Structural Mechanical Behavior Research Articles

Web shear buckling of steel-concrete composite girders – advanced numerical analysis

Load-bearing capacity of plate girders, often used in design of bridges and high-rise buildings, is limited by the shear capacity of connected slender plate elements subjected to shear buckling. To quantify this, experimental investigations on five large-scale steel and steel-concrete composite plate girders loaded solely in shear, with a minimal influence of bending moments, have been conducted and evaluated. In this paper, the phenomenon of web shear buckling is investigated within the numerical analysis using the ABAQUS Software. An advanced numerical model has been developed and results validated against existing experimental findings. One of the focal points of this study represents the methodology of developing such a comprehensive numerical model, implementation of suitable analysis procedures, material models, boundary conditions, finite elements and interactions, in order to correctly replicate the observed response in the tests. In addition, case studies tackling the influence of web slenderness, aspect ratio, initial imperfections, shear connection and concrete classes on the structural-mechanical behavior of steel-concrete composite girders in shear as well as the applicability and suitability of the existing analytical model are also presented and analyzed.

Pressure-induced structural variations and mechanical behavior of silicate glasses: Role of aluminum and sodium

This study investigates the effects of pressure-induced densification on the structural and mechanical properties of albite-like (12.5 % Na2O·12.5 % Al2O3·75 % SiO2) and sodium silicate (12.5 % Na2O·87.5 % SiO2) glasses using Molecular Dynamics simulations. Densification increased the coordination numbers of Al and Na, facilitated Al-O-Al clustering and formation of three-bridging oxygens, reduced T-O-T angles, and packed sodium ions in albite glass. Sodium silicate glass exhibited densification primarily through increased Na coordination, reduction of Si-O-Si angle and reduced Na-Na distances. Elastic modulus calculations revealed increased stiffness with densification due to enhanced atomic packing and glass reticulation. Uniaxial tensile tests showed densified glasses had higher ductility and strength than undensified counterparts, highlighting the positive effects of pressure-induced structural rearrangements. Hydrostatic compression tests demonstrated reversible densification under varying pressure loads, with pre-treatment conditions significantly affecting residual densification.

A molecular dynamics investigation of nano-twins and nano-precipitates effects in CoCrFeNi-based high-entropy alloys

Abstract This study systematically investigates the effects of twin boundaries and precipitates on the performance of CoCrFeNi HEAs matrix using molecular dynamics simulation methods. By constructing corresponding HEAs models and conducting simulations of their structural evolution and mechanical behavior at the nanoscale, the influence mechanisms of nanotwins (NTs) and nano-precipitates (NPs) on the mechanical properties of the material were explored through in-depth analysis of simulation results. The findings suggest that twin boundaries effectively impede the movement and slip of dislocations and stacking faults in the material. As a result, this enhances its mechanical properties and inhibits plastic deformation, ultimately improving its ductility. Meanwhile, precipitates also impact the material's performance, and the shape of precipitates may exert different effects on the material, while the phase interface between precipitates and the matrix can hinder the expansion of defects. The presence of twin boundaries can enhance the strengthening effect of precipitates, further improving the material's performance. This study provides a new perspective for understanding the relationship between the microstructure and mechanical properties of HEAs materials, offering important references for the design and optimization of HEAs materials.

Structural properties and mechanical behavior of three-dimensional cylindrical particle-like systems under in situ loading

To investigate the mechanical behavior of granular systems and their impact on density uniformity during compression, a three-dimensional micro-CT in situ loading experiment was conducted on a cylindrical granular system. The granular system was subjected to tomographic scanning and reconstruction, and the variation patterns of structural parameters such as volume fraction, porosity, and intrinsic density during the in situ loading process were analyzed. Internal pores within the granular system were extracted to obtain changes in pore area at each layer, allowing for an analysis of the evolving patterns of layered pore areas across different regions of the granular system during loading. This characterization elucidated the dynamic evolution process of compaction within the granular system. A contact network model for the granular system was established using particle contact area as a representation of inter-particle contact forces, revealing inherent connections between particle contact networks and macroscopic mechanical behaviors within the granular system.

