A method to simplify the strength design of bolted joints—Case of connecting-rod bolts

This study shows the development of the strength-design system for general bolted joints. Specifically, a simplified method of the strength design for the connectingrod bolts is proposed. The connecting-rod joint is transformed into a single-bolted-joint model by using the ring model. The axial stress on the bolt and separation behavior at the contact plane are discussed. The strength design of the connecting-rod joint can be performed by applying the unified procedure to the single-bolted-joint model. The local deformation of the connecting-rod joint and the stress on the bolt were measured and the analytical results are compared with the experimental results. Both results show fairly good agreement.     

螺栓连接件微动疲劳特性分析

工程中钢结构构件经常采用螺栓连接,被连接部位多处于复杂受力状态,单轴疲劳理论已无法满足该 形式下构件的寿命评估需求．针对现有理论不足,本文建立了螺栓连接件有限元模型,研究了不同工况下被连 接件微动疲劳裂纹萌生位置,并基于临界平面的多轴疲劳理论,比较了四种常用模型的适用性以及预测了连接 件的疲劳寿命．结果表明：(1) 裂纹萌生位置位于受拉端螺栓孔附近的滑移粘着区,在相同螺栓预紧力下,该 位置与施加的疲劳载荷大小无关;(2) 基于临界平面方法的四种模型均可以较好判断裂纹萌生位置,其中SWT (Smith-Watson-Topper)模型对不同载荷水平下的螺栓连接件微动疲劳寿命预测效果较好,大部分预测结果位于± 2倍分散带之内,预测结果优于其他三种模型;(3) 在规范规定的螺栓预紧力范围内,被连接件裂纹萌生区域距 孔边的距离与预紧力大小无关,可能是由于预紧力变化范围内的粘着滑移区未发生明显变化所致,并且随着预 紧力减小,被连接件的寿命预测值反而增大     

轴向交变载荷作用下螺栓联接结构的松动试验研究

在设计、试制螺栓加载装置的基础上,对螺栓联接结构进行了轴向振动的疲劳试验,获取了螺栓夹紧力的时变曲线,并对试验后的螺栓接触表面进行损伤分析,研究螺栓联接结构的松动机理.结果表明:在轴向振动条件下,螺栓联接结构的夹紧力下降较为明显,但拧出力矩相对于预紧力矩变化不大.螺栓的松动过程可分为以下两个阶段:试验初期由于螺栓接触面的塑性变形,夹紧力迅速下降;然后由于接触面之间的微动磨损,夹紧力缓慢下降.螺纹接触面之间的损伤机制主要为黏着磨损、磨粒磨损和剥层.     

An estimation method of bearing strength of bolted joints in fibre reinforced composite

Some researchers have estimated the strength of bolted joints in fibre reinforced composite, using simple and efficient engineering procedures. However, for these procedures the effect of clamping due to the strength of bolted joints is not considered. In this paper, a method is presented for predicating critical bearing strength of single-hole bolted joints in composite on the basis of observing and analysing the results of experiments. The clamping effect of bolts is considered. The calculated results correspond to the test data on Glaphic/Epoxy laminates.     

Size Estimation of Fatigue Crack Appearing at Bolt Joints of Aluminum Alloy Plates by Synchronized SAW Measurement

The synchronized ultrasonic measurement with the surface acoustic wave (SAW) was carried out during the fatigue testing of bolted specimens of the aluminum alloy in synchronization with a fatigue cycle. The stationary SAW measurement was also carried out in the fatigue testing under pausing the fatigue tester at the mean load. In both measurements, the intensity of the scattered wave gradually increased with the number of fatigue cycles in the fretted region ahead of a bolt hole due to surface roughness, and the steep increment occurred following appearance and propagation of the fatigue crack. The steep increment was detected earlier in the synchronized measurement than that in the in-process measurement. In the synchronized SAW measurement, the intensity of the reflection from the fatigue crack increased with increasing stress level in the fatigue cycle. Then, the crack length was estimated with the intensity change of the reflection from the crack in the fatigue cycle following the Elber’s model modified by Suresh on the crack opening and closure following the stress intensity factor. The method developed in the present work shows the potential of the synchronized surface acoustic wave measurement as a tool for the early detectability of the fatigue crack as well as for the evaluation of crack opening/closure behavior in the bolted joint.     

