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1
Wang, Ying, Zhen Wang, and Yuqian Zheng. "Analysis of Fatigue Crack Propagation of an Orthotropic Bridge Deck Based on the Extended Finite Element Method." Advances in Civil Engineering 2019 (July 25, 2019): 1–14. http://dx.doi.org/10.1155/2019/6319821.
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As one of the most fatigue-sensitive parts of an orthotropic steel bridge deck, the weld between the U-rib and the top deck is prone to fatigue cracking under the actions of the stress concentration, welding residual stress, and vehicle load. To investigate the mechanism of fatigue crack propagation and the influence of the welding residual stress on the propagation patterns of fatigue cracks, a multiscale modeling method was proposed, and the static analysis and the dynamic propagation analysis of fatigue crack were carried out in this paper. First, a multiscale finite element model was established, including whole bridge models with a scale feature of 102 m, orthotropic bridge deck models with a scale feature of 100 m, and crack models with a scale feature of 10−3 m. Then, a segmental model of the bridge deck was extracted, which is regarded as a critical location of the bridge, and the shell-solid coupling method is adopted in the segmental model in order to further analyze the crack propagation rule. Moreover, based on the extended finite element method (XFEM), the static crack and dynamic crack propagation in this critical position were analyzed. Finally, thermoelastoplastic analysis was carried out on the connection of the U-rib and deck with a length of 500 mm to obtain the residual stress, and then the results of residual stress were introduced into the segmental model to further study its influence on the evolution of fatigue crack propagation. The analysis of the welding process shows that near the weld region of the connection of the U-rib and deck, the peak value of the residual tensile stress can reach the material yield strength. The static analysis of fatigue cracks shows that under the single action of a standard fatigue vehicle load, the fatigue details at the weld toe of the deck cannot reach the tensile stress required for fatigue crack propagation, and only the fatigue details at the weld toe of the U-rib can meet the requirements of fatigue crack propagation. The dynamic analysis of fatigue cracks reveals that the crack in the weld toe of the U-rib is a mixed-mode crack with modes I, II, and III. The propagation of a fatigue crack without a residual stress field will be terminated until the crack length is extended to a certain length. Nevertheless, when the residual stress field was introduced, the growth angle and size of the fatigue crack would increase, and no crack closure occurs. For the crack in the weld toe of the deck, the crack is in the closed state under the standard fatigue vehicle load. When the residual stress field is introduced, the tensile stress of the fatigue details increases. Meanwhile, the fatigue crack will become a mixed-mode crack with modes I, II, and III that will be dominated by mode I and extend toward the weld at a slight deflection angle. The results of various initial crack sizes at the weld toes of the top deck are analyzed, which shows that the initial crack size has a certain effect on the fatigue crack growth rate, especially the initial crack depth.
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Fang, Chang Yu, and Yao Ting Zhang. "Model Test and Structural Behavior Analysis for Cable-Pylon Anchorage Zone of Cable-Stayed Bridge." Advanced Materials Research 368-373 (October 2011): 495–500. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.495.
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In long-span cable-stay bridges, anchorage zone of cable-pylon is a key part to transfer cable force to pylon. Because of local concentrated force, irregular pylon section and complicated construction measures, a general mechanical analysis is unable to reflect actual stress distribution and working performance of anchorage zone. Based on Maling River Bridge in Guizhou province, China, clear finite element analysis and reliable full-scale model test for cable-pylon anchorage zone segment were carried out. Not only were design of model test and loading program introduced, but also test content and sensor arrangement were documented. In addition, details of finite element modeling were involved too, such as mesh generation, boundary condition and loading cases. Through comparison and analysis of stress increment and crack observation, the location where larger local tensile stress occurred was obtained. Corresponding anti-cracking load coefficient and safety coefficient of crack width were also presented. Parts of research findings have been used for the guidance of bridge construction.
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NEUGEBAUER, R., R. WERTHEIM, and U. SEMMLER. "THE ATOMIC FINITE ELEMENT METHOD AS A BRIDGE BETWEEN MOLECULAR DYNAMICS AND CONTINUUM MECHANICS." Journal of Multiscale Modelling 03, no. 01n02 (March 2011): 39–47. http://dx.doi.org/10.1142/s1756973711000339.
