Test and analysis of mechanism and influential elements of axial drifting of weldment on turning rolls

0　IntroductionTheweldingturningrollsismainlyusedforweldingassemblyofcylindricalweldingcomponents.Duetode viationinfabricationandassemblyofweldingturningrollsandgeometricirregularityofweldment,theweld mentthrobsaxiallywhileitrollsontheweldingturningrolls .Itwillinfluencetheweldingqualityandbreaknor malweldingprocedure .Intheworstcases,theweld mentfallsdownfromtheweldingturningrollsandcaus esaccident.Akindofweldingturningrollsagainstaxialdriftinghasbeeninventedabroadinthemiddleof 1980andhasbee…     

Effects of heat treatment and plastic deformation on structure and properties of Mg-9Al-1.2Nd-0.45Y-0.7Zn Mg alloy

The experiments of heat treatment, hot extrusion and hard drawing were employed to study their effects on the structure and mechanical properties of Mg-9Al-1.2Nd-0.45Y-0.7Zn magnesium alloy. The results indicate that the mechanical properties of the ingot are unstable and exhibit typical brittle failure. After heat treatment （693 K, 24 h）, most β-Mg17Al12 phases decomposed into the a-Mg matrix and the distribution of Rare earths compounds remained the state of as-cast, which have little effects of the mechanical properties of the alloy. As the casting defects disappeared and the grain was refined after hot extruded, the mechanical properties of the alloy were drastically increased. By hard drawing, the ultimate tensile strength and the yield strength of the alloy were sharply increased while the elongation decreased rapidly. The failure of as-cast samples was mainly brittle fracture. After plastic deformation, the fracture patterns all exhibited ductile rupture features.     

High cycle fatigue and fracture behavior of 2124-T851 aluminum alloy

The high cycle fatigue properties and fracture behavior of 2124-T851 aluminum alloy were investigated roundly, including the fatigue crack growth rate, fracture toughness and fatigue S--N curve. Furthermore, the fatigue crack growth rate was analyzed by fitting the curves. And the microstructure of the alloy was studied using by optical microscopy, transmission electron microscopy and X-ray diffractometry, scanning electron microscop1/2 The results show that the fatigue strength and the fracture toughness of 2124-T851 thick plate are 243 MPa and 29.6 MPa.m at room temperature and R=0. 1, respectively. At high cycle fatigue condition, the characteristics of fatigue facture were observed obviously. And the higher the stress amplitude, the wider the space between the fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area and the greater the ratio between the intermittent fracture area and the whole fracture area.     

Hot deformation behavior of Al-Cu-Li-Mg-Zr alloy containing Zn and Mn

The hot deformation behavior of a new AI-Cu-Li-Mg-Zr alloy was studied, and its microstructure and true stress were characterized as function of the deformation temperature and the strain rate using Gleeble-1500 thermal mechanical simulator. The results show that, with the increase of the strain rate from 0.001 s^-1 to 10 s^-1, the peak value of true stress is elevated at the same deformation temperature, and at the same strain rate the peak value of the true stress decreases with the increase of the deformation temperature from 360 ℃ to 520℃. Dynamic recrystallization easily occurs in the new Al-Cu-Li-Mg-Zr alloy under the lower strain rate and the higher deformation temperature, and dynamic recovery can usually be seen in this alloy under the higher strain rate of 10 s^-1 and the lower deformation temperature.     

Study of closure welded joint between penstock and spiral case

0Introduction Inordertoadaptthedistortionofpenstockbetween theplantanddam,thetelescopicjoint,whichliesinthe junctionbetweentheplantanddam,isusuallysetupin thelower horizontalpartofpenstock.Thetelescopicjoint intheexistinghydropowerstationhasleakorwatercre…     

Effects of sintering pressure and temperature on microstructure and tribological characteristic of Cu-based aircraft brake material

A novel Cu-based P/M aircraft brake material was prepared and the effects of sintering pressure and temperature on microstructure and tribological characteristic were investigated. For the constant sintering temperature, when the sintering pressure increases from 0.5 MPa to 1.5 MPa, the porosity, wear loss and friction coefficient decrease remarkably. When the sintering pressure increases from 1.5 MPa to 2.5 MPa, the porosity further decreases but in a little degree and wear behaviors are improved slightly. However, once the sintering pressure is larger than 2.5 MPa, it has no obvious effect on microstructure and tribological characteristic. For the constant sintering pressure, when the sintering temperature increases from 900 ℃ to 930 ℃, the sintered density remarkably-increases, and wear behaviors are obviously improved. For further increasing sintering temperature to l 000 ℃, the density keeps on increasing, but wear behaviors change slightly.     

