Archives of Civil and Mechanical Engineering最新文献

To investigate the seismic capacity of masonry structures corroded by acid rain in acidic atmospheric environments, experimental studies on the seismic performance of masonry walls and the mechanical properties of masonry materials were first conducted through accelerated acid rain corrosion tests. The material tests indicated that acid corrosion weakened the shear strength and axial compressive strength of masonry and decreased the elastic modulus. The quasi-static tests of walls revealed that acid corrosion weakened the energy dissipation capacity and load-bearing capacity of the masonry wall specimens, reduced the initial stiffness, and advanced the failure time after the peak load. Based on the experimental results, degradation models for the mechanical properties of materials and seismic performance parameters of walls were established, and a restoring force model was developed, which accurately reproduced the experimental hysteresis curves. Furthermore, a component performance-based assessment framework for the seismic capacity of masonry structures was proposed and applied to evaluate typical masonry structures with different service ages, number of stories, and fortification intensities. The results showed that seismic capacity decreases with more stories and lower fortification intensity. Additionally, relative seismic capacity gradually declined with increasing service age, falling below the safety threshold of 0.8 for the collapse state after 48 years, significantly increasing the risk of structural collapse during earthquakes. Finally, a BP neural network model was developed to predict the seismic capacity of corroded masonry structures, and its accuracy was validated.

High-entropy alloys (HEAs) possess unique strengthening mechanisms, and a vast design possibility, distinguishing them from conventional alloys. Refractory high-entropy alloys (RHEAs), a subclass of HEA, offer better high-temperature structural stability, making them ideal replacement for traditional high-temperature alloys. This review systematically evaluates the critical role of empirical alloy design parameters and processing methods in influencing the microstructure and mechanical properties of RHEAs. Key parameters, including enthalpy of mixing (ΔH_mix), atomic size difference (δ), valence electron concentration (VEC), Pauling electronegativity, and melting point are analyzed for their impact on phase formation and mechanical performance. Furthermore, the effects of various processing techniques, such as arc melting, powder metallurgy, and magnetron sputtering, are explored for their ability to optimize the microstructure and mechanical response. The review highlights the interplay between these factors, offering pathways for improving yield strength, ductility, and high-temperature softening resistance. These insights provide a foundational understanding of the factors governing the performance of RHEAs for high-temperature applications and outline pathways for future research and development.

This paper presents a controlled experimental investigation into the erosion evolution induced by a 20 kHz ultrasonic pulsating water jet, focusing on its potential for precise material removal. Water droplet volumes of V = 1.53 mm³ were generated and applied to aluminum samples at a pressure of p = 15 MPa. Utilizing extended long nozzles with diameters of 0.4, 0.5, and 0.6 mm, erosion patterns were examined over time intervals ranging from 0.25 to 4 s, with increments of 0.25 s. Scanning Electron Microscopy analysis revealed a progressive degradation process, starting with initial pitting and evolving into complex crater formations. For the 0.6 mm nozzle at 0.25 s, a distinct 'corona jet' footprint indicated a hollow cone jet presence, with erosion activity predominantly by the peripheral thin pulsating part. Quantitative analysis showed a non-linear, often logarithmic, increase in erosion depth, hypothesized to result from a negative feedback mechanism where surface roughening reduces the impact pressure peak and disrupts droplet surface tension. Eroded volume, conversely, exhibited a more linear increase. Furthermore, detailed SEM of craters, such as the open cavity observed at the edge of a 0.5 mm nozzle crater after 4 s, confirmed significant material fracture and removal driven by the hydrodynamic action of the high-frequency pulsating water jet.

Iron (Fe), a common impurity in recycled aluminum alloys, generally promotes the formation of acicular Fe-rich intermetallic phases, which can deteriorate their final mechanical properties, especially their ductility. This study investigated influences of Fe-rich phase morphologies on the tensile behaviors of hypoeutectic Al–Si alloys and the role of manganese (Mn) in modifying these phases. Cast aluminum alloys with varying Fe and Mn contents were examined by means of microstructure characterization, microhardness, tensile test, and a micromechanics-based model using 2D representative volume elements (RVEs). It was found that RVE simulations accurately predicted the stress–strain characteristics of the alloys with different compositions and varying Fe-rich intermetallic phases. Acicular intermetallics occurred certainly led to stress accumulations at boundary regions of eutectic and aluminum matrix phases throughout microstructure, inducing premature failure and decreased total elongations. Moreover, the addition of Mn transformed such acicular morphology into granular or Chinese-script shape, mitigating earlier local plastic localization and risk of crack development. It was highlighted that interplay between the modified morphologies of intermetallic phases and properties of the surrounding phases by the Mn alloying greatly affected local stress and strain distributions and subsequent cracking mechanism, thereby mechanical performances of recycled Al–Si alloys. The RVE approach could provide critical insights for alloy design optimization, particularly in aluminum recycling applications, where essential strength and ductility balance depend on inevitable impurities.