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On cutting tools for high performance cutting (HPC) processes or for hard-to-cut materials, there is an increased importance in so-called superlattice coatings with hundreds of layers each of which is only a few nanometers in thickness. Homogeneity or average material properties based on the properties of single layers are not valid in these dimensions any more. Consequently, continuum mechanical material models cannot be used for modeling the behavior of nanolayers. Therefore, the interaction potentials between the single atoms should be considered. A new, so-called atomic finite element method (AFEM) is presented. In the AFEM the interatomic bonds are modeled as nonlinear spring elements. The AFEM is the connection between the molecular dynamics (MD) method and the crystal plasticity FEM (CPFEM). The MD simulates the atomic deposition process. The CPFEM considers the behavior of anisotropic crystals using the continuum mechanical FEM. On one side, the atomic structure data simulated by MD defines the interface to AFEM. On the other side, the boundary conditions (displacements and tractions) of the AFEM model are interpolated from the CPFEM simulations. In AFEM, the lattice deformation, the crack and dislocation behavior can be simulated and calculated at the nanometer scale.
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Kulynych, Viktoriia, Valerii Chebenko, Ruslan Puzyr, and Iryna Pieieva. "Modelling the influence of gaseous products of explosive detonation on the processes of crack treatment while rock blasting." Mining of Mineral Deposits 15, no. 3 (September 2021): 102–7. http://dx.doi.org/10.33271/mining15.03.102.
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Purpose is mathematical modeling of fracturing as well as influence of gaseous products of explosive detonation on the changes in rock strength. Methods. Mathematical model, using foundations of Griffith theory, has been developed. To explain conditions of bridge formation while exploding lead azide charges, a two-stage description of solid particle condensation at a crack surface and inside it has been applied using the smoothed particle hydrodynamics. The analysis, involved electronic microscope, has helped verified the results experimentally. Findings. The effect of rock mass disturbance, resulting from explosive destruction, is manifested maximally right after the action. Subsequently, it decreases owing to the gradual relaxation of the formed defects. Therefore, an urgent problem is to develop ways slowing down strength restore of the blasted rock mass fragments. The process of rock fragment strength restoring may be prevented by microparticles getting into the microcrack cavities together with the detonation products. The research simulates their action. The data correlate to the simulation results confirming potential influence of the blasted rock on the dynamics of changes in the strength characteristics of the rock mass. Various compositions of charges with shells made of inert solid additions have been applied which solid particles can avoid the process of microcrack closure. Originality. For the first time, the possibility of deposition formation within rock micro- and macrocracks has been proposed and supported mathematically. Practical implications. Strength properties of the finished product and the energy consumption during impulse loading as well as subsequent mechanical processing of nonmetallic building materials depend on the strength properties of rock mass fragments. Hence, the ability to control the strength restore has a great practical value. Moreover, it can be implemented during the blasting operations.
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Yi, J., and J. Li. "Longitudinal Seismic Behavior of a Single-Tower Cable-Stayed Bridge Subjected to Near-Field Earthquakes." Shock and Vibration 2017 (2017): 1–16. http://dx.doi.org/10.1155/2017/1675982.
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Cable-stayed bridges are quite sensitive to large amplitude oscillations from earthquakes and seismic damage was observed for Shipshaw Bridge and Chi-Lu Bridge during past earthquakes. In order to investigate seismic damage of cable-stayed bridges, a 1 : 20 scale model of a single-tower cable-stayed bridge with A-shaped tower was designed, constructed, and tested on shake tables at Tongji University, China. One typical near-field ground motion was used to excite the model from low to high intensity. Test result showed that severe structural damage occurred at the tower of the model including parallel concrete cracks from bottom to nearly half height of the tower, concrete spalling, and exposed bars at top tower 0.2 m above the section where two skewed legs intersect. Posttest analysis was conducted and compared with test results. It is revealed that the numerical model was able to simulate the seismic damage of the test model by modeling nonlinearity of different components for cable-stayed bridges, namely, the tower, bents, superstructure, cables, and bearings. Numerical analysis also revealed that cable relaxation, which was detected during the test, had limited influence on the overall seismic response of the bridge with maximum error of 12%.
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Todo, Mitsugu, Yoshihiro Fukuya, Seiya Hagihara, and Kazuo Arakawa. "Finite Element Modeling of Damage Formation in Rubber-Toughened Polymer." Key Engineering Materials 297-300 (November 2005): 1019–24. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1019.
