金属滑动接触的滑移线场理论之发展现状

本文综述介绍了金属滑动接触的滑移线场理论的基本原理及其发展现状。该理论以一个硬质楞在较软金属表面的滑动作为金属滑动摩擦的基本模式,用滑移线场分析方法考察了滑动过程中的应力和应变,导出了摩擦系数的计算公式,揭示了在粘着理论中被隔离开来的粘着与犁削之间的内在联系。试验结果与理论计算结果有较好的一致性。该理论还提出了非疲劳磨损与疲劳磨损的不同变形和断裂机制,揭示了Archard磨损系数与微凸体发生疲劳断裂的临界受荷周期数之间的定量关系。文章还对该理论的进步意义及其发展趋势作了简要的评述。     

Slip-line field theory of transversely isotropic body

ＳＬＩＰ－ＬＩＮＥＦＩＥＬＤＴＨＥＯＲＹＯＦＴＲＡＮＳＶＥＲＳＥＬＹＩＳＯＴＲＯＰＩＣＢＯＤＹＲｕａｎＨｕａｉ－ｎｉｎｇ（阮怀宁）（ＨｅｈａｉＵｎｉｖｅｒｓｉｔｙ）ＮａｎｊｉｎｇＷａｎｇＷｅｉ－ｘｉａｎｇ（王维襄）（ＣｈｉｎａＵｎｉｖｅｒｓｉｔｙｏｆ...     

大跨度悬索桥施工状态气动弹性模型风洞试验研究

本文通过桥梁气动弹性模型风洞试验，给出了汕头海湾大桥施工状态的颤振、抖振特性．     

Slip-line field solution for ultimate bearing capacity of a pipeline on clay soils

A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account of circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe may degenerate into those for the conventional rectangular-shaped strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils.     

Evidence of Multi-Process Matrix Diffusion in a Single Fracture from a Field Tracer Test

Compared to values inferred from laboratory tests on matrix cores, many field tracer tests in fractured rock have shown enhanced matrix diffusion coefficient values (obtained using a single-process matrix-diffusion model with a homogeneous matrix diffusion coefficient). To investigate this phenomenon, a conceptual model of multi-process matrix diffusion in a single-fracture system was developed. In this model, three matrix diffusion processes of different diffusion rates were assumed to coexist: (1) diffusion into stagnant water and infilling materials within fractures, (2) diffusion into a degraded matrix zone, and (3) further diffusion into an intact matrix zone. The validity of the conceptual model was then demonstrated by analyzing a unique tracer test conducted using a long-time constant-concentration injection. The tracer-test analysis was conducted using a numerical model capable of tracking the multiple matrix-diffusion processes. The analysis showed that in the degraded zone, a diffusion process with an enhanced diffusion rate controlled the steep rising limb and decay-like falling limb in the observed breakthrough curve, whereas in the intact matrix zone, a process involving a lower diffusion rate affected the long-term middle platform of slowly increasing tracer concentration. The different matrix-diffusion-coefficient values revealed from the field tracer test are consistent with the variability of matrix diffusion coefficient measured for rock cores with different degrees of fracture coating at the same site. By comparing to the matrix diffusion coefficient calibrated using single-process matrix diffusion, we demonstrated that this multi-process matrix diffusion may contribute to the enhanced matrix-diffusion-coefficient values for single-fracture systems at the field scale.     

Photoviscoplastic investigations of slip-line fields and principal-stress trajectories in viscoelastoplastic strip for drawing with back tension

Photoviscoplasticity is applied to the drawing with back tension through rollers and wedge-shaped dies in model tests of plane-strain state. The effects of the back tension on the slip-line fields and on the principal-stress trajectories for the strips are discussed in the light of experimental results obtained from the model tests. Actual strips are considered as viscoelastoplastic media in the actual drawing processes. The model specimens used are softened celluloid as the viscoelastoplastic medium for the strip and Araldite as the glassy elastic medium for the dies. At a suitable experimental temperature, the viscoelastoplastic strip is drawn viscoplastically through the gap between the dies mentioned above. The slip-line fields, the principal-stress trajectories in the strip and the normal pressure on the contact surface are greatly influenced by the effect of the back tension.     

