Double-bolted Joint Research Articles

Simulation and experimental study on contact pressure distribution of contact interface in single and double bolted connection structures

Bolted joints play an important role in aerospace, machinery manufacturing, weapons and other fields, and the contact pressure distribution at the connection interface seriously affects the service performance of the bolts. Contact pressure analysis is an essential basis and reference for structural design, calibration, inspection, and safety monitoring of bolted connection structures. Considering the preload force and frictional contact between the joint components, a block mapping hexahedron mesh generation and finite element modeling method for bolted connections is presented, and the finite element models of single and double bolted structures are constructed. Then, an experimental test platform for measuring contact pressure distribution is constructed. Comparison of finite element analysis results with experimental results for the contact pressure distribution in the single and double-bolted joints; the root mean squared error of contact pressure distribution is less than 5%, which verifies the effectiveness of the finite element models. After that, the models are used to study the contact pressure distribution in single-bolted joints and contact pressure coupling effect of double-bolted joints, and the normal stress distribution features within members and contact pressure distribution contour are revealed for single and double-bolted joint. Finally, the finite element models are adopted to investigate the effects of the clamping length, preload, material properties, hole clearance, and bolt size on contact pressure distribution in single-bolted joints. The coupling effect of contact pressure distribution in double-bolted joints under different preloads and geometric parameters are also examined.

Experimental and numerical investigations on fatigue behavior of 42CrMo4 high-strength steel single lap double-bolted joints

Cold extrusion forming is a manufacturing technology that effectively extends the fatigue life of mechanical structures and has been widely used in the processing of ship components. The fatigue behavior of 42CrMo4 high-strength single lap double bolted joints is investigated based on fatigue experiment and numerical simulation. The stress-strain distribution of joint plates under cold extrusion, bolted tightening and longitudinal external loads are evaluated based on the nonlinear finite element software ABAQUS. The fractographic of fatigue specimens is detected by scanning electron microscopy (SEM) to research the initiation location and propagation type of fatigue cracks, and a prediction method for the stiffness of joint plate bolt connections is further proposed. The results indicate that fatigue cracks propagated tortuously and exhibits a more complex distribution state. The combination of cold extrusion forming and bolt preload can effectively improve the fatigue life of high-locked bolted joints. Smooth surface, beneficial residual stress field and cold extrusion hardening phenomenon are considered the main reasons for improving fatigue life.

Identification of bolt state in lap joint based on propagation model and imaging methods of Lamb waves

Bolts are commonly applied to lap joints in various industrial fields. Harsh environment, low quality of operation, and other unfavorable conditions may result in bolt looseness. Due to the structural complexity, conventional Lamb wave-based methods just extract statistical characteristics for looseness detection, while neglecting the information contained in the propagation process of Lamb waves. To take full advantage of the information on bolt states carried by array signals during the propagation, this study proposes a detection procedure based on propagation model and imaging methods of Lamb waves. Firstly, the contact status on the macro and micro scales is investigated with theoretical analysis and finite element simulation, and the theoretical model of Lamb wave propagation across bolted joints is established deriving from the analysis of contact. Subsequently, three imaging methods, including delay-and-sum, minimum variance, and sparse reconstruction, are adapted for the identification of bolt state. Since Lamb waves are mainly transmitted into another plate through the contact area near the bolts based on the proposed propagation model, pixel values are inclined to be concentrated around the bolts. On this basis, imaging intensity near each individual bolt can reveal its fastening state given that the transmitted energy around its location is associated with its torque. Finally, experiments are carried out in both single-bolt and double-bolt joints. The proposed propagation model is verified in the single-bolt joint and loose bolts can be identified in the imaging results of the double-bolt joint, which demonstrates the effectiveness of the proposed method for bolt state identification.

