8,852 results on '"size effect"'
Search Results
2. Size-dependent buckling behaviors of a rotating nanobeam using the integral form of Eringen's nonlocal theory.
- Author
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Yan, Xuesong and Li, Yinghui
- Subjects
- *
TIMOSHENKO beam theory , *ANGULAR velocity , *GALERKIN methods , *PARADOX , *ANGLES - Abstract
Integral forms of Eringen's nonlocal theory are employed to model nanoscale constitutive relations without possible potential paradoxes. The Timoshenko beam theory as well as the element-free Galerkin method are accepted to model rotating nanobeams and develop numerical solutions of critical rotating angular velocities for nanobeams. Optional setting angles as natural defects are taken into account in buckling analyses. Important design parameters, including length-to-height ratios, ratios of hub radii to lengths, setting angles, and additional supports are carefully assessed between local and nonlocal beams. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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3. Size Effects in Strength and Strain Hardening Behavior of Single-Crystal 7075 Aluminum Alloy Micropillars.
- Author
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Li, H., Zhao, D., Cui, Y., Dan, C., Ma, S., Wang, L., Liu, J., Li, Y., Chen, Z., and Wang, H.
- Subjects
- *
ALUMINUM alloys , *HEAT treatment , *STRAIN hardening , *FOCUSED ion beams , *ENGINEERING systems - Abstract
Background: The size effect and deformation instability exhibited by materials at the micro- and nano-scale constrain the development and application of miniaturized devices. Introducing different defects in materials through different technical means to improve the deformation stability of materials has been the main research point of micro- and nano mechanics. Objective: This paper presents a novel strategy to completely eliminate the instability of microscopic deformations by the introduction of high-density precipitates in aluminum alloys by means of suitable heat treatment. Methods: A suitable heat treatment is used to introduce a high density of precipitates in the 7075 aluminum alloy. Using the Focused Ion Beam technique and in situ micropillar compression tests, micron-sized single-crystal micropillars were fabricated and the size dependence of the strength and strain-hardening behavior of 7075 aluminum alloy was systematically analyzed. Results: Compared with precipitate-free Al–Mg alloy micropillars, the micropillars fabricated from 7075 aluminum alloy exhibited more stable deformation behavior, predominantly due to the impediment of dislocation motion by precipitates. The power-law exponent for yield strength relative to pillar size was determined to approach a near-zero value, indicating a negligible dependency of yield strength on specimen size. Similarly, the smaller the size of micropillar, the higher the hardening rate, which can be rationalized by exhaustion hardening. Conclusions: The proposed method can eliminate the size effect of materials with pillar size above 0.5 μm and leads to a stabilization in deformation behavior. These are advantageous for the application of micro- and nano-sized components in advanced engineering systems. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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4. Size Effect on the Ductile Fracture of the Aluminium Alloy 2024-T351.
- Author
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Šebek, F., Salvet, P., Boháč, P., Adámek, R., Věchet, S., Návrat, T., Zapletal, J., and Ganjiani, M.
- Subjects
- *
CONTINUUM damage mechanics , *DUCTILE fractures , *ALUMINUM alloys , *OPTICAL measurements , *FINITE element method - Abstract
Background: Reliably calibrated criteria are needed for an accurate prediction of fracture of various components. However, there is not always a sufficient amount of material available. Therefore, miniature testing provides an alternative that is researched together with the following calibration of the ductile fracture criteria and investigating the size effect. Objective: The aim is to design miniature testing equipment and specimens for tensile testing, which covers various stress states. This is supplemented by the small punch test, which has the same specimen thickness, taken from the literature to broaden the portfolio for calibration. The second part deals with conducting the finite element analysis, which provided a basis for the calibration of the phenomenological ductile fracture criterion applicable to crack-free bodies to indicate the crack initiation. Methods: The steel frame to test thin specimens is designed with optical measurement of deformations. The finite element method is used, within Abaqus and user subroutines, to simulate the tests to obtain the variables needed for the calibration. In addition, the calibration of the criterion using machine learning is explored. Results: The feasibility of the proposed experimental program is tested on the aluminium alloy 2024-T351. Moreover, the numerical simulations, which showed a good match with experiments in terms of force responses, adds to the knowledge of modelling in the scope of continuum damage mechanics. Conclusions: The presented results provide a material basis for the aluminium alloy studied on a lower scale, while they broaden the testing possibilities and analyses the calibration strategies for the best failure predictability possible. [ABSTRACT FROM AUTHOR]
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- 2024
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5. Assessment of fracture criteria for cracking behavior of asphalt concrete using various SCB specimen sizes.
- Author
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Momeni, Ramin and Pirmohammad, Sadjad
- Subjects
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ASPHALT concrete , *CONCRETE fractures , *FRACTURE mechanics , *STRAIN energy , *ENERGY density - Abstract
In this research, five fracture criteria (maximum tangential stress (MTS), generalized maximum tangential stress (GMTS), minimum strain energy density (SED), generalized minimum strain energy density (GSED), and modified maximum tangential stress (MMTS)) were evaluated for asphalt concrete using fracture data from tests conducted under various loading modes and conditions. Tests were performed on semi‐circular bend (SCB) specimens of various sizes. Based on the results, the MTS criterion tends to overestimate fractures, while the GMTS criterion exhibits more precise predictions. The SED and GSED criteria inaccurately predict fractures, especially under certain loading conditions. The MMTS criterion shows superior predictive capability for asphalt concrete fractures. Specimen size influences fracture resistance, with larger specimens exhibiting higher fracture values. Overall, the MMTS criterion closely mirrors the crack growth behavior of asphalt concrete, highlighting its precision in predicting fracture results. The errors between the predictions of the fracture criteria MTS, GMTS, SED, GSED, and MMTS, and the experimental results ranged from 0% to 42.8%, 0% to 22.5%, 0% to 52.7%, 0% to 42.4%, and 0% to 14.5%, respectively. Highlights: Fracture tests were conducted on asphalt concrete under various conditions such as temperatures, loading rates, SCB specimen sizes, and loading modes.Five fracture criteria (MTS, GMTS, SED, GSED, MMTS) were assessed for their applicability to asphalt concrete.The MMTS criterion was found to have the best ability to predict fractures in asphalt concrete compared to the other criteria studied.The size of the specimen has an impact on fracture resistance, with larger specimens showing higher fracture values. All the fracture criteria used in the study accurately reflect this trend. [ABSTRACT FROM AUTHOR]
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- 2024
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6. Influence of structure size on bending-shear-torsion combined mechanical properties of concrete beams with BFRP bars.
- Author
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Lei, Yushuang, Jin, Liu, Zhu, Huajie, and Du, Xiuli
- Abstract
To investigate the effect of beam size on the combined mechanical performance of concrete beams reinforced with Basalt Fiber Reinforced Polymer bars (BFRP-RC beams), the simulation model of BFRP-RC beams under bending-shear-torsion loading was established with the aid of a mesoscale simulation method. The effects of beam size, stirrup ratio and torsion-bending on damage mechanisms of BFRP-RC beams, as well as the size effect law (SEL) were analyzed. Finally, a prediction formula that can characterize the impact of the torsion-bending ratio and stirrup ratio on BFRP-RC beams' SEL under combined loadings was proposed. Research shows (1) the BFRP-RC beams' damage mode changes from shear to torsion with the torsion-bending ratio improving, and there is a mutual weakening effect between shear and torsion. (2) BFRP-RC beams have noticeable size effects under combined loading. Moreover, the torsional and shear size effects are first enhanced and then weakened as the torsion-bending ratio increases. (3) The beams' torsional and shear strengths increase with increasing stirrup ratio, and the corresponding size effects diminish. (4) The SEL proposed in this study is accurate in predicting the shear and torsional capacity of beams under combined loading. [ABSTRACT FROM AUTHOR]
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- 2024
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7. Bi-Helmholtz kernel based stress-driven nonlocal integral model with discontinuity for size-dependent fracture analysis of edge-cracked nanobeam.