Mode I crack propagation in polydimethylsiloxane-short carbon fiber composites

This paper presents a comprehensive analysis of reinforcement toughening and failure mechanisms in polydimethylsiloxane (PDMS)-carbon fiber (CF) composites employing an approach combining experiments and numerical simulations. Through a series of meticulously designed mechanical experiments, the behavior of the composite material under varying conditions is thoroughly examined. The introduction of CFs enhances the stiffness of the material while also leading to debonding and an increased Mullins effect. A constitutive model replicating the observed reinforcement and damage behavior is implemented. Our investigation extends to the analysis of crack growth through both numerical simulations and microscopic morphological examinations. A cohesive zone model is subsequently utilized to simulate crack propagation, providing enhanced understanding of the relationship between structural characteristics and mechanical behaviors. The process of crack propagation subjects the materials to cycles of loading and unloading, highlighted by the reinforcing action of CF pinning and stress transfer, alongside toughening mechanisms attributed to a variety of dissipative processes: interfacial debonding damage, energy loss due to CF pull-out, the Mullins effect, and viscous energy dissipation. This study elucidates the complex mechanical interplay within PDMS-CF composites and suggests pathways for their design optimization, significantly broadening their applicability in numerous domains.

Insights into irradiation-affected structural evolution and mechanical behavior of amorphous carbon

The distinctive hybridization structure of amorphous carbon (a-C) imparts remarkable mechanical and tribological characteristics, making it highly relevant for lubrication applications, particularly in critical sectors such as nuclear energy. In this work, we employed molecular dynamics simulations to examine the effects of irradiation on the structural evolution and mechanical behavior of a-C. The findings indicate that with increasing irradiation doses, the short-range order within the a-C is disrupted, leading to a substantial increase in sp2 hybridization. Then, nanoindentation simulations revealed a reduction in both hardness and elastic modulus as a consequence of irradiation damage, associated with the transition in hybridization from sp3 to sp2 and the associated creation of free volume. Furthermore, nanoscratch mechanical testing showed a slight increase in the friction, primarily attributed to the weakened load-bearing ability of a-C after irradiation. Interestingly, a metastable transition from sp2 to sp3 hybridization was observed on the scratched surface, which was concurrently validated by experiments as Raman spectroscopy and TEM-EELS. This study provides a detailed atomic-level mechanism for the irradiation-induced damage on the structural bonding and mechanical properties of a-C, offering guidance for its performance in nuclear reactors and the aerospace industry.

Harnessing potential of microwave-assisted ultrafast synthesis of reduced graphene oxide/Mn3O4 bioactive nanocomposite hydrogel for bone tissue engineering

The development of functional materials with the potential for bone tissue regeneration along with rapid synthesis and cost-effective approach has been challenging. In this regard, hydrogels have been explored as a potent candidate to behave as a 3D scaffold for bone repair. However, poor mechanical attributes impeded their clinical translation. Enthralling demonstration of the potential of carbon-based nanocomposites in bone tissue engineering has been constantly encouraging the fabrication of advanced nanocomposites. Here, we investigated the fabrication of reduced graphene/manganese (II, III) oxide (RGO/Mn3O4) nanocomposites by taking advantage of the microwave-assisted synthesis approach for cost effective, and ultrafast synthesis. Mn3O4 nanoparticles with uniform distribution in RGO sheets and ∼ 1.7 nm size was fabricated using the approach. Further, fine-tuning of the structural interaction and mechanical behavior of the GelMA-based hydrogels upon reinforcement with RGO/Mn3O4 nanocomposites was investigated as a function of different concentrations of the nanocomposites where upto 50 % increment in the compressive stress was observed compared to native GelMA hydrogel. The ability of these hydrogels was further investigated for their osteogenic behaviour on MC3T3-E1 preosteoblast cells where constant cell proliferation for up to 10 days was witnessed for the hybrid hydrogel with the highest concentration of the nanofillers.

Characterization of Composite Agarose-Collagen Hydrogels for Chondrocyte Culture.

