Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints

The main objective of this study is to compare the mechanical strength of friction stir spot welded (FSSW) joints and adhesive bonded single lap ones. The present study aims to compare the morphology and strength of welded and adhesive bonded joints. The welded joints were done by friction stir spot welding and the adhesive bonded ones by the use of the adhesive Araldite 420 A/B. The produced joints were subjected to morphology and microstructure analyzes, microhardness tests, tensile-shear tests and local strain analyzes. The welded joints have higher strength than adhesive-bonded joints. However, this difference is insignificant, around 5%, which is covered by the standard deviation. The connection by FSSW proves to be an alternative to adhesive bonded joints, offering the same strength, but with the connection at isolated points, inducing local stress concentration

Nugget Formation and Mechanical Behaviour of Friction Stir Welds of Three Dissimilar Aluminum Alloys

The aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool's rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.info:eu-repo/semantics/publishedVersio

Quantification of Residual Stress Relief by Heat Treatments in Austenitic Cladded Layers

The effect of the heat treatment on the residual stresses of welded cladded steel samples is analyzed in this study. The residual stresses across the plate’s square sections were determined using complementary methods; applying diffraction with neutron radiation and mechanically using the contour method. The analysis of the large coarse grain austenitic cladded layers, at the feasibility limits of diffraction methods, was only made possible by applying both methods. The samples are composed of steel plates, coated on one of the faces with stainless steel filler metals, this coating process, usually known as cladding, was carried out by submerged arc welding. After cladding, the samples were submitted to two different heat treatments with dissimilar parameters: one at a temperature of 620 °C maintained for 1 h and, the second at 540 °C, for ten hours. There was some difference in residual stresses measured by the two techniques along the surface of the coating in the as-welded state, although they are similar at the welding interface and in the heat-affected zone. The results also show that there is a residual stress relaxation for both heat-treated samples. The heat treatment carried out at a higher temperature showed sometimes more than 50% reduction in the initial residual stress values and has the advantage of being less time consuming, giving it an industrial advantage and making it more viable economically

Assessment of mechanical shear response using digital image correlation

In this work, a special tool, developed for running shear tests using a universal tensile testing machine is described, as well as the procedures used for strain data acquisition via Digital Image Correlation (DIC). Testing procedures were developed and verified by testing two aluminium alloys widely used in welding construction, the heat-treatable AA6082-T6 and the non-heat-treatable AA5083-H111 aluminium alloys, which are characterized by markedly different strengthening mechanisms, having completely different mechanical behaviour under large plastic deformations. Microstructural analyses were accomplished in order to evaluate the accuracy of strain data acquisition by DIC in capturing the strain gradients along the gage section of the shear samples

Effect of heat input on plastic deformation of undermatched welds

The aim of this work is to study the tensile properties of undermatch welds carried out in high strength quenched and tempered steel, RQT701 (British Steel). Two different heat inputs were used in order to obtain distinct mechanical properties in the weld metal (WM) and the heat-affected zone (HAZ) of the welds. Attention was focused on the microstructure and mechanical properties of the welded joints. Real stress-real strain curves of specimens sampling the WM, the WM in conjunction with the HAZ and the three zones altogether (WM, HAZ and BM) were analysed. The increase of heat input coarsened the microstructure and diminished the hardness in the WM and HAZ. A loss of hardness was also observed in the subcritical zone probably due to carbide precipitation. The increase of heat input increases the yield and tensile strength undermatching of the WM and also produces HAZ undermatching. The undermatch condition induces a concentration of plastic flow in the weakest zone and a loss of strength and ductility of the weld when loaded in tension.http://www.sciencedirect.com/science/article/B6TGJ-46V47VV-5S/1/142b38d73b2d3302571184d9664874c