Search Results (110)

Additive Manufacturing (AM) using Fused Layer Modelling (FLM) often results in polymer components with limited and highly anisotropic mechanical properties, exhibiting structural weaknesses in the layer direction (Z-direction) due to low interlaminar adhesion. The main objective of this work was to investigate and quantify these mechanical limitations and to develop strategies for their mitigation. Specifically, this study aimed to (1) characterize the anisotropic behavior of unreinforced Polycarbonate (PC) components, (2) evaluate the effect of continuous, unidirectional (UD) carbon fiber tape reinforcement on mechanical performance, and (3) validate experimental findings through Finite Element Method (FEM) simulations to support predictive modeling of reinforced FLM structures. Methods involved experimental tensile and 3-point bending tests on specimens printed in all three spatial directions (X, Y, Z), validated against FEM simulations in ANSYS Composite PrepPost (ACP) using an orthotropic material model and the Hashin failure criterion. Results showed unreinforced samples had a pronounced anisotropy, with tensile strength reduced by over 70% in the Z direction. UD tape integration nearly eliminated this orthotropic behavior and led to strength gains of over 400% in tensile and flexural strength in the Z-direction. The FEM simulations showed very good agreement regarding initial stiffness and failure load. Targeted UD tape reinforcement effectively compensates for the weaknesses of FLM structures, although the quality of the tape–matrix bond and process reproducibility remain decisive factors for the reliability of the composite system, underscoring the necessity for targeted process optimization. Full article

To address the limitation of using experimental parameters in the macroscopic strength criterion, a micromechanical strength criterion for root-reinforced soil is developed. In this model, a micromechanical model for a three-phase composite (“root—cemented soil matrix—frictional element”) is constructed, and the novel combination of energy equivalence principles with the M-T method is used to determine the meso-scale prestress and strength criterion for root-reinforced soil under freeze–thaw cycles. The representative volume element (RVE) of root-reinforced soil is conceptualized as a composite material consisting of a bonded element (a cemented-soil matrix with root inclusions) and frictional inclusions. By applying micromechanics, along with the Mori–Tanaka method, the LCC method, limit analysis theory, and macro–micro energy equivalence principles (incorporating both strain and dissipated energy), a micromechanical strength criterion is formulated, revealing failure mechanisms at the microscale. The previously used stepwise procedure for deriving the stationary function is improved, and the microscale prestress is determined through the Mori–Tanaka method combined with macro–micro strain-energy equivalence. The proposed micromechanical strength criterion effectively models the primary strength variation in root-reinforced soil under freeze–thaw cycles, extending the existing shear criterion for soil. Full article

In this work, density functional theory (DFT)-based first-principles investigations are performed by Generalized Gradient Approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) functional in the CASTEP code. These simulations provide the insights of the structural, electronic, optical, thermodynamic, mechanical and hydrogen storage gravimetric ratios of lithium-based tetrahydrides (LiBH₄, LiAlH₄, and LiMnH₄) for hydrogen storage and photovoltaic (PV) applications. All these structures crystallize in orthorhombic Cmcm (No. 63) geometry with different lattice parameters and bonding strengths. Thermodynamic stabilities of hydrides are obtained by dispersion of phonons and phonon density of states. The measured band gaps of hydrides are 3.81 eV (LiBH₄), 4.60 eV (LiAlH₄), and 0.53 eV (LiMnH₄), which are calculated by GGA-PBE approach. Moreover, the optical characteristics with strong optical activity are observed from visible to ultraviolet (2 eV to 6 eV) regions. High dielectric response between 6 and 8 and absorption coefficient up to 10⁵ cm⁻¹ for hydrides are observed. Debye temperature has exceeded from 300 K to 600 K for all hydrides and saturation occurred closer to Dulong–Petit limit ~75 J mol⁻¹ K⁻¹. Mechanical stability in hydrides has been observed by Born-Hung mechanical stability criterion, demonstrating ductile nature. These natural hydrides have shown exceptional hydrogen storage capacities, as 18.5 wt% for LiBH₄, 10.6 wt% for LiAlH₄, and 6.1 wt% for LiMnH₄, are measured; these values have exceeded the U.S department of energy (DOE) targets (5.5 wt% H₂). These analyses prove that LiXH₄ (X = B, Al, Mn) hydrides are promising candidates for solid state hydrogen storage materials. Full article

