A theoretical study on the application of asymmetric rolling for the estimation of friction

In this work, a method for the estimation of friction coefficient is proposed based on the asymmetric rolling operation. Asymmetry is produced by operating the lower and upper rolls at different speeds. A slab method based computer code is developed for estimating the curvature of the rolled sheet under asymmetric rolling conditions. Strain-hardening behavior of the material has been incorporated and Wanheim and Bay's friction model is employed. The developed code is used for solving the inverse problem of estimating the coefficient of friction by measuring the curvature of the rolled sheet under known operating conditions. The simulations show a good potential of the method.     

超越离合器应力应变比较分析

建立了典型的普通滚珠式超越离合器、楔块式超越离合器与多滚柱式超越离合器工作时应力应变状态模型,通过对三种超越离合器进行自锁失效分析,利用模拟仿真方法研究并比较了应力应变的变化对三种超越离合器的使用寿命的影响。     

Stress and residual stress distributions in plane strain bending

Stress and residual stress distributions in bending are important in calculating springback and loading capacity of a sheet-metal bending part. Great differences have been found in springback prediction with the same input (benchmark problems) among different researchers. In order to find out the root cause of these differences, stress and residual stress calculation methods in plane strain bending are briefly reviewed or developed. The influence of deformation theory and incremental theory, repeating bending, unbending and re-bending, cyclic material models and springback calculation methods on the stress or residual stress distributions are examined and shown to be large. This emphasizes the importance of careful selection of these variables in a simulation model in addition to other general input variables, such as material properties, tool geometry and friction condition. This fact also helps to explain the great differences among different research results, and presents a challenge to both the programmers and the users of finite element packages.     

Residual stress in some elasto-plastic problems of rolling contact with friction

The problem or rolling contact is of a great interest from the practical and cognitive points of view. It concerns for example a wheel passage on a rail, as well as many other processes where rolling or rolling with sliding is involved. Particularly, residual stresses distributions in the subsurface area due to plastic deformations are of significant importance: these stresses strongly influence fatigue limit and cracking tendencies of the material. A motion of the wheel on the rail (or of a roller on a strip) often has a very complex character: it consists of rolling, sliding in the longitudinal direction due to brakings and accelerations, sliding in the transversal direction, etc. Investigations conducted on this field by many authors have not yet delivered a unique solution. The aim of this paper is to determine the influence of some of these components of the wheel motion (separately and in common action) on residual stresses distributions. The problem has been investigated numerically by the FEM method, using the program SEGLA developed by the authors. The program can be applied to solving linear and nonlinear 2D, axisymmetric and 3D problems with elasto-plastic effects in the nonlinear contact and fracture mechanics. It uses three, four, six, eight and nine-node elements and also the special “spring” elements to model contact. The applied algorithm allows automatic analysis of these fragments of boundary, which enter and leave the contact; in the area where the “new” contact is created the program introduces additional elements.     

残余应力应变释放系数的有限元分析

通过建立16Mn残余应力盲孔法有限元分析模型,模拟出孔边应力、应变的变化情况.揭示了残余应力引起的孔边应力、应变变化情况与应变释放系数A、B值之间的关系,并用孔边应力、应变的有限元运算结果计算出A、B值.通过应变计中点应变法、应变计中点应力法和平均应变法三种方法去标定和修正应变释放系数,通过对三种方法的比较表明,三种方法的计算结果与实验结果相符.且计算精度较高.证实了残余应力有限元模拟的准确性和A、B值标定和修正方法的多样性.     

滚动转子式压缩机噪音分析与降噪措施的探讨

产生压缩机噪音的原因是多方面的,在进行压缩机噪音源分析的基础上,针对压缩机的关键部件进行了分析,详细阐述了它们产生噪音的主要原因,并总结分析了针对每一个关键部件能采用的降噪措施.     

