Search Results (1,224)

Elasticized expanded polystyrene (EPS-T) is widely used as a resilient layer in floating floors, where dynamic stiffness is the key input for impact-sound prediction, while FEM modelling additionally requires elastic parameters and damping descriptions consistent with the adopted test or modelling configuration. This study investigates whether ISO-type dynamic stiffness testing and acoustic-response modal identification can provide consistent vibroacoustic parameters for EPS-T. Rectangular specimens of different thicknesses were tested for dynamic stiffness and damping using an ISO 9052-1-type setup. Additional cylindrical compression tests were used to examine apparent Young’s modulus and Poisson’s ratio, while impulse-excited acoustic responses of clamped specimens were combined with inverse FEM identification. The ISO-type dynamic stiffness decreased from approximately 53.3 MN/m³ for nominal 17 mm specimens to 27.0 MN/m³ for nominal 53 mm specimens. This trend was described by a compliance model with an effective Young’s modulus of 2.04 MPa and an equivalent contact/support stiffness of 101.2 MN/m³. Acoustic-response inverse FEM gave consistent Young’s modulus values, ranging from 1.77 MPa to 2.16 MPa, with a mean close to 2.05 MPa. Direct use of s′ = E/h overestimated stiffness and underestimated predicted ΔL_w by approximately 2–5 dB. The two routes provided consistent estimates of the effective modulus, but this consistency applies only to modulus identification and not to direct stiffness conversion or damping transfer. Full article

Searching by numerical simulation for structures with optimal damping properties among viscoelastic hollow cylindrical bodies with a filler is usually associated with a large amount of computation. Formulating the mechanical problem as one of natural vibrations and natural wave propagation makes it possible to evaluate the dissipative properties of such a structure independently of external force and kinematic actions, and thereby to reduce the computational cost substantially. The solution of the natural vibration problem for a piecewise homogeneous viscoelastic hollow cylindrical body with a filler yields complex natural frequencies, the real part of which represents the vibration frequency and the imaginary part the damping factor (attenuation rate). The mechanical behavior of the viscoelastic material is described by the linear Boltzmann–Volterra hereditary theory with a three-parameter Koltunov–Rzhanitsyn relaxation kernel, within which the material characteristics are represented by complex dynamic moduli—the shear modulus and the bulk modulus—that, as a rule, depend on frequency. In the natural vibration problem these moduli become functions of the real part of the sought complex natural frequency alone, which makes the standard eigenvalue procedures of commercial finite-element codes inapplicable. The paper presents an algorithm that removes this difficulty. The dispersion relation of the piecewise homogeneous cylinder is obtained analytically in the form of a complex determinant of order 12 for a two-layer and 18 for a three-layer configuration, the elements of which are Bessel and Neumann functions of complex argument; the global stiffness and mass matrices needed for the general configuration can be assembled automatically in a general-purpose finite-element code such as ABAQUS; the resulting complex characteristic equation is solved by Muller’s method—every iteration of which evaluates the determinant by Gaussian elimination with partial pivoting, so that no expansion of the determinant is required. The efficiency of the algorithm is demonstrated for a two-layer viscoelastic hollow cylindrical body with a filler, the outer load-carrying layer being made of Kh12 steel and the inner layer (the filler) of 30 L steel. The real and imaginary parts of the complex natural frequencies, of the phase velocities and of the attenuation are obtained as functions of the dimensionless wave number, of Poisson’s ratio, of the ratio of the layer radii and of the ratio of the instantaneous elastic moduli of the layers. Full article

This study investigates the evolution of microstructural, mechanical, and transport properties in AZ31 magnesium alloy surface composites reinforced with Ti₂AlC MAX-phase particles at volume fractions of 6, 9, and 12 vol.%, which were fabricated by solid-state friction stir processing (FSP). In contrast to conventional brittle ceramics, Ti₂AlC MAX-phase mitigates interfacial reactivity and thermal mismatch. FSP successfully fabricated a highly consolidated, macroscopically defect-free, dynamically recrystallized fine-grained stirred zone with homogeneous particle distribution and metallurgically clean interfaces. Mechanically, the addition of 12 vol.% Ti₂AlC significantly improved the elastic response, increasing the Young’s modulus from 51 GPa to 67 GPa. The microhardness of the stirred zone reached 60.14 HV, a 53.4% increase over the base metal. The controlled electron and phonon scattering, enabled by the introduction of heterogeneous Mg/Ti₂AlC interfaces, decreased the electrical and thermal conductivities from initial values of 1.15 × 10⁷ S/m and 86.0 W/m·K for the unreinforced matrix down to 7.8 × 10⁶ S/m and 76.0 W/m·K, respectively, and caused a significant reduction in the coefficient of thermal expansion. Theoretical analysis, utilizing the Wiedemann–Franz law and Maxwell–Eucken approximations, provided a supportive baseline indicating the dominance of electronic thermal transport and interfacial scattering mechanisms. These results outline a viable route for developing lightweight magnesium-based composites with tailored mechanical and thermal characteristics for advanced structural applications. Full article