- Author
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Tang, Yuan and Qing, Hai
- Subjects
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DIFFERENTIAL forms , *MATHEMATICAL models , *INTEGRALS - Abstract
Mathematical formulation is proposed to deal with average bi-Helmholtz kernel (BHK) based stress-driven nonlocal integral model (SDNIM) with discontinuity, which is converted into equivalent differential form with constitutive constraints. Based on average BHK-SDNIM with discontinuity, mathematical model for size-dependent fracture behavior of mode I and II cracks is established for edge-cracked nanobeam. For different load conditions, the analytical bending deflections are deduced firstly, and the corresponding external works and energy release rates can be calculated explicitly. Numerical study shows that energy release rates decrease with the increase of nonlocal parameter κ , which explains the superior fracture performance of nano-materials. [ABSTRACT FROM AUTHOR]
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- 2024
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8. Size- and shape-effects analysis on the pure torsional performance of CFRP sheet-strengthened RC columns.
- Author
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Jin, Liu, Ji, Yiding, Li, Dong, Lei, Yushuang, and Du, Xiuli
- Abstract
To investigate the torsional performance of reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets, a mechanical analysis model was established using a three-dimensional numerical method. The model considered the heterogeneity of concrete, and the interactions between steel bars/CFRP sheets and concrete, simultaneously. The validity of the numerical model was first verified. Subsequently, pure torsion was added on 40 CFRP sheet-strengthened RC columns to investigate the influences of the fiber ratio, the structure size, and the cross-section shape on their torsional performance. Results showed that (1) size effect can be observed in the nominal torsional strength of both square and circular CFRP sheet-strengthened RC columns; (2) the size effect of square columns was stronger than circular columns due to weaker confinement effects of CFRP sheets on the square columns; (3) the addition of CFRP sheets can simultaneously improve the torsional strength and weaken the size effect, which is beneficial to the torsional performance of the column. Moreover, a torsional size effect law was proposed to predict the torsional strength of CFRP sheet-strengthened RC columns based on current simulation results. [ABSTRACT FROM AUTHOR]
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- 2024
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9. Compression properties of cellular iron lattice structures used to mimic bone characteristics.
- Author
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Nogueira, Pedro, Magrinho, João PG, Silva, Maria B, de Deus, Augusto M, and Vaz, Maria F
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Recently, cellular materials made by the repetition of unit cells, that is, iron lattices have become appealing to mimic the structure of bone. The aim of the study is to choose the most adequate lattice structures, which have the compressive mechanical properties closer to the ones of bone, in the perspective of their use as temporary implants. Five types of unit cells were selected, such as, cubic (C), truncated octahedron (TO), truncated cubic (TC), rhombicuboctahedron (RCO), and rhombitrucated cuboctahedron (RTCO). The mechanical properties were assessed by numerical simulations with a finite-element analysis. The size effect was studied with the comparison of results among samples with different numbers of unit cells. Simulations covered a wide range of relative densities. Graded dense-in and dense-out configurations were constructed with lattices of types RTCO and TO, being the unit cells, themselves graded. Lattice structures RTCO and TO were found to be stable at every relative density studied, while C, TC and RCO lattices are unstable at low densities. The evaluation of size effects was not conclusive, which could be biased by other factors. The Young's modulus of RTCO and TO lattices enable to reproduce the properties of both trabecular and cortical bone, with an appropriate choice of the relative density. To mimic trabecular bone, only RTCO and TO structures with low relative densities, can be used, while arrangements of C, TC and RCO cells can only replicate the properties of cortical bone. Graded cells may have the same properties as non-graded with lower density. [ABSTRACT FROM AUTHOR]
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- 2024
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10. Dynamic Performance Evaluation of Machine Foundations Using Multi-approach Investigation.
- Author
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Das, Gobinda, Surapreddi, Sreyashrao, and Ghosh, Priyanka
- Subjects
ARTIFICIAL neural networks ,BUILDING foundations ,MACHINE performance ,MACHINE design ,ECCENTRICS (Machinery) - Abstract
The current investigation examines the influence of footing shape, the base area of footing (A), the mass of footing-machine assembly (m), and eccentric force settings (m
e e) on the dynamic response and performance of machine foundation systems. Five different footing configurations are employed to perform field block vibration tests involving three square, one circular and one rectangular footing. The experiments are performed at the geotechnical field laboratory of IIT Kanpur, India (N26°30′59.0892″, E80°13′51.6888″). The accuracy and reliability of the experimental results are endorsed by the results obtained from the mass-spring-dashpot (MSD) analysis. In addition, an artificial neural network (ANN) model is created to anticipate the dynamic behaviour of the soil-foundation system. A thorough parametric study demonstrates the efficacy of the developed ANN model. It is revealed from the investigation that the stiffness (k) and the damping ratio (D) of the soil for square foundations increase by 7% and 3%, respectively, with a 40% increase in A. Similarly, the circular foundation exhibits 7 and 3% higher k and 4 and 3% higher D than those obtained for square and rectangular foundations, respectively. For square foundations, a 24% enhancement in m leads to a 42 and 4% increase in k and D, respectively. In contrast, for circular and rectangular foundations, a 13% increase in m results in a 27 and 19% increase in k and D, respectively. In this study, experimental testing, analytical validation, and ANN modelling provide insight into the response of machine foundations under various operating conditions. The results of this study can be utilized to optimize the design of machine foundations. [ABSTRACT FROM AUTHOR]- Published
- 2024
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11. Optimization of high-precision Bekker test plate structure for rarefied soils–example of deep-sea subsoils.
- Author
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Wang, Teng, Tang, Peng, Xie, Baoqi, and Ma, Wenbo
- Subjects
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SOIL compaction , *BEARING capacity of soils , *COMPRESSION loads , *SUBSOILS , *SOILS - Abstract
AbstractThe Bekker apparatus is an important tool for measuring soil bearing capacity; however, it is not entirely suitable for deep-sea sediments, and the size of the loading plate can affect the accuracy of the Bekker bearing parameters. This paper employs the Coupled Eulerian-Lagrangian (CEL) method to explore how different conditions impact Bekker bearing parameters. As the size of the loading plate gradually increases, the soil compression mechanism and load path reach a relatively stable state, leading to the stabilization of Bekker bearing parameters. The study proposes a range of plate sizes for deep-sea soils with varying strengths, noting that the physical mechanisms of low-strength soils are relatively simple, making them more consistent with the ideal conditions described by Bekker’s theory. Furthermore, an analysis of the relationship between Bekker bearing parameters and penetration depth reveals that the parameters corresponding to different strength soils vary almost parallel with depth. This is attributed to the same settlement path, where the distribution of loads and the geometrical shapes of the supporting structures remain unchanged, resulting in a similar trend in the variation of Bekker parameters. The research findings provide a theoretical basis for analyzing the bearing capacity characteristics of soft deep-sea soils. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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12. Shear Mechanical Behaviours and Size Effect of Band–Bedrock Interface: Discrete Element Method Simulation Insights.
- Author
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Wang, Hao, Guo, Xueyan, Liu, Xinrong, Zhou, Xiaohan, and Xu, Bin
- Subjects
DISCRETE element method ,MODULUS of rigidity ,ELASTIC modulus ,ROCKSLIDES ,STRESS concentration - Abstract
The shear band is a prominent feature within the Banbiyan hazardous rock mass located in the Wushan section of the Three Gorges Reservoir area. This band constitutes a latent risk, as the potential for the rock mass to slide along the region threatens the safety of lives and property. Presently, the understanding of the shear mechanisms and the impact of shear band size on the band–bedrock interface is incomplete. In this study, based on band–bedrock shear laboratory tests, DEM simulation is used to investigate the shear-induced coalescence mechanism, stress evolution, and crack-type characteristics of the band–bedrock interface. In addition, the shear mechanical properties of samples considering specimen size, rock step height, and step width are further studied. The results show that the crack initiation and failure crack types observed in the first rock step are predominantly tensile. In contrast, the failure cracks in the remaining rock slabs and steps are primarily characterised by shear mode in addition to other mixed modes. The stress condition experienced by the first step is very near to the position of the applied point load, whereas the stress distribution across the remaining steps shows a more complex state of compressive–tensile stress. The relationship between shear parameters and sample size is best described by a negative exponential function. The representative elementary volume (REV) for shear parameters is suggested to be a sample with a geometric size of 350 mm. Notably, the peak shear strength and shear elastic modulus demonstrate a progressive increase with the rise in rock step height, with the amplifications reaching 91.37% and 115.83%, respectively. However, the residual strength exhibits an initial decline followed by a gradual ascent with increasing rock step height, with the amplitude of reduction and subsequent amplification being 23.73% and 116.94%, respectively. Additionally, a narrower rock step width is found to diminish the shear parameter values, which then tend to stabilise within a certain range as the step width increases. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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13. A quadrilateral non-classical microplate element considering the voltage effect.