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Microscopic studies on the toughening mechanism of rubber-toughened PMMA (RTPMMA) were carried out using a polarizing optical microscope (POM) and a transmission electron microscope (TEM). POM result showed that in a typical RT-PMMA, a damage zone was developed in the vicinity of crack-tip, and therefore, it was considered that energy dissipation due to the damage zone development was the primary toughening mechanism. TEM result exhibited that the damage zone was a crowd of micro-crazes generated around rubber particles in the vicinity of notch-tip. Finite element analysis was then performed to simulate such damage formations in crack-tip region. Macro-scale and micro-scale models were developed to simulate damage zone formation and micro-crazing, respectively, with use of a damage model. It was shown that the damage model introduced was successfully applied to predict such kind of macro-damage and micro-craze formations.
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Sun, Bin, You-Lin Xu, Qing Zhu, and Zhaoxia Li. "Concurrent multi-scale fatigue damage evolution simulation method for long-span steel bridges." International Journal of Damage Mechanics 28, no. 2 (December 29, 2017): 165–82. http://dx.doi.org/10.1177/1056789517750460.
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Fatigue damage is one of the leading causes for structural failure of long-span steel bridges, but fatigue damage evolution of a long-span steel bridge is very complex. This study proposes a concurrent multi-scale fatigue damage evolution simulation method for long-span steel bridges from micro short crack nucleation and growth to macro structural component damage until mega structural failure. As a case study, the fatigue damage evolution of the Stonecutters Bridge in Hong Kong under cyclic vehicle loading is finally simulated using the proposed method. It shows that the proposed method is computationally feasible even for such a large scale structure. The method can provide a clear picture how micro short cracks grow into macro fatigue damage of structural components and eventually lead to mega structural failure.
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Tserpes, Konstantinos, and Christos Kora. "A Multi-Scale Modeling Approach for Simulating Crack Sensing in Polymer Fibrous Composites Using Electrically Conductive Carbon Nanotube Networks. Part II: Meso- and Macro-Scale Analyses." Aerospace 5, no. 4 (October 9, 2018): 106. http://dx.doi.org/10.3390/aerospace5040106.
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This is the second of a two-paper series describing a multi-scale modeling approach developed to simulate crack sensing in polymer fibrous composites by exploiting interruption of electrically conductive carbon nanotube (CNT) networks. The approach is based on the finite element (FE) method. Numerical models at three different scales, namely the micro-scale, the meso-scale and the macro-scale, have been developed using the ANSYS APDL environment. In the present paper, the meso- and macro-scale analyses are described. In the meso-scale, a two-dimensional model of the CNT/polymer matrix reinforced by carbon fibers is used to develop a crack sensing methodology from a parametric study which relates the crack position and length with the reduction of current flow. In the meso-model, the effective electrical conductivity of the CNT/polymer computed from the micro-scale is used as input. In the macro-scale, the final implementation of the crack sensing methodology is performed on a CNT/polymer/carbon fiber composite volume using as input the electrical response of the cracked CNT/polymer derived at the micro-scale and the crack sensing methodology. Analyses have been performed for cracks of two different lengths. In both cases, the numerical model predicts with good accuracy both the length and position of the crack. These results highlight the prospect of conductive CNT networks to be used as a localized structural health monitoring technique.
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Zaami, Amin, and Ali Shokuhfar. "Scale-Dependent Crack Modeling for Investigation the Effect of Geometrically Necessary Dislocations in Micro/Nano Grain Size of Copper." Advanced Engineering Forum 15 (February 2016): 1–16. http://dx.doi.org/10.4028/www.scientific.net/aef.15.1.
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In this study, a scale-dependent model is employed to investigate the size effects of copper on the behavior of the crack-tip. This model includes the homogeneous and non-homogeneous strain hardening based on the wavelet interpretation of size effect. Introducing additional micro/nano structural considerations together with decreasing grain size, different size effects can be obtained. As the size dependency is not taken into account in conventional plasticity, an enhanced theory which is related to the strain gradient introduces a length scale will give more realistic representations of state variables near the crack-tip. Accordingly, the contribution of geometrically necessary dislocations (GNDs) activity on strengthening and stress concentration factor is identified in the crack-tip. Finally, the affected zone which is dominated by presence of GNDs is identified
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Liang, Shixue, Xiaodan Ren, and Jie Li. "A mesh-size-objective modeling of quasi-brittle material using micro-cell informed damage law." International Journal of Damage Mechanics 27, no. 6 (June 9, 2017): 913–36. http://dx.doi.org/10.1177/1056789517713335.
