Archives of Civil and Mechanical Engineering最新文献

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.

The high-rate forming method, such as electromagnetic forming (EMF), can enhance the formability of materials. However, the deformation mechanism of EMF has received little attention for AZ31B magnesium alloy. To this end, the quasi-static stamping (QS) and EMF experiments of AZ31B Mg alloy under uniaxial tension, equiaxial tension and plane strain are carried out in this paper. The results show the maximum forming height and limit strain of EMF samples were 33% and 96.7% higher than QS sample, respectively. In the QS process, the twinning density of AZ31B alloy increases gradually, but the overall number is rare. In the EMF process, the twinning number shows a multiplication—annihilation—stabilization trend, but the overall number is more. This indicates that the deformation mechanism of AZ31B alloy during QS is dominated by dislocation slip, and the twinning–detwinning–dislocation slip occurs sequentially during EMF. That is, EMF induces a transformation in the deformation mechanism. The transformation early consumes severe plastic deformation energy and releases stress, so directly enhances the formability of AZ31B alloy. Meanwhile, the increase of the boundaries and the weakening of the basal texture caused by the transformation indirectly promotes formability of AZ31B alloy. In addition, activation of (11–20) slip system, more pyramidal <c + a> dislocations and wave-like slips induced by EMF is also beneficial to improve the formability of AZ31B alloy.

In-service reinforced concrete (RC) structures trigger complex deterioration mechanisms in seismic performance due to corrosion, leading to difficulties in evaluating the seismic capacity. To scientifically evaluate the seismic capacity of corroded RC frame structures, this paper proposes a quantifiable framework for absolute seismic capacity evaluation. The study establishes numerical models of typical RC frame structures considering the number of stories, service years, seismic fortification intensity, and different versions of design codes. Additionally, classification criteria for structural failure states based on the proportion of component damage are proposed. The seismic capacity of corroded RC frame structures under different failure states is determined using elastoplastic time-history analysis, and the influence of various parameters on the structural seismic capacity is investigated. Based on the results of the structural seismic capacity evaluation, a prediction model for the seismic capacity of corroded RC frame structures is developed using the BP neural network to establish the nonlinear mapping relationship between key parameters and structural seismic capacity. The results indicate that the seismic capacity of corroded RC frame structures continuously decreases with an increase in the service years and the number of stories. Earlier versions of design codes result in smaller residual seismic capacity of RC frame structures under different failure states, with a faster degradation rate. The sensitivity of the structural seismic capacity to various parameters is ranked as follows: structural failure states, the number of stories, seismic fortification intensity, service years, and versions of design codes.

Calcium aluminate cement (CAC) is an important hydraulic cementitious material. It is widely used in construction, metallurgy, chemical industry and other fields due to its high early strength. The factors affecting its strength are also very complex. The research focus of this paper is to establish a prediction model for the compressive strength of CAC paste, so as to assist scientific research and practical engineering to quickly predict the strength of CAC paste at different ages under different mix ratios and curing conditions. In this paper, 273 sets of data are trained and tested based on support vector regression (SVR), random forest regression (RFR), gradient boosting (GB) and extreme gradient boosting (XGB) algorithms. It is found that the prediction accuracy of GB model can reach 89%. Meanwhile, based on the GB model, the feature importance analysis, global interpretation and dependence analysis are carried out. It is found that the main factors affecting the strength of CAC are relative humidity, silica fume content and curing temperature. To obtain high-strength CAC paste, the recommended mix ratio and curing conditions are as follows: Al₂O₃ content is 67%, CaO content is 32%, silica fume replacement rate is 10%, water–cement ratio is 0.1, relative humidity is 90%, curing temperature is 5 °C and low-temperature treatment time is greater than 60 days. Finally, a graphical user interface is established to facilitate direct prediction of CAC paste under new mix ratio and curing conditions.

