Papers by Keyword: Repair

Abstract: Composite sandwich panels are extensively used in aerospace, automotive, and construction applications due to their exceptional strength-to-weight ratio and structural efficiency. However, local surface deviations, such as waviness and dents, often develop during manufacturing and operation, potentially leading to adhesion failures and delamination between the composite skin and the core. This study aims to establish acceptable defect size limits that can be corrected through technological pressing, ensuring structural integrity of composite material while minimizing the negative impact on load-bearing capacity of sandwich panels. An analytical approach was adopted to assess the stress behavior of composite skins with waviness and elliptical dent defects. The analysis was based on beam and plate theory, incorporating the effects of flexural rigidity, material anisotropy, and applied technological pressure. The Hill strength criterion was applied to define permissible defect limits, considering variations in structural criticality levels. The study determined the maximum allowable sizes for waviness and dents in composite sandwich panels, factoring in the responsibility level of the panel, expressed as the maximum stress intensity coefficient. The results show that the acceptable defect size decreases with increasing structural criticality. It was also found that forced compression of dents induces pre-stress zones within the composite skin, potentially altering its stress distribution and reducing its long-term load-bearing capacity. The proposed methodology provides a quantitative framework for evaluating acceptable defect limits, supporting manufacturing quality control and repair optimization. The results offer practical insights for enhancing the reliability and durability of composite structures, ensuring that local surface deviations remain within permissible limits without compromising structural performance.

Abstract: In the automotive industry, parts are mostly made from aluminium alloy due to its lightweight properties and high corrosion resistance. However, the drawback is that the aluminium alloy is easily worn due to wear and friction and will end up in the scrap yard. In order to salvage the aluminium component, the worn part can be repaired. Currently, wire arc additive manufacturing (WAAM) offers flexible remanufacturing of the worn part. However, the wear behaviour of the additively manufactured part needs to be studied first to improve the wear performance of the material. In this study, the gas metal arc welding (GMAW) or MIG-based WAAM machine was utilised to produce a 3D profile from the available aluminium alloy wire grade ER 5356. The wear test was carried out in accordance with ASTM G-99, using a pin-on disc in both dry and wet sliding conditions. It was found that on dry sliding, the specific wear rates are decreasing from 5.3632 x 10^-11 mm³/Nm to 4.3496 x 10^-11 mm³/Nm and 4.1513 x 10^-11 mm³/Nm as the speed increases from 200 to 400 RPM at the constant 20 N load. Meanwhile, for wet sliding, it has been observed that the specific wear rate increases as similar speed values are used in dry sliding conditions, which are 6.8122 x 10^-12 mm³/Nm, 1.1931 x 10^-11 mm³/Nm and 3.7561 x 10^-11 mm³/Nm with a similar constant 20 N load. Next, the coefficient of friction for dry sliding shows that as the speed decreases. In contrast, for wet sliding, it is observed that the coefficient of friction increases.

Abstract: Architectural heritage nowadays includes concrete structures constructed in the 20^th century. These buildings are usually under-detailed, since the actual behavior of reinforced concrete at the time of their construction was not clearly understood, whilst building codes incorporating seismic resistance design, especially in seismic prone areas, did not exist. This inevitably led to inefficient design and consequently to severe damages in many historic concrete buildings during past seismic events. This paper explores the use of novel Engineered (Fiber Reinforced) Cementitious Composites (ECCs), with strain hardening abilities in tension, for the repair and strengthening of old sub-standard reinforced concrete columns, focusing on their confining and shear strengthening potentials. The experimental results show that, when replacing the reinforcement cover with fiber reinforced ECCs, the fibers bridge tensile cracks, limiting their opening and increasing their resistance against volumetric expansion, ultimately leading to increased amounts of energy dissipation. ECCs may thus by used in the repair of historic concrete structural elements.

Abstract: The latest seismic events in Ecuador have allowed to verify some damage typologies on masonry panels of reinforced concrete buildings with frame resistant structures. Therefore, some theoretical and experimental research have been carried out to justify the intervention for repairing the damage to the masonry walls to give them a certain degree of shear ductility to provide for compatibility of the lateral deformations of the structure and of the masonry panels.

