Search Results (6,968)

Resin and interlayer properties play significant roles in the resistance to impact of fibre-reinforced polymer composites (FRPCs). To investigate the contribution of each factor within the coupled variables to the impact resistance ability of FRPCs, in this work, waterborne polyurethane (WPU) with different tensile elastic modulus, tear strength and bonding strength was obtained. To systematically evaluate the impact resistance and failure mechanisms of the composite materials under varying external loads, impact resistance tests, numerical simulations, and relative weight analysis were conducted. The relative weight analysis results quantified the individual contributions of these three factors to the overall energy absorption capacity across diverse loading conditions. The results indicated that with the increasing rate of the external loading, the resin modulus consistently contributed more significantly to energy absorption than tear strength of resin and interlayer strength, reaching up to 44.3%. In ballistic penetration tests, with the increase in resin modulus, the ballistic performance of PE/WPU laminates demonstrated an S-shaped downward trend. Composites prepared with more rigid matrix could lead to unsatisfactory interlayer damage. A more robust structure could result in fibre pull-out and breakage to a greater extent at the point of forced impact while less in the secondary affected area, presenting comparatively lower impact resistant performance. Full article

The freeze–thaw cycles lead to cumulative damage and gradual strength deterioration in concrete, which cannot be accurately represented by traditional empirical models. To address this issue, shale-based lightweight structural concrete (LSC) specimens with four strength grades (LSC20-LSC50) were subjected to basic mechanical performance and freeze–thaw cycle experiments. The study investigated the patterns of mass loss, relative dynamic elastic modulus, and loss of compressive strength in LSC subjected to varying numbers of freeze–thaw cycles. Furthermore, the correlation between the dynamic modulus of elasticity and compressive strength was examined. A Gamma process-based stochastic degradation model for the compressive strength of LSC was then developed. The results show that the compressive strength degradation of LSC under freeze–thaw cycles follows a monotonically increasing trend that gradually stabilizes, with low-strength LSC deteriorating faster than high-strength LSC. After 200 cycles, the compressive strength degradation of LSC30 and LSC50 was only 32.66% and 29.79% of that of their corresponding ordinary concretes (C30 and C50). The proposed Gamma process model showed high fitting accuracy for all strength grades of LSC (R² > 0.96, RMSE < 0.25 MPa, MAPE < 11%). The research results provide a scientific basis for the structural design of concrete in cold regions. Full article

This manuscript presents a transferable and reproducible methodology for quantitative 3D tree-structure mensuration and transparent, rule-based decision support for tree risk management. The workflow integrates (i) Structure-from-Motion/Multi-View Stereo (SfM–MVS) reconstruction from multi-view imagery, (ii) independent referencing to ensure metric scaling and a consistent local frame, and (iii) point cloud analytics to derive branch-level geometric descriptors (e.g., base diameter, length, inclination, slenderness, and projected reach). A clear rule-based layer operationalizes Tree Risk Assessment Qualification (TRAQ)-style risk components and As Low As Reasonably Practicable (ALARP) principles to map geometry and exposure into auditable management recommendations (e.g., monitoring intervals, pruning/weight reduction, supplemental support, and exclusion-zone planning). To provide a real-data example, the demonstration uses the public Fuji-SfM apple orchard dataset, including three neighboring trees with partially overlapping crowns for tree instance extraction and subsequent TRAQ/ALARP scenarios on an outer tree. The proposed decision layer is intentionally based on external geometry and exposure; internal decay indicators and species-specific mechanical properties (e.g., Modulus of Elasticity (MOE), Modulus of Rupture (MOR)) are outside this demonstration and should be incorporated via complementary diagnostics in operational deployments. Full article

