低温BOG压缩机气缸螺栓预紧研究

采用有限元方法对BOG压缩机气缸螺栓进行了模拟计算,得到了预紧螺栓在压力、温度载荷作用下的应力和接触状态.分析了材料属性、预紧力矩值、螺栓排列方式及螺栓个数等对螺栓连接性能的影响.研究结果表明,当气缸和缸盖采用奥氏体不锈钢材料时预紧力矩应比常温下取得大,而采用Ni35时常温下的预紧力矩即可以满足要求;预紧力矩取值越大,被连接件结合越紧密,但同时螺栓的应力也越大;螺栓排列越靠气缸内侧时,所需预紧力越小;而螺栓个数的选取应兼顾气缸密封状态和螺栓应力状态.     

拧螺栓和拧螺母对螺纹轴向预紧力的影响研究

为了研究拧螺栓和拧螺母对轴向预紧力的影响,基于被连接件材料为钢-钢、钢-铝连接结构,将六角法兰面螺栓和六角法兰面螺母分别压钢状态进行拧紧试验,并利用超声波预紧力测量仪监测拧紧实现的轴向预紧力,结果表明拧螺栓较拧螺母实现的预紧力大。经分析导致该现象主要原因为螺栓法兰面实际锥度比螺母法兰面锥度小,即螺栓法兰面较螺母内外圈高度差小,导致前者支承面摩擦内径更小,同目标扭矩条件下扭矩系数小则转化的轴向预紧力更大。结合有限元分析,验证实测样件法兰面不同锥度受载条件下的应力分布情况,钢板最大应力集中位置为支承面摩擦内径,与试验结果相吻合。     

螺栓塑性变形区域转角紧固方法

柴油机的气缸盖、主轴承盖及连杆大头盖等部位，连接螺栓的轴向预紧力决定了螺栓连接牢度、密封性及可靠性。 用扳手拧紧螺栓使其产生轴向拉力时，螺栓同时承受拉应力和扭应力，当拉应力达到材料屈服强度的８０％时，螺栓就会产生塑性变形，因此，紧固螺栓通常是在其弹性变形区域内进行的。 为了充分发挥螺栓的工作能力，螺栓的预紧应力可达材料屈服强度的 ５０％～７０％，预紧力矩约为预紧力与螺纹公称直径之积的０．２倍。约５０％的预紧力矩是由其螺旋面的摩擦力决定的，另５０％则是由螺栓头螺母支承面的摩擦力决定的。用扭力扳手按要…     

带预紧力的螺栓连接有限元分析

在机械通过螺栓连接装配时,绝大数情况螺栓都需要拧紧,使连接在承受工作载荷前,预先受到预紧力作用。施加预紧力的目的在于增加被连接件可靠性和紧密性,防止连接件在工作运转后出现缝隙或相对滑动。基于此,利用ANSYS Workbench软件对法兰用螺栓连接预紧进行有限元分析,证明预紧力可以增加被连接件紧密性;但是当法兰直径过小时,过大预紧力会导致螺栓变形增大,甚至造成螺栓发生塑性变形,而法兰变形也会加大。     

螺栓的塑性区域旋转角度拧紧法

在一些场合,接合面的连接螺栓装配时要求有一定量的预紧力,使连接螺栓工作时确保接合面贴合紧密(对动载螺栓)。目前在生产中连接螺栓M的预紧力一般均通过扭矩扳手控制预紧力矩M来间接控制的。显然,预紧力矩M是很难精确控制的,它受到螺纹间、座面与螺     

大口径法兰三维力学有限元分析

建立了螺栓法兰联接大口径法兰的三维有限元模型，在考虑垫片非线性和接触非线性的基础上，研究了预紧工况和承压工况下螺栓、垫片等元件的受载与变形情况。研究表明螺栓外侧应力与预紧力成正比且随着内压的升高而增加：螺栓内侧应力与预紧力成正比但随着内压的升高而降低；法兰偏转量对垫片和螺栓的应力影响较大，随着内压的升高法兰偏转量增加，垫片变形量减小但不均匀性增加。     

轴套长度对被连接件压缩变形体形状影响的研究

螺栓连接结构在其夹紧区域内压缩变形量的计算会受到压缩变形体形状的影响.为了探究更适宜的压缩变形体等效方式,基于压应力4次分布理论修正了与轴套接触的被连接件内压缩变形体的最小外径,得到被连接件轴向压缩变形量的修正解析式.对有限元仿真的节点应力进行曲线拟合和数值积分计算,得到螺栓的轴向压缩变形量.结果表明:螺栓连接结构夹紧区域内压缩变形体为平头圆锥、圆柱与双平头圆锥的组合形式更为恰当,与轴套接触的被连接件内压缩变形体的最小外径修正为轴套外径与螺栓头支承面直径平均值的1.4倍时,其相对误差不超过7.49％;采取正确的压缩变形体等效方式并引入被连接件压缩变形体最小外径的修正有利于计算含有轴套的螺栓连接结构的轴向压缩变形量.     

