Search Results (3,763)

The mechanical characteristics and the rupture behavior of dry paper and papers immersed in pure water or a carboxymethyl cellulose (CMC) aqueous solution were investigated by measuring the shape changes due to the immersion and by uniaxial tensile tests. The weight changes and dimensional changes for these samples due to the immersion were evaluated by the gravimetric method and image analysis, respectively. The absorption ratio of the paper was 2.3 for pure water, and it increased up to 2.7 with the CMC concentration. A deformation of 5% at maximum was observed in the direction perpendicular to the fiber orientation due to the absorption. All the samples demonstrated similar stress–strain curves in the regions of linear viscoelasticity and plastic deformation. The peak stress, Young’s modulus, and strain energy density of CMC wet paper showed lower values than those of water wet paper, while the peak strain was the same for both samples. Similar behavior was found in the cross direction, although the difference was not significant. These results strongly indicate that the penetration and adsorption of CMC molecules lead to a large expansion, resulting in the disentanglement of paper fibers and a significant reduction in the mechanical properties due to the strong fluid lubrication effect. Full article

Ornamental palm pruning residues represent a locally abundant, underutilized lignocellulosic waste stream with potential as a waste-valorized epoxy reinforcement. This study investigates the flexural behavior of particulate epoxy composites reinforced with Washingtonia robusta leaf stalk residue, evaluating the influence of reinforcement granulometry on mechanical and microstructural response. Four specimen families were fabricated from a Bisphenol A/F epoxy resin cured with a cycloaliphatic amine hardener: neat resin (RS, reference) and composites reinforced with fine (RF), coarse (RG) and mixed-fraction (RM) particles at 20 vol.% loading. Flexural properties were assessed by three-point bending and fracture surfaces were characterized by SEM. The neat resin exhibited a non-monotonic, viscoelastic-dominated response with no fracture within the extended deformation range tested, whereas all reinforced systems fractured within a substantially narrower window (~8–14.5 mm). RF showed the highest observed flexural modulus (≈15.8 GPa), followed by RM (≈15.4 GPa) and RG (≈14.2 GPa). These differences were not statistically significant (one-way ANOVA, p > 0.05). Damage tolerance followed a similar descriptive trend: RG failed earliest, linked to large interfacial pull-out cavities; RF delayed fracture through crack deflection; and RM showed the most favorable overall balance, combining a modulus comparable to RF with superior crack path tortuosity. These results indicate the potential of Washingtonia robusta, particularly in mixed-granulometry form, as a candidate reinforcement for semi-structural epoxy biocomposites, pending further characterization of properties such as tensile strength, impact resistance, moisture absorption, and long-term durability. Full article

Out-of-autoclave (OoA) manufacturing of Fiber Metal Laminates (FMLs) remains challenging because their mechanical performance and failure mechanisms are sensitive to processing-induced variations in phase distribution and interfacial bonding quality. Three FML-2/1 configurations (FML/Al-20, FML/Al-40, and FML/Al-60), where the numerical values indicate the exposure time (minutes) of 3003-H14 aluminum to NaOH alkaline etching, were physically characterized after bonding to a basalt fiber-reinforced polymer (BFRP) core to quantify constituent and void volumetric fractions. Based on previously reported differences in interlaminar strength, FML/Al-40 was selected to evaluate tensile behavior at room temperature and high temperature. The average density across all FML configurations was about 2.15 g/cm³, corresponding to a 21% reduction relative to aluminum. Compositional analysis revealed significant differences among configurations in both the complete FML and the renormalized matrix–fiber–void composition of the BFRP core, indicating that surface treatment is associated with changes in internal phase distribution beyond the metallic contribution. At room temperature, FML/Al-40 exhibited an ultimate tensile strength of 262.7 MPa. Relative to this value, tensile strength was retained at 83%, 54%, and 31% at 100, 150, and 200 °C, respectively, demonstrating a progressive reduction in strength with increasing temperature and a corresponding change in the thermomechanical response associated with evolving failure mechanisms. Full article

