Archives of Civil and Mechanical Engineering最新文献

This research addresses challenges in theoretical modeling of complex metal foam nanoshell structures and introduces a more accurate approach. It utilizes a nonclassical nanomechanics continuum approach to model novel tridirectionally porous metal foam nanoshell structures with varying microstructures, incorporating intrinsic characteristic lengths and spatial variations in material properties. The research endeavors to analyze the buckling response exhibited by multidirectional functionally graded (FG) porous metal foam nanoshells resting on an orthotropic elastic foundation. Employing the nonlocal higher-order strain gradient theory in conjunction with the principle of virtual work, the study establishes static stability equilibrium equations. Methodologically, the Galerkin method is applied to derive analytical solutions for critical buckling loads under diverse boundary conditions. Within the scope of investigation, two distinct types of porous shells are examined: softcore (SC) and hardcore (HC). These shells are further characterized by five distribution patterns: tridirectional (Type-A), bidirectional (Type-B and Type-C), transverse unidirectional (Type-D), and axial unidirectional (Type-E). This model demonstrates its efficacy in analyzing and designing shell element structures across a broad spectrum of industries, including motorcycle helmet manufacturing, petrochemical processing, aerospace engineering, and civil construction.

The present research aims to examine the free vibrational behavior of a sandwich plate comprising a viscoelastic auxetic core and functionally graded graphene nanoplatelets reinforced composite (FG-GPLRC) face layers, which are rested on a Winkler–Pasternak foundation. The macro-mechanical characteristics of the plate’s skins have been determined utilizing the Halpin–Tsai theory. Additionally, for the core layer, besides the features characterized using Gibson’s model, the Zener model is employed to describe its viscoelastic behavior. The equations of motion for the sandwich plate were derived based on Reddy’s third-order shear deformation theory (TSDT), and they were solved using the Galerkin method. To validate the numerical results of the current study, they have been compared with findings documented in prior ones. Overall, the effects of several parameters such as geometrical parameters, various GPL distribution patterns, boundary conditions, Winkler–Pasternak coefficients, and the volume fractions of GPL have been investigated on the natural frequency and loss factor of the sandwich plate.

The influence of copper addition on the structure and selected properties of AlCoCrFeNiSi_0.5Cu_x high-entropy alloys is described. Slowly cooled ingots were prepared by induction melting, and the samples in the form of plates were obtained by pressure casting. The conducted structural studies confirmed the presence of BCC/B2 phase. Microsegregation in the ingots was associated with the formation of intermetallic Cr₃Si and Fe₅Si₃ phases. An increase in the cooling rate stopped segregation by reducing the mobility of Cr and Si. The hyperfine magnetic field distributions indicated the formation of the BCC Fe(Co,Ni,Si,Cr) solid solution for alloys in the form of plates. The lowest corrosion-current density (0.04 μA/cm²) in 3.5%-NaCl solution was obtained for the plate with the lowest copper content. The dominated aluminum surface states for the post-corrosive plates highlighted the binding energies of Al₂O₃. A tendency of reduced coercivity with increased copper content was observed. The positive effect of copper addition on wear resistance was confirmed for the AlCoCrFeNiSi_0.5Cu_0.1 alloy.

In order to gain the stress–strain relationship of ultra-high performance concrete (UHPC) reinforced with basalt fiber reinforced polymer (BFRP) minibars under uniaxial compression, nine kinds of UHPC mixtures with BFRP minibars were designed. In addition, other three kinds of UHPC mixtures were designed to study the effect of fiber modulus on uniaxial compression behavior, the UHPC which were reinforced with no fiber, polypropylene (PP) fibers and steel fibers, respectively. The flowability, porosity, elastic modulus, compressive strength and toughness of UHPC were systematically tested and analyzed. Based on the test results, BFRP minibar significantly enhance the uniaxial compression behavior of UHPC, the stress–strain relationship was gained and it was expressed by a classical model with a good agreement, resulting in a promotion of the structural design for UHPC structures. The compressive strength increased with fibers modulus, content, aspect ratio, and bonding strength between UHPC and fibers. A semi-empirical model with a relative error rate less than 15% was proposed for compressive strength prediction, the model which was based on fibers modulus, content, aspect ratio, and bonding strength. The findings based on this research could enrich the technical basis for the performance design of UHPC in practical applications.

