Clamped Joints Research Articles

Finite Element Analysis of Load Capacity on Coupling Clamps for Pipe

A finite element approach based on Ansys is developed to simulate stress intensity distribution in a three dimensional model of coupling clamp joint, which includes ferrules, pipe caps and bolts. The characteristics of stress intensity distributions of coupling clamp joint under strength pressure loading have been studied by means of the non-linear finite element method. The FE model can also predict the clamp quality and tolerances to be expected under different process conditions and define the most effective process parameters to influence the tolerances. The study could give us a better understanding on the mechanism and basis for optimization design of the coupling clamp joint.

Hybrid welding and mechanical joining procedures

Over the last decades the arsenal of highly-effective welding technologies has been supplemented by new ones, called hybrid technologies. In this paper, we characterize hybrid welding technologies such as laser-electric arc, laser-plasma, light beam-laser and laser-submerged arc as well as hybrid ‘cold’ technologies of manufacture of permanent joints, i.e. mechanical fastenings (clamped and riveted joints) and glue joints, including also mechanical-glue ones.

Predicting the macroscopic shear strength of adhesively-bonded friction interfaces by microscale finite element simulations

Anaerobic adhesives are commonly used to enhance the shear strength of clamped friction joints between metal parts. Experimental results show that the total strength of the friction-bonded interface steadily increases with the clamping pressure. However, if weak anaerobics are used, the combined strength is lower than in the dry (purely friction) joint under high applied pressures. This paper seeks an explanation for this macroscopic behaviour by means of microscale finite-element simulations. The analyses show that the experimental results can be explained by assuming that: (a) however great the clamping pressure, a thin film of adhesive remains trapped between the crests of the mating surfaces; (b) under the high local pressure the shear strength of this film is greater than the regular adhesive’s at no pressure; (c) the stronger adhesives entail a higher increase than the weaker adhesives.

U형 강봉을 사용한 PC 계단 접합부 개발

프리캐스트 콘크리트는 현장작업을 최소화하고 공사품질을 보장할 수 있으며 공사기간을 단축시킬 수 있는 장점을 갖고 있다. 특히 계단실의 경우 재래식 거푸집을 사용할 경우 골조공사의 품질저하와 다수의 인력투입에 따른 생산성의 저하 및 시공의 어려움 등의 문제점이 있다. 본 연구에서는 PC 계단 접합부 상세를 개발하고, 제안한 접합부의 일체성확보와 사용성 및 안전성을 검증하기 위해 구조성능실험을 수행하였으며, 단순 핀접합 실험체에 비해 구속도의 증가, 내력, 강성 및 연성의 증가를 확인할 수 있었다. Compared with the traditional RC system, precast stairs can save construction time, reduce the cost of concrete casting, etc. This paper focuses on an investigation of improved continuous longitudinal joint details for PC stair systems. The performance of the precast concrete stair connections subjected to displacement control cyclic loading is compared with that of the monolithic connection. The developed connection is composed of U-rods and clamp joint metals. This paper proposes precast stair connection with improved structural performance and experimentally evaluates the structural performance of the proposed joints in terms of maximum load, displacement ductiliy, strain, crack and failure modes.

Numerical Simulations on the Cable Clamp of a Concave Cable Arch

The inner concave cable arch structure has been adopted in some engineering applications in recent years. Geometric configuration of the cable clamp joint and its anti-sliding performance is the key to assure the bearing capacity for this type of structure. In this study, nonlinear finite element analysis on the cable clamp joint of a concave cable arch is performed using ABAQUS, with influences of the friction coefficients and the nonlinearity of materials are investigated. The pretension loss of bolts caused by different tightening sequences is also discussed. It is found that nearly 9% of the initial pretension force for each bolt gets lost during the tightening process, and mutual influence of the bolts can be significantly weakened by applying reasonable tightening sequence.