Repeated mining of shallow-buried close-distance coal seams can disturb the fractured strata remaining in the goaf of the upper coal seam. Under gully terrain, mining disturbance is coupled with surface-relief effects, which may reactivate the overburden structure and induce dynamic strata-pressure behavior. In particular, when the working face advances across gullies, the change in surface slope alters the spatial distribution of roof load, while lower-seam extraction further disturbs the fractured rock mass formed by upper-seam mining, increasing the risk of severe strata-pressure behavior and support-crushing accidents. Taking the cross-ditch mining of the 2⁻² and 3⁻¹ coal seams in Anshan Coal Mine as the research object, this study integrates field geological investigation, theoretical calculation, physical similarity simulation, and field engineering verification to analyze overburden structural evolution, key-stratum breaking characteristics, and support-load variation under gully terrain. The results show that gully landforms generate obvious nonuniform loading above the working face. During upslope advance, the roof load gradually increases from the goaf side to the solid-coal side, causing tensile stress concentration at the fixed end of the key stratum and accelerating rock-stratum failure. A cantilever rock-beam mechanical model subjected to parabolic nonuniform loading was established, and the maximum breaking interval of the key stratum was calculated as 24.09 m. With increasing gully slope angle, the load gradient intensifies, the rock-beam breaking interval decreases, and the risk of overburden instability increases. Physical similarity simulation indicates that, when the 2⁻² coal seam working face passes through the 45° steep-slope section, the fractured overburden is more likely to form a stepped rock-beam structure, accompanied by slope rotation, stepped surface subsidence, and a sharp increase in support pressure. Under the 30° gentle-slope condition, The lateral confinement effect is stronger, roof movement is more gradual, and support-pressure fluctuation is reduced. During subsequent extraction of the lower 3⁻¹ coal seam, repeated mining disturbance reactivates the overlying goaf structure, and the upper stepped rock beam and lower hinged rock beam couple to form a double composite structure. When the fracture lines of the upper and lower key strata are staggered, the instability load of the upper structure is mainly buffered by caved gangue and interburden strata. The calculated support resistance in the asynchronous breaking stage is 8248.04 kN, which agrees well with the field-measured value of 8273 kN. When the fracture lines tend to coincide and synchronous breaking occurs, the unstable load of the upper key block is transferred downward and superimposed on the structural load of the lower key block, increasing the required support resistance to 15,165.55 kN, far exceeding the rated working resistance of the ZY9200/15/29 hydraulic support. Sensitivity analysis indicates that gully slope angle is the dominant factor affecting support resistance. As the slope angle increases from 30° to 60°, the support resistance increases from 13,228.65 kN to 18,278.43 kN, and the normalized support-resistance index increases from 0.872 to 1.205. Therefore, synchronous breaking of double key strata is the main mechanical cause of sudden support-load increase and support-crushing risk during cross-ditch mining of shallow-buried close-distance coal seams. The results can provide a basis for hydraulic support selection, roof weakening, weighting-interval control, and dynamic strata-pressure prevention under similar conditions. Full article

Concrete-faced rockfill dams (CFRDs) constructed in narrow and steep valleys are strongly influenced by the mechanical interaction between the dam body and abutment bedrock. Under long-term construction and reservoir impoundment, time-dependent frictional slip along the dam–abutment interface may alter deformation transfer within the dam system. This study investigated the Dashixia extra-high CFRD through large-scale contact rheological tests and three-dimensional finite element analysis. A contact rheological model was established from interface tests and incorporated into a full-scale numerical model considering valley topography, staged construction, and reservoir impoundment. The influence of contact rheology on dam deformation, face-slab response, and peripheral-joint behavior was evaluated. The results show that contact rheology has little effect on global dam settlement but significantly increases horizontal displacement and redistributes local deformation near the abutments. Under the normal reservoir water level, the maximum upstream displacement, downstream displacement, and settlement increase by 0.7, 3.4, and 1.5 cm, respectively. Meanwhile, the maximum peripheral-joint settlement increases from 43.7 to 69.8 mm, and the maximum tensile opening increases from 8.7 to 12.8 mm. For the Dashixia CFRD, inclusion of dam–abutment contact rheology increases the predicted maximum peripheral-joint settlement and tensile opening by 59.7% and 47.1%, respectively, highlighting the greater sensitivity of local joint deformation compared with global dam settlement. Full article

