Search Results (2,231)

The response modification factor R is a fundamental parameter in seismic design, linking the elastic demand expected under strong ground motion to the reduced forces used in practice. It reflects the capacity of well-detailed structures to dissipate energy through stable inelastic behavior while maintaining sufficient strength, stiffness, and deformation capacity to prevent collapse. Accordingly, R directly influences design base shear, member forces, reinforcement demands and expected seismic performance. It is prescribed by seismic codes as a single typology dependent value, although analytical evidence indicates that its magnitude varies systematically with structural configuration. Therefore, this study decomposes R for twelve reinforced concrete moment-resisting frame archetypes that combine three heights (4, 8, and 14 stories) with four span configurations (1–4 spans) over a constant 12 m plan length. All frames are designed per ACI 318-19 and ASCE/SEI 7-22 for the Pedernales, Ecuador, subduction-zone seismic hazard. The response modification factor R is evaluated through a component-based decomposition that separates the effects of ductility, overstrength, and redundancy—namely the capacity ductility ${\mu }_c$, the demand ductility ${\mu }_d$, the overstrength $\Omega$, and a geometric redundancy index ${\rho }_g$, using bilinearized pushover analyses. Dynamic verification, used here as a consistency check, is explicitly restricted to the low-rise class (four-story frames) through nonlinear response-history analysis under eleven spectrum-matched ground-motion records; results for the 8- and 14-story frames are therefore pushover-based only. To bracket the inelastic reduction capacity, a demand-based companion factor $R^{*}$ is reported and defined as the demand-based counterpart of R, providing a capacity-oriented estimate R and a demand-oriented companion estimate $R^{*}$. R ranges from 3.80 to 14.56, whereas $R^{*}$ ranges from 1.82 to 7.63. The component ranges are the capacity ductility ${\mu }_c=6.04$–$11.50$, the demand ductility ${\mu }_d=3.04$–$5.98$, the overstrength $\Omega =1.19$–$1.38$, and the geometric redundancy index ${\rho }_g=0.485$–$1.000$. Capacity ductility saturates in taller frames (about $\sim 12\%$ variation). In addition, $\Omega$ and ${\rho }_g$ exhibit a mechanical trade-off that challenges the independence assumption implicit in the multiplicative decomposition. Dynamic results corroborate the pushover-implied demand only for the low-rise class; no extrapolation to taller frames is claimed. Overall, the findings motivate configuration-sensitive analytical calibration as a prerequisite for any future normative discussion on R. Full article

In this work, we develop a coupled multiphysics model that integrates polymer carriers exhibiting time-dependent thixotropic structural recovery with Darcy flow, linear Biot poroelasticity and advection–diffusion transport in a spherically symmetric, isotropic and homogeneous tissue domain. The formulation explicitly links rheological evolution to pressure-driven flow, interstitial deformation and solute transport through a unified framework, enabling systematic prediction of post-injection behavior. Unlike conventional approaches that assume constant carrier properties, the present model incorporates a time-dependent viscosity evolution, capturing the transition from an initially shear-thinned state to a recovered, highly viscous structure. Numerical simulations using hydroxypropyl methylcellulose and methotrexate parameters as representative components demonstrate that rapid post-injection viscosity recovery suppresses pressure-driven transport and diffusion, thereby enhancing local drug retention near the injection site. A systematic sensitivity analysis identifies the equilibrium viscosity as the dominant parameter controlling spatial localization, whereas tissue mechanical properties exert a comparatively minor influence. An effectiveness metric based on the Kullback–Leibler divergence reveals a tumor-size-dependent trade-off between spatial coverage and retention. The proposed framework thus introduces a predictive tool for analyzing coupled rheological-transport interactions and for the rational design and optimization of thixotropy-enhanced local chemotherapy strategies. Full article