Hard roof strata in deep coal mines commonly cause rib failure and roof collapse, restricting extraction efficiency. This study employs theoretical analysis, numerical simulation, and field experiments to investigate the fractal evolution of damage in coal–rock mass under loading and blasting disturbances, with the aim of quantifying progressive failure and optimizing roof control. Key findings include: (1) The fractal dimension D of fragment size distribution increases monotonically with loading rate, with fine-particle proportion rising from 48.5% to 52.3%, indicating more thorough fragmentation at higher rates. (2) Load intensity, elastic modulus, and seam thickness govern coal bearing capacity and energy accumulation, with D serving as a quantitative damage indicator. (3) Pre-splitting blasting shifts the stress peak away from the working face, with shear fractures dominating the fracture network and tensile fractures playing a secondary role. (4) Field application at Zhangji Coal Mine (9 coal seam, 7–23.5 m sandstone roof) confirms the effectiveness of segmented fan-shaped borehole pre-splitting blasting in controlling roof behavior; fractal dimension derived from borehole images quantifies fracture propagation. Dynamic adjustment of blasting parameters based on geological core samples is recommended to enhance fracture network complexity and improve roof control efficiency under varying hard rock conditions. Full article

This study develops a finite element analysis (FEA) framework to quantify hydrostatic consolidation of ultra-high-molecular-weight polyethylene (UHMWPE) fibril arrays containing interstitial voids. Hexagonal and stochastic representative volume elements (RVEs) were constructed from experimentally measured fibril diameters and embedded in a nearly incompressible Mooney–Rivlin medium to transfer hydrostatic pressure to irregular fibril surfaces. Molecular dynamics (MD)-derived fibril properties at 300 K and 400 K were used to evaluate the effects of temperature, elastic–plastic deformation, and stochastic microstructure on void collapse and effective fiber properties. The 300 K elastic model required pressures approaching 1.3 GPa to reach approximately 1–2% void content, whereas the combined effects of elevated temperature, elastic–plastic fibril behavior, and stochastic fibril packing reduced the corresponding pressure to approximately 160 MPa. The stochastic RVE exhibited a higher initial void content, earlier plastic dissipation, lower initial effective stiffness, and nonuniform fibril–fibril contact evolution compared to the idealized hexagonal RVE. As void content decreased, both models converged toward the dense fibril response. The framework establishes a processing–microstructure–property relationship linking consolidation pressure to the evolving void morphology, fibril shape and contact development, and the resulting effective plane-strain bulk modulus and the transverse compressive stress–strain response, including the Young’s modulus and Poisson’s ratio, of UHMWPE fibers. Full article

Developing Cu-based composites with excellent electrical and mechanical properties under multiphysics-coupled service conditions remains challenging. Novel Cu-Nb-Gr composites were fabricated by high-energy ball milling and High-pressure Multi-field Assisted Rapid Sintering. Experiments combined with computational fluid dynamics (CFD) and finite element method (FEM) simulations were used to investigate how Gr regulates material performance. The incorporation of 3 vol.% Gr promoted the formation of a semi-continuous Gr-rich structure coupled with an Nb-rich load-bearing structure. Under arc erosion, the semi-continuous Gr-rich structure provided efficient heat-conduction pathways, reducing the peak temperature and metal-vapor recoil force, while the Nb-rich load-bearing structure suppressed liquid–metal spattering and stabilized the molten pool. Simultaneously, Gr dynamically spread to form a continuous solid-lubricating film during sliding friction, significantly reducing the coefficient of friction and interfacial shear stress. Furthermore, under compressive loading, the semi-continuous Gr-rich structure coupled with the Nb-rich load-bearing structure alleviated interfacial elastic–modulus mismatch and extreme stress concentration, limiting macroscopic plastic deformation of the matrix. Consequently, Cu-Nb-3Gr achieved a favorable balance of arc-erosion resistance, wear resistance, and compressive performance, providing a new strategy for improving conventional Cu-based composites. Full article

