Papers by Keyword: Metallic Material

Abstract: This paper studies the atmospheric corrosion characteristics of grid metal frame equipment in Chongqing. Through the standard field test method of atmospheric corrosion -"exposure" method, this study carried out the substation site hanging test of the Q₂₃₅ steel of the power transmission and transformation engineering structural material in the atmospheric environment, and mastered the corrosion data of Q₂₃₅ steel in different corrosion stages. It was found that the morphology, quantity and characteristics of corrosion products on the metal surface varied greatly with the progress of corrosion. According to the metal corrosion morphology of different corrosion time, combined with image processing technology and wavelet transform algorithm, the parameters such as gray mean M, corrosion standard deviation σ_m, corrosion energy E, and energy percentage of wavelet image coefficient were selected as corrosion characteristic variable. At the same time, the BP neural network algorithm was used to qualitatively evaluate the corrosion state of the electrical equipment metal. By testing the on-site samples of the two substations, the corrosion state values of the samples were 0.946 and 0.8071, respectively, which is consistent with the actual corrosion degree, and the system had a good evaluation result.

Abstract: In hot forming processes, metallic materials often undergo a series of plastic deformation and heat treatments. Hot working parameters, including deformation temperature, strain rate, and strain, exert great impacts on hot deformation behavior of alloys. Work hardening (WH), dynamic recovery (DRV), dynamic recrystallization (DRX), phase transformation, and metadynamic recrystallization (MDRX) often take place, and affect hot deformation behavior of metallic materials. Therefore, a comprehensive investigation on the intrinsic interactions between microstructural evolution and hot deformation behavior is necessary. In this study, a novel unified dislocation-density based model is presented to characterize the hot deformation behavior of a nickel-based superalloy In the Kocks-Mecking model, a new softening item is proposed to represent the impacts of dynamic recrystallization behavior on dislocation density evolution. The grain size evolution and dynamic recrystallization kinetics are incorporated into the developed model. Material parameters of the developed model are calibrated by a derivative-free method in MATLAB toolbox. Comparisons for the experimental and predicted results confirm that the developed unified model can accurately reproduce the hot deformation behavior, DRX kinetics, and grain size evolution in wide scope of initial grain size, deformation temperature, and strain rate.

Abstract: Auxetic materials exhibit uncommon behaviour, i.e. they will shrink (expand) laterally under compression (tension). This novel feature has attracted intense research interest. However, most of previous works focus on auxetic behaviour in either compression or tension. Most of the auxetic materials are not symmetric in tension and compression under large deformation. Studies on the auxetic performance of metamaterials both in compression and tension are important but rare. As an extension of our previous research on compressive auxetic performance of 3D metallic auxetic metamaterials, numerical simulations were carried out to investigate the auxetic and other mechanical properties of the 3D metallic auxetic metamaterials in tension. The preliminary results indicated that the designed 3D metallic auxetic metamaterials exhibited better auxetic performance in compression than in tension. By increasing a pattern scale factor, auxetic performance of the 3D metallic auxetic metamaterials under tension can be improved. With proper adjustment of the pattern scale factor, an approximately symmetric auxetic performance could be achieved in compression and tension.

Abstract: In order to study thecharacteristics of this new type of quenching process that is atomized waterspray quenching, this article analyzes the influence factors of atomized waterspray quenching based on the newly developed aerosol spray quenching experimentdevice. Based on 2 method, the two factors of water flow and nitrogen pressureare controllable, we analyzed the influences of the two factors of nitrogenpressure and water flow to the quenching cooling time. This paper induces andanalyses the experiment results and numerical calculation results^[1]. The conclusions are: water flow is the main factor ofaffecting the quenching rate, the interaction of the nitrogen pressure andwater flow is significant: when the nitrogen pressure is low ,the water flow ishigh, the quenching cooling rate is guaranteed.

Abstract: Because of excellent mechanical, physical and chemical property Wf/Zr-based amorphous matrix composite attracts people’s interest and becomes the hot spot of science study and engineering application. In this paper, change regulation of hardness of target around crater by Wf/Zr-based amorphous matrix composite projectile and its mechanism are studied after firing test, and it is found that the section can be divided into 3 layers: the Martensite layer, the deformed fine grain layer and the normal matrix from the crater surface to the interior of the steel target and that the thickness of Martensite layer increases first and then decreases in the penetration direction when the velocity of projectile is 1200m/s.

