Search Results (237)

Variscan two-mica granites are widespread in the Trás-os-Montes region (NE Portugal), yet their emplacement ages, petrogenesis, and relationship with Variscan deformation phases remain poorly constrained. This study integrates U–Pb zircon geochronology, whole-rock geochemistry, and oxygen isotope data to characterise four peraluminous two-mica granites in the Trás-os-Montes area (Fornos, Carviçais, Fonte Santa, and Bruçó) and to refine their tectonomagmatic context within the Central Iberian Zone. All granites are S-type, ilmenite-series, and derived from reduced magmas, as indicated by their strongly peraluminous compositions, mineral assemblages (muscovite ± biotite), absence of magnetite and presence of ilmenite, and high δ¹⁸O values (>11‰), consistent with partial melting of metasedimentary crust. U–Pb ages reveal two distinct magmatic pulses: an older event at ~340 Ma (Fornos and Fonte Santa granites), predating the onset of C3 deformation and likely associated with late C1 crustal thickening to early C2 tectonics, and a younger pulse at ~320–318 Ma (Carviçais and Bruçó granites). These magmatic pulses are linked to contrasting structural controls, with the older granites emplaced within regional-scale antiforms and the younger intrusions localised along structures related to C3 deformation. Together, these results document two discrete crustal melting events separated by ~20 Ma and record a progressive shift from fold-controlled to strike-slip-dominated granite emplacement during Variscan orogenic evolution. Moreover, the study highlights that tungsten mineralisation is preferentially associated with reduced, crust-derived granites emplaced during specific tectonic regimes, providing new constraints for metallogenic models in NW Iberia. Full article

The operational reliability of Emergency Diesel Generators (EDGs) is paramount for the safety of nuclear power plants. This study investigates the fretting wear mechanism on the non-working back-face of connecting rod big-end bearings—a critical failure mode that can lead to catastrophic engine damage. A synergistic approach was employed, integrating theoretical pressure calculations, on-site strain measurement experiments, and high-fidelity non-linear finite element analysis (FEA). The results demonstrate that while the theoretical design back-face pressure ranges from 8.1 to 10.1 MPa, the actual pressure is highly sensitive to bolt preload. A 16.2% attenuation in preload (from 550 kN to 461 kN), common during maintenance cycles, causes the interfacial pressure to drop to 6.9 MPa, falling below the recommended safety threshold of 7 MPa required to inhibit fretting. Furthermore, comparative experiments reveal that used bearings exhibit significantly lower and less uniform radial pressure retention compared to new bearings, even when physical dimensions appear compliant. Dynamic FEA indicates that peak inertial loads induce an out-of-roundness (DOR) of 0.295 mm, triggering a transition from a “partial slip” to a “macro-slip” regime at the interface. The findings confirm that the coupling of preload attenuation and loss of bearing elasticity drives the fretting process, providing a theoretical basis for optimized maintenance and selective assembly strategies. Full article

The corrosion of prestressed tendons in concrete structures remains a major durability concern, especially for post-tensioned members exposed to aggressive environments. High-strength aluminum alloy (AA) bars exhibit favorable characteristics such as corrosion resistance, low density, and high ductility and may therefore provide an alternative or supplementary prestressing material in durability-oriented structural design. In this study, a bonded post-tensioned T-shaped concrete beam with hybrid prestressing combining prestressed steel (PS) strands and 7075 AA bars was investigated. A refined finite element model was developed by considering the bond-slip relationship between the AA tendons and grout inside corrugated tubes. The flexural behavior of the beam was analyzed through a combination of finite element simulation and sectional theoretical analysis. In addition, a fatigue-life assessment framework was established based on vehicle fatigue loads and material fatigue constitutive models, and the fatigue performance of the proposed hybrid beams was compared with that of conventional prestressed concrete beams. The theoretical predictions agreed reasonably well with the numerical results. Results indicated that partial replacement of PS strands with corrosion-resistant AA bars could alter the governing fatigue failure mode and improve the fatigue durability of prestressed beams under corrosive conditions. These findings highlight the potential of hybrid AA–PS prestressing as a durability-oriented strategy for concrete beams in corrosive environments. Full article

