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The reactor pressure vessel (RPV) in onshore nuclear power plants is typically analysed for fatigue life by considering the temperature, internal pressure, and seismic effects using a simplified time-domain fatigue analysis. In contrast, the frequency-domain fatigue analysis method is commonly employed to assess the fatigue life of ship structures. The RPV of a floating nuclear power plant (FNPP) is subjected to a combination of temperature, internal pressure, and wave loads in the marine environment. Consequently, it is essential to effectively integrate the frequency-domain fatigue analysis method used for hull structures with the time-domain fatigue analysis method for RPVs in FNPPs or, alternatively, to develop a suitable method that effectively accounts for the temperature, internal pressure, and wave loads. In this study, a quasi-time-domain method is proposed for the fatigue analysis of RPVs in FNPPs. In this method, secondary components of marine environmental loads are filtered out using principal component analysis. Subsequently, the stress spectrum induced by waves is transformed into a stress time history. Fatigue stress under the combined influence of temperature, internal pressure, and wave loads is then obtained through a stress component superposition method. Finally, the accuracy of the quasi-time-domain method was validated through three numerical examples. The results indicate that the calculated values obtained by the quasi-time-domain method are slightly higher than those obtained by the traditional time-domain method, with a maximum deviation of no more than 24%. Additionally, the computation time of the quasi-time-domain method is reduced by 98.67% compared to the traditional time-domain method.

The construction of new renewable energy infrastructures and the development of new ocean resources continues to proceed apace. In this regard, the increasing size and capacity of offshore wind turbines demands that the size of their accompanying supporting marine structures likewise increase. The types of marine structures utilized for these offshore applications include gravity base, monopile, jacket, and tripod structures. Of these four types, monopile structures are widely used, given that they are comparatively easy to construct and more economical than other structures. However, constant exposure to harsh cyclic environmental loads can cause material deterioration or the initiation of fatigue cracks, which can then lead to catastrophic failures. In this paper, a 3D fatigue finite element analysis was performed to predict both the fatigue life and the crack initiation of a welded monopile substructure. The whole analysis was undertaken in three steps. First, a 3D non-steady heat conduction analysis was used to calculate the thermal history. Second, a thermal load was induced, as an input in 3D elastoplastic analysis, in order to determine welding residual stresses and welding deformation. Finally, the plastic strain and residual stress were used as inputs in a 3D fatigue FE analysis in order to calculate fatigue crack initiation and fatigue life. The 3D fatigue finite element analysis was based on continuum damage mechanics (CDM) and elastoplastic constitutive equations. The results obtained from the 3D fatigue finite element analysis were compared with hot spot stresses and Det Norske Veritas (DNV-GL) standards.

Due to the soft stiffness of high-rise buildings in the horizontal direction, strong wind will cause a strenuous structural response. Wind load is one key control load in the design of high-rise buildings. This study analyzes wind-induced fatigue of curtain wall supporting structure of a high-rise building in accordance with dynamic pressure measurement data of wind tunnel, acquiring wind pressure in each part of the structure. The finite element model is established for the curtain wall supporting structure, and the fatigue of corresponding nodes is discussed. Moreover, RBF (radial basis function) neural network regression is introduced to predict the fatigue life of unknown working conditions. Based on the joint distribution model of wind velocity and direction, this study explores the distribution law of fatigue life of supporting structure nodes, proposes a hypothesis of life distribution, and conducts a test. Moreover, working conditions with higher probability life are collected to provide a basis for practical engineering applications. The results show that the average deviation is below 10% by using RBF neural network and the probability life of the sample nodes is between 0 and 1016. Wind velocity is 8~15 m/s and azimuth angles of 50°~100°, 120°~200°, and 260°~300° are found in working conditions with low probability life; about 95% of the fatigue damage takes place in the first 30 conditions, and their fatigue damage values are between 3.5 × 10−3~9.36 × 10−2.

