Search Results (147)

This research explores the application of NiTiNOL-steel (NiTi–ST) wire ropes as nonlinear damping devices for mitigating vibrations in composite stiffened panels. A dynamic model is formulated by coupling the composite panel with a modified Bouc–Wen hysteresis representation and employing the first-order shear deformation theory (FSDT), based on Hamilton’s principle. Using the Galerkin truncation method (GTM), the model is converted into a system of nonlinear ordinary differential equations. The dynamic response to axial harmonic excitations is analyzed, emphasizing the vibration reduction provided by the embedded NiTi–ST ropes. Finite element analysis (FEA) validates the model by comparing natural frequencies and force responses with and without ropes. A newly developed experimental apparatus demonstrates that NiTi–ST cables provide outstanding vibration damping while barely affecting the system’s inherent frequency. The N3a configuration of NiTi–ST ropes demonstrates optimal vibration reduction, influenced by excitation frequency, amplitude, length-to-width ratio, and composite layering. Full article

A novel stainless steel with high Mn and Mo content (much higher than traditional stainless steel), designated CH241SS, was developed as a potential replacement for Cr-Mo-V alloy steel in the cold forging applications of precision industry. Through carbon reduction in an environmentally friendly manner and a two-stage heat treatment process, the hardness of as-cast CH241 was tailored from HRC 37 to HRC 29, thereby meeting the industrial specifications of cold-forged steel (≤HRC 30). X-ray diffraction analysis of the as-cast microstructure revealed the presence of a small amount of ferrite, martensite, austenite, and alloy carbides. After heat treatment, CH241 exhibited a dual-phase microstructure consisting of ferrite and martensite with dispersed Cr(Ni-Mo) alloy carbides. The CH241 alloy demonstrated excellent high-temperature stability. No noticeable softening occurred after 72 h for the second-stage heat treatment. Based on the mechanical and room-temperature tensile fatigue properties of CH241-F (forging material) and CH241-ST (soft-tough heat treatment), it was demonstrated that the CH241 stainless steel was superior to the traditional stainless steel 4xx in terms of strength and fatigue life. Therefore, CH241 stainless steel can be introduced into cold forging and can be used in precision fatigue application. The relevant data include composition design and heat treatment properties. This study is an important milestone in assisting the upgrading of the vehicle and aerospace industries. Full article

The concept of “material effort” appears in continuum mechanics wherever the response of a material to the currently existing state of loads and boundary conditions loses its previous, predictable character. However, within the material, which still descriptively remains a continuous medium, new physical structures appear and new previously unused physical features of the continuum are activated. The literature is dominated by a simplified way of thinking, which assumes that all these states can be characterized and described by one and the same measure of effort—for metals it is the Huber–Mises–Hencky equivalent stress. Quantitatively, perhaps 90% of the literature is dedicated to this equivalent stress. The remaining authors, as well as the author of this paper, assume that there is no single universal measure of effort that would “fit” all operating conditions of materials. Each state of the structure’s operation may have its own autonomous measure of effort, which expresses the degree of threat from a specific destruction mechanism. In the current energy sector, we are increasingly dealing with “low-cycle thermal fatigue states”. This is related to the fact that large, difficult-to-predict renewable energy sources have been added. Professional energy based on coal and gas units must perform many (even about 100 per year) starts and stops, and this applies not only to the hot state, but often also to the cold state. The question arises as to the allowable shortening of start and stop times that would not to lead to dangerous material effort, and whether there are necessary data and strength characteristics for heat-resistant steels that allow their effort to be determined not only in simple states, but also in complex stress states. Do these data allow for the description of the material’s yield surface? In a previous publication, the author presented the results of tension and compression tests at elevated temperatures for two heat-resistant steels: St12T and 26H2MF. The aim of the current work is to determine the properties and strength characteristics of these steels in a pure torsion test at elevated temperatures. This allows for the analysis of the strength of power turbine components operating primarily on torsion and for determining which of the two tested steels is more resistant to high temperatures. In addition, the properties determined in all three tests (tension, compression, torsion) will allow the determination of the yield surface of these steels at elevated temperatures. They are necessary for the strength analysis of turbine elements in start-up and shutdown cycles, in states changing from cold to hot and vice versa. A modified testing machine was used for pure torsion tests. It allowed for the determination of the sample’s torsion moment as a function of its torsion angle. The experiments were carried out at temperatures of 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C for St12T steel and at temperatures of 20 °C, 200 °C, 400 °C, 550 °C, and 800 °C for 26H2MF steel. Characteristics were drawn up for each sample and compared on a common graph corresponding to the given steel. Based on the methods and relationships from the theory of strength, the yield stress and torsional strength were determined. The yield stress of St12T steel at 600 °C was 319.3 MPa and the torsional strength was 394.4 MPa. For 26H2MH steel at 550 °C, the yield stress was 311.4 and the torsional strength was 382.8 MPa. St12T steel was therefore more resistant to high temperatures than 26H2MF. The combined data from the tension, compression, and torsion tests allowed us to determine the asymmetry and plasticity coefficients, which allowed us to model the yield surface according to the Burzyński criterion as a function of temperature. The obtained results also allowed us to determine the parameters of the Drucker-Prager model and two of the three parameters of the Willam-Warnke and Menetrey-Willam models. The research results are a valuable contribution to the design and diagnostics of power turbine components. Full article

