Design Of Bolted Joints Research Articles

Investigation on a novel bolted joint scheme for foam inserted top-hat stiffened composite plates

Joint schemes are very important in the design of bolted joints in huge composite structures. This article describes the scheme, manufacturing method, performance testing and simulation of a novel bolted joint configuration for top-hat stiffened composite plates. Firstly, a bolted joint scheme is proposed for use in top-hat stiffened composite plates, after which the manufacturing method of the joint scheme is presented, as is the fabrication of test specimens and their bending performance are tested. Then, a numerical method is proposed to analyze the performance of these specimens. Drawing on experimental and simulated results, seven failure modes are summarized with varied geometrical parameter. We change the angle of top clamp θ and the length of the foam block Lx, and discuss the relationship between the mutative design parameters and bending performance. Suitable design parameters are obtained and suggestions for the joint scheme are offered. It is found that good mechanical performances can be achieved with the proposed scheme through suitable parameter design, and it is also found the simulated result agrees the experiment well, which provides a useful method for the bolted joint design of foam inserted top-hat stiffened composite plates.

Experimental performance of concrete filled welded steel tube columns

Effectiveness of concrete filled steel tube columns in improving life quality and safety is particularly noteworthy. Assembling columns at story levels by bolted connections is the current practice in the field. Closed section tubes do not allow bolted joint designs at intermediate locations of column length. As a result of such limitation, proper fractions of steel tubes are generally used to minimize steel waste. However, considering vast variety applications of columns, it is not always possible to use proper fractions of the tubes. In order to eliminate steel material waste, lateral welding can be employed to develop intermediate joints. However, there exists limited guidance on lateral weld design for concrete filled steel tube columns. A limited number of studies on seam welded tubes are present in the literature, but the individual paper's conclusions do not reference seam weld behavior under severe compressive loading. This paper presents results of 18 tests which were undertaken to assess the performance of laterally and longitudinally welded columns. Different L/D ratios (short, medium and long columns), D/t ratios and different lateral weld locations were studied. It has been shown that seam weld failures have slight effects on capacity and failure mode. However, seam weld failures certainly reduce ductility. On the other hand, lateral welds are very successful in transmitting compression and bending effects. It can be deduced that lateral weld joints have the potential to lead reliable and economical designs for concrete filled steel tube columns.

A new approach for calculating the stiffness of bolted connections

The stiffness of bolted joint influences the transfer of initial preload and operating force. The determination of stiffness without the gasket is fairly difficult to obtain, because the compression region spreads out between the bolt head and the nut. Bolted joints including bolts and members act as elastic springs under operating conditions. The affected area is not uniform. The stiffness of the bolted joints can be determined using finite element analysis and soft computing techniques. The prediction of the non-dimensional joint stiffness is developed in this paper by using genetic algorithm methods. The proposed model was in good agreement with the experimental results and previous literature and may be considered as a simple and suitable guideline for the design of bolted joints.

Comparative study of bolt spacing formulas used in bolted joint designs

Bolted flange joints are the most popular type of connection between pressure vessels and piping equipment. They are very attractive type of connection because they are simple to mount and offer the possibility of disassembly. However, they are very complex structures to design and analyze and often result in leakage failure. One of the raisons is the loss of tightness that results from the uneven distribution of the gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; bolt load non-uniformity, inadequate flange to gasket stiffness, inappropriate bolt spacing requirements or a combinations of some of these.The variation of the contact stress in the circumferential direction between any two bolts is dictated by bolt spacing. This paper is an extension of the work in which the more accurate analytical solution based on the theory of circular beams resting on a linear elastic foundation is used to validate some existing flange bolt spacing formulas and in particular the TEMA formula, Robert's formula and the one recently developed by Koves. The relationship between bolt spacing and the gasket compression modulus, flange thickness and size is deduced from an analysis that considers a maximum tolerated gasket contact stress difference obtained at the bolt and between two bolts. Comparison between these different methods is also provided.

An investigation into contact pressure distribution in bolted joints

Bolted joints are widely used in modern engineering structures and machine designs due to their low cost and reliability when correctly selected. Their integrity depends on quantitative representation of the contact pressure distribution at the interface during design. Because of the difficulty in reaching and assessing clamped interfaces with traditional experimental methods, presently bolted joint design and evaluation is based on theoretical analysis, with assumptions to quantify pressure distribution at the clamped interface, which may not represent their true operating conditions. The present work utilises a non-intrusive ultrasonic technique to investigate and quantify the pressure distribution in bolted joints. The effect of variation in plate thickness on the contact pressure distribution at bolted interfaces under varying axial loads is investigated. While it was observed that the contact pressure at the interface increases as the applied load increases, the distance from the edge of the bolt hole at which the distribution becomes stable is independent of the applied load on the bolted joint. However, the contact pressure distribution was observed to vary with the plate thickness. Although the variation in the peak value of the average contact pressure distribution in bolted joints does not depend on the plate thickness, the distance from the edge of bolt hole at which the value of the distribution becomes stable increases as the plate thickness is increased. It was also observed that the edge of the bolt head affected the position of the peak value of the contact pressure distribution at the interface, though its effect was dependent on plate thickness. Furthermore, a model based on a Weibull distribution has been proposed to fit the experimental data and a good correlation was observed.