The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and relaxation of strain by recrystallization, and thus, the residual stress in the oxygen-free copper was reduced. The tensile strength and 0.2% proof stress were decreased, and elongation was increased by the heat treatment accompanying recrystallization. The plastic strain in the heat-treated specimen was increased compared with that in the untreated specimen under the same stress amplitude condition, and thus, the low cycle fatigue life of the oxygen-free copper was degraded by the heat treatment. Striation was observed in the crack initiation area of the fractured surface in the case of the stress amplitude less than 100 MPa regardless of the presence of the heat treatment. With an increase in the stress amplitude, the river pattern and the quasicleavage fracture were mainly observed in the fracture surfaces of the untreated specimens, and they were observed with striations in the fracture surfaces of the heat-treated ones. The result of the electron backscattered diffraction (EBSD) analysis showed that the grain reference orientation deviation (GROD) map was confirmed to be effective to investigate the fatigue damage degree in the grain by low cycle fatigue. In addition, the EBSD analysis revealed that the grains were deformed, and the GROD value reached approximately 28° in the fractured areas of heat-treated specimens after the low cycle fatigue test.

One of the most important issues yet to be overcome by engineers is the integrity and reliability of engineering structures. This is to ensure the safety of the engineering structure is at the greatest since the catastrophic failures usually occur due to fatigue crack growth. Due to insufficient studies on the fatigue embedded crack growth, the prismatic bar is chosen as the model of the structure. It is wise to select the solid bar since the analysis can be much simpler, thus making it easier to examine the behaviour of the fatigue crack growth. In this study, the metallic square prismatic with embedded cracks is analysed using S-version Finite Element Modelling (S-version FEM) under tension loading. The S-version FEM is an open source program, that is built from codes previously compiled as a program. The S-version FEM structured using the global-local overlay technique consists of two separate global and local meshes. By using the basic concept from the energy release rate and stress intensity factors (SIF), the behaviour of the fatigue crack growth is analysed. From the linear elastic fracture mechanics concept, the SIF is calculated using the virtual crack closure-integral method. The influences of different initial crack size and aspect ratios on the fatigue crack growth are investigated in this study. In addition, the SIF results from the S-version FEM are compared with the analytical solutions. From the analysis, the root mean square errors (RMSE) are performed to support the validation. The RMSE shows a very small error of 0.227, 0.086 and 0.3089 according to the aspect ratio of 0.5, 1.0 and 2.0, respectively. The results also show significant characteristics and behaviour of the SIF trend along the crack front, corresponding to different aspect ratios. From this study, the S-version FEM is suitable to be used to predict the fatigue crack growth for the cracks embedded in a structure. Subsequently, the S-version FEM is an open source program can be modified for increasingly complex engineering problems.

Sun tracking systems (STS) are one of the main components of large-scale photovoltaic (PV)-projects (PV farms) worldwide. PV farms comprise thousands of STS that are subjected to a number of high variable loads, e.g. the loading due to wind. It is also subjected to mechanical and aerodynamic cyclic stresses that can induce fatigue, thus shortening its lifetime. The main objective of this paper is to perform structural stress and fatigue analyses on the dual axis sun tracking system (azimuth-elevation) under selfweight and critical wind loading of 36 m/s (130km/h). Plain carbon steel is considered as the material structure. The static stress, damage distributions and fatigue life are obtained by means of Finite Element Analysis (FEA). FEA is carried out using the linear static approach. Fatigue analysis is performed using the Stress-Life method. Simulation results show that the stress resistance of the most fragile material is checked with a safety factor higher than 2 and the structure of the STS can withstand a maximum of 11.905 blocks (repeats) after the specified variable amplitude loading event before fatigue will become an issue. These evaluation results indicate that the sun tracking systems satisfy the design requirements of static strength and are safely within its designed fatigue life.

Within the scope of this research, patterns of changes in the fatigue life and limit of metals under cyclic stress were identified and the most informative parameters were determined as the basis for developing a method for the universal transformation of experimental data on the fatigue of metals and alloys for their subsequent generalization. Experimental data on metal fatigue, obtained by a large number of authors for a wide range of grades of steels and alloys, under the influence of various combinations of factors, were systematized. A generalized dependence of the recalculated parameters of fatigue life and limit was obtained, its characteristics were assessed, and a sensitivity analysis was performed, confirming the universal nature of the obtained dependence. A system of parameters has been proposed making it possible to consider and forecast high-cycle fatigue processes for a wide range of metals and alloys, under the conditions of various combinations of operating factors, from unified positions and a more general point of view.

