Archives of Civil and Mechanical Engineering最新文献

Fabricating ultra-large aspect ratio microcylindrical electrode array efficiently, quickly, and reliably while maintaining high quality and low cost presents a continuous challenge. In this paper, a new method is proposed to produce ultra-large aspect ratio microcylindrical electrode array by taking advantage of the peculiar phenomenon that the front end of micro-prismatic electrode array becomes rounded after being worn in electric discharge machining (EDM). Specifically, micro-hole array with rounded outlets is machined on the workpiece using worn micro-prismatic electrode array, and then the micro-prismatic electrode array is converted into micro-cylindrical electrode array by reverse EDM. First, the simulation and analysis of the electric field distribution of the micro-prismatic electrode is carried out to reveal the mechanism of morphology evolution. Then, various micro-prism electrode arrays with different cross-sectional shapes were produced using the low-speed wire EDM technique. Next, the effects of cross-sectional shape, substrate material, peak current, and pulse width on electrode wear are studied. And the process conditions for rapid wear of the electrode front section into a circle and good wear consistency of the electrode array were optimized. The mathematical model of the front-end wear of the micro-prismatic electrode is also established. Following this, the development of electrode morphology was presented, transitioning from micro-prism electrode array to micro-cylindrical electrode array. The process of substrate shape change from square to circular holes was also discussed. The dimensional consistency of the micro-circular hole array was evaluated using image processing technology. Finally, a microcylindrical electrode array, measuring approximately 230 μm in diameter and having an aspect ratio of 18.15, has been successfully prepared and evaluated. This research has the potential to overcome the technological bottleneck of achieving high precision machining of micro-cylindrical electrode array with large aspect ratios.

Lattice structures are becoming more commonly used in the design of components for additive manufacturing. This is due to their ability to reduce the weight of manufactured parts, minimize material consumption, and achieve specific properties by modifying their geometry. As the applications of lattice structures continue to evolve, it is essential to determine whether the process parameters used in the PBF-LB (Laser Beam Powder Bed Fusion) process for manufacturing these structures should be the same as or different from those used for larger cross-sectional components. An analysis of the existing literature revealed insufficient data on this subject, which inspired this study. Experiments conducted using AISI 316L stainless steel showed that lattice structures can be produced with significantly lower volumetric energy density, while maintaining a high relative material density. In the experiment on lattice structures made of BCCZ and gyroid unit cells, a relative material density of over 99.5% was achieved with a volumetric energy density of approximately 33 J/mm³. These findings are significant for the fabrication of lattice structures. The lower volumetric energy density typically allows for greater geometric accuracy and reduced internal stresses. Furthermore, it has been proven that the nodes of the structure are critical places exposed to porosity formation.

Refractory High entropy alloy (RHEA) is a potential material for coating gas turbine blades and pipeline due to its high-temperature mechanical and chemical properties. In this paper, a series of new NbTiCrFeMo_X (x = 0.2, 0.4, 0.6, 0.8, 1) RHEAs were coated on GTD-111 nickel base superalloy by the laser cladding method. The effects of the Mo amount on the microstructure and tensile, creep, corrosion, and wear properties were investigated. XRD results showed that the microstructure of all five coatings included the B2 regular phase, the BCC irregular phase, C14-Laves (FeTi₂), and C15-Laves (Cr₂Nb). However, with the increase of Mo from 0.2 to 1, the amount of the BCC phase increased from 24.1 to 29.5%, the C14 phase increased from 55.1 to 61.4%, and the amount of the C15 phase decreased from 11.2 to 1.8%. The yield strength increased by increasing the volume fraction of BCC and C14-Laves phases from 328 MPa for the Mo0.2 sample to 685 MPa for the Mo1 specimen. The same factor increased the creep life of RHEA from 43 to 54 h under a force of 450 N and temperature of 800 °C by increasing the places of dislocation locking. The simultaneous presence of the BCC solid solution and Laves phase was one of the factors that reduced the coefficient of friction during the wear test from 0.63 to 0.44 with increasing Mo. Electrochemical tests in 3.5 wt% NaCl solution showed that the RHEAs showed significant corrosion resistance. Specimen Mo1 with the smallest I_corr (1.6103 × 10^–6 A cm²) and the highest E_corr (− 1.2025 V) showed the best corrosion resistance.

