Archives of Civil and Mechanical Engineering最新文献

Fibre-reinforced polymer (FRP) sheets have been extensively used to strengthen existing structures in harsh environments (e.g., freeze–thaw and chemical attacks) due to their excellent mechanical properties and durability. However, the effects of FRP sheets on strengthening reinforced concrete columns eroded by chloride and sulphate ions in freeze–thaw environments remain ambiguous. Therefore, this paper investigates the salt frost resistance of basalt fibre-reinforced polymer (BFRP)-reinforced columns subjected to complex salt-frozen environment. The effects of the freeze–thaw medium, reinforcement method, and pre-damage degree on the salt frost resistance of the columns were evaluated, followed by revealing the freeze–thaw damage mechanism of the columns eroded by sulphate and chloride. Moreover, the correlation between the durability and the mechanical properties of the columns wrapped with BFRP sheets was analysed. Results indicate higher concentrations of sodium chloride and sodium sulphate solutions decelerate the deterioration of high-performance concrete (HPC). The double-layer BFRP sheet wrapping method increases the ultimate load of the columns by 84.8%. The partially damaged epoxy resin coatings can serve as a protective layer for the concrete. The ultimate-transition stress ratio of columns wrapped with double-layer BFRP sheets can be used as an index to evaluate the durability. The proposed BFRP retrofit method demonstrates significant potential for enhancing the durability of HPC in salt frost regions. This method provides a theoretical basis for the durability design of reinforced HPC columns wrapped with BFRP sheets in salt frost regions.

The double-gradient hierarchical multi-cell hexagonal tube (DGHMHT) is introduced, featuring gradient designs in both axial and radial directions of the thin-walled tube. This study investigates the impact resistance of this structure under multi-load conditions using the Abaqus/Explicit finite element model, validated by quasi-static tests. Results indicate that the proposed DGHMHT exhibits superior resistance to overall buckling compared to single-gradient hexagonal laminated thin-walled tubes under multi-load impacts. In addition, it significantly reduces the initial peak force without compromising overall energy absorption, achieving a 74.92% reduction for the double-gradient structure compared to a 72.84% reduction for the single-gradient structure of the same order, respectively. Furthermore, increasing mass substantially enhances the structure’s energy-absorption capacity. Mass increment from 0.0729 to 0.3650 kg boosts Specific Energy Absorption (SEA) nearly tenfold, albeit with a corresponding rise in initial peak force. Examining impact angle effects reveals that the double-gradient structure is less susceptible to overall buckling as the angle increases, with the SEA of DGHMHB-3 surpassing that of hexagonal tube by 34.08% at a 10° impact angle. Analyzing the axial gradient length of DGHMHB-3 suggests that appropriately adjusting layer-height distribution can elevate the structure’s energy absorption and deformation resistance. These findings underscore the effectiveness of the proposed double-gradient hexagonal laminated thin-walled tubes in mitigating collisional impacts, particularly under multi-load conditions.

An algorithm for the reliability and durability assessment of stay cables in bridges is presented in this study enabling their probability of failure and a safe working period to be determined under various loading scenarios. The algorithm was originally developed based on data collected from an extensive structural monitoring campaign of the biggest single-pylon concrete cable-stayed bridge in Poland and used to assess the durability of its suspension system. It was then modified to be suitable for the evaluation of stay-cables subjected to wind excitation and structural reliability of the suspension system in a real steel bridge where permanent plastic deformations occurred in the anchor zones of the stay cables. The algorithm takes into account analytical models describing the stay cables and their numerical finite element models (FEM). As such, it is a universal tool having a wide range of applications, also beyond stay cables often encountered in medium- and long-span bridges forming a critical part of the civil engineering infrastructure.

