耦合热弹性接触问题的变分原理

本文给出了考虑库伦摩擦力的热弹性接触问题的一个变分原理，该变分原理在约束条件Ｐｎ≥０和－μＰｎ≤Ｐｔ≤μＰｎ下，在接触边界上自动给出导热条件及剩余互补条件等。从它出发将接触弹性体离散后可直接进行二次规划求解。文中特地引进了因子β，它计及了接触问题中的热量散失和功率损耗     

考虑热弹性变形的角接触球轴承微观热弹流分析

运用点接触热弹性流体动压润滑理论,考虑了润滑油膜温升变化引起的角接触球轴承中滚珠和内圈接触表面的热弹性变形和表面随机粗糙度的影响,提出了一种计入热弹性变形和随机粗糙度影响的角接触球轴承热弹性流体动压润滑分析方法.该方法通过将热弹性变形进行热力转换,得到了滚珠和内圈接触表面的材料线热膨胀系数,计算修正了滚珠和内圈表面因油膜温度场变化引起的热弹性变形,求得了计入热弹性变形和表面粗糙度后的油膜压力、油膜厚度、油膜温升以及热弹性变形等主要润滑特性,研究了内圈转速、滑滚比和滚珠数量的变化对油膜厚度和油膜压力的影响规律,结果表明:最大热弹性变形量与最小油膜厚度处在同一量级,并且内圈转速、滑滚比和滚珠数量的变化对油膜厚度和压力会产生明显的影响.进一步对比分析了几种算法下的最小膜厚,验证了计入热弹性变形的数值算法的可行性.     

摩擦热对Ti6A14V合金摩擦磨损性能的影响

在高速销-盘式摩擦磨损试验机上考察了Ti6A14V销与GCr15钢盘摩擦副的干滑动摩擦磨损行为，并在线测量了销试样的摩擦接触温度，利用扫描电子显微镜、X射线衍射仪及透射电子显微镜分别对Ti6A14V摩擦表面和次表层的微观形貌、组织成分、相结构进行研究．结果表明：Ti6A14V的卢相变点温度接近其摩擦系数和磨损率的转折温度；随着摩擦表面温度升高，在Ti6A14V表面依次形成TiO、TiO2和V2O3；温度骤变促使Ti6A14V表层析出纳米颗粒，高的摩擦温度使空气中的氮渗入表层而形成VN．上述结果共同对Ti6A14V／GCr15摩擦副的摩擦磨损行为产生影响．     

高温冲击拉伸试验中的快速接触加温技术

本文阐述了高温冲击拉伸试验技术中基于大热容量热惯性温升极大值原理的快速接触加温技术;研制了稳定性好、加热效率高、总体热惯性大、断电温升至极大值的稳定时间长的一对新的加温炉。测试结果表明,可以在试件上获得了最高可达1073K的近似稳定和均匀的温度场。通过实验研究建立了试件温度、稳定炉温和加温炉加热自动断电设定温度之间的标定关系。利用此标定关系,可以根据试验所需要的试件温度方便地确定加温炉自动断电设定温度,并通过监控稳定炉温来实施的所需试件温度下的冲击拉伸试验。本文还对高温冲击拉伸试验中的相关问题进行了分析讨论。     

滚滑工况弹流反常温度场的研究

研究了弹流反常温度场的形成机理及影响因素，指出入口温升是压缩功发热和逆流剪切热所致，而出口局部低温是负压缩功吸热的结果，出口温度的再次微幅上升则是压缩功消失后剪切热作用的结果．研究结果表明，入口温升随载荷的增加而增大，随卷吸速度的增加显著升高而几乎与滑滚比无关；在高速小滑滚比工况下，接触区的最高温度有可能出现在入口位置；入口温升增加了材料在工作中经受高温的次数，对其接触疲劳寿命有不利影响；在保证润滑性能的前提下，适当减少供油量可以减小逆流，从而降低入口温升。     

热对流条件下考虑球形夹杂分布的材料热弹接触摩擦热影响分析

机械传动关键活动零部件接触副往往受到力载荷和摩擦热载荷的耦合作用，使得接触界面间的接触力学行为的分析变得极其复杂. 利用基于等效夹杂方法建立的考虑热对流非均质材料热弹接触力学分析模型研究不同摩擦系数、夹杂位置和材料属性等参数对材料表面及内部温升及热应力分布影响规律. 此外，进一步分析了接触副材料中含分布球形夹杂时摩擦热造成的影响. 结果表明:接触副表面温升梯度受热对流系数的影响较大；下表面温升和热应力随摩擦系数增大而增大；分布夹杂则将接触副材料下表面温升及热应力分布变得更为复杂.      

