连接件非均匀面压结合部动态性能建模与分析

基于栓接结合面非均匀面压分布与分形接触理论,通过静力仿真获得了结合部非均匀面压的分布规律,建立了结合面的动态参数的动力学模型,并将结合面的动态参数换算为虚拟材料的弹性模量、切变模量及泊松比等材料属性参数。提出了考虑结合面非均匀面压影响的栓接结合部有限元模型,结合有限元分析获得栓接结合部的理论模态频率及振型。将理论与实验模态相比较,所提出的模型能够准确地描述机械结合部的固有频率及振型等动态特性,可应用于提高数控机床整机的动态性能建模分析准确性。     

基于虚拟材料方法的螺栓预紧力模拟的研究

螺栓的预紧力是影响螺栓连接面力学特性的一个重要的因素,在精度需求较高的含螺栓连接的有限元分析中,需要考虑螺栓的预紧力。运用虚拟材料方法模拟模态分析中的螺栓预紧力,首先根据结合面的参数计算各个预紧力下的虚拟材料属性,在有限元软件中建立含虚拟材料连接面的模型,仿真得到螺栓连接板件的固有频率和振型。仿真结果跟模态实验结果一致,验证了采用虚拟材料方法模拟螺栓预紧力的有效性,为装配体的有限元建模提供了途径。     

基于梯度虚拟材料的栓接结合部连接参数表征

螺栓连接是应用最广泛的装配形式之一,表征栓接结合部连接参数是进行装配体结构动力学分析的关键,针对各向同性虚拟材料模型不能准确表征结合面压力分布不均匀性的问题,提出并开发一种基于梯度虚拟材料的栓接结合面连接参数表征模型。首先根据结合面压力分布特征,以及结合面法向、切向刚度与压力分布间的映射关系,建立了等效虚拟材料参数随位置坐标的变化规律模型;分别采用等参梯度单元和高斯积分点料属性梯度分布单元等效表征结合部连接参数,采用结构静力学、动力学分析方法进行分析,通过对比不同类型单元静力学、动力学计算结果,验证梯度材料单元的准确性;进而研究了基于代理模型的梯度虚拟材料参数辨识方法,采用拉丁超立方采样来获取样本点,采用Kriging模型拟合连接参数,应用遗传算法优化虚拟材料参数。采用均匀虚拟材料模型、各向异性虚拟材料模型及梯度虚拟材料模型的仿真结果与试验数据对比,表明梯度虚拟材料模型是一种表征栓接结合部压力/刚度分布特性的有效方法。     

切向载荷下螺栓结合部静特性分析及试验

为了准确理解螺栓结合部静态特性,基于结合面基础特性建立了螺栓单元结合面解析数学模型,提出了一种等效分步载荷解析算法,可以实现在结合部承受切向载荷时,无需考虑载荷间耦合关系就能对结合部力平衡非线性隐含积分方程组进行快速准确求解。采用自行设计的螺栓结合部切向加载装置进行了结合部扭转和剪切加载试验。试验与解析结果均表明,在切向载荷不超过最大静摩擦力的情况下,螺栓结合面切向变形与外载荷成线性关系。解析与试验结果的一致性验证了模型的正确性,为机械结合面静态特性分析提供了理论和试验支持,求解算法可方便地将结合面研究成果应用于工程实践。     

螺栓预紧力对螺栓结合面特性参数的影响规律研究

高精度空气静压轴承中螺栓结合面的特性受组成结合面的构件的材料、接触面的形貌、接触面的几何精度、接触面的接触形式等因素的影响,其中影响最为显著的是螺栓预紧力。通过有限元仿真和实验模态分析方法辨识了螺栓结合面的特性参数,并研究了螺栓预紧力对螺栓结合面特性参数的影响规律。发现,随着螺栓预紧力的增加,螺栓结合面特征频率随之增加;当螺栓预紧力增加到一定数值时,螺栓结合面在有限元仿真时可以定义为绑定接触。     