Comparison of a Rapidely Converging Phase Field Model for Interfaces in Solids with the Allen-Cahn Model

We compare two phase field models for interfaces in elastic solids carrying low surface energy. One model has hybrid properties of a Hamilton-Jacobi and a parabolic equation, the other is the Allen-Cahn model. For vanishing width of the interface we construct asymptotic solutions of second order for the hybrid model and of first order for the Allen-Cahn model. These constructions show that the width of the diffused interface necessary for tracking accurately the sharp interface can be chosen much larger for the hybrid model than for the Allen-Cahn model, and that moreover the hybrid model can describe interfaces with nonlinear kinetic relation. This explains why numerical simulations based on the hybrid model are considerably more effective. These simulations are discussed in the last section.     

Slip-line modeling of machining with a rounded-edge tool—Part I: new model and theory

The effect of tool edge roundness attracts growing attention from the international machining research community due to ever accelerating applications of precision, super-precision, micro-, and nano-machining technologies in a wide variety of modern industries. A new slip-line model for machining with a rounded-edge tool and its associated hodograph are proposed in this paper. The model consists of 27 slip-line sub-regions, each sub-region having its own physical meaning. It is demonstrated that the model simultaneously takes into account nine effects, such as the shear-zone effect and the size effect, which commonly occur in machining. Eight groups of machining parameters, such as the ploughing (parasitic or non-cutting) force and the chip up-curl radius, can be simultaneously predicted from the model. Furthermore, the model incorporates eight slip-line models previously developed for machining during the last six decades as special cases. An additional special case that involves a parallel-sided shear zone can also be derived from the new model. A mathematical formulation of the model is established based on Dewhurst and Collins's (1973) matrix technique for numerically solving slip-line problems. A purely analytical equation is proposed to predict the thickness of the primary shear zone. This equation is also employed to predict the shear strain-rate in the primary shear zone.     

The Model of Electric Connection of a Low-Conductivity Liquid in High-Frequency Electric Field

This paper describes the study of electroconvection of low-conductivity fluid in a capacitor with boundary conditions of adhesion on a solid surface in the case of rapid charge relaxation. The linear stability of fluid equilibrium in a constant electric field is investigated. The model describing the averaged fluid flow in a high-frequency electric field is obtained. The nonlinear regimes of electroconvection are described. A regime map is constructed. It is obtained that, depending on the frequency of the external field, the transition to chaotic state occurs through quasiperiodic or intermittent structures.     

Comparison of Iterative Methods for Computing the Pressure Field in a Dynamic Network Model

In dynamic network models, the pressure map (the pressure in the pores) must be evaluated at each time step. This calculation involves the solution of a large number of nonlinear algebraic systems of equations and accounts for more than 80 of the total CPU–time. Each nonlinear system requires at least the partial solution of a sequence of linear systems. We present a comparative study of iterative methods for solving these systems, where we apply both standard routines from the public domain package ITPACK 2C and our own routines tailored to the network problem. The conjugate gradient method, preconditioned by symmetric successive overrelaxation, was found to be consistently faster and more robust than the other solvers tested. In particular, it was found to be much superior to the successive overrelaxation technique currently used by many researchers.     

硅晶体纳米压痕试验与应力场分析

采用纳米压入法测量了4种硅晶体的微压痕特性,讨论了加载过程与卸载过程的特征,分析了硅晶体的纳米压入测量结果,同时计算了硅晶体中的应力分布,计算结果表明,剪应力为硅晶体微薄片剥落失效的原因。     

机匣模拟疲劳试验的相似条件研究

理论分析和试验结果表明，受内压的机匣与其相应的平板模型在开孔附近的等效应力分布非常相似；机匣模拟疲劳试验的应力相似条件下可表为，机匣与其模型在控制疲劳寿命的关键部位的等效应力水平和分布相同。     

岩体节理刚度系数的现场声波测试

Ｇｏｏｄｍａｎ教授提出的节理单元模型被广泛地应用于岩石力学与工程实践。然而该模型的分析精度却依赖于对节理的法向刚度ｋｎ切向刚度ｋｓ的准确确定。但这项工作在实验室几乎是不可能的。文中提出了一种在现场利用声波测试ｋｎ和ｋｓ的方法，并讨论了影响ｋｎ、ｋｓ测试精度的因素。     

Interface Conditions for a Phase Field Model with Anisotropic and Non-Local Interactions

An alternative formulation of the phase field method is utilized from an integral equation perspective. The technique allows one to derive macroscopic conditions at the interface from the microscopic potentials. Differential geometry and asymptotic analysis yield interface conditions, in arbitrary spatial dimension, for interactions that may include anisotropy as well as non-local potentials. The interface conditions can be expressed in various formulations, for example, in terms of the principal curvature directions of the interface, or the second order directional derivatives of the (signed) distance function and the Hessian of the surface tension.     