To elucidate the mechanisms of cellular mechanotransduction, it is necessary to employ biomaterials that effectively merge biofunctionality with appropriate mechanical characteristics. Agarose and collagen separately are common biopolymers used in cartilage mechanobiology and mechanotransduction studies but lack features that make them ideal for functional engineered cartilage. In this study, agarose is blended with collagen type I to create hydrogels with final concentrations of 4% w/v or 2% w/v agarose with 2 mg/mL collagen. We hypothesized that the addition of collagen into a high-concentration agarose hydrogel does not diminish mechanical properties. Acellular and cell-laden studies were completed to assess rheologic and compressive properties, contraction, and structural homogeneity in addition to cell proliferation and sulfated glycosaminoglycan production. Over 21days in culture, cellular 4% agarose-2mg/mL collagen I hydrogels seeded with primary murine chondrocytes displayed structural and bulk mechanical behaviors that did not significantly alter from 4% agarose-only hydrogels, cell proliferation, and continual glycosaminoglycan production, indicating promise toward the development of an effective hydrogel for chondrocyte mechanotransduction and mechanobiology studies.

Investigation of an Ancient Wooden Cantilever Covered Bridge in China: Construction Form and Mechanical Properties

Wooden cantilever-covered bridges are typical Chinese constructions due to their structural style and architectural decoration. Yanzi bridge, an ancient wooden cantilever-covered bridge with more than 220 years of history in Anhua, China, has attracted increasing attention in recent years. In this study, its construction form and cultural background were investigated, and the structural components, original materials and mechanical behavior of the bridge were investigated in detail. First, the same type of raw material used for the Yanzi bridge, namely, pinus koraiensis, was tested to better understand its mechanical properties. Then, a finite element model was built to simulate the mechanical behavior of the bridge, and the stress state and internal forces of the cantilever system were obtained. According to the numerical results, when the loads are transferred downward and evened by the beams in the same layers of the cantilevers, the maximum deflection of the bridge of 12.8 mm meets the requirements of not exceeding L/600 in the specification, and the maximum normal stress of 1.35 MPa is much less than the ultimate tensile strength of the wood. This indicates that the structural safety performance of the ancient wooden cantilever-covered bridge is acceptable. Finally, a small amount of tiny damage of the bridge was observed and presented in the paper. This damage is not severe enough to cause brittle collapse, but care and maintenance are necessary to preserve this old historical bridge.

A Mathematical Model for Postimplant Collagen Remodeling in an Autologous Engineered Pulmonary Arterial Conduit.

This study was undertaken to develop a mathematical model of the long-term in vivo remodeling processes in postimplanted pulmonary artery (PA) conduits. Experimental results from two extant ovine in vivo studies, wherein polyglycolic-acid (PGA)/poly-L-lactic acid tubular conduits were constructed, cell seeded, incubated for 4 weeks, and then implanted in mature sheep to obtain the remodeling data for up to two years. Explanted conduit analysis included detailed novel structural and mechanical studies. Results in both studies indicated that the in vivo conduits remained dimensionally stable up to 80 weeks, so that the conduits maintained a constant in vivo stress and deformation state. In contrast, continued remodeling of the constituent collagen fiber network as evidenced by an increase in effective tissue uniaxial tangent modulus, which then stabilized by one year postimplant. A mesostructural constitute model was then applied to extant planar biaxial mechanical data and revealed several interesting features, including an initial pronounced increase in effective collagen fiber modulus, paralleled by a simultaneous shift toward longer, more uniformly length-distributed collagen fibers. Thus, while the conduit remained dimensionally stable, its internal collagen fibrous structure and resultant mechanical behaviors underwent continued remodeling that stabilized by one year. A time-evolving structural mixture-based mathematical model specialized for this unique form of tissue remodeling was developed, with a focus on time-evolving collagen fiber stiffness as the driver for tissue-level remodeling. The remodeling model was able to fully reproduce (1) the observed tissue-level increases in stiffness by time-evolving simultaneous increases in collagen fiber modulus and lengths, (2) maintenance of the constant collagen fiber angular dispersion, and (3) stabilization of the remodeling processes at one year. Collagen fiber remodeling geometry was directly verified experimentally by histological analysis of the time-evolving collagen fiber crimp, which matches model predictions very closely. Interestingly, the remodeling model indicated that the basis for tissue homeostasis was maintenance of the collagen fiber ensemble stress for all orientations, and not individual collagen fiber stresses. Unlike other growth and remodeling models that traditionally treat changes in the external boundary conditions (e.g., changes in blood pressure) as the primary input stimuli, the driver herein is changes to the internal constituent collagen fiber themselves due to cellular mediated cross-linking.

