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Zhaodong, Ding, i Li Jie. "A physically motivated model for fatigue damage of concrete". International Journal of Damage Mechanics 27, nr 8 (13.08.2017): 1192–212. http://dx.doi.org/10.1177/1056789517726359.
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The fatigue problem of concrete is still a challenging topic in the researches and applications of concrete engineering. This paper aims to develop a fatigue damage evolution law based model for concrete motivated by the analysis of physical mechanism. In this model, the fatigue energy dissipation process at microscale is investigated with rate process theory. The concept of self-similarity is employed to bridge the scale gap between microscale cracking and mesoscale dissipative element. With the stochastic fracture model, the crack avalanches and macro-crack nucleation processes from mesoscale to macroscale are simulated to obtain the behaviors of macroscope damage evolution of concrete. In conjunction with continuum damage mechanics framework, the fatigue damage constitutive model for concrete is then proposed. Numerical simulations are carried out to verify the model, revealing that the proposed model accommodates well with physical mechanism of fatigue damage evolution of concrete whereby the fatigue life of concrete structures under different stress ranges can be predicted.
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Zhang, Di, Lu Zheng, Ping Li, Gongnan Xie i Yonghui Xie. "A Combined Numerical and Experimental Analysis on Erythrocyte Damage Mechanism in Microscale Flow". Advances in Mechanical Engineering 5 (styczeń 2013): 962658. http://dx.doi.org/10.1155/2013/962658.
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Chandra, A., Y. Huang, Z. Q. Jiang, K. X. Hu i G. Fu. "A Model of Crack Nucleation in Layered Electronic Assemblies Under Thermal Cycling". Journal of Electronic Packaging 122, nr 3 (5.11.1999): 220–26. http://dx.doi.org/10.1115/1.1286100.
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A model for crack nucleation in layered electronic assemblies under thermal cycling is developed in this paper. The present model includes three scales: (i) at the microscale or the mechanism level, the damage mechanisms such as diffusive void growth or fatigue cracks, determine the damage growth rate; (2) at an intermediate mesoscale, the localized damage bands are modeled as variable stiffness springs connecting undamaged materials; and (iii) at the macroscale or the continuum level, the localized damage band growing in an otherwise undamaged material is modeled as an array of dislocations. The three scales are then combined together to incorporate damage mechanisms into continuum analysis. Traditional fracture mechanics provides a crack propagation model based on pre-existing cracks. The present work provides an approach for predicting crack nucleation. The proposed model is then utilized to investigate crack nucleations in three-layered electronic assemblies under thermal cycling. The damage is observed to accumulate rapidly in the weakest regions of the band. Estimates are obtained for critical time or critical number of cycles at which a macroscopic crack will nucleate in these assemblies under thermal cycling. This critical number of cycles is found to be insensitive to the size of the damage cluster, but decreases rapidly as the local excess damage increases. [S1043-7398(00)00503-X]
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Chen, Junjie, Jinhee Kim, Wenhao Shao, Stephen H. Schlecht, So Young Baek, Alexis K. Jones, Taeyong Ahn, James A. Ashton-Miller, Mark M. Banaszak Holl i Edward M. Wojtys. "An Anterior Cruciate Ligament Failure Mechanism". American Journal of Sports Medicine 47, nr 9 (lipiec 2019): 2067–76. http://dx.doi.org/10.1177/0363546519854450.
