Tubular Lap Joints Research Articles

Failure Analysis of Hybrid FREP Composites Laminated Bonded Tubular Lap Joints

Fibre-reinforced polymer composites have found extensive applications in the oil, gas industries. The use of interlayer Hybrid composite pipes are used in several engineering applications is increasing due to their superior properties such as high specific strength, high chemical resistance and resistance to UV rays .Hybrid composite adherends lap joints need to be explored to develop a cost-effective combination of materials to address the certain complex behavior due to hybridization . It is essential to understand the mechanical behavior of Hybrid Tubular Lap Joints (HTLJ) to provide design guidelines for safe performance of joint. In the present work Failure analysis of the adhesively bonded HTLJ is performed. Stress distributions within the joint region are estimated under tensile load. Failure indices at critical interfaces are evaluated by using Quadratic Failure Criterion (QFC).The failure index values of HTLJ were obtained for different overlap lengths. Effective overlap length for suitable performance of the joint is determined based on the Tsai-Wu failure criterion.

Strength Analysis of Structurally Optimized Aluminium-Composite Tubular Lap Joints

AbstractTruss structures are a stiff, economical, and efficient lightweight design, the limiting factor of these structures are usually the load transfer elements. This paper presents an analytical design method for optimized adhesive tubular lap joints between CFRP tubes and aluminium inserts. The analytically optimized design agrees very well with the numerical simulations and experimental results. Although the experiments show a highly non-linear behaviour, where a linear elastic correlation is expected, the total load capacity is only reached when the adhesive is fully plasticised.

Stress distribution in laminated composite tubular joints with damaged adhesive layer under torsion

ABSTRACT This study investigates the effect of geometric and mechanical properties of the adherends and adhesive layer on the shear stress distribution in a damaged adhesively bonded tubular lap joint (laminated composite to steel) under pure torsion. Using first-order shear deformation theory, the equilibrium equations are deduced and solved by the generalized differential quadrature (GDQ) method, results of which were compared and verified with those of finite element solution. Results show that for the steel and [±15]10 composite adherends, increasing the elastic modulus of the adhesive layer increases the maximum shear stresses in the adhesive layer while increasing the joint length beyond its so-called effective bond length has no additional effect on the peak shear stress in the adhesive. Additionally, selecting a quasi-isotropic lamination setup instead of [±15]10 reduces the peak shear stress, where the use of an orthotropic tube with the lamination sequence of ±45° further reduces this magnitude. Additionally, depending on the size and location of a void or debond in the adhesive layer, the peak shear stresses can gain higher values, with almost similar behaviors for the two defects. Nonetheless, for defects far enough from the adhesive ends, their effects on the adhesive peak shear stress seemed to be negligible.

Mechanical behavior and failure mechanisms of CFRP and Titanium tubular adhesive lap joints at extreme temperatures

In this study, the mechanical behavior and failure mechanisms of thin-walled carbon fiber reinforced polymer (CFRP) and titanium adhesive tubular lap-joints (TLJs) at cold-temperature, room-temperature, and elevated-temperature are investigated. The prediction of TLJ’s performance at extreme temperatures is challenging due to their non-linear behavior and competing damage modes. To better understand their behavior, finite element analysis, static tensile tests, and design of experiments are employed to investigate the competing damage mechanisms within the TLJs, leading to a more detailed damage classification at extreme temperatures. Results show a mixed-mode failure region at elevated-temperature, where TLJs fail by either interlaminar shear or titanium net-section fracture. X-ray micro-computed tomography reveals that the initiation, propagation, and coalescence of delamination at the inserted end of the CFRP are created by shear stresses during deformation of the titanium. By utilizing numerical, experimental, and statistical techniques, this work aims to provide insights into the parameters and damage mechanisms affecting the performance of adhesively bonded thin-walled TLJs at extreme cold and hot temperature conditions.