The article describes to design the parameters of hot rolling and heat treatment technology in a way that would allow for permanent bonding of S355J2 and NANOS-BA® steel into one high-strength clad plates. In the article, guidelines for the hot rolling process of clad plates with two-stage heat treatment were described, which were then verified in a semi-industrial technological line. The materials obtained in this way in different initial states were subjected to metallographic and strength tests. Based on three technological variants of the process, S355J2/ NANOS-BA® clad plates were produced. After additional heat treatment, a nanobainitic microstructure of high strength and ballistic and abrasion resistance was created in the applied layer, which indicates the possibility of using this type of clad plate in the armaments, machine building, or construction industry.

In this paper, a pulse current assisted compression test platform is built to investigate the effects of temperature, strain rate, and current density on flow stress. Based on the Johnson-Cook model and considering the physical mechanism of the electroplastic effect, the constitutive equation for Inconel718 under pulsed current is constructed. By compiling the user subroutine Vumat and importing it into Abaqus for simulation, and comparing it with the electric pulse assisted turning experiment, the influence of electroplastic parameters (0–100 A) on chip morphology and cutting force is explored. The research results are expected to provide technical guidance for expanding the application field of Inconel718.

This study investigates the influence of friction stir welding parameters, specifically tool rotational speed and linear speed, on the electrochemical and mechanical properties of EN AW-6082-T651 butt joints. The research encompassed microstructural analysis, surface roughness measurements, potentiodynamic corrosion tests, hardness profile measurement, and static tensile testing. Results revealed that decreasing the linear speed or increasing the rotational speed during welding intensified heat input, leading to grain growth in the weld nugget zone. The smallest grain size of 3.46 ± 1.11 µm was achieved at 1000 rpm and 250 mm/min. Surface roughness was minimized at 1250 rpm and 200 mm/min, as excessive tool feed caused irregularities. Corrosion resistance improved compared to the parent material, attributed to fine-grained structures promoting compact passive layer formation. Hardness profiling indicated the lowest values in the heat-affected zone, particularly for joints produced at 1250 rpm and 200 mm/min due to the highest heat input and precipitate dissolution. Tensile testing confirmed fracture locations in the heat-affected zone, with maximum tensile strength reaching 69% of the base material and elongation approximately 30%.

Cementitious materials are often exposed to aggressive environments, which have a significant impact on their durability. Proper prediction of concrete corrosion helps to apply the right measures and technologies, to extend the service life of structures. Carbonation and cyclic freezing are recognized among the most common corrosive factors for concrete. Their progress is linked to the penetration of CO₂ and water into the concrete structure. Due to the random arrangement of aggregates and cement paste, concrete is an inhomogeneous material. Therefore, the progress of carbonation and frost-induced damage should be treated as random variables with appropriate probabilistic parameters. Experimental studies on concrete carbonation and freezing were conducted in accordance with the standards EN 12390–12 and EN 12390–9. As observed in the experiments, the progress of carbonation and frost damage of concrete could be described by zigzag, not necessarily monotonic functions. Stochastic differential equations (SDE) were employed to predict the behavior of concrete exposed to elevated CO₂ concentrations and cyclic freezing. The stochastic model consisted of a drift term, which described the general trend of concrete durability exposed to carbonation and frost cycles, as well as a diffusion term, which accounted for the stochastic features of inhomogeneous concrete microstructure. The Euler–Maruyama approximation with Milstein improvement was applied to model the realization of the stochastic changes in concrete microstructure/durability. The proposed approach predicted experimental results with high accuracy. The application of the Monte Carlo (MC) method with 100,000 SDE realizations allowed to calculate the statistical parameters of the processes, such as concrete carbonation and freezing cycles. The probabilistic parameters, such as expected values and standard deviations, calculated using the SDE_MC approach, were in good agreement with experimental results for both problems, i.e. decelerating concrete carbonation and accelerating concrete scaling.

High-speed penetration experiments were performed on traditional sintered 93W alloy (93W–5.4Ni–1.6Fe) and a novel 93W–La alloy (93W–5.5Ni–1.1Fe–0.4La) containing 0.4% La, to impact a 30CrMnMo target at a velocity of 1650 m/s. The results indicated that the incorporation of La enhanced the mechanical properties of the 93W alloy, resulting in an 8.41% increase in the penetration depth of the 93W–La alloy compared with the sintered 93W alloy. The parameters for the Johnson–Cook constitutive equations of the two types of penetrator materials were determined through quasi-static tensile tests and Split-Hopkinson Pressure Bar (SHPB) experiments. Numerical simulations of the high-speed penetration tests were conducted on the LS-DYNA platform using FEM and adaptive FEM–SPH methods. The simulation results were compared with experimental target impact test data, demonstrating that the adaptive FEM–SPH method had superior computational accuracy. The penetration characteristics of both penetrators were analyzed throughout the crater formation, stable penetration, and plugging stages. The 93W alloy penetrator retained a “mushroom head” shape at the tip throughout the penetration process, whereas the 93W–La alloy penetrator exhibited significant adiabatic shear sensitivity, leading to adiabatic shear failure and “self-sharpening” characteristics.