Injectable and self-healing hydrogels hold tremendous promise for biomedical applications; however, synchronously integrating robust mechanical adaptability, excellent cytocompatibility, and intrinsic antibacterial capabilities within a single matrix remains a significant challenge. In this study, we engineered an injectable, self-healing hydrogel based on dynamic cross-linking using guanosine-derived G-quadruplex supramolecular self-assembly and 3-aminophenylboronic acid (3-APBA)-mediated dynamic boronate ester. Systematic evaluation of various phenylboronic acid derivatives, GMP concentrations, K⁺ sources, and 3-APBA levels on gelation behavior yielded an optimized formulation. Scanning electron microscopy revealed that the optimized hydrogel exhibits a continuous, interconnected porous network structure after lyophilization. Thioflavin T fluorescence enhancement assays and circular dichroism spectroscopy further verify the formation of G-quadruplex-related ordered assemblies within the system. Rheological assessments demonstrate elasticity-dominated gel behavior, pronounced shear-thinning characteristics, and reversible structural breakdown and recovery under high and low strain cycles, indicating excellent injectability and self-healing properties. In vitro cytocompatibility evaluations show that the hydrogel possesses favorable cellular compatibility. Further antimicrobial studies reveal excellent in vitro antibacterial activity against Staphylococcus aureus and Escherichia coli. In summary, the injectable, self-healing G-quadruplex hydrogel constructed in this study integrates a porous architecture, dynamic reversibility, and robust biological functionality, highlighting its promising potential in antibacterial applications. Full article

Nanoglasses (NGs) have received much attention due to their superior ductility and well-retained strength compared to their metallic glass counterparts. However, few studies have examined how notch geometry affects the mechanical behavior and deformation mode of NGs. In this work, molecular dynamics simulations are performed on un-notched and symmetric double-edge notched Mg₃₃Cu₆₇ NGs under tensile loading, with focus on the roles of notch depth, height, and sharpness in determining their mechanical properties and failure modes. Our simulation results show that symmetric double-notched specimens exhibit higher strength and plasticity than un-notched counterparts. The improved plasticity is attributed to a transition in the deformation mode. Furthermore, the deformation mode and strength of notched specimens strongly depend on the notch depth and sharpness. The strengthening effect is enhanced with increasing notch depth or sharpness. This enhancement is likely related to the constrained growth of the plastic zone, which requires a higher stress for continued propagation. In addition, by altering notch depth and sharpness, the deformation mode is observed to change from shear banding-dominated to mixed-mode and then to necking-governed behavior. The mixed mode, characterized by the intersection of V-shaped shear bands, can accommodate substantial additional plastic deformation. Our key finding is that the mixed deformation mode, enabled by proper notch geometry, leads to a remarkable enhancement in both strength and plasticity. This work aims to provide significant insights into the deformation and failure mechanisms of notched NGs, offering an effective design strategy for optimizing their strength and ductility. Full article

The development of potash deposits under complex mining and geological conditions requires the implementation of efficient geotechnologies, including backfilling of mined-out voids. Preserving the water-protective strata and preventing mining-induced accidents are impossible without accurate prediction of the stress–strain state of the backfill mass. Traditional models, based on the Mohr–Coulomb criterion, are unable to properly describe physical and mechanical processes occurring in crushed salt rock, including the transition from dilatancy to compaction and nonlinear hardening. This requires the application of specialized models such as the SRP model. The aim of this study is to investigate the mechanical response of crushed salt rock backfill material under complex loading conditions and to calibrate the parameters of the SRP model in order to improve the accuracy of geomechanical calculations. The shape of the plastic flow surface in the deviatoric plane was established, including both shear and cap components. A nonlinear dependence of the friction angle on mean stress was identified and described by a logarithmic function. The law of plastic hardening was determined, and a non-associated plastic flow rule was confirmed in the shear domain. The calibrated SRP model allows for predicting the backfill mass behavior with high reliability, which is a necessary condition for substantiating the parameters of safe potash mining. Full article