Assessing Structural Safety of Bolted Joints Subject to Cyclic Loading Using Advanced Nonlinear FEA

The concepts of structural safety embedded in recognised international standards for the fatigue design of bolted joints, such as VDI 2230 Part 1, are examined and challenged. This is done by means of theoretical investigation of the behaviour of bolted joints using non-linear finite element analysis. Potential differences between actual bolted joint parameters and behaviour, and implicit design assumptions, are reviewed and their effect on the structural safety of bolted joints in operating equipment examined. An approach to the fatigue design of bolted joints is presented which incorporates alternative concepts of structural safety and uses advanced CAE methods as part of the standard design process.

Metal to composite bolted joint behavior evaluated at impact rates of loading

Metal-composite bolted joints form an integral part of a majority of structural components and finds extensive usage in aircraft and automobile industries where they could be subjected to either static or time dependent loadings. Extensive literature exists addressing bolted joint behavior under static rates of loading. However, limited studies exist which define mechanical response of metal-composite bolted joints under dynamic rates of loading. This is vital to better understand its crashworthiness characteristics when it is subjected to impact loading. In our current investigation, we have attempted to address this aspect via experimental characterization of 4142 alloy steel-E glass ply epoxy resin composite bolted joint under impact loading using a split Hopkinson tension bar. Quasi-static measurements have also been conducted simultaneously to distinguish not only the maximum bearing strength but also the operational modes of failure corresponding to different edge distance to hole diameter (e/d) ratios. Dynamic response of the metal-composite bolted joint was observed to be significantly higher than its static counterpart. Asymptotic region of failure mode alteration exists and is observed to be dependent on loading rate transfer. This study provides beneficial information in assisting subsequent design of bolted joints where behavior under impact loading is of main concern.

Fastener effects on mechanical behaviors of double-lap composite joints

Experimental and numerical studies were carried out to reveal the effect mechanisms of different fasteners on mechanical behaviors of composite bolted joints. Double-lap composite joints joined by protruding head or countersink fasteners were focused on and their mechanical behaviors were characterized. Differences in the joint strength, stiffness and failure mode between protruding head joint and countersink joint were depicted experimentally. Further comprehensive understanding of the fastener effects was provided by FE analyses, which embraced net-fit, clearance-fit and clearance-fit with preload cases and considered the influences of contact models. For composite joints with protruding head or countersink fasteners, the changes of contact area, fastener bending, local deformation and stress distributions around fastener hole were detailedly analyzed based on the numerical results. According to the combined investigation of experimental and numerical analysis, some useful conclusions have been deduced, which are helpful for the design of composite bolted joints.

Finite Element Analysis and Design Exploration of a Bolted Joint

The present study demonstrates the use of optimization technology in improving the bolted joint design. Design exploration from ANSYS Workbench is used in the study. The objective of the study was to minimize the bolted joint deformation in order to optimize the joint. Variations of the parameters such as bolt pretension force, friction coefficient and pressure were studied. The optimization study provided response charts of the different design variables on the output. Sensitivity analysis of the input variables helped in identifying the importance of each design variable and their respective effects on the output. Finally the different design points were rated based on a goal-driven optimization study and the best design is chosen. Single Graphical User Interface allowed quick learning and ease-of-use.

Performance of bolted joints in Discontinuous Ceramic Cored Sandwich Structures – Static experimental testing

Thick section composites that consist of discontinuous ceramic tile arrays as a core represent a unique class of sandwich structures. They have been developed to provide a balance of structural, impact, and penetration resistance at minimum weight. Bolted joints are often used to fasten the Discontinuous Ceramic Cored Sandwich Structures (DCCSS) to other structures. Extensive experimental testing has been completed in order to better understand the performance of bolted joints in DCCSS. In this study, pin-loaded specimens are subjected to static in-plane tensile loading to establish the sequence and severity of failure modes and ultimate joint capacity. Static testing was completed on various geometric ratios such as edge distance effects, as well as the influence of tile gaps that exist in the discontinuous tile array. The results from this study establish guidelines for design of bolted joints in DCCSS.