Salt rock, owing to its excellent rheological and self-healing properties, has been widely applied in underground gas storage. However, a numerical method capable of systematically simulating the entire damage–healing process of salt rock is still lacking, which limits the in-depth understanding of fracture evolution mechanisms and the long-term stability of storage caverns. To overcome this limitation, this study improves the parallel bond model within the framework of the Discrete Element Method (DEM) by incorporating a stress-driven healing criterion and a healing-equivalent stress coupling algorithm, thereby enabling the complete simulation of crack initiation, propagation, and closure in salt rock. The results show that the proposed method effectively captures healing effects: under uniaxial compression and tension, the number of cracks decreased by approximately 27% and 23%, with strength recovery of 110.7% and 7%, respectively. Moreover, the reconstruction of particle contact chains closely corresponds to the crystal-bridge phenomena observed in experiments, verifying the model’s reliability in reproducing macroscopic mechanical responses. In addition, the healing process exhibits a temporal characteristic in which crack closure occurs earlier than volumetric strain reduction, indicating an evolution pattern of “structural closure first, macroscopic densification later.” This study not only fills the gap in DEM-based simulation of salt rock damage–healing processes but also provides theoretical support for long-term stability evaluation and operational optimization of underground salt cavern storage. Full article

To improve the ballistic resistance of hydrogen storage tank-grade 316L austenitic stainless steel (ASS) plates that are prone to shear plugging failure under blunt projectile impact, this study proposes a non-bonded bilayer protective configuration: covering the 316L ASS substrate with a thin front layer of 2024-T351 aluminum alloy (AA) plate. Ballistic impact tests were performed on monolithic 5 mm thick 316L ASS plates and bilayer targets composed of a 2.05 mm thick 2024-T351 AA plate and a 5 mm thick 316L ASS substrate (total thickness: 7.05 mm), using a single-stage light gas gun combined with high-speed photography. Parallel explicit dynamics models were established using ABAQUS/Explicit, incorporating a modified Johnson–Cook constitutive model and a Lode-dependent Modified Mohr–Coulomb (MMC) fracture criterion, thereby enabling rigorous mutual validation between experimental results and numerical simulations. Results demonstrate that the addition of a mere 2.05 mm thick aluminum alloy front layer significantly enhances the ballistic limit velocity (BLV) of the 5 mm thick 316L stainless steel target plate, increasing it from 167.5 m/s to 250.7 m/s. The enhancement mechanism is closely related to the transition in the failure mode from localized shear plugging to a combination of bulging, dishing, and plugging. This shift substantially improves the structure’s overall plastic deformation capacity and energy dissipation efficiency. This research provides an effective solution and establishes a reliable experimental–numerical benchmark for the lightweight, impact-resistant design of hydrogen storage tanks. Full article

Pearl color serves as the paramount criterion for quality assessment and commercial valuation in the global pearl industry. Freshwater nucleated pearls, which constitute 95% of global production, exhibit striking chromatic diversity. This study deciphers the chromogenic mechanisms of freshwater nucleated cultured pearls in Hyriopsis cumingii from Zhuji, China, through integrated spectroscopic (UV-vis-NIR and Raman), colorimetric (CIELAB), and trace-element (LA-ICP-MS) analyses. We identify polyene compounds as the primary organic chromophores, with C=C bond counts determining core hue: purple (12 C=C bonds), pink (11 C=C bonds), and white/orange (10 C=C bonds). Color expression is further modulated by nacre microstructure; densely aligned aragonite tablets enhance optical interference in purple pearls, whereas irregular tablet arrangements in pink and orange pearls promote diffuse scattering. Crucially, trace elements (Mn, Fe, Cu, Zn) contribute synergistically via metalloporphyrin formation (e.g., Mn-porphyrin in purple variants) and aragonite lattice substitutions. These findings reveal that pearl coloration arises from the interplay of biological factors (organic matrix), physical structure (nacre architecture), and chemical composition (trace elements), providing insights for quality enhancement and sustainable aquaculture practices. Full article

