Scarf Joints Research Articles

Strength evaluation of scarf joint bonded with adhesive resin. (1st report Adherends of the same metals)

The strength evaluation of adhesively bonded scarf joints having adherends of similar materials was investigated both analytically and experimentally, in order to establish the strength design of adhesive bonding. The strain and stress distributions in the joints of carbon steel (S45C) bonded with epoxy resin were analyzed by applying the elastic finite element method. The strength of the joints was predicted by applying the strength laws to the adherend, adhesive layer and their interfaces. The validity of the predicted joint strength was confirmed by the experimental results. The effects of the joint dimensions on the strength were examined by varying the overlap length (or scarf angle) and the adherend thickness. The analytical strain distributions were in good agreement with the experimental ones. The results of strength prediction coincided approximately with the experimental ones, so the joint strength was successfully predicted by applying the strength laws to those analytical results.

Strength evaluation of scarf joints bonded with adhesive resin.

The strength evaluation of adhesively bonded scarf joints having adherends of the same or dissimilar metal was investigated both analytically and experimentally in order to accomplish a way of strength designing of adhesively bonded materials. The strain and stress distributions in the adhesively bonded joints were analyzed by means of the finite element method. The strengths were calculated on the basis of our criterion. The effect of the mechanical properties of adherends on the joint strength was examined. The deformation state and fracture mode of the joints having adherends of the same metal. It was predicted that the smaller the difference in the Young's moduli between the adherends, the greater the joint strength was.

Strength evaluation of scarf joint bonded with adhesive resin. (2nd report Adherends of dissimilar metals)

The strength evaluation of adhesively bonded scarf joints having adherends of dissimilar materials was investigated both analytically and experimentally, in order to establish the strength design of adhesive bonding. The strain and stress distributions in the joints of dissimilar materials bonded with epoxy resin were analyzed by applying the elastic finite element method. The strength of the joints was predicted by applying the strength laws to the adherend, adhesive layer and their interfaces. The validity of the predicted joint strength was confirmed by the experimental results. The effects of the mechanical properties on the joint strength were examined by varying the materials of the adherends. The analytical strain distributions were in good agreement with the experimental ones. The results of strength prediction coincided approximately with the experimental ones. The deformation state and fracture process of the joints having adherends of dissimilar materials were remarkably different from those of the joints having adherends of similar materials.

Adhesive tensile strengths of scarf and butt joints of steel plates. (3rd report Relation between adhesive layer thicknesses and adhesive strengths of joints)

Adhesive tensile strengths of scarf and butt joints of steel plates. (3rd report Relation between adhesive layer thicknesses and adhesive strengths of joints)

A comparison of predicted strength and experimental result of adhesive joints.

This paper is concerned with a comparison of predicted strength based on the proposed way explained in the 1st report, and experimental results of adhesive joint strength. It is shown that the strength of scarf joints can be predicted by the strength law represented by stress, that of double lap joints can be predicted by strain, and that of single lap joints can be predicted by the energy release rate. The experiments on the effect of scarf angle on the strength of scarf joints, and on the effects of lap length, adherend thickness and adhesive thickness on the strength of double lap joints and single lap joints are performed. As a result, it is shown that the experimental strength agrees well with the predicted strength.

Adhesive Tensile Strengths of Scarf and Butt Joints of Steel Plates : 2nd Report, Relation between Mechanical Properties of Adhesive and Fracture Criteria of Joints

For the investigation of fracture criteria, adhesive tensile strengths of scarf and butt joints bonded by a brittle and two ductile epoxy adhesives have been measure, and three-dimensional finite element analyses have been performed. Deformation of the Joints was influenced considerably by mechanical properties of adhesives. Fracture of the joints bonded by the brittle adhesive satisfied maximum principal stress criterion. At the scarf angles of 15° to 60°, fracture of the joints bonded by the ductile adhesives satisfied the von Mises criterion and at the scarf angles of more than 60°, a brittle (cleavage) fracture occurred in those joints by plastic constraint due to an increase of stress triaxiality in adhesive layer. Locations of fracture initiation and fracture modes of adhesive layers observed with an optical microscope and scanning electron microscope agreed with those expected from experimental results of deformation and adhesive tensile strength, and result of stress analyses.