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Background: Nearly three-quarters of anterior cruciate ligament (ACL) injuries occur as “noncontact” failures from routine athletic maneuvers. Recent in vitro studies revealed that repetitive strenuous submaximal knee loading known to especially strain the ACL can lead to its fatigue failure, often at the ACL femoral enthesis. Hypothesis: ACL failure can be caused by accumulated tissue fatigue damage: specifically, chemical and structural evidence of this fatigue process will be found at the femoral enthesis of ACLs from tested cadaveric knees, as well as in ACL explants removed from patients undergoing ACL reconstruction. Study Design: Controlled laboratory study. Methods: One knee from each of 7 pairs of adult cadaveric knees were repetitively loaded under 4 times–body weight simulated pivot landings known to strain the ACL submaximally while the contralateral, unloaded knee was used as a comparison. The chemical and structural changes associated with this repetitive loading were characterized at the ACL femoral enthesis at multiple hierarchical collagen levels by employing atomic force microscopy (AFM), AFM–infrared spectroscopy, molecular targeting with a fluorescently labeled collagen hybridizing peptide, and second harmonic imaging microscopy. Explants from ACL femoral entheses from the injured knee of 5 patients with noncontact ACL failure were also characterized via similar methods. Results: AFM–infrared spectroscopy and collagen hybridizing peptide binding indicate that the characteristic molecular damage was an unraveling of the collagen molecular triple helix. AFM detected disruption of collagen fibrils in the forms of reduced topographical surface thickness and the induction of ~30- to 100-nm voids in the collagen fibril matrix for mechanically tested samples. Second harmonic imaging microscopy detected the induction of ~10- to 100-µm regions where the noncentrosymmetric structure of collagen had been disrupted. These mechanically induced changes, ranging from molecular to microscale disruption of normal collagen structure, represent a previously unreported aspect of tissue fatigue damage in noncontact ACL failure. Confirmatory evidence came from the explants of 5 patients undergoing ACL reconstruction, which exhibited the same pattern of molecular, nanoscale, and microscale structural damage detected in the mechanically tested cadaveric samples. Conclusion: The authors found evidence of accumulated damage to collagen fibrils and fibers at the ACL femoral enthesis at the time of surgery for noncontact ACL failure. This tissue damage was similar to that found in donor knees subjected in vitro to repetitive 4 times–body weight impulsive 3-dimensional loading known to cause a fatigue failure of the ACL. Clinical Relevance: These findings suggest that some ACL injuries may be due to an exacerbation of preexisting hierarchical tissue damage from activities known to place larger-than-normal loads on the ACL. Too rapid an increase in these activities could cause ACL tissue damage to accumulate across length scales, thereby affecting ACL structural integrity before it has time to repair. Prevention necessitates an understanding of how ACL loading magnitude and frequency are anabolic, neutral, or catabolic to the ligament.
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Cao, Minghua, Konstantinos P. Baxevanakis i Vadim V. Silberschmidt. "Effect of Graphite Morphology on the Thermomechanical Performance of Compacted Graphite Iron". Metals 13, nr 3 (24.02.2023): 473. http://dx.doi.org/10.3390/met13030473.
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Compacted graphite iron (CGI) has gained significant attention in automotive industry applications thanks to its superior thermomechanical properties and competitive price. Its main fracture mechanism at the microscale—interfacial damage and debonding between graphite inclusions and a metallic matrix—can happen under high-temperature service conditions as a result of a mismatch in the coefficients of thermal expansion between the two phases of CGI. Macroscopic fracture in cast iron components can be initiated by interfacial damage at the microscale under thermomechanical load. This phenomenon was investigated in various composites but still lacks information for CGI, with its complex morphology of graphite inclusions. This research focuses on the effect of this morphology on the thermomechanical performance of CGI under high temperatures. A set of three-dimensional finite-element models was created, with a unit cell containing a single graphite inclusion embedded in a cubic domain of the metallic matrix. Elastoplastic behaviour was assumed for both phases in numerical simulations. The effect of graphite morphology on the thermomechanical performance of CGI was investigated for pure thermal loading, focusing on a high-temperature response of its constituents. The results can provide a deeper understanding of the correlation between graphite morphology and CGI fracture mechanisms under high temperatures.
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Lian, Jun He, Xiao Xu Jia, Sebastian Münstermann i Wolfgang Bleck. "A Generalized Damage Model Accounting for Instability and Ductile Fracture for Sheet Metals". Key Engineering Materials 611-612 (maj 2014): 106–10. http://dx.doi.org/10.4028/www.scientific.net/kem.611-612.106.