Study on Tensile Performance of Double-Bolted Joints between Carbon Fiber Reinforced Polymer Plate and Aluminum Plate

Carbon fiber reinforced polymer (CFRP) with high specific strength, specific modulus, and other outstanding properties, which could be used in aerospace, shipbuilding, and railway. The joint of carbon fiber composite material plate and metal material plate plays an important role in the overall performance of the structure. In this paper, a carbon fiber reinforced polymer (CFRP) progressive damage model is developed based on composite laminate theory and 3D Hashian theory. The model of the double bolt single lap joint shear connection is established for the CFRP plate and the finite element method is used to carry out the stress analysis and failure prediction of the lap structure. The effect on structural performance under tensile conditions was studied through the change of double bolt spacing. The results show that the decrease in bolt row spacing can lead to the interference effect between holes. In addition, the progressive damage of the composite plate is located near the center line of the bolt hole.

Parametric Influences of Geometric Dimensions on High Temperature Mechanical Behaviors and Damage Mechanisms of Ceramic Matrix Composite and Superalloy Double Bolted Joints

Given multiple material performance advantages, ceramic matrix composite (CMC) material has become one of the most promising hot structural materials used for thermal protection system in hypersonic vehicles. Under harsh thermal exposure of vehicles in flight, the design of connection structure would be a critical issue in improving load-carrying efficiency and ensuring service safety of aircraft structures in service environments. However, little attention was paid on mechanical behavior and its factors affecting the mechanical property of CMC joining at elevated temperature. To address this concern, a 3D finite element model coupled with progressive damage analysis is carried out to predict high temperature tensile properties and failure behavior of single-lap, double-bolt CMC/superalloy joints assembled by two serial protruding-head bolts. In the implementation of progressive damage analysis of 2D plain-woven C/SiC composites, a user-defined subroutine UMAT including a nonlinear constitutive model, 3D Alvaro failure criterion and Tan’s material degradation rule were embedded into the general package ABAQUS® through Fortran program interface. A parametric study considering geometries of joints was performed to evaluate their resultant influence on high temperature tensile behavior and the associated damage mechanisms for the CMC/superalloy double-bolt joint. New findings were provided for full exploitation of high performance through geometric design of ceramic matrix composite hot structure for hypersonic aircraft.

A novel model for evaluating preload based on spectral problem in system with double-bolted connections

Accurate evaluation of preload in system with double-bolted connections is critical for the service performance of engineering structures or equipment. However, the theoretical framework for assessing preload is imperfect. An equivalent approach from the tightening process of double-bolted joints to second-order spectral problem of the energy-dependent potential is firstly established. This paper proposes a novel nonlinear model of bolt preload considering physical and geometric parameters by proving the completely integrability of systems used bolted connections. The experimental device for hmeasuring displacement and bolt preload was developed to verify the accuracy of proposed model. Results show that the maximum relative error is not more than 3%. Finally, the influences of elastic modulus, density, holes spacing, and height on preload are analyzed.

Enhancing the performance of bolted joints in composites by use of patched steel or titanium inserts

A new insert concept that interlaces metal inserts into composite laminates has earlier been shown to improve the relatively poor bearing strength of holes in fibre reinforced polymer composites, and it is here further and more thoroughly investigated. The concept was invented to increase the efficiency of joints with mechanical fasteners in composite materials and this work presents experiments on double-bolt joints with inserts made of either stainless steel or a titanium (Ti) alloy. In particular the work compares different implementations of the insert concept by reinforcing one or two holes in double bolt joints, and the effect of using different metals in the inserts. Some complementary tests on pin-loaded specimens and open hole tensile specimens are also performed and compared, partly with results that were reported previously.Considerable improvements of the bearing load capacity are attained, i.e. 50%–60% for steel and 35%–45% for Ti, compared to references. The open-hole tensile strength is also improved considerably (almost 30%) when the holes are reinforced with Ti inserts. The fact that the inserts can improve not only the bearing strength but also the performance in open-hole tension implies that the Ti inserts bring nothing but positive effects to the strength of the joints. The test results from single-shear double-bolt specimens with inserts at one hole showed improved strengths of 30% and 20% for specimens with steel and Ti inserts, respectively. Finally, an impressive strength improvement of 40–45% is achieved for single-shear double-bolt specimens having both holes reinforced with inserts of either steel or Ti.