7075铝合金厚板多道次蛇形热轧的分析与预测

研究了蛇形轧制工艺参数对铝合金厚板变形与残余应力分布的影响。基于蛇形轧制的咬入条件与本构模型以及边界条件等关键技术,构建了铝合金厚板的单道次蛇形轧制有限元模型,并与相关文献的仿真结果进行了比较,结果显示其相对误差不超过10%。考虑最小、最大压下量均相等的条件下压下量分配对蛇形轧制的影响,建立了多道次蛇形轧制的有限元模型并进行了仿真实验。结果表明:铝厚板应变不是按板厚中心面呈对称分布,慢速辊一侧的应变明显小于快速辊一侧,而且压下量对称递增分配产生的应变最大,单向递增分配产生的应变最小,对称递增比单向递增分配压下量产生的应变平均要高出20%左右。此外,压下量对称递减分配引起的剪切应变最大,单向递增分配引起的剪切应变最小,对称递减分配比单向递增分配压下量产生的剪切应变要高出2倍。     

超声滚压工艺对TC4钛合金表面残余应力的影响

钛合金关节轴承是航空发动机的重要部件之一,但由于其润滑条件较差,极易产生磨损从而导致失效事故。采用超声滚压工艺对钛合金试件表面进行强化试验,以有效增强试件表面耐磨性能和抗疲劳特性,并着重研究静压力、滚压次数和主轴转速等超声滚压强化工艺参数对钛合金表面残余压应力与剪切应力的影响规律。试验结果与理论分析结果表明,残余压应力随着静压力、滚压次数和主轴转速的提高而增大,剪切应力随着静压力、滚压次数和主轴转速的提高而总体减小;滚压后试件表面可获得-2 000～-500 MPa的残余压应力和-600～-300 MPa的剪切应力。超声滚压技术可以有效提高钛合金材料表面的残余压应力,并有效降低表面的剪切应力。     

楔横轧二次楔轧制大断面收缩率的应力应变场分析

利用有限元软件DEFORM-3D,基于三雏刚塑性的有限元理论,对大断面收缩率轴类零件成形过程成功地进行了楔横轧二次楔轧制成形的数值模拟,模拟所得的轧件形状与实际零件基本相同,给出了楔横轧二次楔轧制过程的应力应变分布等重要信息。模拟结果表明：二次楔轧制大断面收缩率轴类零件的心部发生了很大变形;二次楔轧制中间横截面受的横拉应力时间较长、值较大,所以轧件中心更容易产生内部缺陷。     

压下量对钢筋矫直系统力学性能的影响分析

以十一辊平行辊矫直机为原型,运用有限元分析软件ANSYS/LS-DYNA建立了钢筋矫直系统有限元模型;在理论压下量和实测压下量下,分别对3种不同直径的钢筋进行了动力学仿真分析,得到了钢筋在矫直过程中与矫直后的应力大小及分布情况;分析并比较了在理论压下量和实测压下量下,端面中心节点处与应力最大点处的弹塑性应变变化规律,找到了相对合理的压下量方案。该研究结果对掌握钢筋矫直过程的力学特性变化和提高矫直质量具有一定的参考价值和实际意义。     

Plane strain hot rolling of slab and strip

A numerical solution of the steady-state plane strain hot rolling problem with maximum friction is found in the range from the thick slab to the thin strip rolling geometries. The problem is kinematically determinate, and it is solved on the physical and hodograph planes using the finite-difference approximation of hyperbolic differential equations of the plane strain rigid–plastic flow theory. A sequence of the boundary value problems defined by the slipline field mode is treated as a non-linear vector equation which is solved by Broyden’s secant method. Six versions of the FORTRAN PC programs are written for a wide range of the slab/strip rolling geometries. The solution for the thin strip rolling with large roll radius and small strip thickness reduction is approached to Prandtl’s thin plastic layer with homogeneous velocity field.     

A method for estimating the stress distributions on the centre line of an axisymmetric, two-material, cross-weld, creep test specimen

Finite element analyses have been performed for an axisymmetric, two-material, cross-weld, creep test specimen. Stationary-state stress (and strain-rate) results were obtained for various geometries and relative material properties. Using these results, it has been shown that a simple interpolation technique can be used to obtain the stress distributions for any geometry and relative creep properties.     