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With the requirement of vehicle performance and fuel economy, dual-phase (DP) steels as one of the advanced high stress steels (AHSS) are increasingly used in the automotive industry due to the excellent combination of the tensile strength and ductility. On a microscale the ductile fracture is governed by the void nucleation, growth and coalescence mechanism. In the dual-phase steels this damage mechanism exhibits a rather complex situation: voids are generated by the debonding of the hard phase from the matrix and the inner cracking of the hard phase besides by inclusions. On a macroscale fracture of these materials is observed in the automotive industry with the absence of strain localization or minimal post-necking deformation. Consequently the failure during the forming process is caused by a competitive or combined mechanism of internal damage evolution and metal instability. In this study, the target is to develop a simple and generalized model for metal forming processes accounting for instability, damage and ductile fracture. Theoretical predictions of metal instability by the Hill–Swift necking criterion and the modified maximum force criterion are considered. The damage model is developed by the combination of the prediction of metal instability and ductile fracture of sheet metals. The model is developed in 3D triaxial stress state and the accumulation of damage is stress state dependent. Furthermore, the influence of the hardening curve effected by damage on the forming limit curve is investigated.
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González, Sergio, Gianluca Laera, Sotiris Koussios, Jaime Domínguez i Fernando A. Lasagni. "Simulation of thermal cycle aging process on fiber-reinforced polymers by extended finite element method". Journal of Composite Materials 52, nr 14 (12.10.2017): 1947–58. http://dx.doi.org/10.1177/0021998317734625.
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The simulation of long life behavior and environmental aging effects on composite materials are subjects of investigation for future aerospace applications (i.e. supersonic commercial aircrafts). Temperature variation in addition to matrix oxidation involves material degradation and loss of mechanical properties. Crack initiation and growth is the main damage mechanism. In this paper, an extended finite element analysis is proposed to simulate damage on carbon fiber reinforced polymer as a consequence of thermal fatigue between −50℃ and 150℃ under atmospheres with different oxygen content. The interphase effect on the degradation process is analyzed at a microscale level. Finally, results are correlated with the experimental data in terms of material stiffness and, hence, the most suitable model parameters are selected.
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Chen, Wei, Lei Huang, Yaoyao Liu, Yanfei Zhao, Zhe Wang i Zhiwen Xie. "Oxidative Corrosion Mechanism of Ti2AlNb-Based Alloys during Alternate High Temperature-Salt Spray Exposure". Coatings 12, nr 10 (20.09.2022): 1374. http://dx.doi.org/10.3390/coatings12101374.
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This study investigates the corrosion damage mechanisms of Ti2AlNb-based alloys under high temperature, salt spray and coupled high temperature-salt spray conditions. This alloy was analysed in detail from macroscopic to microscopic by means of microscale detection (XRD, SEM and EDS). The results indicated that Ti2AlNb-based alloy surface oxide layer is dense and complete, and the thickness is only 3 µm after oxidation at 650 °C for 400 h. Compared to the original sample, the production of the passivation film resulted in almost no damage to Ti2AlNb-based alloy after 50 cycles of salt spray testing at room temperature. The tests showed that Ti2AlNb alloy shows good erosion resistance at 650 °C and in salt spray. However, this alloy had an oxide layer thickness of up to 30 µm and obvious corrosion pits on the surface after 50 cycles of corrosion under alternating high temperature-salt spray conditions. The Cl2 produced by the mixed salt eutectic reaction acted as a catalytic carrier to accelerate the volatilisation of the chloride inside the oxide layer and the re-oxidation of the substrate. In addition, the growth of unprotected corrosion products (Na2TiO3, NaNbO3 and AlNbO4) altered the internal structure of the oxide layer, destroying the surface densification and causing severe damage to the alloy surface.
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Falk, Martin, i Michael Hausmann. "A Paradigm Revolution or Just Better Resolution—Will Newly Emerging Superresolution Techniques Identify Chromatin Architecture as a Key Factor in Radiation-Induced DNA Damage and Repair Regulation?" Cancers 13, nr 1 (23.12.2020): 18. http://dx.doi.org/10.3390/cancers13010018.
