Search Results (825)

Reliable nondestructive evaluation of fine weave pierced carbon/carbon (C/C) composites is essential because these materials are increasingly used in critical components, yet ultrasonic inspection is often compromised by dispersion and frequency-selective filtering that distort waveforms and complicate imaging. This study aimed to experimentally characterize the anisotropic acoustic dispersion and frequency-filtering behavior of up-to-date fine weave pierced C/C composites with a pitch-based matrix. Phase velocities along the three principal directions (x, y, z) were measured over a frequency range of 0.5–5.0 MHz. Along the z-direction, phase velocity increases from 7250 m/s to 13500 m/s with rising frequency, revealing four selective passbands. This indicates pronounced geometric dispersion and a wave-filtering effect due to the larger-scale fibers aligned in this direction. In contrast, the x- and y-directions exhibit only a single low-frequency passband dominated by the strong viscoelasticity of the matrix, with phase velocities of 8100 m/s at 0.5 MHz and 7100 m/s at 0.3 MHz, respectively. Furthermore, temperature-dependent measurements in the z-direction demonstrate a transition from viscoelastic-dominated to geometric-dominated dispersion as temperature increases. These results provide frequency-selection guidance for reliable ultrasonic nondestructive evaluation of advanced C/C composite components. Full article

The effects of Fe non-stoichiometry on crystal structure, microstructural evolution, and thermoelectric transport properties were systematically investigated in bornite (Cu₅Fe_1+yS₄; −0.06 ≤ y ≤ 0.06) synthesized by mechanical alloying followed by hot pressing. X-ray diffraction analysis confirmed the formation of a single-phase orthorhombic bornite structure over the entire composition range. Anisotropic lattice distortion was observed with increasing Fe non-stoichiometry, manifested as contraction along the a-axis and expansion along the b- and c-axes, with a non-linear dependence on composition. Crystallite sizes estimated from Lorentzian peak fitting increased from 64.1 nm for the stoichiometric composition to 70.6–76.3 nm for Fe-deficient samples and 73.2–90.9 nm for Fe-excess samples. Hall-effect measurements revealed p-type semiconducting behavior for the stoichiometric composition, degenerate p-type transport with increased hole concentration under Fe-deficient conditions, and a transition to n-type behavior with reduced carrier mobility under Fe-excess conditions. While Fe-deficient samples retained high electrical conductivity and positive Seebeck coefficients, Fe-excess samples exhibited negative Seebeck coefficients at low temperatures with sign reversal at elevated temperatures. As a consequence, the power factor of Fe-deficient samples was enhanced by approximately 20–30% relative to the stoichiometric composition. In addition, the total thermal conductivity remained below 0.8 W·m⁻¹·K⁻¹ for all samples, and Fe non-stoichiometry effectively suppressed lattice thermal conductivity. Consequently, the Cu₅Fe_0.94S₄ composition achieved a maximum dimensionless figure of merit of ZT = 0.61 at 673 K, representing a performance enhancement of approximately 30–70% compared with the stoichiometric composition (ZT = 0.36 at 673 K and 0.47 at 723 K). Full article