On the use of the GP-NARX model for predicting hysteresis effects of bolted joint structures

Structures joined by lap-joints can present complex nonlinear dynamic behavior as a function of the stress to which the lap-joint is subjected, including contact stiffness variations and softening, along with hysteresis effects related to frictional dissipation at the contact interface. Considering applications where the use of non-parametric models that depend only on input and output data is required, this work proposes and details the GP-NARX model’s use to approximate systems’ dynamics with hysteresis. Initially, the proposed model’s predictive applicability is evaluated on a numerical application involving the Bouc-Wen oscillator with hysteretic damping. Then, this work proposes a GP-NARX model to describe the dynamics of the BERT benchmark, an experimental system that contains a symmetric double bolted joint that is nonlinearly dependent upon the applied excitation amplitudes, presenting as a friction joint’s well-known softening effect. The structure also presents data variation related to the presence of uncertainties in the measurement process. Thus, to accommodate the experimental variability, the training step of the GP-NARX model considers several experimental realizations. The results indicate that GP-NARX can make accurate predictions of the response of both investigated applications, emphasizing its practical ability, where the confidence intervals of the proposed model were able to accommodate the noisy experimental data, learning the nonlinear relation between the input and output data points.

An Experimental and Numerical Investigation on Bolted Joints of Woven Glass Fabric/Epoxy Composites

In the present work, an attempt is made to study the mechanical response of woven glass fabric/epoxy composite laminates using numerical modelling and experimentation. For this two different configurations namely double lap joined with single and double bolts are chosen. These laminates are subjected to numerical modelling using finite element analysis to study the joint strength and stress analysis. The joint strength of woven glass fabric composites is studied experimentally by conducting tensile test. Along with this the effect of varying edge distance to diameter ratios are studied both numerically and experimentally to arrive at safe design. Both numerical analysis and experimentally obtained bearing strength of composite laminated bolted joints are correlated. This is done in order to predict the the failure load and failure mechanisms in the composite laminate bolted joints. The variation in the numerically and experimentally obtained bearing strength values were well within 5% diference for both cases of single and double bolted joints.

Variasi Spasi Baut terhadap Kuat Geser Sambungan Baut pada Pelat Baja

Errors in planning the spaces/distances between the bolts can weaken or create defects in the connection. Therefore, a research on the effect of bolt space on shear strength of bolt joints on steel plates is needed to find out the influence of the distance between bolts to the strength of double bolt joints on steel plate joints, whereas the long-term goal of this study is to determine the effect of the distance between bolts to the strength of the bolt connection in a plate connection system having more than two bolts. In the planning, the connection used bolt connecting devices that meet SNI 1729:2015 requirements. A tensile testing machine was used and the direct test method was conducted for shear strength of bolts in the plate joint system using two bolts. The bolt sample was installed in the plate connection system then the connection system was given a tensile load until it broke in the bolt sample. The peak load of the experimental results indicated the shear strength of the double bolt connection on the plate fluctuates. Average peak load for the sample of group I (20 mm bolt space), group II (40 mm bolt space), group III (60 mm bolt space), group IV (80 mm bolt space) and group V (100 mm bolt space) are 21.962 kN, 23.512 kN, 22.925 kN, 23.725 kN and 22.975 kN, respectively. The experimental results from each sample group showed the average peak load strength was greater than the theoretical shear strength value of 17.4974 kN.

Dynamic properties of single and multi-bolted composite joints at different bolt-loads and elevated temperature

ABSTRACT Bolted composite joints are one of the most common joining methods used in aerospace industry for joining of parts and sub-assemblies, where there is a need to transfer high load with consistency and easy to assemble/ dissemble of parts for maintenance. Bolted connection undergoes different types of vibrations during their service life, that make the pre-load on bolted joints to decrease and call for increase in dynamic loading and failure. Regular checking and tightening of bolted joints become a crucial and expensive activity to maintain the structure to perform efficiently. The natural frequency is one of the most important factors of vibration of structure that depends on the geometry and material properties of the structure. In this paper, the effect of pre-load and temperature on the natural frequency of single bolted and double-bolted joints is investigated experimentally and numerically.

