金属材料塑性安定状态的研究

对圆环链用钢23MnNiCrMo54试样进行了一系列循环加载试验,并对试验后的记录结果进行了分析,同时对试样进行了透射电镜分析。试验结果表明,23MnNiCrMo54存在着安定状态现象,并且材料在安定状态发生后,金相组织位错密度有所增加。金属材料安定状态的存在能够为材料利用率的提高提供直接的实验和理论支持,提高目前金属构件设计中材料的许用能力。     

Surface asperity deformation under bulk plastic straining conditions

The paper is concerned theoretically and experimentally with the flattening of asperities by tools in metal-forming processes, a topic important to lubrication in metal forming. It specifically studies the plane strain compression process. It proposes kinematically admissible velocity fields for the crushing of asperities on a plastically flowing foundation and by adjusting independent variables of the fields predicts the actual flows by an energy minimization method. The theoretical predictions are compared with plane strain compression tests on aluminium samples with surfaces abraded in the direction of bulk plastic flow (the condition that the modelling describes). Both theory and experiment predict that asperities are crushed at the start of bulk plastic compression, to generate a real area of contact a certain fraction of the tool area depending on the contact friction and aspect ratio of the flow field, between 0.75 and 0.95 according to theory and between 0.6 and 0.8 according to experiment; but that with further bulk compression these contact fractions do not change. Despite these quantitative differences, it is felt that the method developed in this paper could usefully be extended to study asperity behaviour in other forming processes such as drawing or rolling.     

孔结构热接触弹塑性数值分析

应用ANSYS对实际孔结构进行了热载荷下接触模型弹塑性数值分析,建立了孔边接触弹性模型、孔边接触弹塑性模型和模拟弹性边界孔边接触弹塑性模型等三种不断改进的模型,分别模拟了结构的弹性弹塑性以及固支边界和弹性边界.通过对计算结果的分析比较,表明弹性边界的弹塑性模型更为精确可靠.     

基于单边接触模型的含间隙槽轮机构动力学分析

基于单边接触的间隙模型建立了含间隙槽轮机构的动力学模型,运用ADAMS模拟了机构的工作情况和销子在轮槽中的运动过程,并着重分析了间隙对槽轮机构动力学的影响机理,以及间隙变化、输入转速改变和负载对槽轮机构动力学所产生的影响。     

基于安定理论的微小裂纹疲劳门槛值的分析

通过弹塑性有限元法 ,利用 Melan的安定理论 ,分析了单缺口试件 ,在含有与试件材料晶粒尺寸相当的微小裂纹下的疲劳门槛值。通过对航空齿轮材料试件进行算例分析 ,其结果与相应实验结论比较吻合 ,并且表明 :利用静力安定法所研究微小裂纹疲劳门槛值 ,预测航空齿轮的寿命是较安全的。     

两弹塑性接触粗糙表面的严格解析解

GW干接触模型存在5个缺陷。当相糙峰高度的概率密度为Gauss分布时,给出了数学期望接触点数、总接触面积、总载荷、总电导的严格解析解,采用软件Maple计算了抛物柱面函数。实例计算表明接触点数与载荷近似成凸弧形直线正比例关系;量纲一的间距是联系接触点数、总接触面积、总载荷、总电导的纽带,它依赖名义压应力,但对名义压应力的变化不敏感;接触面积与载荷很接近直线正比例关系,在弹性接触条件下存在一个准弹性接触硬度,接触压应力等于准弹性接触硬度,名义面积对接触面积几乎无影响。     

两弹塑性接触粗糙表面的静密封流量

当峰高的概率密度为指数分布时,利用泰勒公式推导了弹性载荷的近似解析解,给出了塑性载荷的严格解析解,导出了静密封流量的经验表达式。通过密封表面的泄漏量与表高标准差的3次方成正比。在塑性接触状态,存在一个临界塑性指数,当塑性指数大于临界塑性指数时,总载荷与塑性指数、粗糙度参数皆无关,量纲一的塑性泄漏量与较软材料的硬度有关,与两接触粗糙表面的复合弹性模量无关。     

Thermomechanical contact homogenization with random rough surfaces and microscopic contact resistance

We extend an earlier computational thermomechanical contact homogenization framework [Temizer ?, Wriggers P. International Journal for Numerical Methods in Engineering 2010; 83:27-58] to random rough surfaces generated through the random-field model based on the concepts of ensemble averaging and sample enlargement towards the effective limit. Additionally, the homogenization theory is revisited in order to incorporate thermal dissipation at the microscopic contact interface within a thermodynamically consistent approach that preserves dissipation across the scales. Large-scale three-dimensional computations were performed to demonstrate the effectiveness and feasibility of the computational framework for an accurate characterization of the macroscopic thermomechanical response of rough surfaces in contact.     