Carbon nanotube yarns (CNTYs) have received more consideration recently due to their excellent specific mechanical, electrical and thermal properties, making them promising materials for different applications. Until now, the axial properties of the yarn have been thoroughly investigated; however, the transverse or radial properties, orthogonal to the fiber axis, remain relatively unknown due to the challenges associated with their measurement. In this study, the transverse or radial response of the CNTY including its elastic modulus was determined using Atomic Force Microscopy (AFM) and Raman Spectroscopy. Determining transverse properties in fibrous materials presents challenges owing to their geometry, inherent anisotropy, whereby mechanical characteristics exhibit directional disparities; i.e., the properties in the transverse direction may be several orders of magnitude smaller than those in the axial direction. To overcome these difficulties, AFM was utilized to perform nanoindentation experiments, where a tipless flexible cantilever probe was used to apply a controlled force to the CNTY surface. The resulting indentation depth was then analyzed to determine the transversal elastic modulus. Preliminary findings indicate that the transverse elastic modulus of the CNTYs ranges from 10–54 kPa for strain levels below 3%. Complementary Raman spectroscopy provided insight into the bulk-scale mechanical behavior of CNTYs. Incremental compressive loading between microscope slides induced nonlinear upshifts in the 2D Raman band (from ~2686.6 to 2691.4 cm⁻¹), indicating nanoscale tube realignment, inter-tube densification, and compaction. From lateral diameter measurements under load, a stress–strain curve was constructed, revealing three distinct regimes: one with an initial elastic modulus of 3.12 MPa (0.3–11.2% strain), another one with an elastic modulus increasing to 8.46 MPa (11.2–14.4%), and finally one with an elastic modulus peaking at 16.86 MPa beyond 14.4% strain. Together, these methods delineate the hierarchical and anisotropic nature of CNTYs, validating the importance of multiscale mechanical characterization for their deployment in piezoresistive sensors and multifunctional composites. This study establishes a robust framework for quantifying the transverse mechanical response of CNTYs. Full article

Mechanochromism is a phenomenon in which mechanical stimuli change the optical properties of a material, such as its color and emission properties. Various materials exhibiting this behavior have been intensively studied. Mechanochromic materials that exploit liquid crystals have been previously reported. Using liquid crystals, properties different from those of conventional materials, such as anisotropic response and multicolored luminescence due to intermediate aggregation phase stabilization, can be expected. Recently, we reported the preparation and evaluation of the optical properties of liquid-crystalline mechanochromic dyes with cholesterol terminals. The dyes formed gels in some solvents, changed their emission color, and exhibited a friable response without reaching a crystalline state. In addition, film-forming properties, processability, and responsiveness were improved in thin films mixed with polymers. However, the mechanical and thermal stabilities of the gels were low. In this study, a compound similar to the polymerizable unit was synthesized to produce tougher gels. In addition, triblock polymers with a mechanoresponsive dye in the hard segment were synthesized. The xerogel film prepared from the monomer showed an irreversible blue shift in photoluminescent color by mechanical grinding and also exhibited linearly polarized photoluminescence by uniaxial grinding due to force-induced alignment. On the other hand, the xerogel film prepared from the triblock copolymer showed a blue shift in photoluminescent color that can approximately revert to the initial state by thermal annealing, though it showed no anisotropy by uniaxial grinding, indicating that polymerization partially preserves mechanical responsiveness. Full article

This study presents the dynamic characterization of a gas turbine blade manufactured from two different nickel-based superalloys: on the first hand, a superalloy called René 80 and, on the second hand, a directionally solidified (DS) nickel-based anisotropic superalloy, investigated during the validation phase of the development process. Starting from the original CAD geometry, precise and very detailed finite-element models were developed, progressively refined and modified, and consequently validated to ensure mesh-independent modal predictions. The study examines multiple possible sources of discrepancy between experimentally measured and numerically predicted natural frequencies, including geometric deviations, grouping of different interesting points, broach-block test configuration, material anisotropy, and the influence of internal rib turbulators. Statistical analyses of dimensional variations revealed no significant correlation with the observed frequency scatter, redirecting the investigation toward material behavior and modeling fidelity. The inclusion of turbulators in the finite-element model proved essential, reducing prediction errors for the first two modes by approximately 2–3%. For the DS superalloy, the effect of grain orientation was evaluated over permissible angular deviations (extremes were considered); however, no systematic and clear improvement in frequency prediction was observed. Finally, several tuning strategies were assessed, leading to an optimization procedure that simultaneously adjusted the elastic moduli $E_x$ and $E_z$, reducing modal frequency deviations to below 1% for the first two modes. The proposed methodology provides a robust and solid framework for the validation of turbine blade dynamic behavior across different materials and manufacturing conditions. Full article

