压气机过盈配合的弹塑性有摩擦接触的研究

增压器压气机叶轮、轴套和轴采用过盈配合技术联成一体,这是三维多体弹塑性有摩擦接触问题,是两种非线性相互耦合的边值待定问题。采用有限元参数二次规划法,并结合多重子结构技术,充分利用两种方法各自的长处分析求解柴油机涡轮增压器叶轮与轴套、轴套与轴的三维弹塑性有摩擦接触问题,针对不同的过盈量、摩擦因数、转速和轴套壁厚进行了大量计算,获得了叶轮、轴套与轴之间接触应力的相应分布规律。轴套与轴的装配过盈量是影响轮轴接触应力的重要因素。在选择叶轮、轴套和轴三者装配尺寸时,尤其采用压力组装法时应严格控制轴套与轴的过盈量。研究结果表明,此方法对压气机弹塑性接触特性是有效的,能够反映接触区域的接触法向应力、变形以及摩擦力的大小和分布情况。     

考虑支座及限位装置非线性的接触摩擦单元模型

在连续梁桥活动墩上设置限位装置后,活动墩处将包含活动支座的摩擦及限位装置的接触碰撞两种非线性,综合摩擦单元及接触单元的特性,分别考虑接触单元的弹性及弹塑性情况,提出了接触摩擦单元的有限元模型,给出了接触摩擦单元的滞回曲线,针对卸载曲线的不同状态,分别推导出了其卸载刚度;利用接触摩擦单元对设置有分散抗震挡块及活动摩擦支座的连续梁桥进行了非线性地震反应分析,对挡块在降低连续梁桥固定墩地震反应上的分散抗震作用进行了研究,该接触摩擦单元可用于设置有防落梁装置及活动支座桥梁的较为细致的抗震分析模型。     

弹塑性接触边界元法模拟轧制过程

本文用作者开发的弹塑性接触边界元法首次模拟轧制过程。轧辊为弹性体,轧件为弹塑性体,视轧制为有摩擦的弹塑性接触问题,用最少的假定模拟了轧制过程,为分析轧制过程提供了一个有效而精确的数值解法。     

干气密封摩擦界面弹塑性接触刚度模型EI北大核心CSCD

针对干气密封摩擦界面复杂多变的弹塑性变形阶段,基于微凸体在变形全过程满足连续性、光滑性和单调性的特点,通过余弦函数来探究接触面变形量与接触特性之间的关系,建立了具有光滑连续特性的微凸体弹塑性接触模型,然后基于统计学理论,建立摩擦界面整体接触模型,最后将所建立的模型与GW模型、CEB模型、ZMC模型、KE模型和Li模型五种经典模型进行对比分析,并通过理论分析与数值求解得到干气密封摩擦界面的力学特性及影响因素。结果表明:该模型实现了微凸体在变形全阶段的连续性、光滑性和单调性;接触载荷、接触面积和接触刚度与无量纲接触变形量成正相关;与无量纲表面平均接触距离成负相关,且无量纲表面平均接触距离越小,其粗糙表面发生塑性变形的比重就越大;为使干气密封动环和静环更加可靠平稳地运行,应保证动环和静环的接触面尽量光滑平整,使其无量纲表面平均接触距离控制在2.5以下。     

坡膛结构变化对弹带挤进过程影响的研究

基于弹塑性有限元接触理论,引入了弹带材料的初始损伤及累计损伤模型,对弹带挤进、冲击坡膛的过程进行了理论分析,建立了弹带挤进、冲击坡膛的显式非线性有限元模型。对在两种不同结构坡膛条件下的弹带挤进过程进行了分析计算,得到了挤进过程弹丸及弹带的动力学响应,并通过计算分析了坡膛结构变化对挤进冲击力的影响,揭示了坡膛裂纹的形成机理。     

弹塑性有限变接触问题的边界元法

本文建立了弹塑性有限形变（大变形，大旋转）接触（考虑界面摩擦）问题的多重非线性边界元法，并计算机模拟了弹塑性体和弹性体的接触变形过程，可应用于精密轧制，精密塑性加工及铁路，水坝基础等工程领域。     

弹丸惯性卡膛冲击问题动力学研究

基于弹塑性有限元接触理论对弹丸惯性卡膛过程进行了理论分析,建立了弹丸惯性卡膛过程的有限元模型.对弹丸在1 m/s -4 m/s卡膛速度下的惯性卡膛过程进行了分析计算,明确了卡膛过程中弹带的弹塑性形变规律和弹丸的动力学响应,并通过计算分析了摩擦系数对卡膛过程计算结果的影响.     