- Author
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Korayem, Moharam Habibnejad and Hefzabad, Rouzbeh Nouhi
- Abstract
A quadrilateral non-classical Mindlin element that incorporates voltage effects was introduced for examining the bending and free vibration of piezoelectric multilayer plates. The model was developed to examine multilayer plates in the presence of voltage effects. Hamilton's principle was initially employed to formulate the equation of motion for a multilayer Mindlin plate, considering both size and voltage effects. The equations of motion were resolved through the Galerkin's method. The suggested element is a rectangular element featuring four-nodes, each possessing 15 degrees of freedom, accounting for both bending and stretching deformations. This element meets the requirements for C
0 continuity and C1 weak continuity, and incorporates size and voltage effects. The results were examined with both experimental and analytical data. Upon investigating the voltage effect, it was found that the stiffness matrix depends on both the magnitude and sign of the voltage. Furthermore, it has been demonstrated that the natural frequencies of higher modes are less affected by voltage variations compared to lower modes. In the end, the model was compared to experimental results obtained from a multilayer microcantilever. [ABSTRACT FROM AUTHOR]- Published
- 2024
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14. Influences of size effect and workpiece temperature during cryogenic micro milling of soft viscoelastic polymer: an experimental assessment.
- Author
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Mallick, Partha Sarathi and Patra, Karali
- Subjects
- *
CUTTING force , *GLASS transitions , *CRYOGENIC grinding , *TEMPERATURE control , *ELASTIC modulus , *MACHINABILITY of metals - Abstract
AbstractApplication of tool-based micromachining in soft polymer has been limited due to high adhesion and low elastic modulus of this material at room temperature. This study aims to evaluate the machinability of a typical viscoelastic soft polymer and understand the effect of material and process parameters on machining performances. In this study, a micro-milling process using cryogenic-assisted cooling is proposed and the importance of temperature control toward glass transition zone was particularly addressed. To identify insight of machinability in micro domain, this article also determines minimum uncut chip thickness (MUCT) and size effects by considering the variations of cutting force and surface integrity with the ratio of h/re (uncut chip thickness (h) to cutting edge radius (re)). The experimental results reveal that consideration of size effect during micromilling of soft viscoelastic polymer helps in reduction of machined surface roughness (Sa) value. Based on the cutting force pattern, it is evaluated that higher machining stability can be achieved during cryogenic machining by reduction of specific cutting force value. Moreover, temperature range around glass transition zone yields more promising experimental outcomes, outperforming other cooling zones. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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15. Sub‐Nanometer‐Scale Cu9S5 Enables Efficiently Electrochemical Nitrate Reduction to Ammonia.
- Author
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Feng, Chao, Wu, Hanyang, Shao, Jiaxin, Huo, Qihua, Hassan, Afaq, Yang, Hengpan, Hu, Qi, and He, Chuanxin
- Subjects
- *
MATERIALS science , *STANDARD hydrogen electrode , *ELECTROLYTIC reduction , *PHOSPHOTUNGSTIC acids , *CHARGE exchange - Abstract
The sub‐nanometer is a key feature size in materials science. Unlike single‐atom and nanomaterials, size effects and inter‐component cooperative actions in sub‐nanomaterials will effective on its performance is more significant. Here, 0.95 nm ordered arrangement Cu9S5 sub‐nanowires (Cu9S5 SNWs) are synthesized through the co‐assembly effect of inorganic nuclei (Cu9S5) and clusters (phosphotungstic acid‐PTA), achieving a significant increase in the specific surface area of the sample and ≈100% atomic exposure rate, which is the key to its high catalytic activity. PTA clusters not only act as a “charge transfer station” to accelerate the inter‐component electron transfer process, but also facilitate the dissociation of water and provide more hydrogen protons, thus dramatically facilitating the electrocatalytic process. The experimental results show that the Cu9S5 SNWs exhibited excellent nitrate reduction reaction (NO3−RR) properties. The Faraday efficiency (FE) of NO3−RR is 90.4% at the optimum potential −0.3 VRHE (reversible hydrogen electrode) and the ammonia production is as high as 0.37 mmol h−1 cm−2, which is superior to most reported electrocatalysts. In addition, the Zn‐NO3− liquid‐flow battery devices assembled using Cu9S5 SNWs as electrode materials show excellent application results. This work provides a reference for the design of highly efficient sub‐nanoscale NO3−RR electrocatalysts. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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16. 基于偶应力理论的压电材料轴对称接触问题.
- Author
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吕鑫, 柯燎亮, and 苏洁
- Abstract
Based on the couple stress theory, the axisymmetric contact problem between a rigid insulating spherical punch and a transversely isotropic piezoelectric half-space was studied. With the Hankel integral transform and the integral least squares approach, the analytical solutions of the contact pressure were obtained. The effects of the characteristic material length on the contact pressure distribution, the contact radius and the indentation depth were discussed. The results indicate that, the contact pressure obtained based on the couple-stress theory is significantly greater than the classical results. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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17. Size and Interface Effects on Tensile Strength of Polymers with Nano/Micro Particle Inclusions.
- Author
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Yuan, R., Ma, X., Liang, L. H., and Wei, Y.
- Abstract
Polymers with particle inclusions have wide applications, and the mechanical properties of polymer composites affect their reliability in service. The strength of these composites is dependent on factors such as particle fraction, size, distribution, and interface interaction between the two phases, in addition to the properties of the polymers and particles. The size effect of particles and interface damage play an important role and thus draw considerable attention. In this paper, the size- and interface-dependent strength of polypropylene (PP) with nano/micro silica (SiO
2 ) particles of different fractions is studied through a combination of tensile experiments on a series of samples and corresponding three-dimensional (3D) finite element modeling. The results indicate that PP with 2% SiO2 nanoparticles of 50 nm exhibits relatively higher tensile strength, shedding light on the microstructure mechanism where smaller particle sizes lead to better interface bonding. Furthermore, the particle size and interface coupling effect is analyzed based on the size-dependent elastic modulus model and the interface-cohesive model. The simulation demonstrates the local interface damage evolution around a particle of the composites in tension. These findings are beneficial for designing polymer composites with nanoparticle inclusions. [ABSTRACT FROM AUTHOR]- Published
- 2024
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18. Probabilistic Fatigue Life Framework of Notched Specimens Based on the Weibull Distribution Under Multiaxial Loading.
- Author
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Wang, Jie, Liu, Jianhui, Lu, Jumei, He, Yingbao, Pan, Xuemei, and Zhang, Ziyang
- Abstract
In engineering applications, the notch effect and size effect significantly influence the evaluation of fatigue performance in components, necessitating special attention in life prediction. This study proposes a new probabilistic model, based on the theory of critical distance (TCD), to predict fatigue life, with the aim of quantitatively assessing the impact of notch effect and size effect. The stress distribution on the critical plane is first characterized using a sixth-order multinomial function, and the relative stress gradient function is utilized to calculate the value of the critical distance. Furthermore, the effect of the ratio of shear strain to normal strain on fatigue life under multiaxial loading is considered. Additionally, the integration of the Weibull distribution into the TCD is employed for conducting probabilistic modeling of fatigue life. Finally, fatigue experiments are conducted on notched specimens of Q355D steel, demonstrating that the life prediction results under 50% survival probability are superior to the traditional TCD method. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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19. Experimental Study on Basic Mechanical Properties of Polypropylene Fiber-Reinforced Ceramsite Concrete.
