Numerical Optimization by Finite Element Method of Stainless Steel/Glass-Epoxy Composite Bolted Joint under Tension and Compression

The aim of this study was to optimize the geometry and the design of metallic/composite single bolted joints subjected to tension-compression loading. For this purpose, it was necessary to evaluate the stress state in each component of the bolted join. The multi-material assembly was based on the principle of double lap bolted joint. It was composed of a symmetrical balanced woven glass-epoxy composite material plate fastened to two stainless sheets using a stainless pre-stressed bolt. In order to optimize the design and the geometry of the assembly, ten configurations were proposed and studied: a classical simple bolted joint, two joints with an insert (a BigHeadR insert and a stair one) embedded in the composite, two “waved” solutions, three symmetrical configurations composed of a succession of metallic and composites layers, without a sleeve, with one and with two sleeves, and two non-symmetrical constituted of metallic and composites layers associated with a stair-insert (one with a sleeve and one without). A tridimensional Finite Element Method (FEM) was used to model each configuration mentioned above. The FE models taked into account the different materials, the effects of contact between the different sheets of the assembly and the pre-stress in the bolt. The stress state was analyzed in the composite part. The concept of stress concentration factor was used in order to evaluate the stress increase in the highly stressed regions and to compare the ten configurations studied. For this purpose, three stress concentration factors were defined: one for a monotonic loading in tension, another for a monotonic loading in compression, and the third for a tension-compression cyclic loading. The results of the FEM computations showed that the use of alternative metallic and composite layers associated with two sleeves gived low values of stress concentration factors, smaller than 1.4. In this case, there was no contact between the bolt and the composite part and the most stressed region was not the vicinity of the hole but the end of the longest layers of the metallic inserts.

Numerical Computation of Stress Intensity Factors for Bolt-hole Corner Crack in Mechanical Joints

The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.

Residual stress around rail bolt holes after cold-expansion

Focused on rail bolt hole cold-expansion, the theoretical prediction models and results of residual stress analysis on related Problems are summarized. And a stress analyzing method based on both of the strain measurement duringthe Process of cold expansion and elastoc-plastic theory is developed. By the method proposed and the magneto-elasticmethod as well as the stress relief measurement detailed experimental study on the residual stress surrounding the coldexpanded tail bolt hole is performed. Relationship between the distribution of residual stress and cold expansion rateare established. The adaptability and limitation of theoretical predichon are also analyzed by comparing the theoreticaland experimental results.

Influence of Assembly Parameters on Tensile Behavior of Hybrid CMC and Superalloy Bolted Joints by Progressive Damage Analysis

With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of aircraft key structure. In this work, a 3 D finite element model was established to predict tensile performance and failure modes of single-lap, single-bolt 2 D C/SiC composite, and superalloy joint, which considers the progressive damage behavior of 2 D woven C/SiC composites. On the basis of the developed progressive damage model, a parametric study was carried out to illustrate the effects of bolt preload and bolt-hole clearance on mechanical behaviors of the hybrid bolted joint. It was found that the increase in the value of bolt preload made the failure load grow first and then drop, and the optimum value of bolt preload 5.00 kN generated 56.47% rise in the initial failure load and 22.83% rise in the final failure load for the bolted joint in comparison with zero preload case. As the clearance increased from 0 to 2.00%, the initial and final failure loads respectively declined by 45.88% and 24.02% for 2.00% bolt-hole clearance relative to the neat-fit case. The loss in failure loads can be reduced to compressive stress concentration around the fastening hole-edge area, leading to the appearance of earlier damages by the introduction of increasing bolt hole clearance.

