Materials Science Forum Vol. 749

Abstract: The technology of PSA(probabilistic safety assessment) based on fracture mechanics has been applied on the engineering field. However therere few application on the port machines still with some problems. A comprehensive discuss on PSA method was presented in this paper. Firstly, the experiment of the fracture mechanics parameters of Q345 steel used on the port machines structures was made to provide the parameters for PSA. Secondly, probabilistic analysis with the series of the Q345 steels FAC(Failure Assessment Curve) provides the PSA criterion. By using stress analysis, defect detection and material properties, the structures safety of a RMG(Rail Mounted Gantry) of one port in service were assessed, the result show that the key points of the crane are safe in one point service. The technology presented in this paper will be significant for the operation and management of the port equipment.

Abstract: Strain engineering is an effective method to tune the band gap and electronic transport properties of graphene nanoribbons (GNRs). However, strain/stress field may promote the system deviating from the equilibrium state, and the mechanical stability will become one of the key issues for reliable services of relevant devices. In this paper, the size-dependent mechanical properties of GNRs under tensile loading were studied by Molecular Dynamics (MD) simulations. The results indicate that the yield stress of both zigzag and armchair GNRs decreases with the ribbon length changing from 240 Å to 30 Å. However, the ductility of armchair GNRs was significantly improved. Radial Distribution Function (RDF) was employed to analyze the evolution of atomic configurations. It showed that lattice shearing is the main mechanism for the ductility of armchair GNRs.

Abstract: The size and the electronic factor are used to analyze the occupation of doped Co atom in L10 FePt alloy as well as its influence on crystal structure and magnetic property. The Co atom located in Fe sublattice site is determined by the variance of the calculated structure and the doping energy results investigated by the first-principles calculations. The charge-density difference contour plot and Bader charge analysis can quantitatively distinguish the effects of the size and the electronic factor on physical properties of the doping alloy. The effect of the electronic factor on the doping energy is more dominant than that of the size factor. The size factor almost has no effect on saturation magnetization.

Abstract: Nb-Si-Cr alloys have shown great potential as the aviation materials because of their good mechanical properties and high temperature oxidation resistance. The thermodynamic properties of Nb, Cr₂Nb, α-Nb₅Si₃, β-Nb₅Si₃, as the main constituent phases of Nb-Si-Cr alloys, were calculated by first-principles methods combined with quasi-harmonic Debye model. The calculated results are in agreement with available experimental data. Compared the thermo-dynamic properties of different phases, it is found that the thermal expansions of these phases are similar and have the same trend with change of temperature. Thermal expansion coefficient of these phases are dependent with increases with temperature and decreases with pressure, respectively, while the bulk moduli decreases with increasing temperature. At last, the micro stress created by the differences in coefficients of thermal expansion between Nb and Cr₂Nb upon cooling was evaluated. The result showed that the stress is too small to cause cracking at the interface between Nb and Cr₂Nb.

Abstract: H-beam will inevitably produce temperature uneven in cooling process, causing the uneven deformation phenomenon in H-beam cross section, and therefore how to improve H-beam cooling distortion uniformity become a research priority of H-beam. In this paper, the deformation of H-beam was simulated in the cooling process by using finite element analysis software ANSYS, and the simulation results was compared with measured data. Uneven cooling rate between up and down groove of the H-beam caused the out of square. Uneven cooling rate for the R corner and web surface was simulated, the conclusion is that uneven cooling rate for the web is the main reason of the out of square, and that of R corner is the second factor.

Abstract: Atomic structure model of bulk AlCoCrCuFeNi multi-principal-element alloy was build by following the principle of maximum entropy. Morse pair-potentials to describe the inter-atomic interaction among neighboring atoms in the alloy were generated directly from first-principles calculations within density-functional theory. Molecular statics simulation was carried out to achieve the optimized atomic configuration of AlCoCrCuFeNi alloy. The results show that the crystallographic behavior in lattice structure observed experimentally is just caused by the average of the disordered atomic position and composition in wide range since there is neither short-range nor long-range order in the local atomic arrangement of this kind of materials.

Abstract: The influence of deformation and quenching temperature on microstructure and properties for high nitrogen stainless bearing steel was studied using the calculation of Thermo-Calc software and relevant Fe-based database and some experiments. The results showed that there was a small precipitation amount of carbide in the sample after a large deformation. The value of impact toughness (A_KU) was increased from 2.0 J to 12.0 J with the deformation increasing from 71% to 83%. When the quenching temperature reached 1050, the value of the hardness was up to the tiptop. Additionally, according to the calculation, it was found that there was a linear functional relation between the precipitation of carbide M₂₃C₆ (M) and quenching temperature (T). And the relational model could be expressed as: M_M23C6=55.34 - 0.05T (T1000).

Abstract: The microstructure evolution and precipitation behaviors of ordered γ (Ni₃Al) phase in Ni-Al alloys were studied using the phase field dynamic model. Under the interactions of internal elastic strain, the γ phase morphology changes from the separated cuboidal to connected rectangle shape with the decrease of the aging temperature or the increase of the Al concentration. It also shows that the ordering of precipitates is finished instantly when they precipitate from the matrix phase. The γ phase volume fraction and the phase transformation velocity are affected by the aging temperature and composition of the Ni-Al alloys.

Abstract: Tensile experiments were carried out on advanced high strength steel (AHSS) by the test machine Gleeble3500, under the temperature ranging from 650 to 850 and the strain rate of 0.1/s~5/s, and the corresponding stress-strain curves were obtained. The peak stress level decreases with the increasing of deformation temperature or the decreasing of strain rate, which can be represented by a ZenerHollomon parameter in a linear equation. A revised model describing the relationships between the peak stress, strain rate and temperature of advanced high strength steel at elevated temperatures was proposed by compensation of strain and strain rate. The comparison of the predicted and experimental results of stressstrain curve can prove the good predictive power of the model, the Adj. R-Square between the peak stress and the linear equation was reached to 0.97.

Abstract: The rolling process of large size H-Beam NH800×300 in multiple working conditions was simulated by using of commercial finite element method software LS-DYNA. the web wave emerged during rolling of H-Beam was specially demonstrated. The main factor which affected the rolling force during the rolling process has been illustrated. The rolling process under the condition of different horizontal roller radius, different friction coefficient and flange/web stretching ratio were numerically simulated. By means of simulation with different flange/web stretching ratio, it could be concluded that the crucial situation to generate the rolling web wave in typical rolling pass is that the flange/web stretching ratio is about lower than 0.93, which may cause the web unstable and the rolling wave.