Abstract: Extending the lifetime of energy facilities is extremely important today. This is especially true of nuclear power plants, the closure (or modernization) of which poses enormous financial and environmental problems. High-quality repair of reactors can significantly extend their service life. One of the critical parts is heat exchangers, the tubes of which quite often fail. Sealing, as a type of repair of heat exchanger tubes by the plugs, is promising provided that the joint quality is high. Practical experience in the use of welding to solve this problem has shown the need to search technological solutions associated with increasing the depth of penetration and reducing the area of thermal effect. The aim of the work was to develop a highly efficient technology for repair and extension of service life of heat exchangers of nuclear power plants based on the results of studying the technological features of laser welding of joints of dissimilar austenitic steels AISI 321 and AISI 316Ti in the vertical spatial position. Based on the results of the analysis of mechanical test data, visual and radiographic control, impermeability tests and metallographic studies of welded joints, the appropriate modes of laser welding of plugs have been determined. The principal causes of defects during laser welding of annular welded joints of dissimilar stainless steels are determined and techniques for their elimination and prevention of their formation are proposed. Based on the results of the research, technological recommendations for laser welding of plugs in the heat exchange tube of the collector are formulated, which significantly improves the technology of repair of steam generators of nuclear power plants and extends the service life of reactors.

Abstract: Nickel aluminum bronze (NAB) castings possess favourable combinations of strength and resistance to corrosion, biofouling and cavitation/erosion, and so have long been used in naval applications. Nonetheless, in seawater environments NAB castings are susceptible to selective phase corrosion and so such components periodically require either replacement, which is very costly, or repair. However, repairs involving traditional, high heat input welding operations can lead to distortion and microstructural changes that unacceptably degrade NAB corrosion performance, and so repairs are not commonly performed. In the present work, cold spray is explored as an alternative for NAB (alloy CuAl9Fe5Ni5) repair without excessive distortion or base metal degradation, and preliminary results of its performance reported. Suitable cold spray parameters have been determined using an iterative approach by analyzing deposits in terms of microstructure, porosity and adhesion to the substrate. It is intended that these parameters will later be used to create simulated repairs which can be more thoroughly characterized for strength, toughness and corrosion performance.

Abstract: The work presented in this paper is devoted to the formation of thick-layer wear-resistant coatings by technologies based on electrospark alloying, an example of essential components hardening for the heavy-duty processing equipment operating under hydroabrasive wear conditions. The aim of the paper is to improve the manufacturing and repairing technologies for the helical surfaces of the screws made of 65Г, 30X13 and 40X steels and corrosion-resistant stainless steel 12X18H10T. The above aim has been achieved owing to applying the new environmentally friendly technologies for the formation of the surface layers, and also due to the choice of the surface layers that are most resistant against hydroabrasive wear, which choice being provided for by conducting the comparative tests on the samples made of the above said steel grades and strengthened in various ways. The analysis results of the hydroabrasive wear resistance of the samples made of steel and provided with protective coatings is presented.

Abstract: As a countermeasure against deterioration of reinforced concrete structures that have suffered from salt damage, materials containing salt adsorbents have been developed. In this study, the basic properties of the “Hybrid Epoxy Resin Repair Agent” in which a functional adsorbent was added to an epoxy resin were grasped and verified. As a result, chloride ion adsorption effect assuming repair of salt damage and sulfate ion adsorption effect assuming chemical erosion repair was confirmed.

Abstract: The present studies provided for an improvement in the technology of applying protective coatings for metal building structures, primarily coatings being renewed during their repair, modernization or reconstruction of production. At that the main objectives of the research were reduction of the labor coefficient of work relating to the preparation of surfaces of metal building structures, by applying the rust painting method, and creation of anticorrosive materials with universal properties combining the functions of rust, primer and basic coating modifiers.

Abstract: This paper attempts to investigate the fracture toughness of the cracked concrete repaired by polymethyl methacrylate (PMMA) - a thermo-plastic polymer resin. A single-edged notch beam in three-point bending test was conducted to examine the performance of cracked concrete beam after reparation. Three concrete crack widths of 1 mm, 5 mm, 10 mm were designated to be repaired and examed. The fracture properties include critical stress intensity factor K_IC by Jenq and Shah and fracture energy G_F by Hillerburg, were evaluated for the concrete before cracking and after reparation. Four sand contents of 0%, 10%, 20% and 40% by volume were used in the PMMA mortars. From the testing results, it appears that the load capacity and fracture toughness of repaired concrete increased with the increasing sand content. And, the PMMA mortar made repaired concrete better strength and fracture toughness as well.