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A multi-scale approach for mesh size independent finite element analysis of quasi-brittle material is proposed in this article. The homogenization based multi-scale damage representation is first introduced in obtaining the damage law from micro-cell simulation with consideration of microscopic crack propagation. The key idea to remedy the mesh size sensitivity in the 2D macroscopic finite element analysis is to introduce a damage law directly from the micro-cell simulation, where the micro-cell size should be identical to the macroscopic mesh size. The micro-cells with different sizes are generated and the corresponding simulations are presented in the numerical tests to obtain the micro-cell dependent damage law. The mesh independent finite element analysis results of the notched beam and the double-edge notched specimen affirm the strategy of correcting the mesh sensitivity.
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Stentoumis, C., E. Protopapadakis, A. Doulamis, and N. Doulamis. "A HOLISTIC APPROACH FOR INSPECTION OF CIVIL INFRASTRUCTURES BASED ON COMPUTER VISION TECHNIQUES." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B5 (June 15, 2016): 131–38. http://dx.doi.org/10.5194/isprsarchives-xli-b5-131-2016.
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In this work, it is examined the 2D recognition and 3D modelling of concrete tunnel cracks, through visual cues. At the time being, the structural integrity inspection of large-scale infrastructures is mainly performed through visual observations by human inspectors, who identify structural defects, rate them and, then, categorize their severity. The described approach targets at minimum human intervention, for autonomous inspection of civil infrastructures. The shortfalls of existing approaches in crack assessment are being addressed by proposing a novel detection scheme. Although efforts have been made in the field, synergies among proposed techniques are still missing. The holistic approach of this paper exploits the state of the art techniques of pattern recognition and stereo-matching, in order to build accurate 3D crack models. The innovation lies in the hybrid approach for the CNN detector initialization, and the use of the modified census transformation for stereo matching along with a binary fusion of two state-of-the-art optimization schemes. The described approach manages to deal with images of harsh radiometry, along with severe radiometric differences in the stereo pair. The effectiveness of this workflow is evaluated on a real dataset gathered in highway and railway tunnels. What is promising is that the computer vision workflow described in this work can be transferred, with adaptations of course, to other infrastructure such as pipelines, bridges and large industrial facilities that are in the need of continuous state assessment during their operational life cycle.
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Stentoumis, C., E. Protopapadakis, A. Doulamis, and N. Doulamis. "A HOLISTIC APPROACH FOR INSPECTION OF CIVIL INFRASTRUCTURES BASED ON COMPUTER VISION TECHNIQUES." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B5 (June 15, 2016): 131–38. http://dx.doi.org/10.5194/isprs-archives-xli-b5-131-2016.
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In this work, it is examined the 2D recognition and 3D modelling of concrete tunnel cracks, through visual cues. At the time being, the structural integrity inspection of large-scale infrastructures is mainly performed through visual observations by human inspectors, who identify structural defects, rate them and, then, categorize their severity. The described approach targets at minimum human intervention, for autonomous inspection of civil infrastructures. The shortfalls of existing approaches in crack assessment are being addressed by proposing a novel detection scheme. Although efforts have been made in the field, synergies among proposed techniques are still missing. The holistic approach of this paper exploits the state of the art techniques of pattern recognition and stereo-matching, in order to build accurate 3D crack models. The innovation lies in the hybrid approach for the CNN detector initialization, and the use of the modified census transformation for stereo matching along with a binary fusion of two state-of-the-art optimization schemes. The described approach manages to deal with images of harsh radiometry, along with severe radiometric differences in the stereo pair. The effectiveness of this workflow is evaluated on a real dataset gathered in highway and railway tunnels. What is promising is that the computer vision workflow described in this work can be transferred, with adaptations of course, to other infrastructure such as pipelines, bridges and large industrial facilities that are in the need of continuous state assessment during their operational life cycle.
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Chen, Yung Tsang. "An Experimental Study on the use of Fiber-Reinforced Concrete in Bridge Approach Slabs." Applied Mechanics and Materials 361-363 (August 2013): 1217–22. http://dx.doi.org/10.4028/www.scientific.net/amm.361-363.1217.