This research seeks to pinpoint the most robust series by subjecting geopolymer mortars (GMs) to electrical curing (AC) at 20 V based on different NaOH concentrations and GBFS/FA ratios. To enhance the electrical conductivity of GMs displaying optimal mechanical properties, carbon fiber (CF), steel fiber (SF), waste wire erosion (WWE) (0.25%, 0.50%, and 0.75%), and carbon black (CB) (1%, 2%, and 3%) were introduced into the chosen series. A comprehensive assessment encompassing compressive strength, flexural strength, ultrasonic pulse velocities, direct tensile strength and splitting tensile strengths were conducted on mixtures undergoing 24 h of AC. The study's findings indicated a substantial improvement in mechanical properties through electrical curing compared to ambient curing conditions. Notably, a correlation of up to 99% was established between direct and splitting tensile properties. The investigation revealed that the highest compressive strength, reaching 72.41 MPa at 1 day strength, was achieved through the thermal curing method with electric curing, particularly in the 100GBFS series. On the other hand, the optimum bending strength, approximately 19 MPa, was observed in the SFA075WWE series. These results highlight the efficacy of the thermal curing method with electric curing in enhancing the compressive strength of the 100GBFS series and the flexural strength of the SFA075WWE series, underscoring the potential benefits of specific curing methods for different series within the study.

Portland cement (PC), which has been used as a dominant binder material in concrete since its development, is responsible for approximately 8% of global anthropological CO₂ emissions. Alkali-activated materials, which are based on the activation of precursor materials using alkali activators, are binders developed for environmental gains. The significance of this study lies in exploring the mechanical and microstructure properties of hybrid alkali-activated cements containing PC, produced under various parameters. This investigation provides valuable insights into optimizing the composition and processing conditions for these materials. In this study, 34 mixtures were produced to investigate the Na₂SiO₃ to NaOH ratio (2, 2.5, and 3), PC substitution level (5%, 10%, 15%, 20%, and 25%) and curing temperature (25, 50, 75 and 100 °C) effects on the hybrid alkali-activated slag/PC components. The highest compressive strength was obtained at 15% PC substitution. As the Na₂SiO₃ to NaOH ratio increased, the compressive strength of the samples containing 0, 5%, 10% and 15% PC increased. However, the increase in the Na₂SiO₃ to NaOH ratio negatively affected the compressive strength of the samples containing more than 15% PC. The highest compressive strength in both partially PC-substituted and fully slag samples was achieved when the samples were cured at 50 °C. When the sample containing 100% slag was cured at 50 °C, the degree of hydration was higher compared to the sample cured at 25 °C. In the sample with 15% PC, a sharp band corresponding to the Si–O bond was observed at 25 °C. However, as the curing temperature exceeded 50 °C, this band became broader and weaker. This indicates that the amount of hydration products in the PC-blended alkali-activated slag sample decreased at curing temperatures above 50 °C.

The interference between grits and workpiece material during the nickel-based superalloy robot abrasive belt grinding process can cause plastic deformation on the grinding surface, and the evolution of surface deformation microstructure under high-temperature conditions can affect the surface properties of superalloys. Therefore, a high-temperature exposure experiment is devised in this paper, and electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) are used as characterization methods to study the microstructure evolution characteristics and recrystallization behavior of nickel-based superalloy robot abrasive belt grinding surface under high-temperature exposure. In addition, the effects of grinding factors (abrasive belt grit size and normal contact force) on high-temperature exposure recrystallization of grinding surface are explored. The research results indicate that under high-temperature exposure, the surface deformation microstructure consumes dislocations and releases stored energy, evolving into fine equiaxed recrystallized grains within the original grains through subgrain growth nucleation and grain boundary migration. Meanwhile, the recrystallization process is accompanied by twin formation. The recrystallization process is affected by the exposure temperature and time, and exposure temperature has a decisive influence on recrystallization. Furthermore, both the abrasive belt grit size and normal contact force have a profound influence on the recrystallized grain size and the recrystallization area depth.