Coal gangue concrete (CGC) is an effective green building material that can promote the resource utilization of solid waste. To study its durability performance and degradation mechanism under sulfate attack with dry-wet cycles, and to realize the intelligent prediction of mechanical properties, this study prepared CGC specimens with a water-to-binder ratio of 0.4, a fine aggregate replacement rate of 20%, and coarse aggregate replacement rates of 0%, 20%, 50%, 80%, and 100%. The specimens were tested under 30, 60, 90, and 120 dry-wet cycles in 10% MgSO₄ solution. Mass loss, relative dynamic elastic modulus, and compressive and flexural strength corrosion resistance coefficients were used as evaluation indices, and SEM and XRD were adopted to analyze microstructural deterioration. A database compiled from literature data was established, and six machine learning models-random forest (RF), artificial neural network (ANN), decision tree (DT), support vector machine (SVM), particle swarm optimization-artificial neural network (PSO-ANN), and particle swarm optimization-support vector machine (PSO-SVM) were constructed to predict the strength corrosion resistance coefficients. Test results indicate that all macroscopic indices first increased and then decreased with the number of dry-wet cycles. Early ettringite and gypsum products filled internal pores, while prolonged sulfate attack caused decalcification and structural degradation of C-S-H gel, resulting in obvious performance loss. The PSO-SVM model showed the best prediction accuracy, with R² values of 0.912 and 0.981 for compressive and flexural strength corrosion resistance coefficients, respectively. Feature importance analysis shows that dry-wet cycles had the most significant negative impact, followed by the coal gangue fine aggregate replacement rate. This study provides support for the durability evaluation and intelligent prediction of coal gangue concrete in sulfate environments. Full article

Fischer–Tropsch (FT) wax is widely used as an organic warm-mix asphalt (WMA) additive, lowering binder viscosity during construction while improving high-temperature deformation resistance in service; however, the comparative responses of SBS-modified asphalt to different FT wax grades remain insufficiently understood. Sasobit and three FT waxes with different carbon-chain ranges (FT 80, FT 90, FT 100) were incorporated into SBS-modified asphalt at about 7.0 wt%, and their effects on macroscopic performance, rheology, molecular packing, and diffusion were evaluated using physical-property tests, rotational viscosity, dynamic shear rheometer (DSR) testing, and molecular dynamics (MD) simulation. In the MD analysis, the wax additives were represented by linear alkane molecules with different chain lengths, and the systems were subjected to structural optimization, annealing, and NPT equilibration using the COMPASS III force field before the molecular descriptors were evaluated. The experimental results showed that all four additives produced a trade-off between increased high-temperature stiffness and reduced low-temperature ductility. Sasobit gave the strongest viscosity reduction (>70% above 165 °C), while FT 90 and FT 100 showed more stable, predictable viscosity–temperature behavior favorable for a wider construction window. DSR results showed higher complex modulus and lower phase angle for all modified binders at low frequencies, suggesting an increased elastic contribution and greater resistance to deformation under the tested rheological conditions; FT 80 produced the greatest stiffening but also the largest free volume and loosest molecular packing, whereas FT 100 increased cohesive energy density and reduced free volume, reflecting denser packing and stronger intermolecular cohesion. MD simulations revealed that FT wax enhanced short-time local molecular mobility and segment diffusion in its molten state (explaining the warm-mix viscosity reduction), whereas macroscopic stiffening and ductility loss at ambient temperatures were dictated by wax microcrystallization and physical network constraints that restricted long-range chain relaxation. By comparing three FT wax grades and Sasobit under the same experimental dosage and testing framework, this study provides a controlled assessment of the relationships among wax-grade characteristics, binder-scale rheological responses, and MD-derived molecular descriptors. Full article

This study investigates the mechanical performance and non-destructive evaluation of oak (Quercus spp.) glued-laminated timber (GLT), manufactured from predominantly low-quality lamellae (five layers of 20 mm thick lamellae). The other GLT type tested was a veneer-reinforced configuration (4 mm thick veneers in the first and third layers on both sides of the reinforced GLT, combined with five layers of 15 mm thick low-quality lamellae). 18 basic GLT and 5 reinforced GLT beams, with nominal lengths of 2000 mm were produced using polyurethane adhesive and tested under four-point bending, according to EN 408. Their average densities and standard deviations were 759 ± 23 kg/m³ for basic GLT and 781 ± 6 kg/m³ for reinforced GLT. The reinforced GLT exhibited a substantially higher modulus of rupture (70.9 ± 4.6 MPa) compared to the basic GLT (37.6 ± 6.2 MPa), representing an increase of 89%. The bending modulus of elasticity also increased by 17.2% (12.0 ± 0.6 vs. 10.3 ± 0.6 GPa). The 11.4–12.0 GPa dynamic modulus of elasticity values were consistent with static results. Strain increased by +66.7% from 0.15% to 0.25% with reinforcement. Despite similar densities, adhesive-related failures governed performance in basic GLT. Veneer reinforcement significantly improved their strength, stiffness, and structural reliability. Full article