Twofold hidden conformal symmetry of Kerr-Bolt black holes

Previously we have shown that a four-dimensional Kerr-Bolt black hole in non-extremal and also in extremal cases could be described by a holographic two-dimensional （2D） conformal field theory （CFT） [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 074]. Motivated by recent work [Chen C M, Huang Y M, Sun J R, Wu M F and Zou S J 2010 Phys. Rev. D 82 066004], we show that there is another holographic description for these black holes. The first description is called the J-picture, whose construction is based on the black hole angular momentum. The new description is called the Q-picture, whose constructions originate from the nut charge of the black hole. Similar to the previous cases [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 0741, we show that this new picture for a low frequency limit of the wave equation of a massless charged scalar field in the background of a Kerr-Bolt black hole can be written as the Casimir of SL（2, R） symmetry. Our result shows that the entropy of the black hole is reproduced by the Cardy formula. In addition, the absorption cross section is consistent with the finite temperature absorption cross section for a two-dimensional CFT.

盾构隧道管片接缝内外双道密封垫防水性能试验研究

为探究螺栓孔防水对内外双侧布置双道密封垫防水体系的影响,依托某超大直径盾构隧道工程,自主设计新型双道密封垫防水性能测试装置,开展考虑螺栓孔构造的内外双道密封垫防水体系耐水压测试。研究结果表明:1)螺栓孔对内外双侧布置双道密封垫的整体防水性能具有一定的控制作用,当螺栓孔防水能力不足时,其存在将成为内外双道密封垫防水体系的薄弱环节,可能早于内道密封垫发生渗漏,由此降低内外双道密封垫防水性能较单道密封垫的提升水平;2)当螺栓孔防水性能达到要求后,与单道密封垫相比,内外双侧布置双道密封垫防水体系的防水能力大幅提升;3)对于超大直径盾构隧道,当管片接缝采用内外双侧布置双道密封垫时,应确保螺栓孔防水性能满足双道密封垫间的协同防水要求。

变桨轴承用42CrMo钢疲劳裂纹扩展试验及螺栓孔裂纹扩展特性研究

以风电变桨轴承用材料42CrMo钢为基础,从轴承应力集中部位取紧凑拉伸试样(CT试件),在不同载荷和应力比条件下进行CT试件的疲劳裂纹扩展试验,对裂纹扩展过程进行Paris疲劳裂纹扩展模型的数据拟合,由试验数据拟合得到Paris模型参数C和m;利用ABAQUS与FRANC3D软件联合仿真,将试验与仿真得到的不同应力比和不同载荷下的循环次数与裂纹长度进行对比,两者的吻合度较高。通过对风电变桨轴承危险部位进行建模,建立变桨轴承螺栓孔子模型,在危险部位建立初始裂纹进行疲劳裂纹扩展数值模拟,研究不同长深比以及不同角度的疲劳裂纹的扩展规律,结果表明:随着长深比a/b的增大,在裂纹增长同样长度的情况下,所需循环次数减小,初始裂纹形状及角度均对裂纹扩展规律有较大影响。

几何偏差对多螺栓复合材料接头螺栓载荷和应力分布的影响研究

本研究建立了考虑间隙的复合材料双搭接结构的半解析模型,描述了几何偏差对螺栓载荷和应力分布的影响.首先,从典型复合螺栓接头中提取螺栓/孔局部结构作为代表单元,建立考虑随机几何偏差与接触状态的螺栓/孔对的局部刚度模型.基于Reddy高阶剪切板理论,建立复合材料层合板有限元分析模型.将螺栓/孔对的局部刚度模型与层合板全局刚度模型相结合,形成了综合考虑螺栓/孔间隙和孔拉伸变形的多螺栓复合材料接头装配力学分析模型.随机螺栓/孔组合间隙分析结果表明,合理的螺栓间隙设置可以得到更均匀的钉载分布,为多螺栓接头的排孔设计提供理论指导.