This study investigates the nanomechanical response of aluminum substrates coated with crystalline or amorphous equiatomic FeNiCrCo compositionally complex alloy (CCA) layers using molecular dynamics nanoindentation. We evaluated the influence of coating microstructure and pre-relaxation via Monte Carlo/molecular dynamics (MC/MD) on deformation behavior at shallow (35 Å) and deep (65 Å) indentation depths. The relaxation process is critical for equilibrating internal stresses and homogenizing the initial stress field in amorphous phases, while preventing chaotic defect multiplication in crystalline lattices, yet it simultaneously promotes Fe and Cr surface segregation consistent with the equilibrium chemical short-range ordering of the alloy. The results reveal distinct deformation mechanisms: crystalline coatings exhibit higher peak indentation forces of about 300 ± 16 eV/Å characterized by discrete force fluctuations indicative of localized plastic events, while amorphous coatings show lower peak loads (~170–220 ± 12 eV/Å), corresponding to a reduction in load-bearing capacity of roughly 25%–40%, and smooth, continuous deformation governed by shear transformation zones. Notably, in amorphous systems, pressure-induced local crystallization occurs under load, with ordered FCC/HCP regions persisting after unloading, indicating partial irreversibility of the phase transition. Upon deep indentation into the substrate, the amorphous system exhibits a sharp increase in stiffness due to substrate compaction, whereas the crystalline system maintains high load-bearing capacity with reduced defect density in the relaxed state compared to the non-relaxed counterpart. Relaxation significantly reduces force-curve fluctuations in both systems, enhancing the stability of the mechanical response. Compared with uncoated aluminum, which exhibits extensive twin propagation and deep defect penetration, the FeNiCrCo-coated systems approximately halve the defect penetration depth and reduce the defective-atom volume fraction in the substrate by about a factor of two, thereby more effectively confining plastic deformation and preserving substrate integrity under the simulated conditions. These findings demonstrate that the synergy between coating crystallinity and rigorous relaxation protocols governs stress distribution patterns—localized hotspots in amorphous phases versus extended networks in crystalline ones—providing key insights for designing advanced protective coating–substrate systems with optimized mechanical performance. Full article

CO₂ foam fracturing has emerged as a promising stimulation technology for enhancing permeability and improving production performance in deep coalbed methane (CBM) reservoirs while providing additional potential for carbon utilization. However, the multiscale relationship between local mechanical degradation and macroscopic mechanical deterioration and fracture instability induced by CO₂ foam treatment remains insufficiently understood. In this study, four candidate coal samples originating from the Carboniferous–Permian No. 8+9 coal seam system were first comparatively characterized. Based on petrographic characteristics, mineralogical composition, and specimen integrity, representative bright coal and semi-dull coal samples from the Lüliang mining area were selected for subsequent multiscale mechanical investigations. Based on petrographic characteristics, mineralogical composition, and specimen integrity, representative bright coal and semi-dull coal samples from the Lüliang mining area were selected for petrographic analysis, X-ray diffraction (XRD), nanoindentation, conventional triaxial compression, and cracked chevron-notched Brazilian disc (CCNBD) fracture toughness tests. Coal specimens were immersed in CO₂ foam under reservoir-relevant conditions (50 °C, 20 MPa, foam quality of 65%) for different durations (0–6 days), and the coupled evolution of micromechanical properties, macroscopic mechanical behavior, and fracture resistance was evaluated. The results indicate that both coal types exhibit pronounced heterogeneity in maceral composition and mineral distribution. Bright coal is characterized by high vitrinite content and low mineral abundance, whereas semi-dull coal contains higher proportions of inertinite and minerals. Nanoindentation results reveal that mineral-rich regions possess significantly higher Young’s modulus and hardness than organic-matter-rich regions, highlighting pronounced micromechanical heterogeneity within the coal matrix. With increasing immersion time, the micromechanical properties of both coals exhibit a two-stage evolution characterized by rapid initial deterioration followed by a gradual stabilization trend. After 6 days of immersion, the average Young’s modulus and hardness of bright coal decreased by 40% and 30%, respectively, whereas those of semi-dull coal decreased by 30% and 17%. Simultaneously, macroscopic mechanical properties and fracture resistance continuously declined, with fracture toughness reductions of 74% and 55% for bright coal and semi-dull coal, respectively. Compared with semi-dull coal, bright coal exhibited higher damage sensitivity, evolving from dominant single-fracture failure to granular fragmentation, whereas semi-dull coal maintained a multi-crack composite shear failure mode. Combined micromechanical and macroscopic observations suggest that the observed mechanical deterioration may be associated with coupled effects of fluid–coal interaction, matrix softening, and progressive damage evolution. Although pore and crack evolution were not directly observed, the results suggest that coal structure plays an important role in governing damage transfer across scales and thereby influences fracture behavior and mechanical weakening. These findings provide insight into the multiscale mechanical response of coal under CO₂ foam treatment and may support the optimization of stimulation strategies for deep CBM reservoirs. Full article