The mechanical behavior of metallic core–shell nanoparticles is critical for their use as reinforcement particles and additive manufacturing feedstocks, yet their deformation mechanisms remain incompletely understood. This study employs molecular dynamics simulations to investigate the compressive response of a Cu-core/Al-shell nanoparticle and compares it with solid Cu, solid Al, and a hollow Al shell of the same size under uniaxial loading along ⟨100⟩, ⟨110⟩, ⟨111⟩, and ⟨112⟩ directions. The single-material nanoparticles show strong anisotropy: solid Cu exhibits orientation-dependent transitions from dislocation slip to deformation twinning, while introducing a void to form a hollow Al shell reduces stiffness and strength, confines plasticity to the shell wall, and suppresses extended load-bearing twins. The Cu–Al core–shell nanoparticle combines these behaviors in an orientation-dependent manner. Under ⟨110⟩ and ⟨112⟩ loading, deformation is largely shell-dominated, whereas ⟨100⟩ and ⟨111⟩ loading more strongly activates the Cu core. Mechanistically, ⟨100⟩ is characterized by Shockley partial activity and junction/lock formation in the Al shell coupled with twinning in the Cu core; ⟨110⟩ shows primarily shell partials with limited core involvement; ⟨111⟩ promotes partial-dislocation activity in both shell and core; and ⟨112⟩ produces localized, twin-dominated bands in the Al shell with shell-thickness-dependent twin extension into the Cu core. These trends are rationalized using Schmid factor considerations for $\left\{111\right\}⟨110⟩$ slip and $\left\{111\right\}⟨112⟩$ partial/twinning shear, together with the effects of faceted free surfaces and the Cu–Al interface. The core–shell geometry enables two concurrent interface-mediated pathways, i.e., (i) stress transfer and reduced cross-interface transmission and (ii) circumferential bypass within the shell, which together yield only slight flow-stress increases over solid Al while markedly reducing stress serrations compared with both solid Cu and solid Al. Across all orientations, the core–shell structures also exhibit delayed yielding (higher yield strain) relative to solid Cu, indicating enhanced ductility. The results provide an atomistic basis for designing Cu–Al core–shell nanoparticles for robust particle-based processing and additive manufacturing feedstock, and for informing multiscale models with mechanism-resolved, orientation-dependent inputs. Full article

The tensile and compressive behavior of hot-forged Al5Co35Cr30Fe20Ni5 high-entropy alloy (HEA) has been studied at room temperature. The forged HEA has a dual-phase microstructure consisting of a predominant face-centered cubic (FCC) matrix and a body-centered cubic (BCC) phase. The BCC phase embeds a low volume fraction of ordered BCC nanoparticles (B2 structure). During forging, the BCC phase recrystallizes more easily than the FCC phase. Yielding is controlled by the deformation of the FCC phase, although BCC grains assume an additional part of the load transferred by FCC grains, even during the elastic regime. During the onset of plastic deformation, slip is activated preferentially in the FCC phase in those grains that are favorably oriented for slip in planes (111). Dislocation pile-ups at FCC/BCC interfaces induce dislocation slip in the BCC phase. In the BCC phase, B2 particles act as effective obstacles to dislocation motion through the Orowan mechanism. As the deformation proceeds, dislocation activity causes an increase in the misorientation in both phases, resulting in the formation of subgrains whose boundaries are effective for blocking dislocation motion. The combination of high strength and ductility arises from the dual-phase FCC–BCC microstructure of the alloy. The load borne by the BCC phase partially relieves the stress applied to the FCC matrix, enabling the latter to continue deforming. Full article

