机车车轮踏面与钢轨接触的仿真计算及试验研究

应用轮轨型面测量仪测量实际运用中的磨耗后机车车轮,基于标准与磨耗后机车车轮型面,建立轮轨接触三维有限元模型,计算分析不同横移量下的接触斑和等效应力.搭建轮轨接触试验台,使用取自现场的车轮与钢轨试块进行试验,分析不同横移量下轮轨接触状态.针对磨耗前后车轮与标准钢轨接触的有限元计算与试验进行对比分析.结果表明:横移量对轮轨接触状态有着显著的影响,横移量过大会加速机车车轮的磨耗;与标准型面相比,磨耗后车轮型面与标准钢轨接触时的接触斑面积较大,最大等效应力较小;通过轮轨接触试验台所得接触斑形状和大小与仿真计算所得结果一致性较好,证明了有限元仿真计算的可靠性.     

Age- and direction-related adaptations of lumbar vertebral trabecular bone with respect to apparent stiffness and tissue level stress distribution

The objective of this study was to study the age-related adaptation of lumbar vertebral trabecular bone at the apparent level, as well as the tissue level in three orthogonal directions. Ninety trabecular specimens were obtained from six normal L4 vertebral bodies of six male cadavers in two age groups, three aged 62 years and three aged 69 years, and were scanned using a high-resolution micro-computed tomography （micro-CT） system, then converted to micro- finite element models to do micro-finite element analyses. The relationship between apparent stiffness and bone volume fraction, and the tissue level yon Mises stress distribution for each trabecular specimen when compressed separately in the longitudinal direction, medial-lateral and anterior-posterior directions （transverse directions） were derived and compared between two age groups. The results showed that at the apparent level, trabecular bones from 69-year group had stiffer bone structure relative to their volume fractions in all three directions, and in both age groups, changes in bone volume fraction could explain more variations in apparent stiffness in the longitudinal direction than the transverse directions; at the tissue level, aging had little effect on the tissue von Mises stress distributions for the compressions in all the three directions. The novelty of the present study was that it provided quantitative assessments on the age and direction- related adaptation of Chinese male lumbar vertebral trabecular bone from two different levels： stiffness at the apparent level and stress distribution at the tissue level. It may help to understand the failure mechanisms and fracture risks of vertebral body associated with aging and direction for the prevention of fracture risks in elder individuals.     

A fluid flow model in the lacunar-canalicular system under the pressure gradient and electrical field driven loads

The lacunar-canalicular system (LCS) is acknowledged to directly participate in bone tissue remodeling. The fluid flow in the LCS is synergic driven by the pressure gradient and electric field loads due to the electro-mechanical properties of bone. In this paper, an idealized annulus Maxwell fluid flow model in bone canaliculus is established, and the analytical solutions of the fluid velocity, the fluid shear stress, and the fluid flow rate are obtained. The results of the fluid flow under pressure gradient driven (PGD), electric field driven (EFD), and pressure-electricity synergic driven (P-ESD) patterns are compared and discussed. The effects of the diameter of canaliculi and osteocyte processes are evaluated. The results show that the P-ESD pattern can combine the regulatory advantages of single PGD and EFD patterns, and the osteocyte process surface can feel a relatively uniform shear stress distribution. As the bone canalicular inner radius increases, the produced shear stress under the PGD or P-ESD pattern increases slightly but changes little under the EFD pattern. The increase in the viscosity makes the flow slow down but does not affect the fluid shear stress (FSS) on the canalicular inner wall and osteocyte process surface. The increase in the high-valent ions does not affect the flow velocity and the flow rate, but the FSS on the canalicular inner wall and osteocyte process surface increases linearly. In this study, the results show that the shear stress sensed by the osteocyte process under the P-ESD pattern can be regulated by changing the pressure gradient and the intensity of electric field, as well as the parameters of the annulus fluid and the canaliculus size, which is helpful for the osteocyte mechanical responses. The established model provides a basis for the study of the mechanisms of electro-mechanical signals stimulating bone tissue (cells) growth.

