Search Results (6,306)

The present study investigates the effect of low-temperature ion plasma nitriding on the phase composition, microstructure, tribological behavior, and corrosion resistance of 30Cr13 martensitic stainless steel. Plasma nitriding was carried out at temperatures of 400, 450, and 480 °C in a dissociated ammonia atmosphere using a pulsed DC glow discharge. The phase composition and structural evolution of the surface layer were analyzed by X-ray diffraction, while the morphology and thickness of the modified zone were examined using scanning electron microscopy. The tribological properties were evaluated under dry sliding conditions using a ball-on-disk configuration, and corrosion resistance was assessed by potentiodynamic polarization in a 3.5 wt.% NaCl solution. It was established that low-temperature ion plasma nitriding leads to the formation of nitrogen supersaturated martensite (α′N) and the nitride phase ε-(Fe_2–3)N, with their relative fraction governed by the treatment temperature. An increase in the nitriding temperature resulted in a rise in the surface’s microhardness up to 1100–1150 HV and a change in the thickness of the modified layer, reflecting nitrogen redistribution between the solid solution and nitride constituents. The predominance of the α′N phase at 400–450 °C ensured the most stable tribological behavior and reduced corrosion rate, whereas an increased fraction of ε-(Fe_2–3)N at 480 °C led to a higher microhardness and a greater abrasive wear component while maintaining satisfactory corrosion resistance. The obtained results confirm the decisive role of phase composition in the nitrided layer in determining the tribological and corrosion performance of 30Cr13 steel, and may be used for optimizing the surface hardening parameters of components operating under combined friction and corrosive environments. Full article

In this study, hardfacing and a flux-cored/self-shielded powder wire of the FCAW-S-90G13N4 type was employed to produce and investigate the deposits of high-manganese steel. The effects of high-frequency mechanical impact (HFMI) treatment on the microstructure, hardening, and scratch resistance of the deposits were studied to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions. As observed by XRD, SEM, and nanoindentation, the microstructure of deposited metal comprised a soft austenite matrix, dispersed hard carbides, and an ε phase (~26 vol.%). The wear resistance is thus not controlled by carbides alone but arises from the synergistic action of a hard carbide network within a ductile matrix. HFMI resulted in twinning, an increase in dislocation density, a grown volume fraction of ε (>60%) and α′-martensite. The interaction between twins, martensites, and dislocations provides a double/triple increase in microhardness (from HV_0.2 = 2.78 GPa to HV_0.2 = 6–7.69 GPa). After HFMI, scratch tests showed lower restored depths of scratch tracks and a 36–68% deceleration in the wear rate regarding those of the initial deposit. The underlying wear mechanisms were assessed accounting for the SEM observations of the scratch track morphologies and a ‘counterbody penetration vs. shear stresses ratio’ map. The initial plastic deformation-related mechanism (wedge/pile-up formation) changed by HFMI to ploughing. The obtained results allow one to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions. Full article

The objective of this article is to optimise the deposition modes and the content of exothermic additions (EAs) in the core filler in Fe-C-Cr-Ti with Cu additions hardfacing. To achieve this, JMatPro Release 7.0, Sente Software Ltd., 2016 material characterisation software was used to simulate and calculate the equilibrium phase structure and composition of the Fe-C-Cr-Ti-Cu alloy during the welding thermal cycle. A synergistic approach combining the Taguchi–Analysis of Variance (ANOVA)–Factorial design (FD) method with the standard hybrid Taguchi–ANOVA–Principal Component Analysis (PCA)–Grey Relational Analysis (GRA) is used and justified to optimise factors and develop mathematical models for parameters in the L9 orthogonal experimental design. The study examines how the transfers of deoxidisers depend on the content of exothermic additions in the cored wire filler (EA) and the contact tip-to-work distance (CTWD), while the behaviour of carbide formers is influenced by wire feed speed (WFS) and present arc voltage at the power source (U_set). The research specifically investigates the Fe-C-Cr-Ti-Cu system and the role of copper in stabilising austenite. Findings show that high Cu concentrations (7 wt.%) enhance hardenability by 13%, effectively suppressing pearlite transformation and expanding the bainite region. The desired chemical composition of the deposited metal is determined by the distribution of selected factors, as measured by the transfer coefficients of each element. Full article