Adductor canal block (ACB) is widely used for perioperative analgesia in knee surgery because it provides effective pain control while preserving quadriceps muscle strength. With the increasing use of ultrasound-guided regional anesthesia, interest has expanded beyond conventional morphologic imaging toward quantitative assessment of peripheral nerve function and biomechanics. Shear wave elastography (SWE) is an emerging ultrasound-based technique that enables real-time quantification of tissue stiffness and has recently gained attention in peripheral nerve evaluation. Previous SWE studies have primarily focused on chronic neuropathic conditions, including entrapment neuropathy and diabetic neuropathy, in which increased nerve stiffness is commonly observed. However, emerging observations suggest that peripheral nerve stiffness may dynamically decrease following regional anesthesia procedures such as ACB. This finding raises the possibility that nerve stiffness reflects not only chronic structural pathology but also transient physiologic and biomechanical modulation. Potential mechanisms underlying reduced stiffness after ACB include perineural hydrodissection, decreased fascial compression, sympathetic blockade-induced vasodilation, altered intraneural pressure, and changes in surrounding muscle tension. Because the saphenous nerve within the adductor canal is superficial and consistently visualized under ultrasound guidance, ACB represents an attractive model for investigating dynamic changes in peripheral nerve biomechanics. This narrative review summarizes current evidence regarding SWE assessment of peripheral nerves and discusses the potential implications of dynamic stiffness changes after regional anesthesia. We review the biomechanical principles of SWE, factors affecting nerve stiffness, current evidence in neuropathic and perioperative settings, technical limitations, and future clinical applications. Understanding the dynamic behavior of peripheral nerve stiffness may expand the role of SWE from a diagnostic tool for neuropathy to a quantitative biomarker for regional anesthesia and perioperative nerve physiology. Full article

Despite decades of research, the nonlinear mechanics of agar remains poorly understood. In this work, we analyze the mechanical response of soft, hard, and very hard agar hydrogels under nonlinear shear deformation. Low-shear viscoelastic behavior across concentrations was characterized using storage and loss moduli, yield strain, flow point, loss factor, and ductility index. The transition to nonlinear response was examined using Fourier analysis of shear stress signals. To describe the high-shear regime, we employed large-amplitude oscillatory shear (LAOS) rheology. The mechanical response was further analyzed using Lissajous–Bowditch plots (stress versus strain and stress versus shear rate), linking agar network structure to intracycle deformation behavior and energy dissipation. By analyzing strain stiffening, shear thickening, yielding, and intracycle structural dynamics, we quantified dissipation rates across concentrations and constructed fingerprint maps of shear stiffening and thickening at different frequencies. Microstructural insights from rheology were compared with macroscopic characterization using phase-contrast microscopy. The nonlinear rheological analysis revealed that structural reorganization shifts systematically toward lower shear strain values with increasing agar concentration. Full article

The spreading and film formation of organic polymer solutions on liquid surfaces are key processes in coating, printing, and interfacial processing. However, the mechanisms by which aqueous polymers regulate spreading kinetics and film morphology are not yet fully understood. In this study, the free spreading of Poly(3-hexylthiophene-2,5-diyl) (P3HT)/chlorobenzene solution on poly(vinyl alcohol) (PVA) aqueous surface was employed as a model system to investigate how PVA concentration, molecular weight, degree of hydrolysis, and temperature collectively govern spreading behavior and film formation. Video recording was used to monitor the evolution of the spreading and front-edge morphology, while step-profilometry, UV–visible absorption spectroscopy, and atomic force microscopy were employed to characterize the resulting films in terms of thickness distribution, optical uniformity, and surface roughness. The results reveal that PVA can significantly regulate both the spreading kinetics of P3HT/chlorobenzene droplets and the final film morphology. PVA concentration exhibited a non-monotonic effect on spreading behavior, with intermediate concentrations favoring larger spreading areas and more continuous films. Increasing the PVA molecular weight altered the concentration-dependent spreading window and enhanced asymmetry at the spreading front, whereas reducing the degree of hydrolysis decreased interfacial tension and thereby increased the thermodynamic driving force for spreading, yet the actual spreading rate remained constrained by molecular diffusion, interfacial adsorption, and chain-segment rearrangement. Temperature and a saturated chlorobenzene vapor atmosphere further modulated the interplay among solvent evaporation, interfacial driving force, and viscous dissipation. Under optimized conditions, the resulting P3HT films displayed uniform thickness profiles, consistent optical absorption, and nanoscale surface roughness, and could be repeatedly transferred, assembled into well-defined multilayer structures, and printed onto flexible and curved substrates. These findings demonstrate that PVA aqueous subphase provides a tunable low-shear route for transferable P3HT thin-film fabrication and suggests its potential applicability to other polymer film-forming systems. Full article