This study systematically investigates the influence of annealing time on the microstructure and mechanical properties of a (CoCrNi)_93.5Al₃Ti₃C_0.5 medium-entropy alloy. Following hot-rolling, the alloy was subjected to annealing treatments at 900 °C for 10 min (HA900-10) and 60 min (HA900-60). Microstructural characterization revealed that both alloys contained three types of precipitates: intergranular M₂₃C₆ and MC-type carbides, as well as γ′ phase. The HA900-10 specimen exhibited a low degree of recrystallization, whereas prolonged annealing promoted partial recrystallization, leading to the formation of a slightly heterogeneous structure (HA900-60). Additionally, the extended annealing facilitated the intragranular precipitation of nanoscale γ′ phase. Room-temperature tensile tests demonstrated that the HA900-10 and HA900-60 specimens achieved yield strengths of 1276 MPa and 1202 MPa, with total elongations reaching 26% and 28%, respectively. Quantitative strengthening analysis indicated that the strength of HA900-10 primarily originated from dislocation and grain boundary strengthening. For HA900-60, an additional significant contribution arose from the dislocation shearing mechanism induced by the intragranular γ′ precipitates. Analysis of the deformation mechanisms revealed that planar slip, assisted by the formation of stacking faults, dominated the room-temperature deformation, thereby ensuring sustained work-hardening capacity. This research provides a theoretical foundation for tailoring the microstructure and properties of multi-phase medium-entropy alloys through annealing process control. Full article

This work analyzes the non-Newtonian electromagnetohydrodynamic (EMHD) flow in an irregular circular porous microchannel while incorporating the consequences of surface charge-dependent slip boundary conditions. The Jeffrey fluid is employed to examine the non-Newtonian behavior, such as elasticity. The boundary walls of the channel are considered in the form of periodic sinusoidal wave function. The mathematical formulation is developed using the momentum equation, modified Darcy’s law, the continuity equation, and Ohm’s law. The perturbation method is used to derive the solutions up to second-order approximation. The analytical expression for the velocity field and volumetric flow rate are explicitly presented. At the zeroth-order, a nonhomogeneous partial differential equation is solved, and the solutions are presented in terms of Bessel functions. The first-order problem defined by a homogeneous partial differential equation is solved using the method of separation of variables. At the second-order, a homogeneous partial differential equation is obtained, and the solution form is prescribed by the boundary conditions, consisting of a radially varying mean component and a second-harmonic angular contribution. Two- and three-dimensional plots are used to analyze and discuss the impacts of key parameters, namely the Reynolds, Darcy, and Hartmann numbers, channel corrugation amplitude and wave number, surface charge density, and the relaxation and retardation times on the velocity field and flow rate. It is found that elastic memory causes a proportional growth between the flow rate and the relaxation time, emphasizing the consequences of surface charge application in conjunction with corrugations. Conversely, maintaining a short retardation time mitigates changes in wave amplitude and surface charge. While prolonging it lessens the flow rate and diminishes corrugations and surface charge effects. The Darcy number dampens the velocity and the flow rate, while its enhancement reduces the impact of surface charge density and corrugations amplitude. For high Reynolds number, a ring phenomenon emerges which is attenuated by increased Darcy number, preventing the formation of trapped boluses close to the border. Ignoring surface charge amplifies the flow rate while its consideration diminishes the latter with reinforced impacts of surface charge and wall corrugations at higher Reynolds number. Full article

The performance of Zr-2.5Nb alloy pressure tubes in nuclear reactors is critically dependent on the behavior of precipitated hydrides. In this study, a hydrogen-charged Zr-2.5Nb alloy pressure tube was subjected to in situ tensile testing combined with electron backscatter diffraction to elucidate microcrack evolution and microstructural adaptation. Initially, longitudinal hydride–hydride interface cracks nucleated at non-coherent interfaces of two types of hydrides due to the inherent brittleness. Subsequently, stress redistribution by a small proportion of hydride–hydride interface cracks resulted in the emergence of microcracks at the transverse hydride–matrix interfaces, accompanied by partial hydride phase transformation. Finally, under high strain conditions, increased dislocation movement in the matrix triggered a single slip system, leading to the formation of numerous low-angle grain boundaries. As strain further increased, multiple slip systems were activated, and longitudinal matrix–matrix interface cracks began to nucleate at certain grain boundary locations. Full article