A novel approach was proposed, based on the application of the fuzzy logic (FL) method for the fast analysis of the hot deformation process of 80MnSi8-6 steel. In the first stage, the curves developed from plastometric tests and the results of studies of the microstructure of the deformed samples were used as input data for the analysis. Input and output variables were adopted and a set of rules based on cause-and-effect relationships was defined, defining the interactions between the variables. A fast FL-controller was designed, and the correctness of its operation was verified by comparison with experimental results and the results of finite element method (FEM) analysis, carried out taking into account the evolution of the microstructure. The process of hot compression under isothermal conditions of 80MnSi8-6 steel specimens was simulated on the Warmumformsimulator (WUMSI), assuming such parameters and other conditions as were used in real tests. It was confirmed that the proposed method, based on the analysis of flow curves and prior austenite grain size using a fuzzy controller, gave satisfactory results. Subsequently, a novel FL-controller was developed to analyze the kinetics of dynamic recrystallization (DRX), using data obtained from the author’s model of this phenomenon for its construction and calibration. The correctness of the controller was confirmed by comparing the results of its DRX volume fraction calculations with the distributions of this value determined by the model and the model-based FEM analysis method, respectively. It was shown that FL is applicable also when a model of the analyzed phenomenon is available. Unlike model-based calculations, a properly designed controller allows the indication of deviations from general trends that can be pointed out and interpreted by a human expert, but significantly faster. It can also serve as a component of a system analyzing complex processes, such as hot multi-stage forging. Fuzzy controller can be used in parallel with modeling or replace models in calculations.

The softening of aluminum alloy is an important factor affecting its service life. In the present work, the softening characteristics and mechanism in the friction pull plug welding (FPPW) joint of AA2219-T87 plate with a nominal thickness of 18 mm were studied, and an effective measure to mitigate the softening issue was proposed. The softening zone in the thick-plate FPPW joint is located in thermo-mechanically affect zone near the bonding interface and is 6–12 mm away from the top surface of the plate. The disappearance of the strengthening transition phase θ′ is the main cause for the softening; the degree of dynamic recrystallization, which influences the grain size and the work hardening, also affects the softening; but solid solution of Cu atoms in α-Al has little effect on the hardness change in the softening zone. After optimizing the geometric structure of joint and FPPW process parameters, the softening zone was still the weakest point of the joint. After solution and aging treatment on the above-mentioned optimized joint, the minimum hardness in the softening zone increased from 76 HV₁ to 95 HV₁, the tensile strength increased from 318 to 355 MPa, and the fracture position shifted from the softening zone to the plug.

This study investigates a novel Mg-13Gd-2Er-0.3Zr (weight percent) alloy, focusing on the influence of varying double extrusion temperatures (390 °C–450 °C) on the evolution of grain structure, texture, and mechanical properties of double-extruded (DE) alloys. Results show that double extrusion markedly refines the recrystallized grains and enhances the dispersion of fine secondary precipitates, thereby significantly improving the tensile properties compared to a single extruded alloy. A notable increase in the dynamic recrystallization (DRX) and grain size is observed as the deformation temperature rises, with grain sizes enlarging from 2.2 µm at 390 °C to 10.2 µm at 450 °C. The DE alloy extruded at 390 °C demonstrates superior mechanical properties, which was attributed to the synergistic effects of refined recrystallized grains, the presence of un-recrystallized (un-DRXed) grains, abundant fine precipitates, and a weakened basal texture. Additionally, this study highlights that a lower fraction of fine precipitates and a higher fraction of DRX grains contribute effectively to the improvement of elongation (EL) in DE alloys which is ~ 75% higher in the DE alloy at 430 °C than the single extruded alloy. This comprehensive analysis underscores the critical role of extrusion temperature in tailoring the microstructure and mechanical performance of Mg-13Gd-2Er-0.3Zr alloy, offering valuable insights for optimizing the properties of magnesium alloys for industrial applications.

