盲孔法测量焊接残余应力应变释放系数的有限元分析

为探讨简单易行的盲孔法测量焊接残余应力应变释放系数A、B的标定方法，根据盲孔法测量残余应力时应变释放系数A、B试验标定原理和强度理论，建立三维有限元模型，分别对盲孔法测量92lA钢焊接残余应力应变释放系数进行有限元标定和孔边应力集中有限元塑性修正．并由此得出应变释放系数随孔深与孔径比值的关系式和应变释放系数随形状改变比能参量S变化的塑性修正公式；将有限元标定结果与试验标定结果、通孔应变释放系数理论解进行比较，结果表明，有限元标定结果与试验结果、通孔应变释放系数理论值有较好的一致性，经塑性修正，计算结果与试验测量结果的偏差大大减小，建立适当有限元模型，用有限元法标定释放系数和进行孔边塑性变形修正是可行的。     

盲孔法测定焊接残余应力应变释放系数的模糊数学分析

在分析一些引起盲孔法检测焊接残余应力测量误差的不确定因素的基础上,引入模糊数学方法对应变释放系数进行评价.在允许常规模型中的有关参数在一定范围内变动、用隶属函数表示其取值分布情况的前提下,建立应变释放系数的模糊数学模型.将应变释放系数评价模型中的有关参数考虑为正态分布模糊数,利用水平截集概念转化为普通集问题进行求解.以921A钢板焊接的残余应力测量为例,计算出不同置信水平的应变释放系数A和B的数值.结果表明,基于模糊集的应变释放系数评价模型能适当屏蔽一些不确定因素,更准确地反映实际情况.     

盲孔法测量残余应力A,B系数计算公式讨论

文中介绍了基于通孔理论的几种A、B系数计算公式,并与盲孔A、B系数的标定值作了比较,讨论了它们之间差异的原因,建议选用与标定值相接近的A、B系数计算公式.这样在不同的材料上钻孔测量残余应力,当变更钻孔的孔径或者采用不同尺寸的应变花时不必每次进行A、B系数的标定.     

小孔法测量残余应力的应力—应变有限元分析

采用三维八节点等参元的有限元方法,计算试件表面钻一盲孔((?)1.5mm×2.0mm)后的应力—应变分布。结果表明,盲孔周围的应力分布特征与相同状态下通孔情况基本相似,只是由于盲孔底部的拘束和传力作用,使孔边的应力集中系数有所降低(约10%),孔边的应力释放量也比通孔小些。盲孔的最大应力集中系数为2.78,位于孔的中部。实验标定结果表明,当外加应力小于0.7σ_s 时,两者的应力—释放应变曲线基本相同;大于0.7σ_s 时,曲线有所分离,最大差别为30μ∈左右。     

盲孔法测定时计算公式中A,B值的研究

通过三维弹性有限元分析和单向标定实验，分析了盲孔法与通孔解的关系，着重研究了应变释放系数Ａ，Ｂ值，Ａ，Ｂ值随着孔深了孔径之比的增大而增大，当ｈ／ｄ〉１．０－１．５时，Ａ，Ｂ值基本趋于稳定。     

用实验—有限元法确定圆环中残余应力的分布

1 简介为提高高压圆筒的承载能力和疲劳强度,常采用自增强处理工艺,使简体内壁产生残余压应力。残余应力的无损检测方法有X射线法、磁测法、超声法等。X射线法和磁测法只能测定试件表面一薄层材料的残余应力,超声法也只能测定简单应力状态的构件(如螺栓的轴向拉力),而对于象厚壁圆筒经自增强处理后的残余应力,用该法测定十分困难。残余应力的     

环芯法A,B释放系数的有限元计算

根据环芯法测量残余应力的原理,建立了计算环芯法A、B释放系数的有限元力学模型,进行了三维有限元计算。有限元计算的A、B释放系数与以往实验标定的A、B系数极其吻合。     

发动机缸盖残余应力的测量及分析

采用盲孔法测量3组发动机铝合金缸盖裂纹附近和敏感部位的残余应力情况,分析缸盖内的残余应力对其裂纹产生的具体影响。考虑到缸盖的复杂结构特点和选择的测点位置,测试选用钻铣床钻盲孔和铣断通油管及其侧板,并在钻盲孔释放残余应力和铣削过程中通过30通道应变仪DRA-30A记录测点的应变时域曲线。对测试结果的分析和研究表明:通油管部分的残余应力以压应力为主,下缸体的上表面以拉应力为主,这种上压下拉的残余应力分布情况是缸盖内产生裂纹的主要原因;测点4处产生裂纹的可能性较大,测点7处通油管对下缸体的局部拉伸作用最为明显;B90组结构设计和加工工艺在3组试样中最为合理。据此测试结果和研究结论改进产品的结构和工艺后,该种缸盖满足设计要求。     

残余应力引起的铣削变形有限元分析

应用弹性力学理论推导出了二维连续铣削过程中工件内应力再分布及其引起变形的计算递推公式.解决了有限元建模、初始应力加载、变形评估等仿真关键技术,建立了残余应力引起铣削变形的二维有限元仿真模型.最后对实例进行了仿真计算,分析了残余应力引起的加工变形规律,并用解析法对仿真结果的进行了验证.     