一种新的机械结构结合部特性分析方法

提出一种新的基于界面元法的结合部特性分析方法。由于界面元法采用分片刚体位移模式,在数值分析时允许组合结构在结合面上位移不连续,并且无须增加任何形式的接触单元就可以有效地模拟结构的不连续性。基于赫兹理论,根据微凸体法向载荷与法向接触变形之间的关系,由结合部特性的试验拟合公式推导出结合部特性的等效材料参数弹性模量;根据离散单元中的应力波传播条件,得到结合部法向刚度和切向刚度之间关系式,并利用结合部特性的试验拟合公式推导出结合部特性的等效材料参数泊松比。以包含结合部的机械结构为研究对象进行数值分析,并将计算结果和试验测量结果进行比较。比较结果验证了用界面元法对考虑结合部特性的机械结构进行数值分析的可行性和准确性,为深入研究机械结构结合部问题奠定了基础。     

BFPC固定结合面虚拟材料参数识别

为了准确识别玄武岩纤维树脂混凝土(Basalt fiber folymer concrete,BFPC)固定结合面虚拟材料参数,基于两自由度弹簧-阻尼动力学模型建立了BFPC固定结合面动态模型,在此基础上辅以实验测试方法确定了9组不同表面粗糙度和结合面压下的BFPC结合面动态特性参数.基于横观各向同性、赫兹接触理论和分形理论建立了BFPC结合面虚拟材料的动态特性参数数学模型,结合实验结果识别不同表面粗糙度和结合面压下的虚拟材料参数.通过对比含有BFPC结合面的组件模态振型和固有频率理论分析和有限元仿真分析结果,证明了BFPC结合面虚拟材料参数识别方法的正确性.     

基于横观各向同性假定的固定结合部本构关系及有限元模型

提出了一种固定结合部的有限元建模方法。该方法将接触层等效成均质、虚拟的横观各向同性材料。根据结合面的变形和载荷关系,推导了虚拟材料本构矩阵中5个独立变量与法向应力之间的非线性关系。将这个本构关系引入到有限元分析中用以建立机器的固定联接面模型。分析结果与试验结果的对比证实了该方法的有效性。     

基于面压不均匀分布的结合部动力学建模研究

提出了一种基于结合面压力不均匀分布的螺纹固定结合部动力学建模方法。首先,利用Ansys对施加预紧力的装配体整机进行静力学分析,提取结合面处的节点、单元信息及压力分布,基于节点间距离最短的原则对上、下结合面中的节点进行匹配,在匹配好的两节点间建立Matrix27刚度和阻尼单元,以此来描述结合部的动力学特性;其次,基于结合面压力分布及Yoshimura法,求解Matrix27单元中的刚度系数和阻尼系数;最后,将结合部与零部件有限元模型综合成整机有限元模型。对比前四阶理论模态与试验模态可知:理论模态振型与试验模态振型相似且一一对应,理论固有频率与试验固有频率间的误差在0.7%～7.2%范围内,从而验证了该建模方法的有效性。     

基于虚拟材料层的滑动结合部动态特性建模方法

由于弹簧阻尼单元模拟结合部动态特性的方法存在的缺陷,提出采用虚拟材料层和多点约束技术对滑动导轨系统建立有限元模型,并在ANSYS中完成模态分析。通过分析虚拟材料层的材料属性参数(弹性模量、泊松比、密度)和结构参数(虚拟材料层厚度)对滑动结合部动态特性的影响,得到可供工程应用的3个优化设计变量,并将优化结果与试验模态分析结果进行了比较。研究表明,有限元模态计算的固有频率与试验结果误差低于8%,为实际工程应用提供了一种可靠的建模方法。     

基于模型修正的螺栓结合部虚拟材料参数识别及应用

针对螺栓结合部虚拟材料模型建模及参数识别问题,基于结合部显著影响整体结构动力学性能这一特性,提出基于模型修正的虚拟材料动力学模型参数识别方法。针对参数识别中修正方程的病态问题,根据虚拟材料相关参数及结构各阶模态频率相互之间的影响度,构造修正方程的左右加权函数以减轻其病态程度,并通过仿真算例验证参数识别方法的有效性。探讨平板螺栓连接及哑铃状结构用于虚拟材料参数识别的有效性及抗噪性,加工哑铃结构的实验零件,辨识螺栓结合部虚拟材料模型的参数。基于机床螺栓结构的常用工况,建立虚拟材料模型参数库,并在CKX5680数控机床上验证参数库的有效性。结果表明：采用模型修正技术可以准确地识别无噪声时的虚拟材料参数;采用哑铃结构实验试件在有噪声情况下,螺栓结合部虚拟材料参数识别误差小于8%;采用虚拟材料模型模拟螺栓结合部的建模误差小于5.6%。     