Numerical evaluation of tensile-loaded tubular scarf adhesive joints

Tubular adhesive joints are widely employed when joining tubes and rods. The loads to which these joints are subjected may be axial or torsional. When loaded in the axial direction, cylindrical joints present stress concentrations in the adhesive layer, as is the case of lap joints. To improve the joint strength in the axial direction, the cross-section of the tubes can be chamfered to produce a scarf tubular joint. The geometrical variations produced by machining the chamfers increase the overall bonding area, leading to higher joint strength. This study aims to compare the tensile performance of tubular scarf joints (TSJ) with aluminium (AW6082-T651) adherends, considering the variation of the scarf angle (α) from 45° to 3.43°; the joints were bonded with a moderately ductile adhesive, the Araldite® 2015. Firstly, through the comparison of experimental tests and numerical analysis of tubular lap joints (TLJ), the cohesive zone model (CZM) technique and respective cohesive parameters were validated. A CZM analysis was then performed on the TSJ to analyse peel (σy) and shear stresses (τxy) in the adhesive layer. Damage and joint strength analyses were also carried out, as well as the study of the dissipated energy for the different joint configurations. The CZM technique was validated, and the numerical analysed showed a major α effect, with benefits for smaller α, and improved stress distributions over TLJ.

Damage and strength analysis of Carbon Fiber Reinforced Polymer and Titanium tubular-lap joint using hybrid adhesive design

In this study, a Tubular-Lap Joint (TLJ) damage model for Titanium (Ti) and Carbon Fiber Reinforced Polymer (CFRP) is developed to study novel hybrid adhesive joints. The damage model is performed by Finite Element Analysis using Cohesive Zone Modeling to understand stress analysis and investigate damage evolution of failure mechanisms, namely delamination, adhesive and cohesive failure. Results from the numerical damage model are validated with published experimental data from the literature to determine the accuracy of the model. The damage model is further employed to study novel hybrid adhesive joints, utilizing the benefits of brittle (high stiffness and high strength) and ductile (high elongation and high fracture toughness) adhesives to improve CFRP-Ti TLJ performances. This study verifies the importance of geometry considerations for adhesive joints and provides solutions to increase joint strength by utilizing a hybrid adhesive approach.

Experimental investigation on the mechanical behavior of hybrid bonded (rivet/adhesive) tubular lap joint (composite to metal) under pure torsion

The hybrid joints being used in the design of mechanical structures because of their significant advantages. The tubular lap joints are used widely in aerospace, naval, and transport industries such as rudder and elevator rods, driving shafts, pull push rods, anti-roll bar and stabilizer bar in cars, trucks and trains. The torsional behavior of mechanical, adhesively bonded, and hybrid tubular lap joints for aluminum to aluminum, and composite to aluminum subjected to pure torsion have been investigated experimentally. The effect of outer tube material and thickness, the joint’s type, and cured and post-cured temperature (room temperature and 40 °C), have been investigated experimentally. A fixture and a torsional set-up device have been designed and manufactured to apply the required torque to the joint. The outcomes from composite to aluminum joints confirm that the hybrid joint has 39.5% and 276.6% higher torque capacity than the mechanical joint and adhesively bonded joint, respectively. Furthermore, the cured and post-cured process at 40 °C, increased the maximum torque to failure, 37.6% and 57.1% for adhesively bonded and hybrid (rivet/bonded) joint, respectively. It has been observed that by upgrading the mechanical joint and adhesively bonded joint to the hybrid (rivet/bonded) joint, increasing the amount of joint’s strength and torque capacity in comparison with the increase in the weight of the structure is affordable.