Current regulatory principles focus on resistance and durability to ensure long-term robustness while optimizing sections to maximize efficiency and minimize material use, thus enhancing sustainability and reducing environmental impact. Historical ceramic masonry constructions fully adhere to these principles; however, they have been largely supplanted by modern materials. The compressive strength and functional advantages of structures built with ceramic masonry, particularly those featuring extremely thin wall sections, warrant a reassessment of their structural properties. This is exemplified by thin-tile vaults (ranging from 0.015 to 0.020 m in thickness) and hollow brick vaults with a thickness of less than 0.050 m, both of which represent highly efficient solutions. The proposed examples inherently meet these structural system properties due to their low energy dispersion, minimal gravitational weight, superior thermal performance, and monolithic tectonic composition using a single, easily recyclable material. This paper reviews the historical background of these construction systems, emphasizing their relevance in post-war periods when concrete and steel were scarce. It is concluded that these construction systems remain valid and are consistent with the principles of the circular economy, as well as with the structural safety standards of the 21st century. Full article

This study aims to investigate the wear and corrosion–wear behavior of 17-4PH stainless steel specimens, both fabricated via Selective Laser Melting (SLM) and conventional bulk material, after undergoing Solution Treatment (S.T.) in a seawater medium. Microstructural observations indicated that solution treatment contributed to a more uniform distribution of martensitic structures on the sample surface. Moreover, the solution-treated specimens exhibited improved microstructural uniformity and structural stability. SLM specimens exhibit the elimination of fine particles and scanning track traces. Based on the results of dynamic polarization tests, SLM specimens demonstrate superior corrosion resistance. However, in corrosion–wear conditions, the bulk material outperforms the SLM specimens, primarily due to the presence of pores in the latter, which are detrimental under such environments. XPS analysis of the passive film structure indicates that the passive layer is mainly composed of FeO, Cr₂O₃, and NiO, with the inner layer predominantly consisting of chromium oxide. The Cr₂O₃ layer, formed by the reaction between chromium and oxygen, significantly enhances the corrosion resistance of the material due to its extremely low chemical reactivity and high stability. Full article

An integrated hybrid system was developed, incorporating sedimentation, anaerobic digestion, biological filtration, and a two-stage hybrid subsurface flow constructed wetland, horizontal subsurface flow constructed wetland (HSSFCW) and vertical subsurface flow constructed wetland (VSSFCW), to treat rural sewage in southern Jiangsu. To optimize nitrogen and phosphorus removal, the potential of six readily accessible industrial and agricultural waste byproducts—including plastic fiber (PF), hollow brick crumbs (BC), blast furnace steel slag (BFS), a zeolite–blast furnace steel slag composite (ZBFS), zeolite (Zeo), and soil—was systematically evaluated individually as substrates in vertical subsurface flow constructed wetlands (VSSFCWs) under varying hydraulic retention times (HRTs, 0–120 h). The synergy among substrates, plants, and microbes, coupled with the effects of hydraulic retention time (HRT) on pollutant degradation performance, was clarified. Results showed BFS achieved optimal comprehensive pollutant removal efficiencies (97.1% NH₄⁺-N, 76.6% TN, 89.7% TP, 71.0% COD) at HRT = 12 h, while zeolite excelled in NH₄⁺-N/TP removal (99.5%/94.5%) and zeolite–BFS specializing in COD reduction (80.6%). System-wide microbial analysis revealed organic load (sludges from the sedimentation tank [ST] and anaerobic tanks [ATs]), substrate type, and rhizosphere effects critically shaped community structure, driving specialized pathways like sulfur autotrophic denitrification (Nitrospira) and iron-mediated phosphorus removal. Annual engineering validation demonstrated that the optimized strategy of “pretreatment unit for phosphorus control—vertical wetland for enhanced nitrogen removal” achieved stable effluent quality compliance with Grade 1-A standard for rural domestic sewage discharge after treatment facilities, without the addition of external carbon sources or exogenous microbial inoculants. This low-carbon operation and long-term stability position it as an alternative to energy-intensive activated sludge or membrane-based systems in resource-limited settings. Full article