Alumina ceramics used in semiconductor plasma environments require high densification, microstructural homogeneity, and stable performance under increasingly aggressive processing conditions. However, systematic studies linking slurry processing parameters to the plasma resistance of alumina ceramics remain limited. In this study, the effects of slurry preparation parameters—specifically milling and aging—and sintering atmosphere on the densification, mechanical strength, and plasma etching resistance of slip-cast alumina ceramics were systematically investigated. Optimal dispersion stability was achieved under 12 h milling and 12–24 h aging conditions, resulting in homogenized green body packing and a high relative sintered density exceeding 99%. Mechanical strength and plasma resistance were strongly influenced by slurry aging and sintering atmosphere. Specimens aged for 48 h and sintered under a low oxygen partial pressure (N₂ at 1.0 L/min) exhibited the highest flexural strength and significantly improved resistance to SF₆/Ar plasma etching, with reduced etch depth and suppressed surface roughening. These results demonstrate that coordinated slurry processing and sintering atmosphere control is an effective strategy for designing high-reliability, plasma-resistant alumina ceramics for high-demand semiconductor manufacturing environments. Full article

The Yutian region at the southwestern termination of the Altyn Tagh Fault has experienced four moderate-to-strong earthquakes since 2008, providing an opportunity to investigate fault interactions within a transtensional tectonic setting. In this study, we derive the coseismic deformation and slip model of the 2020 Mw 6.3 Yutian earthquake using ascending and descending Sentinel-1 InSAR data. The deformation field exhibits a characteristic subsidence–uplift pattern consistent with normal faulting, and the preferred slip model indicates a north–south-striking fault with slip concentrated at depths of 6–9 km. To place this event in a broader tectonic context, we incorporate published slip models for the 2008 and 2014 earthquakes together with a simplified finite-fault model for the 2012 event to construct a unified four-event source framework. Static Coulomb stress calculations reveal complex interactions among the four earthquakes. Localized positive loading from the 2012 event partially counteracts the negative $\Delta CFS$ imposed by the 2008 and 2014 earthquakes, reshaping the stress field rather than simply promoting or inhibiting failure. The cumulative stress evolution shows persistent unclamping and repeated shear-stress reversals, indicating that the 2020 earthquake resulted from long-term extensional loading superimposed on multi-stage coseismic stress redistribution. These results demonstrate that multi-event stress analysis provides a more reliable framework for assessing seismic hazards in regions with complex local stress fields. Full article

Changes in preservation conditions act as an important environmental filter driving shifts in microbial communities. However, the precise identities, functional traits, and ecological mechanisms of the dominant agents driving stage-specific deterioration remain insufficiently characterized. This study investigated microbial communities and dominant fungal degraders in waterlogged versus dried bamboo slips using amplicon sequencing, multivariate statistics, and microbial isolation. Results revealed compositionally distinct communities, with dried slips sharing only a small proportion of operational taxonomic units (OTUs) with waterlogged slips, while indicating the persistence of a subset of taxa across preservation states. A key discovery was the dominance of Fonsecaea minima (92% relative abundance) at the water-solid-air interface of partially submerged slips. Scanning electron microscopy (SEM) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) indicate that this fungus forms melanin-rich, biofilm-like surface structures, suggesting enhanced surface colonization and stress resistance. In contrast, the fungal community isolated from dried slips was characterized by Apiospora saccharicola associated with detectable xylanase activity. Meanwhile, the xerophilic species Xerogeomyces pulvereus dominated (99% relative abundance) the storage box environment. Together, these results demonstrate that preservation niches select for fungi with distinct functional traits, highlighting the importance of stage-specific preservation strategies that consider functional traits rather than taxonomic identity alone. Full article

This study presents an experimental and numerical investigation into the mechanical behavior of corrugated steel–concrete composite bridge decks with composite dowel shear connectors. Four full-scale specimens were fabricated and subjected to flexural tests to obtain and analyze the load–deflection and load–strain curves. A finite element model was developed and validated against the experimental results. The validated model was subsequently applied to analyze the load-carrying process and to perform parametric sensitivity analysis. The effects of the concrete strength grade, steel strength, corrugated steel plate thickness, concrete slab thickness, and corrugated steel plate height on the ultimate bearing capacity were evaluated. The results indicate that corrugated steel–concrete composite bridge decks were subjected to concrete shear failure. The ultimate bearing capacity of the bridge deck reached approximately 3.36 times the design value, demonstrating a high safety reserve. Throughout the entire flexural failure process, the shear connectors performed effectively, with only minimal relative slip observed at the steel–concrete interface. At the instance of failure, only partial areas of the corrugated steel plate yielded. To fully exploit the structural potential, the key design parameters require rational coordination. Full article

