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To develop a design method for concrete using low-quality recycled aggregates, an experimental study was conducted on applicability to examine the structural strength correction value (S value) and calculation of mix proportion strength of recycled aggregate concrete-Class M, which used recycled aggregate class L mixing with the normal aggregate. Cement used in the experiment was ordinary Portland cement (in this case, fly ash type II was used as a fine aggregate substitute), Portland blast-furnace slag cement type B, and low-heat Portland cement. As a result, the mix proportion strength of recycled aggregate concrete-Class M could be determined using the S value according to JASS 5 (2018) as normal-weight concrete.

This study presents a practical method for estimating the extreme value distribution of von Mises stress for ship structural strength evaluations. The previous methods of calculating this distribution require somewhat complicated numerical calculations, such as multi-dimensional integration. In contrast, the proposed method is based on an asymptotic approximation and can be easily calculated in a similar way to the conventional linear statistical prediction. A closed expression was derived in the case of stress components which have non-zero mean value. The formula is derived under approximations that reflect realistic stress conditions when ships are under severe sea states. Through a structural analysis of a whole ship, it was comprehensively verified that the proposed method has sufficiently high accuracy for structural strength evaluation. Furthermore, a parametric analysis was conducted to clarify its limit of applicability.

With the aim of investigating the assessment methodology for the overall damage effects on an unmanned aerial vehicle (UAV) subjected to a blast wave, the failure criteria for the typical UAV was formulated through an analysis of the structural strength design standards. Specifically, the shear force associated with wing failure can serve as a critical parameter for assessing the overall damage inflicted on the UAV by blast waves. According to the design load criterion of the aircraft, the shear force value corresponding to the overall failure of the typical UAV was calculated. Numerical simulations were conducted to investigate the mechanical response of UAV structures under blast wave loading generated by a 500 g explosive. Combining the critical shear force values obtained from theoretical calculations with the numerical simulation results, two distances between the explosives and the UAV that could produce different damage effects were estimated, namely 1 m and 2.5 m. Subsequently, static explosion experiments with equivalent explosive charges were performed, revealing different damage effects on a typical UAV at two specific distances. The numerical simulation results were highly consistent with the experimental observations, further validating the scientific and rational basis for using shear force as a primary parameter in assessing overall structural damage to fixed-wing UAVs.

Under the condition of complex waters, the long-term action of a vessel-generated wave makes the anti-collision facilities have the risk of structural failure. Taking the Yinzhou lake bridge pier anti-collision structure as the research object, the extreme vessel-generated wave load is calculated, and the structural strength of the floating anti-collision facility under the action of the vessel-generated wave is analyzed using the direct calculation method. The results indicate that the ultimate strength of the overall structure of the anti-collision facilities meets the design requirements, but there is insufficient strength in some parts. A strengthening scheme to meet the design requirements of structural yield strength is proposed.

Aiming at the problem that large-scale ultra-high-pressure pneumatic ball valves opened and closed at large explosion instantaneously are prone to fatigue failure due to dynamic stress concentration under transient impact loads, this study proposes a multi-physics field coupling structural strength optimization design method based on finite element method. A transient dynamic model is constructed through an explicit dynamics algorithm to simulate the dynamic response under high-frequency impact loads during the blasting opening and closing process. Fluid-Structure Interaction (FSI) is introduced to analyze the interaction between fluid impact force and structural deformation. At the same time, the elastic modulus degradation effect of tungsten carbide/nickel-based alloy composites caused by frictional heat is considered, and the wear rate is calculated based on the wear model Archard. Secondly, the variable density method is used to perform topological optimization on the key areas of the valve body (such as the contact surface between the sphere and the valve seat), the internal rib layout is reconstructed to reduce stress concentration, and geometric parameters such as the valve seat inclination angle and the sphere diameter are screened. The nondominated sorting genetic algorithm (NSGA-II) is used to achieve the coordinated optimization of the leakage rate and the coating’s wear resistance and structural strength. By building an ultra-high pressure burst test bench, this paper combines strain gauges and high-speed cameras to verify the accuracy of the model and corrects the simulation boundary conditions based on the Kalman filter algorithm. The experiment shows that after optimization, the maximum equivalent stress peak of the valve body is reduced by 32.7%, the leakage rate is reduced to 0.008%, and the dynamic fatigue life is increased to 1.5 × 10 5 cycles under the commonly used engineering stress amplitude. The stress error between the simulation and the test is always less than 5%. The multi-objective optimization method under dynamic load in this paper can provide a theoretical basis for the reliable design and intelligent operation and maintenance of ultra-high pressure and ultra-wear-resistant pneumatic ball valves and promote their engineering applications in the fields of hydrogen energy storage and transportation and chemical industry.

Changes in the deformation behavior of steel solids and their properties have been considered after different methods of surface treatment (carburizing, nitriding, bombardment with low-energy ions, epilam application). Distinctions between concepts “structural strength of a material” and “structural strength of a workpiece” have been illustrated. It has been shown that, at the same material structural strength, the metal mechanical characteristics of a finished metal workpiece (i.e., the workpiece’s structural strength) change cardinally depending on the genesis of the modified layer (features of the structure that arise at the surface) and its contribution to the general state of the workpiece. After ion bombardment (layer thickness less than 1 μm) for the same material with the full retention of its structural strength, we can obtain in workpieces of the material either a very high (25–40%) strengthening without reducing plasticity or huge growth in the plasticity (increase in the elongation by a factor of 1.6) with enhanced strength. The effect is due to the nondislocation mechanism of plastic deformation of the surface layer nanostructurized upon ion bombardment and competition between strengthening and plasticizing depending on the magnitude of its contribution. The effectiveness of the strengthening action of ion bombardment is shown on connecting rod bolts 10 mm in diameter; the plasticizing effect is observed on thin sheet cold-rolled steels (improved stampability).

This paper systematically investigates the influence of trough-type stiffener dimensions (height, thickness, width) and center distance on the structural strength of an ±800kV converter transformer tank. The results indicate that increasing the height and thickness of the trough-type stiffeners significantly reduces the maximum deformation of both the tank wall and stiffeners. Appropriately adjusting the center distance not only effectively improves the maximum deformation of the tank wall but also maintains the overall weight of the transformer. When the trough-type stiffener height is no less than 230 mm, thickness no less than 12 mm, width no less than 400 mm, and center distance no greater than 1250 mm, the maximum deformation of the tank wall and stiffeners remains below twice the wall thickness, satisfying mechanical strength requirements. The findings provide valuable references for researchers and engineers engaged in the structural design of transformers.