Octopus maya is a fast-growing species from the Yucatán Peninsula with high economic relevance, accounting for a major share of regional fishery production. However, a significant fraction of the organism, rich in type I collagen, is discarded as by-products, representing a promising and underutilized source for sustainable biomaterials. This study evaluated, through a 3² factorial design, the effect of two factors on the rheological and dynamic mechanical properties of film-forming solutions (FFS). The first factor was the type of food-grade polysaccharide: chitosan (Ch), hydroxypropyl methylcellulose (HPMC), or starch (S). The second factor was the proportion of each polysaccharide blended with ultrasound-extracted Octopus maya insoluble collagen (CIPM), using polysaccharide ratios of 30:70, 50:50, and 70:30 (w/w). This approach aims to valorize octopus by-products through the recovery and functional utilization of collagen. Rheological properties were determined by rotational and oscillatory rheometry at 25 °C, with flow curves fitted to the Carreau-Yasuda model. All formulations exhibited pseudoplastic behavior (n < 1), with viscosity decreasing as shear rate increased. Pure CIPM showed high viscosity (190.36 Pa·s at 1 s⁻¹), which decreased (0.3–10.44 Pa·s) in HPMC and chitosan systems, suggesting their potential suitability for applications requiring fluidity, such as spray coatings or film-forming solutions, based on their rheological properties. In contrast, starch-based systems exhibited higher viscosities (33.54–197.53 Pa·s) and a more structured viscoelastic profile (G′ > G″), suggesting potential suitability for thick coatings or gels requiring structural stability, although these applications were not experimentally validated. These results demonstrate that CIPM-polysaccharide systems enable tunable rheological properties, supporting the use of Octopus maya collagen as a sustainable functional material for advanced food and biomaterial design. Full article

A comprehensive experimental dataset for unidirectional carbon fiber pultruded composites is presented, including mechanical testing results, microscopy images, and X-ray computed tomography volumes. In contrast to typical datasets, all measurements consistently describe a single material system, encompassing both the composite and its constituents (carbon fibers and vinyl ester matrix), thereby enabling a comprehensive and coherent multiscale material characterization. X-ray-computed tomography images of samples extracted from three pultruded composite profiles were acquired with a voxel size of 0.55 µm and analyzed to determine the fiber orientation distribution. Scanning electron microscopy with a pixel size of 0.098 µm was used to determine the overall and local fiber volume fractions. Compression testing of 17 composite specimens provided the compressive properties. The tensile and shear properties of the matrix were obtained from tensile and shear tests on seven and four matrix specimens, respectively. The Ramberg-Osgood model was fitted to the matrix’s tensile stress–strain response. Single-fiber tensile testing was conducted on 255 carbon fibers with three gauge lengths to determine fiber properties and Weibull parameters. All mechanical tests were performed up to material failure. The dataset is suitable for semi-analytical predictions and numerical finite-element modeling of composite mechanical behavior. Full article

This study presents an experimental investigation of reinforced concrete T-beams strengthened using ultra-high-performance concrete (UHPC) with steel plates, and in some cases, UHPC with a geotextile layer. Ten reinforced concrete specimens with the same internal reinforcement but different strengthening methods were tested. These included a control specimen and nine strengthened specimens. Four of the strengthened specimens had grooves in the wooden formwork before pouring to secure the strengthening composite plates inside it, four had it directly attached to the RC beam surface, and the last had vertical lines 10 mm deep to enhance bonding. The external composite plate consisted of four types: the first type included a composite of UHPC and steel plates as strips with 220 × 150 mm at 105 mm, while the remaining types consisted of a plate along the shear zones made of UHPC with steel, geotextiles, or steel and geotextiles. This study also included increasing the number of steel plate layers and the direction of strengthening placement. The results showed that all the strengthened beams failed in flexure, unlike the control specimen, which failed in shear. The strengthening systems improved the load-bearing capacity and overall structural behavior of the tested beams. Among the investigated specimens, beam IR-2S90SS, strengthened with two layers of steel plates, showed the highest improvement, achieving a 39.2% increase in ultimate load compared to the control beam. Debonding was observed in some specimens and was identified as one of the governing failure mechanisms. Overall, the investigated strengthening techniques demonstrated their effectiveness in improving the structural performance of reinforced T-beams. Full article