As a commonly used dental restorative material, light-cured composite resin exhibits mechanical properties that closely match those of natural tooth structure. In the process of biting, the filling material falls off severely due to fretting between the filling material and the fixed interface of the teeth, which shortens the life of the filling material. This study aimed to investigate the mechanisms and contributing factors of this phenomenon. In particular, this study investigated the friction and wear mechanisms at the tangential fretting interface between light-cured composite resin and the tooth substrate under varying fretting amplitudes, normal loads, and lubrication conditions. In artificial saliva, the friction coefficient increased with the fretting amplitude and decreased with the increase in the normal load. The result showed that when the fretting amplitude was large or the normal load was small, the fretting was always in the complete slip regime. When the fretting amplitude was small or the normal load was large, the fretting changed from the complete slip zone to the partial slip regime. The minimum friction coefficient in milk was 0.117, and the maximum friction coefficient in artificial saliva was 0.567. Coke and milk have little effect on the fixation of filling materials. Abrasive wear was the predominant mechanism, with small amplitudes or high loads leading to adhesive wear. The composite resin exhibited the least wear in cola and milk, while soda water and artificial saliva caused significantly greater damage. Full article

Due to their superior tribological properties compared to conventional materials, the use of functionally graded materials (FGMs) has long become indispensable in mechanical engineering. The wide variety of in-depth gradings means that solving contact problems requires specific, complex numerical analysis. In many cases, however, the spatial change in Young’s modulus can be approximated by a power law, which allows closed-form analytical solutions. In the present work, integral equations for solving tangentially loaded power-law graded elastic half-planes are derived by using the Mossakovskii–Jäger procedure. In this way, the application of highly complicated singular integrals arising from a superposition of fundamental solutions is avoided. A distinction is made between different mixed boundary conditions. The easy tractability of the novel equations is substantiated by solving the plane strain fretting contact of a rigid parabolic cylinder and a power-law graded (PLG) elastic half-space. The effect of the type of in-depth grading on the dissipated energy density and the total energy lost per cycle is investigated in detail. A comparison of the total dissipated energy per cycle shows that, for very thin stiff layers on soft substrates, the total dissipated energy exceeds that of a homogeneous material. The same trend is observed for thick layers of a functionally graded material whose Young’s modulus gradually increases with depth, matching that of the underlying substrate at the bonded interface. In addition, a closed-form analytical solution for the total dissipated energy per cycle for plane strain parabolic contact of elastically homogeneous material is presented for the first time. Full article

Greenhouse gas (GHG) emissions from maritime transport account for nearly 3% of global totals, making the decarbonisation of this sector a critical priority. In response, the International Maritime Organization (IMO) adopted the GHG Strategy, targeting the full decarbonisation of international shipping by 2050, with interim milestones in 2030 and 2040. This study evaluates the greenhouse gas fuel intensity of three representative vessel types, an oil tanker, a container ship, and a bulk carrier, using one-year operational fuel consumption data in line with the Regulations of the IMO Net-Zero Framework. Both conventional fuels, including conventional marine fuels, and alternative options, encompassing liquefied natural gas (LNG), e-hydrogen, e-ammonia, e-methanol, and biodiesel, are assessed for compliance during 2028–2035. The findings reveal that conventional fuels are unable to meet future targets, resulting in significant compliance deficits and balancing costs of remedial units. LNG provides short-term benefits but is limited by methane slip. In contrast, e-hydrogen and e-ammonia enable long-term compliance and generate surplus units. E-methanol shows a partial potential, while biodiesel delivers only modest improvements. The results underscore the need for a transition toward near-zero-well-to-wake-emission fuels. This study contributes by combining life cycle assessments with regulatory compliance analysis, offering insights for policymakers and industry stakeholders. Full article