滚动轴承寿命计算方法发展的研究与分析

详细介绍了滚动轴承疲劳寿命的概念,并对滚动轴承疲劳寿命的发展历程进行了详细阐述,分析了各个不同时期寿命计算理论的特点,谨供相关人士参考。     

Functional behaviour of PVD coatings under sliding and rolling stress conditions

Whereas wear-resistant PVD coatings are well established in the field of metalcutting, and the functional and tribological behaviour of these coatings is well known under such conditions, PVD coatings are used only occasionally in mechanical engineering. The reason for this seems to be the lack of information concerning the functional behaviour of these coatings in closed tribosystems. To evaluate new areas of application together with optimised coating compounds, model wear tests were performed under sliding, rolling and slip-rolling stress conditions. In addition, the test parameters, such as sliding speed, load, ambient temperature, and number of revolutions were varied, as were the coating compounds and their thicknesses. The results obtained show that friction and wear of PVD coatings are both strongly influenced by the kind of stress and the test parameters themselves. Coatings that perform well under certain test conditions can break down quickly under some other stress conditions. TiN coatings, for example, which display low friction and wear under sliding friction, fail under rolling conditions very shortly afterwards.     

轧钢机械设备轴瓦的检修要点分析

轧钢机械设备是当前工业发展的重要设备之一,其运行效果、效率可以说直接关系着其性能的发挥,为了使轧钢机械设备能够正常运转,那么提高轧钢机械设备轴瓦的运转效果也是非常关键的。本次研究结合轧钢机械设备轴瓦的具体情况,对轧钢机械设备轴瓦检修存在的问题及检修要点进行分析,旨在提高轧钢机械设备的运行效果。     

Elastic-plastic thermal stress analysis of an aluminum composite disc under parabolic thermal load distribution

An elastic-plastic thermal stress analysis was carried out on an orthotropic aluminum metal matrix composite disc with a hole by using an analytical solution. The thermal load distribution was chosen to vary parabolically from inner surface to outer surface. An aluminum composite disc reinforced curvilinearly by steel fibers was produced under hydraulic press. The mechanical properties of the composite disc were obtained from experiments by using strain gauges. A computer program was developed to calculate the thermal stresses under a parabolic temperature from inner surface to outer surface. The material was assumed to be non-linear hardening. The elastic-plastic solution was performed for the plastic region expanded around the inner surface by an analytical method. The magnitude of the tangential stress component for elastic and elastic-plastic was higher than the magnitude of the radial stress component. Besides, the tangential stress component was compressive on the inner surface and tensile on the outer surface. The magnitude of the tangential residual stress component was the highest on the inner surface of the composite disc. The plastic region began at the inner surface of disc. This paper was recommended for publication in revised form by Associate Editor Joo Ho Choi Gürkan Altan is a Research Assistant of Mechanical Engineering at the University of Pamukkale, Denizli, Turkey. Gürkan Altan received the B.E. degree (1999) in mechanical engineering from Dokuz Eylül University, Izmir, and the M.S. degree (2004) in mechanical engineering from Pamukkale University, Denizli. Gürkan Altan is interested in production and applications of composite materials. Currently he is involved in the development and application of joints of composite structures.     

花键冷滚压成形力测试与分析

根据花键冷滚压加工原理,按机床受力,将加工过程中的滚压力分为主轴转矩和径向进给力两部分。设计测试方案,用计算机数据采集系统测得了主轴转矩和径向进给力在滚压过程中的实时变化曲线,分析了它们的变化特征,得出压入阶段结束时滚压力取最大值。对不同的工艺参数进行实验,得到了工艺参数对最大滚压力的影响规律。     

A comparison of methods to estimate the roll torque in thin strip rolling

An energy balance method is used to calculate the roll torque associated with non-circular thin strip rolling and the results for the torque are compared with the moments of the forces exerted on the roll by the strip. An example is given in which the results of the two methods are quite different. This probably indicates that the axis of the roll is not at the point about which the moment is taken. The energy balance method is also used to estimate the torque associated with circular arc rolling. The results are compared with those calculated with Hill's formula in one example and, in another example, the comparison is made between the results from the energy method formulated in this paper and a commercial package which also uses both an energy method and Hill's formula.     

轧辊直径对楔横轧大型轴类件应力应变影响分析

合理选择轧辊直径是楔横轧成形大型轴类件的重要技术指标,采用ANSYS/LS-DYNA有限元分析软件,对楔横轧轧制大型轴类件进行模拟,分析轧辊直径对楔横轧大型轴类件应力应变影响规律,阐明轧辊直径对于楔横轧大型轴类件轧件质量的影响程度,研究结果为实现大型轴类件楔横轧经济化生产提供理论依据.     

热套连接过程的热应力试验研究

轴与轴连接经常采用热套连接的方式,热套连接过程中轴套表面产生的热应力很难直接测量。采用一种间接测量的方法测量轴套表面热应力。