Papers by Keyword: Repair

Abstract: This paper illustrates the results of the activities of analysis and structural assessment of the Assumption of the Virgin Mary chapel, in Prague. The chapel, an oval-shaped building covered with a dome, was built at the end 16th century and can be considered the last example of renaissance architecture and at the same time the first example of baroque architecture in Prague: it is a significant testimony of the close connection between local artists and their Italian teachers. The building closed to visitors during the last decades for the presence of some structural damages and because severely degraded due to lack of maintenance, was reopened in the 2017 after a notable restoration process. This paper gives attention to the interdisciplinary approach used to diagnosis and structural assessment of the chapel, based on the activities of the “knowledge path,” the subsequent structural analysis and the intervention design. Particular attention was paid to the contribution of the historical review, geometric laser scanner survey and mechanical characterization of the structural materials. All these steps result necessary to identify potential vulnerabilities and to enable the understanding of the effective structural models, also in view of proposing adequate retrofit solutions. A numerical model of the chapel was prepared and calibrated. Finally, the structural assessment for the vertical and seismic loading was performed.

Abstract: Turbine and generator rotors and shafts undergo high stresses during regular working life and, from a safety and operational aspect, are the most significant components of a power generation system. Depending on the appropriate operating conditions, like temperature and/or corrosion the, shafts can be fabricated out of low/high alloy heat resistance material or of low alloyed, highly toughened material for different application. Despite known good practice and developed operation procedures, the failures of shafts sometimes occur. The right and well-defined failure analysis is the basis for feasibility analysis of repair method in the power generating industry. The analysis of direct and indirect costs of repair after the failure analysis as well as the analysis of the repair and post-repair conditions of the repaired element is the vital for decision on the key question. Is it possible to repair this element and what is the optimal repair strategy This paper compares and analyses two approaches, by weldability analysis and weld cycle simulation, in order to determine welding feasibility analysis of cracked hydro turbine shafts.

Abstract: High pressure cold spray has been showing increasing promise and application for structural repairs and coating applications where wrought like strengths are required. For example, numerous applications have been developed for repairing high cost and long lead time parts for the aerospace and defense market, such as aircraft skin panels, titanium hydraulic lines, aluminum valve actuator internal bores, hardened and chromed steel shafts, gas turbine engine parts, magnesium castings, and many more. These processes also have direct application in commercial markets like transportation and heavy industry. In particular, parts with lead times in excess of 12 months have been successfully repaired and re-introduced into service. This saves not only the direct cost of the part, but also returns the system to service much sooner. Additional benefits of field application with a hand-held nozzle assembly are also possible, particularly for power plants, refineries, and other large industrial plant operations. Cold spray consequently has a tremendous opportunity to enhance manufacturing sustainability by repairing parts that previously could only be replaced and recycled. It is environmentally friendly, as there are no toxic fumes or other harmful emissions from cold spray. Furthermore, because parts are being repaired and refurbished rather than replaced, there is tremendous cost, energy, and overall environmental benefit, making cold spray a “green” technology and an excellent technology for enhancing the long-term sustainability of high value assets.

Abstract: TiAl alloys are increasingly used as a lightweight material, for example in aero engines, which also leads to the requirement for suitable repair techniques. Transient liquid phase bonding is a promising method for the closure of cracks (in non-critical or non-highly loaded areas). The brazing solder Ti-24Ni was investigated for brazing the alloy Ti-45Al-5Nb-0.2B-0.2C (in at. %). After brazing, the joint exhibits different microstructures and phase compositions. The transient liquid phase bonding process was investigated in the middle of the joint region in situ to acquire time resolved information of the phases, their development, and thus the brazing process. These investigations were performed using high-energy X-ray diffraction at the “High-Energy Materials Science” beamline HEMS, located at the synchrotron radiation facility PETRA III at DESY in Hamburg, Germany. For this, we used an induction furnace, which is briefly described here. During the analysis of the diffraction data with Rietveld refinement, the amount of liquid was refined with Gaussian peaks and thus could be quantified. Furthermore, while brazing four different phases occurred in the middle of the joint region over time. Additionally, the degree of ordering of the β_o phase was determined with two ideal stoichiometric phases (completely ordered and disordered). Altogether, the phase composition changed clearly over the first six hours of the brazing process.

