Tubular Single Lap Joint Research Articles

Failure analysis of adhesively bonded tubular joints of laminated FRP composites subjected to combined internal pressure and torsional loading

Finite element analysis has been carried in the present research to study individual and combined effect of internal pressure and torsional loading on stress and failure characteristics in case of an adhesively bonded Tubular Single Lap Joints (TSLJ) made of laminated Fiber reinforced polymer (FRP) composite materials. Effect of changing torsional load magnitude on an internally pressurised adhesively bonded TSLJ on interlaminar stresses and onset of different joint fracture modes (adhesion and cohesion failures) has also been studied in the present analysis. Three dimensional stress analysis of the adhesively bonded TSLJ has been carried out through suitable ANSYS Parametric Design Language (APDL) of ANSYS 14.0. Tsai-Wu coupled stress criterion has been used for predicting the onset of joint failures in the TSLJ. It has been observed that stresses (σr, σθ, σz, τrz) induced within the joint region under pure internal pressure loading are least affected through introduction of a torsional loading in the TSLJ. However, the stresses (τrθ and τθz) which are considered to be significant under pure torsional loading get tremendously enhanced due to the varying torsional loading. The interface between the outer tube and adhesive of the TSLJ has been observed to be the most critical bondline interface which is prone to undergo adhesion failure towards the free edges under pure internal loading conditions. However, under pure torsional loading conditions it tends to fracture through adhesion failure towards the clamped edge of the TSLJ. Under combined torsional and internal pressure loading the joint fails towards the clamped edge of the along the critical path which happens to be within the bondline interface, indicating predominance of torsional loading over the pure internal pressure loading. A comparative study based on the magnitude of failure index revealed that torsional loading marginally affects the joint failure as the internal pressure loading improves the compactness of the bonded joint hence improving the resistance of the TSLJ against initiation of joint fractures.

Regularization of torsional stresses in tubular lap bonded joints by means of functionally graded adhesives

This paper describes the analytical stress analysis of a tubular single lap joint under torsion with a functionally graded modulus adhesive (FGA). The adhesive technology offers several advantages in structural applications, such as bonding dissimilar materials, but suffers from severe stress concentrations in the bondline which often act as a trigger for fracture phenomena. To overcome these problems, FGA with nanoparticles distributed inside the polymer can be used, as proposed recently in technical literature. The aim of the work is to retrieve which is the optimal stiffness of the adhesive layer to regularize the stresses. The peculiar geometry analyzed permits a straightforward analytical approach since pure torsion on tubes do not cause any bending and no Poisson's effect creates peel stress in the adhesive, therefore only shear stress are to be considered. The work first develops the equations which govern the shear stress distribution in the adhesive and then by forcing the shear stress to be constant is able to find out which is the stiffness profile along the bondline. The axial distribution of the stiffness of the FGA layer along the overlap is provided and the dependence on the elasto-geometrical parameters is discussed. The findings of the paper can be used to tailor the reinforcement distribution, under the hypothesis of a continuously changing adhesive stiffness.

Delamination damage analysis of laminated bonded tubular single lap joint made of fiber-reinforced polymer composite

Onset and growth of delamination damages in laminated fiber-reinforced polymer composite made bonded tubular single lap joints have been thoroughly studied through a finite element analysis-based simulation technique developed in the present research. The model provides sufficient scope for a comprehensive parametric study of the bonded structure in terms of three-dimensional stress analyses within the joint, studying the delamination damage onset and growth characteristics, and investigating its effect on stress distributions in the joint and both the adherends (outer and inner). Quadratic failure criterion has been used to depict delamination damage-induced cohesion failure within the adhesive layer. Whereas Tsai–Wu coupled stress criterion has been used for locating the delamination and adhesion failure prone regions at ply-interfaces of the adherends and adherend–adhesive interfaces within the joint, respectively. Three-dimensional stress analyses revealed that outer adherend of the bonded tubular single lap joints experiences comparatively higher interlaminar peel ([Formula: see text]) and shear stress ([Formula: see text]) concentrations at the free edge of the first ply-interface and is likely to delaminate at this edge. Accordingly, pre-embedded through-the-circumference delamination damages have been simulated at this edge, and contact finite element analyses have been performed in order to avoid interpenetration of delaminated surfaces. Strain energy release rate calculated using modified crack closure integral vis-à-vis virtual crack closure technique has been used as the characterizing parameter for assessing the growth of the damages. Free edge delamination in the outer adherend has been observed to propagate in a self-similar manner mainly in the in-plane shearing mode. It causes peel and shear stress concentrations in regions of the adherend–adhesive interfaces and first ply-interface of the inner adherend, localized to the clamped edge of the joint making the joint and the adherend prone to adhesion failure and delamination damage, respectively.