确定法兰螺栓预紧力的EN法与Waters法对比研究

为了验证不同方法计算所得的螺栓预紧力能否满足密封性要求,选取2种不同尺寸和工况的管法兰-螺栓-垫片模型,进行有限元分析。运用ANSYS Workbench有限元软件建立三维模型,施加温度载荷后得到法兰系统的温度场分布。根据EN13445附录G和Waters方法确定了螺栓预紧力,分别作为初始预紧力施加在对应的管法兰系统上并进行热-结构耦合。对预紧工况和操作工况下的法兰系统进行模拟分析,并对其密封及其强度性能进行评定。结果表明:通过EN法和Waters法计算所得的螺栓预紧力,均能使法兰系统满足密封条件且符合安全评定要求;但EN13445附录G方法确定的螺栓预紧力能保证应力在法兰上更均匀地分布,且应力水平更低;EN13445附录G方法在计算时考虑了整个法兰连接接头的密封要求及其强度要求,相较于Waters法考虑情况更加全面。     

Surface contact stress-based nonlinear virtual material method for dynamic analysis of bolted joint of machine tool

The components of machine tools are mainly fixed and connected by bolts. The performance of the assembly can be affected by the dynamic characteristics of the bolted joints. This paper presents a nonlinear virtual material method based on surface contact stress to describe the bolted joint for accurate dynamic performance analysis of the bolted assembly. Fractal geometry theory is used to describe the surface topography. The elastic modulus and shear modulus of one micro-contact are derived based on fractal contact theory. The equivalent elastic modulus, Poisson ratio, and density of the bolted joint can be obtained through the weighted mean method. In order to obtain the stress distribution, the contact surface is assumed flat in the macro-scale, and the uneven distribution of contact stress can be obtained by the finite element method (FEM). The contact surface can be divided into several sections, and the parameters of a virtual material layer can be determined based on the mean contact stress. Both theoretical and experimental results for a bolted joint are obtained for a box-shaped specimen under equal pre-tightening force and bending moment effect. The results show that the theoretical mode shapes are in good agreement with the experimental mode shapes. The relative errors between the theoretical and experimental natural frequencies are less than 4.41%, which indicates that the present nonlinear virtual material method is appropriate for the bolted joint in modeling CNC machine tools.     

基于ANSYS Workbench水轮发电机螺栓法兰连接有限元分析

根据机械设计理论,分析了只承受预紧力和预紧力与工作载荷同时作用两种情况下螺栓连接的受力情况,并利用ANSYS Workbench对水轮发电机螺栓法兰连接结构进行模拟,创建了有限元模型,施加了相应的约束、预紧载荷与工作载荷,进行了结构静力学分析.有限元分析结果与理论运算结果进行比较,有限元模型的正确性、可靠性得到验证.该模拟分析结果为螺栓的选用与装配提供了依据,提高了产品的可靠性和设计水平.     

随机参数柔性移动副运动性能的可靠性分析

以平行四杆柔性移动副为研究对象,基于伪刚体模型,采用虚功原理对机构的整体刚度进行了分析。在此基础上,将加工误差、作用载荷、杆长尺寸、弹性模量等参数均视为随机变量,建立了柔性移动副输出运动精度的可靠性分析模型,通过算例分析了柔性移动副中各项随机参数的变化对运动精度可靠度的影响。     

Longevity enhancement of bolted joints for aircrafts

New designs of bolted joints with bolt countersunk heads having high longevity in comparison with the used ones were proposed. One type of joint has the bolt heads with the reduced surface taper of the bolt head and in a joined part. Two other types have a spherical head surface, which is in contact with a tapered countersink surface. The rise in the fatigue life is achieved owing to the balance of the radial tension along the contact surfaces of the head and the countersink. Designs of a washer from the direction of a nut are proposed. These washers have ring bulges of wedge-shaped cross section that form areas of plastic deformations around a bolt body during the bolt tightening and reduce the concentration of contact stresses close to an edge of the contact surfaces of the bolt and joined parts. Procedures of fatigue tests were developed. Results of tests of the proposed bolted joints supporting their high longevity are presented. Findings of experimental investigations verify the efficiency of the application of proposed types of bolted joints in the designs of aircrafts.     

