ANALYSIS OF A WWII T2-TANKER USING A VIRTUAL 3D MODEL AND CONTEMPORARY CRITERIA

The S.S. Ohio that saved the Maltese from capitulation during WWII made it to Malta barely afloat on the 15th of August 1942. Historical literature provides three main hypotheses as to why the tanker did not sink under heavy attack, namely: the use of water pumps partially restored buoyancy, the cargo density and a strong fully welded hull. A stability, floodable length and residual strength analysis was conducted to confirm or disprove the hypotheses. The results indicated that the vessel was stable, the water pumps partially restored buoyancy and was sinking despite her welded structure and cargo on-board. A challenge was to draw a comparison between the results and applicable criteria. At the time, criteria only governed the ship’s scantlings and did not focus on stability, floodable length and residual strength. The research provided engineering evidence on how the S.S. Ohio survived, whilst contemporary criteria were identified to assess the tanker’s characteristics.

Fatigue Strength Evaluation of Welded Structure on Aluminum Alloy Car Body Based on Multi-Axial Stress

With the continuous development of the subway, the demand for its safety and stability is getting higher and higher. It is of great significance to accurately evaluate the fatigue life of the carbody to ensure the subway's safe operation. In this paper, the finite element model of a subway head carbody was established, and the fatigue strength of the welded structure on the carbody was evaluated based on Multi-axial stress. The local coordinate system was defined according to the geometrical characteristics of the welds. Local stresses perpendicular and parallel to the weld seam were obtained to calculate the stress ratio, stress range, and allowable stress value corresponding to the stress component. According to the joint fatigue resistance, the components of the degree of utilization and comprehensive degree of utilization are calculated to evaluate the structural fatigue strength under the survival rate of 97.5% and load cycles of 10 7 . The evaluation of the fatigue strength of the pivotal weld joints shows that the fatigue strength of the aluminum alloy carbody meets the design requirements, the weld of the carbody has a strong ability to resist fatigue damage. The fatigue strength of the weld is mainly affected by the normal stress component, while the shear stress has little effect on the fatigue strength of the structure. In addition, compared with the filleted weld joint and the butt-welded joint, the normal stress parallels to and perpendicular to the weld direction and shear stress have the greatest effect on the lap-welded joint. Meanwhile, the comprehensive degree of utilization of the lap-welded joint is the largest at 0.49. The introduction of multi-axial stress for the fatigue strength evaluation is beneficial when considering the material utilization degree in multiple structural directions. This research results provide a reference for fatigue strength evaluation of subway carbody's welded structure.

Research on anti-fatigue design method of welded structure oriented to stiffness coordination strategy

PurposeIn order to obtain the relationship between the geometry and stress concentration of load-bearing welded joints, the fatigue design method of welded structures based on stiffness coordination strategy is studied.Design/methodology/approachBased on the structural stress theory, a new method for anti-fatigue design of welded structures oriented to stiffness coordination strategy is proposed, and the detailed implementation process of this method is given. This method is also called the three-stage anti-fatigue design method for welded structures, which includes three stages, namely, identification, analysis and relief of stress concentration.FindingsThrough the experimental analysis of welded joints in IIW standard, the effectiveness of stiffness coordination in welded joint design is proved. The method is applied to the design of welded parts and products, and the feasibility of the method in alleviating the phenomenon of stress concentration and improving the fatigue resistance of welded structures is verified.Originality/valueIn this study, based on the principle of coordinated design of weld stiffness, a three-stage anti-fatigue design method of welded structure is proposed. The method has practical value for the optimization design and anti-fatigue performance improvement of welded structure in engineering products.

Selection of Weld Structure of Bogies Based on Sub-Model

In order to effectively deal with the problems in the allowable fatigue strength data of weld joints of steering structures, it is necessary to carry out comparative tests and analyses according to various structural stress methods and data. Therefore, on the basis of understanding the applied strength standard of bogie welded structure in China, and aiming at the application of weld structural stress at the present stage, this paper constructs the fatigue diagram and S-N curve of Q345 weld seam based on the actual tested structural stress, and starts with the result study.

Study on Fatigue Performance of Non-Uniform Thickness Markless Laser Lap Welding

In this paper fatigue properties of three groups of unequal thickness unmarked overlap laser welding of the external wallboard connected of type A and B vehicle were studied. In addition, a group of overlap penetration welded structures of 1.5mm-301L-HT+0.8mm-301L-DLT is designed to study the impact of penetration rate to the mechanical properties. The influence of the weld geometry and plate combination on fatigue fracture behavior and fatigue property is studied based on the combination of fatigue test and simulation stress analysis. Fatigue studies have shown that in spite of the thickness of the two lap unequal thickness welded plate is disparities -- unmarked non-penetration welding outer plate is thicker but it appears fatigue fracture on the outer plate. The safety fatigue limit of three different non-penetration welded structures of plate combinations and weld structures is close which further proofs that the stress state and microstructure of non-penetration outer plate is not conducive to fatigue fracture. It is consistent with the results of the finite element simulation. The fatigue limit of lap welded structure increase with the increase of plate thickness.

Automated and interactive evaluation of welding producibility in an multidisciplinary design optimization environment for aircraft components

The automation capabilities and virtual tools within engineering disciplines, such as structural mechanics and aerodynamics, enable efficient Multidisciplinary Design Optimization (MDO) approaches to evaluate and optimize the performance of a large number of design variants during early design stages of aircraft components. However, for components that are designed to be welded, in which multiple functional requirements are satisfied by one single welded structure, the automation and simulation capabilities to evaluate welding-producibility and predict welding quality (geometrical deformation, weld bead geometrical quality, cracks, pores, etc) are limited. Besides the complexity of simulating all phenomena within the welding process, one of the main problems in welded integrated components is the existing coupling between welding quality metrics and product geometry. Welding quality can vary for every new product geometrical variant. Thus, there is a need of analyzing rapidly and virtually the interaction and sensitivity coefficients between design parameters and welding quality to predict welding producibility. This paper presents as a result an automated and interactive welding-producibility evaluation approach. This approach incorporates a data-based of welding-producibility criteria, as well as welding simulation and metamodel methods, which enable an interactive and automated evaluation of welding quality of a large number of product variants. The approach has been tested in an industrial use-case involving a multidisciplinary design process of aircraft components. The results from analyzing the welding-producibility of a set of design variants have been plotted together with the analysis results from other engineering disciplines resulting in an interactive tool built with parallel coordinate graphs. The approach proposed allows the generation and reuse of welding producibility information to perform analyses within a big spectrum of the design space in a rapid and interactive fashion, thus supporting designers on dealing with changes and taking fact-based decisions during the multidisciplinary design process.

Design Implications and Opportunities of Considering Fatigue Strength, Manufacturing Variations and Predictive LCC in Welds

Fatigue strength dictates life and cost of welded structures and is often a direct result of initial manufacturing variations and defects. This paper addresses this coupling through proposing and applying the methodology of predictive life-cycle costing (PLCC) to evaluate a welded structure exhibiting manufacturing-induced variations in penetration depth. It is found that if a full-width crack is a fact, a 50% thicker design can result in life-cycle cost reductions of 60% due to reduced repair costs. The paper demonstrates the importance of incorporating manufacturing variations in an early design stage to ensure an overall minimized life-cycle cost.