All-light shale ceramsite concrete (ALSCC) is a lightweight building material suitable for self-weight-sensitive flexural members in prefabricated and long-span structures, but experimental data on its flexural behavior remain limited. This study aims to characterize the physical and mechanical properties of ALSCC and evaluate its flexural behavior under the present test conditions through comparison with C30 normal concrete. Cubic material-property tests and four-point bending tests on simply supported beams were conducted. Material tests showed that the average density of ALSCC was 65.2% of that of normal concrete, while its cube compressive strength and splitting tensile strength were 80.6% and 82.3% of the corresponding values for normal concrete, respectively. Cracks in the ALSCC material specimens tended to propagate through the ceramsite aggregates, indicating a relatively brittle fracture response at the material level. Three ALSCC beams (AL-B1, AL-B2, and AL-B3) and one normal-concrete control beam (NC-B1) were tested to analyze failure modes, load–deflection responses, sectional strain distributions, and reinforcement-strain responses. Test results showed that the ALSCC beams exhibited typical under-reinforced flexural failure, with cracking loads of 5.0–6.5 kN and peak loads of 40.4–42.5 kN, which were comparable to the 41.6 kN peak load of the normal-concrete control beam. The peak loads of the ALSCC beams occurred at midspan deflections of 13.10–14.47 mm. Under continued displacement-controlled loading, maximum recorded midspan deflections of 38.01–40.45 mm were reached at test termination. Within the present test program, the ALSCC beams exhibited lower elastic-stage stiffness than the normal-concrete control beam, while approximately linear sectional strain distributions were observed within the measured load range. The reinforcement-strain responses of the ALSCC beams were also broadly comparable to the response of the control beam. This work provides preliminary material-specific experimental evidence on the flexural behavior of ALSCC simply supported beams under the present test conditions and provides a basis for further validation using larger specimen sets. Full article

This study developed surface-functionalized polylactic acid (PLA) films by depositing electrospun gelatin/chitosan (GE/CH) nanofibrous coatings formulated with and without bioactive phenolic compounds (curcumin and anthocyanin). Evaluating various polymer blending ratios and operational parameters revealed that a GE:CH ratio of 7:3 (v/v), processed at an applied voltage of 25 kV and a collector speed of 300 rpm, provided the most stable electrospinning behavior among those tested, yielding a uniform nanoscale fibrillar network. The deposition of this selected GE/CH layer onto the PLA substrate significantly improved the composite bilayer film’s tensile strength and oxygen barrier properties, although it increased macroscopic opacity. Furthermore, active coatings containing 0.25% and 0.50% (w/w) curcumin or anthocyanin were successfully processed. This 0.50% level was the maximum concentration quantitatively evaluated in the present study, as preliminary observations suggested poorer processability at higher concentrations, which induced premature gelation and needle clogging. While interactions (mostly non-covalent physical interactions) associated with the phenolic compounds synergistically reinforced the mechanical rigidity and reduced the water vapor permeability of the bilayer films, the macroscopic bioactive functionality was limited. The low loading concentrations, coupled with severe optical masking and restricted aqueous extraction, resulted in moderate antioxidant activity (10.31–30.46% DPPH radical inhibition) and no visually detectable halochromic (pH-responsive) color changes. Overall, these findings highlight a significant functional trade-off in the design of active coatings, where structural and mass transport barrier enhancements are achieved, but macroscopic bioactive functionality is constrained, underscoring the necessity for advanced encapsulation strategies in future developments. Full article