两圆柱体结合面的接触热导分形模型研究

基于三维分形理论，在考虑微凸体的弹性变形、弹塑性变形和塑性变形的基础上，建立了两圆柱体结合面接触热导分形模型。通过数值仿真，分析了分形维数，分形尺度参数、圆柱体曲率半径和接触类型对接触热导的影响。研究结果表明：接触热导随着分形维数的增大而增大，随着分形尺度参数的增大而减小；相同参数下，内接触比外接触的接触热导要大；此外，当固定其中一个圆柱体的曲率半径时，随着另一个圆柱体曲率半径的增大，接触热导增大。该模型为开展齿轮等曲面接触热导的研究提供了理论基础。     

摩擦热对Ti6Al4V合金摩擦磨损性能的影响

在高速销-盘式摩擦磨损试验机上考察了Ti6Al4V销与GCr15钢盘摩擦副的干滑动摩擦磨损行为,并在线测量了销试样的摩擦接触温度,利用扫描电子显微镜、X射线衍射仪及透射电子显微镜分别对Ti6Al4V摩擦表面和次表层的微观形貌、组织成分、相结构进行研究.结果表明:Ti6Al4V的β相变点温度接近其摩擦系数和磨损率的转折温度;随着摩擦表面温度升高,在Ti6Al4V表面依次形成TiO、TiO2和V2O3;温度骤变促使Ti6Al4V表层析出纳米颗粒,高的摩擦温度使空气中的氮渗入表层而形成VN.上述结果共同对Ti6Al4V/GCr15摩擦副的摩擦磨损行为产生影响.     

含人工脱粘层固体装药结构应力应变场分析

针对某翼柱型固体装药结构,选取1/16子结构进行了有限元分析。通过将其分割成若干具有单一拓扑型式的组合体,获得了精度较高的结构化网格。在三维线性粘弹性理论和边界非线性理论基础上,基于接触算法模拟了人工脱粘层的边界条件;研究了固化降温过程含人工脱粘层固体装药结构的变形特征和应变场,并与无人工脱粘层的计算结果进行了对比,结果表明:人工脱粘层可以显著地改善固体装药结构端部的应变水平,最大的等效VonMises应变从无人工脱粘的30.1%下降为23.0%。此外,探讨了人工脱粘层前缘的应力水平以及工程上界面脱粘的快速近似计算方法。     

有限长滚子线接触热弹流润滑分析

应用多重网格解法 ,求出了有限长滚子线接触热弹流润滑的完全数值解 .结果表明 :在滚子的中部 ,油膜压力、温度和最小膜厚与无限长线接触热弹流润滑的解几乎一致 ;在滚子端部的圆角处 ,油膜压力、温度和最小膜厚与中部均显著不同 ,且最大油膜压力、最大油膜温度和最小油膜厚度均发生在此处 ,端部圆角半径对弹流润滑性能有显著影响 .同时 ,将有限长线接触热解与有限长线接触等温解进行了比较 .     

A combined parametric quadratic programming and precise integration method based dynamic analysis of elastic-plastic hardening/softening problems

The objective of the paper is to develop a new algorithm for numerical solution of dynamic elastic-plastic strain hardening/softening problems. The gradient dependent model is adopted in the numerical model to overcome the result mesh-sensitivity problem in the dynamic strain softening or strain localization analysis. The equations for the dynamic elastic-plastic problems are derived in terms of the parametric variational principle, which is valid for associated, non-associated and strain softening plastic constitutive models in the finite element analysis. The precise integration method, which has been widely used for discretization in time domain of the linear problems, is introduced for the solution of dynamic nonlinear equations. The new algorithm proposed is based on the combination of the parametric quadratic programming method and the precise integration method and has all the advantages in both of the algorithms. Results of numerical examples demonstrate not only the validity, but also the advantages of the algorithm proposed for the numerical solution of nonlinear dynamic problems. The project supported by the National Key Basic Research Special Foundation (G1999032805), the National Natural Science Foundation of China (19872016, 50178016, 19832010) and the Foundation for University Key Teacher by the Ministry of Education of China     

A note for analysis of thermo-mechanical contact problems

A discussion about the bifurcation and non-uniqueness of solutions in the analysis of thermo-mechanical contact problems with initial gap is given. Without loss of generality, a mechanical contact problem coupled with steady heat transfer is studied and an example of non-uniqueness of solutions caused by the thermo-mechanical mechanism is presented. The important work is that the non-uniqueness of solutions, which is different from that found in the analysis of the traditional frictional contact problems, is studied in detail. The possible oscillation and non-convergence problems in the iteraction process of the numerical computation are discussed, and an enhanced algorithm is put forward to overcome the difficulties. Project sypported by the National Natural Science Foundation of China (Nos. 50178016, 10225212 and 19872016), the National Key Basic Research Special Foundation (No. G1999032805) and the Foundation for University Key Teacher by the Ministry of Education.     

An adaptive algorithm of precise integration for transient analysis

This paper presents an improved precise integration algorithm for transient analysis of heat transfer and some other problems. The original precise integration method is improved by means of the inverse accuracy analysis so that the parameterN, which has been taken as a constant and an independent parameter without consideration of the problems in the original method, can be generated automatically by the algorithm itself. Thus, the improved algorithm is adaptive and the accuracy of the algorithm is not dependent on the length of the time step in the integration process. It is shown that the numerical results obtained by the method proposed are more accurate than those obtained by the conventional time integration methods such as the difference method and others. Four examples are given to demonstrate the validity, accuracy and efficiency of the new method. Project supported by the National Natural Science Foundation of China (No. 19872016, 19872017), the National Key Basic Research Special Foundation (G1999032805) and the Foundation for University Key Teachers by the Ministry of Education of China.     

