Stress Analysis Of Adhesive Joints Research Articles

An improved four-parameter model with consideration of Poisson’s effect on stress analysis of adhesive joints

An improved four-parameter model considering Poisson’s effect is presented to analyze interface stresses of adhesively bonded joints. The existing theoretical models of adhesive joints analyze the adhesive layer as a beam without considering Poisson’s effect, which violates the Hooke’s law and cannot satisfy the compatibility condition of the adhesive layer; furthermore, the bending moment of the adhesive layer is neglected by assuming the thin thickness of adhesive layer. To eliminate these flaws, the present study models the adhesive layer as a 2-D elastic continuum in which both the Hooke’s law and equilibrium equations are fully satisfied. The longitudinal strain caused by the transverse stress is also considered, and it is proved to have a significant effect on the interface stress distributions. The present model regains the missing bending moment of the adhesive layer which is absent in the existing models, and it satisfies all the boundary conditions. The validity of the new model is demonstrated by its excellent agreements with the results from the numerical finite element analysis when predicting the interface stress distributions for the single-lap joints and CFRP-strengthened reinforced concrete beams, and the broader applicability of the present model can be expected. The new model developed presents explicit closed-form solutions for the interface stresses and beam forces, and it provides an accurate tool for design analysis of adhesively bonded joints or interfaces.

On the intralaminar and interlaminar stress analysis of adhesive joints in plated beams

An improved bimaterial adhesive joint model is proposed for the intralaminar and interlaminar stress analysis of adhesively-bonded interfaces in plated beams with thin or moderately thick adhesive layer. To overcome the limitations or unreasonable assumptions in the existing theoretical joint models, both the shear and normal stresses along two adherend–adhesive interfaces are assumed to be different in the present model, and the adhesive layer is modeled as a simplified 2-D elastic continuum. Deformable interfaces are assembled to establish the continuity conditions between the adherend–adhesive interfaces, and the local deformations near the end of the adhesive layer are fully captured. The longitudinal and transverse displacements of the adhesive layer are introduced as two new independent parameters, and the missing “degrees of freedom” in the conventional elastic foundation models are retrieved. Differential governing equation of an adhesively-bonded bi-layer beam is established, and explicit closed-form expressions of beam forces and interface stresses are derived. Comparisons of the present solution with the existing elastic foundation models as well as the full 2-D continuum elastic solutions by the finite element analysis are conducted to validate the presented model. Parametric studies are then conducted to reveal the roles of the adhesive thickness and local interface deformations on the stress distributions both along the adherend–adhesive interfaces (interlaminar) and through the adhesive layer thickness (intralaminar), from which a feasible measure to reduce the strain or stress concentrations is obtained. The present improved adhesive joint model in plated beams sheds light on the effect of adhesive layer thickness in bimaterial bonding assembly and provides a better understanding of potential interface debonding initiation and its propagation path.

Carbon-fibre composites for strengthening steel structures

The use of composite materials for strengthening and repair of steel structures has attracted a great deal of attention during the last years. In this paper, the research work conducted at Chalmers University of technology during the last five years in this field is reviewed. The results from various types of tests are summarized and discussed. Aspects related to stress analysis of adhesive joints, joint modification and failure modes in steel elements strengthened with bonded CFRP-laminates are discussed. Research needs within the studied problems are also highlighted.

接着継手の応力解析の現状と今後の課題

接着継手の応力解析の現状と今後の課題

Standard finite element techniques for efficient stress analysis of adhesive joints

The paper documents ongoing research in the field of stress analysis of adhesive bonded joints and aims at developing efficient and accurate finite element techniques for the simplified calculation of adhesive stresses. Goal of the research is to avoid the major limitations of existing methods, in particular their dependency on special elements or procedures not supported by general purpose analysis packages. Two simplified computational methods, relying on standard modelling tools and regular finite elements are explored and compared with the outcome of theoretical solutions retrieved from the literature and with the results of full, computationally intensive, finite element analyses. Both methods reproduce the adherends by means of structural elements (beams or plates) and the adhesive by a single layer of solid elements (plane-stress or bricks). The difference between the two methods resides in the thickness and in the elastic properties given to the adhesive layer. In one case, the adhesive thickness is extended up to the midplane of the adherends and its elastic modulus is proportionally increased. In the other case, the adhesive layer is maintained at its true properties and the connection to the adherends is enforced by standard kinematic constraints. The benchmark analyses start from 2D single lap joints and are then extended to 3D configurations, including a wall-bonded square bracket undergoing cantilever loading. One of the two simplified methods investigated provides accurate results with minimal computational effort for both 2D and 3D configurations.