This study compared and evaluated the working performance and mechanical properties of LC50 fly ash microbead lightweight high-strength concrete (FLHSC) using fly ash microbeads, cement, water-reducing agent dosage, water–cement ratio, and types of additives as variables. Through reasonable design of expansion tests, bulk density tests, and mechanical strength tests, the basic optimal combination was obtained. The research results indicate that the optimal mix ratio of FLHSC is: fly ash floating beads 230 kg/m³, ceramsite 200 kg/m³, cement 1200 kg/m³, water 360 kg/m³, water-reducing agent 20.4 kg/m³. The water–binder ratio is selected as 0.3, type II water-reducing agent is selected, and the dosage is 1.7% of the cementitious material. Its slumps is 680 mm, and its dry bulk density is 1562.0 kg/m³, the 28-day strength is 52.4 MPa. On this basis, the microstructure and hydration products of FLHSC under different conditions were analyzed in depth using scanning electron microscopy and infrared spectroscopy, and the interface enhancement mechanism and failure mode were studied in depth. It is found that the failure of FLHSC is close to the vertical failure mode, and the crack always passes through the lightweight aggregate. In addition, a life cycle assessment and CO₂ emission calculation from production to application were conducted on FLHSC. In addition, a life cycle assessment and CO₂ emission calculation were conducted on FLHSC from production to application, and the results showed that FLHSC has better environmental benefits than ordinary C50 concrete, with a CO₂ emission of 632.443 (kgCO₂/t). Finally, the application of LWHSC was analyzed.

Refill Friction Stir Spot Welding (RFSSW) has a number of advantages that make it a possible alternative to riveting and resistance welding in aerospace structures, the automotive industry and other applications. Adequate determination of technological parameters which ensure the desired properties of welds and their functioning in various operating conditions requires, among others, appropriate fatigue life of connections. The article presents the results of comparative tests of the mechanical properties of welds (load-bearing capacity and fatigue life at selected three load levels) made with a basic tool (G0) and a tool with a modified geometry (G4). The samples were made of 1.27 mm thick clad sheets of 2024-T3 aluminum alloy with an additional oxide anodic coating. It has been shown that the modified geometry of the working surface of the inner sleeve of the RFSSW tool improves the conditions and course of the plasticization and stirring process of the joined materials. The use of a G4 geometry tool allowed for approximately 30% higher joint load-bearing capacity and approximately twice as long fatigue life (at lower load levels) compared to welds made with the G0 tool.

To overcome the lower bearing strength of coral concrete and the high cost of conveying raw materials from the mainland to the island, a new method was presented. This method suggested to apply the coral aggregate instead of the natural coarse aggregate (NCA) in seawater concrete, which was denoted as CAC. In this paper, 18 axial loading prism specimens and 90 cubic lateral loading specimens were cast. Two concrete strengths, three replacement ratios of coral coarse aggregate (CCA) (50%, 75% and 100%) and five biaxial stress ratios (0, 0.15, 0.3, 0.45 and 0.75) were designed. A Digital Image Correlation (DIC) system was used to investigate all the failure patterns and stress–strain curves, which were used to analyze the influence of the above parameters on the peak stress and the peak strain. In addition, the lateral–axial strain relationship and biaxial failure criterion were also established. After determining the biaxial failure surface, a hardening law and a softening law were proposed to describe the uniaxial stress–strain curves based on the Weibull distribution and Guo’s model, respectively. Finally, a new constitutive model for CAC under biaxial stress was developed using the two-dimensional incremental constitutive model. The results indicated that the crack development of CAC was similar to that of natural coarse aggregate concrete (NAC), and the failure patterns of biaxial specimens were related to the biaxial stress ratio. Furthermore, the biaxial stress showed an increase in the peak stress and the peak strain. The increase in CCA replacement weakened the enhancement effect on the peak stress, while it slightly influenced the peak strain. Additionally, the proposed lateral–axial strain model and biaxial failure criterion were in good agreement with the measured results. Through comparison, the proposed biaxial incremental constitutive model was verified using the tested curves.