Finite Element Analysis of Behavior of Bolted Flange Connections under Bending Loading

Only a limited number of experimental and analysis reports exist concerning bolted flange connections under bending loading. In order to investigate the complex nonlinear phenomena, three dimensional elasto-plastic finite element analyses are performed. In those analyses, frictional contact model with small sliding option is applied between contacting pair surfaces of all connecting elements. Bolt pretension force is introduced in the initial step of analysis. From this study, the following results are obtainted:1) proposed finite element analysis method can be applicable to estimate complex nonlinear behavior of bolted flange type connections; 2) There is a sharp change in bending stiffness during loading, and lateral slip between two jointed flanges cause the bolt to carry shear load. The design of bolted joints should consider the interaction among cylinders, flanges and bolts.

ボルト締結体における軸直角方向疲労強度予測法

In transverse fatigue of a bolted joint, althogh the real fatigue limit (the highest nominal stress at the root of the first thread of bolt without generating fatigue failure) is the same for bolts with the same size and property class, the apparent fatigue limits (the highest amplitude of transverse vibration force which can be applied to the bolted joint without generating fatigue failure) vary according to the bolt tightening conditions. Hence, it is necessary to develop a guideline for safety and design of bolted joints under transverse vibration. In this study, the relationship between the apparent fatigue limit and the real fatigue limit has been experimentally revealed. The method to predict the apparent fatigue limit using the real fatigue limit has been developed.

Dependence of fatigue limit of high-tension bolts on mean stress and ultimate tensile strength

High tension bolts in critical joints in internal combustion engines are susceptible to fatigue failure. Computeraided bolted joint design procedures require knowledge of the dependence of bolt fatigue limit on the mean stress and ultimate tensile strength. This dependence is investigated with staircase fatigue limit tests. The test results show that when the bolt fatigue limit is estimated with the nominal stress of the bolt, it decreases with increasing tensile strength and nominal mean stress. However, there is a range of the nominal mean stress where the bolt fatigue limit is almost constant. The test results are interpreted with finite element analysis.

Finite-Element-Based Methods for the Fatigue Design of Bolts and Bolted Joints

Due to the increase of computer performance, modern screw design is more and more based on finite element analyses. Depending on the problem, different possibilities of modelling bolted joints are reasonable. Traditionally, a nominal stress approach is used for the fatigue design of bolted joints. But, in modern lightweight constructions it is more and more common to connect threaded components directly without using a classic bolted connection. In this case a local approach has to be used. In several investigations at the Fachgebiet und Institut fur Werkstoffkunde (Chair and Institute for Materials Technology) in Darmstadt and the Robert Bosch GmbH in Schwieberdingen different concepts for a local approach have been tested for the fatigue design of threaded connections. As a result, an overview can be given, which design concept and which model can be properly used for calculations.

Finite Element Based Member Stiffness Evaluation of Axisymmetric Bolted Joints

For a reliable design of bolted joints, it is necessary to evaluate the actual fraction of the external load transmitted through the bolt. The stiffness of the bolt and the member of the joint decide the fractions of external load shared by the bolt and the member. Bolt stiffness can be evaluated simply by assuming the load flow to be uniform across the thickness and the deformation is homogeneous. Then, bolt may be modeled as a tension member and the stiffness can be easily evaluated. But, the evaluation of the member stiffness is difficult because of the heterogeneous deformation. In the present work, joint materials are assumed to be isotropic and homogeneous, and linear elastic axisymmetric finite element analysis was performed to evaluate the member stiffness. Uniform displacement and uniform pressure assumptions are employed in idealizing the boundary conditions. Wide ranges of bolt sizes, joint thicknesses, and material properties are considered in the analysis to evaluate characteristic behavior of member stiffness. Empirical formulas for the member stiffness evaluation are proposed using dimensionless parameters. The results obtained are compared with the results available in the literature.