For the impact-resistance evaluation of thermoplastics, the DuPont impact test is widely used to replicate multiaxial stress states inherent in actual product environments. However, conventional evaluation methods remain constrained by probabilistic pass/fail judgments or empirical calculations of absorbed energy. Consequently, quantifying the “material-specific fracture criterion,” which is indispensable for high-fidelity computer-aided engineering (CAE) analysis, persists as an important challenge. While our previous works established the derivation of CES from uniaxial tensile tests, the core originality of this study lies in extending this mechanical framework to the dynamic and multiaxial stress states of the DuPont impact test. By integrating a mathematical model with the probabilistic results of the staircase method, we enable for the first time the quantitative identification of material-specific fracture thresholds directly from standard drop-weight impact configurations. For this study, a novel mechanical model for deformation and fracture behavior in the DuPont impact test is constructed. Then a quantitative evaluation method is proposed for the “Critical Expansion Stress (CES),” a material-specific threshold triggering fracture under multiaxial stress. Specifically, using thermoplastic materials of five types and seven grades (including PP, POM, PS, ABS, and PC), the surface impact energy absorbed per unit volume was calculated via the DuPont impact test using the staircase method, accounting for size effects. Furthermore, microscopic parameters (shear modulus G and critical void volume fraction f0) were identified theoretically based on the mechanical properties obtained from short-beam shear tests. These parameters were integrated into a mathematical model to derive the CES. Comparing the derived CES with the true-stress-based uniaxial tensile strength, which incorporates the necking behavior during large deformations, revealed a distinct correlation governed by their mechanical relation (the 1:3 rule) based on the theoretical definition of hydrostatic stress. For the highly ductile polymer exhibiting significant strain hardening, this correlation holds universally when evaluated at the initial plastic flow stage prior to massive molecular orientation. The proposed method serves as a practical quantitative screening tool for evaluating the surface impact characteristics of plastic materials, providing an accessible framework for identifying material-specific fracture thresholds. Full article

Sandstone–marble waste powder concrete composite structures serve as common load-bearing systems in tunnels, underground caverns, and similar engineering projects, where the interface roughness characteristics directly govern their overall stability and service safety. To investigate the influence of interface roughness on the failure behavior of the composite, four groups of sandstone–concrete composite specimens made with marble waste powder concrete were prefabricated with different joint roughness coefficients (JRC = 0, 7.84, 17.99, 20.79). The concrete matrix was prepared with marble waste powder incorporated at 25 wt% of the total binder, corresponding to 20.45 wt% of the total mixture, and the water-to-binder ratio was 0.20. Uniaxial compression tests were conducted with synchronous acoustic emission (AE) and digital image correlation (DIC) monitoring to examine the roughness-dependent mechanical response, energy evolution, damage activity, and strain localization of the composites. The results show that the peak stress and elastic modulus of the composite increase continuously with increasing JRC. When JRC increases from 0 to 20.79, the peak stress increases by 170.3% and the elastic modulus increases by 201.1%. The energy evolution mechanism transitions from progressive damage with gradual energy dissipation at low roughness to a three-stage mode at high roughness, characterized by initial frictional energy dissipation, intermediate energy storage, and rapid elastic energy release and dissipated energy increase near failure. DIC results further reveal that increasing interface roughness suppresses interfacial shear slip and promotes tensile-dominated strain localization, whereas excessive roughness may induce local stress concentration around asperities and increase the tendency toward abrupt post-peak instability, the failure mode changes from mixed tensile–shear failure with obvious interfacial slip to tensile-dominated failure. Full article