Structural Integrity of Welded Structures XII

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Authors: Alin Constantin Murariu
Abstract: Hydro-energetic equipment and installations are part of a national energy system. Age and their wear, lack of implementation of the risk-based inspections on the structural integrity of components and a proper risk management system can lead to unexpected in-service failure, which causes temporary disturbances in electricity distribution networks and financial losses. Paper presents the structural integrity analysis of the cause of failure of a spindle from a hydro-aggregate. For the material characterization, tensile tests, notch impact tests, hardness tests and non-destructive visual and magnetic particle tests (NDT) were performed. The experimental program also includes complementary investigation for chemical and structural analysis using Energy-Dispersive X-ray spectroscopy (EDX) and Scanning Electron Microscopy (SEM) techniques to assess the quantity and dispersion of elements in different areas of the fractured surface to highlight the particularities of material degradation. Connecting the inspections results leads to an in-depth understanding of the components failure mechanisms, which allows increasing the safety level in operation of the installations by adopting specific measures for avoidance of similar failure. From analysis and experimental results of this study, overload by shock in operation, particularly low steel toughness and non-metallic aligned or clustered inclusions are shown to be the main reason of spindle failure.
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Authors: Miodrag Arsić, Srđan Bošnjak, Vencislav Grabulov, Mladen Mladenović, Zoran Savić
Abstract: Technical diagnostics of hydromechanical equipment, is based on testing procedures including the history of the exploitation with expert knowledge of structures and operating conditions, as well as, on the analysis of results performed by experts with appropriate experience and knowledge in design, exploitation, maintenance, reliability, fracture mechanics etc. Degradation of properties of the material and/or welded joints of hydro-mechanical equipment is being caused by the simultaneous influence of a large number of factors. First of all, it is thought of technological, metallurgical, structural and conditions of exploitation. In this paper, the selection of methodology for the rehabilitation of hydro-mechanical equipment is presented based on the previously conducted assessment of state of equipment using the nondestructive testing methods. Repair welding, repair of damaged surfaces by cold metallization, corrections of existing structural solutions of metallic components in order to improve their technical characteristics and extend the service life are presented.
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Authors: Florian Vladulescu
Abstract: This paper presents a summary of a live demonstration for a numerical simulation of laser welding process using Ansys Workbench platform. The main steps of this simulation are: creating the geometric model, mesh generation, defining contacts, applying initial conditions and boundary conditions, defining thermal loads, general setting and solving the transient thermal analysis and finally the coupling of this analysis with a structural one to predict stresses due to the thermal field generated by the thermal analysis. After solving, the results are visualized and interpreted.
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Authors: Daniel Tihanov Tanasache, Daniela Dinica, Emilia Florina Binchiciu, Horia Binchiciu
Abstract: The paper presents representative aspects of the blades and the characterisation of excavator blades, namely frontal loader in the quall resistance to wear version. In exploitation the active surfaces of the blades are subjected to wear through abrasion under high and medium pressure, combined with mechanical fatigue with variable cycles. Retiring the blades is determined by significant degradation of the side zones. The solution developed in order to confront the mentioned phenomena is of modular type, namely equipping the blades with intelligent protection and self-protection systems to wear, which are deposited by cladding with welding on the supports. The blades support is made out of low alloyed steel, which have a controlled hardness and are micro alloyed with boron. The rods used to develop the wear protection systems are type Fe-25%Cr-4%W-Ti-V-La which deposit layers that have a minimum hardness of 55HRC. The challenges solved are related to welding compatibility, in working conditions, of the base materials and the welding ones, through manual electric welding procedure and respective deformation due to residual tensions in the welded structure.
