Dissimilar Material Joints Research Articles

Analysis of Singularity at a Vertex in 3D Transversely Isotropic Piezoelectric Single-Step Bonded Joints with Various Thicknesses by Boundary Element Method

The stress singularity fields are one of the main factors responsible for debonding under mechanical or thermal loading. Stress singularity frequently occurs at a vertex in an interface of joints due to a discontinuity of materials. Stress singularity is related to debonding and delamination at interface of the bonded joint. However, the singularity at a vertex in two-phase transversely isotropic piezoelectric dissimilar material joints has not been made clear until now. In this paper, intensity of singularity at a vertex is investigated in transversely isotropic piezoelectric dissimilar material joints. The orders of singularity at a vertex and at a point on singularity lines for piezoelectric bonded joints are determined using eigenanalysis. The stress and electric displacement distributions on an interface and the intensity of singularity at the vertex are investigated using BEM. From the numerical results, it is shown that the 3D intensity of stress singularity increases and the 3D intensity of electric displacement singularity decreases with the increase of material thickness in joint.

W308 レーザによる異材接合のプロセスとその接合体強度

W308 レーザによる異材接合のプロセスとその接合体強度

The Effects of Materials Properties & Angle Junction on Stress Concentration at Interface of Dissimilar Materials

In dissimilar material joints, failure often occurs along the interface between two materials due to stress singularity. Stress distribution and its concentration depend on materials and geometry of the junction as the stress concentration depends on grain orientation and its stiffness matrix of neighboring grains in micro-scale. Inhomogenity of stress distribution at the interface of junction of two materials with different elastic modules and stress concentration in this zone are the main factors resulting in rupture of the junction. Effect of materials properties, thickness, and joining angle at the interface of aluminum-polycarbonate will be discussed in this paper. Computer simulation and finite element analysis by ABAQUS showed that convex interfacial joint leads to stress reduction at junction corners in compare with straight joint. This finding is confirmed by photoelastic experimental results.

TIG-FSW 하이브리드 용접을 이용한 이종재 맞대기 용접부의 온도 분포 특성

Three-dimensional finite element analysis is performed to study the temperature distribution phenomenon of TIG assisted friction stir welding (TAFSW) between dissimilar plates (Al 6061-T6 and stainless steel 304). TAFSW is a solid-state welding process that integrates TIG (Tungsten Inert Gas) into a friction stir welding (FSW), to preheat the harder material ahead of FSW tool during welding. In order to facilitate the industrial application of welding, 3D numerical modeling of heat transfer has been carried out applying Finite Element Method (FEM). The temperature distribution due to heat generation during TAFSW on dissimilar materials joint is analysed using in-house solver. Moving heat source along with frictional heat between the work specimens and tool surface is considered to calculate the heat input. The analytical model used predicts successfully the maximum welding temperatures that occur on the dissimilar materials during TAFSW. Comparison with the infra red camera and thermocouple measurement results shows that the results from the current numerical simulation have good agreement with the measured data.

Microstructural evolution of aluminum/magnesium lap joints welded using MIG process with zinc foil as an interlayer

Dissimilar material welding between 1 mm-thick magnesium and aluminum alloy plates in lap form was performed using the MIG process with zinc foil as the interlayer material. The zinc foil acted as a barrier layer that restrained reactions between the aluminum and magnesium atoms, and a crack-free lap joint of dissimilar materials was obtained. The interfacial layer between the fusion zone and the unmelted magnesium substrate was mainly composed of Mg–Zn binary intermetallic compounds. The tensile strength of the lap joint was 64 MPa, and a fracture occurred at the interface between the fusion zone and the unmelted magnesium alloy.

Microstructural analysis on creep properties of dissimilar materials joints between T92 martensitic and HR3C austenitic steels

This paper reports the creep rupture behaviors of T92/HR3C dissimilar materials joints. HR3C austenitic steel is welded with T92 martensitic steel to obtain T92/HR3C dissimilar materials joints. After welding, creep test is carried out at 625 °C in the stress range 110–180 MPa. The rupture locations of creep specimens are examined by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the creep rupture mechanism of the joint is dependent on stress. When stresses ≥140 MPa, rupture location is at the T92 base material part and the connection of adjacent dimples results in transcrystalline fracture. For stresses <140 MPa, rupture location is at the T92 coarse-grained HAZ (CGHAZ) and M 23C 6 particles grown up as well as Laves phase ((Fe, Cr) 2 (W, Mo)) precipitation on grain boundaries leads to the creep cavities and intergranular fracture.