Modelling and Simulation of Delamination Damages in Analyses of Laminated FRP Composite Made Bonded Tubular Single Lap Joints

The present research deals with a Finite Element (FE) based simulation technique for the through-the–circumference delamination damage analyses of Tubular Single Lap Joints (TSLJ) in laminated FRP composites. ANSYS a FE based software has been used for this simulation. Three-dimensional non-linear FE analyses have been carried out to study the effects of through-the-circumference delaminations on interlaminar stresses in the bonded TSLJ. Stress analyses revealed that the interface of surface ply (in contact with the adhesive) with the next ply i.e. first ply-interface of both the adherends shows maximum intensity of interlaminar out-of-plane stress concentration, which is gradually reduced for the subsequent ply-interfaces. Tsai-Wu coupled stress criterion has been used to identify the location of delamination damage initiation in the adherends. Accordingly, free edges of the first ply-interfaces of both the adherends showing maximum values of failure index are simulated with delamination damages using sub laminate technique. Contact FE analyses have been performed in order to avoid interpenetration of delaminated surfaces

Free Vibration Analysis of an Adhesively Bonded Functionally Graded Tubular Single Lap Joint

In this study, the three-dimensional free vibration analysis of an adhesively bonded functionally graded tubular single lap joint was carried out using the finite element method. The functionally graded tubes of the adhesive joint are composed of ceramic (Al2O3) and metal (Ni) phases varying through the tube thickness. The adhesive material properties, such as modulus of elasticity, Poisson's ratio, and density were found to have negligible effect on the first ten natural frequencies and mode shapes of the adhesive joint. The optimal design parameters of the adhesive joint, such as overlap length, inner radius of the inner tube, outer and inner tube thicknesses, and the through-the-thickness material composition variation were searched using both the artificial neural networks (ANNs) and the genetic algorithms (GAs). For this purpose, the natural frequencies and modal strain energy values were calculated for an adhesive joint with random geometrical properties and material compositions through the tube thicknesses, and were used for training the proposed artificial neural network models. The outer tube thickness, the inner tube-inner radius, and the compositional gradient exponent had considerable effect on the natural frequencies, mode shapes, and modal strain energies of the functionally graded tubular single lap joint, whereas the overlap length and the inner tube thickness had a minor effect. The GAs integrated with ANNs was employed to determine optimal design parameters satisfying both maximum natural frequency and minimum modal strain energy conditions for each natural mode of the tubular adhesive joint.

Adhesion failure analyses of bonded tubular single lap joints in laminated fibre reinforced plastic composites