Replicating the nonlinear, pressure-dependent mechanical behavior of native arteries remains a central challenge in small-diameter vascular graft design, where compliance mismatch between synthetic grafts and host vessels is strongly linked to graft failure. Building on a silk fiber-reinforced alginate–polyacrylamide interpenetrating polymer network (IPN) hydrogel platform, we investigated whether biomimetic vascular structural motifs, specifically fiber reorientation and crimp, can be used as programmable design parameters to tune the tensile and pressure-dependent mechanical response of tubular constructs toward native coronary artery behavior. Three architectures were fabricated: a cross-plied (CP) baseline, a 25° reoriented configuration, and a crimped CP configuration. Under internal pressurization, fiber reorientation and crimp significantly increased compliance at low physiological pressures, with a consistent directional trend across the full pressure range, by extending the low-stiffness toe region preceding fiber recruitment while preserving tensile stiffness. Across the investigated pressure range, all architectures exhibited compliance within the reported range of native coronary arteries, with crimped constructs producing pressure–diameter behavior that most closely resembled young coronary arteries, whereas the CP baseline more closely resembled aged coronary arteries. These findings demonstrate that biomimetic structural motifs, without altering material composition, can serve as programmable design parameters for engineering vascular mechanics, enabling a single material platform to reproduce distinct physiological mechanical phenotypes through architecture alone. Full article

This study investigates the direct tensile mechanical behavior of cement mortar plates reinforced with a galvanized steel mesh and randomly incorporated alkali-resistant glass fibers. An experimental program was executed using direct tensile tests on thin mortar specimens containing fiber volumetric fractions of 0%, 4%, 6%, 8%, and 10% relative to the cement volume. To rigorously characterize the mechanical response, the study quantified the apparent initial stiffness, 0.2% offset stress, ultimate tensile strength, and post-offset energy absorption capacity. Results indicate that increasing alkali-resistant glass-fiber content systematically modified the global tensile response of the composite system. At 10% glass-fiber content, the mean crosshead-derived apparent initial tensile stiffness was 10.43 times that of the reference group without glass fibers. The characteristic stress determined using the adopted 0.2% offset criterion and the ultimate tensile strength increased by 154.5% and 74.1%, respectively, while the apparent post-offset energy absorption increased by 68.4%. Because strain was derived from crosshead displacement, the apparent stiffness and energy-absorption parameters represent the global specimen–grip–machine response rather than intrinsic material properties. The experimental results exhibited acceptable repeatability, although the apparent tensile stiffness showed greater variability than the strength-related parameters. These findings support the continued development of the investigated composite configuration for thin cementitious elements requiring improved tensile response and damage tolerance. Full article

Glass fiber-reinforced polymer (GFRP) and carbon/glass hybrid fiber-reinforced polymer (HFRP) laminates with two vinyl ester resin systems were investigated to evaluate their early environmental response, residual mechanical performance, and damage behavior after moisture-assisted low-temperature exposure and freeze–thaw cycling (FTC). After 150 days of moisture preconditioning, the conditioned specimens were exposed to −50 °C or subjected to FTC between −50 °C and 22 °C. Tensile, compressive, flexural, in-plane shear, interlaminar shear, and compression-after-impact (CAI) tests were conducted. Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) were used to examine chemical structure, thermomechanical response, and damage morphology. FTIR spectra showed no obvious changes in the characteristic absorption bands of the vinyl ester matrix. DMA showed condition-dependent changes in thermomechanical behavior, with the largest decrease in glass transition temperature reaching 5.5 °C after Condition 3. Tensile and in-plane shear properties were largely retained, whereas compressive, flexural, interlaminar shear, and CAI properties were more sensitive; the largest CAI strength loss was 19.1%. Hybrid stacking affected the property retention and damage tolerance of the laminates under the designed FTC condition. SEM observations identified interfacial debonding, matrix microcracking, and interlaminar crack growth as the main damage features. Full article