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Authors: Emilia Florina Binchiciu, Traian Fleșer, Ionelia Voiculescu, Victor Geanta
Abstract: The paper presents the concept of designing active hammer edges of horizontal mills for grinding tungsten carbide waste by making composite layers deposited by welding. The new generation of hammers is carried out on the principles of preventive and repetitive maintenance, by endowment with wear addition, predetermined as volume and geometric configuration, depending on the specific conditions of uninterrupted use for a period of time established for economic reasons. The main demands that affect the integrity of the active areas of grinding mills (high pressure abrasion wear, thermo-mechanical fatigue) generate both material losses and output from working rates, as well as excessive elongation of the support elements under the combined action of centripetal force and of the pressure exerted by the ground load. Under these conditions, the technically and economically optimized solution is to design the modular active elements in the form of easily assembled detachable components, made of a low alloy steel with average tear resistance (450-600MPa) on which we deposit by welding layers of composite austenitic steel, hardened by compression, so as to increase the lifetime of the hammers by up to 35% compared to the present solution, which can be upgraded up to 3 times for reuse.
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Authors: Marius Adrian Constantin, Ana Boşneag, Eduard Niţu, Lia Nicoleta Boţilă
Abstract: Welding copper and its alloys is usually difficult to achieve by conventional fusion welding processes because of high thermal diffusivity of the copper, which is at least 10 times higher than most steel alloys, in addition to this, there are the well-known disadvantages of conventional fusion welding represented by necessity of using alloying elements, a shielding gas and a clean surface. To overcome these inconveniences, Friction Stir Welding (FSW), a solid state joining process that relies on frictional heating and plastic deformation, is being explored as a feasible welding process. In order to achieve an increased welding speed and a reduction in tool wear, this process is assisted by another one (TIG) which generates and adds heat to the process. The research includes two experiments for the FSW process and one experiment for tungsten inert gas assisted FSW process. The process parameters that varied were the rotational speed of the tool [rpm] and the welding speed [mm/min] while the compressive force remained constant. The purpose of this paper is to correlate the evolution of temperature, tensile strength, elongation and microscopic aspect with the linear position on the joint (local process parameters) for each experimental case and then make comparisons between them, and to identify and present the set of process parameters that has the best mechanical properties for this material.
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Authors: Ana Boşneag, Marius Adrian Constantin, Eduard Niţu, Cristian Ciucă
Abstract: Friction Stir Welding, abbreviated FSW is an innovative joining process. The FSW is a solid-state welding process with a lot of advantages comparing to the traditional arc welding, such as the following: it uses a non-consumable tool, it results of good mechanical properties, it can use dissimilar materials and it have a low environmental impact. First of all, the FSW process was developed to join similar aluminum plates, and now, the technology was developed and the FSW process is used to weld large types of materials, similar or dissimilar. In this paper it is presented an experimental study and the results of it, which includes the welding of three dissimilar aluminum alloy, with different chemical and mechanical properties. This three materials are: AA2024, AA6061 and AA7075. The welding joints and the welding process were analyzed considering: process temperature, micro-hardness, macrostructure and microstructure.
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Authors: János Lukács, Ádám Dobosy, Marcell Gáspár
Abstract: The objective of the paper is to present the newest results of our complex research work. In order to determination and comparison of the fatigue resistance, fatigue crack growth tests were performed on different grades of S690QL quenched and tempered, and S960TM thermomechanically rolled high strength steels. 15 mm and 30 mm thick base materials were used for our investigations. Welded joints were made from these base materials, using gas metal arc welding with matching, overmatching, and undermatching filler metals. In the paper, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the fatigue crack growth examinations executed on the base materials and its welded joints. Statistical aspects were applied both for the presenting of the possible locations of the cracks in the base materials and the welded joints and for the processing of the measured data. Furthermore, the results will be compared with each other, and the possibility of derivation of fatigue crack propagation limit curves will be referred.
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Authors: Lia Nicoleta Boţilă, Radu Cojocaru, Cristian Ciucă, Ion Aurel Perianu
Abstract: The paper presents new techniques for joining of materials, proposed for development by ISIM Timisoara. It shows the general considerations and preliminary results regarding two new methods of joining by riveting, methods based on friction processes: - a joining process by riveting with hybrid effect, that means mechanical grip - friction stir welding - a joining process by friction riveting. Experiments for joining by riveting were carried out for couples of metallic materials (rivet and base materials) similar and dissimilar (aluminum alloys, steel, copper). There are presented conditions and requirements for the joining processes, how to form the riveted joint, positive results and limits of the application. Primary technical data on process principle, data on technological parameters, rivet configuration and influence factors were obtained.
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