The effects of different heat treatment regimes on the microstructure and corrosion behavior of selectively laser melted (SLM) Corrax (CX) stainless steel were systematically investigated. Three distinct thermal processing approaches solution treatment (ST), aging treatment (AT), and combined solution aging treatment (ST + AT) were comparatively examined to assess their microstructural evolution and corrosion performance. The results demonstrated that the SLM-processed CX sample initially consisted of martensite and retained austenite. After solution treatment at 900 °C for 0.5 h, microsegregation was eliminated, and the retained austenite fully transformed into martensite. During direct aging at 525 °C for 3 h (AT), a portion of the martensite reverted to austenite, accompanied by grain refinement that reduced the average grain size to 1.79 μm. When the CX was solution-aged at 900 °C for 0.5 h and then 525 °C for 4 h (ST + AT), the retained austenite transformed completely into martensite. The results of potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) revealed that the aged specimen demonstrated comparatively superior corrosion resistance with reduced surface accumulation of corrosion products relative to both ST and ST + AT specimens. The electrochemical test results indicate that the selection of heat treatment parameters has a significant impact on the corrosion resistance of SLM-formed CX samples. Compared to ST and ST + AT, the corrosion performance of AT-treated samples is improved to a certain extent, with the highest E_pit (322 mV) and the largest ΔE (742). The corrosion potential is relatively high (E_corr, −414 mV vs. SCE), and the corrosion current density is relatively low (I_corr, 0.405 μA·cm⁻²). This indicates that the AT samples exhibit good corrosion resistance. Full article

To investigate the seismic performance of steel tube-reinforced concrete (ST-RC) columns after fire on one side, this study employs numerical simulation and theoretical analysis methods. A numerical analysis model of ST-RC columns post-fire is established using ABAQUS to simulate and analyze their seismic performance under cyclic loading. The characteristics of the hysteresis curves of ST-RC columns after fire on one side under cyclic loading are described in detail. Comparisons are made between the skeleton curves, ductility, stiffness degradation, and energy dissipation capacity of ST-RC columns under three conditions: unexposed to fire, exposed to fire on all sides, and exposed to fire on one side. Finally, multiple influencing factors, including heating time, slenderness ratio, section size, core area ratio, external concrete strength, reinforcement ratio, and load ratio, are selected for parametric analysis of the ductility coefficient, stiffness, and viscous damping coefficient. Mathematical formulas for the ductility coefficient, stiffness, and viscous damping coefficient of ST-RC columns after fire on one side under cyclic loading are derived through regression analysis. The results show that the seismic performance of ST-RC columns is attenuated after fire on one side, and the ductility and initial stiffness of ST-RC columns decreases by 5.62% and 24.69%, respectively, compared with those without fire. The energy dissipation capacity of the ST-RC column increases significantly when it enters the plastic deformation stage under the action of reciprocating load. Full article

This study investigates the impact of material selection on the performance of linear slideways in ultraprecision machines used for freeform surface machining. The primary objective is to address challenges related to load-bearing capacity and limited bandwidth in slow tool servo (STS) techniques. Multi-body dynamic (MBD) simulations are conducted to evaluate the performance of two materials, alloy steel and metal matrix composite (MMC), within the linear slideway system. Key performance parameters, including acceleration, velocity, and displacement, are analyzed to compare the two materials. The findings reveal that MMC outperforms alloy steel in acceleration, velocity, and displacement, demonstrating faster response times and greater linear displacement, which enhances the capabilities of STS-based ultraprecision machining. This study highlights the potential of utilizing lightweight materials, such as MMC, to optimize the performance and efficiency of linear slideways in precision engineering applications. Full article