Determination and application of stress-based forming limit diagram in aluminum tube hydroforming

The stress-based forming limit diagram（FLSD） established with limit stress is independent of the strain paths. Compared with traditional strain-based forming limit diagram（FLD）, it is more convenient and practical to use as the criterion of forming limit under complex strain paths. The forming limit of 3A21 aluminum alloy sheet was tested and its forming limit diagram（FLD） was determined. Then the FLSD of 3A21 was constituted by transformation formulas between limit strain and limit stress. This FLSD was used in conjunction with LS-DYNA finite element simulations to predict the onset of fracture and limit forming pressure in tube hydroforming. The results indicate that the fracture often occurs in the transition region between corner and straight side of the tube, and the limit forming pressure is 46.4 MPa. The simulation result agrees with the experimental result, and the FLSD is able to predict the forming limit of tube hydroforming with remarkable accuracy.     

Discussion and prediction on decreasing flow stress scale effect

Based on crystal plasticity theory and surface layer model, relation of flow stress to billet dimension and grain size was built, and rationality of derived relation was verified with tensile tests of different size billets. With derived expressions, relation of decreasing flow stress scale effect to billet dimension, grain size as well as billet shape was discussed and predicted. The results show that flow stress is proportional to billet size; with decrease of grain size, flow stress is less influenced by billet dimension. When both cross section area and grain size are same, flow stress decrease of rectangular section billet or sheet is larger than that of circular section billet.     

Modeling of microstructural evolution and flow stress of aluminium alloy during thermomechanical process

The evolution of microstructural variables, including the densities of mobile dislocation, immobile dislo-cation at the cell interiors, immobile dislocation in the cell walls, as well as total dislocation density, of an Al-Mg-Si aluminium alloy during thermomechanical processing were simulated based on a three-internal-variables-model (3IVM) involving dislocation climb and interaction. Optimization was carried out to fit the calculated stress--strain curves to the experimental data of the Al-Mg-Si alloy with minimum mean deviation. Precipitations were taken into consideration of modeling. The stress--strain curves predicted by the kinetic equations of state in the 3IVM have a good agreement with the experimental data.     

Solution for slab forging with bulge between two parallel platens by strain rate vector inner-product integration and series expansion

1INTRODUCTIONSlab forging with bulge between two parallelplatens is shown in Fig.1.Friction over the sur-face decreases the velocityvxat the surface,andcauses the centery=0to move faster with a result-ant bulge as shown in Fig.1(a).Therefore,thisvelocity gradient from the surface to the interiorintroduces a shear strain rateε.xy.Fig.1Slab forging with bulge betweentwo parallel platensIt is the bulge that make the forging more dif-ficult to be analytically solved[1].However,nu-merical m…     

Effect of working pressure and temperature on ZnO film deposited on free-standing diamond substrates

The structure characteristic and electric performance of ZnO film deposited on nucleation side of free-standing diamond substrates under different heating temperatures (T_h) of substrate and working pressures (p) were studied. The structure of the ZnO films tested by X-ray diffraction shows that ZnO film of high c-axis orientation is deposited on the nucleation side of free-standing diamond substrate which is extremely smooth when T_h=250 °C and p=0.4 Pa. After annealing at 480 °C in N₂ atmosphere, the SEM and the AFM analyses demonstrate that the c-axis orientation of ZnO film is obviously enhanced. The resistivity of ZnO films also increases up to 8×10⁵ Ωcm which is observed by I–V test.     

Theoretical study and numerical simulation of the stress fields of the Al2O3 joints brazed with composite filler materials

Non-linear finite element code MSC. Marc was utilized to analysis the field of stress of the Al2O3 joints brazed with composite filler materials. The properties of the filler materials were defined by using the mixing law, method of Mori-Tanaka and theory of Eshelby to ensure the accuracy and reliability of results of finite element method （FEM）. The results show stress in brazed beam is higher than that in base material. The maximal stress can be found in the interface of joint. And the experimental results show that the shear strength of joints increases from 93.75 MPa （ Al2O3p Ovol. % ） to 135.32 MPa （ Al2O3p 15vol. % ） when composition of titanium is 3wt% in the filler metal.     