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DNA double-strand breaks (DSBs) have been recognized as the most serious lesions in irradiated cells. While several biochemical pathways capable of repairing these lesions have been identified, the mechanisms by which cells select a specific pathway for activation at a given DSB site remain poorly understood. Our knowledge of DSB induction and repair has increased dramatically since the discovery of ionizing radiation-induced foci (IRIFs), initiating the possibility of spatiotemporally monitoring the assembly and disassembly of repair complexes in single cells. IRIF exploration revealed that all post-irradiation processes—DSB formation, repair and misrepair—are strongly dependent on the characteristics of DSB damage and the microarchitecture of the whole affected chromatin domain in addition to the cell status. The microscale features of IRIFs, such as their morphology, mobility, spatiotemporal distribution, and persistence kinetics, have been linked to repair mechanisms. However, the influence of various biochemical and structural factors and their specific combinations on IRIF architecture remains unknown, as does the hierarchy of these factors in the decision-making process for a particular repair mechanism at each individual DSB site. New insights into the relationship between the physical properties of the incident radiation, chromatin architecture, IRIF architecture, and DSB repair mechanisms and repair efficiency are expected from recent developments in optical superresolution microscopy (nanoscopy) techniques that have shifted our ability to analyze chromatin and IRIF architectures towards the nanoscale. In the present review, we discuss this relationship, attempt to correlate still rather isolated nanoscale studies with already better-understood aspects of DSB repair at the microscale, and consider whether newly emerging “correlated multiscale structuromics” can revolutionarily enhance our knowledge in this field.
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Xu, Zhi-Hui, Young-Bae Park i Xiaodong Li. "Nano/micro-mechanical and tribological characterization of Ar, C, N, and Ne ion-implanted Si". Journal of Materials Research 25, nr 5 (maj 2010): 880–89. http://dx.doi.org/10.1557/jmr.2010.0117.
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Ion implantation has been widely used to improve the mechanical and tribological properties of single crystalline silicon, an essential material for the semiconductor industry. In this study, the effects of four different ion implantations, Ar, C, N, and Ne ions, on the mechanical and tribological properties of single crystal Si were investigated at both the nanoscale and the microscale. Nanoindentation and microindentation were used to measure the mechanical properties and fracture toughness of ion-implanted Si. Nano and micro scratch and wear tests were performed to study the tribological behaviors of different ion-implanted Si. The relationship between the mechanical properties and tribological behavior and the damage mechanism of scratch and wear were also discussed.
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Sirinakorn, T., i V. Uthaisangsuk. "Investigation of damage initiation in high-strength dual-phase steels using cohesive zone model". International Journal of Damage Mechanics 27, nr 3 (19.11.2016): 409–38. http://dx.doi.org/10.1177/1056789516679718.
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Dual-phase steels have been increasingly used for several vehicle structural parts due to their great combination of high strength and good formability. However, for an effective forming process of such steel sheets, their complex failure mechanism on the microscale plays an important role. In this work, damage initiation occurrences in two dual-phase steel grades were examined by a micromechanics-based final element modeling approach. Two-dimensional representative volume element models were applied to take into account amount, morphologies, and distributions of each constituent phase. Uniaxial tensile tests and fractography of the examined steels were carried out in order to characterize crack formation in the microstructure. According to a dislocation-based theory and local alloys partitioning, stress–strain curves were defined for the individual phases and interphases, where geometrically necessary dislocations were present due to austenite–martensite transformation. Cohesive zone model with extended finite element method and two-dimensional damage locus were applied in the representative volume elements for describing crack initiation induced by martensite cracking and ductile fracture of ferrite, respectively. Parameters of the damage models were identified by means of correlation between experimental and final element simulation results. The states of damage initiation of both dual-phase steels were predicted. Local stress, strain, and damage distributions in the dual-phase microstructures were determined and discussed.
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Abbas, Yassir M. "Microscale Cohesive-Friction-Based Finite Element Model for the Crack Opening Mechanism of Hooked-End Steel Fiber-Reinforced Concrete". Materials 14, nr 3 (1.02.2021): 669. http://dx.doi.org/10.3390/ma14030669.
