Papers by Keyword: Joint Strength

Abstract: Post-weld heat treatment (PWHT) was investigated to evaluate its effects on dissimilar friction stir welded (FSWed) T-joints of AA6061 and low carbon steel. The non-PWHT joint was compared with four PWHT conditions involving solution treatment, quenching, natural aging, and subsequent artificial aging at 0-12 hours. Microstructural characterization revealed a largely continuous Al/steel interface in the non-PWHT joint, while PWHT promoted interfacial cracking and modified precipitation behavior in the stir zone and heat-affected zone of AA6061. Hardness increased monotonically with aging time, reaching ~95–100 HV after PWHT artificial aging at 12 hours. Tensile strength peaked at 212MPa after 4 hours of artificial aging, while maximum strain decreased from ~9% to ~5.3% after 12 h artificial aging, indicating ductility loss under prolonged aging. Fracture location after PWHT consistently occurred at SZ, highlighting a critical failure region governed by joint geometry and microstructural heterogeneity.

Abstract: The early failure of single-lap adhesive joints in carbon fiber reinforced polymer (CFRP) composites is typically induced by stress concentration at the edges of the overlap region. To address this issue, this study proposes a novel local pre-curing process system based on gradient thermal curing regulation. Through multi-physical field modeling of the temperature-curing coupling effect and a gradient curing control strategy, active optimization of the adhesive layer stress distribution is achieved. By optimizing the interface stress distribution, the proposed technique demonstrates the potential to enhance the overall joint performance by 3-6%. This research combines Abaqus finite element simulation and experimental verification. A CFRP single-lap joint model considering the temperature-curing coupling effect was established to analyze the influence of local pre-curing on the stress distribution of the adhesive layer. The results show that: 1. Local pre-curing can reduce the peel stress in the critical edge danger zone by about 3 - 5% while improving the shear strength in the middle region. 2. The preferential curing at the center of the adhesive layer can induce stress redistribution, relieve the stress concentration at the edges, and thus improve the overall load-bearing capacity of the joint. This study provides a low-cost and easily implementable solution for optimizing the performance of CFRP joints, showing potential applications in the field of lightweight aerospace structures. Through the synergistic effect of precise thermal management and regulation of the adhesive's rheological properties, it offers new insights for advanced composite joining technologies.

Abstract: The usage of adhesively bonded lap joints in industrial applications has been growing in recent years because of the numerous advantages compared to other joining processes such as fastening, welding, and riveting. For effective design of the adhesively bonded engineering lap joints, it is essential to govern the failure potential of a particular adhesive joint under a certain load causing some stress and strain. In this work, study has been carried out by the application of multiple adhesives along the bondline region of lap joint. The objective of this paper is to experimentally examine the results of applications of single and multi-adhesives material with very different mechanical behavior along the bondline region in the single lap adhesive joint. Experimental investigations have been carried out for extracting load displacement data using tensile testing machine, Tensometer, having a capacity of 2 tonne. Multi Adhesive joint can minimize the stress concentration and improve joint strength by using different adhesive stiffness along the bondline region of lap joint and the outcome shows computable increase in the strength of the multiple adhesive bonded lap joints associated with those in which single adhesives were used over the full length of the bondline region.

Abstract: This work presents a comparative study of the mechanical properties of resistance spot welded joints (RSW). RSW is widely used in sheet joining. Hence, the mechanical properties and their strength are presented. The main parameter is the welding current that has a big role on the heat generation and joint strength. The strength improvement due to the current increasing is regular and more effective than the weld time and the electrode pressure. Stainless steel has good weldability in sheet form. Galvanized steel, aluminum and carbon steel have been widely spot-welded. Moreover, dissimilar materials are also spot weldable where the two sheets of different metals can be joined. For the same sheet thickness at 1 mm, it was shown the shear strength of mild steel 3.8 KN, while for aluminum 1.4 KN this mean the shear strength of mild steel higher than aluminum. For the same metals, the increasing of the thickness will increase the strength. This is due to the weld area increasing. All the values were taken at the pull-out fracture condition. Hence, the suitable weld area at the welding condition was assumed. Fatigue strength for some metals has been presented. Fatigue strength of MS1300 is higher than those of steel DQSK, and steel DP800 at the for 1.6 mm thickness and stress ratio, R= 0.1. Because of the thickness, it has a minor effect on the fatigue properties of spot welded joints.