The long-term stability of embankments is directly influenced by the stress paths associated with river water level fluctuations. To investigate the anisotropic characteristics of slope soil in embankments under such drainage-induced gradual loading conditions, a series of drained directional shear tests was conducted on slope soil to investigate the coupled effects of the principal stress direction angle α and the intermediate principal stress coefficient b on its strength, deformation, and non-coaxial characteristics. Results showed that radial strain exhibited minimal sensitivity to variations in the principal stress direction angle α at the constant principal stress coefficient b. The circumferential and axial strain directions demonstrated symmetry. Specimens initially contracted then dilated during shearing. Octahedral shear strain anisotropy was more significant at b = 0.5 and 1 than at b = 0. For a constant α, the normalized strength at b = 0.5 exceeded that at b = 0 and 1. Strength showed significant anisotropy across angles α at a constant b. Specimens exhibited significant non-coaxial behavior under axial-torsional shear loading. This study offers theoretical insight into embankment slope behavior under anisotropic stress paths. Full article

Protein crystals are intrinsically hydrated systems, and their structural integrity is strongly influenced by environmental humidity. Understanding the effects of relative humidity (RH) variation on crystal stability is therefore essential for both fundamental research and applied studies. In this work, the structural response of tetragonal hen egg-white lysozyme (HEWL) to controlled RH variation was investigated using in situ X-ray powder diffraction (XRPD). Polycrystalline HEWL samples were subjected to systematic gradual dehydration and rehydration cycles, as well as to non-gradual RH variation protocols. Pawley analysis of the XRPD data enabled monitoring of the evolution of unit cell parameters and unit cell volume as a function of RH. Under all experimental conditions, the tetragonal polymorph (space group P4₃2₁2; a = 79.105 (4) Å, c = 38.231 (2) Å) was preserved. RH variation induced smooth, continuous and anisotropic lattice changes, characterized by a decrease in the a (=b)-axis and a concomitant increase in the c-axis upon dehydration, while rehydration resulted in the opposite behavior. The overall magnitude of lattice variation remained limited (within ±2%), indicating a high degree of structural stability. Partial degradation of crystallinity was observed only after prolonged exposure to low RH levels. These findings demonstrate the remarkable structural resilience of tetragonal HEWL and highlight the effectiveness of in situ XRPD as a powerful tool for probing hydration-driven lattice responses in protein crystals under realistic environmental conditions. Full article

This study investigates the crack damage evolution in Chinese fir using an anisotropic bilinear cohesive zone-based constitutive model. The crack initiation and propagation processes were numerically modeled and simulated, and the results were validated through double cantilever beam (DCB) fracture tests. By exploiting the bijective relationship between the equivalent linear elastic fracture mechanics (LEFM) resistance curve (R-curve) and the cohesive softening law, the bilinear cohesive parameters were inversely identified from experimental data. The simulation results show good agreement with experimental observations in terms of crack path, propagation rate, and failure mode. The accuracy of the maximum load simulation results for mode I fracture of wood beams is 96.8%. These results further demonstrate the accuracy and applicability of the proposed cohesive zone model in describing crack propagation behavior in Chinese fir and provide a reliable theoretical and numerical framework for predicting fracture performance in timber structures. Full article

Polymer–ceramic hybrid composites are emerging as attractive candidates for lightweight, corrosion-resistant absorber components in solar thermal collectors; however, their adoption is constrained by the intrinsically low thermal conductivity of polymers, processing-induced anisotropic heat transport, interfacial thermal resistance at tube/laminate joints, and durability challenges under outdoor exposure. This review provides a collector-centered synthesis of polymer–ceramic hybrid materials, emphasizing the translation of composite properties into collector-level outcomes rather than conductivity enhancement alone. A structure–property–performance mapping approach is presented to connect directional thermal conductivity ((k_in-plane), (k_perp)), thermal diffusivity, heat capacity, coefficient of thermal expansion, and service temperature with collector performance parameters such as heat removal effectiveness, overall heat losses, and stagnation behavior. Ceramic fillers (e.g., boron nitride, aluminum nitride, silicon carbide, alumina) are examined for stable conduction-network formation, coating compatibility, and long-term reliability, while carbon fillers (graphite, graphene nanoplatelets, carbon nanotubes) are evaluated for combined heat spreading and solar absorption benefits, with attention to emissivity penalties. Hybrid ceramic–carbon architectures and multilayer absorber designs are identified as the most promising routes to balance thermal transport, optical selectivity (high solar absorptance and low thermal emittance), manufacturability, and durability under UV, humidity, and thermal cycling. Full article