Fiber-reinforced polymer (FRP) bars have better resistance to corrosion and higher tensile strength than steel bars, thus being a prospective material for concrete structures in marine engineering. However, it is less fire-resistant, and the residual bearing capacity of FRP-reinforced concrete members after the fire needs to be clarified. This study explores the impact resistance of Glass FRP-reinforced concrete (GFRP-RC) columns at high temperatures using finite element models. To assess the accuracy of the model, the simulation results were compared with the test results in terms of fire resistance and impact resistance, respectively. Based on these, the impact behavior of GFRP-RC and steel-RC columns were compared and analyzed. The results show that GFRP-RC columns were more severely damaged by impact loading after high temperatures than steel-RC columns. The peak impact forces of the GFRP-RC columns and steel-RC columns are nearly identical. However, the former has a smaller reaction force and a more significant mid-span displacement. Furthermore, the residual axial bearing capacity of GFRP-RC columns after high temperature and impact loading is significantly reduced compared to steel-RC columns. Exposure to high temperatures takes a more significant proportion in the reduction than impact loading. In addition, a relationship between the damage index (based on residual bearing capacity) and the lateral displacement of the columns after fire and impact loadings was established. In contrast, the corresponding damage classification criteria were determined.

This paper primarily investigates the deformation behavior of lightweight aggregate concrete (LWAC) with lightweight expanded clay aggregate (LECA) at early ages. Comparative experiments were conducted on specimens prepared with pre-wetted and dry aggregates and with different water-to-cement ratios. The digital image correlation (DIC) technique was used to measure deformation and calculate the principal strains on the surface of specimens. The variation of global strains and local strains in mortar and aggregates at early ages were analyzed. The results showed that pre-wetted lightweight aggregates can enhance the effect of internal curing, thereby reducing the early-age shrinkage of concrete, and weakening the discreteness of strain distribution in concrete, thus theoretically reducing the risk of cracking. The minimum principal strains of mortar and aggregates did not exhibit a simultaneous increase and decrease trend, but rather interacted with each other, and reached a dynamic equilibrium with moisture transfer between them. The maximum principal strains of aggregate were significantly greater than those of mortar. The effectiveness of internal curing does not increase linearly with an increase in the water-to-cement ratio, but first increases and then decreases, with the optimal internal curing effect achieved around a water-to-cement ratio of 0.40 at early ages.

Water jet impact technology has more advantages in environmental protection, safety and quality. This paper innovatively puts forward the new technology of temperature–hydrodynamic coupling effect rock breaking, which can fully utilize the water jet energy and effectively improve the mining and excavation capacity of granite, especially suitable for high-temperature rocks. Taking the common granite in the actual project as an example, the mechanical test and water jet impact test are carried out to study and analyze the temperature–water jet coupling effect. Rock-breaking technology, acoustic emission technology, image recognition technology and nuclear magnetic resonance technology are used to analyze the mechanism of the temperature–water jet coupling effect, supplemented with numerical simulation to verify and analyze. The test results show that: under the action of temperature–hydrodynamic coupling, the granite crushing is more obvious, the degree of influence of liquid nitrogen impact time 120 s > 180 s > 240 s > 300 s > 60 s, and the crushing efficiency is improved by 117%; through numerical simulation to analyze the comprehensive damage factors, the temperature–hydrodynamic coupling effect produces a large number of minor damages in the internal granite; analyzing the stress characteristics of granite. Under the effect of temperature–hydrodynamic coupling, granite is mainly subjected to tensile damage, thus generating cracks to promote granite crushing. The results of the study provide theoretical guidance for practical engineering.