平面编织复合材料胶螺混合连接接头拉伸性能分析

对平面编织复合材料胶螺（单排螺钉）混合连接结构拉伸性能进行了试验研究,分析了螺钉直径为4mm和6mm两种情况下连接结构的破坏形式。基于ANSYS平台建立了胶螺混合连接三维损伤扩展模型,其中融入了非线性接触问题,数值计算的结果与试验结果吻合良好。研究发现,机械连接可以通过分担部分载荷而起着加强胶接连接的作用;如果机械连接工艺稳定的话,应该有螺钉直径越大,其加强效果越明显的规律;对于胶接与多钉混合连接复合材料结构的拉伸性能分析和计算确实存在很大困难,应该谨慎使用。研究结果与分析方法可以为今后的复合材料胶螺混合连接接头的设计提供一定的依据与技术支撑。     

Mixed-mode stress intensity factors and critical angles of cracks in bolted joints by weight function method

Summary   Mechanical joints, such as bolted or riveted joints, are widely used in structural components. Reliable determination of stress intensity factors for cracks in bolted joints is required to evaluate their safety and fatigue life. The weight function method is an efficient technique to calculate stress intensity factors for various loading conditions by the stress analysis of an uncracked model. In this paper, the mixed-mode stress intensity factors for cracks in bolted joints are analyzed by the weight function method, and coefficients included in the weight function are determined by finite element analysis for reference loadings. The critical angle at which mode I stress intensity factor becomes maximum is determined, and the effects of the amount of clearance and crack length on the critical angle are investigated. Received 28 February 2001; accepted for publication 22 June 2001 RID=" ID=" The authors are grateful for the support provided by a grant from the Korea Science & Engineering Foundation (KOSEF) and Safety and Structural Integrity Research Center at the Sungkyunkwan University.     

高锁螺栓连接件动态拉伸响应与失效机理

飞机坠撞过程中结构的变形模式和吸能对乘员保护具有重要意义，而连接结构的载荷传递和失效形式是影响飞机结构变形的重要因素之一。为了获取航空高锁螺栓连接件在坠撞载荷下的动态响应和失效机理，基于抗剪型平头高锁螺栓设计了2种材料（2024-T3和7050-T7451）的单钉单搭接连接件，利用高速液压伺服材料试验机进行4种速度（0.01、0.10、1.00和3.00 m/s）下的拉伸测试，得到连接件的动态响应、极限载荷、能量吸收和失效模式随速度的变化规律，并分析了连接件的失效机理。结果表明，连接件的失效模式受母材和高锁螺栓/螺母材料强度影响较大，而受加载速度影响较小；当速度从0.01 m/s增加到3.00 m/s时，2024-T3连接件的极限载荷和能量吸收分别增加了2.17%和34.43%，7050-T7451连接件的极限载荷和能量吸收分别增加了5.53%和6.58%。     

Scaling of size/time/temperature — Part 2: Progressive damage in uniaxial compressive specimen

This work is concerned with predicting the fatigue failure initiation of a wing/fuselage bolt assembly. Accounted for in the analysis are both the influence of energy dissipation and damage accumulation as the structure is subjected to repeated cyclic loading. Results involving the location and number of cycles to initiate a fatigue crack 10⁻² in. are obtained. They agreed both qualitatively and quantitatively with the experimental findings. Also discussed is the influence of pre-torque in the bolt which tends to decrease the number of cycles to fatique crack initiation. Fatigue life may be extended by altering the load path so as to decrease the accumulation of energy near the site of failure initiation. This can be accomplished without major modification of the design. The methodology that makes use of the strain energy density criterion can be used to optimize the fatigue strength of other structural sub-assemblies by appropriate combination of material and geometry for specified load conditions.     