Frequency Based Substructuring for Structure with Double Bolted Joints: A Case Study

Adopting dynamic substructuring schemes is a common practice in the field of structural dynamics, where the dynamic behaviour of a structure is predicted by combining the multiple subsystems that are analysed individually. This paper investigated the dynamic behaviour of a structure with doubled bolted joints using the frequency based substructuring (FBS) method. In the attempt, the substructures were combined with the frequency domain that can be numerically derived or experimentally measured. However, the applicability of this method suffered from several issues where most of them were related to the frequency response function (FRF) of the rotational degree of freedom (DOF) at the subsystem’s interface. In some cases, the system’s interface vibrated in the rotary motion of certain modes, for instance, a car side rear view mirror. Therefore, excluding the rotational FRF during the coupling process could lead to a completely different result. This paper presents the use of the FBS method for a structure with double bolted joints by using the equivalent multipoint constraint (EMPC) method through which rotational DOFs can be completely neglected. The actual tested structure for this study was an assembled structure consisting of two substructures: a simple beam and an irregular plate steel structure. The FRFs of both substructures were derived from using the FRF synthesis from finite element models and combined together via the FBS method. This study reveals that the use of the FBS method with the EMPC method for a structure double bolted joints has led to very promising results.

Non-uniform virtual material modeling on contact interface of assembly structure with bolted joints

Accurate modeling of contact interface in bolted joints is crucial in predicting the dynamic behavior for bolted assemblies under external load. This paper presents a contact pressure distribution based non-uniform virtual material method to describe the joint interface of assembly structure, which is connected by sparsely distributed multi-bolts. Firstly, the contact pressure distribution of bolted joints is obtained by the nonlinear static analysis in the finite element software ANSYS. The contact surface around bolt hole is divided into several sub-layers, and contact pressure in each sub-layer is thought to be evenly. Then, considering multi-asperity contact at the micro perspective, the relationship between contact pressure and interfacial virtual material parameters for each sub-layer is established by using the fractal contact theory. Finally, an experimental platform for the dynamic characteristics testing of a beam lap structure with double-bolted joint is constructed to validate the efficiency of proposed method. It is found that the theoretical results are in good agreement with experimental results by impact response in both time- and frequency-domain, and the relative errors of the first four natural frequencies are less than 1%. Furthermore, the presented model is used to examine the effect of rough contact surface on dynamic characteristics of bolted joint.

Strength of composite plate with parallel offset misalignment double-bolted joint under bending moment

The connection concept of placing only two bolts in offset misalignment against the bending load along the wing span was used for an aerobatic airplane designed in Thailand as a KIT plane to minimize the impact of drilling numerous holes. This concept can deviate the force direction on the holes. The two suitable drilling positions should have the lowest resultant force and highest strength of fiber reinforcement structure. To investigate the strength of the fastener hole when the force deviated from the original orientation, specimens, made from twill weave carbon fiber-epoxy and laid up at ±45-degree orientation, were tested under bearing load according to ASTM D5961 standard. The experimental results revealed that the bearing strength of CFRP material decreases when the force deviation angle increases, so zero-angle deviation of the resultant force on the drilling hole is the most suitable orientation to absorb bolt bearing load. The most suitable pattern of two offset misalignment holes is the greatest horizontal distance at zero vertical distance when it was considered only the effect of the bearing strength and the deviation angle. Moreover, the failure pattern begins to deviate along the fiber orientation when the inclination angle increased.

End Restraints in Steel Angles in Lattice Towers

Introduction: Test data on single angle compression members with various end connection arrangements is used to develop adjustment factors for effective buckling lengths. A connection length parameter is proposed and evaluated based on test data. Results from a total of 31 equal leg test angles with single-, double- bolts and fixed ends are used. Methods: Slenderness ratios considered ranged from 150 to 312. Angle sizes ranged from 38 x 38 x 3.2 (mm) to 89 x 89 x 6.4 (mm). Estimated connection lengths were about 12.5% of the member length for single-bolt joints; 24.7% for double-bolt joints and 45.6% for fixed joints. Computed effective length factors ranged from 0.544 to 0.875. Results: Results seem to indicate that it is possible to define and calculate connection length of a lattice tower angle member. Suggestions for incorporating connection length issues in routine designs are made.