An experimental investigation of the bolt clamping force and friction effect on the fatigue behavior of aluminum alloy 2024-T3 double shear lap joint

In this article, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated. To do so, fatigue tests were carried out on the bolt clamped double shear lap joint specimens made of aluminum alloy 2024-T3. These fatigue tests were conducted with applied torques of 0.25, 2 and 4 N m at different cyclic longitudinal load levels in un-lubricated and lubricated states. From these tests the stress–life ( S– N) data for different clamping forces for un-lubricated and lubricated states were obtained. The results show that clamping force increases fatigue life compared to clearance fit specimens. In general, at higher tightening torque higher fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting phenomenon. Also lubricating the parts of the specimens reduces the advantage of clamping force or torque tightening.

Nonlinear Deformation Behavior of Clamped Bolted Joints Under a Separating Service Load

The nonlinear deformation behavior of clamped bolted joints under a separating service load is investigated using finite element and experimental techniques. Although the materials for the bolted joint remain in the linear elastic range, the interface contact area between the clamped plates is sensitive to both the magnitude and the location of the separating force. This often causes nonlinear deformation behavior of the bolted joint. This finite element analysis study investigates the variation in the tension of a tightened bolt and the corresponding change in the joint clamp load due to a separating service load that is placed at various distances from the bolt center. The separating force is symmetrically placed at locations (from the bolt center) that are equal to 3–5 times the nominal diameter of the bolt. Experimental verification of the finite element results is provided.

Refining bioreactor design using autoclavable glass bonding

Selecting the right design of bioreactors is crucial for guaranteeing the reproducibility of bioprocesses. Up to now, conventionally designed bioreactors consist typically of melted or clamped joints. Since melting of borosilicate glass leads to large deformed areas along the joint, the desired geometric reproducibility is not ensured. Moreover, clamping complicates and greatly restricts the bioreactor design. Bonding, however, is advantageous in that it does not alter the material joined and it is easy to use. Furthermore, it has been recently shown that specially developed glass bonding techniques withstand multiple autoclaving cycles. The current research investigated practice-relevant parameters influencing the lifespan of epoxy-or (urethane) acrylate-bonded glass bioreactors. Hereby, the influence of cleaning and sensitivity to fermentation compounds (ethanol and acetic acid) was quantified using glass-glass and glass-stainless steel specimens. Whereas cleaning did not adversely affect the durability of glass bonds, high concentrations of the fermentation compounds ethanol and acetic acid resulted in accelerated corrosion and subsequent bond failure. Moreover, no effect of eight different epoxy and (urethane) acrylate adhesives was observed on selected model organisms Escherichia coli K12 and Hansenula polymorpha wild type. Another objective of this study was to refine the design of two small-scale bioreactors (ca. 250 mL) by replacing clamps and melted joints by adhesive joints. It was found that the bonded bioreactors yielded a higher geometric reproducibility than that of conventional melted or clamped ones. In conclusion, bonded glass joints greatly enhance the geometric reproducibility of bioreactors and, in turn, the reproducibility of bioprocesses. As glass bonding is easy to handle, it opens up new opportunities to design bioreactors that had been previously too expensive and complicated.

Failure analysis of bolted joints: Effect of friction coefficients in torque–preloading relationship

The aim of this study is to provide an experimental methodology useful to determine the friction coefficients in bolted joints and, therefore, to relate precisely the tightening torque to the preloading force. The components under investigation are clamped joints made of aluminium alloy and used in front motorbike suspensions to connect steering plates and legs, or legs and the wheel pin: static failures of clamps occurred during the tightening, because of the bending stress introduced by the preloading forces. Some specific specimens have been appropriately designed and realised with the same process of the actual components. The bolt torque is given by a torque wrench whereas the preloading force has been evaluated by means of a strain gauge. The overall friction coefficient and the torque coefficient (nut factor) have been calculated. Experimental tests have been carried out by applying the Design of Experiment method in order to obtain an accurate mathematical model that involves the significant friction variables and their interactions. Then, results of present study have been applied to actual components: the tightening torque has been precisely related to the preloading force by means of the friction coefficients definition and the tensile state of clamps have been evaluated both experimentally (strain gauges) and numerically (FEA) in order to shed light on the failures which occurred during the tightening.