Stress analysis of adhesive-bonded tubular-coupler joints with optimum variable-stiffness composite adherend under torsion

In this paper, a mathematical model of an adhesive-bonded tubular-coupler joint with a variable-stiffness composite coupler is formulated. The joint is assumed to be axisymmetric, linearly elastic, and subjected to a uniform torsion. Due to symmetry the joint is considered as a pair of two identical tubular-lap joints. Varying fiber orientation is analyzed by discretizing a tubular-lap joint into a finite number of sufficiently small segments, each of which can be approximated to have constant fiber angle. Stresses developed in the joint are determined by employing elasticity equations. This model is applied to search for the optimal variable-fiber orientation in the coupler that induces the minimum adhesive hoop shear stress. Finally, the influence of geometries of the optimum joints on all of the stress components in the adherends and adhesive stresses is studied. A design guideline for the optimum coupler joint is provided at the end of the paper.

Strain energy release rate based damage analysis of functionally graded adhesively bonded tubular lap joint of laminated FRP composites

ABSTRACTStrain energy release rate (SERR) based damage analyses of functionally graded adhesively bonded tubular lap joints of laminated fiber reinforced plastic (FRP) composites under varied loadings have been studied using three-dimensional geometrically non-linear finite element (FE) analyses. FE simulations have been carried out when a tubular joint is subjected to axial and pressure loadings. SERR is utilized as the characterizing and governing parameter for assessing damages emanating from the critical location. Individual and total SERR over the damage front have been computed using modified crack closure integral (MCCI) based on the concept of linear elastic fracture mechanics. Results reveal that damage initiation locations in tubular joints subjected to axial and pressure loadings are entirely different. Furthermore, modes responsible for propagation of such damages in tubular joints under axial and pressure loadings are also different. Based on the FE simulations, tubular joints under pressure loading are found to be more vulnerable for damage initiation and its propagation. Furthermore, the damage propagation behavior of tubular joints with pre-embedded damages at the critical location has been compared between conventional mono-modulus adhesives and functionally graded adhesives with appropriate material gradation profile. Results indicate that material gradient profile of the adhesive layer offers excellent reduction in SERR for shorter interfacial failure lengths in tubular joints under axial loading which is desired to delay the damage growth. Improved crack growth resistance in the joint enhances the structural integrity and service life of the tubular joint structure. However, considerable reduction in SERR has not been noticed in the said joint when subjected to pressure loading. Hence, the use of functionally graded adhesive along the bond layer is recommended for the designer/technologist while designing tubular joint under general loading condition.

Environmentally friendly joining of tubes by their ends

Abstract This paper proposes an environmentally friendly joining process for connecting tubes by their ends that has the potential to replace current solutions based on fastened, crimped, welded, brazed or adhesive bonded joints. The process is based on a new type of tubular lap joint produced by local plastic instability and compression beading that has a substantial overlap with the counterfacing surfaces of the mating tubes to be joined. The presentation combines independent characterization of the materials, experimentation and numerical simulation of the process in order to identify the modes of deformation and the process feasibility window, and destructive testing to establish the working limits of tubular lap joints under different type of loading conditions. Results demonstrate that the proposed joining process is a flexible and cost-effective technology for connecting tubes by their ends with a better performance than current environmentally friendly alternatives based on tubular butt joints produced by plastic deformation.

A multi-objective optimization procedure for bonded tubular-lap joints subjected to axial loading

A multi-objective optimization method was used to identify globally optimized configurations of bonded tubular single-lap (TSL) joints bearing axial load. Designs for optimal bonding of TSL joints often face conflicting objectives: in general, the main source of conflict centers around minimizing the mass and maximizing the mechanical strength of the joint. This paper presents a three-step method in providing TSL joint configurations which represent the best compromises between these objectives. This method involves creating a fully parameterized finite element model, a parametric study, defining and computing the optimization studies. The parametric study shows that all geometric parameters, aside from the substrates extremity angle, influence the stress profile in the adhesive. Based on the scope of application, the optimization problem is set to consider six optimization variables, four objectives and three constraints. Four studies were conducted with the mass of the joint and the maximum normal, shear, and/or equivalent stress in the adhesive as objectives. The three-step procedure provides 27–173 optimal configurations for all studies and favors mostly joints with a thin layer of adhesive, a long adhesive bond length, and a large inner diameter of internal substrate.

