平面应力条件下弹塑性材料的起裂与裂纹稳态扩展

根据有限元计算分析的弹塑性裂纹体在平面应力条件下的裂纹尖端应力应变场,采用滑移线浸蚀以及断裂力学的试验方法,研究了该条件下的起裂和稳态扩展现象。结果表明,在裂纹尖端存在着HRR近程场以及取决于试样几何类型的远程场。起裂由单参数J控制,而稳态扩展行为则受远程应变场影响,不能由单参数描述。     

一种微分型全量弹塑性有限元算法及其应用

推导了一种坐标更新的微分型全量弹塑性有限元算法,用它模拟金属的压缩失稳现象,计算结果同实测值非常接近,并优于增量算法和刚塑性算法的结果。表明这一算法用于模拟金属的压缩失稳现象非常有效。     

理想弹塑性材料Ⅱ型平面应力裂纹线场极坐标解

以平衡方程、Mises屈服条件为基本方程,推导了理想弹塑性材料Ⅱ型平面应力裂纹线场弹塑性极坐标幂级数形式解和弹塑性边界(塑性区范围)。在极坐标系下,以弹塑性边界上应力满足连续条件直接进行匹配,不需要进行坐标变换补充匹配方程,简化了匹配过程。通过对裂纹线上塑性区长度的比较分析表明,应力强度因子断裂理论求解得到的塑性区范围只适用于应力荷载较小的情况,随着应力荷载的增大,精度降低。     

弹塑性转变温度及其应用

众所周知,金属工件在无相变冷却过程中,当热应力超过某温度下金属的屈服强度时则产生塑性变形,相反则产生弹性变形。这种由塑性变形过渡到弹性变形(或加热时,由弹性变形过渡到塑性变形)的温度称为金属的     

平面应力问题广义滑移线方程的推导

提出平面应力问题的广义滑移线概念，推导出对平面问题具有普遍意义的广义滑移线方程，并初步探讨了其应用。     

整体壁板增量压弯过程应力应变模拟

整体壁板结构特点为蒙皮和纵横交错的加强筋为一整体,将机械加工后的平面外形的壁板毛坯成形为具有复杂曲面外形的壁板零件具有很大的难度。本文采用MARC有限元软件分析了整体壁板成形过程中应力应变变化情况。研究表明:整体壁板成形过程中,筋条处的应力状态最为恶劣,筋条与蒙皮过渡区处于三向拉应力状态,同时有剪切塑性应变发生,容易导致该处开裂,对于高筋条来说,还容易导致失稳现象发生;筋条的塑性变形既有凸模下压导致的塑性变形,又有蒙皮回弹导致的塑性变形;塑性变形区主要集中于筋部,蒙皮几乎不发生塑性变形;成形后的壁板将保留较大的残余应力,该应力主要是由蒙皮弹性回复所引起。     

一种计算空间平面的平面度误差新方法

利用迭代逼近法计算空间平面形状误差,在小误差条件下,用点到坐标平面的距离,构造坐标变换的迭代公式;经过多次循环迭代,最终获得的平面度是最小区域意义下平面度误差良好的近似。实验表明本文提出的算法运行过程稳定,结果准确可靠,算法的平均相对误差在5%之内。     

交变载荷作用下平面应力状态焊接接头焊趾处应力应变理论解的推导

基于弹塑性力学理论计算对接接头交变载荷作用下焊趾处应力和应变,以准确预测交变载荷作用下平面应力状态对接接头焊趾处的应力和应变值为目标,考察了不同加载情况下平面应力状态对接接头焊趾处应力和应变的理论计算方法,并给出了交变载荷作用下平面应力状态对接接头焊趾处应力和应变的理论解.结果表明,在材料参数、载荷大小以及焊趾应力集中系数已知的前提下,根据提出的理论解的计算式可获得相应载荷时接头焊趾处的应力应变,为焊接接头在交变载荷下的疲劳失效预测提供理论指导.     

几种典型件成形过程的弹塑性有限元数值模拟

本文用独立开发的板料成形静力隐式弹塑性有限元数值模拟软件SHEETFORM-Ⅰ对几种典型件的成形过程进行了数值模拟, 得到了和实际情况较为一致的结果, 证明所开发的软件是可靠的。     

An enhanced analytical model for residual stress prediction in machining

The predictions of residual stresses are most critical on the machined aerospace components for the safety of the aircraft. In this paper, an enhanced analytic elasto-plastic model is presented using the superposition of thermal and mechanical stresses on the workpiece, followed by a relaxation procedure. Theoretical residual stress predictions are verified experimentally with X-ray diffraction measurements on the high strength engineering material of Waspaloy that is used critical parts such as in aircraft jet engines. With the enhanced analytical model, accurate residual stress results are achieved, while the computational time compared to equivalent FEM models is decreased from days to seconds.     

