科创中国

This paper presented the mechanism of fretting fatigue failure that happened on the contact surfaces between sleeve and roll neck of oil-film bearing under the rolling load. Based on the analysis of distribution characteristics of the oil-film pressure, the contact stress concentration and the micro-slip distribution regularity at the edge of the contact zone were given by the finite element method, and the reasons for the fretting fatigue failure developed on the contact surfaces between sleeve and roll neck with interference fit were illustrated. By an equivalent principle of the local stress fields derived from the classical analysis for sharp-edged contact problem and the crack-tip fields obtained according to the fracture mechanics methods, the mechanics condition of the fatigue crack initiation and propagation occurred from the corrosive pitting was analyzed. The result was also certified by the practical damage state and simulation test.

Huijian Li;Guangxian Shen;庆学 黄

Zhongguo Jixie Gongcheng/China Mechanical Engineering

2008-2-25

Influences of hydraulic pressure on forming features in micro hydro deep drawing are different from those in normal drawing due to the small size of specimens. In this study, micro hydro deep drawing of SUS304 sheets was carried out in order to study the impacts of the hydraulic pressure on the quality of the drawn cup. Experimental results indicate that there is a critical hydraulic pressure range from 3 to 6 % of the blank’s initial yield stress, where wrinkling and earing development trends change twice. The wrinkling and the earing of the drawn cup also reach their local extremes in the critical pressure range. The cup earing value moves in the opposite direction from the wrinkling value. Hydraulic pressure affects the wrinkling and the earing of the drawn cup through changes in the micro-frictional condition, the shape of the blank and its strain-stress state. Micro-finite element (FE) simulation which takes these factors as well as the material size effects into consideration showed similar results to the experimental ones, thus validating the experimental results and the suitability of the micro-simulation model for micro-forming FE simulation. The experimental and simulation results indicate that the critical hydraulic pressure based on the blank’s initial yield stress can restrict the wrinkling and the earing of the drawn cup. Ultra-high pressure has the potential to avoid the cup wrinkling and earing.

Liang Luo;Dongbin Wei;Xiaogang Wang;Cunlong Zhou;庆学 黄;Jianzhong Xu;Di Wu;Zhengyi Jiang

International Journal of Advanced Manufacturing Technology

2017-4-1

A 1/8 mill screw pair experiment model of heavy and medium plate mill is made to analyses the rapping mechanism and the forming reason of plastic bulge quantitatively. Based on the experiment model, a series of experiments are done like rapping distance testing, vibration experiment and FEM numerical simulation of the copper nut tooth plastic bulge. The mill screw pair is oriented on medium radius, which is force constraint and is unreliable. There is time difference between the mill screw and balance mechanism when bite and toss of steel, which is the main reason for the forming of rapping and plastic bulge. Compound nut is provided, which can take place of force constraint with geometric constraint which depends on the rear of nut tooth. In the compound nut, the back side of slave nut tooth is the working face. The results of 1/8 model experiment show that it can control screw-pair dynamic gap, realize self-balance of screw, reduce the effect of mill screw-pairs rapping and prevent the emergence of a plastic bulge of copper nut tooth with compound nut. At the same time, adopting compound nut can reduce the abrasion of copper nut effectively and elongate the nut lifetime.

Xiumin Chen;Guangxian Shen;庆学 黄

Jixie Gongcheng Xuebao/Chinese Journal of Mechanical Engineering

2007-4

The hydraulic system of hydraulic rolling-shearer was designed according to rolling-shear principle. Based on rolling-shear equation, the position of cylinders was controlled by proportion servo valves and transducers to realize rolling-cut. Transfer function of whole hydraulic system was given by establishing three equations for it. The simulation for the positioning control effect of hydraulic cylinder was set up by Simulink, from which the scope of controlling parameters can be achieved, but overshoot vibration generated in the process of changing control parameters can not be detected directly from simulation, without proper adjustment in actual debugging process. The controlling of hydraulic system should have superior robustness and self-adjustment ability to ensure relatively stable compensation accuracy under different circumstances. The position precision of cylinders and high-quality steel cross section of production prototype proved the designing validity of the hydraulic system.

He Yong Han;庆学 黄;Li Feng Ma;Jing Wang;Hong Zhang

Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition)

2011-5

AZ31B Mg/5052 Al laminated composite sheet with superior mechanical property and good sheet shape was fabricated by novel corrugated roll/flat roll corrugating rolling and flat roll/flat roll flat rolling (CFR) at elevated temperatures. The microstructural evolution and mechanical behavior variation of the composite sheet under CFR hot rolling condition were investigated by experimental and numerical simulation methods. The results show that first-pass corrugated rolling induces relatively high and inhomogeneous shear strain in the Mg side and various corrugated interface positions at a low reduction of 35%. It leads to significant grain refinement, outstanding basal texture modification as well as tensile twin activation Mg alloy, which perfectly coordinates the plastic deformation between hard-to-deform Mg and ductile Al and achieve the strong interface metallurgy bonding in Mg/Al sheet and also significantly improves the mechanical properties of Mg/Al composite sheet. The annealing before second-pass flat rolling causes the pronounced static recrystallization and grain growth of Mg alloy in corrugated-rolling Mg/Al sheet, and the formation of ~25 μm thick interfacial compound layer consisted of Mg₁₇Al₁₂ and Al₃Mg₂ two sublayers. Second-pass flat rolling with a reduction of 30% further imposes severe inhomogeneous shear deformation on the composite sheet, which results in the formation of a wave-shape three-dimensional bonding interface, and the interface compound layers cracking at peak and waist interface positions or fragmenting into well-aligned discrete particles to the bonding interface, in addition to substantial matrix microstructure refinement, texture modification and twin activation in Mg alloy. Such interface structure greatly enhances the interface bonding force of the Mg/Al composite sheet by the larger interface contact area, mechanical gearing effect as well as particle pinning effect. Hence the significant microstructural refinement, strong interface bonding and low residual stress induced by CFR process account for the excellent performance of the Mg/Al laminated composite sheet.