- Author
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GU Fei, LI Congqi, YANG Ying, LI Huilong, JIN Ziran, WANG Xin, and LIU Hushan
- Subjects
FIBER-reinforced concrete ,POLYPROPYLENE ,ELASTIC modulus ,COMPRESSIVE strength ,POLYPROPYLENE fibers - Abstract
In order to improve the strength and brittleness of ceramsite concrete, polypropylene fiber was added to ceramsite concrete in this study. A total of 180 polypropylene fiber-reinforced ceramsite concrete specimens were prepared, and cube compressive test, splitting tensile test, axial compressive test and elastic modulus test were carried out. The results show that polypropylene fiber can effectively improve the splitting tensile strength and tension-compression ratio of ceramsite concrete, and has little effect on compressive strength and elastic modulus. Based on the experimental results, the conversion relationship model between splitting tensile strength and cube compressive strength, axial compressive strength and cube compressive strength, and the numerical model of elastic modulus of polypropylene fiber-reinforced ceramsite concrete were proposed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
20. 氮化镓/金刚石异质结构界面热输运特性的 分子动力学研究.
- Author
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陆吕杰 and 魏 宁
- Abstract
Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2024
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21. Grain‐Size‐Dependent Plastic Behavior in Bulk Nanocrystalline FeAl.
- Author
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Gammer, Christoph, Mangler, Clemens, Karnthaler, Hans‐Peter, and Rentenberger, Christian
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MATERIAL plasticity ,TRANSMISSION electron microscopy ,DISLOCATION density ,ALLOYS ,ELECTRON diffraction - Abstract
While the deformation behavior of nanocrystalline ductile metals and alloys is extensively studied, there is little understanding for brittle intermetallic alloys with very small grain sizes. Herein, B2‐ordered FeAl with different grain sizes is produced and deformed by high‐pressure torsion. At a grain size of 120 nm, conventional dislocation processes remain dominant, resulting in a disordered saturation structure with highly defected grains of around 100 nm. The situation is different for an initial grain size of 30 nm; grain‐boundary‐mediated processes appear along with dislocation processes and deformation shows a tendency toward extreme localization in the form of thin bands. Interestingly, the saturation structure is not reached after severe plastic deformation. The nanocrystals remain ordered with a grain size of 30 nm; only within the deformation bands, some degree of disordering and an increase of the dislocation density are revealed by profile analysis using selected electron diffraction. This result demonstrates an extreme stability of ordered FeAl at very small grain sizes, and indicates that the deformation behavior in brittle intermetallics can strongly depend on the grain size. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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22. Size Effect on Pore-Scale Variables and Heterogeneous Pore-Network Characteristics in Carbonate Rocks.
- Author
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Shou, Yundong, Zhao, Zhi, Zhou, Xiaoping, and Chen, Junwei
- Abstract
Pore-scale variables, specifically porosity and permeability, are vital in deep resource exploration projects like geothermal energy and shale gas. Digital rock measurement techniques (DRMTs) are commonly employed to match these variables with experimental results. However, limited attention has been given to identifying errors and size effects on pores and pore scale variables, as well as spatial heterogeneous characteristics of pore-networks. In this research, we define pore scale variables and investigate the size effects on these variables through statistical analysis. Additionally, we propose novel empirical formulas for predicting porosity and permeability based on X-ray CT images acquired at varying resolutions from the same carbonate rock sample. Our results indicate that the scanning direction has minimal influence on the physical and hydraulic properties, while these properties are significantly affected by image resolution. The porosity and permeability calculated using the proposed formulas show good agreement with experimental results, with errors below 10%. Consequently, the proposed formulas prove to be effective and reliable in evaluating physical and hydraulic properties based on DRMTs. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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23. Investigating Size Effects on Gradient-Related Crack Behavior in Frozen Sand Samples: A Simplified Approach and Application.
- Author
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Zhao, Xiaodong, Cai, Xu, Li, Ruilin, Zhang, Xiao, Zhou, Jie, and Chen, Jun
- Abstract
The stability performance of the frozen curtain formed under standpipe freezing is closely associated with the weak zone penetrated by thermal gradient-related fracture (TGF). The TGF-rich zone further affects the liquid phase flow when the frozen curtain is thawed. However, there is a lack of studies on the TGF-rich zone within the frozen curtain. To address this gap, a simplified and practical 2D bonded particle model-based numerical simulation strategy was developed to identify the possibility of acquiring field characteristics of the TGF-rich zone by conducting numerical tests on samples considering size effects. The results, validated by the experiment, indicated that the influence of size on crack localization zone was comparable to that of the parameter gradient but had a weaker characteristic on crack orientation, which represents the orientation of TGF. In particular, the characterization result of the TGF-rich zone using crack localization zone in the simulation closely matched that using lateral strain localization zone both in simulation and experiment. Regarding the size effects of the TGF-rich zone revealed in the simulation, the estimated field length of the TGF-rich zone accounted for approximately 30% of the zone width characterized by a horizontal thermal gradient, with maximum orthotropic deformation occurring at about 10% of the zone width. These observations validate the existence of TGF within the frozen curtain and contribute to the development of a precise grouting technique to mitigate subsidence within soil deposits subjected to freeze-thaw. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
24. Numerical Simulation on Effect of Indenter Radius During Point Load Test.
- Author
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Wang, Zhi, Ouyang, Yiping, and Yang, Qi
- Abstract
Copyright of Journal of Shanghai Jiaotong University (Science) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2024
- Full Text
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25. Selectivity Modulation of Multistep Reduction Reactions by Gold Nanoclusters.
- Author
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Zhang, Jing‐Zheng, Zhang, Yi‐Bao, Chai, Hui‐Li, Luo, Hui‐Ling, Du, Chen‐Xia, Huang, Ren‐Wu, and Zang, Shuang‐Quan
- Abstract
The selective synthesis of valuable azo‐ and azoxyaromatic chemicals via transfer coupling of nitroaromatic compounds has been achieved by fine‐tuning the catalyst structure. Here, a direct method to modulate nitrobenzene reduction and selectively alter the product from azobenzene to azoxybenzene by employing the size effect of Au is reported. Au nanoclusters (NCs) with smaller sizes embedded in ZIF‐8 controllably converted nitrobenzene into azoxybenzene, while supported Au nanoparticles (NPs) selectively catalyzed nitrobenzene reduction to azobenzene. X‐ray photoelectron spectroscopy (XPS) and Diffuse reflectance infrared Fourier transform spectroscopy on CO adsorption (CO‐DRIFTS) of Au NC/ZIF‐8 revealed a higher valence state and a lower electron density of Au than that of Au NP/ZIF‐8, combined with the desorption of azoxybenzene from the Au NC and Au NP surface, suggesting that the Au NCs with lower electron density exhibit stronger adsorption. Density functional theory (DFT) calculations and charge density difference maps indicated that azoxybenzene bonded to Au NC/ZIF‐8 with greater adsorption energy, resulting in more electron transfer between azoxybenzene and the generated Au sites, which inhibited further reduction of azoxybenzene and resulted in high azoxybenzene selectivity. The application of the size effect of Au particles to regulate nitrobenzene transfer coupling provided new insights into the structure‐selectivity relationships. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
26. Size Effects in Climatic Aging of Epoxy Basalt Fiber Reinforcement Bar.
- Author
-
Gavrilieva, Anna A., Startsev, Oleg V., Lebedev, Mikhail P., Krotov, Anatoly S., Kychkin, Anatoly K., and Lukachevskaya, Irina G.