Stress Analysis of Adhesive Scarf Joints of Steel Plates in Pure Bending and Contraction of Adhesive by Finite Element Method

Two-dimensional elastic stress analysis in plane strain state has been made for adhesive scarf and butt joints. Bending stresses in adhesive layers at distances greater than several times the layer thickness from the free surfaces show almost linear distributions and are zeros near the mid-width of joints. Maximum principal stresses caused by contraction of adhesive are uniform in the region of adhesive layers greater several times the thickness away from free surfaces and their directions agree with the longitudinal directions of adhesive layers. Distributions of bending stresses corrected for the stress gradients by bending and stress distributions caused by contraction of adhesive show mutual similarity in the vicinity of the free surfaces of adhesive show mutual similarity in the vicinity of the free surfaces of adhesive show mutual similarity in the vicinity of the free surfaces of adhesive layers provided the aspect ratios of the adhesive layers are greater than 20 (bending) or 1020 (contraction). Maximum stresses in both cases appear at the corners of free ends of the layers. Bending stresses in this analysis almost agree with those analyzed by photoelastic method.

End effects in scarf joints

Scarf joints with small scarf angles are especially sensitive to stiffness mismatch between adherends and to adherend tip bluntness. Pre-assembly breakage of an adherend tip where it is only a few microns thick can cause significant reduction in joint strength. Mathematically, the reason for such sensitivity is that the solutions to the governing differential equation develop boundary layer character when the scarf angles are small. The boundary layers are regions with large adhesive stresses. Experimental strength data for laminated composite adherends agree with the results of this analysis.

Adhesive tensile strengths of scarf and butt joints of steel plates (2nd report, Relation between mechanical properties of adhesives and fracture criteria of joints)

Adhesive tensile strengths of scarf and butt joints of steel plates (2nd report, Relation between mechanical properties of adhesives and fracture criteria of joints)

Analysis of composite-to-metal joints with bondline flaws

Stress analysis techniques have been developed for load transfer in metal-to-composite adhesively bonded joints with bondline flaws such as variable bondline thickness and debond in the adhesive layer. Two joint configurations, namely, single-step-lap bonded joint and smoothly tapered scarf joint, have been investigated. The problem is formulated on the basis of the assumptions that both the metal and the composite are under generalized plane stress conditions and that the adhesive acts as a shear spring. Differential equations are obtained for the load transfered from the metallic layer to the composite layer. Numerical results are obtained for the force and stress in the composite layer, the stress in the metal and the stress in the adhesive. The influence of bondline flaw location on the stresses in the adhesive and the adherends has been investigated.

Adhesive Tensile Strengths of Scarf and Butt Joints of Steel Plates : 1st Report, A Case of Brittle Adhesive

Adhesive tensile strengths, o f scarf joints with various scar f angles and butt joints with various adhesive layer thicknesses have been measured to establish fracture criterion for joints of steel plates bonded by brittle epoxy adhesive. A three-dimensional elastic stress analysis of these joints was performed by FEM. Fractures of both joints were explained quantitatively by introducing a boundary layer depth of 0.035 mm at free surfaces of adhesive layers and obeying maximum principal stress criterion. In adhesive layers of scarf joints with 0.1 mm layer thickness, the boundary layer depth of 0.035 mm included most of stress concentrated area at free surfaces. Locations of fracture initiation and fracture modes of adhesive layers observed with an optical microscope and a scanning electron microscope agreed with those expected from stress distributions and boundary layer conception.

