Archives of Civil and Mechanical Engineering最新文献

An experimental study was conducted to examine the uniaxial tensile and biaxial bulging behavior of 304 austenitic stainless steel (ASS) to elucidate its strain-hardening characteristics at cryogenic temperature (CT). Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses were employed to quantitatively correlate the macroscopic deformation properties with microstructural evolution. Furthermore, ASS samples with pre-strains of 5%, 15%, and 25% were prepared at both room temperature (RT) and CT, which was then followed by tensile testing at CT. The results revealed that the yield strength (YS) of ASS increased with increasing pre-strain at CT, exhibiting a reduction in ductility. Notably, the YS of cryogenically pre-strained samples increased by 15.4%, 26.5%, and 33.8%, respectively, compared with those pre-strained at RT. Under biaxial loading, the bulging load of ASS also increased with decreasing temperature. The highest hardness values were consistently observed at the bulge apex and increased with increasing bulge height. Consequently, the enhanced YS primarily increased from martensitic transformation and dislocation strengthening during cryogenic pre-strainings. The findings of this study offered valuable insights for optimizing the lightweight design and improving the operational safety of cryogenic storage tanks.

In this work, the asymmetric rolling (ASR) is employed to improve the formability of 2195 Al-Li alloy, which has been widely used in the aerospace and automobile fields. The microstructures and mechanical properties of 2195 Al-Li alloy in ASR under different velocity ratios and strain paths are explored through experimental characterization. Compared with conventional rolling, ASR can effectively refine the grain. As the velocity ratio increases, the average grain size gradually decreases, and the surface grain contacted with the faster roll is finer, which can be attributed to more severe shear deformation. The complex strain path will increase the shear component. Under the same velocity ratio, the grain refinement effect of double-direction asymmetrical rolling is more significant. Moreover, the shear component generated by ASR causes some textures to deviate or split from the ideal positions. Most of the recrystallization textures are eliminated. During ASR, the rolling texture of the surface in contact with the faster roll tends to evolve into the shear texture. In terms of improving the uniformity of microstructure, adjusting the velocity ratio is more effective than changing the strain path. The grain size and texture of the top and inner layers of the ASR sheet with a velocity ratio of 1.8 are closer. These findings provide theoretical guidance for achieving high-performance manufacturing of Al-Li alloy components.

This article presented a comprehensive and accurate nonlinear mathematical model to analyze the mechanical response of multi-directional functionally graded material porous (MDFGMP) plates, for the first time. The model includes a differential quadrature method (DQM) with a quasi-3D theory to investigate bending and vibration responses MDFGMP plates. A nonlinear quasi-3D plate theory is exploited to present the kinematic fields including the effect of normal strain, thickness stretching, and satisfy the zero-shear strain/stress at the top and bottom surfaces without shear correction factor. The power 3D function distribution is used to portray gradation of material constituents through thickness and in-plane directions. Two types of porosity are selected to describe the distribution of voids and cavities through the thickness of the plate. Hamilton’s principle is employed to derive the nonlinear governing differential equations of motions in terms of stress resultants. The differential integral quadrature method (DIQM) is manipulated to discretize the structure spatial domains. The accuracy and reliability of the proposed method have been validated by comparing its numerical results to those of available works. Parametric studies are provided to exhibit the significant impacts of kinematic normal and shear relations, gradation indices, porosity type, and boundary conditions on MDFGMP plates. It is found that frequency mode shapes are symmetric for homogeneous plates but exhibit non-symmetric profiles if the material properties change in the in-plane directions. In contrast, changing material properties in the thick direction, although changing the frequencies, it preserves symmetric mode shape patterns. The present model and results can be implemented as benchmarks for future nonlinear mechanical response of MFGMP plates structures. The proposed model can be implemented in selection and design of the nuclear reactors, marine and aerospace structures manufacture from MDFGMP plates.