In this study, Nd-Fe-B magnets with different degrees of alignment were prepared by adjusting the strength of the alignment magnetic field. The mechanism of influence of alignment degree on the densification of magnets was systematically investigated. The shrinkage rates of the magnets after sintering were calculated, and the results showed that the unoriented magnets exhibited similar shrinkage in different directions, displaying isotropic shrinkage behavior. With the increase in the degree of alignment, the magnets showed significant differences in shrinkage across different directions, presenting anisotropic shrinkage characteristics. In addition, the microstructural analysis revealed that the alignment degree also exerted a certain influence on the micromorphology of the magnets. The grain size parallel to the c-axis was larger than that parallel to the a-axis, which indicates that the alignment degree plays a crucial role in the anisotropic densification of the Nd-Fe-B magnets. Full article

The development and utilization of unconventional shale oil and gas have enhanced the resilience of global energy security. Hydraulic fracturing is the primary method for enhancing unconventional shale oil and gas extraction. Previous studies have predominantly employed homogenized geomechanical models to simulate fracture propagation in rock masses. However, bedding planes and inhomogeneous mineral distributions introduce mechanical anisotropy in shale, rendering conventional homogenized models insufficient for accurately representing hydraulic fracturing in real reservoirs. For this, millimeter-scale indentation testing was employed to systematically quantify the depth-dependent distribution of mechanical parameters across varying bedding orientations, using fragmented shale samples obtained from the Qingshankou Formation of the Songliao Basin, northern China. Then, hydraulic fracturing simulations were performed using the mechanical properties derived from the indentation tests. The key findings include: (1) The elastic modulus of the Qingshankou Formation shale reservoir exhibits significant anisotropic properties in both the depth and bedding orientations. The elastic modulus measured parallel to bedding (10.23–65.08 GPa) is 28% higher than that measured perpendicular to bedding (9.60–47.24 GPa) due to shale bedding anisotropy. The mineralogical composition predominantly governs the depth-dependent anisotropy, with an elevated brittle mineral content increasing the elastic modulus and a higher clay content reducing it. (2) The simulation results reveal that the depth-dependent anisotropy of elastic modulus induces asymmetric hydraulic fracture propagation, with the fractures preferentially extending along the orientations exhibiting a higher elastic modulus. This behavior arises due to the enhanced brittleness and reduced deformation resistance of high-modulus rocks, facilitating fracture advancement. The study offers critical insights for hydraulic fracturing design and operational implementation in bedded shale reservoirs. Full article

In geotechnical engineering, operations such as foundation pit excavation, slope cutting, and tunnel boring often involve lateral unloading under plane strain conditions. This unloading pattern exhibits significant differences from the traditional axisymmetric triaxial loading path. To investigate the mechanical behavior of silt under such conditions, a series of plane strain tests were conducted using a self-designed plane strain apparatus, focusing on both vertical loading (constant lateral stress) and lateral unloading (constant vertical stress) paths. The results indicate that the failure of soil during unloading can be identified as the stage where the vertical deformation rate first increases and then decreases, corresponding to a distinct inflection in the stress–strain curve. The internal friction angle remained essentially constant regardless of the stress path, dry density, or consolidation stress ratio, while cohesion was higher under loading than under unloading. Failure deviatoric stress increased linearly with vertical consolidation stress and was unaffected by the consolidation stress ratio. The classical limit equilibrium condition remains valid for unloading under both isotropic and anisotropic consolidation. These findings provide a practical criterion for failure detection and highlight the necessity of adopting plane strain parameters in the design of lateral unloading engineering works. Full article