Steel fibers (STs), polyvinyl alcohol fibers (PVAs), and polyethylene fibers (PEs) were selected to systematically investigate the effects of different fiber types and dosages on the workability (slump and spread) and mechanical properties (compressive strength and splitting tensile strength) of slag–Yellow River sand geopolymer eco-cementitious materials. By combining microstructural testing techniques such as thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), the influence mechanisms of fibers on the characteristic products and microstructure of the matrix were thoroughly revealed, and the role of fibers in the strength development of Yellow River sediment-based geopolymers was elucidated. The results show that as the fiber content increases, the workability of the mixture significantly decreases. The appropriate incorporation of steel fibers and PVAs can significantly enhance the strength and toughness of the matrix. When the fiber dosage is 1%, the 28-day compressive strength of specimens with steel fibers and PVAs increased by 25.93% and 21.96%, respectively, compared to the control group, while the splitting tensile strength increased by 50.00% and 60.34%, respectively. However, the mechanisms of action differ significantly; steel fibers primarily enhance the compressive performance of the matrix through their high stiffness and strength, whereas PVAs inhibit crack propagation through their flexibility and excellent bonding properties. In contrast, the strength improvement of PEs is mainly reflected in toughening. When the fiber dosage is 1.5%, the 28-day splitting tensile strength of PE specimens increased by 72.61%, and the tensile-to-compressive ratio increased by 92.32% compared to the control group. Microstructural analysis indicates that the incorporation of different types of fibers does not alter the types of characteristic products in alkali-activated cementitious materials, but excessive fiber content affects the generation of gel-like products and the distribution of free water, thereby altering the thermal decomposition behavior of characteristic gel products. Additionally, the matrix incorporating PEs forms a honeycomb-like amorphous gel, resulting in weak interfacial bonding between the fibers and the matrix. This is one of the main reasons for the limited reinforcing effect of PEs at the microscopic scale and a key factor for their inferior long-term performance compared to steel fibers and PVAs. This study provides theoretical foundations and practical guidance for optimizing the performance of fiber-reinforced geopolymer materials. Full article

This research investigates the effects of steel (ST) and synthetic (SYN) fibers on the workability and mechanical properties of HPFRC. It also analyzes their influence on the material’s microstructural characteristics. ST fibers improve tensile strength, fracture toughness, and post-cracking performance owing to their rigidity, mechanical interlocking, and robust adhesion with the matrix. SYN fibers, conversely, mitigate shrinkage-induced micro-cracking, augment ductility, and enhance concrete performance under dynamic stress while exerting negative effects on workability. Hybrid fiber systems, which include ST and SYN fibers, offer synergistic advantages by enhancing fracture management at various scales and augmenting ductility and energy absorption capability. Scanning electron microscopy (SEM) has been crucial in investigating fiber–matrix interactions, elucidating the effects of ST and SYN fibers on hydration, crack-bridging mechanisms, and interfacial bonding. ST fibers establish thick interfacial zones that facilitate effective stress transfer, whereas SYN fibers reduce micro-crack formation and enhance long-term durability. Nonetheless, research deficiencies persist, encompassing optimal hybrid fiber configurations, the enduring performance of fiber-reinforced concrete (FRC), and sustainable fiber substitutes. Future investigations should examine multi-scale reinforcing techniques, intelligent fibers for structural health assessment, and sustainable fiber alternatives. The standardization of testing methodologies and cost–benefit analyses is essential to promote industrial deployment. This review offers a thorough synthesis of the existing knowledge, emphasizing advancements and potential to enhance HPFRC for high-performance and sustainable construction applications. The findings facilitate the development of new, durable, and resilient fiber-reinforced concrete systems by solving current difficulties. Full article