Effects of resistance spot welding parameters on microstructures and mechanical properties of dissimilar material joints of galvanised high strength steel and aluminium alloy

Intermediate frequency resistance spot welding has been adopted to join dissimilar materials of H220YD galvanised high strength steel and 6008 aluminium alloy. The effects of welding current and welding time on microstructures and mechanical properties of the welded joints were investigated. A thin intermetallic compound layer composed of Fe2Al5 phase and Fe4Al13 phase formed at the steel/aluminium interface. The interfacial intermetallic compound layer has higher nanohardness compared with the aluminium alloy nugget and galvanised steel. With increasing welding current (4–11 kA) and welding time (50–300 ms), the nugget diameter increased, the interfacial layer structure became coarser and the tensile shear load of the welded joints had an increased tendency. The maximum tensile shear load reached 3309 N at 9 kA for 250 ms. Crack initiated at the interfacial intermetallic compound layer of the tensile shear specimens, then propagated through the interfacial layer principally, and meantime through the aluminium alloy fusion zone near the interface partially.

Microstructure and mechanical properties of dissimilar materials joints between T92 martensitic and S304H austenitic steels

In this paper, T92 martensitic steel and S304H austenitic steel were welded by gas tungsten arc welding (GTAW) process. Microstructural features and mechanical properties of T92 and S304H dissimilar materials joints were investigated. The results showed that the part of the joints with relatively weak tensile strength was T92 coarse-grained heat affected zone (CGHAZ), while the part of the joints which revealed relatively weak toughness was weld metal. The decrease of tensile strength in T92 CGHAZ was due to its coarse tempered martensite structure. Weak toughness of the joints was resulted from the coarse dendritic austenite of the weld metal. However, the weld metal in transverse direction of the joints was provided higher tensile strength by the orientation distribution of grains compared with T92 CGHAZ.

Asymptotic Analysis for the Singular Stress Behaviour around an Interface Edge of Dissimilar Power-Law Hardening Materials Joint

An asymptotic analysis for singular stress fields around an interface-edge of dissimilar power-law hardening materials joint has been presented under plane strain condition and J2 deformation plasticity theory. Both the balance of force and the continuity of displacement are satisfied on the interface. In the higher order approximation, the nonlinear effective stress term was expanded by Taylor series. An iteration method is proposed for the determination of singular fields around interface edge. Multiple stress singular terms exist for in the higher order approximation. The order of stress singularity has a dependency with the combination of hardening exponents, .

202 二次元接合体に対するエンリッチ有限要素法の適用 : 2つの特異性のオーダがある場合(OS2.接着・接合・界面・薄膜の理論と実験および信頼性評価(1),OS・一般セッション講演)

In this study, the enriched finite element method is applied to compute the intensity of singularity for dissimilar material joints with 2-real singularities. Different mesh types and different size of the enriched region are applied to improve an accuracy of the results. It is shown that the results from applied the enriched FEM to the 3-material junction is agreed with those using a conventional FEM. In addition, numerical error is reduced by changing mesh types from linear to quadratic elements.

Strength of Dissimilar Materials Joint between A5052 and PET Joined by Using Friction Stir Heating

A new direct joining method for dissimilar materials between a metal and a plastic by using friction stir heating technique is introduced. A5052 and polyethylene terephthalate (PET) were used as materials used in this study. The joining strength was evaluated under tensile shear loading condition. The fracture surface and the cross section of the joined specimens were observed in order to understand characteristics of the joints. The results show that A5052 and PET were successfully welded by the present joining method. Similar strength of the joints was obtained regardless of the joining conditions. Melting and softening behaviors of PET and formation of bubbles observed in welded area might affect the joining strength.

Evaluation of Intensity of Stress Singularity for 3D Dissimilar Material Joints Based on Mesh Free Method

We present the intensity of stress singularity for 3D dissimilar material joints based on mesh free method. When load is applied to surface of the bonded structure, stress at vertex on interface drastically increases and it appears that this stress singularity occur delamination of the bonded structure. Intensity of stress singularity can be expressed by stress distribution and the intensity of stress singularity. Therefore, it is necessary to obtain the stress distribution precisely. In this study, we focus on the mesh free method for the computation of the stress distribution. When this method is applied to compute stress distribution, incompatible cell can be employed and geometrical data for a target structure can be simply prepared. To confirm the validity of the results of mesh free method, comparison of the intensity of stress singularity between the mesh free and the boundary element methods is carried out.

Laser-FSW Hybrid 접합기술을 적용한 이종재료(Al6061-T6/SS400) 접합부의 접합성 및 기계적 특성에 관한 연구

This study intends to investigate the weldability and mechanical characteristics of butt weld joints by LAFSW for dissimilar materials (Al6061-T6 and SS400). At optimum welding conditions, the tensile strength of dissimilar materials joints made by FSW is found to be lower than that of LAFSW. Due to the increase in plastic flow and formation of finer recrystallized grains at the TMAZ and SZ by laser preheating in LAFSW, the hardness in LAFSW appeared to be higher than that of FSW. Compared with FSW, finer grain size is observed and elongated grains in parent metal are deformed in the same direction around the nugget zone in TMAZ of Al6061-T6 by LAFSW. Whereas, at weld nugget zone, coarse grain size is appeared in LAFSW compared to FSW, which is owing to more plastic flow due to laser preheating effect. In dissimilar materials joints by LAFSW, ductile mode of fracture is found to occur at Al6061 side with fewer brittle particles. Mixed mode of cleavage area and ductile fracture is observed at SS400 side.