Abstract: The article deals with the urban environment key aspects and the fixed assets reproduction on the system level, analyses the results achieved in the course of the state policy, proposes a conceptual model for the urban environment objects expanded the reproduction management.

Abstract: The heterogeneity of manual arc welded samples of low-carbon steel St3sp meant for bridge construction to be used in Cameroon has been investigated. The chemical analysis of the material was carried out and the arc welding processes used, then the probes were subject to mechanical testing such as tensile test, low-cycle fatigue test, and micro hardness study. A total inclusion of weld defects in the specific welded sample and especially in the cyclic loading specimes has been discovered. Premature fracture was revealed below the plastic limit in some probes during the tension and low-cycle test. A micro structural examination and micro hardness measurements were done in order to determine what exactly could be the reason of this catastrophic failure. The structural analysis revealed the differences in mechanical properties conditioned by phase distribution and carbon content in weld, heat affected zone and base metal. To determine the heterogeneity in mechanical properties the elastic modulus distribution has been calculated due to relationship between the micro hardness and materials strength.

Abstract: Aim of this work is the evaluation of FRCM capacity in repairing pre-damaged clay brick walls under out of plane loads. Full scale experimental tests have been performed damaging clay brick walls subjected to out of plane loads; then, tests are performed on damaged walls repaired with innovative composite grids with inorganic matrix (FRCM). The boundary constraints of the walls (two adjacent edges constrained and the other two free) allowed to simulate a non-uniform out of plane behaviour of the wall subjected to a pointwise normal load applied at the free corner. The aim of this study was to assess the potentiality of FRCM to recover stiffness after significant damage and to improve the lateral (out-of-plane) capacity of the repaired wall. Experimental evidences demonstrated that the externally bonded strengthening was not strongly affected by debonding and it was able to prevent a flexural failure; the collapse of the wall occurred at almost double load with respect to the unreinforced configuration, despite previous significant damage, and that the failure was governed by shear sliding. Future developments include experimental tests of strengthened walls not previously damaged, to investigate on the effect of pre-damage on out of plane strengthening capacity of FRCM.

Abstract: Indications were detected on dissimilar metal welds (DMW) of steam generators (SG) after 20 years of operation during NDT inspections. Indications started slowly growth every year. DMW on SGs had to be repaired. Paper describes experimental analysis and degradation mechanism of SG weld joints failures.

Abstract: The cold spray technology is an innovative technique used to coat metallic and non-metallic substrates for protection from corrosion and/or to improve surface functionalities. It is well known that surface degradation (i.e. corrosion) is not merely an aesthetic issue; its consequences may affect the structural behaviour and the usability of structures or parts of them. This paper addresses the use of cold spray technology as a potential innovative tool for the repair of an extruded 6005A-T6 aluminium alloy item. The specimens investigated have a complex geometry and are used for a new kind of bolt-channel joints to secure the passenger seats to the frame of buses. In order to simulate environmental degradation, samples were exposed to aerated synthetic seawater for 15, 60 and 240 days and, subsequently, cold spray coated using a pure aluminium powder. Results acquired show that layers obtained using Cold Spray process are effective against corrosion, restore volume and geometry shape of corroded metals components without showing visible traces of the repair.

Abstract: This work focuses on welding repair of aluminium alloy 6082 T6 by TIG welding process. Two types of filler, 4043 and 5356 were used. A comparison at I= 120A,140A, welding speed 20cm/min and gas flow rate 15 L/min was studied. Physical characteristics, macrostructure and microstructure at weld metal and Heat Affected Zone (HAZ) were investigated. Which at 140A can welding repair. The parameter 140A have complete melting and fail area at HAZ and mechanical properties more than 120A.