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Fiber-reinforced concrete is well known for crack control by bridging cracks in the concrete. Short, discontinuous fibers are added into plain concrete to provide post-cracking ductility to the fiber-reinforced concrete. Although fiber-reinforced concrete has been used in various civil engineering applications, the practical application of fiber-reinforced concrete in bridge approach slabs is rarely found. In this paper, steel fibers, serving as macro-fibers, and polyvinyl alcohol fibers, serving as micro-fibers, were added to the approach slab concrete for crack control purpose. This paper describes flexural tests of four fiber-reinforced concrete beams and loading test of a full scale fiber-reinforced concrete approach slab. Results from the flexural beam test show that the addition of fibers greatly improves the fracture toughness of the concrete. Results from the loading test show that the overall performance of the slab is comparable to conventional reinforced concrete approach slabs, and the surface cracks on the slab due to negative moment can be adequately controlled by the addition of steel and polyvinyl alcohol fibers into concrete, even without top reinforcement mat.
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Li, Bei Xing, Ai Jun Guan, and Ming Kai Zhou. "Preparation and Performances of Self-Compacting Concrete Used in the Joint Section between Steel and Concrete Box Girders of Edong Yangtze River Highway Bridge." Advanced Materials Research 168-170 (December 2010): 334–40. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.334.
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The joint section between steel and concrete box girders is the key localization of the super-long span hybrid girder cable-stayed bridge in the Edong Yangtze River, a high strength self-compacting concrete (SCC) was required to use in the joint section. This paper systematically investigated the performances of three types of C55 grade self-compacting concretes (SCCs), such as plain SCC, micro-expansion and polypropylene fiber reinforced SCC and steel fiber reinforced SCC. The results indicated that the steel fiber reinforced SCC had the best workability and mechanical properties. The flexural toughness of the steel fiber reinforced SCC was much better than that of the other two types of concretes. The addition of steel fiber, or polypropylene fiber and expansive agent improved the crack resistance of SCC, and the micro-expansion and polypropylene fiber SCC reinforced had better crack resistance than steel fiber reinforced SCC. The three types of SCCs have very high chloride penetration resistance and advanced freezing and thawing resistance. Moreover, the test achievement of concrete casting technology for the full-scale model of steel girder chambers in the joint section is introduced. The steel fiber reinforced SCC was preferred to be used in the steel-concrete joint section.
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Tserpes, Konstantinos, and Christos Kora. "A multi-scale modeling approach for simulating crack sensing in polymer fibrous composites using electrically conductive carbon nanotube networks. Part I: Micro-scale analysis." Computational Materials Science 154 (November 2018): 530–37. http://dx.doi.org/10.1016/j.commatsci.2018.07.048.
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Gong, Fuyuan, Yuya Takahashi, and Koichi Maekawa. "Multi-scale computational modeling for concrete damage by mixed pore pressures – case of coupled alkali–silica reaction and cyclic freeze/thaw." Engineering Computations 35, no. 6 (August 6, 2018): 2367–85. http://dx.doi.org/10.1108/ec-11-2017-0431.
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Purpose This paper aims to propose a multi-scale simulation approach for the concrete macro-mechanical damage caused by mixed micro-pore pressures, such as the coupled alkali–silica reaction (ASR) and freeze-thaw cycles (FTC). Design/methodology/approach The micro-physical events are computationally modeled by considering the coupling effect between ASR gel and condensed water in the mixed pressure and motion. The pressures and transport of pore substances are also linked with the concrete matrix deformation at macro-scale through a poro-mechanical approach, and affect each other, reciprocally. Once the crack happens in the nonlinear analysis, both the micro-events (water and gel motion) and the macro mechanics will be mutually interacted. Finally, different sequences of combined ASR and FTC are simulated. Findings The multi-chemo mechanistic computation can reproduce complex events in pore structures, and further the macro-damages. The results show that ASR can reduce the FTC expansion for non-air-entrained concrete, but may increase the frost damage for air-entrained concrete. The simulation is examined to bring about the observed phenomena. Originality/value This paper numerically clarifies the strong linkage between macro-mechanical deformation and micro-chemo-physical events for concrete composites under coupled ASR and FTC.
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Hu, Jiang. "Multi-scale numerical simulation analysis for influence of combined leaching and frost deteriorations on mechanical properties of concrete." Multidiscipline Modeling in Materials and Structures 12, no. 4 (November 14, 2016): 648–71. http://dx.doi.org/10.1108/mmms-03-2016-0013.