In this work, kyanite-reinforced alumina ceramics were prepared using the prestress reinforcement method and the particle enhancement method. The effects of different preparation methods on the mechanical properties and microstructures of kyanite-reinforced alumina ceramics were investigated. The results showed that, compared to the pure alumina ceramic, the prestressed alumina ceramic (labeled as P-Al₂O₃) prepared by the prestress reinforcement method exhibited a significant improvement (31% higher than that of pure alumina) in flexural strength. This is mainly attributed to the fact that the compressive stress existing on the surface of P-Al₂O₃ inhibited crack propagation; therefore, the fracture energy and strength were increased. However, due to the numerous pores and cracks in the fracture surface caused by the decomposition reaction of kyanite, the alumina composites fabricated through the particle enhancement method (labeled C-Al₂O₃) displayed lower flexural strength and hardness than those with P-Al₂O₃. Additionally, an increase in kyanite content led to a decrease in properties such as flexural strength, Vickers hardness, density, the elastic modulus, and the thermal expansion coefficient, while resulting in an increase in porosity. This work demonstrates the importance of using a suitable preparation method aligned with the specific composite. Full article

The aim of this work is to investigate the possibility of improving the performance properties of 40CrMnMo7 steel by conducting duplex surface modification treatment. Chemical-thermal treatment processes were used—nitrocarburization and ion-nitriding and subsequent application of a nanostructured multilayer coating, Cr/(Cr-C)ml. The resulting structures and their influence on the adhesion of the applied coating, as well as their influence on the tribological properties of the coating, were studied. By conducting Glow Discharge Optical Emission Spectroscopy (GDOES), it was established that the penetration of nitrogen into the depth is greater in the ion-nitriding process, and the results of the conducted optical metallography and hardness measurement show that after ion-nitriding, the obtained hard layer has a greater thickness and hardness. The data obtained from the studies of the phase composition of the hard layers show that after nitrocarburization the non-stoichiometric, but crystalline phase Fe₃N_1.1 (ξ)—98.4% was formed. In the composition of the hard layer formed after the ion-nitriding process, the presence of Fe₃N (ξ-phase) in an amount of 79.5% and Fe₄N (γ′-phase) in an amount of 19.1% was established. On the chemically and thermally treated surfaces, a Cr/(Cr-C)ml coating was applied through the unbalanced magnetron sputtering technology. The applied coating has a hardness of 17.1 ± 0.6 GPa and a modulus of elasticity of 289 ± 8.7 GPa. The thickness of the coating applied on the test bodies not subjected to diffusion enrichment is 1.967 µm, and the adhesion class is classified as HF-2. It has been established that the profile of the surfaces obtained after the application of the chemical-thermal treatment processes has an impact on the thickness of the applied coating and on its adhesion. After nitrocarburization, the thickness of the coating is 2.9 µm, and the adhesion of the coating is classified as HF-0. The thickness of the applied coating on the test bodies subjected to ion-nitriding is 2.4 µm, and the adhesion class is HF-1. The results of the conducted tribological tests show that the used chemical-thermal treatment processes have an impact on the coefficients of friction and wear of the coating. The coefficient of friction for the combination of the nitriding process and Cr/(Cr-C)ml coating has the highest value (µ ≈ 0.38), while that of the ion-nitrided sample with subsequent coating has a value (µ ≈ 0.21) slightly higher than the COF of the test body with only the coating applied (µ ≈ 0.18). The lowest value of the coating wear coefficient is registered for the combination of the ion-nitriding and coating process (k = 7.96 × 10⁻⁵), while for the combination of nitriding and coating, it is the highest (k = 12.4 × 10⁻⁴). The relevance of the present work is related to the implementation of surface modification of 40CrMnMo7 steel by using established technological processes of chemical-thermal treatment and subsequent deposition of nanostructured multilayer Cr/(Cr-C)ml coating. The other novelty in the present study is related to the use of MF pulsed DC power supplies, operating at a fixed frequency of 100 kHz and a specific pulse shape, similar to the shape of HiPIMS pulses, for the deposition of nanostructured multilayer Cr/(Cr/a-C)ml coatings. Full article

