its mechanical and physical properties. In particular grain growth is very important phenomenon in material science. However, it is very difficult to examine the dynamic solidification microstructure evolution at high temperatures or during deformation processes. Computer simulations have been used as an effective solution for that difficulty. Cellular Automaton (CA) is one of the techniques that have been used to simulate the evolution of grain growth. In this study 2D grain growth simulations of Al-1%Mg alloy was simulated using CA model based on different transition principles. The first is based on low energy principle. In this method the changes of boundary energy value is compared for each cell and then choosing the one that can minimize the energy system to the largest extent. The second method is based on changes of thermal energy that is computed for each grain boundary. The transition only occurs at the highest energy value. The third method is based on starting with a number of random distributed nucleuses within the simulation area with different orientations. At each CA steps these nucleuses will grow into a grain without effecting in the other grains. The morphology and grain kinetics are studied and discussed for each case.
Abstract: In this work, the microstructural evolution of aluminum containing commercial grade TRIP steels during gas tungsten arc (GTA), Laser beam (LB) and resistance spot (RS) welding have been studied. Microstructural analysis was carried out using optical and scanning electron microscopy. Results show that fusion zones of welded TRIP steels contain complex inclusions with similar size distribution. The energy dispersive spectroscopy analysis of inclusions indicated that these inclusions are primarily oxides of aluminum with epitaxial enrichment of manganese and phosphorous. The fusion lines of GTA and LB welded aluminum containing TRIP steel contain a zone of polygonal ferrite with a size of about 200 m and 50 m respectively. It is found that aluminum partitioned from the liquid weld to the solidified delta ferrite in the fusion line causing enrichment and resulting in ferrite stabilisation. This ferrite zone was not found in the case of resistance spot welded samples due to faster cooling rates.
Abstract: A model for intergranular damage propagation in polycrystalline materials is proposed, based on Markov Chain theory, Monte Carlo simulation and percolation concept. The model takes into account crack branching and coalescence, multiple crack nucleation sites, crack-turning etc., as well as the effect of grain boundary plane orientations with respect to the external stress direction. Both honeycomb and voronoi microstructures were utilized as the input microstructures. The effect of multiple crack nucleation sites has been found to have great influence on the crack propagation length. It has been observed that percolation threshold reported in the literature based on hexagonal microstructure is not applicable when the effect of external stress direction on the susceptibilities of grain boundaries is considered. The successful integration of voronoi algorithm with the Markov Chain and Monte Carlo simulations has opened up the possibilities of evaluating the intergranular crack propagation behaviour in a realistic manner.