Analysis of tubular adhesive joints with a functionally modulus graded bondline subjected to axial loads

The strength and lifetime of adhesively bonded joints can be significantly improved by reducing the stress concentration at the ends of overlap and distributing the stresses uniformly over the entire bondline. The ideal way of achieving this is by employing a modulus graded bondline adhesive. This study presents a theoretical framework for the stress analysis of adhesively bonded tubular lap joint based on a variational principle which minimizes the complementary energy of the bonded system. The joint consists of similar or dissimilar adherends and a functionally modulus graded bondline (FMGB) adhesive. The varying modulus of the adhesive along the bondlength is expressed by suitable functions which are smooth and continuous. The axisymmetric elastic analysis reveals that the peel and shear stress peaks in the FMGB are much smaller and the stress distribution is more uniform along its length than those of mono-modulus bondline (MMB) adhesive joints under the same axial tensile load. A parametric evaluation has been conducted by varying the material and geometric properties of the joint in order to study their effect on stress distribution in the bondline. Furthermore, the results suggest that the peel and shear strengths can be optimized by spatially controlling the modulus of the adhesive.

Strength based reliability of adhesively bonded tubular lap joints

The strength of adhesively bonded tubular lap joints is affected by various factors, which are diametrical clearance, type of assembly, type of material, operating temperature, loading type, surface roughness, etc. Since many factors affect the strength of adhesively bonded joints, there are doubts concerning the reliability of this type of joining technology. In this study, a total of 44 adhesively bonded tubular lap joint specimens were produced for the strength experiments, half of them were tested statically and other half were tested dynamically under defined conditions. Failure loads of 12 specimens were experimentally found and 10 specimens were loaded without failure under both static and dynamic loading conditions. The reliability of joints was determined on the basis of randomly selected applied loads.

Elastic stresses in an adhesively-bonded functionally-graded tubular single-lap joint in tension

In this study, the elastic stress analysis of an adhesively-bonded tubular lap joint with functionally-graded Ni-Al2O3 adherends in tension was carried out using a 3D 8-node isoparametric multilayered finite element with 3 degrees-of-freedom at each node. Stress concentrations were observed along the edges of both outer and inner tubes in the overlap region. Thus, the outer tube region near the free edge of the inner tube and the inner tube region near the free edge of the outer tube experienced considerable stress concentrations. Normal σzz and shear σrz stresses were dominant among the stress components. In addition, both edges of the adhesive layer experience stress concentrations, and the von Mises σ eqv stress decreases uniformly across the adhesive thickness at the free edge of the outer tube, whereas it increases at the free edge of the inner tube. However, different compositional gradients had only a small effect on the through-the-thickness normal and shear stress profiles of both outer and inner tubes, and the peak von Mises σ eqv stresses occurred inside the tube walls. As the ceramic phase in the material composition of the outer and inner tubes was increased, peak von Mises σ eqv stress appeared in the ceramic layer. However, its magnitude was increased 1.75-fold in both tubes. In addition, the peak adhesive stresses appeared at the edge of the outer tube–adhesive interface near the free edge of the inner tube and at the edge of the inner tube–adhesive interface near the free edge of the outer tube. Increasing the ceramic phase in the material composition caused 1.22–1.67-times higher von Mises stresses along the free edges of the adhesivetube interfaces. In addition, with increasing number of layers across the inner and outer tubes the profiles of the normal σzz , shear σr and von Mises σ eqv stresses across the tube walls and adhesive layer become similar. Increasing the ceramic phase in the material composition of the tubes causes also evident increases in the normal σzz and von Mises stresses while it does not affect their through-the-thickness profiles. However, it affects only shear σr and von Mises stresses across the adhesive layer. Finally, the layer number and the compositional gradient do not affect considerably through-the-thickness normal and shear stress profiles but levels in a functionally graded plate subjected to structural loads.