Precast reinforced concrete (RC) structures offer advantages in terms of construction efficiency and quality control; however, their seismic performance is governed by the behavior of the beam–column connections. This study presents an experimental investigation of the cyclic response of precast RC beam–column joints that include a composite steel connection, designed to enhance strength, stiffness, and damage control in critical regions. A composite joint specimen was tested under displacement-controlled cyclic loading, and its behavior was compared with that of a corresponding pure RC connection. Experimental results showed that the composite configuration effectively prevented premature failure at the beam–column interface, relocated plastic hinges away from the joint core, and significantly improved the load-carrying capacity, stiffness, and energy dissipation. To interpret the experimental observations and examine the internal stress transfer and evolution of damage, a three-dimensional nonlinear finite-element model was developed. The simulations reproduced the observed modes of failure, shapes of deformation, hysteretic responses, and moment distribution trends, particularly in the post-yield and strain-hardening ranges. Although the pinching effects observed experimentally were not fully captured numerically, the overall levels of agreement in the ultimate strength and plastic hinge locations were satisfactory. The combined results indicate that composite steel-reinforced precast beam–column joints represent a promising solution for improving seismic performance. Full article

A correct description of quarkonia production and kinematics is still one of the most challenging assignments for Quantum Chromodynamics. This document presents a study of the ${\rm Y}$(1S), (2S) and (3S) mean transverse momentum ($⟨p_{\mathrm{T}}^{{\rm Y}}⟩$) as a function of the charged particle multiplicity ($N_{\mathrm{Track}}$) in proton–proton collisions at $\sqrt{s}$ = 7 TeV generated with Pythia 8.312 CUETP8M1 tune. The comparison to real data collected by the CMS experiment indicates that the agreement is much better for the excited states than for the ground state. The observed fast increase in the $⟨p_{\mathrm{T}}^{{\rm Y}}⟩$ at small values of $N_{\mathrm{Track}}$ is mainly due to the contribution from the away region. Furthermore, when computing the $⟨p_{\mathrm{T}}^{{\rm Y}}⟩$ from jetty and isotropic events, a clear $p_{\mathrm{T}}$ hardening is observed in jetty events. Finally, analyzing the fragmentation of jets containing an ${\rm Y}$(nS), a new method is proposed to test the new quarkonia shower present in the Monte Carlo event generator. Full article

In this study, the tensile properties, low-cycle fatigue behavior, and microscopic fatigue-failure mechanisms of 316H stainless steel in the temperature range of 600–800 °C were systematically investigated by means of tensile tests, high-temperature low-cycle fatigue tests, and scanning electron microscopy (SEM) analysis of fatigue fracture surfaces. Based on experimental data fitting, a life prediction model for the material in the high-temperature regime was established. The results indicate that the mechanical behavior of 316H stainless steel under both static and cyclic loading is significantly influenced by temperature and strain amplitude. Compared with its room-temperature properties, at 800 °C, the elastic modulus of 316H stainless steel decreases by approximately 30%, the tensile strength drops by about 60%, while the elongation after fracture increases by roughly 100%. Within the temperature range of 600–800 °C, the fatigue performance deteriorates with the increasing temperature, and the cyclic hardening rate accelerates as the temperature rises. The fracture mode in the instantaneous fracture zone of the fatigue fracture surface transitions from predominantly transgranular fracture to a mixed mode of transgranular and intergranular fracture as the temperature increases to 800 °C. Under higher strain amplitudes (around 0.6%), 316H stainless steel exhibits Masing behavior and dynamic strain aging (DSA). Correspondingly, the crack-initiation mode on the fatigue fracture surface shifts from a single surface source to multiple surface sources. A three-parameter model was employed to fit the strain–amplitude versus fatigue–life relationships of 316H stainless steel in the 600–800 °C range, showing good agreement with the experimental data, with most data points falling within a factor-of-two error band. Full article