ANCF Finite Element/Multibody System Formulation of the Ligament/Bone Insertion Site Constraints

The focus of this investigation is to study the mechanics of the knee joint using new ligament/bone insertion site constraint models that require the integration of multibody system and large displacement finite element algorithms. Two different sets of clamped end conditions at the ligament/bone insertion site are examined using nonlinear large displacement absolute nodal coordinate formulation (ANCF) finite elements. The first set of end conditions, called the partially clamped joint, eliminates only the translations and rotations at a point, allowing for the cross section stretch and shear at the ligament/bone connection. The second joint, called the fully clamped joint, eliminates all the translation, rotation, and deformation degrees of freedom of the cross section at the ligament/bone insertion site. In the case of the fully clamped joint, the gradient vectors do not change their length and orientation, allowing for the use of the constant strain assumptions. The partially clamped joint, on the other hand, allows for the change in length and relative orientation of the gradient vectors at the bone/ligament insertion site, leading to the cross section deformation induced by knee movements. Nanson’s formula is applied as a measure of the deformation of the cross section in the case of the partially clamped joint. In this study, the major bones in the knee joint consisting of the femur, tibia, and fibula are modeled as rigid bodies while the ligaments structures are modeled using the large displacement ANCF finite elements. Two different ANCF finite element models are developed in this investigation: the first model employs the fully parameterized three-dimensional beam element while the second model employs the three-dimensional cable element. The three-dimensional fully parameterized beam element allows for a straight forward implementation of a neo-Hookean constitutive model that can be used to accurately predict the large displacement as experienced in knee flexation and rotation. At the ligament bone insertion site, the ANCF fully parameterized beam element is used to define a fully or partially constrained joint while the ANCF cable element can only be used to define one joint type. The fully and partially clamped joint constraints are satisfied at the position, velocity, and acceleration levels using a dynamic formulation that is based on an optimum sparse matrix structure. The approach described in this investigation can be used to develop more realistic models of the knee and is applicable to future research studies on ligaments, muscles, and soft tissues. In particular, the partially clamped joint representation of the ligament/bone insertion site constraints can be used to develop improved structural mechanics models of the knee.

Experimental and numerical analysis of clamped joints in front motorbike suspensions

Clamped joints are shaft-hub connections used, as an instance, in front motorbike suspensions to lock the steering plates with the legs and the legs with the wheel pin, by means of one or two bolts. The preloading force, produced during the tightening process, should be evaluated accurately, since it must lock safely the shaft, without overcoming the yielding point of the hub. Firstly, friction coefficients have been evaluated on “ad-hoc designed” specimens, by applying the Design of Experiment approach: the applied tightening torque has been precisely related to the imposed preloading force. Then, the tensile state of clamps have been evaluated both via FEM and by leveraging some design formulae proposed by the Authors as function of the preloading force and of the clamp geometry. Finally, the results have been compared to those given by some strain gauges applied on the tested clamps: the discrepancies between numerical analyses, the design formulae and the experimental results remains under a threshold of 10%.

Analysis of Bolt Joint Using the Finite Element Method

Analysis of Bolt Joint Using the Finite Element Method A numerical analysis of the initially clamped bolt joint subject to the working pressure is presented in the paper. Special, hexahedral 21- and 28-node isoparametric finite elements have been employed to model the contact zone. In this model, one takes into account loading due to the working pressure in the gap between the gasket and the flange arising as an effect of the progressing joint opening, what has not been considered in recent papers. Nonlinear stiffness characteristics of the bolt and the flange with the gasket are developed. Working pressure corresponding to the critical bolt force resulting in the joint leakage (complete opening between the gasket and the flange) is determined. FE computational results are compared with the available experimental results. The numerical results are presented using the authors' own graphical postprocessor.

Experimental study of friction in aluminium bolted joints

This study aims at developing an experimental tool useful to define accurately the friction coefficients in bolted joints and, therefore, at relating precisely the tightening torque to the bolt preloading force in some special components used in front motorbike suspensions. The components under investigation are some clamped joints made of aluminium alloy. The preloading force is achieved by applying a torque wrench to the bolt head. Some specific specimens have been appropriately designed and realized in order to study the tribological aspects of the tightening phase. Experimental tests have been performed by applying the Design of Experiment (DOE) method in order to obtain a mathematical model for the friction coefficients. Three replicas of a full factorial DOE at two levels for each variable have been carried out. The levels include cast versus forged aluminium alloy, anodized versus spray-painted surface, lubricated versus unlubricated screw, and first tightening (fresh unspoiled surfaces) versus sixth tightening (spoiled surfaces). The study considers M8x1.25 8.8 galvanized screws.