Adhesive Tensile Strength of Scarf and Butt Joints of Steel Plates : 1st Report, A Case of Brittle Adhesive

Adhesive Tensile Strength of Scarf and Butt Joints of Steel Plates : 1st Report, A Case of Brittle Adhesive

Three-dimensional Finite Element Analysis of Adhesive Scarf Joints of Steel Plates Loaded in Tension

Three-dimensional Finite Element Analysis of Adhesive Scarf Joints of Steel Plates Loaded in Tension

Stress Analysis on Adhesive Scarf Joints of Steel Plates in Pure Bending and Contraction of Adhesive by Finite Element Method

Stress Analysis on Adhesive Scarf Joints of Steel Plates in Pure Bending and Contraction of Adhesive by Finite Element Method

Three-Dimensional Stress Analysis by Finite Element Method of Adhesive Scarf Joints of Steel Plates Loaded in Tension

鋼のスカーフおよびバット接着試験片の三次元および二次元弾性有限要素解析を行って,接着層においては自由端から厚さの数倍内側へ入った点までを除く大部分では平面ひずみ状態でしかも一定応力であり,その近似値は簡易計算式により求められることを示した.また接着層の自由端ではアスペクト比によらず応力分布がほぼ相似性を示すことを明らかにし,さらに本解析結果は光弾性実験結果および厳密解にほぼ一致することを示した.

Fracture toughness of composite adherend adhesive joints under mixed mode I and III loading

A tapered double cantilever beam specimen was modified in order to evaluate the fracture toughness of scarf joints. The modification was relatively simple: the bond line which is normally perpendicular to the applied load with this type of specimen was inclined to form the scarf joint. With this change, both normal and shear components of force act on the crack plane. Hence, in addition to measuring the total strain energy release rate, Gtotal, its two components, the opening mode toughness, GI, and the edge shearing or tearing toughness, GIII, were measured as well. In spite of the fact that the separation loads increased continuously with increasing scarf angle, or over-lap length, Gtotaland GIII only increased so long as the ratio of over-lap length to thickness did not exceed 1.75∶1. Further increases in over-lap length decrease the toughness because of separation of fibres within the composite adherends.

Scarf Repair Joints in Carbon Fibre Reinforced Plastic Strips

Abstract Various theoretical models are developed for scarf joint repairs in unidirectional carbon fibre reinforced plastic strips subjected to a tensile load. for the type of joint where the fibres of both the original and repair materials (the adherends) are aligned along the longitudinal axis of the joint (a dry/dry joint), a uniform shear stress is predicted in the adhesive layer. When the repair material is laid directly on to the scarf surface with the fibres inclined to the longitudinal axis (a wet/dry joint), it is shown that the degree of shear stress uniformity is a function of the scarf angle, but reaches a uniform state at slopes smaller than 1 : 30 when the joint stresses can be calculated very simply. The theoretical work is supported by tests on a number of joints of both types. The test results show that the dry/dry joints are more efficient than the wet/dry joints, and that it is possible to achieve joint efficiencies at failure, under a static load, in the region of 90% with slopes less ...

Interfacial cracks in adhesively bonded scarf joints

The interfacial crack behavior in adhesively bonded scarf joints is investigated. The study is conducted by using a method of analysis formulated on the basis of conservation laws of elasticity for nonhomogeneous solids and fundamental relationships in fracture mechanics of interfacial cracks. Solutions for interfacial crack-tip responses are determined for the joints with various adherend and adhesive properties, interface crack lengths, and adhesive-layer thicknesses. Also studied is the change of structural stiffness due to the presence of interfacial debonding. Of particular interests are the effects of geometric and material variables on the crack-tip response. Results are presented in terms of mixed-mode stress intensity factor solutions and energy release rates to illustrate the fundamental nature of fracture in adhesively bonded scarf joints.

Repair of Advanced Composite Structures

This paper presents the concluding results of the large area composite structure repair program in which five large panels were repaired and subjected to static tests. A description of the Northrop bonded-cocured scarf joint repair is given with a review of strength and durability test results. Application of this technique to the problem presented in each of five panels is discussed. Finally, the repair of a speedbrake damaged in service is described. Repairability of advanced composite structure is fully demonstrated.

Stress distribution in carbon fibre-reinforced plastic joints

Three bonded joints in carbon fibre-reinforced plastic were analysed by finite element methods to obtain the elastic stress distribution. The first joint was a symmetric butt strap joint; the second was similar, but its geometry was modified to reduce the stress concentrations; and the third was a scarf joint. This work was undertaken as a first step towards the explanation of the poor fatigue life of these joints when compared to the fatigue life of the adhesive in pure shear. All the joints had areas of high stress concentration.