浅谈工程机械螺栓预紧力控制方法

正1螺栓预紧的作用绝大多数螺栓连接件在装配时都必须拧紧,以使其在承受工作载荷之前,预先受到拉力作用,这个预加作用力称为预紧力。预紧的目的在于增强连接的可靠性和紧密性,防止受载后被连接件出现缝隙或发生相对滑移,最终保证紧固件可靠地连接在一起。大量研究及实验表明,螺栓连接预紧力的大小将对螺栓总载荷、连接临界载荷、抵抗     

航空结构中螺栓连接预紧力设计研究

螺栓预紧力表示的是螺栓在拧紧过程中,螺栓与其他连接件之间在拧紧力矩的作用下沿螺栓轴线方向的力。影响螺栓预紧力的因素有很多,比如:螺母与连接件之间产生的静摩擦力、螺母与螺栓之间产生的静摩擦力以及螺栓的拧紧力矩。航空结构中有许多部位需要螺栓连接的,因此,研究航空结构中的螺栓预紧力对于飞机整体的稳定性有一定的帮助。     

轴流压缩机机壳螺栓预紧力的分析及计算

以某轴流压缩机为例,计算了机壳中分面螺栓的理论预紧力和预紧力矩,分析机壳螺牙是螺栓连接强度的限制因素,对机壳螺牙的强度作了校核,确定出了预紧力矩值的范围,并与实际情况作了对比验证,总结了轴流压缩机机壳中分面螺栓预紧力的分析及计算方法。     

Note on the complete contact between a flat rigid punch and an elastic layer attached to a dissimilar substrate

The contact pressure distribution is found for a square ended rigid punch, pressing normally onto an elastic layer, itself attached to an elastically dissimilar half-plane, under plane deformation. Each interface may be either frictionless or adhesive, and it is shown that the shear traction assumption has only a very small influence on the contact pressure, which is found as a perturbation on the classical Flamant half-plane solution. For thin layers the contact pressure distribution is only weakly dependent on the pad aspect ratio.     

大型500 kV变压器主密封法兰系统受力分析

利用有限元分析软件ABAQUS对油浸式变压器的主密封界面的螺栓、垫片、法兰系统进行建模,分析预紧状态下法兰螺栓受力及变形情况,探讨接触应力随橡胶垫片压缩率、流体压力、橡胶垫片硬度的变化规律。结果表明:在螺栓预紧载荷作用下,法兰偏转使螺栓受力不均,箱沿连接处为法兰最易损坏位置,可在箱沿与箱体处加额外刚性固定来增加强度;随着压缩率与流体压力的增大,橡胶垫片的接触应力和von Mises应力均增大;橡胶垫片硬度越大,相同流体压力下的接触应力和von Mises应力也越大,因此当密封界面承受较大流体压力时,应选用硬度大的橡胶垫片。     

基于有限元的弹性接触问题的探讨

探讨了组合结构法在弹性接触问题中的应用,并以螺栓联接为例,建立了用弹性力学有限元的组合结构法解决繁杂弹性接触问题的力学模型。该模型综合考虑了设计精度、制造误差、装配情况及载荷工况等因素对螺栓受力的影响,能够精确给出螺纹载荷和根部应力分布规律以及螺栓联接的变形情况。     

The derivation and application of a semi-infinite flat and rounded asymptotic frictionless contact

The solution is found for the contact pressure distribution between a semi-infinite flat and rounded, frictionless, elastic punch pressed onto an elastically similar half-plane. This is used to obtain an asymptotic form of wide-ranging applicability, for finding the near-edge contact pressure in a contact which is nearly complete in character, and this is illustrated by example.     

Contact analysis of three-dimensional rough surfaces under frictionless and frictional contact

A methodology for surface and sub-surface stress calculation of nominally flat on flat rough surface contact has been developed. This methodology is applicable for both large area contact (Hertzian contact) and small area of asperity contact (point load contact) with and without surface friction. A total of nine rough surfaces are generated by the computer with specified standard deviation of surface heights, σ, of 0.3, 1.0 and 3.0 nm, and correlation length, β^*, of 0.1, 0.5 and 0.9 μm. Under the typical applied load at the magnetic head slider-disk interface, small numbers of contact points are obtained and the deformation is purely elastic. Since these contact points are scattered and isolated, asperity contact behaves like point load contact. As β^* becomes larger, more adjacent points will be in contact at a certain contact spot and this is especially true at small σ. All the cases of flat on flat rough surface contact yield maximum von Mises stress on and near the surface at both frictionless and frictional contacts; no local maximum occurs in the sub-surface. In general, the friction effect in the vicinity of contact point is to increase the stress magnitude, while outside this region it also alters the stress distribution. For a surface of small β^* and large σ at high load of 1000 times of the nominal pressure at the head-disk interface, the contact pressure reaches the hardness at a few contact points and plastic deformation takes place in the near surface.     