Abstract: The paper reveals the hybrid structure strength studies results, which consists of composite and metal parts. The object of the study was an experimental transmission shaft of an aircraft high-lift system. It consisted of a composite tube and metal flanges. New high-strength composites, modern metal powders and additive technology were used for its manufacture. This is the feature that differ the shaft from the typical metal structures used at present. The shaft strength investigation included static tests and calculations. During the tests, the maximum torque and the corresponding shaft twist angle were determined. Based on the computational analysis results, the critical stresses and reserve factors of its structural elements were calculated. The assessment of the effectiveness of the new technologies application for joining structural elements using discrete pins was carried out.

Abstract: The effects of welding conditions such as the electrode type and welding current were investigated on the microstructure and joint strength of the resistance weld of A5052 and GA590. The reaction layer formed at the joint interface was inferred to consist of Fe-Al based intermetallic compounds (IMCs) which are FeAl, FeAl₂, Fe₂Al₅ and FeAl₃ by quantitative analysis. Although the thickness of the IMCs layer decreased from the center of the nugget towards the edge of it. When the DR type electrode was used, the cross tensile force became higher than those of the joints formed with the R type one. This is because the thickness of the reaction layer formed at the nugget end of A5052 was thin in the case of the DR type electrode. Also, it was found that cross tensile force increases when the thickness of the reaction layer is thin by multiple regression analysis.

Abstract: This work, Seamless Austenitic 213 tube is welded with Seamless Austenitic 387 tube plate through friction welding of tube to tube plate using an external tool (FWTPET) method in presence of backing block by using clearance fit method. Further, the analysis of microstructural features on the interface of weld exhibit that the FWTPET is able to generate flawless welds. In all nine various work specimen which welded under the various circumstances, the hardness value, tensile strength have taken. In this work, two type of specimen has taken where one kind is the tube which contains no hole and another one is with the hole in the circumference. 806.28 MPa and 746.5 MPa were the optimum strength for the workpiece which is not a having a hole and having the hole on the circumference.

Abstract: Microstructures and mechanical properties of lap fillet welded joints of several high and ultra-high tensile strength steel by arc welding were investigated. Steel plates having tensile strength of 400 (SPH400W), 590 (SPC590Y, SPC590R), 980 (SPC980Y) and 1500 MPa (SAC1500HP) class with 2 mm thickness were prepared. Four types of joints were formed by MAG welding; SPH400W/SPH400W, SPC590Y/SPC590Y, SPC980Y/SPC980Y and SAC1500HP/SPC590R. In joints with SPC590Y, SPC980Y and SAC1500HP steel which matrixes are martensitic microstructures, the HAZ softens due to transformation of martensite into ferrite with precipitating cementite. By using high and ultra-high tensile strength steel, the weld metal is strengthened due to dilution of the matrix into the weld metal and thus tensile shear strength of the welded joint increases. In the fatigue test, similar S-N diagrams were obtained in the all welded joints investigated. It seems that the effect of stress concentration due to the shape of the welded joint on fatigue properties is larger than that of the strength of the matrix.

Abstract: High-strength steel sheets (HSSs) have been increasingly used to reduce the weight of automobile bodies. It is necessary to enhance the reliability of their joint strength in order to realize optimal usage. Projection welding (PW) is one of the important welding methods for HSSs; however, research on PW is insufficient. In this research, therefore, the effect of welding conditions on maximum load in the press-peel test for joints, made by PW HSS of 590 MPa grade and square weld nuts, was investigated. It is found that the maximum load showed a tendency to increase with an increase in the current and a decrease in the electrode force. In several cases of the press-peel test, four welds of one joint fractured one by one in sequence and showed a peak load each time it broke. The first or second peak load became the maximum load of each joint. SEM (Scanning Electron Microscope) observation of the welds fractured at the early stage in the press-peel test revealed that the fractured surface can be classified into a good weld region and a bad one. The former was a dimple fracture surface or cleavage one and the latter was a relatively flat fracture surface with many oxides. The same analysis was conducted for joints with several welding conditions. It was consequently found that there is a good correlation between the area of good weld region and the maximum load. In addition, it was considered that the scattering of moderate expulsion during PW was effective for reducing oxides.

Abstract: If resistance spot welding (RSW) is conducted when there is a gap between a steel sheet and an unmovable electrode, the steel sheets are bended by a movable electrode, and the quality of RSW is influenced. Therefore, it is necessary to understand the effect of the gap on RSW. In this study, two high-tensile strength steel sheets were welded with the gap. In addition, cross-section observations and cross tension tests were conducted to verify the effect of the gap on weldability and joint strength. Consequently, two notable results were obtained. First, the observation indicated that deformation around the corona-bond was varied depending on the gap. Second, the cross tension tests showed that the gap decreased the joint strength even though the nugget was large enough. These result indicated that controlling the gap is important to ensure the quality of RSW.