混合润滑状态下结合面的法向接触刚度研究

针对润滑条件下机械结合面的接触特性受油膜影响的问题,基于结合面接触刚度由油膜接触刚度和固体表面接触刚度组成的思想,建立混合润滑状态下结合面的法向接触刚度模型。采用三维的Weierstrass-Mandelbrot函数获得具有分形特征的粗糙表面,并基于统计学方法建立干摩擦条件下结合面的法向接触刚度模型,考虑了微凸体的完全弹性变形、弹塑性变形以及完全塑性变形过程。在此基础上,求解了油膜的等效厚度并建立油膜的接触刚度模型。结果表明:结合面的法向接触刚度随法向载荷的增加而增加,且混合润滑状态下结合面的接触刚度大于干摩擦条件下结合面的接触刚度;该模型避免了油膜厚度测量难的问题,为机械结构的润滑状态预测提供了帮助。     

计算铁路车轮轮周磨耗量的两种方法对比

建立了车轮磨耗理论计算模型并发展了相应的数值程序,模型中包含了车辆轨道耦合动力学模型、轮轨滚动接触理论和材料摩擦磨损模型.根据该理论模型提出了两种磨耗叠加方法计算车轮轮周磨耗量,即简化方法和改进方法,探讨了它们对车轮型面磨耗及其演化规律的影响.简化方法假定车轮滚过一个接触斑长度时,接触斑信息不变,因而只计算一个步长即可...     

板材成形模拟的研究和应用

介绍了板材成形数值模拟技术的研究和应用在国内外发展的概况,并从基本算法、单元模型和网格划分、材料模型、接触摩擦、起皱问题、破裂问题和回弹计算等方面介绍了弹塑性有限元的基本原理、关键技术和主要难点,结合在工厂实际生产中的使用情况和存在的问题,展望了板材数值模拟技术今后的发展方向.     

Frictional contact analysis of multiple cracks by incremental displacement and resultant traction boundary integral equations

Based on the merits of the dual boundary element technique, a modified dual boundary element technique is extended to deal with the frictional contact of a finite plate with arbitrarily distributed multiple cracks. Besides establishing the incremental displacement boundary integral equation on the outer boundary, the resultant traction boundary integral equation on one of the crack surfaces is also developed. Since the resultant traction instead of incremental traction on the crack surface is introduced, the computed resultant contact tractions under sliding condition satisfy the Coulomb's friction law directly. Hence, as compared with the authors' previous work, only very few computation iterations are required by this method to accurately describe the contact situations of crack surfaces. As a result, not only the linear cracks, but also other types of multiple cracks, for example, curved and kinked cracks, can be tackled. The effects of friction and interaction among cracks on the computation of stress intensity factors are also displayed.     

Analysis of crack closure problem using the dual boundary element method

A numerical procedure of the crack closure problem solved by the dual boundary element method is developed in this paper. The dual boundary element method is used to allow for the solution to a general mixed-mode crack problem with a single regional formulation. The frictional contact problem on the crack surface is formulated with the complementary problem adapting the Coulomb's friction law. Several examples are shown to demonstrate the validity of the present procedure.     

A general boundary element method approach to the solution of three-dimensional frictionless contact problems

A direct boundary element method is presented for three-dimensional stress analysis of frictionless contact problems. The isoparametric formulation of the boundary element method is implemented for the general case of contact in the absence of friction, which is limited to linear elastic homogeneous and isotropic materials. An iterative procedure is employed to determine the correct size of the contact zone by finding a boundary solution compatible with the contact condition. The applicability of the procedure is tested by application to three problems of advancing and conforming contact. The computed results are compared with numerical and analytical solutions where possible.     

A finite element and experimental study of rigid-plastic compression

This paper is concerned with the effect of material properties, boundary friction, and inertia on the flow and strain patterns in material undergoing large plane strain compression. Experimental results are presented for both the rapid compression of Plasticine and the quasi-static compression of aluminium. In addition, a finite element code for rigid-plastic material behaviour is discussed, and approximate procedures are described for both in-plane and platen friction. Provision in the code was also made for strain hardening and strain rate sensitive material properties, and inertia effects. Comparison of the finite element and experimental results showed good agreement. Finite element calculations revealed that in-plane friction had a very significant effect on the strain patterns observed in the Plasticine experiments. Finite element calculations also showed that strain hardening was of fundamental importance in determining the strain patterns that were observed to occur in the quasi-static compression of aluminium.     