This study investigated the resistance of recycled aggregate concrete (RAC) to chloride penetration under freeze-thaw cycles using both numerical simulation and experimental validation. A five-phase mesoscale model of RAC was developed. The salt freeze-thaw test was conducted to validate the simulated values and explore the effects of different recycled coarse aggregate (RCA) substitution ratios, as well as varying dosages of fly ash and superfine fly ash, on chloride concentration in RAC. The experimental data showed satisfactory agreement with the simulated values, confirming the model’s validity. Additionally, the RCA volume fraction, interfacial transition zone (ITZ) thickness, and adhesive ratio of old mortar were analyzed using simulation. The variation patterns of compressive strength, relative dynamic elastic modulus, and mass loss of RAC also revealed the mechanisms by which RCA substitution ratio and the dosages of fly ash and superfine fly ash act under salt freeze-thaw conditions. This study provides guidance for enhancing the resistance of RAC to chloride penetration and its durability under freeze-thaw conditions. Full article

Sodium hydride (NaH) is the main by-product generated during the operation of the cold traps in a sodium-cooled fast reactor. Its thermal decomposition releases hydrogen gas, posing a safety hazard. However, understanding the atomic-scale decomposition mechanism remains challenging because conventional simulation methods are limited in the accessible length and time scales. This study developed a deep neural network potential (DP) for the NaH system using the DP-GEN active learning framework. Benchmark tests show that the DP model accurately reproduces density functional theory (DFT) reference energies, forces, equations of state, elastic properties, and phonon spectra. In particular, the DP-predicted bulk modulus and lattice constant are in good agreement with DFT results and close to experimental values, significantly outperforming the empirical ReaxFF potential. Subsequently, we conducted large-scale Deep Potential Molecular Dynamics (DPMD) simulations to investigate the thermal decomposition behavior of NaH clusters and a slab model. The simulation results reveal model-dependent thermal responses of NaH. In the original Na₄₈H₄₈ cluster simulation heated from 100 to 1200 K, a structural transition and disordering were observed, but no H₂ formation occurred within the simulation time. In contrast, the slab model heated from 300 to 1500 K exhibited surface disordering, Na-H bond cleavage, H-H bond formation, cluster detachment, and H₂ formation and release at elevated temperatures. A supplementary higher-temperature Na₄₈H₄₈ cluster simulation further showed cluster dissociation in the 1000–1500 K range. These results provide atomistic insight into the model- and temperature-dependent decomposition behavior of NaH and suggest that the DP model is a useful tool for studying hydrogen-related processes in alkali metal hydrides. Full article

This study proposes a prediction method for ceramic matrix composite thin plates (CMCTPs) with protective coatings under high-temperature conditions, based on the first-order shear deformation theory and the energy principle while considering thermal effects. It can successfully predict the variations in natural frequencies and resonant responses of CMCTPs over the experimentally validated temperature range of 25 °C to 800 °C, using a thermo-vibrational platform with a maximum temperature capability of 1500 °C. In addition, a thorough investigation of multiple key parameter influences on the dynamic characteristics of CMCTPs with and without coating is performed, with special focus on the effect of the coating on enhancing the thermo-vibrational resistance of such structures. The analytical results demonstrate that the protective coating significantly enhances the thermo-vibrational resistance of the structure. Optimization of the coating-to-substrate thickness ratio, elastic modulus ratio, and thermal expansion coefficient ratio is recommended to maximize vibration suppression performance, providing critical guidance for the dynamic design of coated CMCTP components in aerospace. Full article