Thermal non-linear elastic stress analysis of an adhesively bonded T-joint

Adhesive joints consist of adherends and an adhesive layer having different thermal and mechanical properties. When they are exposed to uniform thermal loads the mechanical-thermal mismatches of the adherends and adhesive layer result in uniform but different thermal strain distributions in the adhesive and adherends. The thermal stresses arise near and along the adherend-adhesive interfaces. The present thermal stress analyses of adhesively bonded joints assume a uniform temperature distribution or a constant temperature imposed along the outer boundaries of adhesive lap joints. This paper outlines the thermal analysis and geometrically non-linear stress analysis of adhesive joints subjected to different plate edge conditions and varying thermal boundary conditions causing large displacements and rotations. In addition, the geometrically non-linear thermal stress analysis of an adhesively bonded T-joint with single support plus angled reinforcement was carried out using the incremental finite element method, which was subjected to variable thermal boundary conditions, i.e. air streams with different temperatures and velocities parallel and perpendicular to its outer surfaces. The steady state heat transfer analysis showed that the temperature distribution through the joint members was non-uniform and high heat fluxes occurred inside the adhesive fillets at the adhesive free ends. Based on the geometrically non-linear stress analysis of the T-joint bonded to both rigid and flexible bases for different plate edge conditions, stress concentrations were observed at the free ends of adhesive-adherend interfaces and inside the adhesive fillets around the adhesive free ends, and the horizontal and vertical plates also experienced considerable stress distributions along outer surfaces. In addition, the effect of support length on the peak thermal adhesive stresses was found to be dependent on the plate edge conditions, when a support length allowing moderate adhesive stresses was present.

A three-dimensional finite element model for stress analysis of adhesive joints

This paper presents a new model for three-dimensional finite element analysis of adhesive joints. The model considers geometric and material nonlinearities and uses solid brick elements as well as specially developed interface elements. The interface elements allow the calculation of stresses at the adherend–adhesive interfaces. The application of the model to a single-lap joint is presented. The results of a linear elastic analysis highlight the three-dimensional nature of the stresses and stress concentrations at interfaces. The influence of material nonlinearities on the behavior of the joint is also discussed.

603 光ファイバー変位計による接着層の剛性率測定(OS 接着・界面)

Young's modules and Poisson's ratio of adhesive layer are important constants for stress analysis of adhesive joints. These constants are usually determined from testing of adhesive bulk material. There are controversy as to whether these constants are equal to those of adhesive, for reason that thickness of adhesive layer is very thin and stress field of adhesive layer is complicated for bonding interface. In this paper, a highly sensitive displacement measuring system using optical fiber sensor is demonstrated to exactly evaluate Yong's modules of adhesive layer in adhesive butt joints under tensile load. The apparent Yong's modules is compared with those of strain gage method and adhesive bulk material.

366 メッシュレス法による接着継手の応力解析

366 メッシュレス法による接着継手の応力解析

Effects of adherend deflections in single lap joints

The well-known analysis of the single lap joint by Goland and Reissner provided important contributions to the literature on stress analysis of adhesive joints by clarifying not only the importance of adhesive peel stresses in joint failure, but also the role of bending deflections of the joint in controlling the level of the stresses in the adhesive layer. Subsequent efforts have suggested the need for corrections to the Goland and Reissner analysis because of what have been conceived as deficiencies in the model used to describe bending deflections of the central part of the joint where a classical homogeneous beam model without shear or thickness normal deflections was used. The present paper addresses the issue through the use of a more realistic model in which adhesive layer deflections are allowed to decouple the two halves of the joint in the bending deflection analysis, as well as in the analysis of adhesive layer stresses where such a decoupling was allowed by Goland and Reissner. It is found that many of the predictions of the Goland-Reissner analysis are recovered in the limit of large adherend-to-adhesive layer thickness ratios, although substantial differences from the Goland-Reissner analysis can occur for relatively thin adherends.