旋转流场下模型大幅俯仰运动实验研究

在中航气动院FL-8低速风洞中,采用单自由度振荡机构进行了旋转流场下大幅俯仰运动的气动特性实验研究。模型在绕风速轴连续旋转的同时,进行给定频率和振幅绕体轴的俯仰振荡运动。测量了模型的动态气动特性,着重分析了不同运动参数对模型气动特性的影响。实验结果表明,旋转速度的存在使大振幅俯仰振荡实验中的滚转力矩和偏航力矩产生了明显的迟滞特性,但对俯仰力矩和法向力的迟滞特性影响不大。     

SLIP-LINE FIELD THEORY OF PLANE PLASTIC STRAIN DEALING WITH MOHR’S CRITERION EXPRESSED BY QUADRATIC LIMITING CURVES

In this paper, the slip-line field theory of plane plastic strain dealing with Mohr’s criterion expressed by quadratic limiting curves is preliminarily established. It takes the classical slip-line field theory as its special case, and it can be applied to the analysis of plane-strain problems in metal processing, rock and soil mechanics and tectonomechanics. As preliminary application, the slip-line field and limiting loads of flat punch indenting problem are determined by numerical solution, and the slip-line field of bedded medium gravity-sliding problem is determined and discussed.     

Slip-line modeling of machining with a rounded-edge tool—Part II: analysis of the size effect and the shear strain-rate

Part II of the present study quantitatively analyzes orthogonal metal cutting processes based on the new slip-line model proposed in Part I. The applicable range of the model is illustrated, followed by an explanation of the non-unique nature of the model. It is suggested that the tool edge roundness be comprehensively defined by four variables. Namely: tool edge radius, position of the stagnation point on the tool edge, tool-chip frictional shear stress above the stagnation point on the tool edge, and tool-chip frictional shear stress below the stagnation point on the tool edge. The effects of these four variables on eight groups of machining parameters are investigated. These include (1) cutting force, thrust force, resultant force, and the ratio of cutting force to thrust force; (2) ploughing force; (3) chip up-curl radius; (4) chip thickness; (5) tool-chip contact length; (6) thickness of the primary shear zone; (7) average shear strain in the primary shear zone; and (8) average shear strain-rate in the primary shear zone. The importance of tool edge roundness is further reinforced by a series of new research findings made in this paper. It is revealed that the size effect highly depends on the material constitutive behavior in machining. The dependence of the thickness of the primary shear zone and the dependence of the magnitude of shear strain-rate in the primary shear zone on the tool edge radius are well demonstrated. A surprisingly good agreement between theory and experiments is reached.     

用模态试验结果修改力学模型初探

利用试验模态分析结果,对有限元力学模型本身或其中某些参数进行修改是必要的和有工程意义的。这一“修改”既是数学上的优化问题又是工程设计问题。本文介绍自研制的“结构动力修改程序”,述及一般原理及框图,并给出一个悬臂梁实例。     

高温超导带材多场特性测试系统研制进展(Ⅰ)

高温超导带材具有高的临界电流密度,高磁场下优异的载流特性以及良好的成型性在强电领域如高场磁体、超导电缆等方面应用潜力巨大。在其应用过程中,不可避免的低温-大电流-强磁场环境将对超导材料的载流能力产生影响,而加工过程中的残余应力以及洛伦兹力的存在会显著的降低超导材料的临界电流,造成相应超导装置功能性难以达到设计要求、且成为重要的安全隐患。本文介绍一种新型的适用于超导带材的力-磁-电多场耦合测试系统,该系统目前采用浸泡式制冷,可实现的主要功能有:(1)超导材料临界电流密度测试;(2)拉伸应变对超导带材临界电流的影响研究;(3)磁场对超导带材临界电流的影响研究;(4)力磁耦合情形下超导材料临界电流的变化规律;(5)超导材料磁通稳定性测试。该设备的成功研制将为我国先进超导材料研发提供基础测试平台。