Archives of Civil and Mechanical Engineering最新文献

High-power lasers have been shown to be more effective for welding plates with thicknesses of 10 mm or greater. In the present research, a heat-resistant P92 steel plate was welded using the laser beam welding process. The laser-welded joint underwent mechanical testing and metallographic characterization in both the as-welded condition and after post-weld heat treatment (760 °C for 2 h). The macrostructure analysis revealed that the welded joint had full penetration with negligible internal defects. The widths of the heat-affected zone (HAZ), the weld metal at the top, and the weld metal in the root region were 1.77 mm, 3.83 mm, and 3.12 mm, respectively. Inhomogeneity in both the microstructure and microhardness was observed along the welded joint. The coarse-grained structure with negligible precipitates in the coarse-grained HAZ resulted in a maximum hardness of 432 HV, while a minimum hardness of 225 HV was measured in the inter-critical HAZ, likely due to the formation of a complex microstructure. Another important observation in the fine-grained HAZ and inter-critical HAZ was the presence of two types of grain boundaries: one decorated with a high density of precipitates and the other free from precipitates. This contributed significantly to the heterogeneity in the microstructure. The weld metal exhibited a lath-elongated martensitic microstructure, which showed significant hardness variation due to the presence of soft ferrite patches. The hardness of the untempered martensite in the weld metal ranged from 385 to 403 HV, with an average of 398 ± 7 HV. In contrast, the hardness of the soft ferrite patches was measured in the same range of 234–349 HV. The ultimate tensile strength and percentage elongation were 1014 ± 11 MPa and 27 ± 3%, respectively, which are significantly close to those of the P92 base metal, as fracture occurred in the P92 base metal. The Charpy toughness measured higher than the recommended value of 47 Joules, confirming the suitability of the welded joint for USC boiler applications. The PWHT significantly reduced the inhomogeneity in microstructure and mechanical properties, though some variation remained. There was a notable decrease in hardness for the weld metal, coarse-grained HAZ, and fine-grained HAZ after PWHT, while the hardness of the delta ferrite patches and inter-critical HAZ remained relatively unaffected, leading to continued microstructural heterogeneity. The tempering of martensite due to PWHT resulted in a drop in ultimate tensile strength and an increase in percentage elongation, with failure still occurring in the P92 base metal in the PWHT condition. Additionally, Charpy toughness increased significantly after PWHT, confirming the applicability of the PWHT for welded joints of P92 steel before final application. A good correlation between microstructure and mechanical properties was established based on these findings.

PYROWEAR 53 steel is a special carburizing steel used mainly for the production of machine parts for the aviation industry. Machine parts are surface-strengthened in the carburizing process and subsequent heat treatment (hardening, freezing, and low tempering). The carburizing temperature recommended and used in industrial practice is 921 °C. After saturating the surface layer with carbon, it is recommended to reheat for hardening and cooling in oil. This work assessed the possibility of increasing the carburizing temperature and hardening the layer immediately after saturating the surface layer with carbon, after cooling to the recommended hardening temperature of 913 °C. The carburizing process was carried out using the LPC (low-pressure carburizing) FineCarb technology. The condition for increasing the carburizing temperature was to maintain the required grain size of the prior austenite—G6. This study examined the tendency to grow the austenite grain and determined the highest austenitization temperature ensuring the required grain—G6. At this temperature, the carburizing process then heat treatment were carried out in accordance with the requirements of manufacturers of machine parts for the aviation industry. The microstructure of the layer, its phase composition, the content of retained austenite, the value of residual stresses and surface hardness, and its changes at depth were determined.

This article explores the potential and accuracy of spring–mass–damper (SMD) pedestrian load modelling strategies for assessing human-induced vibrations of in-service footbridges. To this aim, a recent SMD modelling proposal based on uncoupled single-body measures (SMD-0, in the following) is specifically used for the calibration of key input parameters. Finite element numerical assumptions and findings are robustly supported by original experimental tests carried out on a case-study footbridge in Poland, proving that the proposed approach can serve as an effective tool for analysing vibrations in pedestrian systems. The research study, most importantly, integrates theoretical modelling with empirical and experimental validations, to enhance the credibility of the obtained results, as well as to support the general applicability of the presented methodology. Complex in-field tests are in fact conducted on the selected footbridge, aiming to assess the effects of pedestrians on its dynamic response. Numerical analyses, which are successively performed in ABAQUS/Standard, for a set of examined walking configurations, confirm the high sensitivity of the footbridge to resonance, which was also observed during the in-field tests. The presently used SMD-0 approach is further assessed towards past SMD literature proposals. As shown, the comparison of standard structural performance indicators (such as the peak acceleration value, root mean square and CREST factor) reveals a significant sensitivity of the footbridge response to the input parameters for the analyzed SMD models. Besides, the presently addressed SMD-0 model has the advantage of being based on single-body sensor measurements and its calibration is not affected by structural features. As such, potential applications of present findings could include the improvement of design standards and safety measures for similar structures.