Study for 2D moving contact elastic body with closed crack using BEM

Using a sub-regional boundary element method, an algorithm for the two-dimensional elastic bodies with a closed crack loaded by a moving contact elastic body is proposed. Since the extent and status of the contact surface of two elastic bodies and the crack within the body are all not known in advance, a double iterative contact algorithm is used. The BEM program for solving the closed crack problems is developed, some numerical examples are calculated, and the results of the center crack cases are shown to be in good agreement with the analytical solution in the classical fracture mechanics. In the condition of friction and non-friction, some coupling computational results of the SIF for the closed crack, with different angles and loaded by a moving contact elastic body, are also obtained by a numerical computation. The project supported by the National Natural Science Foundation of China (10172053) and NJTU Foundation of China (PD-157)     

Time discontinuous Galerkin finite element method for dynamic analyses in saturated poro-elasto-plastic medium

A time-discontinuous Galerkin finite element method for dynamic analyses in saturated poro-elasto-plastic medium is proposed. As compared with the existing discontinuous Galerkin finite element methods, the distinct feature of the proposed method is that the continuity of the displacement vector at each discrete time instant is automatically ensured, whereas the discontinuity of the velocity vector at the discrete time levels still remains. The computational cost is then obviously reduced, particularly, for material non-linear problems. Both the implicit and explicit algorithms to solve the derived formulations for material non-linear problems are developed. Numerical results show a good performance of the present method in eliminating spurious numerical oscillations and providing with much more accurate solutions over the traditional Galerkin finite element method using the Newmark algorithm in the time domain. The project supported by the National Natural Science Foundation of China (19832010, 50278012, 10272027) and the National Key Basic Research and Development Program (973 Program, 2002CB412709)     

传热与接触两类问题耦合作用的有限元分析

考虑传热接触耦合作用的热力学分析问题大量存在于工程中,分析的难点是必须考虑热与可移动接触边界间的耦合作用。针对这类问题的求解,该文给出了接触边界上热交换与温度边界条件,并在此基础上建立了两类变分方程,一类是热力学变分泛函,其考虑了接触区域对结构热传导的影响;另一类是二维热弹性接触分析的参数变分原理,可以方便地对接触问题进行求解。文中给出有限元分析的离散公式,并进一步给出两类问题耦合分析的迭代算法,其中接触分析的惩罚因子是可以消除的,数值结果验证了该文的理论与算法。     

Effective numerical methods for elasto-plastic contact problems with friction

Several effective numerical methods for solving the elasto-plastic contact problems with friction are presented. First, a direct substitution method is employed to impose the contact constraint conditions on condensed finite element equations, thus resulting in a reduction by half in the dimension of final governing equations. Second, an algorithm composed of contact condition probes and elasto-plastic iterations is utilized to solve the governing equation, which distinguishes two kinds of nonlinearities, and makes the solution unique. In addition, Positive-Negative Sequence Modification Method is used to condense the finite element equations of each substructure and an analytical integration is introduced to determine the elasto-plastic status after each time step or each iteration, hence the computational efficiency is enhanced to a great extent. Finally, several test and practical examples are presented showing the validity and versatility of these methods and algorithms. The Project Supported by National Natural Science Foundation of China.     

Application of scaled boundary finite element method in static and dynamic fracture problems

The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled. The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang.     

AN ANALYSIS OF 3D FINITE CRACKED BODIES

The new-type traction boundary integral equations developed by Hu and with no hypersingular integral are applied to analysis of 3D finite cracked bodies. A numerical algorithm for general 3D problems and a semi-analytical one for axisymmetric problems are presented. Some examples of thick plates and cylindrical columns including penny-shaped crack(s), and rectangular plates including an elliptical crack normal to the surface are analyzed. The comparison between present results and those in literature shows the high accuracy and effectiveness of the present method. Project supported by the National Natural Science Foundation of China (No. 19972060) and the Foundation of Key Laboratory of the Ministry of Education, Tongji University.     

A contact searching algorithm for contact-impact problems

A new contact searching algorithm for contact-impact systems is proposed in this paper. In terms of the cell structure and the linked-list, this algorithm solves the problem of sorting and searching contacts in three dimensions by transforming it to a retrieving process from two one-dimensional arrays, and binary searching is no longer required. Using this algorithm, the cost of contact searching is reduced to the order ofO(N) instead ofO(Nlog₂ N) for traditional ones, whereN is the node number in the system. Moreover, this algorithm can handle contact systems with arbitrary mesh layouts. Due to the simplicity of this algorithm it can be easily implemented in a dynamic explicit finite element program. Our numerical experimental result shows that this algorithm is reliable and efficient for contact searching of three dimensional systems. The project supported by the National Natural Science Foundation of China (59875045), and the State Key Laboratory of Automobile Safety and Energy Saving (K9705)