- Subjects
- *
GLASS transition temperature , *GLOBAL warming , *BENDING strength , *PLASTIC fibers , *PULTRUSION - Abstract
The purpose of this study was to obtain information on the influence of the size factor on the climatic aging of circular fiber plastics produced by pultrusion. The kinetics of moisture transfer was obtained in humidification and drying modes at 60 °C in samples of epoxy basalt fiber reinforcement bars: after 28 months of exposure in the extremely cold climate of Yakutsk and 30 months of exposure in the moderately warm climate of Gelendzhik. It was shown that the 2D Langmuir model adequately describes the kinetics. The diffusion coefficients in the reinforcement direction for bars with diameters of 6, 8, 10, 16 and 20 mm turned out to be significantly higher than in the radial direction. To clarify the aging mechanism of the bars and the tensile, compressive and bending strength, the coefficient of linear thermal expansion and the glass transition temperature of the epoxy matrix of the bars with a diameter of 6, 8 and 10 mm after 51 months of exposure in Yakutsk and 54 months of exposure in Gelendzhik were measured. It was shown that after climatic exposure, the deformability of the bars decreased with increasing diameter of the bar; the glass transition temperature increased more significantly in the bar with a smaller diameter. In 6 mm diameter bars, the compressive and bending strength limits decreased by 10–25 % due to the plasticizing effect of moisture. With the same depth of moisture penetration into the volume of the samples, its effect on the strength of thin bars was significant, and for thick bars, it was insignificant. An increase in the glass transition temperature by 6 °C, associated with the additional curing of the polymer matrix, occurred in the surface layer of the epoxy basalt fiber reinforcement bars and was revealed in bars with a smaller diameter. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
27. Non-Propagating Cracks at the Fatigue Limit of Notches: An Analysis of Notch Sensitivity and Size Effect.
- Author
-
Chapetti, Mirco Daniel
- Subjects
- *
FATIGUE limit , *FRACTURE mechanics , *FATIGUE cracks , *CRACK propagation (Fracture mechanics) , *SENSITIVITY analysis , *HIGH cycle fatigue , *NOTCH effect - Abstract
The issues of the high-cycle fatigue resistance of notches and the role of non-propagating short cracks in defining the fatigue notch sensitivity and fatigue limit of the configuration are addressed. A fracture mechanics approach is employed to determine the threshold configuration that defines the associated fatigue limit. The influence of notch sharpness, notch size, intrinsic fatigue limit, microstructural dimensions, and the threshold for crack propagation is examined. A simple expression is proposed to estimate the maximum fatigue notch factor, kfMax, which incorporates the influence of these non-propagating cracks. The fatigue limits for both blunt and sharp elliptical notches are analyzed and predicted based on experimental results reported in the literature. Additionally, shallow notches or small defects are analyzed, where it is found that the same hypothesis may not be applicable. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
28. Mechanical Properties of Silicon Nitride in Different Morphologies: In Situ Experimental Analysis of Bulk and Whisker Structures.
- Author
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Wang, Bokang, Bai, Tanglong, Wang, Weide, and Zhang, Hongti
- Subjects
- *
MECHANICAL loads , *STRAINS & stresses (Mechanics) , *SILICON nitride , *NANOINDENTATION tests , *TENSILE tests , *NANOINDENTATION - Abstract
Silicon nitride (Si3N4) is widely used in structural ceramics and advanced manufacturing due to its excellent mechanical properties and high-temperature stability. These applications always involve deformation under mechanical loads, necessitating a thorough understanding of their mechanical behavior and performance under load. However, the mechanical properties of Si3N4, particularly at the micro- and nanoscale, are not well understood. This study systematically investigated the mechanical properties of bulk Si3N4 and Si3N4 whiskers using in situ SEM indentation and uniaxial tensile strategies. First, nanoindentation tests on bulk Si3N4 at different contact depths ranging from 125 to 450 nm showed significant indentation size effect on modulus and hardness, presumably attributed to the strain gradient plasticity theory. Subsequently, in situ uniaxial tensile tests were performed on Si3N4 whiskers synthesized with two different sintering aids, MgSiN2 and Y2O3. The results indicated that whiskers sintered with Y2O3 exhibited higher modulus and strength compared to those sintered with MgSiN2. This work provides a deeper understanding of the mechanical behavior of Si3N4 at the micro- and nanoscale and offers guidance for the design of high-performance Si3N4 ceramic whiskers. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
29. Size‐Dependent Catalytic Activity Over MOF‐Derived Cobalt Oxide Supported PdO Nanoparticles in Suzuki Reaction.
- Author
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Pan, Shiguang, Chen, Xue, Chen, Yang, Liu, Dan, Guo, Jia, Kuvarega, Alex T., Mamba, Bhekie B., and Gui, Jianzhou
- Subjects
- *
NANOPARTICLE size , *HETEROGENEOUS catalysis , *METAL nanoparticles , *SUZUKI reaction , *CATALYTIC activity - Abstract
ABSTRACT Palladium nanoparticles immobilized on ZIF 67‐derived porous CoOx were prepared by wet‐impregnation method, followed by calcination at different temperatures. The calcination temperature has been employed to effectively manipulate the size of metal nanoparticles, where higher calcination temperatures resulted in larger sizes. The experimental results revealed that by manipulating the calcination temperature, the synthesis of palladium nanoparticles with varying sizes could be effectively controlled. Increasing the calcination temperature resulted in larger particle sizes. At a calcination temperature of 350°C, the synthesis process produced the smallest palladium nanoparticles, averaging 1.35 nm in size, facilitating the reaction between aryl halides and arylboronic acids with yields ranging from 83% to 99%. Furthermore, these nanoparticles demonstrated superior catalytic activity and recyclability. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
30. Seeding Co Atoms on Size Effect‐Enabled V2C MXene for Kinetically Boosted Lithium–Sulfur Batteries.
- Author
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Song, Yingze, Sun, Yingjie, Chen, Le, Song, Lixian, Yang, Qin, Shi, Zixiong, Chen, Liang, and Cai, Wenlong
- Subjects
- *
CHEMICAL kinetics , *SYNCHROTRON radiation , *DENDRITIC crystals , *SEED size , *SULFUR , *LITHIUM sulfur batteries - Abstract
Lithium‐sulfur (Li–S) batteries are facing a multitude of challenges, mainly pertaining to the sluggish sulfur redox kinetics and rampant lithium dendrite growth on the cathode and anode side, respectively. In this sense, MXene has shown conspicuous advantages in serving as a dual‐functional promotor for Li–S batteries throughout the morphologic engineering, but still suffers from poor electrocatalytic activity and insufficient lithophilic sites. Herein, atomically dispersed Co sites are seeded onto the size effect‐enabled V2C MXene spheres (Co‐VC), leading to the generation of unique coordination configurations and rich active sites. Electrochemical tests combined with synchrotron radiation X‐ray 3D nano‐computed tomography and theoretical calculations unravel that Co‐VC with optimal coordination environments simultaneously boost sulfur reaction kinetics and lithium nucleation. As a consequence, Li–S batteries with Co‐VC modified separator can sustain a stable operation over 700 cycles with negligible capacity decay at 1.0 C, and delivers an areal capacity of 9.0 mAh cm−2 and desired cyclic performance at a high sulfur loading of 7.6 mg cm−2 with a lean electrolyte dosage of 4.0 µL mgS−1 at 0.1 C. The work opens a new avenue for boosting atomic‐scale site design with the aid of 2D substrates toward pragmatic Li–S batteries. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
31. Numerical verification of torsion-bar models based on the modified couple stress theory.
- Author
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Kwon, Young-Rok
- Abstract
AbstractThis study verifies the suitability of the classical Saint–Venant’s displacement field, originally intended for macroscale torsional behavior, to microscale torsion-bar models within the modified couple stress theory framework. Finite element analysis was conducted for bars with circular and rectangular cross-sections, and the results align closely with analytic solutions, which is confirmed by the energy ratio analysis. These results affirm the appropriateness of the displacement field for microscale torsion bars. Additionally, warping effects are observed to be minimal, even at the microscale. These findings validate torsion experiments for determining a material’s length scale parameter, advancing the understanding of microscale torsion. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
