An optimization method for radial forging process using ANN and Taguchi method

In this study, the artificial neural network (ANN) and the Taguchi method are employed to optimize the radial force and strain inhomogeneity in radial forging process. The finite element analysis of the process verified by the microhardness test (to confirm the predicted strain distribution) and the experimental forging load published by the previous researcher are used to predict the strain distribution in the final product and the radial force. At first, a combination of process parameters are selected by orthogonal array for numerical experimenting by Taguchi method and then simulated by FEM. Then the optimum conditions are predicted via the Taguchi method. After that, by using the FEM results, an ANN model was trained and the optimum conditions are predicted by means of ANN (using genetic algorithm as global optimization procedure) and compared with those achieved by the Taguchi method. The optimum conditions are verified by FEM, and good agreement is found between the two sets of results.     

圆螺纹套管接头应力分布规律研究

根据弹塑性力学理论建立圆螺纹套管接头的计算模型，利用有限元分析和全尺寸实验相结合的方法，详细分析套管接头在使用工况(包括上扣、上扣后加拉伸载荷、上扣后加内压载荷等)下的应力分布规律，指出载荷在各个螺纹牙上分布的不均匀性是制约套管接头性能的主要原因，提出改进接头应力状态、减少应力集中的主要措施。研究结果提高了对套管接头应力水平的认识，对改进套管连接螺纹设计，提高套管接头的连接质量具有一定的参考价值。     

An enriched finite element algorithm for numerical computation of contact friction problems

In this paper, the extended finite element method (XFEM) is employed to model the presence of discontinuities caused by frictional contact. The method is used in modeling strong discontinuity within a standard finite element framework. In extended finite element method (XFEM) technique, the special functions are included in standard FEM to simulate discontinuity without considering the boundary conditions in meshing the domain. In this study, the classical finite element approximation is enriched by applying additional terms to simulate the frictional behavior of contact between two bodies. These terms, which are included for enrichment of nodal displacements, depend on the contact condition between two surfaces. The partition of unity method is applied to discretize the contact area with triangular sub-elements whose Gauss points are used for integration of the domain of elements. Finally, numerical examples are presented to demonstrate the applicability of the XFEM in modeling of frictional contact behavior.     

A concise finite element model for three-layered straight wire rope strand

A concise finite element model (FEM) of three-layered straight helical wire rope strand under axial loads (tensile and torsional) is presented in this paper. Three-dimensional solid elements were used for structural discretization. The helical symmetry of the strand was used to establish accurate boundary conditions. Contact, friction and plastic yielding were also taken into account. For the global behaviour of wire rope strand, i.e. load vs. strain and load vs. torque (fixed-end) or load vs. strand twist rate (free-end), the finite element results showed better agreement with the experimental results of Utting and Jones (Journal of Strain Analysis for Engineering Design 1988;23(2):79–86) than those calculated using the analytical strand model of Costello (Theory of Wire Rope, 2nd ed. New York: Springer, 1997). In addition, the FE model allows the localised stress distribution to be determined. In particular, this model reveals the non-uniform stress distribution in the outer layer helical wires caused by the trellis point contact. This is particularly relevant in the fixed-end case, where the present analysis predicts an axial tensile rigidity in good agreement with the experimental observations (Utting and Jones), whereas Costello’s model predicts a significantly higher rigidity.     

滚动轴承接触问题的数学规划法

将滚动轴承的接触分析采用有限元弹性问题计算,可以获得一个与实验结果比较一致的解。本文通过讨论摩擦接触问题的本构模型,利用参变量分原理获得一个解有间隙带摩擦弹性接触问题的数学规划法。为使滚动轴承的接触分析更能符合实际情况,考虑轴承箱与外圈的摩擦,得到不同摩擦状况下轴承的接触区及接触力分布。从而为轴承接触问题分析提供了一个有效的数值方法。     

少齿差内啮合齿轮轮齿接触问题研究

本文以有限元弹性接触分析理论为基础,提出了一种对少齿差内齿轮副啮合过程中齿间载荷分配、齿面载荷分布的分析计算方法;建立了少齿差内啮合齿轮多齿接触时的有限元模型,具体分析了一齿差内齿轮在运转中,形成多齿接触时齿间载荷、齿面载荷及位移场、应力场的分布规律。     

2D FEM estimate of tool wear in turning operation

Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. In this paper, modelling techniques on continuous chip formation by using the commercial FEM code ABAQUS are discussed. A combination of three chip formation analysis steps including initial chip formation, chip growth and steady-state chip formation, is used to simulate the continuous chip formation process. Steady chip shape, cutting force, and heat flux at tool/chip and tool/work interface are obtained. Further, after introducing a heat transfer analysis, temperature distribution in the cutting insert at steady state is obtained. In this way, cutting process variables e.g. contact pressure (normal stress) at tool/chip and tool/work interface, relative sliding velocity and cutting temperature distribution at steady state are predicted. Many researches show that tool wear rate is dependent on these cutting process variables and their relationship is described by some wear rate models. Through implementing a Python-based tool wear estimate program, which launches chip formation analysis, reads predicted cutting process variables, calculates tool wear based on wear rate model and then updates tool geometry, tool wear progress in turning operation is estimated. In addition, the predicted crater wear and flank wear are verified with experimental results.     