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The entire mechanical properties of steel fiber-reinforced concrete (SFRC) are significantly dependent on the fiber–matrix interactions. In the current study, a finite element (FE) model was developed to simulate the pullout response of hooked-end SFRC employing cohesive–frictional interactions. Plain stress elements were adapted in the model to exemplify the fiber process constituents, taking into consideration the material nonlinearity of the hooked-end fiber. Additionally, a surface-to-surface contact model was used to simulate the fiber’s behavior in the pullout mechanism. The model was calibrated against experimental observations, and a modification factor model was proposed to account for the 3D phenomenalistic behavior of the pullout behavior. Realistic predictions were obtained by using this factor to predict the entire pullout-slip curves and independent results for the peak pullout load. The numerical results indicated that the increased fiber diameter would alter the mode of crack opening from fiber–matrix damage to that combined with matrix spalling, which can neutralize the sensitivity of the entire pullout response of hooked-end steel fiber to embedment depth. Additionally, the fiber–matrix bond was enhanced by increasing the fiber’s surface area, sensibly leading to a higher pullout peak load and toughness. The developed FE model was also proficient in predicting microstructural stress distribution and deformations during the crack opening of SFRC. This model could be extended to fully model a loaded SFRC composite material by the inclusion of various randomly oriented dosages of fibers in the concrete block.
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Zhu, Wei, Liang Gao, Yingai Zhao, Chao Yang, Wei Sun i Pengqiang Yu. "Stability Analysis of Jointed Rock Cutting Slope Based on Discrete Element Method". Advances in Civil Engineering 2022 (16.07.2022): 1–10. http://dx.doi.org/10.1155/2022/4915820.
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The joints in the rock mass are essential for the stability of rocky slopes, and the destabilization damage of the slope is often directly related to the joints. In this study, in order to reveal the instability process and mechanism of rock slopes from a microscale perspective, the DEM simulations for rocky slopes of the K88 + 400∼K88 + 540 section of Zhongkai Expressway are carried out considering the influence of joints. Based on the findings of the on-site jointed structural surfaces, a rocky slope model containing two sets of intermittent joints was constructed, and the linear parallel bond model and the smooth joint model are used to characterize the rock body and joints, respectively. The evolution of microfracture, contact force chain, and particle displacement are analyzed to explore the micromechanism of slope instability. Finally, the triple reinforcement scheme of anchor cable frame and grass planting is proposed. The research results can provide a reference for stability analysis and reinforcement of similar rocky slope projects.
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Zhang, Yi, Aaron D. Mickle, Philipp Gutruf, Lisa A. McIlvried, Hexia Guo, Yixin Wu, Judith P. Golden i in. "Battery-free, fully implantable optofluidic cuff system for wireless optogenetic and pharmacological neuromodulation of peripheral nerves". Science Advances 5, nr 7 (lipiec 2019): eaaw5296. http://dx.doi.org/10.1126/sciadv.aaw5296.
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Studies of the peripheral nervous system rely on controlled manipulation of neuronal function with pharmacologic and/or optogenetic techniques. Traditional hardware for these purposes can cause notable damage to fragile nerve tissues, create irritation at the biotic/abiotic interface, and alter the natural behaviors of animals. Here, we present a wireless, battery-free device that integrates a microscale inorganic light-emitting diode and an ultralow-power microfluidic system with an electrochemical pumping mechanism in a soft platform that can be mounted onto target peripheral nerves for programmed delivery of light and/or pharmacological agents in freely moving animals. Biocompliant designs lead to minimal effects on overall nerve health and function, even with chronic use in vivo. The small size and light weight construction allow for deployment as fully implantable devices in mice. These features create opportunities for studies of the peripheral nervous system outside of the scope of those possible with existing technologies.
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Darabi, Roya, Erfan Azinpour, Andre Ferreira, Jose Cesar de Sa, Ana Reis i Jan Dzugan. "Damage Evolution Simulations via a Coupled Crystal Plasticity and Cohesive Zone Model for Additively Manufactured Austenitic SS 316L DED Components". Metals 12, nr 7 (26.06.2022): 1096. http://dx.doi.org/10.3390/met12071096.