     

脊柱L3-L5段机械模型的力学特性分析

借助计算机辅助设计软件SolidEdge,根据人体解剖学数据建立了人体脊柱L3-L5段近似三维几何模型,并利用有限元分析软件ANSYS进行赋值,模拟了脊柱L3-L5段的结构特性、材料特性、接触特性。将椎骨划分为皮质骨、松质骨等结构,用接触连接的方法模拟了椎骨与椎间盘之间、小关节之间的连接情况,采用实体单元Solid187对其进行网格划分。对该三维有限元模型进行加载分析,得到其在200N轴向力作用下和100N侧向力作用下的应力和变形数据,该数据可以为脊柱生物力学的研究和侧凸脊柱的病因及矫正提供一定的参考依据。     

Two Kinds of Contact Problems in Dodecagonal Quasicrystals of Point Group 12 mm

In this paper,two kinds of contact problems in 2-D dodecagonal quasicrystals were discussed using the complex variable function method:one is the finite frictional contact problem,the other is the adhesive contact problem.The analytic expressions of contact stresses in the phonon and phason fields were obtained for a flat rigid punch,which showed that:(1) for the finite frictional contact problem,the contact stress exhibited power-type singularities at the edge of the contact zone;(2) for the adhesive contact problem,the contact stress exhibited oscillatory singularities at the edge of the contact zone.The distribution regulation of contact stress under punch was illustrated;and the low friction property of quasicrystals was verified graphically.     

A generalised stress intensity approach to characterising the process zone in complete fretting contacts

The known analytical contact solution for the stress field induced by a rigid, square-ended punch, sliding on an elastic half-plane defines the stress state everywhere in the half-plane. An asymptotic approach is then used to determine the characteristic stress field at the edge of the contact, which is matched with the contact solution. Hence, the regions over which the asymptotic solution is valid are found. Using a method analogous to the crack-tip stress field, a generalised stress intensity factor is defined, with the aim of providing a single variable characterisation of the stress state at the punch corner. The crack initiation process zone for a fretting fatigue crack is therefore captured, and the conditions for small scale yielding explicitly found.     

New,real fundamental solutions to the transient thermal contact problem in a piezoelectric strip under the coupling actions of a rigid punch and a convective heat supply

A thermo-electro-mechanical contact analysis has been performed for a finite piezoelectric strip, which is subjected to the joint actions of a rigid, flat punch and a transient convective heat supply. The Laplace transform and Fourier sine and cosine transforms were applied in solving the governing equations. A detailed analysis of the characteristic roots of the corresponding characteristic equation was made. Real fundamental solutions were derived, which can readily lead to real solutions to the thermo-electro-mechanical quantities. A Cauchy-type singular integral equation was obtained for the stated problem and then solved numerically. Closed form solutions of a special case were obtained. To obtain the accurate solution in the time domain, an effective numerical inversion algorithm of the Laplace transform was applied. Detailed analyses were performed to reveal the variation law of temperature, contact stress beneath the punch, stress intensity factor at the punch edge and strain with time. Parametric studies were performed to discover the effects of the layer thickness on the distribution of temperature, contact stress beneath the punch and stress intensity factor at the punch edge.     

Numerical study of contact forces for crack closure analysis

Plasticity induced crack closure (PICC) has been widely studied using numerical models. Different numerical parameters can be considered to quantify the opening level, namely one based on the analysis of contact stresses at minimum load. A modified version of this parameter is proposed here, based on nodal contact forces instead of contact stresses. The predictions were found to be similar to those obtained from the contact status of 2nd node behind crack tip. The PICC_contact parameter was also found to be very consistent and adequate for parametric studies of the influence of different physical parameters. The contributions to the opening stress intensity factor of different points along crack flank were found to strongly decrease with distance to crack tip. The cumulative K_open between the crack tip and a distance of 0.1 mm was found to vary from 30% to 100%, increasing with stress ratio, R. Finally, a K solution was developed for punctual forces applied on crack flank and compared with a literature solution for infinite plates. A good agreement was found for plane strain state but significant differences of about 10% were found for plane stress state.     

氧化锆口腔种植体的动态植入过程分析与设计

在牙科种植领域常使用的种植体材料多为纯钛或钛合金,然而钛金属种植体存在美学缺陷及潜在的致敏可能等问题.氧化锆陶瓷由于其高强度、美观性与生物相容性被认为是钛金属种植体的理想替代品,但目前国内对于氧化锆种植体的研究仍处于起步阶段.本文通过对氧化锆种植体及骨组织进行有限元建模,并对种植体的动态植入过程进行仿真,分析了骨组织内部的应力-应变状况.结果发现,随着植入深度的增加,种植体与骨组织的接触面积增大,松质骨内应力增加.考虑到骨组织的具体结构,将松质骨内的最大应力-应变作为分析的主要对象,结合损伤分析,对种植体模型进行了优化.此外,还设计了3种具有自攻刃设计的种植体模型,分别进行应力应变分析后确定了最优设计.之后建立了具有自攻刃设计的种植体模型,并模拟了临床的3种植入方案:螺纹成形、螺纹切割、螺纹成形与切割进行分析,通过分析得到螺纹成形与切割种植方案更为安全的结论.本文结果可以指导氧化锆种植体的结构设计以及植入时的条件设定等,为我国自主研发的氧化锆种植体进行了理论指导,为其早日进行临床应用指明了方向.     