Substantial time-dependent deformation and support failure in deep tunnels through water-rich red-bed soft rock present critical engineering challenges, yet the underlying mechanisms under hydro-mechanical coupling remain inadequately quantified. This study integrates wireless remote monitoring, laboratory testing, and theoretical analysis to investigate the stress-deformation behavior of surrounding rock and support structures. Results reveal that deformation evolves through four distinct stages as follows: sharp, slow, stable, and creep, with the creep stage—governed by pore-water pressure—accounting for over 40% of total displacement. Groundwater-induced clay mineral hydration and stress redistribution significantly weaken rock self-support capacity. Support elements exhibit degraded performance; rock bolts suffer interfacial bond failure, steel arches yield asymmetrically, and the secondary lining resists transmitted deformation pressure. A novel deformation rate-based failure criterion is proposed, revealing a progressive “local breakthrough-chain transmission–global instability” failure pathway. These findings provide a theoretical basis for stability control in deep buried tunnels under hydro-mechanical coupling. Full article

The purpose of this in silico study was to evaluate the main difference of the adhesion strength of direct and semi-direct composite resin restorations in dentin using micro-tensile testing (μTBS) and finite element analysis (FEA). This in silico study employed cohesive zone traction and shear laws to investigate interfacial damage in both restoration groups. Tridimensional finite element models of both restoration specimens were created. A 20 μm thick resin cement layer was created for the semi-direct case. The Clearfil SE Bond 2 adhesive system and the restorative material, Ceram X Spectra ST HV composite resin, were used on both restorations. The numerical bond strength of both restoration techniques was evaluated using two different analysis assumptions. In the first assumption, the numerical analysis procedure included only the non-linear behavior of dentin and the von Mises damage criterion, whereas cohesive zone models were included in the second analysis assumption. The influence of dentin-adhesive cohesive mechanical properties was studied using values reported in the literature, and a sensitivity study helped improve the correlation between experimental and numerical results. The mechanical properties of the composite cohesive zone were defined assuming that the interface strength of dentin and composite follows the values reported by the manufacturer of Spectra ST. Damage initiation and progression were analyzed, and strains and stresses of the cohesive zone models (CZM) were compared with the corresponding perfect bonded models. The experimental µTBS results for the direct restoration strategy showed an adhesive strength of 38.156 ± 10.750 MPa, while the CZM predicted a slightly higher value of 40.4 ± 10.8 MPa. For the indirect restoration strategy, the experimental adhesive strength was 25.449 ± 10.193 MPa, compared to a numerically predicted strength of 28.1 ± 9.3 MPa. Overall, the CZM tends to overestimate the adhesive strength relative to experimental values. The statistical analysis of dentin extension strains for direct (DR) and semi-direct (SR) group models reveals that the SR configuration yields higher strain levels. Hence, these results suggest that, assuming identical dentin properties across both restoration groups, the material configuration in the direct restoration offers better mechanical protection to the dentin. These findings highlight the critical role of incorporating damage mechanics to more accurately characterize stress distribution during tooth rehabilitation. Full article

Metal hydrides are emerging hydrogen-storage materials that have attracted much attention for their stability and practicality. The novel magnesium-based metal hydride Mg₂CsH₉ was investigated using the CALYPSO software (version 7.0). First-principles predictive methods were then employed to investigate the structural, mechanical, electronic, optical, and hydrogen-storage properties of Mg₂CsH₉ and its alkali metal substitution structure Mg₂RbH₉. The negative formation energy, compliance with the Born stability criterion, and absence of imaginary modes in the phonon spectrum collectively confirm the thermodynamic, mechanical, and dynamic stability of Mg₂XH₉ (X = Cs, Rb), fulfilling the basic criteria for practical hydrogen-storage applications. Mg₂RbH₉ is particularly outstanding in terms of its hydrogen-storage capacity, with a gravimetric capacity of 6.34 wt% and a volumetric capacity as high as 92.70 g H₂/L, surpassing many conventional materials. The pronounced anisotropic characteristics of both compounds further enhance their practicality and adaptability to complex working conditions. An analysis of Poisson’s ratio revealed that the chemical bonding in both compounds is predominantly ionic. The details of the band structures and density of states indicate that Mg₂CsH₉ and Mg₂RbH₉ are semiconductors. Their optical properties confirm them as being high-refractive-index materials. Full article