A key component of automotive and aerospace applications is Scalmalloy components, which are produced using the laser powder bed fusion (LPBF) process. However, alternative cooling conditions were used during the heat treatment process to enhance the performance of the Scalmalloy parts. This research investigated the nano-level, tribo-mechanical and microstructural properties of the heat-treated Scalmalloy parts. In this study, Scalmalloy was heat treated at 325º C for 4 h and then cooling was performed under different conditions such as cooling in the furnace, air and water (FC, AC and WC, respectively). The development of Al3(Sc, Zr) nano-precipitates in the < 111 > , < 200 > , and < 220 > lattice planes was verified by XRD. OM and FESEM analysis confirmed that the heat-treated Scalmalloy under the WC condition possessed enhanced grain refinement compared to the other conditions. Moreover, EBSD analysis also substantiated the phenomenon observed during the microstructural analysis. It was also confirmed that heat-treated Scalmalloy with the WC condition had a reduced grain size of 5.5 µm which was 74% and 66% lower than the FC and AC conditions, respectively. This grain refinement was attributed to the improved nano-hardness of 3.2 GPa with a minimum indentation depth of 19.45 nm, which was 69% and 41% lower than the FC and AC conditions, respectively. Similarly, nano-wear analysis also confirmed that the WC condition showed a maximum COF of 0.81 and 49% enhanced wear resistance with a minimum worn-out depth and pile-up of − 78.16 nm and 48.41 nm, respectively. Further, various wear mechanisms such as abrasion, oxidation and delamination were also examined based on the worn-out surface of the wear specimens. Tensile performance revealed that the WC condition possessed a more brittle fracture with a maximum tensile strength of 535 MPa, whereas the FC condition displayed a more ductile fracture with a maximum elongation of 10%. These differences in their fracture mechanics justified the grain refinement of the heat-treated specimens with different cooling conditions.

The present research conducts free vibration analysis of annular rotating discs made from functionally graded porous materials, and nanocomposite reinforced carbon nanotubes facesheets. Pores distribution in the porous core is considered based on three different patterns, namely Nonsymmetric, Symmetric, and Monotonous ones across the thickness, and also, carbo nanotube dispersion in the facesheets is investigated randomly by considering their agglomeration effect. Kinematic relations of the mentioned structure regarding the shear deformation effects and based on the first-order theory are described, and then, variations of strain and kinetic energies by considering rotation via the calculus variation method are calculated. To extract the governing motion equations and associated boundary conditions, Hamilton's principle is employed, and then they are solved with the aid of the generalized differential quadrature method. After ensuring the correctness of the results obtained from the scripted code by comparing them in the simpler state with the previous research, the effect of different parameters such as pores’ distribution patterns, carbon nanotubes dispersion patterns and their agglomeration, core and face sheets thickness, and other parameters on the natural frequencies of the structure is investigated. Considering the obtained results, it can be found that increasing the porosity leads to a slight increment in the natural frequencies, generally, and increasing the carbon nanotubes’ mass fraction leads to significant enhancement in them. The outcomes of this study can be used in different industries, such as aerospace, military, and marine industries.

The aim of the study was to analyze the effectiveness of hard hat helmets in mitigating head injuries from high-energy falling objects through a real-world case study, advanced numerical simulations and an uncertainty study. The study aims to answer the following research questions: (a) to what extent would the use of the protective helmet limit the kinetic energy of the falling construction prop, (b) whether the hard hat helmet would be damaged, and if so, to what extent, according to the helmet standards? A fatal construction accident involving a falling prop impact on the victim’s head was reconstructed using multi-body dynamics simulations and finite element analysis (FEA) based on uncertainty-based determination of initial conditions. The study quantified the impact energy, helmet damage and its energy-absorbing capabilities, and potential injury reduction compared to scenarios without a helmet. While the helmet absorbed significant energy (245% of the standard requirement) and reduced the Head Injury Criterion by 8–11%, the high impact energy ultimately proved fatal. This study highlights the limitations of hard hat helmets in extreme scenarios with high kinetic energy impacts. While helmets offer valuable protection, unrealistic expectations should not be placed on their ability to prevent all head injuries. The study not only enhances our understanding of the biomechanics of head injuries in such incidents but also provides practical implications for safety protocols and regulations.