Theoretical and Finite Element Analysis of Static Friction Between Multi-Scale Rough Surfaces

The current work considers the multi-scale nature of roughness in a new model that predicts the static friction coefficient. This work is based upon a previous rough surface contact model, which used stacked elastic–plastic 3-D sinusoids to model the asperities at multiple scales of roughness. A deterministic model of a three-dimensional deformable rough surface pressed against a rigid flat surface is also carried out using the finite element method (FEM). The accuracy of the deterministic FEM model is also considered. At the beginning of contact, which is surface-point contact, the asperities or peaks are isolated, sharp, and the contact areas consist of an inadequate number of elements and sources of error. In this range of contact, the results are not presented as real or accurate. As the normal load increases, the number of the contact elements become larger, and thus, the results become more accurate. That is, the deterministic FEM results are most accurate at high loads. Spectral interpolation is used to smooth the geometry in between the original measured nodes. The effects of normal load and plasticity index on static friction are then analyzed. The results predicted by the theoretical model are also compared to other existing rough surface friction contact models and the FEM results. They are in a good qualitative agreement, especially for higher loads and higher plasticity indices. The FEM model also has significant error, but it is more accurate at higher loads where the proposed multi-scale static friction model and FEM model are in better agreement.     

某型装甲破障车车体结构强度有限元仿真研究

某型装甲破障车的车体结构在复杂组合载荷作用下,必须同时满足强度和海上浮力储备等技术要求,有限元仿真技术为快速经济地实现这样的设计目标提供了可能。首先建立车体结构的三维实体有限元模型,其中对车体各部件之间复杂的接触条件和部件形状进行简化处理,给出车体结构承受的外挂部件重力、爆破器发射冲击力、发动机离心力和最大输出扭矩等载荷的等效静力学表达,确定车体结构的边界约束条件。仿真计算各种载荷作用下车体结构的变形和应力分布状况,指出车体结构强度和刚度的薄弱部位,分析导致计算的最大应力超过材料屈服强度的原因,提出并仿真验证车体主要承载部件的设计改进方案。     

基于有限元法的柴油机连杆强度分析研究

采用有限元接触分析的方法,利用ANSYS有限元分析软件对某型柴油机连杆进行了疲劳强度分析。根据连杆的实际工作状况,建立了按多体接触的三维模型,模拟了连杆零部件之间的接触;根据连杆的受载情况,分别就连杆承受的最大压力和最大拉力两种工况计算了连杆工作载荷,并利用APDL语言编程,将载荷以油膜压力分布的方式施加到连杆的轴瓦和衬套上。通过有限元的方法,基于接触理论对连杆进行了结构强度计算分析。实践证明,该方法能有效地指导连杆的设计工作。     

Multi-body contact modeling and statistical experimental validation for hub-bearing unit

A multi-body contact FEM model is initially established to simulate an internal stress distribution of the flexible hub-bearing system. It reveals that several peak load/stress values appear on the bearing raceway along its circumference, which is different from the conventional cosine curve distribution. Based on the simulation, hub-bearing unit performance was analyzed and its failure modes were predicted. Asymmetry of stress distribution demonstrates strong coupling effect with rigidity distribution of the flexible surrounding structure. Consequently, this will result in several typical failure modes for given load conditions. In this paper, the failure characteristics of the same type of 600 sets of failed hub-bearing units were statistically analyzed and compared with the simulation result. This comparison confirms that the FEM modeling is a potential approach to optimize the main geometrical parameters of the hub-bearing system, taking specific external load, friction, and heating into account.     

Analysis of the drop forging of a piston using Slip-Line Fields and FEM

The paper analyses the process of a forging piston-type product. The Finite Element Method (FEM) is used to determine the forging loads and the kinematics of metal flow during the press forming process analysed. The Slip-Line Field Method (SLFM) is used to obtain a simplified solution. This helps to determine the distribution of material-tool contact pressures which is the basis for computing the forging load. The results from both methods were verified experimentally and good agreement was obtained. In addition a comparison is made between the forging load values obtained in the present study and those given by selected equations from the literature.     

Contact of rough surfaces: A review of experimental work

In recent years engineers have come to realize that the determination of the contact geometry of rough surfaces is of critical importance in the solution of many tribological and conduction problems. The theoretical study of the contact of rough surfaces is well advanced whereas the experimental work on this topic has not received the attention that was due. This paper presents a review of the experimental investigations that have been carried out so far. Their findings and experimental methods are discussed. The main topics of experimental study are the separation of the surfaces, the real area of contact, the number of contact spots, the spatial distribution of the contact spots and the distribution of their sizes, and the relation of all these to roughness and to the normal load. Experimental techniques have included total internal reflection, Nomarski interferometry, neutrography, thermal and electrical resistance and computer simulation. The consensus of experimental results is as follows: the real area of contact increases with the load and this increase is due mainly to an increase in the number of micro-contacts, their mean size remaining approximately constant; the separation of the contacting surfaces is approximately inversely proportional to the logarithm of the load; the distribution of contact spot sizes is approximately log normal. However, it appears that the density and average size of micro-contacts can vary over several orders of magnitude for different surfaces at the same load. It also appears that, contrary to established belief, the real area of contact does not vary as the load but increases as its 0.8 power.     