Directional control of heat flow is essential for advanced energy and electronic systems, yet strategies for tuning anisotropic phonon transport in low-dimensional materials remain limited. Hollow tellurium (Te) nanowires were synthesized via a solvothermal method and modified through Pd electroless plating to achieve tunable anisotropic thermal transport. Structural analyses confirmed Pd incorporation as nanoscale surface deposits without crystalline Pd phases, while SEM observations revealed cavity enlargement due to galvanic displacement at higher PdCl₂ concentrations. Bulk films prepared by cold pressing exhibited direction-dependent behavior. Thermal conductivities remained nearly unchanged below 2.2 mM PdCl₂, but at 5.5 mM, the in-plane value increased to 2.14 W/(m·K) and the cross-plane value decreased to 0.39 W/(m·K), enhancing the anisotropy ratio from 2.71 to 5.49. This divergence arises from direction-selective phonon scattering, where Pd-rich regions promote in-plane heat flow while junction irregularity suppresses cross-plane transport. These results demonstrate a controllable approach for engineering anisotropic thermal properties in functional energy materials. Full article

Valvular heart disease remains a major global health burden, with currently available prosthetic heart valves failing to fully reproduce the adaptive, regenerative, and long-term functional properties of native valves. Tissue-engineered heart valves (TEHVs) have emerged as a promising alternative, aiming to develop living valve replacements capable of growth, remodeling, and physiological integration. However, despite substantial progress, the clinical translation of TEHVs remains limited, indicating the need for design strategies that go beyond material selection toward functionally mature constructs. This review presents recent advances in TEHV development from a biomimetic perspective, using native heart valves as a biological reference characterized by hierarchical structure, anisotropic mechanical behavior, mechanoresponsive cell populations, immune regulation, and temporally coordinated remodeling. We integrate current understanding of valve biology and mechanobiology with advances in scaffold materials and architecture, bioactive functionalization, biomechanical conditioning, and emerging fabrication and monitoring technologies. We discuss how biomimetic scaffold designs aim to replicate native extracellular matrix organization and nonlinear mechanics, how biological cues are used to regulate thrombosis, immune response, and cell recruitment, and how dynamic bioreactor systems support functional tissue maturation through controlled mechanical stimulation. Finally, key challenges for clinical translation are highlighted, and future directions are outlined, emphasizing integrated and biomimetically informed design approaches. Overall, this review aims to define guiding principles that may accelerate the development of durable, regenerative, and clinically translatable tissue-engineered heart valves. We argue that successful TEHV translation requires synchronized control of scaffold anisotropy, immune modulation, and mechanical conditioning rather than incremental material optimization. Full article

While diverse previously fabricated pristine and hydrogenated borophene lattices have been characterized predominantly by their metallic nature, a recent experimental breakthrough has introduced α′–B₈H₄, a semiconducting hydrogenated borophene phase, opening new avenues for boron-based nanoelectronics. Spurred by this breakthrough, herein we utilize a comprehensive first-principles framework to investigate the critical properties of α′–B₈H₄ monolayer. Stability analyses confirm the considerable dynamical and thermal robustness of the α′–B₈H₄ monolayer. Calculations using hybrid functionals show that suspended single-layer α′–B₈H₄ exhibits an indirect semiconducting behavior, with band gaps of 2.06 eV and 2.45 eV predicted by HSE06 and PBE0, respectively. Optical response calculations reveal strong in-plane absorbance in the UV region, with the first notable peak at ~3.65 eV and the main peak occurring between 4.20 and 4.45 eV, both of which are clearly within the ultraviolet range. Mechanical analysis reveals that α′–B₈H₄ exhibits decent in-plane strength (>10 N/m), while phononic transport calculations yield a moderately low room-temperature lattice thermal conductivity of ~20 W/m·K, both displaying slight anisotropic behavior. These results provide a comprehensive first-principles characterization of the α′–B₈H₄ monolayer, highlighting the rare emergence of semiconducting behavior in borophene derivatives and underscoring its potential for UV optoelectronics and nanoscale device applications. Full article