32. Scaling effects on the strain rate sensitivity of unidirectional and [+45/−45]s laminates under tensile loading.
- Author
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Siddiqui, Md Tareq and Keshavanarayana, Suresh Raju
- Subjects
- *
STRAIN rate , *CARBON composites , *FIBROUS composites , *CARBON fibers , *GLASS fibers - Abstract
The effects of geometric scaling on the strain rate sensitivity of unidirectional and [+45/−45]s laminates under uniaxial tensile loading has been investigated experimentally. Two material systems, Toray T800/3900-2B carbon/epoxy unitape and Newport NB321/7781 fiberglass/epoxy fabric, were used in the study. The nominal strain rates investigated ranged from quasi-static (0.0002 s−1) to moderate strain rates of 50 s−1 across the scaled specimen geometries. The geometric scaling effects at different strain rates were quantified in terms of the Weibull modulus. At each strain rate, the average failure stress of [0]4 carbon, [0]4 fiberglass, and [±45]s fiberglass showed a declining trend with increasing specimen size. However, the percentage of the strength reduction was less significant at higher strain rates compared to the quasi-static strain rate. In contrast to the other stacking sequences, [+45/−45]s carbon specimens showed a maximum percentage in strength reduction at a high strain rate compared to the quasi-static strain rate, indicating increased scaling effect with strain rate. The magnitude of Weibull modulus (m) for the specimens increased with strain rate indicating diminishing scaling effects, while [+45/−45]s carbon specimens exhibited an opposite trend. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
33. Behavior of geometrically-similar Basalt FRP bars-reinforced concrete beams under dynamic torsional loads.
- Author
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Lei, Yushuang, Jin, Liu, Yu, Wenxuan, and Du, Xiuli
- Subjects
- *
STRAIN rate , *POLYMER-impregnated concrete , *CONCRETE beams , *DYNAMIC loads , *DUCTILITY , *TORSIONAL load - Abstract
A numerical model utilizing 3D mesoscale simulation methods was developed to investigate the influence of strain rate on the torsional performance of geometrically similar Basalt Fiber Reinforced Polymer bars-reinforced concrete (BFRP-RC) beams, as well as the corresponding size effects. The model incorporates concrete heterogeneity, material strain rate effects, and the dynamic bond-slip relationship between BFRP bars and concrete. The torsional performance of BFRP-RC beams with different structural sizes and stirrup ratios was analyzed under different strain rates. The study yielded the following findings: (1) The damage degree of BFRP-RC beams increases with the rising strain rate. (2) Increasing strain rate and stirrup ratio enhances the beams' torsional strength and ductility while attenuating the size effect, albeit not eliminating it. (3) The impact of increasing strain rate on beam strength, ductility, and size effect outweighs that of increasing stirrup ratio. Finally, based on the Bažant size effect law (SEL) combined with the simulation results, a new size effect law was proposed that can quantitatively consider the effect of strain rate and stirrup ratio on the torsional strength of BFRP-RC beams. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
34. Torsional vibration of a flexoelectric nanotube with micro-inertia effect.
- Author
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Hrytsyna, O., Sladek, J., Sladek, V., Deng, Q., and Hrytsyna, M.
- Subjects
- *
STRAINS & stresses (Mechanics) , *STRAIN tensors , *ENERGY density , *TORSIONAL vibration , *FREE vibration , *LAMINATED composite beams , *ROTATIONAL motion , *NANOTUBES , *QUADRUPOLES - Abstract
The modified strain gradient theory (MSGT) with flexoelectric and micro-inertia effects is developed to study the free vibration of tube made of elastic centrosymmetric materials. Within this theory, the internal energy density is the function of the strain tensor, deviatoric part of stretch gradient and rotation gradient tensors, dilatation gradient, polarization vector, and electric quadrupoles. The linear coupled governing equations and boundary conditions are derived from the Hamilton variation principle. The torsional vibration problem is analytically solved for non-piezoelectric nanotube with fixed edges. The effect of the nanotube geometry, flexoelectric coefficient, micro-inertia, and micro-stiffness parameters on the natural frequency is studied. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
35. A Comparative Study on Shear Size Effect of Steel-And BFRP-RC Shear Walls Under Cyclic Lateral Loads.
- Author
-
Jin, Liu, Miao, Liyue, Chen, Fengjuan, Li, Dong, and Du, Xiuli
- Subjects
- *
REINFORCING bars , *SHEAR walls , *LATERAL loads , *CYCLIC loads , *SHEAR strength , *REINFORCED concrete - Abstract
This paper presents a comparative study on the size effect behaviors of shear performances of concrete shear walls reinforced by steel bars and Basalt Fiber Reinforced Polymer (BFRP) bars. All the works are conducted through a two-dimensional meso-scale numerical simulation model representing the concrete shear wall. The horizontal reinforcement ratio and the sectional size are the main parameters concerned by the present study. Both the seismic behaviors under cyclic loading and the size effect behaviors of the shear performances were simulated and investigated. It can be concluded from the simulation results, (1) the use of steel bars or BFRP bars as horizontal reinforcement does not change the shear failure modes of concrete shear walls, (2) the size effect on the nominal shear strength of BFRP reinforced concrete (BFRP-RC) shear wall is more significant compared to that for steel-RC shear wall, (3) the increase of horizontal reinforcement ratio improves the shear capacity of the concrete shear wall, while weakens the size effect on the nominal shear strength, and (4) the size effect law for the nominal shear strength of steel-RC shear wall is applicable to BFRP-RC shear wall. Finally, the importance of considering size effect in the evaluation of shear performance of steel-/BFRP-RC shear wall is manifested by comparing the predictive results of several popular design codes with the simulation results. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
36. 基于名义粒径的砂岩颗粒破碎强度及颗粒集合 抗剪强度的尺寸效应研究.
- Author
-
邱珍锋, 雷蕊忆, 陈人瑗, 刘景红, 冯 毅, and 方 俊
- Abstract
Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2024
- Full Text
- View/download PDF
37. 基于 PFC-GBM 非均质模型的砂岩裂纹演化 细观规律研究.
- Author
-
张国桥, 孙 鹏, 吴祥业, 王婧雅, 郭文斌, and 田宇航
- Subjects
ACOUSTIC emission ,MINERALS ,CRYSTAL models ,FAILURE mode & effects analysis ,COMPRESSIVE strength - Abstract
Copyright of China Mining Magazine is the property of China Mining Magazine Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2024
- Full Text
- View/download PDF
38. Nanoindentation Creep Behavior of Hexagonal Close-Packed High-Entropy Alloys.
- Author
-
Wang, Z., Yang, X. W., Zhang, Q., and Qiao, J. W.
- Abstract
The effects of maximum load and loading rate on the creep behavior of the single-phase hexagonal close-packed structured GdHoLaTbY alloy at room temperature were investigated by nanoindentation. The hardness, creep depth, creep rate, and stress exponent strongly dependent on the maximum load and loading rate. The creep behavior of the alloy at different maximum loads shows a significant indentation size effect. The creep behavior is dominated by free diffusion at the sample surface at low load retaining loads and by dislocation sliding at high load retaining loads. The creep behavior of the current alloy is greatly sensitive to the indentation loading rate at different loading rates. High loading rates give rise to stress fields with high dislocation density and high strain gradients, which results in a large stress index during the loading retention stage. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
39. REV and Three-Dimensional Permeability Tensor of Fractured Rock Masses with Heterogeneous Aperture Distributions.
- Author
-
Huang, Na, Han, Shengqun, Jiang, Yujing, and Han, Songcai
- Subjects
RADIOACTIVE waste sites ,GEOLOGICAL mapping ,ROCK permeability ,GEOLOGICAL maps ,FRACTURING fluids - Abstract
This study performed a representative elementary volume (REV) and 3D equivalent continuum study of rock fractures based on fluid simulations of 3D discrete fracture networks (DFNs). A series of 3D DFNs with heterogeneous aperture distributions (the DFN-H model) and uniform apertures (the DFN-I model) were established, in which the fractures were oriented according to the geological field mapping of a high-level radioactive waste candidate site in China. The 3D DFNs of the different model sizes were extracted and rotated in a number of directions to check whether there was a tensor quality of the permeability at a certain scale. The results show that aperture heterogeneity increases the REV size and results in a necessarily larger model size to reach an equivalent continuum behavior, and this effect is more obvious when the fracture density is smaller. The shape of the 2D permeability contour is irregular, with some breaks when the model size is small. As the model size increases, its shape gradually tends to become smooth and approaches an ellipse. The shape of the permeability contours of the DFN-H model is slender compared to the DFN-I model, indicating a larger difference between the minimum and maximum values of the permeability. For the DFN-H model, there is no appropriate approximation for the equivalent permeability tensor over the studied model size range, whereas a good fit of the permeability ellipsoid is obtained for the DFN-I model, and the 3D directional permeability is calculated at this model scale. The corresponding magnitude and direction of the principal permeability are obtained, which can be viewed as the equivalent permeability tensor for the approximated continuum medium. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
40. Experimental Study on Scale Effect of Eccentrically Compressed Reinforced Concrete Columns Strengthened with Carbon Fiber-Reinforced Polymer.