Carbon nanotuballs: Can they drive the future of nanofibers?

Nanofibers are extremely thin fibers produced from materials such as carbon, polymers, ceramics, and metals with diameters in the nanometer range that gained significant interest due to their unique properties. Carbon nanotubes, which could be considered the most popular fibers in the nanoscale, have gained widespread recognition primarily due to their remarkable strength derived from their cylindrical hexagonal lattice formed by carbon covalent bonds. Here, a new family of carbon nanofibers is proposed, arising from the combination of the tubular hexagonal configuration of carbon nanotubes and the spherical nanostructure of carbon fullerenes. These novel nanofibers, hereafter named carbon nanotuballs, are expected to demonstrate new advantaged characteristics such as better cross-section properties, enhanced interfacial interactions, and other unique physical attributes when used as fillers within other phases. Some preliminary theoretical investigations based on molecular dynamics are provided here to test the structural stability and mechanical behaviour of some single-walled carbon nanotuballs.

DEM simulation of microscopic structure and macroscopic mechanical behavior of clay in oedometer and triaxial compression tests

An updated DEM simulation scheme for clay is implemented by incorporating convex polygon shaped platelets and robust algorithm for physico-chemical–mechanical interaction between clay platelets. Clays with two typical microscopic structures, i.e., card-house structure and book-house structure, are simulated in oedometer test and triaxial compression test. Virtual Mercury Intrusion Porosimetry (MIP) and pore segmentation algorithms are utilized to extract pore statistics from the numerical samples. The simulation results and experimental results from the literature are thoroughly compared at both macroscopic and microscopic scales. It is found that the implemented DEM simulation scheme can satisfactorily reproduce the experimentally observed macroscopic behavior of clay. Especially, in triaxial compression tests, the critical state behavior, stress-dilatancy relationship and over-consolidation effects are generally consistent with existing experimental results. General consistency in pore size, orientation and shape distributions in DEM simulations and experiments can be observed. Clay platelets tend to rotate to align their normal directions along the major principal stress direction, while pores tend to align their long-axis directions in the confinement direction, leading to dynamically evolving fabric anisotropy. In the book-house structure clay, clay domains experience multiple deformation modes, including uniaxial compaction, shear distortion, spatial spin, and their combinations.

Investigation of the stability and physical properties of the newly synthesized Ta2AC (A=Co and Ni) MAX phases from first principles

Recently, the MAX phase compounds Ta2NiC and Ta2CoC have been successfully synthesized. In order to theoretically explore their properties, we conducted first-principles calculations based on density functional theory to investigate the structural stability, elastic anisotropy, mechanical behavior, electronic, and thermodynamic properties of these MAX phases. Our results reveal that the calculated structural parameters agree well with the experimental data. The MAX phases under investigation have been observed to exhibit thermodynamic, dynamic, and mechanical stability. Their electrical conductivity primarily originates from the d states of Ta, Ni, and Co at the Fermi level. They are ductile, elastically anisotropic, and demonstrate favorable machinability. The thermal parameters obtained from our calculations were compared with the reported values of a well-established material commonly used in thermal barrier coatings (TBCs). It has been concluded that the newly synthesized MAX phases Ta2NiC and Ta2CoC are potential thermal barrier coating materials.

Unveiling the impact of Cd and Zn substitutions on the structural, mechanical, electronic, and optical properties of SrS: A first principles analysis

This study employs ab-initio calculations based on density functional theory (DFT) to comprehensively investigate the multifaceted effects of Cd and Zn substitutions on the structural stability, mechanical behavior, electronic characteristics, and optical properties of SrS alloy. Structural analysis unveils a marginal reduction in lattice parameters for both doped compounds, signifying a subtle influence on the crystalline structure. Mechanical evaluation reveals that SrS and Sr0.75Cd0.25S keep their intrinsic brittleness, whereas the inclusion of 25 % Zn imparts a subtle ductile nature. The conservation of rigidity is observed post-doping, albeit with anisotropic features and differing degrees of stiffness among the compounds. Investigating electronic properties, the band gap of Sr0.75Cd0.25S persists as an indirect transition between M and Γ points, mirroring SrS's behavior. In contrast, a remarkable transformation is noted with 25 % Zn doping, shifting SrS to a direct band gap semiconductor. Interestingly, Cd and Zn incorporation leads to a band gap reduction, suggesting potential avenues for tuning the material's electronic behavior. Dielectric constant analyses unravel intriguing phenomena. The binary compound exhibits Mie resonance across the visible-infrared spectrum, a feature that contracts to the infrared range after doping. This nuanced shift has direct implications on the material's interaction with incident light and its resulting optical properties. Evaluation of the refractive index, absorption coefficient, reflectivity, and optical conductivity demonstrates a striking resemblance in the optical behavior of Sr0.75Zn0.25S and Sr0.75Cd0.25S to the pristine SrS alloy.