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Purpose The multi-scale numerical simulation method, able to represent the complexity of the random structures and capture phase degradation, is an effective way to investigate the long-term behavior of concrete in service and bridges the gap between research on the material and on the structural level. However, the combined chemical-physical deterioration mechanisms of concrete remain a challenging task. The purpose of this paper is to investigate the degradation mechanism of concrete at the waterline in cold regions induced by combined calcium leaching and frost damage. Design/methodology/approach With the help of the NIST’s three-dimensional (3D) hydration model and the random aggregate model, realistic 3D representative volume elements (RVEs) of concrete at the micro-, the meso-, and the macro-scales can be reconstructed. The boundary problem method is introduced to compute the homogenized mechanical properties for both sound and damaged RVEs. According to the damage characteristics, the staggering method including a random dissolution model and a thermo-mechanical coupling model is developed to simulate the synergy deterioration effects of interacted calcium leaching and frost attacks. The coupled damage procedure for the frost damage process is based on the hydraulic pressure theory and the ice lens growth theory considering the relationship between the frozen temperature and the radius of the capillary pore. Finally, regarding calcium leaching as the leading role in actual engineering, the numerical methodology for combined leaching and frost damage on concrete property is proposed using a successive multi-scale method. Findings On the basis of available experimental data, this methodology is employed to explore the deterioration process. The results agree with the experimental ones to some extent, chemical leaching leads to the nucleation of some micro-cracks (i.e. damage), and consequently, to the decrease of the frost resistance. Originality/value It is demonstrated that the multi-scale numerical methodology can capture potential aging and deterioration evolution processes, and can give an insight into the macroscopic property degradation of concrete under long-term aggressive conditions.
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Nosov, Victor V., Egor V. Grigoriev, Sabina A. Peretyatko, and Artem P. Artyushchenko. "Nanotechnologies of Strength Control of Materials." Materials Science Forum 1040 (July 27, 2021): 101–8. http://dx.doi.org/10.4028/www.scientific.net/msf.1040.101.
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The strength of materials is determined by their atomic molecular structure and the process of decay of atomic molecular bonds, which must be taken into account when optimizing materials strength control technologies. The fracture photomicrograph of metal microdamage of welded joint at various moments of time, a multilevel model of flow of acoustic emission signals of materials are presented. The physical meaning, the scale level of parameters included in the model are revealed. The structure of the mathematical model of the flow of AE signals with components of its informative elements of different scale level by strength characteristics of structural materials and resource of technical objects is shown. The multilevel model of the AE signal flow is hierarchically structured, obtained by generalizing deterministic-statistical variability. It describes the process of randomly recording deterministic accumulated damages in the material both before and after the formation of a crack at the stage of waiting for its next leap. It is shown that the proposed nanotechnology of strength control of materials is reduced to non-destructive determination of parameters of prognostic homogeneous destruction, identification of which is based on multilevel modeling of time dependence of micro-crack formation, formulation of criterion of strength homogeneity, registration of AE parameters related to the model of a specific product, which can be automated processing of registration results and determination of universal strength nanoconstants from already published reference data of fatigue tests of standard material samples.
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Statnik, Eugene S., Semen D. Ignatyev, Andrey A. Stepashkin, Alexey I. Salimon, Dilyus Chukov, Sergey D. Kaloshkin, and Alexander M. Korsunsky. "The Analysis of Micro-Scale Deformation and Fracture of Carbonized Elastomer-Based Composites by In Situ SEM." Molecules 26, no. 3 (January 22, 2021): 587. http://dx.doi.org/10.3390/molecules26030587.
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Carbonized elastomer-based composites (CECs) possess a number of attractive features in terms of thermomechanical and electromechanical performance, durability in aggressive media and facile net-shape formability, but their relatively low ductility and strength limit their suitability for structural engineering applications. Prospective applications such as structural elements of micro-electro-mechanical systems MEMS can be envisaged since smaller principal dimensions reduce the susceptibility of components to residual stress accumulation during carbonization and to brittle fracture in general. We report the results of in situ in-SEM study of microdeformation and fracture behavior of CECs based on nitrile butadiene rubber (NBR) elastomeric matrices filled with carbon and silicon carbide. Nanostructured carbon composite materials were manufactured via compounding of elastomeric substance with carbon and SiC fillers using mixing rolling mill, vulcanization, and low-temperature carbonization. Double-edge notched tensile (DENT) specimens of vulcanized and carbonized elastomeric composites were subjected to in situ tensile testing in the chamber of the scanning electron microscope (SEM) Tescan Vega 3 using a Deben microtest 1 kN tensile stage. The series of acquired SEM images were analyzed by means of digital image correlation (DIC) using Ncorr open-source software to map the spatial distribution of strain. These maps were correlated with finite element modeling (FEM) simulations to refine the values of elastic moduli. Moreover, the elastic moduli were derived from unloading curve nanoindentation hardness measurements carried out using a NanoScan-4D tester and interpreted using the Oliver–Pharr method. Carbonization causes a significant increase of elastic moduli from 0.86 ± 0.07 GPa to 14.12 ± 1.20 GPa for the composite with graphite and carbon black fillers. Nanoindentation measurements yield somewhat lower values, namely, 0.25 ± 0.02 GPa and 9.83 ± 1.10 GPa before and after carbonization, respectively. The analysis of fractography images suggests that crack initiation, growth and propagation may occur both at the notch stress concentrator or relatively far from the notch. Possible causes of such response are discussed, namely, (1) residual stresses introduced by processing; (2) shape and size of fillers; and (3) the emanation and accumulation of gases in composites during carbonization.