- Author
-
Jianhui Si, Yuan Zhou, Zhaobao Zeng, Kai Li, Jiannan Hu, Zewei Liu, and Xinchao Ding
- Subjects
CARBON fiber-reinforced plastics ,CONCRETE columns ,REINFORCED concrete ,STEEL bars ,DUCTILITY - Abstract
Strictly following the similarity principle of specimen size, eccentricity, and carbon fiber-reinforced polymer (CFRP) strengthening layers, three groups of reinforced concrete square columns with different scales were designed. Experimental studies on eccentric compression of unstrengthened columns and CFRP-strengthened columns were carried out. The failure characteristics of specimens of various sizes were obtained, as well as the bearing capacity, ductility coefficient, lateral deflection, CFRP, and steel bar strain were analyzed. The test results showed an improved ductility, stiffness, and bearing capacity of eccentrically compressed reinforced concrete columns, strengthened with CFRP. However, the strengthening effect is inversely proportional to the size of the specimen and has a more obvious size effect. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
41. Regulating photocatalytic overall water splitting of ferroelectric heterostructures by size effect.
- Author
-
Ye, Zixing, Yu, Daifu, Zhang, Ruian, Qin, Fei, Sun, Yiran, Huang, Jie, Zhou, Zhanqi, Tian, He, Han, Gaorong, Ren, Zhaohui, and Liu, Gang
- Subjects
FERROELECTRIC materials ,FERROELECTRICITY ,OXYGEN evolution reactions ,PHOTOCATALYSTS ,HETEROSTRUCTURES - Abstract
In the past decade, ferroelectric materials have been intensively explored as promising photocatalysts. An intriguing ability of ferroelectrics is to directly sperate the photogenerated electrons and holes, which is believed to arise from a spontaneous polarization. Understanding how polarization affects the photocatalytic performance is vital to design high-efficiency photocatalysts. In this work, we report a size effect of ferroelectric polarization on regulating the photocatalytic overall water splitting of SrTiO
3 /PbTiO3 nanoplate heterostructures for the first time. This was realized hydrothermally by controlling the thickness and thus spontaneous polarization strength of single-crystal and single-domain PbTiO3 nanoplates, which served as the substrate for selective heteroepitaxial growth of SrTiO3 . An enhancement of 22 times in the photocatalytic overall water splitting performance of the heterostructures has been achieved when the average thickness of the nanoplate increases from 30 to 107 nm. A combined experimental investigation revealed that the incompletely compensated depolarization filed is the dominated driving force for the photogenerated carrier separation within heterostructures, and its increase with the thickness of the nanoplates accounts for the enhancement of photocatalytic activity. Moreover, the concentration of oxygen vacancies for negative polarization compensation has been found to grow as the thickness of the nanoplates increases, which promotes oxygen evolution reaction and reduces the stoichiometric ratio of H2 /O2 . These findings may provide the opportunity to design and develop high-efficiency ferroelectric photocatalysts. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
42. The Effect of Monomer Size on Fusion and Coupling in Colloidal Quantum Dot Molecules.
- Author
-
Levi, Adar, Hou, Bokang, Alon, Omer, Ossia, Yonatan, Verbitsky, Lior, Remennik, Sergei, Rabani, Eran, and Banin, Uri
- Subjects
atomistic pseudopotential calculations ,colloidal quantum dots ,electronic coupling ,quantum dot molecules ,size effect - Abstract
The fusion step in the formation of colloidal quantum dot molecules, constructed from two core/shell quantum dots, dictates the coupling strength and hence their properties and enriched functionalities compared to monomers. Herein, studying the monomer size effect on fusion and coupling, we observe a linear relation of the fusion temperature with the inverse nanocrystal radius. This trend, similar to that in nanocrystal melting, emphasizes the role of the surface energy. The suggested fusion mechanism involves intraparticle ripening where atoms diffuse to the reactive connecting neck region. Moreover, the effect of monomer size and neck filling on the degree of electronic coupling is studied by combined atomistic-pseudopotential calculations and optical measurements, uncovering strong coupling effects in small QD dimers, leading to significant optical changes. Understanding and controlling the fusion and hence coupling effect allows tailoring the optical properties of these nanoscale structures, with potential applications in photonic and quantum technologies.
- Published
- 2023
43. Grain size dependence of twin nucleation in magnesium alloys
- Author
-
Hai Xin, Mei Zhan, Yudong Lei, Zhiyan Sun, Pandi Zhao, Yuyang Wang, and Zebang Zheng
- Subjects
Magnesium alloy ,Crystal plasticity ,Twin nucleation ,Size effect ,Stored energy density ,Mining engineering. Metallurgy ,TN1-997 - Abstract
Twinning plays a prominent role in the plastic deformation of low-symmetry crystals such as magnesium alloys. However, the capture of twin nucleation has been challenging since the process is rapid and difficult to predict, making it impossible to observe directly. Because of this, the understanding of the fundamental twinning mechanism through experiments and simulation techniques incorporating twinning has progressed slowly. In this study, a quantitative analysis integrating an in-situ three-point bending experiment and crystal plasticity modeling was conducted on the twin nucleation in AZ31 magnesium alloys with different grain sizes. The threshold for triggering twin nucleation has been quantified. The prediction ability of three widely used criteria for twin nucleation, i.e., geometrically necessary dislocation (GND) density, von Mises stress, and stored energy density, is evaluated. The results suggest that only the stored energy density is able to capture the twin nucleation location accurately in all the considered grain sizes. The critical value exhibits an exponential reduction with the increase in grain size. Based on the quantitative analysis, the mechanism of the grain size effect on twin nucleation is proposed.
- Published
- 2024
- Full Text
- View/download PDF
44. Size effect of amorphous layers on radiation resistance in Cu/Nb multilayers.
- Author
-
Yan, Zhe, Yang, Wenfan, Pang, Jingyu, Yao, Jiahao, Zhang, Jian, Yang, Lixin, Zheng, Shijian, Wang, Jian, and Ma, Xiuliang
- Subjects
COPPER ,MULTILAYERS ,RADIATION ,INTERFACE structures ,THERMAL stability ,MULTILAYERED thin films - Abstract
• The multilayers with ultra-thin amorphous layers exhibit the best radiation resistance. • The amorphous thickness can affect the interface structure during amorphous crystallization. • The hardness change is attributed to amorphous crystallization, dislocation nucleation-induced softening and radiation defects-induced hardening. Utilizing multilayer engineering to connect crystalline and amorphous can not only improve the mechanical properties but also enhance the radiation resistance of multilayers. However, the non-monotonic dependence of radiation resistance on the amorphous thickness necessitates an in-depth investigation into the size effect of the amorphous layer. Taking the Cu-Nb system as the prototype, we reveal the radiation resistance of Cu/Nb multilayers with varying thicknesses of the CuNb amorphous layer. After irradiation, multilayers with 0, 0.8, and 2 nm amorphous show flat or non-flat interface structures due to distinct crystalline growth processes during amorphous crystallization. Notably, multilayers with 0.8 nm amorphous exhibit the optimal radiation response, because the ultra-thin amorphous layer shows better thermal stability and slower crystallization rate that can annihilate more radiation defects and effectively inhibit defects growth. Furthermore, a quantitative analysis elucidates the reasons for hardness changes, which are attributed to amorphous crystallization, dislocation nucleation-induced softening, and radiation defects-induced hardening. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