Characterisation of Contact Pressure Distribution in Bolted Joints

Abstract: The quantification of contact area and pressure distribution in a bolted joint is essential information, as it determines the integrity of the coupling. Current bolted joint design standards are based on analytical solutions of the pressure distribution, which, because of the inherent assumptions, frequently do not accurately represent the real conditions in a joint. This study uses a non‐intrusive ultrasonic technique to quantify the contact pressure distribution in a bolted connection. The advantage of this experimental technique is that the effect of actual contact conditions can be determined. An ultrasonic wave is focused onto the clamped interface, and the reflected sound signal recorded. In areas where the contact pressure is high, most of the ultrasound is transmitted, and the reflected sound signal is weak. Whereas, when the contact pressure is low, the vast majority of the ultrasound is reflected back. A parallel experimental calibration is then used to find the relationship between the reflected sound signal and contact pressure. In this way, the pressure distribution in a clamped interface is determined for a series of different bolt torques. Two different interfaces were investigated: the first consisted of two ground surfaces clamped together, and the second a turned profile pressed against a ground surface. The effect of a washer underneath the bolt head was also considered. The turned profile was found to cause the contact to spread; there was also a certain degree of fragmentation leading to higher peak pressures than in the ground interface case. With a washer positioned under the bolt head for the turned case, the clamping performance of the bolt was improved. Good agreement was found when comparing the ultrasonic measurements with previous studies, with respect to the spread of the contact pressure distribution. However, in this study, the peak contact pressure was found to occur away from the edge of the bolt hole, and to be influenced by the edge of the bolt head.

Experiences with Modeling Friction in Composite Bolted Joints

Finite element analyses of composite bolted joints are common in the literature. However, the important issue of friction is often given superficial treatment. Friction introduces added difficulties to an already complex contact problem in terms of numerical convergence, and there can be a temptation to accept any method that will give a convergent solution. However, friction can significantly alter the stress distribution in the laminate at the bolt-hole interface, and carries a major proportion of the load in torqued joints; hence is important to model correctly. In the present study, experiences with modeling friction in composite bolted joints using commercial code MSC.Marc are presented. Unlike previous studies, both physical friction parameters and nonphysical convergence parameters within the available models are examined in detail and the findings should be helpful to other researchers analyzing similar problems. Two available models within the code are examined for their ability to model load transfer by friction in torqued joints, and the stress distribution at the bolt-hole interface in a pinned joint. The torqued joints include a large clearance so that both static and kinetic friction effects occur as the joint begins to slide and clearance is taken up. Results from the torqued joint models are compared with the experimental results. The stress distribution at the bolt-hole interface of the pinned joint is compared with a solution from an analytical method. It has been found that only one of the two models available in the code is capable of producing satisfactory results, and even with that model significant modification to the default friction parameters was required. It has also been found that using friction coefficients measured under ideal (clean) conditions in the model of the torqued joints did not give very good agreement with the joint experiments, which involved routine handling of the specimens. Finally, the developed friction model is used in a case study of a multibolt joint with variable degrees of bolt torque and bolt-hole clearances, and it is shown that such models can provide useful information for the design of composite bolted joints.

Unique Challenges for Bolted Joint Design in High-Bypass Turbofan Engines

Bolted joints are used at numerous locations in the rotors and carcass structure of modern aircraft turbine engines. This application makes the design criteria and process substantially different from that used for other types of machinery. Specifically, in addition to providing engine alignment and high-pressure gas sealing, aircraft engine structural joints can operate at high temperatures and may be required to survive very large applied loads which can result from structural failures within the engine, such as the loss of a fan blade. As engine bypass ratios have increased in order to improve specific fuel consumption, these so-called “Ultimate” loads increasingly dominate the design of bolted joints in aircraft engines. This paper deals with the sizing and design of both bolts and lever flanges to meet these demanding requirements. Novel empirical methods, derived from both component test results and correlated analysis have been developed to perform strength evaluation of both flanges and bolts. Discussion of analytical techniques in use includes application of the LS-DYNA™ code for modeling of high-speed blade impact events as related to bolted joint behavior.

Shape Memory Alloy in Tension and Compression and its Application as Clamping Force Actuator in a Bolted Joint: Part 2 — Modeling

The mathematical modeling of a bolted joint with a Shape Memory Alloy (SMA) actuator ring is presented. In this way, phase transformation, constitutive and displacement compatibility equations are used. The obtained model is utilized to show how the application of the SMA actuator ring in the bolted joint can help the joint to recover a significant amount of its lost clamping force. The model is run using the experimental data obtained for the Ni-55.7%wt Ti SMA in the companion paper (Part 1). The mechanical properties of SMA are calculated using the mentioned equations and compared to the experimental findings. It is observed that the final clamping force obtained theoretically is close to the measured value. The proposed method can, therefore, be a starting point in order to perform the analysis and design of bolted joints with SMA actuator rings.

高強度ボルトの衝撃強度に及ぼす初期締付け力の影響(機械要素)

In strength design of bolted joints subject to impact load, tightening was performed initial tightening force of bolted joints in the elastic area, and the additional force by impact load are experimentally considered from the study result. From the viewpoint of guideline for design of bolted joints, the permissible maximum external force should determined, assuming that initial tightening force of bolt lowered by external impact load should be under 10%. And the result clarified that the maximum impact load (external force) would be allowed up to 54 thru 65% of yield point force of bolt.