小模数齿轮传动的时变啮合刚度计算方法

小模数齿轮传动中心距较小,其动态性能对中心距误差非常敏感,且中间级齿轮常被设计在固定轴上高速旋转,齿轮中心孔与轴之间存在间隙,考虑这些特征,建立了中心距误差与轴孔配合间隙影响下的齿轮啮合特性参数与时变啮合刚度计算模型,研究了二者对啮合刚度的影响规律。研究结果表明:中心距误差会改变齿轮副的重合度与啮合刚度;轴孔配合间隙使实际中心距围绕理论中心距上下周期性波动,导致整个周期内啮合刚度强化区域与弱化区域共存;中心距误差与轴孔配合间隙的影响在不同的转角范围内存在既有相互叠加又有相互削弱的现象,这一现象使得各轮齿的啮合刚度有差异,存在诱发更大振动与不同噪声的风险。

CFRP沉头孔锪窝深度误差对连接性能的影响

沉头螺栓连接能保证结构良好的气动外形,常被应用于飞机蒙皮等结构。沉头孔的制备过程中,由于设备条件限制,会导致锪窝深度误差较大,给复合材料叠层结构带来隐患。针对这一问题,结合有限元仿真分析进行单钉单剪的静拉伸试验,研究锪窝深度误差对CFRP连接性能的影响。结果表明:对比于齐平状态的标准窝深值,锪窝较浅对静强度影响较小,较深则会导致结构的静强度下降,且锪窝越深,静强度下降越快。

跨模态特征融合模板驱动的盾构隧道管片孔缝智能识别

基于点云的隧道数据处理方法已逐步替代人工用于盾构管片接缝识别中。但常规点云处理算法提取螺栓孔和接缝时会存在因附属设施遮挡造成错误识别的问题,导致目标识别精度降低。针对此问题,以广州2003年开通的某地铁线路某段地铁隧道数据为例,提出一种跨模态特征融合模板驱动的盾构隧道孔缝识别方法。首先将隧道断面点云的几何中心作为视点,以扫描测线为单元进行逐测线投影生成隧道二维图像;然后通过Canny边缘检测和Hough变换缓冲识别纵缝,对二维图像进行环片分割,并基于双模板匹配实现盾构环分类,依据环片模板进行螺栓孔和横缝的粗定位;最后利用螺栓孔点云DBSCAN聚类后的中心坐标对环片模板进行精校正,实现盾构隧道管片孔缝智能识别。研究结果表明:该方法在附属设施遮挡干扰等情况下能较好地实现孔缝精确识别。其中,设计的基于局部形态特征双模版驱动的盾构环片分类方法,可实现盾构环片的精确分类;设计的顾及盾构管片空间位置关系的孔缝识别方法,可有效提升孔缝识别精度。在识别率与耗时相近的情况下,本方法比同类方法识别精度更高,平均偏差更少,具有更好的准确性和鲁棒性。该方法将盾构隧道三维点云和二维点云投影图像进行数据特征融合的同时,能够顾及局部形态特征凭借双模板实现盾构环片的精确分类以及依据盾构管片的空间位置关系进一步提高孔缝识别精度。研究结果为进一步自动化精准识别盾构隧道接缝和螺栓孔目标信息提供参考。

塔筒安装条件下法兰盘受力变形分析研究

法兰盘是塔筒的重要部件,起到连接风机塔筒的作用。塔筒翻身吊装施工过程中,法兰盘及螺栓孔容易发生损伤变形,导致螺栓连接失效,严重影响塔筒的安全稳定性。因此,研究吊装条件下塔筒法兰盘的受力变形特征有着重要意义。采用有限元数值分析软件,对吊装条件下法兰盘及螺孔受力及变形特征进行分析研究,结果表明:塔筒吊装翻身过程中,当塔筒处于水平状态下法兰盘螺孔变形最大;法兰盘螺孔最大变形随法兰盘厚度增大而减小,随塔筒壁厚以及长度增大而增大。基于敏感性分析数据,提出了基于非线性拟合方法的法兰盘螺孔最大变形预测公式,平均误差仅为6.79%,可以为吊装条件下法兰盘螺孔最大变形预测提供有效的理论支持。

Structural optimization of uniaxial symmetry non-circular bolt clearance hole on turbine disk