45. Symplectic solutions for orthotropic micropolar plane stress problem.
- Author
-
Chen, Long, Tang, Zhaofei, Wu, Qiong, and Gao, Qiang
- Abstract
The symplectic approach was utilized to derive solutions to the orthotropic micropolar plane stress problem. The Hamiltonian canonical equation was first obtained by applying Legendre’s transformation and the Hamiltonian mixed energy variational principle. Then, by using the method of separation of variables, the eigenproblem of the corresponding homogeneous Hamiltonian canonical equation was derived. Subsequently, the corresponding eigensolutions for three kinds of homogeneous boundary conditions were derived. According to the adjoint symplectic orthogonality of the eigensolutions and expansion theorems, the solutions to this plane stress problem were expressed as a series expansion of these eigensolutions. The numerical results for the orthotropic micropolar plane stress problem under various boundary conditions were presented and validated using the finite element method, which confirmed the convergence and accuracy of the proposed approach. We also investigated the relationship between the size-dependent behaviour and material parameters using the proposed approach. Furthermore, this approach was applied to analyze lattice structures under an equivalent micropolar continuum approximation. [ABSTRACT FROM AUTHOR]
- Published
- 2025
- Full Text
- View/download PDF
46. Nonlocal dual-phase-lag thermoelastic damping in small-sized circular cross-sectional ring resonators.
- Author
-
Hai, Liang and Kim, Dong Jun
- Abstract
The purpose of current research is to establish a theoretical size-dependent framework for estimating the amount of thermoelastic damping (TED) in miniaturized rings with circular cross section via the nonlocal dual-phase-lag (NDPL) generalized thermoelasticity theory, as one of the most exhaustive non-Fourier heat conduction models. The method used to achieve this goal is based on the definition of TED in the energy dissipation (ED) approach. To do so, after deriving heat equation in the context of NDPL model, the distribution of temperature all over the volume of the ring is specified. Then, the relations of dissipated thermal energy and strain energy in the ring are obtained. Lastly, by employing ED approach, a formula comprising the nonclassical parameters of NDPL model is rendered to determine TED value in small-scaled toroidal rings. By presenting various numerical examples, the dependence of TED on influential parameters including nonclassical thermal constants in NDPL model, ring geometry, vibrational mode number and ring material is surveyed. The Findings enlighten that the inclusion of nonlocal parameter into the model can have conspicuous impacts on TED value, especially in smaller rings or higher vibrational mode numbers. The results also reveal that among the investigated materials (i.e. silicon, copper, silver, and lead), rings made of lead and silicon exhibit the maximum and minimum TED values, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
47. Variational-based modeling of a piezoelectric/elastic bilayer beam with flexoelectricity.
- Author
-
Fan, Tao
- Abstract
Flexoelectricity incorporating electric polarization and strain gradients exists in all dielectrics. In the present work, the function of Hamilton's principle of the elastic dielectric materials considering the flexoelectric effect is established and its stationary conditions are also obtained. A bilayer beam composed of elastic and piezoelectric parts is modeled to investigate flexoelectricity under both mechanical and electrical loads. Based on Hamilton's principle, the governing equation and boundary conditions of a piezoelectric/elastic bilayer beam with generalized supporting ends are deduced. Accordingly, the analytical solutions to the horizontal displacements are derived. It is found that the flexoelectric effects depend on the size heavily, which is dominant for the structures at nanoscale but had hardly influence on the larger ones. Moreover, the piezoelectric/elastic bilayer beam behaves much better on controlling of the bending flexibility by adjusting the thickness ratio of the two parts. It's hopeful to provide guidance for designing and optimizing nanoscale electronic devices. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
48. Sound transmission loss optimization of clamped double-panels.
- Author
-
Zhang, Yumei, Li, Ye, Xiao, Xinbiao, Zhao, Yue, Yao, Dan, Ai, Yi, and Pan, Weijun
- Abstract
The panel cavity structure is one of the key components of the aircraft (vehicle) body and is among the main noise transmission pathways. Based on the modal superposition and Galerkin method, this paper realizes the theoretical model of sound insulation of the clamped, double-panel structure. The non-dominated sorting genetic algorithm-II (NSGA-II) is used to realize the sound insulation of the clamped double-panel structure. Through optimization, the fitting function and law of structural surface density and the optimized normal weighted sound insulation Pareto fronts were obtained. The results show that among the optimization, for the Pareto front cases, their double-panel thickness ratio h 1/ h 2 is relatively far away from 1, and the corresponding cavity thickness H is relatively large. The influence of boundary conditions and size effects of lightweight sound insulation optimization are also discussed. The research on the influence of boundary and size indicates that the difference in the optimal weighted sound insulation Pareto fronts corresponding to the same surface density is mostly within the 1 dB range. Both the boundary and thickness of the panel will affect the frequency STL, while the boundary conditions or structure size changed, even the total thickness of panels needs to be the same, and the structure can also have similar weighted sound transmission loss (R w) when the thickness ratio of the double-panel structure is chosen properly. The difference of material effects is also discussed. This research provides a method for the sound insulation optimization of clamped double-panel structures concerning the boundary and size effect. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
49. Mesoscopic simulation of coal cylinders confined by CFRP with different sizes
- Author
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Qingwen LI, Ying LI, Xinggang ZENG, Kangkang XU, and Xiangdong ZHANG
- Subjects
size effect ,coal cylinders ,carbon fiber reinforced polymer(cfrp) ,strength model ,uniaxial compression ,Mining engineering. Metallurgy ,TN1-997 - Abstract
In order to study the size effect law of carbon fiber reinforced polymer (CFRP) constrained coal cylinders, a numerical model of coal circular confined by carbon fiber reinforced polymer (CFRP) sheet is established by a three-dimensional PFC-FLAC coupling method. The validity of the model was verified with experimental data. On this basis, the study of the size effect of 0, 1, 2 and 3 layers of CFRP sheet on different sizes (50 mm, 100 mm, 150 mm) of coal cylinders were studied; the functional relationship of the evolution law of compressive strength under different layer number (L) is obtained; the functional relationship of elastic modulus evolution under different number of layers is obtained; a modified Richart strength analysis model of coal cylinder confined by CFRP sheet is established. The results show that when the number of CFRP sheets is constant, the compressive strength of coal cylinders is constrained by different sizes of CFRP sheets, and the size effect is obvious; the relative peak strength enhancement ratio of coal cylinder constrained by CFRP sheet increases with the increase of the size. The elastic modulus of a coal cylinder with a diameter of 50 mm increases with the number of CFRP layers. The elastic modulus of a coal cylinder with a diameter of 100 mm and 150 mm increases first and then decreases at 0≤L≤3 layers, showing an obvious layer effect law. The accumulation of cracks increases with the increase of the number of CFRP layers.
- Published
- 2024
- Full Text
- View/download PDF
50. Study on the size effect of rock burst tendency of red sandstone under uniaxial compression
- Author
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Feng Chen, Jinyang Du, Jinguo Lv, Chun’an Tang, and Yishan Pan
- Subjects
Rock burst ,Deformation modulus ratio ,Uniaxial compressive strength ,Size effect ,Energy conversion law ,Medicine ,Science - Abstract
Abstract The study of rock burst tendency of rock masses with different sizes plays a key role in the prevention of rock burst. Through theoretical analysis, it is proposed that uniaxial compressive strength and deformation modulus ratio are the key mechanical parameters affecting rock burst occurrence. In order to find out the size effect of uniaxial compressive strength and deformation modulus ratio, theoretical analysis and uniaxial compression experiment are carried out on rock samples with different heights, different cross-sectional areas and different volumes. The results show that the smaller the uniaxial compressive strength is, the larger the deformation modulus ratio is, and the more likely rock burst are to occur. On the contrary, rock burst is still not easy to generate. The uniaxial compressive strength of rock samples with different heights, different cross-sectional areas and different volumes increases with the increase of rock sample size. The deformation modulus ratio of rock samples with different heights and different volumes shows an upward trend on the whole, while that of rock samples with different cross-sectional areas shows a downward trend on the whole. The fracture forms of rock are analyzed using the energy conversion law in the process of deformation and failure for three kinds of rock with different shapes and sizes.
- Published
- 2024
- Full Text
- View/download PDF
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