Joining Aluminium to Red Copper by High-Frequency Induction Brazing with Argon Shielding

Joining Cu to Al has been carried out by high-frequency induction brazing without filler metal. Experimental results showed that the eutectic structure was the main phase of the brazing seams and a regular Cu-Al intermetallic compound layer also appeared near the Cu side. The maximum shear strength of the dissimilar materials joint could be reach 22.5MPa.

Microstructure and fracture behaviour of Ti3Al/TC4 dissimilar materials joints welded by electron beam

Electron beam was used to join TC4 alloy to Ti3Al-based alloy. The composition of the weld was analysed by XRD and TEM and the results showed that the weld mainly composed of α′ martensites. The change of heat input had little influence on the composition of the weld but can make the grain size increasing. The fracture path of the joints was mainly decided by the microstructure of the weld and started from coarse grain zone to HAZ and base metal of Ti3Al alloy.

Deformation behaviour of spot-welded high strength steels for automotive applications

Numerical simulation of component and assembly behaviour under different loading conditions is a main tool for safety design in automobile body shell mass production. Knowledge of local material behaviour is fundamental to such simulation tests. As a contribution to the verification of simulation results, the local deformation properties of spot-welded similar and dissimilar material joints in shear tension tests were investigated in this study for a TRIP steel (HCT690T) and a micro-alloyed steel (HX340LAD). For this reason, the local strain distribution was calculated by the digital image correlation technique (DIC). On the basis of the hardness values and microstructure of the spot welds, the differences in local strain between the selected material combinations are discussed. Additionally, the retained austenite content in the TRIP steel was analysed to explain the local strain values. Results obtained in this study regarding similar material welds suggest significant lower local strain values of the TRIP steel HCT690T compared to HX340LAD. One reason could be the decrease of retained austenite in the welded area. Furthermore, it has been ascertained that the local strain in dissimilar material welds decreases for each component compared with the corresponding similar material weld.

Influence of disbond on notch crack behaviour in single bonded lap joints

The behaviour of the adhesive bonded joints due to the imposed eccentric loading generates a very complex distribution of the stress in the structure. Good adhesion between substrate and adhesive ensures a successful and lasting assembly. In this study the finite element method is used to analyze the behaviour of a bonded lap joint of dissimilar materials. The effects of the mechanical properties of the joints on the shear stress variation with and without presence of a circular notch are investigated. The results show that the maximum shear stresses are located at a distance of about 18% that of the lap length whatever the type of material used. In addition, the stress intensity factor is amplified by the presence of the negative effect of disband whose increase is linearly proportional to the square of the stress intensity factor. It reached its maximum value for a crack length equal to two-fifths of the notch radius.

Characteristics of Singular Stress Distribution at a Vertex in Transversely Isotropic Piezoelectric Dissimilar Material Joints

Stress singularity frequently occurs at a vertex in an interface due to a discontinuity of materials. The stress singularity fields are one of the main factors responsible for debonding under mechanical or thermal loadings. The stress distribution near the vertex in the interface is very important to maintain the reliability of joints. In this paper, stress singularity at a vertex in transversely isotropic piezoelectric dissimilar material joints are analyzed. Eigen analysis based on FEM is used for stress singularity field analysis of piezoelectric dissimilar material joints. The eigen equation is used for calculating the order of stress singularity, and the angular function of elastic displacement, electric potential, stress and electric displacement. Stress and electric displacement fields demonstrate that the values near stress singularity line of the joint are larger than that at the inner portion. From the numerical result, it is suggested that delamination of the interface may occur at the interface edge of the dissimilar piezoelectric material joints due to the higher angular function at the free edge.

1601 メッシュフリー法による応力解析に基づく三次元異材接合体界面端における特異応力場の強さ(OS16. 表面・薄膜・接合部の力学と信頼性評価(1),オーガナイズドセッション講演)

1601 メッシュフリー法による応力解析に基づく三次元異材接合体界面端における特異応力場の強さ(OS16. 表面・薄膜・接合部の力学と信頼性評価(1),オーガナイズドセッション講演)

The effect of adhesive thickness on spot weld-bonded joints of dissimilar materials using finite element model

In present work, the bonded and spot weld-bonded of dissimilar materials joints for three dimensional models using the finite element technique were studied for different adhesive thicknesses. The results show that the stresses in adhesive bonded joints are concentrated at the ends of the overlapped area. When the spot-welding is combined with the adhesive bonding, the stresses are concentrated at the adhesive bond ends and at both ends of the weld nugget. The results show also that the stresses are more concentrated towards the material of the lowest melting point. Changing the thickness of the adhesive layer for various dissimilar material models give us the optimal thickness for each case that one can use in designing lap joints of two dissimilar materials. The results in general show that the thinner the adhesive is, the higher is the peak stresses developed in the weld-bonded joint.