Viscoelastic and viscoplastic stress analysis of adhesive joints

Abstract The viscoelastic and viscoplatic effects in an adhesively bonded joint are very important to understand. Most of the adhesives used in structural applications exhibit some viscoelastic-viscoplastic behaviour, especially at high temperatures and high stress levels. The redistribution of stresses and strains that occur in joints during the viscoelastic-viscoplastic deformation influences the strength of the joints considerably. At low load levels a linear viscoelastic material model may be applicable, and at higher load levels both linear viscoelastic and non-linear viscoplastic material models are active at the same time. This paper presents results from the stress analysis of single lap joints, both with and without a crack, and with viscoelastic and viscoplastic adhesives. The influence of the stress redistribution on the failure load of the joint is discussed, as well as a ‘rule of thumb’ which can account for the viscous effects in the engineering design. The influence of flaws in the joints is also discussed.

Viscoelastic and viscoplastic stress analysis of adhesive joints

The viscoelastic and viscoplatic effects in an adhesively bonded joint are very important to understand. Most of the adhesives used in structural applications exhibit some viscoelastic-viscoplastic behaviour, especially at high temperatures and high stress levels. The redistribution of stresses and strains that occur in joints during the viscoelastic-viscoplastic deformation influences the strength of the joints considerably. At low load levels a linear viscoelastic material model may be applicable, and at higher load levels both linear viscoelastic and non-linear viscoplastic material models are active at the same time. This paper presents results from the stress analysis of single lap joints, both with and without a crack, and with viscoelastic and viscoplastic adhesives. The influence of the stress redistribution on the failure load of the joint is discussed, as well as a ‘rule of thumb’ which can account for the viscous effects in the engineering design. The influence of flaws in the joints is also discussed.

Analysis of elastic and elastic-plastic adhesive joints using a mathematical programming approach

This paper is concerned with the stress analysis of adhesive joints. Aiming at a geometrically two-dimensional treatment of the adhesive, a linear displacement field through its thickness is assumed. Using the principle of virtual work and assuming linear elastic behaviour, equilibrium and constitutive equations are derived. In the case of a thin adhesive, these equations are simplified and the description so obtained is used also in the case of an elastic-perfectly plastic adhesive. In the case of elastic adhesive two different variational formulations are given: one in displacements and one mixed in displacements and adhesive tractions. In the elastic-plastic case a mixed formulation is given. Using these variational formulations finite element discretizations are performed. The matrix equations obtained in the elastic-plastic case are shown to be equivalent to a problem of mathematical programming: a parametric linear complementarity problem (LCP) involving derivatives. A solution algorithm previously used for contact problems with friction is proposed. As an application of the theory presented, an elastic-plastic analysis of a shear loaded adhesive joint test specimen is carried out.

Stress analysis of adhesive joints in composite structures through half-fringe photoelasticity

Half fringe photoelasticity (HFP) incorporates digital image analysis and interactive computer technology into a photoelastic system. The image analysis sytem divides the photoelastic field into 640 × 480 picture elements, or pixels. At any pixel, it records the gray level with 8-bit resolution, giving rise to 256 gray levels between the darkest and the brightest points in the chosen field. This is equivalent to a fringe multiplication of 512 in classical photoelasticity. HFP is used in this research to automate the data collection, analysis and display of full-field normal stresses. The results are presented for adhesively bonded single lap joint models of isotropic-isotropic and isotropic-orthotropic adherends under uniaxial tension. The initial birefringence of the models was accounted for in the analysis, and equilibrium checks were performed to confirm the validity of the results.

Surface roughness effects on the stress analysis of adhesive joints

A finite element program was used to perform a parametric analysis of stresses generated by adherend surface roughness in lap and butt joints. Roughness asperities were idealized as having tip radius of curvature R1, height H1, and slopes A1. Failure criteria (maximum stress, yield, and fracture) were related to the geometric parameters by functions of the form: σ = σ o + cR rH hA a The specific material properties used for the analysis were those of tooth enamel and an orthodontic cement. Qualitatively however, these results are applicable to all structural adhesives.

Viscoelastic Analysis of an Adhesive Tubular Joint

Abstract The investigations so far available with regard to stress analysis of adhesive joints assume that the adhesive is elastic. In the present analysis the time dependent properties of the adhesive are taken into account by assuming that the adhesive is viscoelastic. The viscoelastic analysis of a tubular joint has been attempted using a prony series fitting for the relaxation modulus of two adhesives. The long term redistribution of the stresses in the adhesive is evaluated using the finite element method. Viscoelastic analysis of an adhesive tubular joint has been performed for the first time, using the finite element method with a prony series fitting for the relaxation modulus of the adhesive. For a typical epoxy it has been found that not only the elastic stresses are different at different levels but also the viscoelastic response shows considerable variation from one level to another. As large a reduction as 57 % is noticed in the normal stress and an even larger reduction of 62% is noticed in ...