Contact analysis of three-dimensional rough surfaces under frictionless and frictional contact

A methodology for surface and sub-surface stress calculation of nominally flat on flat rough surface contact has been developed. This methodology is applicable for both large area contact (Hertzian contact) and small area of asperity contact (point load contact) with and without surface friction. A total of nine rough surfaces are generated by the computer with specified standard deviation of surface heights, σ, of 0.3, 1.0 and 3.0 nm, and correlation length, β^*, of 0.1, 0.5 and 0.9 μm. Under the typical applied load at the magnetic head slider-disk interface, small numbers of contact points are obtained and the deformation is purely elastic. Since these contact points are scattered and isolated, asperity contact behaves like point load contact. As β^* becomes larger, more adjacent points will be in contact at a certain contact spot and this is especially true at small σ. All the cases of flat on flat rough surface contact yield maximum von Mises stress on and near the surface at both frictionless and frictional contacts; no local maximum occurs in the sub-surface. In general, the friction effect in the vicinity of contact point is to increase the stress magnitude, while outside this region it also alters the stress distribution. For a surface of small β^* and large σ at high load of 1000 times of the nominal pressure at the head-disk interface, the contact pressure reaches the hardness at a few contact points and plastic deformation takes place in the near surface.     

循环热-机械载荷下螺栓法兰结构的安定性分析

利用通用有限元软件ABAQUS研究了循环温度和恒定机械荷载下螺栓法兰结构的安定性,并探讨了螺栓和法兰的材料属性对安定域的影响,得到了相应的经验设计公式。结果表明,当操作压力小于泄漏压力时,安定极限载荷与操作压力无关,但与螺栓和法兰的热膨胀系数比和弹性模量比有关,并给出了相应的经验公式。本文研究对循环温度和恒定机械载荷下螺栓法兰结构的安定性分析有一定的指导意义。     

Damage evolution and thermal coupled effects in inelastic solids

Mechanical degradation and ductile failure in metal forming operations can be successfully modelled using Continuum Damage Mechanics. In addition to elastic-plastic deformations, heat transfer affects material behaviour, imposing further effects upon damage evolution. This paper addresses modelling aspects and presents a numerical discussion of the coupled effects between ductile damage and temperature evolution. The heat transfer problem is formulated based on a transient heat conduction approximation, in which heat transfer at the free surfaces and heating due to dissipation of the inelastic work are accounted for. Damage is modelled using an elastic-plastic fully coupled approximation, in which differences in tensile and compressive stress states are included.     

两接触粗糙表面的椭圆弹塑性模型

视两单峰的接触区为椭圆,给出了两接触相糙表面的椭圆弹性通解.根据两单峰塑性接触时单个相糙峰的椭圆抛物面体积守恒推导了椭圆塑性通解.临界弹性干涉量随有效半径比增加而减小.塑性指数越小,临界弹性干涉量减小量越大.临界弹性干涉量随表面粗糙度增加、材料硬度减小而减小.椭圆、GW模型的临界弹性干涉量之比随有效半径比增加而减小.GW模型高估了临界弹性干涉量.椭圆、GW模型的塑性指数之比随有效半径比增加而增加.GW模型低估了塑性指数.有效半径比越大,偏差量越大.     

Limit analysis of frames involving unilateral supports with frictional contact

We consider the classical limit analysis problem of frame structures made up of rigid perfectly plastic members and involving some supports in unilateral frictional contact with the ground. A direct formulation as a mixed complementarity problem (MCP) is used. For the Coulomb case, which forms the focus of this paper, the corresponding MCP may admit multiple upper bound collapse load solutions. In order to identify the least upper bound solution, we propose two algorithms. The first one attempts to enumerate the possible multiple solutions, or at least map the solution space if the solutions are connected. The second scheme tries to find the least upper bound by directly formulating and solving a single nonconvex optimization problem, known in the literature as a mathematical program with equilibrium constraints (MPEC). Two simple examples are provided to illustrate application of these approaches. They also serve to highlight some key features of such structures.     