This study presents a calibrated analytical micromechanical framework for predicting the linear elastic behavior of unidirectional glass fiber/epoxy and carbon fiber/epoxy composites over a wide range of fiber volume fractions. The approach combines the classical rule of mixtures for the longitudinal Young’s modulus with the semi empirical Halpin–Tsai equations to estimate the transverse Young’s modulus and the in-plane shear modulus. The framework is specifically formulated to support durability-oriented composite design through rapid and physically consistent estimation of elastic properties governing load transfer and stress distribution. Material parameters, including fiber and matrix Young’s moduli (Ef, Em), shear moduli (Gf, Gm), Poisson’s ratios (νf, νm), and fiber volume fraction (Vf up to 0.80), are taken from established material property databases and implemented within a literature-informed modeling scheme. To preserve physical realism at high fiber contents, a shear correction factor is introduced for Vf > 0.50 to account for microstructural interaction and fiber clustering effects. The predicted effective elastic constants (E₁, E₂, G₁₂, ν₁₂) exhibit consistent and physically meaningful trends across the full fiber volume fraction range. The model predictions were evaluated against trends widely reported in the composite micromechanics literature, and the results showed overall agreement in the nonlinear reduction in stiffness gains at elevated fiber volume fractions. Comparative results indicate that carbon fiber/epoxy composites achieve up to approximately 30% higher stiffness than glass fiber/epoxy systems at equivalent fiber contents, reflecting the influence of stiffness contrast on composite response. The analysis further indicates that stiffness saturation begins approximately in the Vf = 0.60–0.70 range, where the incremental gains in E2 and G12 become noticeably smaller for both composite systems. This behavior provides design-relevant guidance by showing that, beyond this range, further increases in fiber content may offer limited stiffness improvement relative to the associated manufacturing complexity. Overall, the calibrated Halpin–Tsai methodology offers a practical and computationally efficient tool for preliminary evaluation and design-stage optimization of the elastic performance of high-performance composite structures. Full article

Dental tissue regeneration, particularly alveolar bone and gingival repair, remains a major challenge in regenerative medicine. 3D bioprinting offers patient-specific and anatomically precise constructs, representing an advanced alternative to conventional grafting. In this study, nanohydroxyapatite (nHA), chitosan (CS), and collagen (CoL) were combined to fabricate and characterize 3D bioprinted dental grafts. SEM revealed a highly porous, interconnected architecture favorable for cell infiltration and nutrient exchange. EDS confirmed Ca/P ratios of 2.06 for nHA/CoL and 1.83 for nHA/CS/CoL, both of which are above the stoichiometric 1.67, indicating the presence of additional mineral phases and ion substitutions. FTIR and XRD verified characteristic functional groups and crystalline phases, including B-type HA with carbonate substitution. Mechanical testing showed that pure nHA exhibited the lowest compressive strength, whereas CoL incorporation improved stiffness. The nHA/CS/CoL composite achieved the highest compressive strength, elastic modulus, and toughness, demonstrating superior mechanical resilience. DSC analysis indicated endothermic peaks at 106.49 °C and 351.91 °C, with enthalpy values (264.91 J/g and 15.09 J/g) surpassing those of nHA alone. TGA revealed ~28.8% weight loss across three degradation stages, confirming enhanced thermal stability. In vitro cytocompatibility testing using L929 fibroblasts validated the biocompatibility of the composites. Collectively, the synergy between bioceramics and biopolymers markedly improved both mechanical and thermal performance. These findings position the nHA/CS/CoL scaffold as a promising candidate for clinical applications in dental tissue regeneration. Unlike conventional grafting materials, this study introduces a synergistically optimized nHA/CS/CoL bio-ink formulation specifically designed for extrusion-based 3D bioprinting of patient-specific dental constructs. The core innovation lies in the precise integration of nHA within a dual-polymer matrix (CS/CoL), which bridges the gap between mechanical resilience and biological signaling, achieving a compressive strength that mimics native alveolar bone while maintaining high cytocompatibility. Full article