This research presents a finite element based simulation technique for the analysis of adhesively bonded joints in tubular Fibre Reinforced Plastic (FRP) composite structures using Finite Element Method (FEM). Results of the bonded Tubular Single Lap Joint (TSLJ) have been compared with those available in literature and are found to be in good agreement. Effective overlap length for suitable performance of the joint is determined based on the Tsai-Wu failure criterion. Three-dimensional stress analyses have been carried out which revealed the importance of not neglecting the three-dimensional effects in the joint. Shear stress ( τ θr ) is found to be extremely sensitive to three-dimensional effects as compared to other out-of-plane stresses ( τ zr , σ r ). Failure indices at different critical interfaces are evaluated using Quadratic Failure Criterion (QFC) within the adhesive and Tsai-Wu coupled stress criterion for the adherend–adhesive interfaces. Based on the later criteria, locations prone to adhesion failure initiation are identified to be existing at the interface of the loaded tube and the adhesive at the edge of the overlap length nearer to the clamped end of the TSLJ. Strain Energy Release Rate (SERR) calculated using Virtual Crack Closure Technique (VCCT) is used as the characterizing parameter for assessing the growth of adhesion failure. Adhesion failure damage propagation has been observed to be self-similar and it is found to propagate mainly in inplane shearing mode. Angle-ply fibre oriented adherends are found to be more susceptible to the opening mode of adhesion failure, whereas GR/E [45/−45] 4s and GR/E [30/60] 4s fibre oriented adherends are least resistive to mode-II growth of adhesion failure. Plies oriented in the direction of applied load, especially GR/E [90] 16, are found to offer better resistance to both the opening and inplane shearing mode growths of adhesion failure and hence are the most preferred fibre orientations for the bonded TSLJ under tension. Increasing the degree of anisotropy of the composite adherends improves the adhesion failure damage growth resistance. Boron/Epoxy (B/E) FRP composites are found to be the best among the various FRP composite adherends considered in the present study.

Free Vibration Analysis and Optimal Design of a Cantilevered Adhesively Bonded Composite Tubular Single Lap Joint

This study reports the most effective design parameters for the three-dimensional free vibration and modal stress state of an adhesively bonded cantilevered composite tubular single lap joint. The effects of fibre angle, fibre volume fraction, overlap length, tube thicknesses and inner tube radius on the first ten natural frequencies and mode shapes of the adhesive tubular joint were investigated, using the back-propagation Artificial Neural Network (ANN) method. In order to train and test the proposed artificial neural network models used to predict the first ten natural frequencies, as well as the corresponding modal strain energies, a series of free vibration and stress analyses was carried out. The finite element method was used for random values of the design parameters, such as the fibre angle, the fibre volume fraction, the overlap length, the tube thicknesses and the inner tube radius. The ANN models indicated that increasing each of all the design variables resulted in increases in the first ten natural frequencies as well as in the modal strain energies, whereas increasing the inner tube thickness reduced the natural frequencies but increased the modal strain energies. The fibre angles above 20° and the inner tube radius were more effective design parameters than the overlap length and the outer tube thickness. The Genetic Algorithm indicated completely different values of the design parameters of an optimal joint based on three objective functions, in which i) the natural frequency only was maximised, ii) the modal strain energy was minimised and iii) the previous objective functions were balanced. Thus all design parameters were maximised as possible except the inner tube thickness, and the fibre volume fraction became optimal at 70%.

Nonlinear analysis of adhesively bonded tubular single-lap joints for composites in torsion

The nonlinear analysis of tubular single-lap adhesive joints with composite adherends was performed by incorporating the nonlinear behavior of the adhesive into the analysis. For this purpose, the stress and strain in the laminated composite tube were first calculated under a general loading scheme, and then the iterative solution of the joints was derived by including the nonlinear properties of the adhesive. The stress distributions in the adhesive were investigated for different types of composite adherends and compared with the results of the linear analysis. The effect of the bonding length on torque transmission capability was also taken into consideration. The results indicate that the nonlinear analysis relieves the stress concentration at the edge of the joint, resulting in a more accurate prediction of joint strength.