The common wisdom in the literature about clinker aggregate (CA) is that it improves the performance properties of mortar or concrete to some extent. The current study, in this context, investigated the physical characteristics and mechanical performances of alkali-activated composites (AACs) made entirely with CA. The CA was used in three particle sizes of 0–2 mm (named No.10), 2–4 mm (named No.5), and 4–8 mm (named medium). To examine the impact of the fine CA-size fraction on the characteristics of AAC, No.10 CA was partially replaced by No.5 CA up to 50%, while the content of the medium CA was kept constant in all AAC mixtures. Moreover, to evaluate the influence of the 8-h curing temperature on the performance of the AACs, different temperature-based curing strategies (ambient, 45, and 75 °C) were applied to the AACs. In the production of AACs, granulated blast furnace slag was employed as an aluminosilicate-rich raw material, and a sodium silicate and sodium hydroxide combination was used as an alkaline activator. Physical properties (flowability, water absorption, capillary water absorption, and dry unit weight), and 8-h strength performances (flexural and compressive) were determined. Furthermore, to monitor the influence of high temperatures on the characteristics of the AAC, the mixtures were exposed to elevated temperatures (200, 500, and 800 °C). In SEM image analysis, it was determined that spherical CSH gels were formed in the heat-cured AACs. It has been observed that the geopolymerization products decompose in AACs exposed to 800 °C. To evaluate statistically the experimental results, a multi-factor analysis of variance (ANOVA) was also applied. The results revealed that increasing the coarser fine aggregate fraction led to higher water absorption and apparent porosity capacities and lower unit weight. Besides, strength performance was improved by applying a heat-curing strategy to the AAC, whereas a decrease was observed by increasing the No.5 CA fraction. There was a remarkable reduction in compressive strength and considerable loss of mass when the AAC mixes were exposed to high temperatures.

The hydrothermal dynamical effectiveness and usefulness of highly responsive spinning mechanisms under slanted Hall currents is a significant issue in several manufacturing and experimental functions. Hybridized nanoparticles have novel properties that are advantageous for a range of technical uses. Compared to trihybrid, bihybrid, or mono-nanofluid, tetrahybrid nanofluid (Tetra HNF) is a new idea in research that enables a faster cooling process. These motivate us to research the effects of oblique Hall currents on a non-Newtonian couple stress tetrahybrid nanofluid flow in an oblique channel with oscillatory heating under strong external magnetic attraction with Hall currents in a magneto-gyrating environment. To create tetrahybrid nanofluids (Cu–TiO(_2)–Ag–Al(_2)O(_3)/WEG), copper, titania, silver, and alumina nanopowder forms are dispersed in a colloidal solution of water and ethylene glycol (vol. 60–40(%)). We discuss four kinds of nanoparticles: spheres, bricks, cylinders, and platelets. Mechanical circumstances and presumptions are used to build the partial differential equations (PDEs) that describe the mechanical problems. The dimensionless energy and momentum with related wall constraints are resolved using an analytical approach. Multiple kinds of graphic representations and tabulated data are presented to fully accomplish and demonstrate the mechanical aspects of important developing parameters on the hydrothermal trends and their practical significance. Our results demonstrate that the resultant velocity rapidly rises over growing changes in inclined Hall currents. The velocity profile gets an elevation for the inclination of the channel in the range (pi /4<alpha <pi /2), but reversal flow occurs for a slight angle of inclination ((0<alpha <pi /4)). Platelet-shaped NPs transport higher heat than other shapes (spherical, brick shaped, or cylindrical). Tetrahybrid nanofluid achieves higher heat transport than other base fluid types (pure WEG or mono/bi/trihybrid nanofluids). An artificial neural network (ANN) model is also developed based on testing datasets generated via the analytical evaluation. This ANN architecture achieves an astounding (99.98%) accuracy in predicting critical flow amounts. Our simulations can be applied to the development of reliable oblique Hall sensors and to several manufacturing procedures, including the interaction of nano-polymers and the use of composite nano-lubricants in regulating temperature.

The present study proposes a new fuzzy finite element method for dynamic multibody interaction with consideration for structural damage. Here, fuzzy parameters are equivalently transformed into stochastic parameters using information entropy, and the fuzzy response of the structure is obtained by fuzzy calculation combined with the new point estimation method. Numerical examples are used to illustrate the accuracy and efficiency of the presented methods, and scanning method simulations are implemented to validate the computational results. Considering that the damage degree of the pier is uncertain, namely fuzzy uncertainty, stiffness reduction is used to simulate the damage of the pier. The fuzzy dynamic response of the train–bridge system is investigated when the pier structure and the mass of the train are fuzzy parameters. The response of the train–bridge interaction considering damage far exceeds that obtained from conventional deterministic parameter calculations. To ensure running safety, studying the response of the vehicle-system coupled vibration with fuzzy parameters is of great significance.

The paper presents mathematical models and their implementation in C # language describing the phase transformations occurring in the process of austempered ductile iron (ADI) manufacture. The research includes two main stages: austenitization and isothermal holding at the bainitic range. The influence of free energy of austenite and ferrite on transformations was taken into account. Parameters of models were identified based on inverse analysis and experimental research. As part of the research, verification and validation of the developed models was carried out based on the results of experimental research. The tool developed and implemented enables the analysis of phase transformations occurring during heat treatment with isothermal holding of ductile iron with Ni addition.