Procedia Structural Integrity最新文献

Various approaches for studying the jump-like deformation of AMg6 aluminum alloy are being compared. AMg6 alloy is characterized by instantaneous deformation increases during uniaxial stretching in the area of plasticity. It was assumed that the process of jump-like tensile deformation is caused by the cracking of dispersoids in the volume of the material. Based on that assumption, the methods that predict the initiation and magnitude of jump-like deformation depending on the proportion of destroyed inclusions were proposed. In particular, the ANSYS software complex was used to predict jump-like deformation, in which the groups of finite element models were developed to determine the main patterns of influence of structural heterogeneity parameters of the simulated environment on the stress-strain state. In addition, given the large amount of experimental data, it is important to learn how to solve such problems using machine learning (ML), particularly neural networks. It has been established that the prediction accuracy by one of the most common ML methods, that was neural networks, comprised more than 90%.

The problem of plate bending, weakened by rectilinear through crack, taking into account the contact of defect faces is considered. A detailed analysis of the analytical solution obtained previously by the classical theories of the plates within the framework of a model of crack closure along the line is performed. According to the data for intensity factors of forces and moments, the distribution of stress intensity factor across the plate thickness has been restored. We pay particular attention to the problem of determining the value of the fracture bending load. Process of propagation of the crack with non-uniformly stressed front in conditions of bending consists of two stages: irregular over its thickness consistent growth of the crack when load reaches its lower limiting value and unstable propagation of the crack when load reaches its upper limiting value. Analytical estimates of such limiting values are made using of the force and energy criteria of linear mechanics of fracture. The authors’ experience with the determine the limiting bending loads for some contact cracks systems in infinite and semi-infinite plate sis illustrated too.

Experimental studies of the influence of harmful elements (hydrogen, sulphur, oxygen) on the degradation of structural steels of underground sewer systems and the nature of their distribution in the metal of pipelines operated for a long time in aggressive environments have been carried out. It is shown that with an increase in the service life, the surface layers of the metal are enriched by hydrogen, oxygen and sulfur, adversely affecting the metal’s corrosion-mechanical properties. Combined with structural transformations, this leads to local metal embrittlement and, under favourable conditions (under alternating cyclic loads), to the formation of micropores, the coagulation of which leads to crack formation. An increase in the service life of sewage steel pipe structures leads to an increase in the values of the parameter of the body-centred cubic crystal lattice of the α-solid solution and an increase in microstresses in the structure. At the same time, part of the carbon from the decomposed cementite passes to the interface of the α-matrix. The second part, apparently, remains on dislocations, turning into microcracks, and also goes to the formation of new finely dispersed carbide particles; relatively large carbide particles form at the grain boundaries between pearlite and ferrite.

The stress-strain state data for various types of intermediate supports in two-span continuous perforated beams were obtained through calculations using the finite element method within the "Lira" software complex. The calculations were performed under the influence of a symmetrical evenly distributed load applied across the spans. It was determined that the design of the intermediate support has minimal influence on the magnitude of maximum deflections and stresses within the beam span. However, it somewhat changes the nature of its operation, especially in the case of using a support part without transverse stiffeners and with unwelded holes to the left and right of the axis of the support. The maximum normal stresses were observed at the characteristic design point of the cross-section with the hole in the supporting part of the beam, specifically without the stiffening rib and with unwelded holes on both sides of the support. Additionally, comparable stress values were noted with the inclusion of stiffeners, albeit still with unwelded holes. In all cases, these stresses remain below the calculated yield point resistance of the steel. The inclusion of welded holes and support stiffeners proves beneficial in enhancing the performance of the support components. This is attributed to a significant reduction in the concentration of both tangential and normal stresses, despite stress values in all scenarios remaining below the calculated resistance of steel.

This study is devoted to the determination of the effect of hydrogen concentration in metal C_H on the residual durability N_f of defected pipelines. Three different cases of defected pipes were considered, namely: pipe with longitudinal semi-elliptical crack at outer surface; pipe with longitudinal semi-elliptical crack at inner surface and pipe with circumferential semi-elliptical crack at inner surface. It has been shown that the presence of the crack-like defects in the pipelines is very dangerous from the point of view of their further reliable operation. This danger significantly increases with the increase of the hydrogen concentration in the metal. The increase of the danger of crack-like defects in the pipes may be expressed by the sequence: longitudinal semi-elliptical crack at outer surface – longitudinal semi-elliptical crack at inner surface – circumferential semi-elliptical crack at inner surface. The residual durability of defected pipe N_f was chosen as the basic parameter for the assessment of its further serviceability. Thus, all defects detected in the pipeline after inspection can be compared with received data and on this base the expert conclusion for the evaluation of the potential risk of each defect can be made.