Mechanical and failure behavior of three-dimensional six-directional braided composites bolted joint

Experiments and finite element simulation were used to investigate the influence of geometric parameters on failure response of a single-lap bolted joint. Single- and double-bolt joints in three-dimensional six-directional braided composites were tested. The failure modes and mechanisms of the joints were evaluated. To accurately predict bearing strength, a three-dimensional composite damage model was used, which included the Yamada–Sun failure criteria based on the characteristic curve method. The finite element method (FEM) was validated by experimental results. The geometric reference value and failure envelope for the single-lap bolted joint were obtained. The results showed that the carrying capacity of the single-lap bolted joint decreased and the failure mode also changed owing to the secondary bending. It can also be obtained that increased the number of bolt rows can effectively reduce the secondary bending of the plates and thus generated less severe net tensile stresses.

Design Optimization of Double-array Bolted Joints in Cylindrical Composite Structures

A design optimization is performed for the double-bolted joint in cylindrical composite structures by using a simplified analytical method. This method uses failure criteria for the major failure modes of the bolted composite joint. For the double-bolted joint with a zigzag arrangement, it is necessary to consider an interaction effect between the bolt arrays. This paper proposes another failure mode which is determined by angle and distance between two bolts in different arrays and define a failure criterion for the failure mode. The optimal design for the double-bolted joint is carried out by considering the interactive net-tension failure mode. The genetic algorithm (GA) is adopted to determine the optimized parameters; bolt spacing, edge distance, and stacking sequence of the composite laminate. A purpose of the design optimization is to maximize the burst pressure of the cylindrical structures by ensuring structural integrity. Also, a progressive failure analysis (PFA) is performed to verify the results of the optimal design for the double-bolted joint. In PFA, Hashin 3D failure criterion is used to determine the ply that would fail. A stiffness reduction model is then used to reduce the stiffness of the failed ply for the corresponding failure mode.

Failure Mode Analysis of Aluminium Alloy 2024-T3 in Double-Lap Bolted Joints with Single and Double Fasteners; A Numerical and Experimental Study

This paper aims to study the mechanical behaviour and failure mode of Al 2024-T3 in double-lap bolted joints. To accomplish this, the effect of geometric parameters was investigated in both configurations of single and double fasteners. Using ABAQUS/Standard, a three-dimensional finite element model was developed and verified against the experimental results of the joints loaded in tension. In general, double bolt joints were found to have greater load carrying capacities than single bolt joints (by 40%–49%). In single bolt joints, the plate width had insignificant effect on the behaviour of the joint under tensile loading; whereas, increasing the distance of the hole from the edge, considerably enhanced the strength of the joint. In double bolt joints, changing the edge distance had almost no effect on the behaviour of the joint. However, increasing the plate width from 25.4 to 30 mm increased the load carrying capacity by 28%. This study showed that in single bolt connections, with increasing the edge distance, the failure mode can favourably shift from shear-out to bearing. Also, double bolt joints with wider plates (increased width) can beneficially shift the failure mode from net-tension to bearing. The geometric parameters were found to play an important role in controlling the failure mode so that catastrophic failure modes of net-tension and shear-out can be prevented in bolted joint.

Large Lateral Deformation Analysis of Angle Steel with Double Bolt Joints

In the past time, it was neglected that different types of the deformation have an important effect on the Load-Displacement (L-D) relationship in bolt slippage. In this paper, 3D finite element models with double bolt joints are established by the ANSYS finite element package and a series of bolt slippage tests are conducted. The large lateral deformation in the process of bolt slippage is put forward for the first time. Numerical and experimental results show that large lateral deformation makes the stiffness of bolt joint smaller.

Progressive bearing failure modeling of composites with double-bolted joints at mesoscale level

Both numerical and experimental researches are carried out to study the strength of the composite double-bolted joints and the bearing damage propagation. A mesoscale level progressive damage model along with analytical formulation is used to predict the bearing failure of carbon–epoxy composite plates. This damage model is introduced as a user material subroutine in the commercial software ABAQUS, and the maximum failure load is calculated. In order to validate the numerical results, experimental tests are also conducted in which comparison between the results shows an excellent agreement. Furthermore, the effects of the bolt distances on the maximum failure load are studied. The results reveal that there is an optimum bolt distance that outcomes maximum failure loads.