トラスモデルによるコンクリート充填鋼管差し込み形式柱継手の荷重-変形骨格曲線算定法

A Concrete-Filled Tubular Lap-Joint is a coupling where a slightly smaller circular steel tube is inserted to another circular steel tube, and the gap between tubes is filled up with mortar if necessary. In this paper, an elasto-plastic analysis to estimate relationship between deformation and external force in the model that substituted a truss for outside steel tube was suggested. In addition, analysis results were compared with results of experiments, and the elastic stiffness almost agreed with experimental value, but it was shown that the evaluation was slightly conservative after yield.

Optimization of tubular double lap‐joint configuration

AbstractThe potential of using composite materials with a polymer base in the automotive industry has grown rapidly. However, one of the main problems encountered is bonding the composite part to metal conventional parts. This paper studies a proposed tubular double lap joint to bond a composite shaft to a metallic end. The automotive driveshaft will be taken as an application throughout this paper. A mathematical model of this joint is presented and a finite element solution has been carried out in order to validate the mathematical model. The optimization objective is to minimize the shear stress level in the adhesive layer. The results show that one can obtain up to 50% reduction in the level of adhesive shear stress. This can be achieved through an optimum selection of lap geometry.

Nonlinear Analysis of theTorque Transmission Capability of Adhesively Bonded Tubular Lap Joints

Calculated torque transmission capability of adhesively bonded tubular lap joints using linear elastic material properties is usually much less than the experimentally-determined one because the majority of the load transfer of the adhesively bonded joints is accomplished by the nonlinear behavior of rubber-toughened epoxy adhesives. Although the adhesively bonded tubular double lap joint has better torque transmission capability and reliability than the single lap joint, the nonlinear analytic or numerical analysis for the adhesively bonded tubular double lap joint has not been performed because of numerical complications. An iterative solution that includes the nonlinear shear behavior of the adhesive was derived using the analytic solution. Since the iterative solution can be obtained very quickly due to the simplicity of the algorithm, it is an attractive method of designing adhesively bonded tubular single and double lap joints.

Hygrothermal effects on the strength of adhesively bonded joints

The strength of adhesively bonded joints degrades when the joints are exposed to a high temperature or high humidity environment because of the degradation of the adhesive. In this paper, the strength and modulus of adhesives under hygrothermal environments were measured with respect to the absorbed moisture content and temperature. Then the strength of adhesively bonded tubular lap joints was investigated with respect to the absorbed moisture content. From the investigation it was found that the strength of the adhesives decreased as the absorbed moisture content increased, but the strength of the adhesively bonded tubular lap joints decreased less compared with that of the adhesives, due to the moisture swelling effect. Also, it was found that chemical surface treatments of the adherends improved the strength retention of the joint under a hygrothermal environment.

Torque Capacity of Co-Cured Tubular Lap Joints

The co-cured joint is an efficient joining technique because both curing and joining for composite structures are achieved simultaneously. In this paper, the torque capacities of the co-cured tubular lap joint with and without knurling of the pyramid type were experimentally measured. From the experiment, it was found that the excess resin of composite prepreg should not be extracted much because the excess resin played a role as an adhesive in the co-cured tubular lap joint whose steel adherends were not knurled. Also, it was found that the torque capacity of the co-cured joint was increased as the knurling size of the pyramid type on the surface of the steel adherend was increased.

A Study on the Strength and Failure Mode of Co-cured Composite Joints

The joint design and manufacture of the composite structure have become an important research area because the structural efficiency of the composite structure is often determined by its joint not by its basic structure. The co-cured joint is an efficient joint technique because both curing and jointing for composite structures are achieved simultaneously. In this paper, the torque capacities of the co-cured tubular lap joint with and without knurling of the pyamid type were experimentally measure. From the experimental resuts, it was found that the excess resin played a role as an adhesive in the co-cured tubular lap joint whose steel adherends were not knurled. Also, it was found that the torque capacity of the co-cured joint was increased as the knurling size of the pyramid type on the surface of the steel adherend was increased.