This study proposes a parameterized model of a uniaxial symmetry non-circular hole, to improve conventional circular bolt clearance holes on turbine disks. The profile of the model consists of eight smoothly connected arcs, the radiuses of which are determined by 5 design variables.By changing the design variables, the profile of the non-circular hole can be transformed to accommodate different load ratios, thereby improving the stress concentration of the area near the hole and that of the turbine disk. The uniaxial symmetry non-circular hole is optimized based on finite element method（FEM）, in which the maximum first principal stress is taken as the objective function. After optimization, the stress concentration is evidently relieved; the maximum first principal stress and the maximum von Mises stress on the critical area are reduced by 30.39% and 25.34%respectively, showing that the uniaxial symmetry non-circular hole is capable of reducing the stress level of bolt clearance holes on the turbine disk.

应急抢修钢桁梁动力响应销孔间隙影响分析

以某128 m跨新型应急抢修钢桁梁为对象,利用ANSYS与UM联合开展车桥耦合分析,选取销孔间隙和钢销直径为关键参数,探究支点存在高差时销孔间隙对钢桁梁结构及车辆响应的影响规律。研究表明:钢桁梁存在支点主桁高差或对角高差,在钢销直径恒定时,钢桁梁和车辆响应均随间隙增大而增大;在销孔间隙恒定时,钢桁梁和车辆响应均随直径增大而降低。相较于主桁高差,当存在对角高差时,销孔间隙对钢桁梁动力响应显著,而对车辆响应影响较小。此外,相较于钢桁梁竖向动力响应,销孔间隙对于横向水平动力响应的影响更为显著,设计与工程应用中应重点关注。

排气孔参数及叶顶间隙对除气泵性能影响的研究

以一种由半开式离心主泵和内置液环真空泵组合而成的新型半开式除气泵为研究对象,探究其离心叶轮后盖板开设的排气孔的参数以及叶顶间隙对此泵除气性能的影响,由孔径d、孔的径向位置r、孔的周向位置θ、叶顶间隙δ组成四因素三水平的9组正交试验方案,通过正交试验探究出各因素的最优组合方案,得到最终的优化组合方案为d=19 mm,r=70 mm,θ=20°,δ=0.6 mm。对比设计流量下优化除气泵与初始除气泵的除气率发现,优化除气泵的除气率提高了22.82%,达到了优化除气泵性能的目的。观察优化前后除气泵内流场的变化发现,优化除气泵离心叶轮流道内的气相聚集区域更少,湍动能更小,由此可见合理地布置排气孔以及调整叶顶间隙可以改善除气泵内的气液两相分布情况与流动状态,进而提升泵的性能。

不同销钉加固胶合木螺栓洞口处节点拉伸性能

木结构螺栓节点在螺栓洞口周围易因应力集中而导致螺孔周围木材开裂,降低节点承载力。采用销类连接件垂直于木材纹理加固有望改善上述破坏现象。为探究不同种类销钉垂直于木材纹理的加固时对胶合木螺栓洞口处节点的增强效果,以及为木钉在增强胶合木螺栓洞口处节点的工程应用上提供试验基础和理论依据,以销钉的材料种类及直径为变量,参考美国标准(ASTM D1761-20)对4组共26个开孔胶合木试件在顺纹方向进行了1 mm/min的匀速单调加载拉伸试验。记录分析了试验前后各个试件洞口处节点的破坏形态、荷载-位移曲线、极限承载力、刚度和能量耗散。结果表明:(1)木钉和钢钉垂直于试件纹理的钉入对试件洞口处节点的破坏模式影响不大,但对试件节点的承载性能有一定提升;(2)木钉对试件洞口处节点的增强效果明显优于钢钉,木钉增强组SS2、SS3和钢钉增强组SS4试件与未加固组SS1试件相比,极限承载力分别提高了19.75%,19.18%和10.83%,能量耗散分别提高了87.48%,82.59%和28.33%;(3)木钉直径的较小变化对节点的增强效果影响不大。采用木钉垂直于木材纹理加固可显著提升螺栓洞口的承载力,有利于提升木结构螺栓节点的承载力。