Accurate stress computation in plane strain tensile tests for sheet metal using experimental data

The advances achieved in phenomenological constitutive laws and their implementation in finite element codes for predicting material behavior during forming processes have motivated the research on material identification parameters in order to ensure prediction accuracy. New models require experimental points describing a bi-axial stress state for proper calibration, and the features of the plane strain tensile test have made it one of the most used. The test's principal inconvenience is the influence of the free edges on strain field homogeneity and stress computation.     

可压缩材料轴对称和平面应变单位挤压力之间的关系

在轴对称子午面和平面应变变形平面几何尺寸相同、外摩擦一致的前提下,利用有限元法、滑移线法和实验方法探讨了可压缩材料轴对称正挤和平面应变正挤间单位挤压力的关系。结果表明,轴对称单位挤压力与平面应变单位挤压力间的比值是一个数值范围,Px＝(1．2—2．1)Pp;该比值与相对密度、挤压比、摩擦条件以及材料状态有关。     

An analytical expression for the stress field around an elastoplastic indentation/contact

The stress distribution outside the contact-induced plastic zone can be estimated by the superposition of a Hertzian field and the field for an embedded center of dilatation (ECD) in a half-space, while the residual stress distribution can be estimated by the ECD field alone. This model has a simple closed-form analytical expression, matching with finite element results nearly perfectly.     

预应力钢丝缠绕厚壁缸筒三维模型和平面应力模型分析

本文给出预应力钢丝缠绕有限元分析的三维模型和轴截面平面应力模型两种模拟方法。以80MPa内压的50MN预应力钢丝缠绕液压缸为算例进行有限元模拟,将钢丝层简化为六层圆筒,分别施加预应力和边界条件,两种模型均能得到相同的计算结果。但轴截面平面应力模型计算效率更高,结果更容易收敛。在求解方法处理上,将各钢丝层预应力按一个载荷步施加;将每层钢丝载荷工况定义为一个载荷步文件,后一载荷步文件删除前一载荷步载荷,采用载荷步文件法求解,按工况组合的方法将这些载荷步计算的结果叠加在一起;以及采用多载荷步方法计算。三种方法得到了相同的结果。     

A study of high-performance plane rake faced twist drills.: Part I: Geometrical analysis and experimental investigation

A study of a modified drill point design with plane rake faces for drilling high-tensile steels is presented. A geometrical analysis has shown that the modified drill point design yields positive normal rake angle on the entire lips and point relieving in the vicinity of the chisel edge. This drill geometry can be expected to reduce the cutting forces and torque, and hence reduce the possible drill breakages when drilling high-tensile steels. An experimental study of drilling an ASSAB 4340 high-tensile steel with 7–13 mm titanium nitride (TiN) coated high-speed steel (HSS) drills has shown that the modified drills can reduce the thrust force by as much as 46.9%, as compared to the conventional twist drills under the corresponding cutting conditions, while the average reduction of torque is 13.2%. Drill-life tests have also been carried out and confirmed the superiority of the modified drills over the conventional twist drills. In some cases, the conventional drills were broken inside the workpiece, while the modified drills performed very well under the same cutting conditions. To mathematically predict the drilling performance and optimise the drilling process using the plane rake faced drills, predictive models for the cutting forces, torque and power will be developed in the second part of this investigation.     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

Prediction model of surface residual stress within a machined surface by combining two orthogonal plane models

The variation of surface residual stress within a machined surface layer caused by face turning was studied. The size of the tool’s corner radius and the feed rate affect residual stress. A process model using the finite element method is proposed and the mechanical effects of the corner radius and feed rate on a machined surface were discussed. When a tool with a small corner radius is used, surface residual stress perpendicular to the cutting direction becomes compression stress. As well, surface residual stress changes from tension to compression as the feed rate decreases. The process model consists of an orthogonal cutting simulation and an indentation-like simulation of a corner radius into a work piece surface. The simulated results show quantitative agreement with the residual stress measured experimentally. The integrity of the machined surface will be controlled more efficiently if the cutting conditions during finishing are determined with the proper consideration of the surface generating process.     

CAD model based virtual assembly simulation,planning and training

This paper reviews the state-of-the-art methodologies for developing computer-aided design (CAD) model based systems for assembly simulation, planning and training. Methods for CAD model generation from digital data acquisition, motion capture, assembly modeling, human–computer interface, and data exchange between a CAD system and a VR/AR system are described. Also presented is an integrated methodology for designing, planning, evaluating and testing assembly systems. The paper further describes the implementation of these methods and provides application examples of CAD model based simulation for virtual assembly prototyping, planning and training. Finally, the technology gaps and future research and development needs are discussed.     

限制自由度单元及其在板料成形过程数值模拟中的应用

根据板料成形过程的特点，提出一种用于板料成形分析的新单元模型－三维限制自由度单元模型，这种单元既没有膜单元不能考虑横向剪应力的遗憾，也不受壳单元对于局部大的限制毛坯后机加工同时克服了体单元解决板结构问题时刚度矩阵奇异的缺点。