Stress Analysis of an Adhesively Bonded Functionally Graded Tubular Single Lap Joint Subjected to an Internal Pressure

Stress Analysis of an Adhesively Bonded Functionally Graded Tubular Single Lap Joint Subjected to an Internal Pressure

Thermal residual stresses in an adhesively bonded functionally graded tubular single lap joint

Elastic thermal residual stress analysis of an adhesively bonded functionally graded tubular joint was carried out for a uniform temperature drop using an isoparametric axisymmetric layered finite element. The hoop stress σ θθ , axial stress σ zz and transverse shear stress σ rz were dominant for both free and constrained models of the tubular joint. The stress concentrations occurred around the adhesive free ends, especially at the left and right free edges of the inner tube–adhesive interface and at the left free edge of the outer tube–adhesive interface. Increasing layer number played important role on the peak stress values in the ceramic layer of the metal-rich composition and in the metal layer of ceramic-rich composition since a sudden transition between two phases in these layers, whereas its effect on the through-the-thickness stress profiles was minor. In addition, the through-the-thickness stress profiles at the critical locations in both tubes and in the adhesive layer were affected evidently by the directional material composition variation. The compositional gradient had a minor effect on the through-the-thickness stress profiles whereas only the peak stress values were affected. The hoop, axial and shear stresses increased with increasing compositional gradient. In the free joint model, the effects of the compositional gradient, layer number and the directional compositional variation on the through-the-thickness stress variations were apparent whereas the effect of the boundary condition became noticeable in the constrained joint model.

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.

Temperature effects on the torsional fatigue characteristics of adhesively bonded tubular single-lap joints

Rubber-toughened structural epoxy adhesives are widely used for bonding structures because of their high toughness characteristic. However, the mechanical properties of structural epoxy adhesives degrade much at high environmental temperature, which affects the performance of the adhesive joints severely. Therefore, in this study, the temperature effects on the static and fatigue characteristics of adhesively-bonded tubular single-lap joints were measured. Then the relations between the parameters of S-N curves and the static strength of adhesively-bonded tubular singlelap joints were obtained, from which a fatigue life prediction model for the adhesively-bonded tubular single-lap joints at elevated temperatures was developed.

Geometrically non-linear thermal stress analysis of an adhesively bonded tubular single lap joint

In this study, the geometrically non-linear thermal stress analysis of an adhesively bonded tubular single lap joint subjected to airflows having different temperature and velocity outside and inside its inner and outer tubes was carried out using the incremental finite element method. Since the thermal expansion coefficients of tubes and adhesive were different the thermal strains arising along the adhesive–tube interfaces resulted in high thermal stresses in the adhesive layer and tubes for different end conditions applied to the ends of its outer and inner tubes. The joint region was considerably deformed, and serious stress concentrations occurred around the adhesive free ends. This effect became more evident in cases the tube edges were fully restrained. The peak thermal adhesive and tube stresses occurred at the free ends of the adhesive–tube interfaces. In addition, increasing the overlap length had an effect of reducing the peak adhesive and tube stresses, and an optimum overlap length/joint length ratio of 0.2 was determined.

Prediction of the Tensile Load Capability of Co-Cured Steel-Composite Tubular Single Lap Joints Considering Thermal Degradation

Co-cured joints composed of composite and steel structures are realized by the excess resin extracted during cure of composite prepreg and the coupling pressure due to residual thermal stresses generated by the difference of coefficients of thermal expansion between the two materials. Although the excess resin from the composite prepreg is less dependent on the environmental temperature compared to conventional epoxy adhesives in which rubber is added to strengthen toughness, the coupling pressure is much dependent on the environmental temperature. In this study, the tensile load capability of co-cured joints composed of carbon fiber epoxy composite and steel adherends was experimentally investigated with respect to the stacking sequence of the composite and the environmental temperature. Also, the stress distributions in the composite were calculated by finite element method, from which the failure index of the composite adherend was calculated considering thermal degradation of the composite. The co-cured steel-composite tubular single lap joint under tensile loads might be applied to hybrid structures such as golf clubs and automotive composite propeller shafts which have a conventional adhesively-bonded joint by epoxy adhesives with fillers between a carbon/epoxy shaft and a metal shaft.