Influences of post-annealing and internal stress on magnetoresistance properties of Ni80Fe20 films

Ni80 Fe20 films with thickness about 54 nm were deposited on K9 glass and thermally oxidized silicon substrates at ambient temperature by electron beam evaporation with deposition rate about 1.8 nm/min. The as-deposited films were annealed at 350, 450 and 570 ℃ respectively for 1 h. After annealing at 570 ℃, the anisotropic magnetoresistance ratio(RAM) of the films is greatly improved. It increases to 3%- 3.5% nearly about three times of that of the as-deposited films. The grain size increases with the annealing temperature and the [111] crystal orientation is obviously enhanced after annealing at temperature above 450 ℃. The internal stress in the films deposited on K9 glass is compressive and the resistance measurement shows that RM∥ is larger than RM⊥ in these films. However, in the films deposited at the same conditions but on oxidized silicon substrates, the internal stress is tensile and RM⊥ is larger than RM∥. The differences of RM∥ and RM⊥ in two series of specimens are discussed.     

Effects of temperature and pressure on morphologies of quasi-one-dimensional ZnO nanostructures fabricated via thermal evaporation

Quasi one-dimensional zinc oxide nanomaterials were synthesized by thermal evaporation. The structure, morphologies and composition of ZnO nanomaterials prepared under different conditions were studied by XRD, TEM, SEM and EDX. The morphologies are strongly sensitive to the temperature and the pressure during growth, including nanowires, nanobelts, nanocombs and pyramidal-like nanomaterials.     

一种充气皮囊式压力缓冲装置及其使用方法研究

针对某型流体机械附件试验过程中因压力脉动导致的试验管路内压力无法准确测量问题,将一种充气皮囊式蓄压油箱作为压力缓冲装置连接在试验管路中,并通过试验确定了使试验管路内压力脉动最小的缓冲装置最佳充气压力,从而有效消除了试验过程中管路内压力脉动,提高了压力检测精度。     

加压对铝合金消失模铸造的影响

试验研究了浇注后型腔压力对消失模铸造的铝件表面状态、力学性能影响的趋势。加压后提高了铝液充型能力,有利于消除铸件表面的颗粒状和冷隔,抑制气孔形成,使抗拉强度、密度略有提高;加大压力作用在浇口及铸件表面的时间差,铸件表面将出现凸起、粘砂;过早卸压将恶化铝件性能。     

Influence of nitrogen gas on structure and properties of DLC films prepared by XeCl pulsed laser deposition

Diamond-like carbon （DLC） films were prepared by PLD process using 308 nm（XeCl） laser beam with high power （500 W） and high fi＇equency（300 Hz）. The effects of nitrogen pressure on the structure and properties of the DLC films under such extremely high power and repetition rate were studied. The results indicate that the microstructures of the films are varied fi＇om amorphous carbon to graphitized carbon in long-order with the increase of N2 pressure, and the optical properties of the films are deteriorated as compared to that of DLC films without nitrogen.     

周向引入旋流喷嘴参数优化的仿真和实验研究

周向引入旋流喷嘴能够有效提高喷嘴内部的液体流速和外流场的雾化效果。针对影响旋流喷嘴的关键参数(射流管直径、喷嘴出口直径、射流水压),分别利用流体动力学软件仿真和实验测试研究了旋流喷嘴内外流场。结果表明:旋流喷嘴上部中心区域压力较低,旋流提高了喷嘴内部水流的速度;在旋流喷嘴内部,随着射流管直径的增大,喷嘴轴线的速率会随之增加,喷嘴内部射流速度均沿着轴线方向表现出单调增加的变化规律;雾化粒度D50随着射流水压和射流管直径的增加而减小;雾化粒度D50随喷嘴出口直径的增加均表现出单调增加的变化。确定最佳喷嘴出口直径为3 mm,射流管直径为4 mm。     

液压拉深中液体压力控制的研究

本文研究了液压拉深中工作液体压力——行程曲线的设计方法，建立了压力——行程控制曲线，设计了过程控制软件，采用以可编程控制器（ＰＬＣ）为中央处理器的压力控制系统，进行有关实验研究。结果表明，所建立的液体压力——行程曲线正确，对成形过程的控制有效。