Carbon fiber reinforced concrete (CFRC) often suffers from weak bonding between its cement matrix and carbon fibers (CF) because the fibers have an inert surface.To overcome this limitation, we introduce phenylpropyl emulsion (SAE) as an interfacial modifier and examine its strengthening mechanism through macroscopic and microscopic experiments and multiscale simulations using discrete element and molecular dynamics methods. Macroscopic experiments show that both CF and SAE significantly improve the mechanical properties of CFRC, although the effectiveness of SAE depends on its dosage. Specifically, a 4% SAE dosage increases the compressive and shear strengths of CFRC (with 1.5% CF) by 16.5% and 12.1%, respectively, while a 2% dosage boosts early flexural strength by 24.4%. At the microscopic level, SAE enhances the bond at the interface by providing physical anchorage through benzene rings and by forming chemical interactions via COO⁻-Ca²⁺complexes. Discrete element simulations confirm that the modified material has higher ultimate strength and toughness, and molecular dynamics simulations show that SAE lowers the interfacial energy and strengthens the bond between CF and the matrix through ionic and hydrogen bonding. This work offers a solid theoretical basis for improving CFRC interfaces and informs the design of innovative polymer modifiers.

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The safety and durability of reinforced concrete (RC) structures face significant impacts from the combined action of corrosion conditions and fatigue stress. To determine the corrosion-fatigue life of RC structures under combined corrosion environment and fatigue loading, a corrosion-fatigue life assessment model for RC structures under the combined action of carbonation environment, chloride-contaminated environment, and fatigue loading, aiming to analyze their corrosion-fatigue life, was developed. Taking a 6 m-span RC crane beam in an industrial plant as an example, the proposed model was illustrated, and its corrosion-fatigue life was evaluated. Effects of crane operating frequency, lifting capacity, carbonation environment grade, chloride-contaminated environment grade, ambient temperature, and relative humidity on corrosion-fatigue life were explored. Results indicate that increased loading frequency and stress range shorten the corrosion-fatigue life of RC structures. The combined action of corrosion and fatigue notably reduces corrosion-fatigue life. Compared with single carbonation or chloride-contaminated environments, the combined carbonation and chloride-contaminated environment has a stronger effect on the corrosion-fatigue performance of RC structures. Additionally, ambient temperature and relative humidity influence the corrosion-fatigue life of RC structures. This study can establish a basic framework for assessing the corrosion-fatigue life of RC structures under combined multi-corrosion environments and fatigue loading.

To enhance the real-time sensing and explosion location recognition capabilities in underground engineering, this study investigates structural vibration responses under different detonation source locations through model testing and numerical simulations. By integrating the simplex method with an improved particle swarm optimization algorithm, a novel localization algorithm is proposed, leveraging the moment differences of peak acceleration. The algorithm’s accuracy is validated through model tests and numerical results. The findings reveal that when the detonation source is located in the middle and far field, significant dispersion exists between the distance from the measurement point to the detonation source and the peak acceleration. While the general trend shows an increase in distance correlating with a decrease in peak acceleration, a negative correlation is observed only at very short distances. Numerical simulations confirm that the time of peak vibration acceleration and detonation source distance exhibit a strong linear positive correlation, with the coefficient ranging between 0.00218 and 0.00336. Furthermore, the larger the distance difference, the greater the time difference in peak acceleration. Peak vibration acceleration time as a principle, combined with the simplex method and improved particle swarm optimization algorithm can be inverse performance and the real detonation source coordinates similar to the distance of the detonation source coordinates. And the improved particle swarm algorithm of detonation source location calculation results are more accurate, based on the numerical simulation data positioning accuracy analysis results show that its accuracy is stable at more than 99%.

Bone regeneration remains a persistent clinical challenge, with optimal therapeutic strategies yet to be established. Magnesium alloys reinforced with bioactive particles represent an emerging biomaterial class demonstrating favorable tribological properties and inherent osteogenic potential. The study presents a comparative investigation of the dry reciprocating wear behavior of AZ91D magnesium alloy and its friction stir processed surface composites, each reinforced with 15 wt% of bioactive nanoparticles: HA, ZrO₂, and Y₂O₃. Wear tests were conducted using a ball-on-disc tribometer under a 5 N load, 5 Hz frequency, and 5 mm stroke length for 900 s against ZrO₂, Si₂N₄, and SS440 counterface balls. Among the composites, the AZ91D matrix reinforced with ZrO₂ exhibited the lowest wear volume, showing reductions of 24.2% and 38.7% compared to the Y₂O₃ and HA-reinforcement, respectively, along with a relatively lower coefficient of friction. This synergistic enhancement is attributed to the uniform distribution of fine reinforcement, which suppressed adhesive and delamination wear while increasing load-bearing capacity during repeated sliding. Microstructural and surface characterizations using SEM, EDS, and XRD confirmed a transition in the dominant wear mechanism from adhesive and abrasive modes in the monolithic alloy to more abrasive and erosive mechanisms in the composites. The presence of reinforcement and in situ formation of protective magnesium-based oxides played a key role in this shift. The novelty of this work lies in revealing the tailored tribological behavior of AZ91D through bioactive reinforcement via friction stir processing for improved wear resistance in magnesium-based composites.