Tao Wang;Yuelin Wang;Liping Bian;庆学 黄

Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing

2019-9-23

Due to the three-segment loop-like damage axially along inner surface of bearing sleeve under rolling loadcases, to quantitatively analyze damage mechanism, a mathematical model of oil-film bearing in the process of roll was developed by 3-D elastic contact boundary element method. A program of automatically creating 3-D surface grid model has been developed to check data and display deformation, the properties of stress and deformation fields have been analyzed, the rules of 3D contact pressure distribution among contact areas have been quantitatively described, which provided an effective way to decrease wear and adhesive damage of sleeve, and to increase load capacity of oil-film bearing and its service life as well.

Wang Jian-mei;庆学 黄;Yang Shi-chun

2005

Hardness, tribological properties and electron work function (EWF) of AZ31 alloy pre-deformed at high and low strain rates were investigated. It was observed that the pre-deformation lowered hardness of the magnesium alloy, ascribed to the formation of micro-cracks/voids in addition to dislocations. The deformation at the higher strain rate resulted in larger decrease in hardness and consequently more material loss during wear tests. XRD diffraction analysis did not provide clear clues in regard to residual strain that is related to the dislocation density. However, the observed influences of the strain rate-dependent pre-deformation on the properties of the alloy are explainable based on corresponding changes in work function. It was observed that the lower strain rate led to a larger decrease in EWF, corresponding to a higher fraction ratio of dislocations to micro-cracks/voids, which affected the performance of the alloy. First-principle calculations were conducted to investigate changes in EWF caused by dislocation and vacancy cluster, respectively, which support the explanation. This study demonstrates that the work function can provide supplementary information towards clarification of underlying mechanisms for the observed phenomena.

Vikas Kumar;Lei Li;Hailian Gui;Xiaogang Wang;庆学 黄;Q. Y. Li;Fatma Mokdad;Daolun Chen;D. Y. Li

Wear

2018-11-15

According to revised Cailikefu's rolling shear force formula, motion path equation of spatial seven-bar path is built, and mechanical model, with such new structural features as asymmetric and negative offset, is thus successfully established for 2800 mm heavy shear of some Iron&Steel Company. Shear force and bar force of steel plate, before and after adoption of asymmetric and negative offset structure, are analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. The discovery is that back-wall push force could be kept large enough at rolling start-up (i.e. the time that the maximum rolling shear produces), meanwhile, back-wall push force is the most approximate to side forces with adoption of 60mm-100mm offset. Theoretical results and on-site shear quality both indicate that new structural features such as asymmetric and negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant, which provide an effective means to improve quality of steel plate.

Yugui Li;Lifeng Ma;庆学 黄;Siqin Pang

Key Engineering Materials

2008

This work presents a fine microstructure and local misorientation study of various oxide phases in the tertiary oxide scale formed on a hot-rolled steel strip via electron back-scattering diffraction (EBSD). Local strain in individual grains of four phases, ferrite (α-Fe), wustite (FeO), magnetite (Fe₃O₄) and hematite (α-Fe₂O₃), has been systematically analysed. The results reveal that Fe₃O₄ has a lower local strain than α-Fe₂O₃, in particular, on the surface and inner layers of the oxide scale. The multiphase oxides along the cracking or α-Fe₂O₃ penetration generally develop a high local misorientation. Localised stain along the cracks demonstrates that the misorientation tends to be strong near grain boundaries. The high fraction of small Fe₃O₄ grains accumulate at the oxide-substrate interface, which leads to a dramatic increase in the intensity of local stain. This variation is due mainly to the phase transformation among the oxide phases, i.e., the Fe₃O₄ particles during their nucleation and growth. The combined action of stress relief and re-oxidisation is proposed to explain the formation of Fe₃O₄ seam at the oxide-steel interface. The present study offers an intriguing insight into the deformation behaviour of the tertiary oxide scale formed on steels, and may help with understanding the stress-aided oxidation effect of metal alloys.

Xianglong Yu;Zhengyi Jiang;Jingwei Zhao;Dongbin Wei;济 周;Cunlong Zhou;庆学 黄

Surface and Coatings Technology

2015-9-15

The cold-rolled bonding process of copper/aluminum bimetal plate was investigated by the velocity field of finite element method (FEM). At the same time, deformation characteristics of metal were analyzed in the bonding process. The study method was to combine theory calculation with field data. The circumferential velocity of rollers, rolling reduction rate, synchronous rolling of non-equal sized rollers and asymmetrical rolling of non-equal sized rollers were analyzed. Results show that the velocity field can explain the cold-rolled bonding process of copper/aluminum bimetal plate more effectively; the synchronicity of metal flow on bonding surface decreases with the increase of circumferential velocity about rollers near the exit of deformation area, and the bonding strength is reduced; in the process of synchronous rolling about non-equal sized rollers, diameter ratio of the rolls is 1.4~1.6 with a great synchronicity of metal flow near the exit of deformation area and a high bonding strength; in the process of asymmetrical rolling about non-equal sized rollers, the circumferential velocity rate of rollers is 1.2 with a great synchronicity of metal flow near the exit of deformation area and a high bonding strength.

庆学 黄;Jiang Zhang;Lin Zhu;Li Jiang;Xiangyu Gao

Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering

2017-7-1