Strain aging of structural steels is generally considered as an important factor in their embrittlement. In the laboratory, it is initiated by preliminary plastic deformation of a metal for the generation of dislocations, followed by short-term heating. In the study, a new hypothesis about the possibility of strain ageing occurring without any initial plastic deformation at the micro-scale under the presence of hydrogen in the process that induces internal stresses in steel was proposed. It was presumed that areas with local plastic deformation induced by hydrogen would be the preferred locations for steel to undergo strain aging during subsequent heating. This assumption was substantiated through experimental tests using the low-alloy pipe steel in different states (as-delivered state, after low-temperature tempering and after preliminary electrochemical hydrogen charging followed by low-temperature tempering). The mechanical properties of the steel, including strength, plasticity, impact strength, fracture toughness, and resistance to stress corrosion cracking, were assessed. Low-temperature tempering did not affect the mechanical behaviour of the steel. However, the steel subjected to the procedure of combining preliminary hydrogen charging with subsequent low-temperature tempering was characterized by a significant decrease in fracture toughness and resistance to stress corrosion cracking. Hydrogen had an impact on the embrittlement of the steel through the strain aging at local sites being preferable for hydrogen diffusion.

The proposed computational model for crack propagation in high-temperature creep in metallic materials under the influence of a hydrogen environment and neutron irradiation is based on the first law of thermodynamics and the balance of the rates of change of energy components for an elementary crack propagation act in a metallic body under long-term static loading, high temperature, hydrogen-containing environments, and neutron irradiation. The application of the model for determining the residual life of bodies with cracks under the mentioned loading conditions in specified operational conditions is demonstrated using an analogy to Griffith’s problem, which represents a two-dimensional problem for thin-walled structural elements.

The potential of employing nanostructured metallic multilayer to increase the durability and extend the service life of welded joints of metal structures is analyzed. Using a nickel and copper-based multilayer nanocoating as an example, a notable increase in the durability of the welded joint of up to 300...600% is observed. Corrosion tests reveal that the use of nickel and copper nanostructured metallic multilayer leads to the localization of corrosion processes at the "base metal-nanocoating" boundary. Considering the significant improvement of fatigue characteristics of welded joints and lower corrosion rate compared to welds without lamination, Ni-Cu nanocoatings can be used on offshore structures, provided that the condition of the protective anti-corrosion coating is monitored to mitigate the risk of galvanic corrosion at the base metal-nanolamination boundary.

The organization of the movement of freight trains in Ukraine is an important factor in integrating the country’s railway transport into the European system. A situation that requires a significant renewal of the freight wagon park with modern wagons to meet the freight transportation requirements has arisen. Also, a significant drawback of railway transport in Ukraine is the limitation of the speed of trains, which include freight wagons with a reduced container in an empty state, therefore, at the moment, the issue of improving the methodological and software and instrumental testing tools for evaluating the quality and safety indicators of the movement of such wagons is relevant at the moment. At present, laboratory wagons are used during field tests related to the evaluation of traffic quality indicators, acceptance and admission to operation of railway rolling stock, but the modern state of development of measuring equipment allows in most cases to abandon the use of such wagons during running tests of units rolling stock in favor of mobile hardware and software complexes.

This study deals with the evaluation of corrosion resistance and other utility properties of selected austenitic nodular cast irons and their comparison with other (non-austenitic) nodular cast irons. For the investigations, two types of austenitic nodular cast iron were selected: nickel-manganese nodular cast iron EN-GJSA-XNiMn13-7 and nickel-chromium nodular cast iron EN-GJSA-XNiCr20-2. Basic mechanical properties, such as yield strength, tensile strength, elongation, absorbed energy and hardness, were evaluated using mechanical tests. The fatigue limit was determined using low-frequency fatigue tests. Corrosion properties, such as average corrosion rate, corrosion potential and corrosion current density, were determined by the exposure immersion test and the electrochemical potentiodynamic polarisation test. Both corrosion tests were performed in a 3.5% NaCl solution (to simulate seawater) at room temperature. The results of mechanical, fatigue and corrosion tests show that austenitic nodular cast irons have lower strength and fatigue properties but significantly higher plastic properties and corrosion resistance compared to non-austenitic nodular cast irons.