Concrete structures are prone to cracking during service, and epoxy grouting is a widely adopted technique for structural intervention. However, the inherent brittleness and poor durability of neat epoxy under complex loading and environmental exposure remain critical challenges. This study systematically evaluates the mechanical performance of epoxy-grouted concrete interlayer systems modified by carbon fiber (CF), glass fiber (GF), and polyethylene microspheres (PE). A comprehensive experimental program was conducted, including compression, three-point bending, and Brazilian splitting tests at three loading angles, combined with digital image correlation for surface strain monitoring. The effects of grout thickness and wet–dry cycles were systematically investigated. Results demonstrate that reinforcement modification helps to improve the performance of grouted concrete, with optimal behavior highly dependent on loading mode. CF-reinforced specimens with strong interfacial bonding exhibit the highest compressive strength, which is 150% higher than the bearing capacity of intact concrete, but are prone to brittle fracture under loading involving tension-shear interaction. GF reinforced specimens with moderate interfacial bonding exhibit better load-bearing capacity under tensile-shear stress interaction, reaching a normalized splitting peak load of 0.95 at a grouting thickness of 5 mm. PE-reinforced specimens with weak interfacial bonding provide relatively extensive energy dissipation. A 3 mm grouting layer shows favorable performance among the tested thicknesses, balancing load transfer enhancement and defect control. A single wet–dry cycle temporarily improves performance, possibly due to epoxy post-curing and pore filling, whereas repeated cycling generates cumulative micro-damage. GF- and CF-reinforced systems demonstrate the most stable resistance to short-term wet–dry conditioning. These findings provide guidance for loading-mode-dependent reinforcement selection in epoxy grouting applications. Full article

The continuous joining of aluminum alloys to engineering thermoplastics has emerged as a promising manufacturing path for lightweight hybrid structures, yet the influence of polymers’ mechanical behavior on friction stir joining remains poorly understood. This work investigates the role of melt rheology on the morphology, joining interface, and mechanical strength of dissimilar joints that combine AA6082-T6 with two engineering-grade thermoplastics, Noryl^® GFN2 and SustaPEEK^®. Two joining strategies were assessed under identical processing conditions: conventional friction stir joining (FSJ) and through-slot friction stir joining (TS-FSJ), the latter incorporating thin titanium strips intended to reduce heat transfer to the polymer. Joint morphology was assessed by optical and scanning electron microscopy, mechanical performance was evaluated through quasi-static tensile-shear testing, and the rheological behavior of both polymers was characterized by steady shear and oscillatory measurements. Conventional FSJ produced defect-free aluminum–Noryl joints, with a mechanical strength of 111.3 ± 8.4 kN/m, whereas aluminum–PEEK joints exhibited localized polymer overflow, poor surface finish and scattered strength performance of 116.7 ± 77.2 kN/m. Rheological measurements showed that PEEK exhibited higher melt viscosity and viscoelastic moduli, restricting polymer flow and promoting unstable interface formation. Although titanium inserts reduced heat transfer in TS-FSJ, their deformation reduced the effective joining area, resulting in lower tensile strength. Polymer rheology was identified as one of the key factors governing material flow, defect formation, process stability, and the joints’ mechanical performance, emphasizing the importance of tailoring the processing parameters reflecting the rheological characteristics of each polymeric base material. Full article

Thin spray-on liner (TSL) technology provides rapid and highly automated surface support for underground coal mine roadways. However, in deep roadways affected by high in situ stress, mining-induced disturbances, and fractured surrounding rock, conventional TSL materials require improved tensile–shear resistance, deformation compatibility, and support adaptability. Although fiber reinforcement is an effective method for enhancing polymer composites, systematic studies on the effects of fiber type and dosage in reactive polymer-based TSL materials remain limited. In this study, a commercially available two-component polyurea-silicate-based TSL matrix was reinforced with polyvinyl alcohol (PVA) fibers, polypropylene mesh fibers, and toughened polypropylene fibers at volume fractions of 0.25–1.50%. A stepwise experimental program, including uniaxial compression, variable-angle shear, tensile, circular-indenter buffered shear, and true triaxial tests, was conducted to evaluate the mechanical behavior and support-related performance of the fiber-reinforced TSL materials. The basic mechanical tests showed that the 0.75% toughened polypropylene fiber group maintained favorable compressive and shear resistance, achieving a cohesion of 8.65 MPa and an internal friction angle of 24.12°. PVA fibers exhibited higher tensile reinforcement efficiency at relatively low contents, with the 0.25% PVA fiber group reaching a peak tensile stress of 13.61 ± 1.00 MPa. The 1.0% PVA fiber group showed good deformation coordination, with a compressive strength of approximately 49.87 MPa. In the circular-indenter buffered shear test, the 1.0% PVA fiber group reached a peak load of 0.636 ± 0.055 kN and an absorbed energy of 3.118 ± 0.832 J at 10 mm displacement. Under true triaxial loading, the 1.0% PVA fiber group absorbed 311.4 J of energy at a displacement of 10 mm, approximately 5.5% higher than that of the 0.75% toughened polypropylene fiber group. Therefore, 1.0% PVA fiber reinforcement is recommended as the optimal reinforcement scheme for polymer-based TSL materials used in deep, fractured, and large-deformation coal mine roadways. Full article