Aluminum alloy plates show great potential in energy storage and transportation applications. Nevertheless, the low surface strength of aluminum alloy plates negatively impacts their performance and safety. Aluminum alloys exhibit characteristics such as a low melting point, high reflectivity, and a rapid dilution rate, posing significant challenges for laser cladding coatings. This paper presented the surface modification mechanism of aluminum alloy plates. A stainless steel coating was successfully prepared on the surface of aluminum alloy substrates by using high-speed laser cladding technology. The microstructure, microscopic morphology, and microhardness of the coatings were conducted. The surface and sides of coatings were analyzed by XRD, SEM, EBSD, and microhardness testing, respectively. It is found that larger cellular crystals and carbides predominate at the junction of the substrate and the coating. The middle part of the 0.5-mm coating from the connection and the heat-affected zone are mainly dendritic crystals. The top of the 1-mm coating from the connection is mainly fine crystals. This means that local grain refinement occurs in the stainless steel coating via high-speed laser cladding. There is a transformation of FCC to BCC in the coating. Moreover, the cross-section of the coating exhibits a relatively high microhardness, ranging from 517 to 679 HV. The microhardness at the substrate is measured at 67 HV. The maximum microhardness of the coating is ten times that of the substrate. The bottom of the coating maintains a relatively high microhardness due to the presence of a large amount of carbides. The microhardness of the coating gradually increases from the middle to the surface of the coating. This is primarily attributed to solid solution strengthening and fine grain strengthening mechanisms. Columnar crystals at the metallurgical bond between the substrate and the coating transform into fine grains at the top, leading to a gradual refinement of the microstructure. High-speed laser cladding technology facilitates the enhancement of surface properties and the improvement of surface strength in traditional aluminum alloys.

Replacing elements made of conventional plastics (like polystyrene) with biodegradable substitutes is part of the trend of sustainable development and waste reduction. The manuscript covers issues related to the design, manufacturing and testing of sports helmet protective inserts made of biodegradable material. The FEM numerical simulations carried out by the authors allowed to determine the optimal desirable mechanical properties (R_e = 8.5–65 MPa, E = 500–8000 MPa for 30 × 30 mm inserts; R_e = 10.5–60 MPa, E = 500–7500 MPa for 48 × 48 mm inserts; R_e = 13–95 MPa, E = 400–8500 MPa for 55 × 55 mm inserts) and geometric parameters (wall thickness equal to 0.2–0.5 mm, height of 20 mm), ensuring the formation of a plastic fold, which is the most effective energy-absorbing mechanism. The conducted quasi-static compression, bending and dynamic tensile strength tests allowed to determine blends with appropriate proportions of durable PLA with more plastic PBAT, PBS and TPS that meet the established criteria: PLA50PBAT50, PLA30PBAT70 and PLA30TPS70.

Faced with the urgent need to develop environmentally friendly alternatives to cementitious materials, geopolymers, made from combinations of various by-products, offer a promising solution. In recent years, statistical optimization methods have begun to be applied in the field of engineering. This study focuses on sustainable geopolymer mortars by incorporating industrial by-product powders, specifically blast furnace slag (SP), waste glass powder (GP), and ceramic powder (CP) as partial replacements. Compressive strength, flexural strength, workability, and density were evaluated for various ternary compositions using a Mix Design Model (MDM) approach. The main results revealed a synergistic interaction between SP and CP, with a 20% replacement of CP leading to a 16% increase in compressive strength, indicating optimal performance. Microstructural analysis using SEM, TGA, and FTIR highlighted a dense, crack-free matrix with extensive calcium aluminosilicate gel phases, particularly in the SP–CP mixture. Optimization through desirability profiling identified a 30% CP replacement as ideal for maximizing strength and workability. Controlled optimization of multi-component geopolymer synthesis using by-products streams proves to be a promising method for developing next-generation sustainable construction materials.