Key Engineering Materials Vol. 991

Abstract: The structural integrity and safety of the vessels depends significantly on the quality of their welded joints, particularly at specific nodes where high-stress concentrations are common. This research leverages computer-aided design, artificial intelligence and materials science advancements to develop an innovative software tool that integrates expert knowledge, and best practices, for inland vessel welding. The proposed expert software system offers several key features, including the visualization of specific ship nodes, their parameters, as well as the residual stresses and strains that are specific to each node. By integrating these functionalities, the software aims to minimize human error, reduce inspection time, and ultimately improve the overall structural reliability of inland vessels.

Abstract: Welding technologies are constantly evolving, and their applicability is expanding, considering also the construction domain. Steel structures benefit from the advances in welding technologies due to the use of thin gauge steel sheets which can now be connected at high quality and automatically. The resistance of the connection between the thin steel sheets is crucial for the durability and safety of a structure made of built-up thin-walled cold-formed steel elements. Generally, self-drilling screws or bolts are used for the connection between thin-walled elements, but the quantity of time and manpower necessary for a large number of connections demands an improved solution. Conventional welding techniques are unsuitable for joining thin sheets, ranging from 0.4 to 1.0 mm to thicker ones measuring 1.0 to 3.5 mm. This article compares the results of an experimental investigation into lap joints connected by spot welding and MIG brazing with the design code provisions. The study examines single-lap joints in steel sheets of 0.8, 1.0, 1.2, 1.5, 2.0 and 2.5 mm thickness, connected using these welding technologies. The results obtained are then compared with analytical relations and processed according to EN 1990. Depending on the thickness of the connected sheets, spot welding can lead to two failure modes: button pull-out fracture and interfacial fracture. MIG brazing, a welding technology that deposits material below the melting point of the base material, is known for its advantages, such as low energy consumption, spatter-free operation, high welding speed, and compatibility with thin sheet metals. However, its application in the structural engineering of cold-formed elements lacks documentation. In the study, the MIG brazed specimens failed in the heat-affected zone of the connection. The results indicate the dependence of the spot weld lap joint resistance on the connected sheets' thickness, while the resistance of the MIG brazed lap joints is influenced by the minimum thickness of the connected steel sheet. The study aims to demonstrate the feasibility of the proposed solutions, evaluate their performance, and establish the limits of their applicability. A statistical interpretation of the results highlights the precision and reliability of joint resistance.

Abstract: The role of welding in fracture mechanics development is considered from historical point of view. Starting point was analysis of Schenectady ship failure during the II World War, leading to development of linear elastic, as well as elastic-plastic fracture mechanics, soon afterwards. Two case studies are described to illustrate weldment fracture mechanics and structural integrity assessment.

Abstract: Copper and stainless steel possess distinct properties that make them suitable for different applications (i.e. e-mobility, nuclear power plants, etc.). However, the high thermal conductivity of copper presents a significant challenge in welding. In fact, researchers have explored various fusion welding processes for joining copper to steel and concluded that fusion welding is generally difficult or even unsuitable for obtaining sound and defects free joints. The present study investigated the feasibility of dissimilar lap joint between copper and stainless-steel thin plates using Cold Gas Tungsten Arc Welding (CGTAW) without a filler material and with no significant geometrical distortion of welded plates. The weld was created by consecutive partially overlapped spots, whose welding time varied between 100 and 150 ms, in upgraded conventional TIG machine equipped with cold TIG welding function. Samples made with 150 ms welding time showed a near-uniform distribution of equiaxed copper grain microstructure, while those obtained with 100 ms exhibited significant differences in grain size with the presence of steel inclusions in globule and vortex shapes. The joints demonstrated exceptional flexibility, allowing it to be bent up to a 180º angle without any visible damage. The maximum tensile strength of sample obtained with a welding time of 150 ms was 220 MPa with a fracture located in the heat-affected zone. The sample welded with a welding time of 100 ms exhibited 171 MPa of tensile strength with the fracture along the melting spot area due to pronounce mixing of welded materials. All the samples showed ductile behavior in the fracture zone. Eventually, the application of CGTAW resulted in promising at obtaining joint with good mechanical properties.