Hydrogen embrittlement (HE) critically limits the application of ultra-high-strength press-hardened steels (PHS) in hydrogen-containing environments. This study investigated the effect of Nb microalloying on HE resistance of 1500 MPa-grade PHS. Even with higher hydrogen contents, steel 1500Nb exhibits better HE resistance than steel 1500. The results show that Nb addition plays effective role in grain refinement, mitigating stress concentration, and effectively postponing the initiation of intergranular cracks under hydrogen-charged conditions. Additional, hydrogen diffusivity in 1500Nb steel is lower than 1500 steel, attributed to both grain refinement effect and solute drag effect of Nb. Full article

The present study aimed to determine the optional alginate and CaCl₂ concentrations in the encapsulation formulation to produce alginate beads of Stachys byzantina, thereby offering a potential alternative method for its propagation. Stem explants were derived from in vitro cultures grown on Murashige and Skoog (MS) medium supplemented with 10 μM benzyladenine (BA) and were evaluated for their germination and regeneration potential after a short-term storage period (1, 2, and 3 months). Three different sodium alginate concentrations (2%, 2.5% and 3%) were used for the preparation of alginate beads. For the hardening of the alginate beads, calcium chloride dihydrate (CaCl₂·2H₂O) at four concentrations (50, 100, 200 and 400 mM) was employed for 35 min. The combination of 100 mM calcium chloride with sodium alginate at concentrations of 2.0%, 2.5%, or 3.0% resulted in high germination rates, ranging from 73.33% to 76.60%. However, germination rates declined with increased storage duration. Among the formulations, 2.5% sodium alginate consistently supported higher germination over time, with rates of 53.33% and 36.66% observed after 2 and 3 months of storage, respectively. The decline in germination rate was followed by an increase in bead hardness over time. The optimal encapsulation matrix composition was identified as 2.5% sodium alginate with 100 mM CaCl₂, which yielded the highest regeneration rate of explants after 1, 2 and 3 months of cold storage at 4 °C. Full article

The mechanical behavior, the necking process and the geometry of the neck in rectangular cross-section single-crystal copper specimens under macroscopic uniaxial large-strain tensile conditions were numerically simulated and analyzed using the classical Chaboche combined hardening model and the crystal plasticity constitutive model including the effect of back stress. The simulation results show that, although the classical Chaboche model can simulate the load–displacement curve during the tensile process, it cannot simulate the geometric shape change in the cross-section of the single-crystal copper specimen during the necking process. However, simulation using the crystal plasticity model can not only accurately simulate the macroscopic load–displacement mechanical curves of specimens with different crystal orientations (considering eight off-axis states) but also successfully displays the complex necking morphologies, consistent with experimental observations in the literature for various orientations. The research indicates that the classical Chaboche model lacks the ability to describe the deformation characteristics of single-crystal copper specimens; meanwhile, the crystal plasticity model has a significant advantage in simulating the necking process and characteristics of single-crystal materials under slip mechanisms and can effectively capture the differences in necking morphology caused by the crystal orientation, revealing, to a certain extent, the plastic deformation mechanism in single-crystal metallic materials. Full article