Glass fiber-reinforced epoxy composites were modified with carbon nanotubes (CNTs), Al₂O₃, and TiO₂ nanoparticles to comparatively evaluate their influence on tensile, flexural, and low-velocity impact performance within an integrated experimental–numerical framework. Nanoparticles were incorporated at controlled weight fractions to identify dispersion-controlled reinforcement regimes and the onset of heterogeneity-driven mechanical transitions. Among all formulations, 0.5 wt% CNTs provided the most pronounced static mechanical enhancement, increasing tensile strength to 419.50 MPa (≈21% improvement over the reference GF laminate) and flexural strength to 230.23 MPa (≈26% increase). In contrast, impact performance exhibited a non-monotonic evolution; the highest absorbed energy (9.64 J) was observed at 2 wt% CNTs, indicating that dynamic energy dissipation mechanisms do not necessarily scale proportionally with static strength gains. Oxide-filled systems demonstrated stiffness-dominated behavior, where increasing filler content amplified elastic mismatch and progressively reduced strength despite modulus enhancement. Finite element simulations conducted in ANSYS LS-DYNA (MAT_022) reproduced global stiffness trends within the dispersion-controlled regime. Tensile strength predictions agreed within 0–9% at optimal CNT loading, whereas larger deviations (up to ~33%) emerged under bending-dominated loading in oxide-rich systems, reflecting amplified sensitivity to microstructural heterogeneity. The coupled evolution of stiffness–strength decoupling (SSDI) and FEM deviation (η) enabled identification of a Composite Heterogeneity Threshold (CHT), defined as the nanoparticle concentration beyond which stiffness enhancement no longer translates into proportional strength or toughness improvement. Beyond this threshold, dispersion-induced heterogeneity not only reduces mechanical efficiency but also marks the boundary of homogenized continuum model adequacy across static and dynamic loading conditions. Full article

To investigate the deterioration law of the mechanical properties of PVA-fiber-reinforced rubber concrete under the combined action of high-temperature and salt erosion, physical index tests, dynamic mechanical property experiments, and microstructural morphology observations were carried out on specimens subjected to different temperatures (ambient temperature, 100 °C, 300 °C) and various solution attacks (water, 5% NaCl, 5% Na₂SO₄, and 5% NaCl + 5% Na₂SO₄ mixture). The results show that, after exposure to 300 °C, the PVA fibers melt and the rubber pyrolyzes, since this temperature exceeds their melting points. A residual pore network is formed inside the matrix, and the damage degree of ultrasonic pulse velocity is about 2.3 times that of the 100 °C group. Although salt solution and its crystallization products can physically fill the pores and cause a partial recovery of pulse velocity, this change is mainly due to the alteration of the pore medium and does not represent a substantial restoration of the microstructure. The effects of different salt solutions on dynamic mechanical properties vary significantly: Sulfate erosion improves the dynamic performance significantly at ambient temperature by forming gypsum and ettringite to fill pores, but this strengthening effect disappears after 300 °C. Sodium chloride attack generates Friedel’s salt and consumes C₃A, leading to general strength deterioration. In composite salt erosion, the competitive and synergistic effects of Cl⁻ and SO₄²⁻ destabilize erosion products and weaken interfacial bonding, resulting in consistent decreases in dynamic compressive strength and elastic modulus under all temperatures and impact pressures. The strength reduction reaches 66.2% after 300 °C. Microscopic analysis confirms that composite salt erosion leads to the dissolution of ettringite and loose structure, which verifies the synergistic deterioration law of macroscopic properties. This study systematically reveals the damage evolution mechanism of PVA-fiber-reinforced rubber concrete under the coupled action of high-temperature and salt erosion, and provides a theoretical basis for the dynamic bearing capacity evaluation and durability design of concrete structures in such coupled environments. Full article