Three-dimensional investigation of thick single-lap bolted joints

Stresses in single-lap bolted joints of thick plates are complex and difficult to analyze. Previous studies involving stresses through the thickness of bolted joints have been limited to finite element method (FEM) simulations and have been implemented only for the joining of relatively thin plates. In this paper we report on several experimental and numerical analyses that were conducted to evaluate the stress distribution inside thick bolted plates along the bearing plane normal to the plate surface. Experimental analysis was conducted via embedded-polariscope photoelasticity and embedded resistance strain gages. The FEM analysis was performed with the ABAQUS commercial code using material properties and other data obtained experimentally as input. Experimental and numerical results agreed reasonably well, and are believed to depict the behavior of the joint under load well enough to assist in development of improved joint design.     

Behaviors of a single crack in multiple bolted joints

This paper examines the pin load ratios and the stress intensity factors (SIFs) of a single crack in the multiple bolted joints by using finite element analyses. Cubic-spline contact elements and rigid links were used to model the contact surface between the bolt and the rigid pin. The least-squares method was used to determine the SIFs. The finite element results indicate that the cracked hole can still sustain the major part of the original loading at the uncracked condition. The first hole sustains the largest pin load and mode-I SIF, which are reduced little for crack propagation. This critical condition cannot be reduced by the arrangement of more pins in the plate. In this paper, two simple formulae were also investigated to fit the load ratios and SIFs of the multiple bolted-joints problems.     

锚固正交各向异性岩体的本构关系和破坏准则

从理论上对由系统锚杆加固的正交各向异性岩体,取出包含锚杆的表征单元.根据“等效材料”的概念,在原岩体的本构关系和破坏准则中计人锚杆刚度和强度的“贡献”,从而建立了相应锚固岩体的木构关系和破坏准则.然后列举算例,考察了表征单元的应力-应变关系和破坏强度随锚杆安置角度变化的各向异性表现.最后将计算与一个简单试验的结果作了对比,看到二者的吻合程度较好,因而初步地验证了所提力学模型的可靠性.     

Simulation of stochastic loads for fatigue experiments

A simple direct simulation method for stochastic fatigue-load generation is described in this paper. The simulation method is based on the assumption that only the peaks of the load process significantly affect the fatigue life. The method requires the conditional distribution functions of load ranges given the last peak values. Analytical estimates of these distribution functions are presented in the paper and compared with estimates based on a more accurate simulation method. In the more accurate simulation method samples at equidistant times are generated by approximating the stochastic load process by a Markov process. Two different spectra from two tubular joints in an offshore structure (one narrow banded and one wide banded) are considered in an example. The results show that the simple direct method is quite efficient and results in a simulation speed of about 3000 load cycles per second using a personal computer. Finally the proposed simulation method for fatigue-load generation is tested by comparing some fatigue damage measures obtained by the simulation methods.     

机匣安装边结构研究

本文利用多种实验力学方法研究了航空发动机机匣安装边结构的连接特性和力学行为以及机匣在安装，受载过程中的安装边的变形、应力和螺栓内力、应力等的规律；讨论了安装边结构设计参数的选择范围     

螺栓扭矩系数影响因素的试验研究

在螺栓连接结构中,为保证连接的可靠性,必须为螺栓提供合适的预紧力。工程中通常采用扭矩法装配螺栓连接结构,因此需要确定预紧力与扭矩之间的关系(即扭矩系数),以施加合适的装配扭矩。本文对输电塔中常用的M16镀锌螺栓进行预紧力试验研究,测试分析了螺栓强度等级、有无垫圈和有无润滑对螺栓连接副扭矩系数的影响。研究结果表明,高强度螺栓比普通螺栓的扭矩系数小,数据离散性也小;无垫圈的螺栓比有垫圈的螺栓扭矩系数小,但数据离散性大;有润滑的螺栓比无润滑的螺栓扭矩系数小,数据离散性也小。本文同时探讨了如何控制、调整扭矩系数,以及螺栓连接中要注意的问题,为设计和施工单位提供参考。     