In recent years, notable advancements have been achieved in the field of material science, particularly in metallurgy and ceramic materials. Electrical discharge machining (EDM) has become an indispensable non-conventional machining process, especially suited for intricate shaping of tough materials like ceramics and composites. This comprehensive review delves into the core mechanisms of EDM, focusing on the interplay of thermal energy and electrical discharges. The influence of dielectric fluids and cutting-edge electrode materials is highlighted for their significant role in enhancing machining performance and material removal efficiency. Various EDM techniques, including dry EDM, powder-mixed EDM, micro-EDM, and wire EDM, are explored with a particular focus on their effects on precision, surface quality, and overall material integrity. In particular, the machining of advanced ceramic composites, such as Si₃N₄–TiN and MoSi₂–SiC, is emphasized, where optimizing process parameters becomes crucial to overcoming machining challenges. Key aspects like surface roughness, the formation of recast layers, and alterations in microstructure are scrutinized for their impact on the durability and properties of the final product. The review also sheds light on advanced optimization strategies, including Artificial Neural Networks (ANN), fuzzy Multi-Objective Optimization (MO), genetic algorithms, and hybrid methods like Particle Swarm Optimization (PSO) and Teaching–Learning-Based Optimization (TLBO). These tools are essential for boosting EDM performance, especially in applications demanding high precision. The paper ends with some observations about the expanding use of EDM in biomedical applications, especially in the manufacturing of implants and other medical devices.

The article presents an experimental and numerical study on the effectiveness of an additional shield mounted under the vehicles in reducing the penetration capability of the scattered mines, using the example of the MN-123 mine. For this purpose, the formation of the EFP (explosive formed penetrator) was analyzed for the classic scattered mine system with a double EFP-shaped charge. Then, after validating the numerical results against the experiment for the static tensile test, the authors performed a numerical analysis for a protective structure made of elastomer, placed between the mine and the bottom of the protected vehicle (parallel to the ground surface). Three variants of the thickness of the rubber element from 10 to 30 mm were analyzed in order to determine the impact of the shield thickness on the EFP formation process. In the final phase, the selected system was experimentally tested on a military training ground. The results obtained indicate that the use of analyzed shielding protecting bottom part of vehicles against mines and EFPs can significantly decrease the mine penetration capability. In addition, the use of the smoothed-particle hydrodynamic (SPH) method to describe the formation of the EFP projectile allowed to take into account the highly dynamic nature of the phenomenon. A novelty in the applied study is the use of an elastomeric cover in the immediate vicinity of the mine, which limits the EFP formation process and also limits the speed of the projectile. This is crucial because the key factor determining the penetrating capabilities of EFP is the high kinetic energy of the formed projectile. Based on the research conducted, areas of potential application of this type of covers can be distinguished. These will primarily be all types of heavy, armored vehicles moving in armed conflict zones, exposed to mines/IEDs/EFPs, such as armored infantry fighting vehicles and tanks.

The time reversal principle is exploited for damage detection of a homogeneous metallic beam, representative of a structural element, at its different health states. Then, a damage index is used for quantifying detected damages. It is shown that even with a limited number of transducers and restricted ultrasonic frequencies e.g., around 30 kHz, the damages are detectable. This study, is a primary step for monitoring civil engineering structural elements such as bridge cables for detection of their damages at their early developments.

Network structured titanium matrix composites exhibit significantly enhanced mechanical properties compared to the base titanium alloy. However, the existing research on the composites is mostly conducted at room temperature. Studying the interactive effects of reinforcement distribution and temperature on the mechanical properties of the composites is of great importance for material applications. This paper fabricated in-situ ({text{TiB}}_{{text{w}}} {text{/Ti6Al4V(TC4)}}) composites with different distribution of TiB through fast hot-pressing sintering. Tensile experiments at different temperatures were conducted to elucidate the interactive effects of TiB distribution and temperature on the mechanical properties of the composites. The influence of network size on the mechanical performance of network-structured composites was also analyzed. Additionally, room temperature in-situ tensile tests were performed on the composites with homogeneous and network-distributed TiB. The fracture mechanisms of the composites with different distributions of TiB were revealed by examining the fractography. The results showed that the composites with a homogeneous distribution of TiB exhibit brittleness at low temperatures, yet they demonstrate superior mechanical properties at high temperatures compared to those with network-distributed TiB. The small network structured composites have stronger grain refinement and higher TiB load-bearing efficiency and have better mechanical properties than the large network structured composites. At low temperature, the fractography shows that the network-distributed TiB can promote crack deflection and increase the fracture strain of the composites. However, at high temperature, the fracture modes of the composites with different distribution of TiB are similar due to the softening of the matrix.

Advanced Self-Compacting Concrete (SCC) is a highly flowable concrete that completely avoids vibration during casting. This paper explains the properties and performance in formwork of this highly flowable SCC, and the lateral pressure exerted on the sides of the formwork. In this investigation, a lightweight plastic system panel was used to cast the concrete column. The reactions of materials in real time and how the process of hardening occurs were investigated. Thus, this study discusses the casting rate, rheology, workability, lateral pressure, and plastic shrinkage of SCC. Using Digital Image Correlation, it also discusses physical and mechanical properties at early ages and at the hardening stage of 28 days. The properties at these time points are critical facts that should be considered during the design of formwork. In this paper, the most advanced techniques are used to measure lateral pressure exerted at different heights on the sides of the formwork.

This paper aims to explore a system with two linear oscillators coupled in a circular pipeline and clarify the synchronous mechanism from the viewpoint of energy transfer. Considering the mass of the motor housing and stator, etc., this paper presents a continuous model of a pipeline system with concentrated mass and discretizes it using the Galerkin method under simply supported conditions. The synchronization criteria are then derived from the energy integration of the motion equations. The mutual comparison of the characteristic analysis and the numerical results verifies the effectiveness of the theoretical investigation in the present paper, and the system exhibits synchronous behavior in the non-resonant region. The Sommerfeld effect near the 1st-order resonance region is explored, and the minimum supplied power frequency threshold is found for the system to pass through the capture-jump behavior. Additionally, the influence of structural parameters such as pipeline internal diameter, oscillator mass, and excitation location on the synchronization behavior of the system is discussed. These results are expected to provide good support for understanding the synchronous behavior in pipelines and vibration utilization techniques in pipeline transportation.