Experimental and direct numerical analysis of hard-disk drive

The purpose of this paper is to study methods for enhancing the reliability and performance of hard-disk drives (HDD) because it is essential for improving recording density, speed of data access, and output signal. This study also investigates various techniques that can be used for head/disk contact detection. The acoustic emission (AE) and friction signal characteristics were observed with respect to the durability of the head/disk interface (HDI) under various operating conditions using a contact start-stop (CSS) test. In addition, to study the influence of surface topography on the stiction performance of the HDI, a modified and polished laser pump was proposed and CSS investigations were accomplished. Moreover, the static and dynamic properties of an HDD air slider were studied using a finite element method (FEM).     

数控机床误差补偿技术及应用载荷误差补偿技术

利用有限元法对机床的结构进行受力变形的分析,并用接触理论对导轨的受力变形进行分析计算,提出了计及载荷误差的机床空间误差通用计算模型。用此计算模型在多种载荷下对ＸＨ７１５加工中心的空间误差进行计算,其结果与实测值基本吻合。     

On Reciprocating Elastomeric Seals: Calculation of Film Thicknesses Using the Inverse Hydrodynamic Lubrication Theory

The elastohydrodynamic lubrication (EHL) problem of an axi-symmetric, elastomeric, reciprocating seal may be considered as one of a heavily loaded line contact with only small piezo-viscous effects. A method is presented to calculate the overall film thickness for the stationary, isothermal situation with sufficient lubricant supply and negligible surface roughness effects. It applies the inverse theory to the frictionless dry contact pressure distribution, considering the influence of the boosting action in the entry zone of the film. Its validity is shown for the isoviscous EHL of the Hertzian contact. The finite element method (FEM) may be used to calculate the contact situation of mounted and pressurized seals. Important aspects of such calculations are discussed. To calculate film thicknesses using such FEM results, a computer program PROGRES was written. Good correspondence between the predictions of PROGRES and experimental outstroke film thicknesses are obtained for a rectangular rod seal with rounded edges.     

子午线轮胎静态侧倾性能有限元分析及试验研究

采用三维非线性有限元分析方法,在模型中考虑了轮胎的几何非线性、材料非线性以及轮胎接触非线性,计算了子午线轮胎195/60R14在不同角度侧倾接地时的变形情况,与试验结果进行了比较。分析了轮胎在静态不同角度侧倾接地状况下载荷-下沉量变化、接地区压力分布、接地区摩擦力分布、侧倾侧向力-侧倾角变化关系;采用连续加载-卸载方式,开展了轮胎侧倾接地试验,实时记录了轮胎受力与变形关系,采用压力敏感膜测量了轮胎侧倾接地时的接地区压力分布状况。结果表明,轮胎侧倾接地状况下的变形及接地区压力分布趋势的计算结果与试验测试结果一致。     

大型结构的螺栓连接有限元简化方法与验证

优化了一种考虑大型结构的螺栓连接有限元模型的简化方法。简化方法仅需要对有限元模型施加均匀压力,而不需要对所有螺栓完全建模。该简化方法不仅提高了螺栓连接模型有限元计算时的收敛性,而且节约了计算成本。详细分析了该简化方法的假设。为了验证简化方法的准确性和可靠性,对螺栓连接结构的建立了简化模型,计算三种不同载荷作用下模型的多个关键特征量与接触应力云图,并与传统建模的结果对比,得出使用方法的简化模型的适用条件。     

Finite element analysis of axisymmetric sheet stretching process

The incremental updated Lagrangian elasto-plastic finite-element method (FEM) was employed in this study to analyse sheet stretching under the axisymmetric condition. The extended r _min technique is utilized such that each incremental step size is determined not only by the yielding of an element Gaussian point, but also the change of the boundary condition along the tool-metal interface. The frictional force in the contact region between the sheet and the tools is computed by the application of Coulomb’s friction law. Low-carbon (BA-DDQ) sheet plates were used throughout the experiments, which were later performed using a hemispherical punch head. Experimental tests were performed to demonstrate formulation of the theory and development of the computer code. The experimental load shows good agreement with the value of the punch load predicted by the finite-element method. When performing numerical calculation, the entire loading process history, the deformed geometry, the nodal velocity, and the distributions of strain and stress are also obtained by considering carefully the moving boundary condition. From the results of the experiment and the FEM, it may be concluded that the method proposed here provides a good model for simulating the axisymmetric sheet stretching process.     

LOAD SHARING AND CONTACT OF HOURGLASS WORM GEARING

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