复合材料螺栓连接性能的分散性和可靠性分析

本文通过对35个复合材料层合板螺栓连接试验件进行钉孔挤压试验,得到各个试件的挤压强度,然后采用统计分析的方法,研究复合材料层合板螺栓连接挤压强度的分散性规律。研究表明,复合材料层合板螺栓连接挤压强度的分散性模型可以用正态分布、对数正态分布以及威布尔分布三种模型模拟,其中以威布尔分布拟合效果最好,其次是正态分布。另外,本文采用极大似然估计方法给出了三个模型的分布参数。最后,利用蒙特卡洛法和雷-菲法计算了三种分布模型下的失效概率。结果表明,威布尔分布的失效概率最大,而对数正态分布的失效概率最小。     

Modeling and nonlinear dynamic analysis of bolt joints considering fractal surfaces

Nonlinear Dynamics - The surface morphology has an important influence on the dynamic response and bolt loosening of bolted joints. In this paper, based on the fractal contact model, an original...     

Monitoring of L-Shape Bolted Joint Tightness Using Thermal Contact Resistance

In this paper, we describe the possible use of hermal contact resistance measured under ambient conditions as a non-destructive feature to monitor L-shape bolted joints. We demonstrate that thermal contact resistance can be correlated to the contact pressure of L-shape bolted joints and thus can be used to infer joint tightness. Five different torque levels of bolt tightness in an L-shape bolted joint were measured for contact pressure and thermal contact resistance using Fuji Prescale® pressure-sensitive film and a test setup in ambient conditions. Using probabilistic analysis, probability density functions (PDFs) and intervals developed from the PDFs, the contact pressure and thermal contact resistance were developed and correlated. By examining the intervals of the contact pressure and thermal contact resistance at each torque level, it was concluded that thermal contact resistance measured under ambient conditions can be used to describe bolted joint tightness.     

锚固体红外温度场与应力场特性研究

为了研究锚固体力-热耦合机制,分别对不同类型的锚固体加载变形破坏过程进行试验研究。应用红外热像技术,获得红外温度场,同时对锚固体进行应力场数值分析。结果显示:中心位置布置单根锚杆的锚固体;应力峰值前,随着荷载的增加,红外温度场呈现整体均匀性升温变化;应力峰值后,在锚杆周围形成一个由多条不同等温线组成的区域,其形状是以锚杆为中心的近似圆形区域,由内向外,温度逐步降低;有锚杆一侧围岩红外温度高于无锚杆一侧,锚杆周围形成一个近似"喇叭"状的等温线图,高温等温线对应高应力区,低温等温线对应低应力区,红外温度场与应力场之间存在空间分布对应关系。     

Numerical-experimental Method for the Analysis of Residual Stresses in Cold-expanded Holes

Hole cold expansion is a technique widely used to improve the fatigue life of components with holes, e.g. bolted or riveted joints. As it has been demonstrated in literature by analytical, numerical and experimental analyses carried out by several authors, the compressive residual stresses introduced by the hole cold expansion have a beneficial influence on both the static and the fatigue strength of the treated component, because they reduce significantly the typical stress peaks around the hole due to stress concentration. In the literature, various analyses of the residual stresses introduced by the hole cold expansion have been performed by using several methods such as X-ray diffraction, neutron diffraction and the modified Sachs method. Unfortunately, all these method are affected by some limitations: low measurement depth (X-ray method), complex measurement procedure (neutron diffraction method) and approximate formulation (Sachs method). In order to overcome such drawbacks, in this study a new mechanical method, based on an innovative extension of the “rectilinear groove method” associated with the classical “integral method” calculation procedure, is proposed. Experimental assessment of the proposed method has been performed by using aluminum 5083 H321 specimens with holes subjected to various levels of cold expansion.