Objectives: To study the effects of internal and marginal polymerization shrinkage stress and distribution in different resin composite class III dental restorations in relation to the restorative technique using numerical finite element analysis (FEA). Methods: A 3D model of a human hemi-maxilla with a sound maxillary central incisor were created. Four class III distal cavities were shaped and differently restored. Four groups of resin composite combinations were analyzed: group C (three increments of conventional composite); group B (two increments of bulk-fill composite); group FC (flowable base + three increments of conventional composite); and group FB (flowable bulk-fill base + two increments of conventional composite). The resulting four models were exported to FEA software for static structural analysis. Polymerization shrinkage was simulated using thermal analogy, and stress distribution was analyzed using the Maximum Principal Stress criterion at the marginal and internal cavity interfaces. Results: Group FC showed the highest stress at the level in the proximal region (9.05 MPa), while group FB showed the lowest (4.48 MPa). FB also exhibited the highest internal dentin stress, indicating potential risks for long-term bond degradation. In the cavo-surface incisal angle, the average peak stress across all groups was 3.76 MPa. At the cervical cavo-surface angle, stress values were 3.3 MPa (C), ~3.36 MPa (B), 3.41 MPa (FC), and 3.27 MPa (FB). Conclusions: Restorative technique did not significantly influence marginal stress distribution in class III composite restorations. However, the bevel area at the cervical margin showed the highest concentration of shrinkage stress. Full article

Roof water inrush accidents in coal mine driving roadways occur frequently in China, accounting for a high proportion of major coal mine water hazard accidents and causing serious losses. Aiming at the lack of research on the mechanism of roof water inrush in driving roadways and the difficulty of predicting water inrush accidents, this paper constructs a local damage criterion for coal–rock mass and a seepage–fracture coupling model based on peridynamics (PD) bond theory. It identifies three zones of water-conducting channels in roadway surrounding rock, the water fracture zone, the driving fracture zone, and the water-resisting zone, revealing that the damage degree of the water-resisting zone dominates the transformation mechanism between delayed and instantaneous water inrush. A discriminant function for the effectiveness of water-conducting channels is established, and a single-index prediction and evaluation system based on damage critical values is proposed. A “geometry damage” dual-control water inrush prediction model within the PD framework is constructed, along with a non-local action mechanism model and quantitative prediction method for water inrush. Case studies verify the threshold for delayed water inrush and criteria for instantaneous water inrush. The research results provide theoretical tools for roadway water exploration design and water hazard prevention and control. Full article

This study investigates the mechanical properties and optimization of hybrid composites composed of flax, vetiver, and mahogany fruit fillers (MFFs) using epoxy resin as the matrix material. Nine distinct composite configurations were fabricated using different MFF concentrations (0, 5, and 10 wt.%) to evaluate their influence on tensile strength, flexural strength, and impact resistance. The MFF was subjected to alkali treatment and characterized using FTIR, XRD, and particle size analysis to enhance its compatibility with the polymer matrix. Vetiver and flax fibers also underwent alkali treatment to improve interfacial bonding. The composite fabrication process followed the Taguchi L9 orthogonal array to optimize the design. Mechanical testing revealed that the incorporation of MFF significantly improved the overall performance, with FVM9 (10 wt.% MFF) exhibiting the highest tensile strength (56.32 MPa), flexural strength (89.65 MPa), and impact resistance (10.46 kJ/m²). The CRITIC–EDAS method was employed to rank the composite configurations, and FVM9 was identified as the optimal configuration. Comparisons with alternative MCDM methods (WASPAS, COPRAS, TOPSIS, and VIKOR) validated the reliability of the rankings, and FVM9 consistently performed the best. The sensitivity analysis demonstrated the robustness of the CRITIC–EDAS approach, as the rankings remained stable despite variations in the criterion weights. The synergistic effect of flax, vetiver, and MFF, along with improved interfacial bonding, contributed to the superior mechanical properties of the hybrid composites. These findings highlight the potential of FVM composites as sustainable, high-performance materials for various industrial applications in the automotive, construction, and aerospace sectors. Full article