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。     

Closed-form solutions of the frictional sliding contact problem for a magneto-electro-elastic half-plane indented by a rigid conducting punch

This paper focuses on the study of a frictional sliding contact problem between a homogeneous magneto-electro-elastic material (MEEM) and a perfectly conducting rigid flat punch subjected to magneto-electro-mechanical loads. The problem is formulated under plane strain conditions. Using Fourier transform, the resulting plane magneto-electro-elasticity equations are converted analytically into three coupled singular integral equations in which the main unknowns are the normal contact stress, the electric displacement and the magnetic induction. An analytical closed-form solution is obtained for the normal contact stress, electric displacement and magnetic induction distributions. The main objective of this paper is to study the effect of the friction coefficient and the elastic, electric and magnetic coefficients on the surface contact pressure, electric displacement and magnetic induction distributions for the case of flat stamp profile.     

Experimental analysis of contact for the indentation of a flat rounded punch

The ‘plane vs. plane’ contact involving flat punches has been the subject of many investigations, even in recent years, mainly due to the crucial role that such components play in phenomena, such as fretting fatigue and indentation tests. While the problem has been deeply approached from a theoretical point of view, there is a noteworthy lack of experimental verifications due to the limited number of laboratory techniques capable of supplying detailed information about contact parameters. In order to make a partial contribution towards gaining an understanding of such problems, this study proposes the investigation of flat rounded punch contact with an ultrasound-based technique, which exploits the properties of ultrasonic waves to be differently reflected by a contact interface depending on its stress state. A suitable setup was built in such a way as to ensure a good level of control of contact conditions, and the interface was scanned with a high-frequency ultrasonic transducer so as to acquire the reflection data. While the graphic processing of the ultrasonic coefficient of reflection may easily be displayed as a ‘contact map’, the quantitative accuracy of the method was also investigated by comparing experimental results with those obtained from a Finite Element model of the system. The results show a good level of agreement between the two approaches, thus confirming that the ultrasonic technique can be effectively employed to investigate many contact problems which to date have never (or scarcely) been experimentally validated.     

Monitoring of parallel galleries in the region of horizontal motion of lithospheric plates

The problem of estimating the stress-strain state of underground openings of solid minerals, which form long parallel underground galleries, is considered. Several papers studied the local causes of accidents that occur in underground galleries during mineral extraction due to variations in the stress-strain state of the medium. The influence of formation of new galleries, which violate the balance of vertical stresses in the walls between the galleries, is also studied. At the same time, the problem on the influence of horizontal displacements of lithospheric plates on the stress-strain state of parallel galleries is little studied. These displacements affect the horizontal components of the contact stress vector arising between the upper and lower layers and the walls between the galleries. In this paper, the theory of estimating the stress-strain state in underground openings with arbitrarily many parallel galleries of various dimensions is developed under the assumption that the tangential components of the stress vector exist in the contact regions between the layers and the walls. The study is based on factorization methods, block element method, and a topological approach.     

Estimates of the influence of the transverse strain in a contact problem with free boundary

We use the contact problem with free boundary for a “heavy cylindrical shell-over-support reinforcement ring” system as an example to study the influence of transverse shear on the stress state in the shell. To obtain the equilibrium equations for the shell and the reinforcement ring, we apply an express algorithm developed by one of the authors to take into account transverse strains in Kirchhoff versions of the theory of shells. The contact problem with free boundary is solved by the generalized reaction method proposed earlier. We use numerical examples to show that the corrections introduced in the stress state by taking into account the transverse shears are by an order of magnitude larger than the traditional estimate of errors in the Kirchhoff hypotheses.     

润滑状态下球-盘点接触摩擦副的低速轻载滑滚特性研究

选用镀Cr膜的玻璃盘和GCr15球作为摩擦副,在NGY-6纳米润滑膜测量仪上开展球-盘点接触摩擦副在润滑状态下的低速轻载滑滚特性试验,研究不同接触应力、钢球转速、滑滚比等参数对摩擦副的摩擦系数及对应油膜厚度的影响规律.结果表明:当接触应力和钢球转速一定时,摩擦系数随滑滚比的增大逐渐增加后达到稳定状态,当滑滚比较大时,滑滚比的变化对油膜厚度几乎没有影响;当滑滚比一定时,摩擦系数随接触应力的增大逐渐增大,随钢球转速的增大逐渐减小,油膜厚度随接触应力的增大逐渐减小,随钢球转速的增大逐渐增大.摩擦副在弹流润滑状态下,摩擦系数的增加幅度随接触应力的变化较小,而在薄膜润滑状态下,其增加幅度变大.摩擦副在薄膜润滑状态下,当滑滚比在0.10~0.50变化时,摩擦系数和油膜厚度基本处于稳定状态.     