Optimum design of co-cured steel–composite tubular single lap joints under axial load

In this paper, an optimum design method for co-cured steel-composite tubular single lap joints under axial load is proposed based on a failure model which incorporates the nonlinear mechanical behavior of the steel adherend and the failure mode of joints such as composite adherend failure and steel adherend failure. The design parameters considered were the test temperature, the stacking sequence of the composite adherends, the thickness ratio of the steel adherend to the composite adherend, and the existence of scarf in the steel adherend. Stress analysis of the cocured steel-composite tubular single lap joints was performed considering the nonlinear mechanical behavior of the steel adherend, and the fabrication residual thermal stress and thermal degradation of the composite adherend. The method developed may be employed in the joining of hybrid composite structures such as golf clubs and automotive composite propeller shafts in which a carbon/epoxy shaft has normally been bonded to a metal shaft with epoxy adhesives.

The effects of surface roughness and bond thickness on the fatigue life of adhesively bonded tubular single lap joints

Since the surface roughness of adherends greatly affects the strength of adhesively bonded joints, the effect of surface roughness on the fatigue life of adhesively bonded tubular single lap joints was investigated analytically and experimentally by a fatigue torsion test. The stiffness of the interfacial layer between the adherends and the adhesive was modelled as a normal statistical distribution function of the surface roughness of the adherends. From the investigation, it was found that the optimum surface roughness of the adherends for the fatigue strength of tubular single lap joints was dependent on the bond thickness and applied load.

Optimum Design of Co-cured Steel-Composite Tubular Single Lap Joints

In this paper, a failure model for co-cured steel-composite tubular single lap joints has been proposed incorporating the nonlinear mechanical behavior of steel adherends and different failure mode s such as steel adherend failure and composite adherend failure. The characteristics of the co-cured steel-composite tubular single lap joint were investigated with respect to the test temperature, the stacking sequence of composite adherend, the thickness ratio of steel adherend to composite adherend, and the scarf ratio of steel adherend. Thus, the optimum design method for the co-cured steel-composite tubular single lap joint was suggested

Prediction of the Tensile Load Capability of Co-cured Steel-Composite Tubular Single Lap Joints Considering Thermal Degradation

Co-cured joints composed of composite and steel structures are realized by the excess resin extracted during cure of composite prepreg and the coupling pressure due to residual thermal stresses generated by the difference of coefficients of thermal expansion between the two materials. Although the excess resin from the composite prepreg is less dependent on the environmental temperature compared to conventional epoxy adhesives in which rubber is added to strengthen toughness, the coupling pressure is much dependent on the environmental temperature. In this study, the tensile load capability of co-cured joints composed of carbon fiber epoxy composite and steel adherends was experimentally investigated with respect to the stacking sequence of the composite and the environmental temperature. Also, the stress distributions in the composite were calculated by finite element method, from which the failure index of the composite adherend was calculated considering thermal degradation of the composite. The co-cured steel-composite tubular single lap joint under tensile loads might be applied to hybrid structures such as golf clubs and automotive composite propeller shafts which have a conventional adhesively-bonded joint by epoxy adhesives with fillers between a carbon/epoxy shaft and a metal shaft.

Strength of Adhesively-Bonded Thbular Single Lap Carbon/Epoxy Composite-Steel Joints

The static tensile load bearing capability of adhesively-bonded tubular single lap joints if calculated using the linear mechanical adhesive properties is usually less than the experimentally determined one because the majority of the load transfer of adhesively-bonded joints is accomplished by the nonlinear behavior of the rubber-toughened epoxy adhesive. In this paper, both nonlinear mechanical properties and fabrication residual thermal stresses of adhesive were included in the stress calculation of adhesively-bonded tubular single lap carbon/epoxy composite-steel joints. During calculation, nonlinear tensile properties of adhesive were approximated by an exponential equation that was represented by the initial tensile modulus and ultimate tensile strength of adhesive obtained from tensile tests. From the tensile tests and the stress analyses of adhesively-bonded tubular single lap carbon/epoxy composite-steel joints with respect to stacking angles of carbon/epoxy composite adherends, the failure model for the adhesively-bonded tubular single lap carbon/epoxy composite-steel joint under the axial tensile load was proposed with considering fabrication residual thermal stresses.

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.