Squeezed branch piles, originally developed for building and bridge foundations, have been downsized and deployed at larger pile spacing for reinforcing embankments over soft soils. However, the working mechanism of squeezed branch pile-supported embankments remains unclear. In this study, a three-dimensional numerical model of this embankment was established based on field tests. The analyses consider different pile types (squeezed branch piles and straight piles) and pile-head structures (beam-type cap and plate-type cap). These concrete components were modeled utilizing an advanced concrete model, which captures the strain-softening/hardening and yielding behavior. Simulation results show that squeezed branch piles provide better settlement control in the subsoil beneath the embankment than straight piles for the studied cases. The beam-type cap with squeezed branch piles behaves as a pile-beam foundation that reduces maximum settlement by around 38% compared to that of the plate-type cap, while the plate-type cap system functions as a composite foundation that enhances surcharge capacity by about 35–40%. The instability of the embankment is driven by tensile failure in concrete: The beam-type cap leads to a localized failure along the ground beam, and the plate-type cap system induces a progressive failure centered on the squeezed branch piles. Within the plate-type cap, the dimensions of the pile-head plate significantly influence settlement control and the stability of the embankment in soft soil. Full article

The growing consumption of natural aggregates in concrete production has raised significant environmental and sustainability concerns, motivating the search for alternative and waste-based materials. Walnut shells (WSs), an abundant agricultural by-product, have attracted increasing attention as a potential partial replacement for fine and coarse aggregates in concrete. This study presents a comprehensive review and comparative analysis of published experimental data examining the influence of WS incorporation on the fresh and hardened properties of concrete. Data from the literature covering WS replacement ratios ranging from 1% to 50% were systematically compiled and evaluated with respect to compressive strength, splitting tensile strength, flexural strength, slump, and density. The results indicate that low WS replacement levels (generally ≤10%) may preserve acceptable mechanical performance while contributing to sustainability objectives, whereas higher replacement ratios lead to pronounced reductions in strength, particularly in splitting tensile and flexural capacities. Workability consistently decreases with increasing WS content due to the porous structure and high water absorption of the shells, while density reductions suggest the potential for producing lightweight concrete. Overall, the findings demonstrate that WSs can be effectively utilized in concrete at limited replacement levels, provided that mix design parameters and performance requirements are carefully balanced. The study also highlights the need for further research focusing on durability, long-term behavior, and optimization strategies to enhance the practical applicability of WS-based sustainable concrete. Full article

This paper argues that digital identity in AI-mediated environments has become a central mechanism through which contemporary societies organise recognition, participation, and belonging. Digital identity is no longer simply a technical representation of the individual. It is produced through infrastructural processes of classification, ranking, and credibility signalling that determine who becomes visible, who is treated as legitimate, and who is able to participate meaningfully in social and civic life. The paper develops a conceptual framework that treats AI-driven platforms as social infrastructures rather than neutral intermediaries. It shows how identity is inferred through data-driven systems rather than negotiated through social interaction, how recognition is operationalised through visibility and credibility metrics rather than ethical judgement, and how participation becomes conditional on algorithmic allocation of attention rather than guaranteed by access alone. Visibility is identified as the key conversion point through which inferred identity becomes social consequence. Drawing on interdisciplinary literature, the analysis demonstrates that misrecognition, exclusion, and inequality in platform environments are not primarily the result of isolated error or intentional bias. They are patterned outcomes of ordinary optimisation processes that distribute legitimacy and opportunity unevenly across social groups. These dynamics reshape group formation, harden social boundaries, and concentrate risk among populations that are already more vulnerable to misrecognition and reduced contestability. The paper concludes that governing digital identity is a societal challenge rather than a purely technical one. As platforms increasingly perform institutional functions without equivalent accountability, digital identity governance becomes a critical site of social ordering. Addressing this challenge requires public standards for how visibility, recognition, and participation are allocated, meaningful avenues for contestation, and protections against the normalisation of stratified belonging in AI-mediated societies. Full article