螺旋滚筒炉生产线调试和改进

针对国内某电炉生产线调试过程中存在的问题，采取了相应的解决措施，效果良好。     

An analysis of three-dimensional elasto-plastic sinusoidal contact

Researchers have developed many models to simulate the elasto-plastic contact of spheres. However, there does not appear to exist a closed-form analytical model for elasto-plastic three-dimensional sinusoidal contact. This work uses a finite element model (FEM) to characterize elasto-plastic sinusoidal contact. Although at initial contact the sphere and sinusoidal case are very similar and can both be described by the classic elastic Hertz contact case, once the contact is pressed past a certain range of deformation the two cases are very different. The model produces equations which can be used to approximately relate the area of contact to the contact pressure for elasto-plastic sinusoidal contact. The equations are fit to the FEM results and existing elastic solutions of sinusoidal contact. An empirical expression for the average pressure which causes complete contact between elasto-plastic sinusoidal contacts is also provided.     

On the elastic contact of rough surfaces: Numerical experiments and comparisons with recent theories

Some numerical experiments are conducted for studying the decrease of the elastic contact area in the elastic contact of fractal random surfaces when adding components of roughness of progressively smaller wavelengths. In particular, Fourier and Weierstrass random series are used, and a recent accurate and efficient method developed by the authors is used, involving superpositions of overlapping triangles. Some comparisons are made using two recent theories, that of Ciavarella et al. published in 2000 on the deterministic Weierstrass fractal profile, and that of Persson published in 2001 on random generic contact. We show that both theories tend to underpredict the contact area by a significant (and similar) factor in these representative cases in the region of light loads (partial contact), where the non-linearities of the contact mechanics are not included in neither of the formulations. In Persson's theory case, the discrepancy is particularly large at high fractal dimensions of the profile, where in theory the numerical experiments should be more closely reproducing a true Gaussian process. The Ciavarella et al. “Archard-like” theory, is only accurate when the parameter γ (the ratio of successive wavelengths) is unrealistically large. However, we only tested the Ciavarella et al. theory in the simplified “Hertzian approximation” form assuming partial contact at the peaks of contact, although we don’t expect the full version to improve dramatically the results.     

焊接坡口对焊接接头安定性的影响研究

结合非线性叠加法和通用有限元软件ABAQUS研究了循环热-机械载荷下对焊接接头的安定性,并比较了UV形、双U形、X形、U形、单面焊及V形等6种焊接坡口形式对焊接接头安定性的影响。结果表明,选用U形坡口(焊接厚度20 mm≤t≤60 mm)及选用双U形坡口(焊接厚度t>60 mm)连接时焊接接头的安定域较大,在循环热-机械载荷下具有更好的承载能力。此研究对厚壁压力容器及管道对焊焊接接头的设计有一定指导意义。     

An elastic–plastic contact model of ellipsoid bodies

A theoretical model for the elastic–plastic contact of ellipsoid bodies is presented in this paper. Relation of the contact parameters, such as the mean contact pressure, the contact area and the contact load as a function of the contact interference are modeled in the three different contact regimes: elastic, elastic–plastic and fully plastic. The model is verified by experimental results and is compared with published theoretical models. Very good agreement between the present model and the experimental results are found compared to the prediction of the other contact models.     

Numerical and finite element contact temperature analysis of real composite-steel surfaces in sliding contact

Numerical techniques have been developed and used to evaluate the contact temperature distribution between real composite-steel surfaces in sliding contact. To characterise the contact temperature problem of composite materials new definitions for composite Peclet numbers have been introduced. In case of `slow sliding' problems a stationary numerical technique was applied, whereas for `intermediate and fast sliding' problems transient finite element (FE) solutions were preferred. At first sliding contacts of a single steel asperity over polyetheretherketone (PEEK) or carbon fibre (CF)/PEEK composite surfaces were modelled in order to study the contact temperature development on a microscopic level. It was followed by contact temperature results for real composite-steel sliding surfaces; the latter helped to provide information about the actual stress conditions, which are necessary to model the wear process of this pair of materials in future works.