A systematic and precise study of deformed Zr52.5Cu17.9Ni14.6Al10Ti5 BMGs for notable shear bands towards better global plasticity

Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit 105) bulk metallic glasses with varying deformation strains (1.6, 4.5, 6.6, 8.7, 10.8, and 12.5 %) were subjected to compressive deformation. The evolution of shear bands was systematically and mathematically conducted to investigate the impacts of largest plastic strains. It was observed that the average length of shear steps per unit area of surface increased with increasing plastic strain. The protruded areas exhibited non-uniform heights, which appeared to gradually extend as the plastic strain was increased. Mathematical formulation was employed to calculate the contribution of individual shear bands to the total strain, aiming to explore the microstructure and mechanical features of BMGs. This approach provided insights into the relationship between atomic-scale structure, local dynamics, and macroscopic mechanical behavior. Moreover, the contribution of shear bands to normal strain along with the assessment of congruent results for normal strain originating from shear bands were evaluated for attaining better global plasticity.

ALSTNet: Autoencoder fused long‐ and short‐term time‐series network for the prediction of tunnel structure

AbstractIt is crucial to predict future mechanical behaviors for the prevention of structural disasters. Especially for underground construction, the structural mechanical behaviors are affected by multiple internal and external factors due to the complex conditions. Given that the existing models fail to take into account all the factors and accurate prediction of the multiple time series simultaneously is difficult using these models, this study proposed an improved prediction model through the autoencoder fused long‐ and short‐term time‐series network driven by the mass number of monitoring data. Then, the proposed model was formalized on multiple time series of strain monitoring data. Also, the discussion analysis with a classical baseline and an ablation experiment was conducted to verify the effectiveness of the prediction model. As the results indicate, the proposed model shows obvious superiority in predicting the future mechanical behaviors of structures. As a case study, the presented model was applied to the Nanjing Dinghuaimen tunnel to predict the stain variation on a different time scale in the future.

Structural Design and Mechanical Behavior Investigation of Steel–Concrete Composite Decks of Narrow-Width Steel Box Composite Bridge

Steel–concrete composite decks are commonly employed in narrow-width steel box composite girder bridges to augment their lateral spanning capabilities, while the concurrent omission of longitudinal stiffeners leads to a substantial reduction in the number of components, thereby yielding a structurally optimized bridge configuration. This paper delineates the structural design parameters of a narrow-profile steel box composite girder bridge and assess the mechanical behavior of its incorporated steel–concrete composite deck under static and fatigue loading conditions. To this end, two full-scale segment specimens from the composite bridge decks were subjected to equal amplitude cyclic fatigue tests. The investigation specifically concentrated on the impacts of two types of shear connectors—namely, perforated steel plates combined with shear studs and perfobond rib shear connectors (PBL connectors)—on the static and fatigue performance, including fatigue stiffness, of the steel–concrete composite bridge decks. The results indicate that, under the static bending condition, the composite deck specimen equipped with stud connectors demonstrates superior overall flexural stiffness in comparison to the specimen featuring PBL connectors. Furthermore, the flexural stiffness of the steel–concrete composite specimens experiences a negligible alteration across two million fatigue loading cycles. Upon the completion of two million fatigue loading cycles, the composite deck specimens incorporating the shear connectors composed of perforated steel plates and shear studs exhibit relatively wider crack widths under the static peak load. Both configurations of the steel–concrete composite bridge deck specimens manifest evident interfacial detachment, signifying insufficient tensile pull-out stiffness of the shear connectors. It is recommended to increase the quantity of the shear connectors or select the pertinent types in order to enhance the interface shear resistance.