Hot-extruded aluminum alloy profiles with complex cross-sectional characteristics are widely used in new energy vehicles, rail transportation and aerospace industries. By optimizing the structure of die, a uniform flow rate at the profile die outlet is obtained, thereby reducing the possibility of defects. Subsequently, the extrusion transient simulation is performed by setting the billet skin. The two flow modes of the billet skin during the extrusion process are explained through transient simulation, and the front- end defect of the profile and the rear-end defect of the billet are simulated and determined. An extrusion experiment is carried out based on the process parameters in the simulation, and EBSD tests are performed on the as-cast billet, the as-cast billet after homogenization treatment, the rear-end defect, the front-end defect and the normal profile. By analyzing the ODF of the as-cast billet, it is found that the billet cast by low-frequency electromagnetic casting formed a <110> // ND texture and <110> // TD texture due to characteristics similar to directional solidification. Homogenization treatment can effectively alleviate the segregation and slightly increase the grain size. The flow pattern of the billet skin in the simulation is verified by analyzing the grain size and fiber texture of the back-end defect. By analyzing the grain size of the profile and combining it with simulation, the extrusion coarse-grained ring effect is revealed. By comparing the front-end defect and the texture of the profile, the reason why the front-end defect is difficult to reach the normal profile usage standards is explained from a microscopic perspective.

In this study, a novel hybrid manufacturing process (HMP) is proposed to improve the global yield strength and hardness of 316L stainless steel (316L SS) by integrating interlayer laser directed energy deposition (LDED) additive, milling subtractive, and ultrasonic rolling (UR) equivalent manufacturing processes. The results showed that the porosity of 316L SS subjected to HMP decreased by 96.4% to 0.02%, grain size refined by 58.9% to 20.2 μm, dislocation density increased by 145.5% to 2.7 × 10¹⁵ m^-2, hardness increased by 25.5% to 269.1 HV_0.1, yield strength improved by 41.4% to 670.3 MPa, and ultimate tensile strength improved by 26.1% to 746.7 MPa than those obtained by the single LDED process. The dislocation strengthening and grain refinement strengthening were responsible for the enhanced global yield strength and hardness of 316L SS. The HMP can be applied to realize the defect-free and high-performance manufacturing of metals by eliminating internal defects, reconstructing gradient structures of grain sizes, dislocation densities, grain boundary angles, texture intensities, and twins.

High-strength engineered cementitious composites (ECC) with polyethylene fiber exhibits superior strength characteristics; however, its crack width is significantly larger, which compromises both its transmission performance and self-healing capability compared to conventional ECC with polyvinyl alcohol. To this end, this study prepared a lightweight high-strength ECC by synergistically utilizing fly ash cenospheres (FAC) and expanded vermiculite (EV) as lightweight fillers. The tensile and compressive properties of ECC with different contents of FAC and EV were examined experimentally, and its self-healing behavior was verified through wet-dry cycling tests. Additionally, the microstructure of the matrix was analyzed using scanning electron microscopy. The results indicated that, compared to reference ECC with only FAC (FE0), the incorporation of EV led to a maximum increase in density of 14%, while the compressive strength decreased by up to 9%. Despite this, the maximum density reached 1777 kg/m³, and the minimum compressive strength was 65.8 MPa, still placing it within the category of lightweight, high-strength ECC. The number of cracks increased from 21 in FE0 to 123 in FE75 (a combination of EV and FAC), while the crack width decreased from 75 μm to 20 μm. These narrow cracks contributed to the near-complete self-healing of cracks within the tensile specimens, except for those that led to ultimate failure.