This study presents a simple and innovative design to join a 2 mm thick steel sheet to a 5 mm thick aluminium sheet in a butt configuration. Thickness differences were addressed using support plates, while an aluminium run-on plate was employed to prevent the FSW tool from plunging into the steel. The process produced a unique S-shaped Al/St interface, the formation mechanism of which is analysed in this study. Scanning electron microscopy (SEM) observations revealed a gradient in the thickness of intermetallic compounds (IMCs) along the joint interface, decreasing from the top to the bottom. This S-shaped interface led to a 150% increase in the ultimate tensile strength (UTS) of the joint. The mechanism underlying this enhancement, attributed to the curved geometry of the interface and its alignment with the loading direction, is discussed in detail. These findings highlight the potential of this approach for improving the performance of dissimilar material joints in lightweight structural applications. Full article

STS304L is widely used in liquefied natural gas cargo containment systems for cryogenic liquefied gas storage because of its excellent mechanical properties at low temperatures. However, unpredictable sloshing impacts can induce excessive plastic deformation, leading to phase transformation from austenite to martensite. This study investigated the impact resistance of STS304L under cryogenic conditions through drop-weight impact tests. Temperature sensitivity was analyzed using electron backscatter diffraction to quantify plastic deformation and phase fraction. The results showed that, as the temperature decreased, the energy absorption and stiffness increased, whereas the plastic deformation remained relatively constant. Energy absorption increased by 59.63% at −100 °C and 68.80% at −193 °C compared with that at 20 °C. The martensite fraction, measured at the end of the hemispherical impact region, increased from 19.26% at 20 °C to 77.85% at −100 °C and 96.87% at −193 °C, indicating significant strain-induced martensitic transformation at cryogenic temperatures. Full article

The equipment of refineries and oil production facilities is subject to corrosion due to the supply of crude oils with a high content of mineralized water. The use of inhibitors is one of the most common corrosion protection methods. However, increasing requirements of environmental standards give impetus to developing new types of corrosion inhibitors from natural raw materials. The article deals with the synthesis conditions of new corrosion inhibitors (CIs) produced from distilled higher acids of beef fat (DHFAs) or vegetable oils (VO), as well as research on the protective effect of the synthesized corrosion inhibitors compared with industrial inhibitors (5 samples). The gravimetric method studied the protective effect in a solution of salts and jet fuel using a St20 steel plate. At 50 °C and a CIs content of 100 ppm, the protective effect of corrosion inhibitors based on VO and triethanolamine was 9.7–75.6%. Under similar conditions, CIs obtained from DHFAs and diaminoethyl exhibited a protective effect of 81.6–94.1%. When DHFAs and diethanolamine were used to synthesize CIs, the protective effect was 93.0–95.6%. CI synthesized at 130 °C and a DHFAs: diethanolamine ratio of 72:28 showed a 99.2% protective effect at 50 °C and a CI content of 200 ppm, which was higher or equal to the impact of using industrial inhibitors (91.6–99.5%). The results prove the possibility of alternative use of animal fats and waste from their production as new resources for obtaining highly effective equipment corrosion inhibitors. Using alternative inexpensive raw materials (fats, vegetable oils, waste from their output) to obtain CIs will improve the economic performance of inhibitor production. In addition, at least the fatty (oil) part of organic CIs is biodegradable and will not harm the environment. Full article

In the first part of this article devoted to the assessment of the fatigue life of structural steels at low temperatures, a study was conducted on the effect of pre-cycling in a low-cycle fatigue mode on the time dependences of acoustic emission parameters. Commonly used St-3 steel was tested at −60 °C with varying durabilities, after which it was fractured once during static tests. The multilevel acoustic model used made it possible to estimate the structural parameter $\gamma$ at the stage of elastoplastic deformation. The stage of active development of microcracks and their coalescence corresponds to a homogeneous fracture with stable acoustic emission characteristics (signal duration, amplitude variation coefficient, etc.). It was shown that regardless of the maximum voltage (460, 480, and 500 MPa) in the cycle and the operating times of up to 0.3, 0.5, and 0.7, the structural parameter remains within the known limits. The parameters of the Weibull law distribution and the logarithmically normal distribution for the coefficient γ were obtained, theoretical and calculated fatigue curves were plotted, and a method was proposed for evaluating the number of cycles before fracture under irregular loading conditions in the real operation of pressure vessels based on the “rainflow” cycles counting method. Full article