齿轮箱螺栓结合面的有限元建模研究

在实际工程应用中,针对如何有效地利用ANSYS软件对齿轮箱螺栓结合面进行有限元建模分析的问题,通过对螺栓结合面建模的难点和关键点—螺栓预紧力的模拟、螺栓接触面的模拟以及螺栓实体有限元模拟的建模方法的研究,系统地阐述了基于ANSYS的7种类型的齿轮箱结合面螺栓有限元建模方法,利用ANSYS软件对其中4种典型的螺栓有限元建模方式进行了静力分析和模态分析,分析比较了不同建模方法在静力学和动力学方面的结果差异。研究结果表明,在仿真效率和仿真精度方面,耦合螺栓模型是一种更为合适的建模方法,但在实际应用中采用实体螺栓有限元模型模拟实际结构中的螺栓时,能够更好的反应实际工作中螺栓连接结构的应力变化,是各种建模方法中的优选方案。     

Can extra-articular strains be used to measure facet contact forces in the lumbar spine? An in-vitro biomechanical study

Experimental measurement of the load-bearing patterns of the facet joints in the lumbar spine remains a challenge, thereby limiting the assessment of facet joint function under various surgical conditions and the validation of computational models. The extra-articular strain (EAS) technique, a non-invasive measurement of the contact load, has been used for unilateral facet joints but does not incorporate strain coupling, i.e. ipsilateral EASs due to forces on the contralateral facet joint. The objectives of the present study were to establish a bilateral model for facet contact force measurement using the EAS technique and to determine its effectiveness in measuring these facet joint contact forces during three-dimensional flexibility tests in the lumbar spine. Specific goals were to assess the accuracy and repeatability of the technique and to assess the effect of soft-tissue artefacts. In the accuracy and repeatability tests, ten uniaxial strain gauges were bonded to the external surface of the inferior facets of L3 of ten fresh lumbar spine specimens. Two pressure-sensitive sensors (Tekscan) were inserted into the joints after the capsules were cut. Facet contact forces were measured with the EAS and Tekscan techniques for each specimen in flexion, extension, axial rotation, and lateral bending under a +/- 7.5 N m pure moment. Four of the ten specimens were tested five times in axial rotation and extension for repeatability. These same specimens were disarticulated and known forces were applied across the facet joint using a manual probe (direct accuracy) and a materials-testing system (disarticulated accuracy). In soft-tissue artefact tests, a separate set of six lumbar spine specimens was used to document the virtual facet joint contact forces during a flexibility test following removal of the superior facet processes. Linear strain coupling was observed in all specimens. The average peak facet joint contact forces during flexibility testing was greatest in axial rotation (71 +/- 25 N), followed by extension (27 +/- 35 N) and lateral bending (25 +/- 28 N), and they were most repeatable in axial rotation (coefficient of variation, 5 per cent). The EAS accuracy was about 20 per cent in the direct accuracy assessment and about 30 per cent in the disarticulated accuracy test. The latter was very similar to the Tekscan accuracy in the same test. Virtual facet loads (r.m.s.) were small in axial rotation (12 N) and lateral bending (20 N), but relatively large in flexion (34 N) and extension (35 N). The results suggested that the bilateral EAS model could be used to determine the facet joint contact forces in axial rotation but may result in considerable error in flexion, extension, and lateral bending.     

考虑高温蠕变的螺栓和法兰材料的选配*

螺栓和法兰材料的选择是影响螺栓法兰接头密封性能的重要因素,特别是在高温条件下服役,螺栓法兰发生蠕变的情况下。分别选择法兰蠕变速率大于螺栓蠕变速率以及小于螺栓蠕变速率的两组配合方式,通过传热分析、热-结构耦合分析以及高温蠕变分析,对比研究其密封性能。结果表明:螺栓蠕变和法兰蠕变都会引起螺栓应力重新分配,随着时间延长螺栓蠕变的累积会导致螺栓截面应力越来越均匀;但法兰蠕变的累积会降低法兰刚度,致使偏转角增大进而导致螺栓内外侧受力相差越来越大;法兰蠕变速率越大,法兰整体刚度下降越快,法兰服役周期越短,因此选择高温服役的螺栓法兰接头材料时,选取的法兰材料蠕变速率不能太大,且抗蠕变性能要比螺栓材料强。