In-field experimental stress analysis in the elastic and plastic fields on motorbike handlebar clamped joints

In a motorbike different types of shaft-hub couplings are used to join the handlebar to the suspension legs of the front wheel. Some papers were recently published with reference to the experimental determination of the starting friction coefficient of the fork-pin compression coupling [1], to the development of FEM assisted design strategies for the fork-pin [2], fork-leg [3] and leg-pin couplings [4]. On the other hand, another important joint, the clamping between the fork and the handlebar has been less investigated. The clamp (aluminum alloy, EN AW-6082, Figure 1A, B) consists of two parts, the lower one (connected to the fork by two screws), interfacing with the lower part of the handlebar, and the upper one, shaped to lodge the upper part of the handlebar. The assembly procedure consists in the insertion of the handlebar between the two clamp parts and in screw tightening, according to a particular procedure. Screws indicated as 1 and 2 are tightened first to create contact between mating surfaces of the two clamp parts, screws 3 and 4 are then applied to complete clamp closing.

Clamped end conditions and cross section deformation in the finite element absolute nodal coordinate formulation

In the finite element absolute nodal coordinate formulation (ANCF), the elimination of the relative translations and rotations at a point does not necessarily define a fully clamped joint, particularly in the case of fully parameterized ANCF finite elements that allow for the deformation of the cross section. In this investigation, the formulations and results of two different sets of clamped end conditions that define two different joints are compared. The first joint, called the partially clamped joint, eliminates only the translations and rotations at a point on the cross section. The second joint, called the fully clamped joint, eliminates all the translation, rotation and deformation degrees of freedom at a point on the cross section. The kinematic equations that define the partially and fully clamped joints are developed, and the dynamic equations used in the comparative numerical study presented in this paper are shown. As discussed in this investigation, the fully clamped joint does not allow for the deformation of the cross section at the joint node since the gradient vectors remain orthogonal unit vectors. The partially clamped joint, on the other hand, allows for the deformation of the cross section. Nanson’s formula is used as a measure of the deformation of the cross section in the case of the partially clamped joint. A very flexible pendulum that has a rigid body attached to its free end is used to compare the results of the partially and fully clamped joints. The numerical results obtained using this very flexible pendulum example show that, while the type of joint (partially or fully clamped) does not significantly affect the gross reference motion of the system, there are fundamental differences between the two joints since the partially clamped joint allows for the cross section deformations at the joint node.

Design improvement of clamped joints in front motorbike suspension based on FEM analysis

This paper aims at defining the tensile state in shaft–hub joints realized between the clamp (hub) located at the end of the suspension leg of the front motorbike suspensions and the wheel pin (shaft). The clamp under investigation has an asymmetric shape and a slot useful for the assembly operation: one or two bolts (depending on the vehicle performances) are tightened in order to generate the coupling pressure which is necessary to lock the pin. The fundamental objective of this work is to define a mathematical model to calculate the maximum stress generated on the clamp by the tightening forces. The mathematical model was defined by comparing the De Saint Venant theoretical bending stress (the maximum stress on the clamp) with several FEM results. Thus a sort of theoretical stress concentration factor was calculated in function of the dimension and of the location of the spot facings of the clamp. The new developed model is useful to optimize and to verify, in a very short time, this type of coupling without performing any complex numerical analysis. The validity of the model has been demonstrated by several FEM results and by some experimental tests carried out on a high performance vehicle.

