Papers by Keyword: Bolted Joint

Abstract: The axial tension remaining in a bolt after the hydraulic tightening is less than the initial tension from the hydraulic load, and the ratio of the residual tension to the initial tension, an effective tensile coefficient, is the most critical factor to securely tighten a pressure vessel. In this study, an analysis model simulating the hydraulic joint processes by using a finite element model was developed to clarify the effects of various joint parameters on the effective tensile coefficient. The analysis model could estimate the effective tensile coefficient within a 5% error compared to the hydraulic tightening experimental results. The simulated results of the analysis model showed that the effective tensile coefficient changed largely depending on the thickness and the surface pressure of the flange, and that the coefficient hardly changed by the height of the nut and the friction coefficient at the bearing surface.

Abstract: Experimental work on tensile behaviour and failure mechanism of composite double lap bolted joint has been carried out. Chopped strand mat (CSM) coir, glass and coir-glass/epoxy composite plates were fabricated by hand lay-up method. The bolted joint specimens were of 155 mm length and 48 mm width. Steel bolts of 4 mm and 8 mm diameters were used. Effect of material type, number of layers and width to diameter ration (w/d) on tensile load, bearing strength and failure behaviour were examined. Results show that, the maximum load obtained from the glass/epoxy, coir/epoxy and coir-glass/epoxy specimens increased with the increase in the number of layers and (w/d) ratio. Maximum load obtained from the six layers glass/epoxy with w/d ratio of 12 is found higher respectively 15.2% and 50.14% than that obtained from hybrid coir-glass and coir/epoxy composite specimens. The percentages of difference were 14.2% and 42.97% for the specimens with w/d ratio of 6. It has been found that the maximum strength of the six layers glass/ epoxy specimens was found higher in the range between 17.5% to 18.46 % and 51.67% to 57.74 % than the hybrid coir-glass and coir/epoxy specimens respectively. Net tension failure and cleavage failure modes were observed for the two and four layers coir/ epoxy specimens with w/d ratios of 6 and 12. Bearing failure mode was observed for the six layers coir, glass and hybrid coir-glass/epoxy specimens.

Abstract: The interface of bolted joint commonly focuses on the research of non-linear damping and stiffness, which affect structural response. In the article, the non-linear damping model of bolted-joint interface is built, consisting of viscous damping and Coulomb friction. Energy balancing method is developed to identify the dry-friction parameter and viscous damping factor. The corresponding estimation equations are acquired when the input is harmonic excitation. Then, the vibration experiments with different bolted preloads are conducted, from which amplitudes in various input levels are used to work out the interface parameters. Also, the fitting curves of dry-friction parameters are also obtained. Finally, the results illustrate that the most interface of bolted joint in lower excitation levels occurs stick-slip motion, and the feasibility of the identification approach is demonstrated.

Abstract: To investigate factors affecting contact interface pressure distribution in bolted joint, a parametric model was established by ANSYS APDL language in this paper. The contact pressure distribution on bolted joint interface was obtained through interpolating and revising contact interface forces. It is observed that the position of peak interface pressure is between the edge of bolt hole and the edge of bolt head. The contact pressure linearly changes with the bolt load while the distribution trend and radius remain unchanged. When the total thickness of clamped members is fixed, the contact pressure distribution varies from concentrated to uniform with the increasing member thickness ratio, and the maximum contact radius is reached while the member thickness is equal. When one clamped member thickness is fixed, increasing the other’s thickness can also reduce the contact pressure concentration, but the effect gradually weakens. Increasing bolt diameter can slightly increase the absolute contact radius but decrease the normalized contact radius. The inclusion of a washer under the nut can slightly promote interface clamping.

Abstract: In this study, a non-linear finite element model for a simplified single-bolted joint structure model is built. Static analysis on the structure under different shear force and pretension effect is done, and the non-linear contact behavior is analyzed. Through comparing datum, it is found that interface area of each bolted joint region can be described an annular region around bolt hole, whose outer radius has increased by 85% compared with radius of bolt hole. Also, the frequency responses of the multi-bolted joint structure under sinusoidal excitation are investigated. Simulation results show that the resonance regions basically remain unchanged in different pretension effect and the largest amplitude will increase with the increasing preloads. Finally, the vibration experiments are conducted. Interface nonlinear affect dynamic stiffness considerably. The test results illustrate that dynamic behaviors of bolted joint agree with the simulation results and the proposed non-linear contact model was reasonable.