This study investigated the enhancement mechanisms and optimal mix proportion of basalt fiber (BF) in concrete for ship lock galleries. It focused on improving crack resistance, freeze–thaw resistance, impermeability, and abrasion–erosion resistance under complex hydraulic environments. Single-factor tests first determined the reasonable parameter ranges, which were subsequently used in a three-factor, four-level orthogonal experiment to analyze the effects of the water-to-binder ratio, fiber content, and fiber length on concrete’s mechanical properties. Range analysis of the orthogonal experiment indicated that the water-to-binder ratio was the most dominant factor (R = 57.4), followed by fiber content. Based on this, further durability tests were conducted, including ring restraint cracking, impermeability, freeze–thaw resistance, and abrasion–erosion resistance. Multi-objective optimization was performed using full factorial experiments and a comprehensive performance evaluation system. The final optimal mix proportion was determined as: a water-to-binder ratio of 0.35, a fiber content of 0.2%, and a fiber length of 12 mm. With this mix, the concrete’s ring cracking time was extended by 69.9%, the relative dynamic elastic modulus retention reached 73.0% after 100 freeze–thaw cycles, the relative permeability coefficient was 1.04 × 10⁻⁶ cm/h, and the abrasion–erosion resistance strength increased to 7.05 h·m²/kg, which achieved an optimal synergy among the mechanical properties, key durability indicators, and their workability. Mechanism analysis revealed that BF formed a three-dimensional, randomly distributed fiber network that comprehensively enhanced concrete performance through multi-scale mechanisms, including bridging, pore refinement, and energy dissipation. This research has provided systematic experimental evidence and mix proportion support for the durability design and engineering application of BF concrete in ship lock galleries. Full article

Background/Objectives: Osgood–Schlatter disease (OSD) is a common overuse condition in adolescents characterized by increased stiffness of the rectus femoris muscle, which contributes to pain and functional limitations around the knee. We investigated whether repeating 10 min passive joint movements of the hip and knee produces additional immediate reductions in elevated rectus femoris (RF) stiffness in adolescents with OSD. Methods: Fifteen patients (10–14 years of age) diagnosed with bilateral OSD were included. The legs of the participants were randomly assigned to either the intervention or the non-intervention side (control). The intervention side received two sets of 10 min of passive joint movement to the hip and knee, while the control side rested. RF stiffness was measured before the intervention and immediately after one and two sets of passive joint movements. Results: On the intervention side, RF stiffness decreased significantly from pre to post-1 and from pre to post-2; however, RF stiffness did not differ significantly between post-1 and post-2. None of the parameters changed significantly on the control side (rest condition). Conclusions: Passive joint exercise beyond one repetition (one set for 10 min) did not result in a further decrease in RF stiffness and is likely unnecessary for RF muscle stiffness due to OSD. Full article

Carbon-fiber-reinforced polymer (CFRP) cables have emerged as promising alternatives to conventional prestressing tendons because of their high tensile strength, excellent corrosion resistance, and low self-weight. Their use is particularly advantageous in infrastructure exposed to aggressive environments, such as chloride-induced corrosion, where improved durability and reduced maintenance are critically required. In this study, a 10 mm diameter round-bar-type CFRP cable was developed using a pultrusion process, and its applicability to structural systems was comprehensively evaluated through material testing and field implementation. Mechanical performance was assessed through tensile, relaxation, and fatigue tests. The developed CFRP cable exhibited an average tensile strength of 3019 MPa and an elastic modulus of 176.9 GPa, demonstrating mechanical properties comparable to or better than those of conventional prestressing tendons. The final relaxation ratio was measured as 2.25%, satisfying the low-relaxation criterion specified in KS D 7002. In the fatigue test, the cable sustained 2,000,000 loading cycles under a stress range corresponding to 60–66% of the ultimate tensile strength without fracture or significant stiffness degradation, confirming its excellent fatigue durability. In addition, the developed CFRP cable was implemented in a cable-net structure to verify its constructability and structural applicability in practice. The field application confirmed that the lightweight CFRP cable enabled convenient transportation and installation, while stable prestress introduction was achieved using the same tensioning procedure as that for conventional steel cable systems. The results demonstrate the integrated feasibility of the developed CFRP cable in terms of both material performance and practical structural application. This study provides experimental evidence supporting the structural use of CFRP tendons and offers a technical basis for the future development of design provisions and broader infrastructure applications. Full article