This study presents a peridynamic model formulated using the micromodulus function and bond deformation. The model is derived by establishing energy equivalence between a modified virtual internal bond (VIB) and a peridynamic bond. To address surface effects in peridynamics, a stress-based correction method utilizing nodal stress is introduced, enhancing the model’s numerical accuracy. The model was implemented using an in-house Cython code and validated through the following numerical examples: a plate under traction, a plate with a hole under displacement boundary conditions, a uniaxial compression test on granite with a deformation-based mixed-mode bond failure criterion, and a comparison with an existing strain-based peridynamic model. For the plate under traction, the deformation-based method performed similarly to the strain-based model in the loading direction and better in the unloaded direction. The stress concentration obtained from the proposed model (240 MPa) near the hole in the rectangular plate simulation differed from FEM (252 MPa) by 4.7%. The granite test predicted a UCS of 111.88 MPa and a Young’s modulus of 20.67 GPa, with errors of 0.1% and 1.57%, respectively, compared to the experimental data. Full article

Silicone structural glazing (SSG) sealants are crucial sealing materials in modern building curtain walls, whose performance degradation may lead to functional and safety issues, posing significant challenges to building safety maintenance. This study comprehensively investigated the effects of temperature, humidity, stress, and ultraviolet (UV) irradiance on the durability of SSG sealants through multi-gradient matrix aging tests, revealing the influence patterns of these four aging factors on tensile bond strength (TBS). Based on aging test data and degradation patterns, a novel degradation model for TBS aging was established by incorporating all four aging factors as variables, enabling the model to reflect their combined effects on TBS degradation. The unknown parameters in the model were calculated using the Markov chain Monte Carlo (MCMC) algorithm and validated against experimental data. A recursive algorithm was developed to predict TBS degradation under actual service conditions based on the degradation model and environmental records, with verification through outdoor aging tests. This study established a service life prediction methodology that combines the degradation model with environmental data through recursive computation and standard-specified strength limits. The results demonstrate that increasing temperature, humidity, stress, and UV irradiation accelerates TBS changes, with influence intensity ranking as UV irradiation > temperature > humidity > stress. Synergistic effects exist among all four factors, where UV irradiation shows the most significant coupling effect by amplifying other factors’ combined impacts, while UV’s primary influence manifests through such synergies rather than independent action. Among temperature, humidity, and stress combined effects, temperature contributes approximately 50%, temperature–humidity interaction about 35%, with temperature-related terms collectively accounting for 90%. The degradation model calculation results show excellent agreement with experimental data (R² > 0.9, MAE = 0.019 MPa, RMSE = 0.0245 MPa). The characteristic TBS minimum value considering material discreteness and strength assurance rate serves as a reliable criterion for service life evaluation. The proposed prediction method provides essential theoretical and methodological foundations for ensuring long-term safety and maintenance strategies for glass curtain walls. Full article

Tensile strength perpendicular to the plane of the board (also known as the Internal Bond—IB), determined in accordance with standard EN 319, is one of the most critical properties in particleboard quality control. Given the need for efficient, rapid methods to assess the IB in industrial contexts, artificial neural networks (ANN) have been used as a predictive modelling tool. However, one of the main limitations of these techniques is the absence of estimates associated with the uncertainty of their predictions. The present study addresses this shortfall by applying bootstrap techniques to obtain confidence intervals using estimates generated by ANN. To achieve this, multiple models were trained and validated using experimental data taken from real production processes. The results show that the methodology proposed can be used to obtain a high level of accuracy (determination coefficient R² = 0.96) and a coverage probability of 93%. It also provides a robust criterion to assess conformity with standard specifications. This study concludes that adding bootstrap to ANN modelling is a very useful tool for application in industrial quality control systems, as it allows decision making based on confidence intervals rather than individual values. Full article