一种主螺栓孔清洗装置的研制

提出一种主螺栓孔清洗装置的研制方案和系统构成,对该清洗装置的基本功能及关键技术进行了理论研究。对清洗装置的行走状态,以及清洗组件和定位干燥组件升降模组进行了分析,分析结果表明,该装置可正常行走且不打滑、可完成升降模组的升降操作。提出一种新型自适应定位系统,该清洗装置通过接近开关感应清洗位置实现粗定位,再利用定位干燥筒的导向定位段实现精定位;支架组件始终提供一个径向拉力,车架组件受拉力有向中移动的趋势,但由于侧轮作用将始终与法兰外圆贴紧,从而实现清洗装置的完全定位。对精定位后的误差进行了分析,清洗组件轴线偏差不超过0.3453mm,满足要求。提出利用弹簧片对清洗刷进行限位和复位的方法,并对其设计参数进行仿真优化分析,结果表明,当弹簧片厚度取0.4mm时可有效清洗螺孔。

反应堆压力容器主螺栓孔的视频扫查装置

反应堆压力容器螺栓孔是压力容器顶盖设备的重要组成部分。由于每次换料大修均需通过主螺栓的旋出和旋入来开关反应堆压力容器顶盖,故主螺栓孔容易产生接触损伤。针对此问题,开发了一套螺栓孔内表面视频扫查装置,介绍了该装置的研制方案和系统构成,并对其进行了功能测试,对压力容器的螺栓孔进行检查,测试结果表明,该装置可以在压力容器法兰表面绕中心轴周向行走,运动准确,可靠性好,采集的视频图像清晰,畸变率低,满足使用需求。同时,该套视频扫查装置集成程度高,操作简单,兼具手动及自动模式,可显著降低现场工作人员承受的辐射剂量,提高在役检查的效率。

多层全装配式综合楼设计与施工

全装配式混凝土结构可极大提升建筑建造效率及施工质量,减少建筑建造过程的湿作业。通过分析国内针对多层全装配式建筑的研究成果,根据项目特点选取适宜项目的预制构件连接方式,并应用于长沙地区某具体采用多层全装配式墙板结构体系建造的学校综合楼项目中;该综合楼的结构构件竖向承重墙、楼板、梁、楼梯均采用全预制,竖向承重剪力墙间连接设计基本采用预留手孔螺栓连接;全预制楼板之间连接设计采用预埋钢板螺栓连接,详细阐述该栋建筑的结构设计、预制构件设计、施工,并探讨该类多层全装配式墙板结构体系的应用价值。

筒体悬挂结构若干问题分析

以菏泽博物馆新馆项目为背景,从计算方法、构件受力和设计、整体屈服机制等八个方面对筒体悬挂结构体系做了较全面的研究。结果表明:1)计算筒体悬挂结构水平地震作用时无需调整层质量;2)规范底部轴力法、振型分解反应谱法并不适用筒体悬挂结构竖向地震作用计算,考虑最小限值调整后的吊柱设计仍可能偏不安全;3)采用长孔螺栓节点设计能让筒体悬挂结构吊柱在各工况下处于理想轴向拉压受力状态;4)中高烈度区吊柱在大震组合作用下可能受压,有必要复核其受压稳定和承载力;5)吊柱受力在小震阶段为恒、活载控制,大震阶段其恒、活载占比降低,地震逐渐起控制作用;6)合理的吊柱布置除满足建筑条件外,还需兼顾核心筒顶受力,减小筒顶不平衡弯矩;7)核心筒顶上包与否均能实现与屋面悬挂桁架的有效刚性连接;8)合理的筒体悬挂结构屈服机制就是落地核心筒的延性破坏过程,即始于连梁开裂破损,终于筒底墙肢钢筋拉屈、混凝土压溃。