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Kim, Hoejin, Bethany R. Wilburn, Edison Castro, Carlos A. Garcia Rosales, Luis A. Chavez, Tzu-Liang Bill Tseng, and Yirong Lin. "Multifunctional SENSING using 3D printed CNTs/BaTiO3/PVDF nanocomposites." Journal of Composite Materials 53, no. 10 (September 27, 2018): 1319–28. http://dx.doi.org/10.1177/0021998318800796.
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This research studied multifunctional sensing capabilities on nanocomposites composed of poly(vinylidene) fluoride (PVDF), BaTiO3 (BT), and multiwall carbon nanotubes (CNTs) fabricated by fused-deposition modeling 3D printing. To improve the dielectric property within BT/PVDF composites, CNTs have been utilized to promote ultrahigh polarization density and local micro-capacitor among BT and polymer matrix. The 3D printing process provides homogeneous dispersion of nanoparticles, alleviating agglomeration of nanoparticles, and reducing micro-crack/voids in matrix which can enhance their dielectric property. In this research, we demonstrated that by utilizing unique advantages of this material combination and a 3D printing technique, sensing capabilities for temperature and strain can be engineered with different content variations of included BT and CNTs. It is observed that the sensing capability for temperature change with respect to a 25–150℃ range can be improved as both BT and CNTs’ inclusions increase and is maximal with 1.7 wt.% CNTs/60 wt.% BT/PVDF nanocomposites, while the sensing capability for strain change in a 0–20% range is maximal with 1 wt.% CNTs/12 wt.% BT/PVDF nanocomposites. In addition, it is found that the best combination for mechanical toughness is 1 wt.% CNTs/12 wt.% BT/PVDF with 24.2 MPa and 579% in ultimate tensile strength and failure strain, respectively. These results show the technique to 3D print multifunctional nanocomposites with temperature and strain sensing capabilities as well as increased mechanical property. Furthermore, this research demonstrated the feasibility for large-scale multifunctional sensor device manufacturing with freedom of design, low-cost, and an accelerated process.
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Thomas, Akhil, Ali Riza Durmaz, Thomas Straub, and Chris Eberl. "Automated Quantitative Analyses of Fatigue-Induced Surface Damage by Deep Learning." Materials 13, no. 15 (July 24, 2020): 3298. http://dx.doi.org/10.3390/ma13153298.
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The digitization of materials is the prerequisite for accelerating product development. However, technologically, this is only beneficial when reliability is maintained. This requires comprehension of the microstructure-driven fatigue damage mechanisms across scales. A substantial fraction of the lifetime for high performance materials is attributed to surface damage accumulation at the microstructural scale (e.g., extrusions and micro crack formation). Although, its modeling is impeded by a lack of comprehensive understanding of the related mechanisms. This makes statistical validation at the same scale by micromechanical experimentation a fundamental requirement. Hence, a large quantity of processed experimental data, which can only be acquired by automated experiments and data analyses, is crucial. Surface damage evolution is often accessed by imaging and subsequent image post-processing. In this work, we evaluated deep learning (DL) methodologies for semantic segmentation and different image processing approaches for quantitative slip trace characterization. Due to limited annotated data, a U-Net architecture was utilized. Three data sets of damage locations observed in scanning electron microscope (SEM) images of ferritic steel, martensitic steel, and copper specimens were prepared. In order to allow the developed models to cope with material-specific damage morphology and imaging-induced variance, a customized augmentation pipeline for the input images was developed. Material domain generalizability of ferritic steel and conjunct material trained models were tested successfully. Multiple image processing routines to detect slip trace orientation (STO) from the DL segmented extrusion areas were implemented and assessed. In conclusion, generalization to multiple materials has been achieved for the DL methodology, suggesting that extending it well beyond fatigue damage is feasible.