Abstract: Bolt load in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. When the separating force is applied off the bolt center, 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 variation of the bolt load, the deformation etc. An analytical model is proposed to obtain the expression for the nonlinear bolt load under a separating service load. Finite element modeling is used for evaluating the accuracy of the proposed model.

Abstract: Joint member stiffness in a bolted connection directly influence the safety of a design in regard to both static and fatigue loading as well as in the prevention of separation in the connection. Thus, the accurate determination of the stiffness is of extreme importance to predict the behavior of bolted assemblies. In this paper, An analytical 3D axisymmetric model of bolted joints is proposed to obtain the joint stiffness of Bolted Joints. Considering many different analytical models have been proposed to calculate the joint stiffness, the expression based force equilibrium can be a easy way to choose the best expression for the joint stiffness as a judgment criteria.

Abstract: In order to investigate fatigue characteristics of nonferrous bolts at elevated temperature, fatigue tests of bolted joints which were tightened with three kinds of nonferrous bolts were been conducted at 100°C atmosphere. The test bolts were made of A5056 aluminum alloy and AZ31 and AZX912 magnesium alloy. Creep tests of the bolts at 100°C atmosphere were also conducted. The results showed that the fatigue limit of A5056 bolt was the highest of all regardless of the ambient temperature. The fatigue limits of AZ31 bolt and AZX912 bolt also were a half of the fatigue limit of A5056 bolt at both ambient temperature. Bolt clamping force losses due to creep deformation were observed for all bolts during fatigue tests at elevated temperature. Hence as additional tests, the creep tests which was controlled either the tensile force or the displacements respectively were conducted. As the results it was seen that the clamping force losses for all bolts were remarkably large although the each creep deformation was different for each bolt material. Therefore the results indicates that we have to pay attention to the clamping force reduction due to creep deformation if we use the nonferrous bolt in high temperature.

Abstract: The present study is concerned with the development of a fracture criterion for the impact fracture of jointed steel plates of a lap bolted joint used in the suspension parts of a car body. For the accurate prediction of crash characteristics of car bodies by computer-aided engineering (CAE), it is also necessary to examine the behaviour and fracture of the jointed steel plates subjected to impact loads. Although the actual impact fracture of jointed steel plates of a lap bolted joint in cars is complicated, for simplifying it is classified into the shear fracture and the extractive fracture of jointed steel plates. Three kinds of steel plates, i.e., common steel with the tensile strength of 270 MPa and two high tensile strength steels with the tensile strength of 440 and 590 MPa level used for vehicles, are examined. In the impact shear test, the specimens are made of two plates and jointed by a bolt, and in the impact extractive test the specimens are made of a plate and drilled in the centre for a bolt. The impact shear test of jointed steel plates of lap bolted joints is performed using a modified split Hopkinson bar apparatus, while the impact extractive one is performed using one-bar method. Numerical simulations by a FEM code LS-DYNA are also carried out in order to understand the mechanism of shearing and extractive fractures process of jointed steel plates. The obtained results suggest that a stress-based fracture criterion may be developed for the impact shearing and extractive fractures of jointed steel plates of lap bolted joints used in a car body.

Abstract: A review of some of the various fatigue models introduced over the years for both metallic materials, in particular aluminium alloys followed by fatigue and durability concerns associated with composite materials. The move towards light weight and high stiffness structures that have good fatigue durability and corrosion resistance has led to the rapid move from metal structures to composite structures. With this brings the added concern of certifying new components as the damage mechanisms and failure modes in metals differ significantly than composite materials such as carbon fiber reinforced polymers (CFRP). The certification philosophy for composites must meet the same structural integrity, safety and durability requirements as that of metals. Hence this is where the challenge now lies. Substantial work has been conducted in the reparability of composite structures through bonding using various adherend thicknesses and joint types and has been shown to have higher durability than mechanically fastened repairs for thin adherends however these are currently unacceptable repair methods as they cannot be certified. Repairs are designed on the basis that the repair efficiency can be predicted and should be designed conservatively with respect to the various failure modes and include the surrounding structure.