Abstract: Through a series of standard tests conducted on homogeneous metallic materials (carbon steel, stainless steel and non ferrous metal alloys) we have obtained the corresponding values of the elastic module. Non-destructive local penetration tests in the elastic field are carried out on materials identical to each of those indicated above. For each of the aforementioned materials the results obtained by the two tests described above are correlated. Lastly, we have calibrated the measuring chain created especially for the micropenetration tests, and then validated the measurement procedure.

Abstract: W_f/Zr-based amorphous matrix composite is supposed as a potential penetrator material of armor-piercing projectile because it has both advanced piercing performance and environmentally friendly property, and it becomes the hot spot of science study and engineering application. To get a deeper understand of the penetration mechanism and the influence of temperature rise on structure of target, target which is penetrated by penetrator made of W_f/Zr-based amorphous matrix composite is studied by SEM and micro-hardness tester. Oxidation of back of target is severe, and Martensite transformation happens around the crater. From the crater surface to the interior of the steel target, the section can be divided into 3 layers: the Martensite layer, the deformed fine grain layer and the normal matrix. Martensite transformation indicates the target steel around crater is heated and softened in penetration, so this phenomenon is beneficial to penetrate and get a deeper understand of the penetration mechanism. CLC: TJ04 Document code: A

Abstract: Nickel-base alloys with different boron contents were prepared by vacuum arc furnace. The effect of the boron contents to metallography was characterized simultaneously by XRD and SEM with EDS part. The thermal behavior was analyzed by DSC curves which mainly represents the eutectic temperature of alloys. The Vickers hardness and ball-on-flat wear test were carried out to reveal the relationship between metallographic phase formation and wear resistance. The results indicated that main composites are eutectic Ni-Cr as matrix and CrB, Ni₃B as precipitated phase. A considerable amount of dislocation and stacking faults exist in the specific orientation (200) of Ni₃B. 2.0~4.0%B alloys melt at 1060oC, while the boride-poor alloy melts at 1085oC. 3.0~4.0%B alloys performed the best on wear resistance. Wear volume reduces along with increasing hardness at the beginning, and then keeps invariant. Borides are main reinforcing phases, which affects hardness and wear resistance greatly.

Abstract: The fatigue limit and S-N curve of Q500q bridge steel were obtained by high-cycle fatigue test. The experimental results show that the fatigue limit of the experimental steel is 552.5MPa at room temperature with stress ratio R=0.1.There are some differences from the traditional fatigue fracture of high-cycle fatigue, the experimental steel’s rapid propagation area shows the morphology feature of both plastic fracture and brittle fracture. From analyzing the fatigue facture, the morphology feature of plastic fracture is mainly caused by the high fatigue limit. The little size (2~4μm) of inclusions in the experimental steel and the acicular ferrite’s microstructure feature of sub-lath structure with high-density dislocation reduce the crack initiation. And that’s the main reason why the steel has such high fatigue limit.

Abstract: In the structural analysis of mechanical elements, both in the design and testing phase, the Young’s modulus value influences the precision of the results and must be taken into consideration during the calculation. The E value is usually shown in tables that do not report precise values, but ranges of values that are characterized by a certain amplitude. In the structural calculation analytically or numerically developed, an approximate reference E value that is hypothesized constant in the material is usually used. Moreover, this value does not take into consideration possible thermal-chemical-mechanical treatments used on the material. A mechanical designer needs to know the precise E value of the material in the final operation state in order to develop a structural analysis. According to what has been specified above, it is necessary to know the value of the elastic characteristics for every point of material in order to associate a value in the development of a correct and deepened numerical analysis for every zone in examination. We have developed a finely tuned experimental system having the following main steps: - measurement of the penetration of a metallic microsphere, as a function of the applied load, in a single point of the analyzed material; - determination of Young's modulus. This procedure allows for E to be measured, if necessary, at points very close to each other in such a way as to be able to take into consideration, when performing structural analysis requiring a high degree of accuracy, the influence of the gradient of the longitudinal elastic modulus. The precision of the punctual values obtained for E is comparable with that of traditional experimental methodologies (e.g. tensile test), since the proposed procedure expects the use of the experimental calibration curve, which is precisely constructed based upon the data obtained through the above methodologies.