This study evaluated eleven resin cements used as core build-up materials by examining the following properties: (a) push-out force between root dentin and the fiber post; (b) pull-out force between the fiber post and the core build-up material; (c) shear bond strength of the resin cement to root dentin; (d) flexural strength of the resin cement; and (e) flexural modulus of elasticity of the resin cement. The purpose of this investigation was to clarify the relationships between recently available universal adhesives, core build-up materials, resin cements, and fiber posts. All experiments were performed at two evaluation periods: after 1 day of water storage (Base) and after 20,000 thermocycles (TC 20k). For the push-out test, simulated post spaces were prepared in single-rooted human premolars. The specimens were sectioned perpendicular to the long axis into 2 mm-thick slices and then subjected to push-out testing to assess the bond strength of the dentin–resin cement–fiber post complex. No significant differences in bonding performance were found between Base and TC 20k. These findings suggest that universal adhesives used for pretreatment of multiple substrates in fiber post cementation can provide not only strong but also durable adhesion over time. Full article

The current study explored the martensite structures of Fe₃Pt alloys, specifically $Cmmm$-Fe₃Pt, $P{6}_3/mmc$-Fe₃Pt, $P4/mmm$-Fe₃Pt, and $R\overline{3}m$-Fe₃Pt, aiming to provide a comprehensive understanding of the mechanisms that govern their physical and chemical properties. We have focused on their structural, thermodynamical, magnetic, electronic, mechanical, and dynamical characteristics, utilizing the density functional theory (DFT) technique. Our study revealed that in addition to the previously reported austenitic cubic $Pm\overline{3}m$-Fe₃Pt and martensite tetragonal $I4/mmm$-Fe₃Pt with L1₂ structure, there exist additional Fe₃Pt phases that exhibit excellent structural, thermodynamic, magnetic, and mechanical properties. The calculated enthalpies of formation were found to be negative and less than −0.39 eV in all the structures considered, indicating thermodynamic stability and formation under experimental synthetic conditions. Moreover, the computed magnetic moments are in the range 2.94 to 3.04 ${\mathsf{\mu }}_{\mathrm{B}}$, which is relatively comparable to 3.24 ${\mathsf{\mu }}_{\mathrm{B}}$ of the widely reported $Pm\overline{3}m$-Fe₃Pt alloy. The analysis of the electronic structure also revealed strong magnetism due to the presence of asymmetry in the spin-up and -down states of the density of states (DOS) plots. To determine the mechanical response of Fe₃Pt structures under loading conditions, we computed the independent elastic constants, macroscopic properties, and stress–strain relationship under hydrostatic stress. All four phases were studied, but the hypothetical $P{6}_3/mmc$-Fe₃Pt showed excellent mechanical stability at ambient conditions and exceptional hardness and resistance to compression in the elastic region 0% ≤ strain ≤ 10%. This evidence is provided by satisfying the Born necessary stability conditions, large bulk modulus, and a strong linear relationship fit ($R^2$) of greater than 0.94. Moreover, the phonon dispersion curves revealed dynamical stability for $Cmmm$-Fe₃Pt and $R\overline{3}m$-Fe₃Pt, and metastability for $P4/mmm$-Fe₃Pt, while the hypothetical $P{6}_3/mmc$-Fe₃Pt is unstable. Full article

Titanium alloys, particularly β-type Ti-13Nb-13Zr, are promising biomedical materials due to their low elastic modulus and excellent biocompatibility. However, their bioactivity needs improvement for better bone integration. In this study, a calcium-phosphate (Ca/P) coating was prepared on a Ti-13Nb-13Zr alloy via micro-arc oxidation (MAO) in an electrolyte containing calcium acetate and dipotassium hydrogen phosphate. The effect of applied voltage (300 V, 400 V, and 500 V) on the phase composition, surface morphology, and in vitro bioactivity of the coatings was investigated. Surface characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). The results show that increasing the voltage increased the surface roughness, average pore size, and rutile TiO₂ content in the coating. The Ca/P ratio in the coating approached 1.67 at 500 V, similar to that of natural bone. After immersion in simulated body fluid (SBF) for 20 days, the coating formed at 500 V induced the highest deposition of hydroxyapatite (HA), completely covering the microporous surface. These findings indicate that MAO treatment at 500 V significantly enhances the bioactivity of the Ti-13Nb-13Zr alloy, making it a promising candidate for orthopedic implants. Full article