A finite element formulation of three-dimensional contact problems with slip and friction

The paper describes a special finite element for three-dimensional, large displacement analysis of contact problems with slip and friction. This element may be used to model contact between several finite element bodies or contact between a finite element body and a flexible or rigid geometrical surface fixed in space or moving with time. The contact formulation is based on the concept of a spring-supported, moving disk that transfers normal contact forces and Coulomb friction forces. The contact surface has a finite, prescribed boundary.The contact element has been incorporated into the general-purpose, nonlinear, finite element program FENRIS. Three examples of its application are described in the paper.J. W. Simons was previously NTNF Fellow, Division of Technology, Trondheim, Norway     

Simulation of Turbulent Flow Past Bluff Bodies on Coarse Meshes Using General Galerkin Methods: Drag Crisis and Turbulent Euler Solutions

In recent years adaptive stabilized finite element methods, here referred to as General Galerkin (G2) methods, have been developed as a general methodology for the computation of mean value output in turbulent flow. In earlier work, in the setting of bluff body flow, the use of no slip boundary conditions has been shown to accurately capture the separation from a laminar boundary layer, in a number of benchmark problems. In this paper we extend the G2 method to problems with turbulent boundary layers, by including a simple wall-model in the form of a friction boundary condition, to account for the skin friction of the unresolved turbulent boundary layer. In particular, we use G2 to simulate drag crisis for a circular cylinder, by adjusting the friction parameter to match experimental results. By letting the Reynolds number go to infinity and the skin friction go to zero, we get a G2 method for the Euler equations with slip boundary conditions, which we here refer to as an EG2 method. The only parameter in the EG2 method is the discretization parameter, and we present computational results indicating that EG2 may be used to model very high Reynolds numbers flow, such as geophysical flow.     

A new boundary element approach for contact problems with friction

A new boundary element solution algorithm for two-dimensional and axisymmetric contact problems with friction, based on an independent discretization of the contacting surfaces and under static and proportional loading conditions, is presented. The solution procedure uses the element shape functions to distribute the geometry, tractions and displacements on each contact element. The contact constraints are then applied between each contacting node and the opposite contact segment. The overall boundary element matrix equations for the contacting bodies are coupled using the contact conditions at the interface without introducing any additional variables into the solution matrix. The algorithm is applied to several two-dimensional and axisymmetric frictional contact examples and the results obtained are in very good agreement with finite element and analytical solutions.     

Modeling friction effects on the ballistic impact behavior of a single-ply high-strength fabric

It has been shown through experiments that interfacial friction affects the energy absorption of fabrics subjected to ballistic impact. However, how the friction plays a role is not well understood. In this paper, a commercially available finite element analysis code, LS-DYNA, is used to model the ballistic impact of a square patch of single-ply plain-woven fabric. Three types of boundary conditions are applied on the fabric: four edges clamped, two edges clamped, and four edges free. The friction between yarns at their crossovers and the friction between projectile and fabric are taken into account. Effects of the friction during the phase prior to yarn failure are parametrically studied. Simulation results show that at a given time, the fabric with high friction absorbs more energy than the fabric with no friction. For the boundary condition with four edges free, friction contributes to increasing the fabric energy absorption mainly through the mechanism of frictional sliding dissipated energy. For the boundary conditions with two or four edges clamped, the energy dissipated through frictional sliding only accounts for a very small portion of the total absorbed energy; however, both the yarn strain energy and the yarn kinetic energy are increased when there is friction. Friction has an indirect effect on the fabric energy absorption by influencing the number of yarns that become involved. Simulation results also indicate that the boundary conditions significantly affect the fabric deformation, stress distribution, and time history of energy absorption.     

BEM and FEM analysis of Signorini contact problems with friction

In this paper, we present a comparative study of the boundary element method (BEM) and the finite element method (FEM) for analysis of Signorini contact problems in elastostatics with Coulomb's friction law. Particularities of each method and comparison with the penalty method are discussed. Numerical examples are included to demonstrate the present formulations and to highlight its performance.     

轿车顶盖多点成形边界条件的处理

本文将多点成形技术应用在轿车顶盖成形过程中。以Hill关于弹塑性材料唯一性的充分性条件为理论基础,采用虚功率增率型原理,建立了多点成形时具有强烈弯曲效应的材料、几何与非连续性接触边界条件三、重非线性空间曲壳有限元列式,给出了非连续动态接触边界及库仑摩擦边界条件的处理方法,引用经典的J2流动理论研究了轿车顶盖的多点成形过程,并通过试验得到了验证。