Localized densification of nanoporous silica under combined mechanical compression and elevated temperature involves coupled pore collapse, skeletal rearrangement, and thermally activated sintering. Clarifying how local pre-compression regulates these processes is important for understanding the surface and near-surface densification of nanoporous silica and related porous materials. In this study, the microscopic sintering behavior of a silica-inspired aerogel-like nanoporous model under the coupling of non-uniform local stress and high-temperature fields (indentation depths of 50–150 Å and temperatures of 298–1800 K) was systematically investigated using molecular dynamics simulations combined with a three-dimensional (3D) topological recognition algorithm (probe sphere method and DBSCAN clustering). The results indicate that the sintering densification of the silica-inspired aerogel model exhibits significant pore-size dependence and a “depth-temperature inverse relationship”: the local pre-compression induced by the 150 Å indentation facilitates thermally activated atomic rearrangement and shifts the onset of densification to a lower temperature, leading to an early bimodal splitting of the pore size distribution at 1300 K, accompanied by a significant jump in the elastic modulus from 3.0 to 10.07 GPa. In contrast, the 50 Å shallow region requires heating to 1800 K to achieve an equivalent densification effect. Furthermore, topological analysis quantitatively reveals the phase transition process of the pore network from connected to isolated: taking 1300 K as an example, the number of connected pore clusters decreases from the initial 86 to 70 (at 1000 ps), marking the fracture of the connected network; subsequently, the number of isolated pores surges to 4861, and the residual connected framework is severely fragmented into 136 micro-clusters. Based on the above microstructural and topological evolution data, a four-stage thermo-mechanical synergistic evolution process of the silica-inspired aerogel model is summarized. These findings provide quantitative fundamental data that conceptually supports the design of functional gradient structures with alternating “dense-thermally-conductive” and “porous-thermally-insulating” layers within a single continuous aerogel matrix; such structures may be realized in the future through strategies such as arrayed nanoindentation combined with high-temperature sintering. Full article

The diverse properties and applications of chitosan materials require a broad spectrum of characterization techniques. In the meantime, due to chitosan’s high gel-forming capability, the rheological properties of chitosan solutions vary significantly depending on their state, i.e., solution or gel. To elucidate the solution and gel-based characteristics of chitosan, the present study was conducted to thoroughly investigate its rheological characteristics at different concentrations (1.25%, 2.5%, and 4% w/v), using various steady and dynamic rheological measurements and different mathematical models. The results showed that the concentration of chitosan solutions strongly affects their rheological properties in terms of shear stress, viscosity, and various dynamic rheological characteristics, through strain, angular frequency, and temperature sweep tests. In this regard, an elastic behavior was observed for low concentrations of chitosan solutions at lower shear strains, while the higher concentrations and higher shear strains exhibited predominantly viscous behavior. In frequency sweep measurements, the 1.25% and 2.5% w/v chitosan solutions showed viscous-like behavior and the 4% w/v solution exhibited solid-like behavior with almost constant storage and loss modulus profiles over the studied frequency range. According to temperature sweep measurements, viscous-like behavior was dominant at lower temperatures, which resulted in elastic gel structures at higher temperatures. Investigating the recoverability of prepared solutions by cyclic strain measurements revealed that the higher-concentration solutions of chitosan possess the desired capability to recover their structure. The results of this study provide detailed rheological insights into chitosan solutions suitable for designing and developing various chitosan-based products for different applications. Full article

High-voltage porcelain column-type equipment systems comprise various equipment units whose porcelain columns generally have circular cross-sections and approximately axisymmetric geometries. Although this geometric symmetry results in nominally equivalent lateral mechanical properties at the component level, differences among equipment types and multiple uncertainty sources may lead to heterogeneous seismic responses at the system level. To investigate the combined effects of ground-motion randomness and uncertainties in the elastic modulus and diameter of porcelain sleeves and damage control indices, Latin hypercube sampling was employed to generate 100 structural models with different modeling parameters. These models were randomly paired one-to-one with 100 selected ground-motion records, and uncertainty in the damage control indices was incorporated into the dynamic response and fragility analyses. The results indicate that the variability in structural seismic responses arises from the combined effects of modeling-parameter uncertainty and ground-motion randomness. These effects are propagated to the fragility curves through changes in the median ground-motion intensity and total logarithmic standard deviation of the fragility functions. The fragility curves accounting for multiple uncertainty sources generally fluctuate around the baseline curves considering ground-motion randomness alone, without exhibiting a consistent upward or downward shift. No strictly monotonic relationship was observed between the coefficients of variation in the uncertain parameters and the total dispersion of the fragility results, although larger parameter variability produced greater deviations from the baseline in some cases. Nevertheless, the overall differences remained limited, with a maximum absolute difference of 0.043. From the perspective of symmetry, the results demonstrate that component-level geometric symmetry coexists with system-level response heterogeneity and cannot alone eliminate the effects of equipment-specific characteristics and stochastic uncertainties on seismic fragility. Within the scope of this study, fragility curves considering ground-motion randomness alone may therefore provide a reasonable approximation for engineering assessment. Full article