Tunable viscoelasticity of bulk fullerene network via high-temperature annealing

Although the experimental transformation of C60 bulk into various functional carbon materials at a certain temperature and pressure has been extensively explored, the understanding of the structural transformation mechanisms and the energy dissipation mechanisms of the derived topologies at the atomic scale is still poor. By using the molecular dynamics (MD) simulations method, the structural transformation of C60 bulk to various carbon materials is studied. Besides, the mechanisms of energy dissipation of three typical structures are revealed and the effects of loading frequency, temperature, loading amplitude, and pre-strain on the storage, loss modulus, and dumping ratio of three typical structures were investigated by dynamic mechanical analysis (DMA). The results show that due to the difference in structural morphology and mechanical behaviors under cyclic loading, three typical structures show different viscoelastic mechanical properties which could also be tuned by changing related parameters. This work systematically investigates the viscoelastic mechanical properties of bulk fullerene network during different annealing processes and corresponding energy dissipation mechanisms and provides important references for further design and application.

Mechanical Behavior of Precast Circular Semi-Continuous CFST Columns under a Uniaxial Eccentric Load

For this study, we conducted a detailed examination and comprehensive comparative analysis of the structural responses and mechanical behavior of bolted sleeve connections in precast circular semi-continuous steel tubular concrete (PCSCFST) columns. The research involved fourteen specimens, and we considered the impacts of various parameters, including eccentricity, external steel sleeve thickness, bolt diameter, and slenderness ratio. The findings revealed that the external steel sleeve significantly enhances the protection of the connection area, enabling the bolts to effectively withstand eccentric loads. However, sleeves that are too thick may lead to premature bolt failure, reducing their ultimate load-bearing capacity. Using bolts to transfer loads to the concrete significantly strengthens the restraining effect of the steel sleeve. Nonetheless, increasing the bolt diameter beyond a certain threshold may diminish this beneficial impact, potentially leading to connection failure and a decrease in ultimate load-bearing capacity. A new ‘cooperative value q’ measures component collaboration at ultimate capacity, showing that shorter columns offer less effective coordination than longer ones. Through regression analysis, we formulated a prediction for axial ultimate bearing capacity, closely aligning with the experimental data (Npre-a/Nu average value of 1.003, variance 0.00248). Three N–M curves, including the Eurocode 4 method, offered conservative predictions, with Eurocode 4 closely matching the experimental results. A refined prediction method following Eurocode 4 was developed, yielding an average Ppre-U/Pu value of 0.971 and a variance of 0.0107.

Unsteady Mixed Convection Flows in a Rectangular Duct and Dynamical Behaviors of Flow Channel Insert

Buoyancy-assisted upward MHD flows and dynamical behaviors of flow channel insert (FCI) in the dual-coolant lead-lithium (DCLL) blanket are studied numerically. Based on our internally developed and validated solver, the dynamical behaviors of magneto-thermo-fluid-structure coupled multiphysical field are investigated. A large amplitude, low frequency, and quasiperiodic unsteady reverse flow at high Re (31000), high Gr (3.5×1011), and moderate magnetic field (0.7~1.7T) is found in the DCLL blanket. This intricate phenomenon has been discovered for the first time, representing a combination of separate experimental results from Melnikov et al. (2016) and Khanal and Lei (2012). In our study of this large amplitude, low frequency, and quasiperiodic unsteady reverse flows, the importance of the cold helium gas to the instability of fluid flow in the bulk region and the thermal conductivity of the FCI to convection structure and instability are first found and recognized. Additionally, we take into account the effects of the temperature field and flow field on structural deformation and mechanical behavior of FCI, and we have discovered several intriguing phenomena, such as (1) the stability of fluid flow in the bulk region depends on the strength of the heat source, the magnitude of the magnetic field, and thermal conductivity of FCI; (2) the instability and periodicity of the fluid flow are primarily related to the unsteady reverse flow, which rises up and falls down periodically in the bulk region; (3) the physical mechanism of unsteady flow influenced by reverse flow, pressure drop, and Lorentz force has been concluded. It has been discovered that the breakdown of a reverse flow vortex causes a rapid reduction in pressure drop. (4) To avoid this phenomenon in engineering, a phase map of unsteady and steady flows in the DCLL blanket has been created. (5) The quasiperiodic characteristics of solid (flow channel insert) affected by flow are found and analyzed.