一种骨小管中液体流动产生的流量及切应力模型

骨组织受力变形后其内部液体就会流动,同时在其微观结构——骨单元壁中扩散,并进一步产生一系列与骨液流动相关的物理效应,如流体剪切应力、流动电位等,这些物理效应被细胞感知并做出破骨或成骨等反应,来使骨适应外部载荷环境.鉴于骨组织产生的内部液体流动很难实验测定,理论模拟是目前的主要研究手段.基于骨单元的多孔弹性性质建立了骨小管内部液体的流动模型,该模型将骨单元所受的外部载荷与骨小管内部液体的压力、流速、流量和切应力联系起来,并进一步可以研究其力传导与力电传导机制.骨小管模型的建立分别基于中空和考虑哈弗液体的骨单元模型,并考虑了骨单元外壁的弹性约束和刚性位移约束两种边界条件.最终得到骨单元在外部轴向载荷作用下,骨小管内部液体的流量及流体切应力的解析解.结果表明:骨小管中的液体流量与流体切应力都正比于应变载荷幅值和频率,并由载荷的应变率决定.因此应变率可以作为控制流量和流体切应力的一种生理载荷因素.流量随着骨小管半径的增大而非线性增大,而流体切应力则随着骨小管半径的增大而线性增大.此外,在相同的载荷下,含哈弗液体的骨单元的模型中,骨小管中液体的流量和切应力均大于中空骨单元模型.     

瓷修复体界面断裂行为的模拟实验研究

本文利用云纹干涉法和云纹干涉－－有限元混合法，对瓷修复体的模拟双材料模型界面断裂问题进行了实验研究。用云纹干涉和数字错位云纹干涉法测量带边裂纹的双材料四点简支梁在剪切作用下界面表面的剪应变分布及界面两侧局部表面的位移场，实验表明，由于界面两两侧材料力学性质不同，表现出界面剪切断裂问题的非称性和裂尖附近复合型断裂的特点；用云纹干涉法和有限元法相结合的混合法对粘接界面角点应力奇异性进行研究，并对角点附近应力应变场作了分析，得到了应力奇异指数与边界楔角，载荷的关系，证明了用界面应力强度因子Kf来描述界面端部区域应力分布的公式，并得到了双材料界面端部区域的应力应变分布情况。本文的实验结果为进一步研究口腔金瓷修复体界面的优化设计提供了基础，同时也说明云纹干涉法对于双材料界面断裂行为的研究是有效的。     

Analysis of the stress-strain state of an anisotropic plate with an elliptic hole and thin elastic inclusions

We solve the problem of determining the stress-strain state of an anisotropic plate with an elliptic hole and a system of thin rectilinear elastic inclusions. We assume that there is a perfect mechanical contact between the inclusions and the plate. We deal with a more precise junction model with the flexural rigidity of inclusions taken into account. (The tangential and normal stresses, as well as the derivatives of the displacements, experience a jump across the line of contact.) The solution of the problem is constructed in the form of complex potentials automatically satisfying the boundary conditions on the contour of the elliptic hole and at infinity. The problem is reduced to a system of singular integral equations, which is solved numerically. We study the influence of the rigidity and geometry parameters of the elastic inclusions on the stress distribution and value on the contour of the hole in the plate. We also compare the numerical results obtained here with the known data.     

Axisymmetric contact problem of cubic quasicrystalline materials

The axisymmetric elasticity theory of cubic quasicrystal was developed in Ref. [1]. The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function, based on which, the exact analytic solutions for the elastic field of an axisymmetric contact problem of cubic quasicrystalline materials are obtained for universal contact stress or contact displacement. The result shows that if the contact stress has order −1/2 singularity on the edge of the contact domain, the contact displacement is a constant in the contact domain. Conversely, if the contact displacement is a constant, the contact stress must have order −1/2 singularity on the edge of the contact domain. Project supported by the National Natural Science Foundation of China (No. 19972011).     

Micromechanical analysis of kinematic hardening in natural clay

This paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress–strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material.