The mechanical compatibility between dental restorative materials and the natural tooth structure is a relevant factor for long-term clinical performance. Although zirconia (yttria-stabilized tetragonal zirconia polycrystal, Y-TZP) and lithium disilicate are widely used for full-coverage crowns, their biomechanical interaction with the underlying dentin and pulp under functional loading remains insufficiently characterized. This study reports a comparative finite element analysis (FEA) of a mandibular first molar under vertical (200 N, axial) and oblique (200 N, 30°) loading, evaluating three configurations: an intact healthy tooth, a zirconia Y-TZP full-coverage crown, and a lithium disilicate full-coverage crown. The three-dimensional geometry was obtained from a cone-beam computed tomography (CBCT) study of a caries-free mandibular first molar, previously described and verified by the present group, and was analyzed in ANSYS Workbench (Static Structural). Von Mises equivalent stress, maximum principal stress and total deformation were obtained for enamel or restoration, dentin, and pulp in each configuration. Zirconia produced the highest stress concentrations in the coronal restoration (88.4 MPa vertical; 174.5 MPa oblique), exceeding the healthy enamel baseline by 57.6% and 89.7%, respectively. Both restorative materials reduced dentin stress relative to the healthy tooth, consistent with the stress-shielding effect driven by elastic-modulus mismatch. Under oblique loading, the maximum principal stress in healthy enamel reached 61.7 MPa, approaching or exceeding the upper bound of the reported tensile strength range (~10–40 MPa) and identifying oblique loading as the more demanding of the two conditions analyzed. Within the limitations of the present finite element model, lithium disilicate demonstrated a more favorable stress distribution, with dentin stress values closer to the intact-tooth baseline. The model does not include a luting cement layer, a periodontal ligament, the dentin–enamel junction, anisotropic tissue behavior or cyclic loading, and no experimental validation was performed; the results are therefore presented as a controlled numerical comparison between three configurations under the specific conditions simulated, and not as direct clinical selection criteria. Full article

Continuous bending under tension (CBT), also known as cyclic bending under tension, is an experimental deformation technique capable of achieving large plastic strains under relatively low tensile loads. However, the broader application of CBT testing remains dependent on the availability of dedicated experimental setups and the suitable adaptation of conventional mechanical testing systems. This study presents the design and development of a CBT testing device intended for integration with conventional universal testing machines. The proposed system consists of four main subsystems: specimen grips, a roller train, a motor system, and a supporting structure. The developed device was experimentally assessed using DP600 advanced high-strength steel and AA6022-T4 aluminum alloy sheets with nominal thicknesses of 1.5 and 2.0 mm, respectively, under selected CBT operating conditions. The system successfully performed CBT tests, enabling the acquisition of force–elongation responses, cycles to fracture, and post-test specimen observations. The experimental results reproduced the characteristic CBT response, showing significantly higher total elongation compared with uniaxial tensile testing while requiring substantially lower tensile forces. The developed device demonstrated operational and mechanical stability, providing a practical platform for laboratory-scale investigations of sheet metal deformation behavior under CBT loading conditions. Full article