Mechanical tests on bone plates are mandatory for regulatory purposes and, typically, the ASTM F382 standard is used, which involves a four-point bending test setup to evaluate the cyclic bending fatigue performance of the bone plate. These test campaigns require a considerable financial outlay and long execution times; therefore, an accurate prediction of experimental outcomes can reduce test runtime with beneficial cost cuts for manufacturers. Hence, an analytical framework is here proposed for the direct estimation of the maximum bending moment of a bone plate under fatigue loading, to guide the identification of the runout load for regulatory testing. Eleven bone plates awaiting certification were subjected to a comprehensive testing campaign following ASTM F382 protocols to evaluate their static and fatigue bending properties. An analytical prediction of the maximum bending moment was subsequently implemented based on ultimate strength and plate geometry. The experimental loads obtained from fatigue testing were then used to verify the prediction accuracy of the analytical approach. Results showed promising predictive ability, with R 2 coefficients above 0.95 in the runout condition, with potential impact in reducing the experimental tests needed for the CE marking of bone plates.

As offshore wind power continues to extend into deeper waters, the operational environment has expanded from shallow to deep seas. Self-elevating and self-propelled installation vessels have been widely adopted due to their jack-up systems and self-propulsion capabilities. The structural integrity of wind turbine installation vessels is crucial to ensure successful operations, among which the strength of the jacking frame is particularly critical. This study focuses on the bracket made of E550 steel at the root of the jacking frame. Shape optimization of the bracket was performed using parametric modeling technology, resulting in a 26% reduction in peak stress and a 12% decrease in bracket mass. Following the optimization, a full-scale fatigue test targeting local fatigue hot spots of the bracket was carried out. Based on the experimental data, the fatigue S-N curve of the bracket was obtained. Finally, a fatigue assessment was conducted on the high-stress region at the toe of the bracket. The results indicate that the bracket with unequal arm lengths exhibits lower stress concentration. Fatigue cracks of the bracket initiate at the weld toe, and the fatigue strength of the E550 steel toe joint obtained from the test is superior to that of the D-curve specified in the standards. Based on the derived S–N curve, a spectral fatigue analysis was further carried out to verify the fatigue performance of the optimized bracket. The total fatigue damage of the optimized structure over a 20-year design life was calculated as 0.6, which is below the allowable limit of 1.0, demonstrating that the optimized design satisfies the fatigue safety requirements.

Loess subgrades are prone to significant strength reduction and deformation under cyclic traffic loads and moisture ingress. Permeable polyurethane polymer grouting has emerged as a promising non-excavation technique for rapid subgrade reinforcement. This study systematically investigated the fatigue behavior of polymer-grouted loess using laboratory fatigue tests and numerical simulations. A series of stress-controlled cyclic tests were conducted on grouted loess specimens under varying moisture contents and stress levels, revealing that fatigue life decreased with increasing moisture and stress levels, with a maximum life of 200,000 cycles achieved under optimal conditions. The failure process was categorized into three distinct stages, culminating in a “multiple-crack” mode, indicating improved stress distribution and ductility. Statistical analysis confirmed that fatigue life followed a two-parameter Weibull distribution, enabling the development of a probabilistic fatigue life prediction model. Furthermore, a 3D finite element model of the road structure was established in Abaqus and integrated with Fe-safe for fatigue life assessment. The results demonstrated that polymer grouting reduced subgrade stress by nearly one order of magnitude and increased fatigue life by approximately tenfold. The consistency between the simulation outcomes and experimentally derived fatigue equations underscores the reliability of the proposed numerical approach. This research provides a theoretical and practical foundation for the fatigue-resistant design and maintenance of loess subgrades reinforced with permeable polyurethane polymer grouting, contributing to the development of sustainable infrastructure in loess-rich regions.