模量面内变化的梯度功能弹性薄层接触应力分析

针对材料均匀去除要求,提出了一种基于梯度功能研抛盘的加工新方法,研究了模量面内变化的梯度功能弹性薄层接触应力问题。用半逆解法推导出梯度功能弹性薄层无摩擦接触应力方程,引入补偿函数来补偿平面位移的影响,简化了解析过程;利用ANSYS建立了梯度功能研抛盘无摩擦接触模型,得到位移加载下试样表面的等效应力分布;通过与应力方程拟合,获得了应力预测方程解析式及相应的补偿函数关系。最后,建立了试验平台,试验对比结果显示误差在10%以内,验证了接触应力预测方程解析式的正确性。     

小冠头双线螺栓用衬套过盈配合研究

小冠头双线螺栓用衬套在过盈配合过程中,套身容易出现裂纹或卷边。针对此问题,运用Abaqus有限元软件对小冠头双线螺栓用衬套、薄壁件分别定义为0Cr18Ni9、Q235钢的材料属性,通过改变小冠头双线螺栓用衬套与薄壁件孔配合的过盈量和小冠头双线螺栓用衬套套身长度,对配合过程中的应力(装配应力)、接触压力以及所需压装力的影响规律进行研究;用压力可控的压铆设备针对有限元模拟中的各种情况进行压装实验。研究结果表明:装配应力随着过盈量的增加而增大,衬套套身长度对装配应力影响不大;接触压力、所需压装力随着过盈量的增加和衬套套身长度的增长呈递增趋势;当过盈量达到0.1 mm时,小冠头双线螺栓用衬套容易出现压扁现象,衬套套身长度越长越容易发生卷边。     

车联网环境下考虑前方车辆驾驶人意图的汽车主动预警防撞模型

前方车辆驾驶人意图信息对后方车辆预警防撞模型危险判断至关重要,针对传统防撞模型误警率高、制动不及时等问题,设计了一种考虑前方车辆驾驶人意图的汽车主动预警防撞模型。首先,选择BP神经网络（Back-propagation neural network,BPNN）和隐马尔可夫模型（Hidden Markov model,HMM）作为驾驶行为层与驾驶意图层的主体模型,并利用驾驶模拟器采集的前车制动踏板、加速踏板和车速等意图观测数据作为输入构建意图识别模型,从而实现对前车驾驶人加速驾驶、匀速驾驶、正常制动和紧急制动意图的识别;其次,利用车联网将前车驾驶人意图识别结果与路面附着信息传递给后方车辆,建立考虑前车驾驶人意图的汽车主动预警防撞模型,动态判断碰撞危险并调整预警及制动执行逻辑;最后,为验证所提出的意图识别模型准确性和主动预警防撞模型的有效性,搭建基于Simulink、Carsim及PreScan的联合仿真平台,并进行多工况试验测试。结果表明,所提出的BP-HMM模型对前车驾驶人意图的平均识别准确率为94.17%,优于传统BP或HMM识别模型;主动预警防撞模型在预警测试中的平均正警率为93.43%,与TTC、Mazda及考虑后车驾驶人意图的三种模型相比,平均误警率分别降低了16.12%、23.43%和26.67%,且在自动紧急制动测试工况中均能成功避免碰撞,两车最短相对距离大多保持在2～8 m范围内,平均值为3.698 m,具有更高的安全性和稳定性。     

Electro-elastic fields of piezoelectric materials with an elliptic hole under uniform internal shearing forces

The existing investigations on piezoelectric materials containing an elliptic hole mainly focus on remote uniform tensile loads. In order to have a better understanding of the fracture behavior of piezoelectric materials under different loading conditions, theoretical and numerical solutions are presented for an elliptic hole in transversely isotropic piezoelectric materials subjected to uniform internal shearing forces based on the complex potential approach. By solving ten variable linear equations, the analytical solutions inside and outside the hole satisfying the permeable electric boundary conditions are obtained. Taking PZT-4 ceramic into consideration, numerical results of electro-elastic fields along the edge of the hole and axes, and the electric displacements in the hole are presented. Comparison with stresses in transverse isotropic elastic materials shows that the hoop stress at the ends of major axis in two kinds of material equals zero for the various ratios of major to minor axis lengths; If the ratio is greater than 1, the hoop stress in piezoelectric materials is smaller than that in elastic materials, and if the ratio is smaller than 1, the hoop stress in piezoelectric materials is greater than that in elastic materials; When it is a circle hole, the shearing stress in two materials along axes is the same. The distribution of electric displacement components shows that the vertical electric displacement in the hole and along axes in the material is always zero though under the permeable electric boundary condition; The horizontal and vertical electric displacement components along the edge of the hole are symmetrical and antisymmetrical about horizontal axis, respectively. The stress and electric displacement distribution tends to zero at distances far from the elliptical hole, which conforms to the conclusion usually made on the basis of Saint-Venant’s principle. Unlike the existing work, uniform shearing forces acting on the edge of the hole, and the distribution of electro-elastic fields     

Frictionless contact between an elastic layer on a rigid base and a circular flat-ended punch with rounded edge or a conical punch with rounded tip

The axi-symmetric frictionless indentation problem involving an elastic layer on a rigid base and a rigid indenter (punch) having either a rounded edge or a rounded tip profile has been investigated. The layer is either firmly attached to a rigid base (bonded layer) or resting without friction on a rigid base (unbonded layer). A set of asymptotic solutions for the contact pressure is derived for thin layers. Numerical and theoretical results showed good agreement.