A coupled finite element and meshfree analysis of erosive wear

Erosive wear is a kind of material degradation, which is largely involved in many industries, and caused a series of serious problems and economic loss. Many theoretical models and numerical models have been established to study the erosion phenomena. In this study, a coupled finite element and meshfree model was developed for the simulation and prediction of erosive wear. By utilizing the meshfree technique, the error due to mesh distortion and tangling at impacted area in the finite element analysis could be effectively avoided. The fundamental mechanisms of erosion by solid particle impact were investigated as well. Comparison against the results of analytical erosion models and finite element model are made. It is shown that the predicted results are in agreement with reported results. The present study could be very useful and efficient in studying erosive wear.     

Finite element modeling of residual stresses in machining induced by cutting using a tool with finite edge radius

A thermal elastic-viscoplastic finite element model is used to evaluate the residual stresses remaining in a machined component. An improvement in the accuracy of the predicted residual stresses is obtained by: (a) using a modified Johnson–Cook material model that is augmented by a linearly elastic component to describe the material behavior as non-Newtonian fluid; (b) using a remeshing scheme to simulate the material flow in the vicinity of the rounded cutting tool edge without the use of a separation criterion; (c) properly accounting for the unloading path, and (d) considering the thermomechanical coupling effect on deformation. Case studies are performed to study the influence of sequential cuts, cutting conditions, etc., on the residual stresses induced by orthogonal machining.     

手机静态机械特性的有限元仿真

采用有限元技术对手机的静态机械特性进行仿真试验分析。仿真建模采用I-DEAS软件,用分组的方式建立装配 模型。单元划分采取划分子区域的方法。仿真结果与实物试验相吻合。     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

基于有限元法的滚切外齿轮齿根应力分析

利用ANSYS有限元软件对滚切外齿轮进行建模,并对滚切外齿轮的齿根应力分布进行了分析.通过对比传统的滚切外齿轮计算方法与有限元分析方法,提出了轮齿的总体应力分布具有梁的分布特性,齿根危险截面应力的最大值位于现行算法所确定的平面上方的齿根圆角处.     

Dynamic analysis of a rig shafting vibration based on finite element

In recently, finite elements method (FEM) has been used most popular for analysis of stress, vibration, heat flow and many other phenomena. Taking a rig shafting as an example, this paper studies the lateral vibration of the rig shafting with multi-degree-of-freedom by using FEM. The FEM model is created and the eigenvalues and eigenvectors are calculated and analyzed to find natural frequencies, critical speeds, mode shapes and unbalance responses. Then critical and mode shapes are determined. Finally, responses of unbalance force are analyzed in case of undamped and damped system, and peaks of response are compared.     

FEM-based strain analysis study for multilayer sheet forming process

Fiber metal laminates have many advantages over traditional laminates (e.g., any type of fiber and resin material can be placed anywhere between the metallic layers without risk of failure of the composite fabric sheets). Furthermore, the process requirements to strictly control the temperature and punch force in fiber metal laminates are also less stringent than those in traditional laminates. To further explore the novel method, this study conducts a finite element method-based (FEM-based) strain analysis on multilayer blanks by using the 3A method. Different forming modes such as wrinkling and fracture are discussed by using experimental and numerical studies. Hydroforming is used for multilayer forming. The Barlat 2000 yield criteria and DYNAFORM/LS-DYNA are used for the simulations. Optimal process parameters are determined on the basis of fixed die-binder gap and variable cavity pressure. The results of this study will enhance the knowledge on the mechanics of multilayer structures formed by using the 3A method and expand its commercial applications.     

A new stress-based model of friction behavior in machining and its significant impact on residual stresses computed by finite element method

Friction modeling in metal cutting has been recognized as one of the most important and challenging tasks facing researchers engaged in modeling of machining operations. To address this issue from the perspective of predicting machining induced residual stresses, a new stress-based polynomial model of friction behavior in machining is proposed. The feasibility of this methodology is demonstrated by performing finite element analyses. A sensitivity study is performed by comparing the cutting force and residual stress predicted based on this new model with those based on a model using an average coefficient of friction deduced from cutting forces and a model using an average coefficient of friction deduced from stresses. The average coefficient of friction computed based on the measured cutting forces is the conventional approach and is still widely used. The average coefficient of friction due to stresses can be considered as a simplified version of the proposed model. Simulation results show significant difference among the predicted residual stresses. As the proposed model is able to capture the relationship between the normal stress and shear stress on the tool rake face better than the conventional approach can, it has a potential for improving the quality of the prediction of the residual stresses induced by machining.