This study investigates the utilization of Abies alba exudate resin for the development of hybrid resins intended as matrices for composite materials. The novelty of this work lies in demonstrating that physically hybridized, bio-derived resin systems based on Abies alba exudate can exhibit distinct mechanical and dynamic behaviors solely by adjusting the solvent-assisted formulation route, without intentional chemical modification and without spectroscopic evidence of co-network formation within the limits of ATR-FTIR analysis, although limited interfacial interactions cannot be excluded. Two formulation routes were explored: (i) dilution of Abies alba exudate in turpentine derived from pine buds, (ii) dilution in ethanol (96%). The diluted resins were subsequently blended with a commercial epoxy system, which was cured with its amine hardener to form solid matrices in which the Abies alba component was physically incorporated. The resulting hybrid resins were characterized by multiple testing methods and further applied in the fabrication of cotton fiber-reinforced composites. The turpentine-based hybrid resin (HR1) showed a rigid mechanical response, with tensile strengths of approximately 13.2–13.5 MPa, compressive strengths of about 30 MPa, Shore D hardness values of 56–58.5, and a low damping ratio (≈0.026). In contrast, the ethanol-based hybrid resin (HR2) exhibited a highly deformable mechanical response, characterized by low tensile strength (≈0.5 MPa), very high elastic recovery, low hardness (<10 Shore D), and a significantly higher damping ratio (≈0.139). To demonstrate their applicability in composite manufacturing, the HR1 matrix was reinforced with cotton fabric, leading to a substantial improvement in tensile strength (25–26 MPa) and flexural strength (35–36 MPa), together with an increased natural frequency. Water absorption tests revealed limited moisture uptake for the neat hybrid resins (≤0.04 g), while the cotton-reinforced composite exhibited higher but largely reversible water absorption (≈21.5%), associated with the hydrophilic nature of the reinforcement. Full article

The unbalanced excitation of a rotor has a significant impact on the dynamic stiffness of the bearing. Traditional unbalanced excitation force models for the calculation of bearing stiffness are usually simplified as single-directional excitation models, which cannot fully reflect the impact of unbalanced excitation of the rotor on the dynamic stiffness of the bearing. A bidirectional excitation model based on orthogonal decomposition is used in this paper and is introduced into the finite element model of the bearing based on ABAQUS. The proposed bearing mechanics model is verified through numerical software and a bearing rotor system test rig. The effects of single/bidirectional excitation models on the dynamic stiffness of bearings were compared. The variation in bearing dynamic stiffness characteristics under rotor excitation and axial load were discussed. The results show that the presented model has good consistency with experimental results (the proposed model yields a maximum stress deviation of only 2.42% compared to MESYS numerical results and a maximum dynamic stiffness difference of 9.12% against experimental data). The traditional unidirectional excitation force model can only consider the influence of excitation frequency on the dynamic stiffness of bearings. However, the unbalanced excitation force model considering bidirectional excitation can further take into account the influence of excitation amplitude on the dynamic stiffness of bearings. Under the combined effect of excitation frequency and excitation amplitude, the radial dynamic stiffness of bearings shows a quadratic nonlinear hardening trend with rotational speed. As the rotational speed increases, the contribution of axial load to the radial stiffness significantly enhances: in the low-speed zone, its influence is only approximately 8%, while in the high-speed zone, it increases to 34%. Although the modeling method formed in this paper does not take into account the thermal–fluid dynamic coupling effect of the lubricating oil film, the obtained laws can provide a basis for the dynamic design of rotor systems of actual liquid rocket engines and have certain engineering application value. Full article

In this study, the continuous strengthening behavior of CoCrNi medium-entropy alloy at 1.2–4.2 nm twin spacings was revealed by molecular dynamics simulation. It was found that the yield strength increased linearly with the decrease in twin spacing, up to 12.526 GPa, and there was no softening inflection point. The strengthening mechanism is mainly due to the effective obstruction of coherent twin boundaries (TBs) to the dislocation slip, especially the stair-rod and Lomer–Cottrell lock structures generated by ISF and ESF stacking faults when crossing the interface. These structures significantly enhance the work-hardening capacity of the alloy by inducing dislocation stacking, although the very dense twin boundary will reduce the dislocation growth rate by limiting dislocation propagation. This precise interface control provides an important atomic-scale basis for the design of novel high-strength and high-work-hardening alloys. Full article