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Shang, Jian Ku, and R. O. Ritchie. "Crack-Tip Shielding in Metal-Matrix Composites: Modelling Of Crack Bridging by Uncracked Ligaments." MRS Proceedings 120 (1988). http://dx.doi.org/10.1557/proc-120-81.
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AbstractAs part of an investigation into the micro-mechanisms of crack-tip shielding associated with the growth of fatigue cracks in metal-matrix composites, simple models are developed for the role of crack bridging in high-strength aluminum alloys reinforced with SiC particulate (AI/SiCp). Based on experimental observations of crack growth, crack-tip shielding and crack-path morphology in these alloys, the bridges are found to be associated with uncracked ligaments in the wake of the crack tip, and are modelled in terms of approaches based on a critical crack-opening displacement or critical tensile strain in the ligament.
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Jiang, Hongyong, Yiru Ren, and Qiduo Jin. "A novel synergistic multi-scale modeling framework to predict micro- and meso-scale damage behaviors of 2D triaxially braided composite." International Journal of Damage Mechanics, July 25, 2021, 105678952110339. http://dx.doi.org/10.1177/10567895211033974.
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A novel synergistic multi-scale modeling framework with a coupling of micro- and meso-scale is proposed to predict damage behaviors of 2D-triaxially braided composite (2DTBC). Based on the Bridge model, the internal stress and micro damage of constituent materials are respectively coupled with the stress and damage of tow. The initial effective elastic properties of tow (IEEP) used as the predefined data are estimated by micro-mechanics models. Due to in-situ effects, stress concentration factor (SCF) is considered in the micro matrix, exhibiting progressive damage accumulation. Comparisons of IEEP and strengths between the Bridge and Chamis’ theory are conducted to validate the values of IEEP and SCF. Based on the representative volume element (RVE), the macro properties and damage modes of 2DTBC are predicted to be consistent with available experiments and meso-scale simulation. Both axial and transverse damage mechanisms of 2DTBC under tensile or compressive load are revealed. Micro fiber and matrix damage accumulations have significant effects on the meso-scale axial and transverse damage of tows due to multi-scale coupling effects. Different from existing meso-/multi-scale models, the proposed multi-scale model can capture a crucial phenomenon that the transverse damage of tow is vulnerable to micro fiber fracture. The proposed multi-scale framework provides a robust tool for future systematic studies on constituent materials level to larger-scale aeronautical materials.
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Deng, Zhifei, Hongshun Chen, Ting Yang, Zian Jia, James C. Weaver, Pavel D. Shevchenko, Francesco De Carlo, Reza Mirzaeifar, and Ling Li. "Strategies for simultaneous strengthening and toughening via nanoscopic intracrystalline defects in a biogenic ceramic." Nature Communications 11, no. 1 (November 10, 2020). http://dx.doi.org/10.1038/s41467-020-19416-2.
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Abstract While many organisms synthesize robust skeletal composites consisting of spatially discrete organic and mineral (ceramic) phases, the intrinsic mechanical properties of the mineral phases are poorly understood. Using the shell of the marine bivalve Atrina rigida as a model system, and through a combination of multiscale structural and mechanical characterization in conjunction with theoretical and computational modeling, we uncover the underlying mechanical roles of a ubiquitous structural motif in biogenic calcite, their nanoscopic intracrystalline defects. These nanoscopic defects not only suppress the soft yielding of pure calcite through the classical precipitation strengthening mechanism, but also enhance energy dissipation through controlled nano- and micro-fracture, where the defects’ size, geometry, orientation, and distribution facilitate and guide crack initialization and propagation. These nano- and micro-scale cracks are further confined by larger scale intercrystalline organic interfaces, enabling further improved damage tolerance.
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Buehler, Markus J., Alexander Hartmaier, and Huajian Gao. "Constrained Grain Boundary Diffusion In Thin Copper Films." MRS Proceedings 821 (2004). http://dx.doi.org/10.1557/proc-821-p1.2.
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AbstractIn a recent study of diffusional creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in micro- and nanostructured materials.