Experimental investigation of energy-absorption characteristics of components of sandwich structures

Two series of experiments are performed to investigate the dynamic response of various essential components of a class of sandwich structures, under high-rate inertial loads. One consists of dynamic inertia tests and the other involves dynamic impact tests. A split Hopkinson bar apparatus is modified and used for these experiments. First, the energy-absorbing characteristics of the plate material in a sandwich structure are investigated using novel dynamic inertia tests, paralleled by detailed finite-element simulations. The loading conditions in this case are similar to those in high-rate pressure loading situations, and hence more closely simulate potential blast effects on structures. Plates made of DH-36 naval structural steel are used in the dynamic inertia tests. The plates subjected to inertia loading show membrane deformation behavior, but as the deflection or thickness increases, the bending deformation near the clamped joint becomes significant. Second, the dynamic behavior of the core material in a sandwich structure is studied through dynamic impact (compression) tests, using high-speed photography. In addition, both the quasi-static and dynamic response of the material is quantified using hydraulic testing machines and the Hopkinson-bar techniques. Aluminum foam as a core material is used in these experiments. Aluminum foam is a lightweight material with excellent plastic energy absorbing characteristics. The experimental results show a localized deformation in the metal foam specimens, at suitably high impact velocities. The simulation results correlate well with the test results in the overall behavior of the metal foam specimens. With these two experimental methods, the dynamic behavior of sandwich structures under high-rate inertial loading conditions can be examined minimizing the need for direct pressure-induced impulse experiments. Each series of experiments is relatively simple and can be performed separately to study the complex behavior of sandwich panels in simple and well-controlled tests. The validity of separate performance test is shown by a finite element analysis with aluminum foam core sandwich specimen subjected to blast loading.

Optical Monitoring of Bolt Tightening Using 3D Electronic Speckle Pattern Interferometry

An optical method is presented for the real-time monitoring of the bolt tightening process that provides the necessary clamping force in bolted assemblies. The method uses the 3D electronic speckle pattern interferometry (ESPI) technique to measure and monitor the joint deformation and strain fields in the joint around the tightened fastener, and establish a reliable correlation with the clamp load provided by the fastener tightening. Because the relationship between the clamp load and joint deformation is independent of the frictional variables of the fastener, the direct monitoring of the deformation and strain fields in the clamped joint would provide a more reliable measure of the clamp load level, as compared to the conventional reliance on the tightening torque to predict the resulting clamp load level. This technique is beneficial, especially for monitoring, with high precision, the proper tightening of critical bolted connections such as those used in many pressure vessels in the nuclear power industry. The validity of the optical technique is also ascertained by comparing the results to that obtained by using finite element analysis and other classical mechanics of materials methods.

Clamp Load Loss due to Fastener Elongation Beyond its Elastic Limit

The amount of clamp load due to an externally applied separating force is determined for a boiled assembly in which the fastener is elongated past its proportional limit, while the clamped joint remained within its elastic range. After the initial tightening of the fastener, the joint is subsequently subjected to a tensile separating force, which further increases the fastener tensile stress into the nonlinear range. Such separating force will simultaneously reduce the clamping force in the bolted joint. Upon the removal of the separating service load, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the fastener tension is reduced from its value at initial assembly, due to the plastic elongation of the fastener. The reduction in fastener tension translates into a partial—yet permanent—loss of the clamping load that may lead to joint leakage, loosening, or fatigue failure. A nonlinear model is established in order to describe the fastener behavior past the proportional limit of its material, and to determine the clamp load loss due to the permanent set in the fastener after the separating force has been removed. Two fastener materials with significantly different rates of strain hardening are used for modeling the behavior of the bolted joint system. The effect of three nondimensional variables on the amount of clamp load loss is investigated. The first variable is the stiffness ratio of the joint and the fastener. The second is the ratio of initial fastener tension to the fastener elastic limit, and the third variable is the ratio of the separating force to the force that causes joint separation to start. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications. Experimental verification of the analytical results is presented.

Clamping effects on the dynamic characteristics of composite machine tool structures

Substituting composite structures for conventional metallic structures has many advantages for structural dynamic characteristics because composite materials have the higher specific stiffness and damping characteristics than conventional materials. However, the dynamic characteristics such as the fundamental natural frequency and damping of composite structures are influenced much by their joints. In this work, the effects of clamping conditions on the dynamic characteristics of cantilever type composite machine tool structures with clamped joint were investigated to increase the natural frequency and damping of structures. In order to improve the shear property of the clamping part of composite machine tool bar, a new method for the clamping part was developed with metal core or sleeve inserted in the composite body at the clamping part. From the finite element and experimental results, suitable clamping conditions for the maximum dynamic stiffness were obtained for the composite structures with clamped joint.