Conventional ultra-high performance concrete (UHPC) has excellent development potential. However, a significant quantity of CO₂ is produced throughout the cement-making process, which is in contrary to the current worldwide trend of lowering emissions and conserving energy, thus restricting the further advancement of UHPC. Considering climate change and sustainability concerns, cementless, eco-friendly, alkali-activated UHPC (AA-UHPC) materials have recently received considerable attention. Following the emergence of advanced prediction techniques aimed at reducing experimental tools and labor costs, this study provides a comparative study of different methods based on machine learning (ML) algorithms to propose an active learning-based ML model (AL-Stacked ML) for predicting the compressive strength of AA-UHPC. A data-rich framework containing 284 experimental datasets and 18 input parameters was collected. A comprehensive evaluation of the significance of input features that may affect compressive strength of AA-UHPC was performed. Results confirm that AL-Stacked ML-3 with accuracy of 98.9% can be used for different general experimental specimens, which have been tested in this research. Active learning can improve the accuracy up to 4.1% and further enhance the Stacked ML models. In addition, graphical user interface (GUI) was introduced and validated by experimental tests to facilitate comparable prospective studies and predictions.

The present research analyzes the impact of heat treatment atmosphere followed by finishing surface machining of small elements of Inconel 939 fabricated through laser powder bed fusion (LPBF). The analysis involved annealing in two gas mediums, solution treatment, and aging to achieve the desired microstructure and mechanical properties. The finishing surface was performed using various variants of abrasive machining. A more than fivefold reduction in the average roughness height Ra from 5.6 µm to 1.15 µm was achieved using metal balls as an abrasive, which was required for further processing. Residual stress tests have shown that due to heat and abrasive treatment, tensile stresses change into compressive ones. After printing, samples are characterized by tensile residual stresses on the surface (+ 428 MPa), while after heat treatment, compressive stresses occur (− 179 MPa). Abrasive machining with metal balls increases the value of compressive stresses to − 464 MPa. In addition, the impact of post-processing on the microstructure of Inconel 939 was discussed in terms of mechanical properties. The yield strength of 1184 MPa and elongation values of 19.3% were obtained for samples after HT in an argon atmosphere and abrasive machining with a ceramics roller. These studies provide valuable new information on the effective heat treatment and optimization of the finishing machining of Inconel 939, especially in achieving the desired surface roughness, microstructure, and mechanical properties for aerospace applications.

In this study, the changing of dynamic characteristics of masonry arches at varying geometric parameters and temperature histories was investigated through a combination of experimental and numerical methods. First, the dynamic characteristics of laboratory-built arch models were determined both pre- and post-high-temperature test using ambient vibration testing. Then, the finite element (FE) models of the arches were developed for both, allowing for dynamic characteristics to be assessed numerically. To refine the accuracy of numerical models, FE analyses were adjusted based on experimental data. These updated FE models were used to investigate the dynamic characteristics of arches with different spans, heights, widths, and thicknesses under different temperature history scenarios. Finally, utilizing the data repository obtained, formulation and graphs/charts, providing valuable insights into the dynamic response of masonry arches under fire conditions, were developed and presented for practical application. The experimental study revealed that the natural frequencies of arches decreased by 55% with increasing temperature exposure.

The stabilizing pile represents a promising solution for enhancing the seismic resilience of unsaturated slopes. This study introduces a novel analytical framework for assessing the stability of unsaturated slopes reinforced with piles, amalgamating the minimum potential energy approach with the pseudo-dynamic method. The formulation of the external potential energy arising from the self-weight of the landslide mass and seismic forces is derived. Furthermore, traditional plasticity theory is extended to unsaturated soil slopes to account for the augmenting influence of matric suction on the lateral pressure exerted by stabilizing piles. The efficacy of reinforcing unsaturated soil slopes with piles is gauged through the definition of the safety factor (SF), delineated as the ratio of resistance moment to sliding moment. Additionally, a fresh interpretation of the critical slip surface (CSS) for unsaturated soil slopes is proposed, alongside an original criterion for identifying CSS, introduced herein for the first time. The validity of the proposed methodology is substantiated through examination of three case studies, yielding results indicative of its efficacy and rationality. The analysis underscores the substantial fortifying impact of matric suction on the stability of unsaturated slopes, as well as the reinforcing influence of piles. Moreover, an exploration into the ramifications of seismic and pile-related parameters on slope performance and CSS is conducted. In conclusion, this approach serves as a valuable reference for the design of unsaturated slopes fortified with stabilizing piles.