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This study presents a microstructural model applicable to additively manufactured (AM) austenitic SS 316L components fabricated via a direct energy deposition (DED) process. The model is primarily intended to give an understanding of the effect of microscale and mesoscale features, such as grains and melt pool sizes, on the mechanical properties of manufactured components. Based on experimental observations, initial assumptions for the numerical model regarding grain size and melt pool dimensions were considered. Experimental observations based on miniature-sized 316L stainless steel DED-fabricated samples were carried out to shed light on the deformation mechanism of FCC materials at the grain scale. Furthermore, the dependency of latent strain hardening parameters based on the Bassani–Wu hardening model for a single crystal scale is investigated, where the Voronoi tessellation method and probability theory are utilized for the definition of the grain distribution. A hierarchical polycrystalline modeling methodology based on a representative volume element (RVE) with the realistic impact of grain boundaries was adopted for fracture assessment of the AM parts. To qualify the validity of process–structure–property relationships, cohesive zone damage surfaces were used between melt pool boundaries as the predefined initial cracks and the performance of the model is validated based on the experimental observations.
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Srivatsa, Shreyas, Paweł Paćko, Leon Mishnaevsky, Tadeusz Uhl i Krzysztof Grabowski. "Deformation of Bioinspired MXene-Based Polymer Composites with Brick and Mortar Structures: A Computational Analysis". Materials 13, nr 22 (17.11.2020): 5189. http://dx.doi.org/10.3390/ma13225189.
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In this work, the deformation behavior of MXene-based polymer composites with bioinspired brick and mortar structures is analyzed. MXene/Polymer nanocomposites are modeled at microscale for bioinspired configurations of nacre-mimetic brick-and-mortar assembly structure. MXenes (brick) with polymer matrix (mortar) are modeled using classical analytical methods and numerical methods based on finite elements (FE). The analytical methods provide less accurate estimation of elastic properties compared to the numerical one. MXene nanocomposite models analyzed with the FE method provide estimates of elastic constants in the same order of magnitude as literature-reported experimental results. Bioinspired design of MXene nanocomposites results in an effective increase of Young’s modulus of the nanocomposite by 25.1% and strength (maximum stress capacity within elastic limits) enhanced by 42.3%. The brick and mortar structure of the nanocomposites leads to an interlocking mechanism between MXene fillers in the polymer matrix, resulting in effective load transfer, good strength, and damage resistance. This is demonstrated in this paper by numerical analysis of MXene nanocomposites subjected to quasi-static loads.
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Caggiano, Antonio, Diego Said Schicchi, Sha Yang, Stefan Harenberg, Viktoria Malarics-Pfaff, Matthias Pahn, Frank Dehn i Eddie Koenders. "A Microscale Approach for Modelling Concrete Fatigue Damage-Mechanisms". Key Engineering Materials 827 (grudzień 2019): 73–78. http://dx.doi.org/10.4028/www.scientific.net/kem.827.73.
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A micro-scale-based approach for the numerical analysis of cement-based materials, subjected to low-and high-cycle fatigue actions, is presented in this paper. The constitutive model is aimed at describing the evolving microstructural changes caused by cyclic loading protocols. More specifically, statistically representative microscopic geometries are equipped with a fracture-based model combined with a continuous inelastic constitutive law accumulating damage induced by the cyclic stress. The plastic-damage-based model is formulated combining the concepts of fracture-energy theories and damage stiffness degradations, representing the key phenomena occurring in concrete under fatigue. The paper explores the potential of the technique for assessing fatigue microcracks formation and growth, and their influence on the macroscopic behavior.
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Liu, Shuang, Zongjun Tian, Lida Shen i Mingbo Qiu. "Numerical Simulation and Experimental Investigation of Laser Ablation of Al2O3 Ceramic Coating". Materials 13, nr 23 (2.12.2020): 5502. http://dx.doi.org/10.3390/ma13235502.
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This paper presents an evaluation of the molten pool laser damage done to an Al2O3 ceramic coating. Mechanism analysis of the laser damage allowed for a 2D finite element model of laser ablation of the Al2O3 ceramic coating to be built. It consisted of heat transfer, laminar flow, and a solid mechanics module with the level set method. Results showed that the laser damage mechanisms through laser ablation were melting, gasification, spattering, and micro-cracking. The ablation depth and diameter increased with the increasing laser ablation time under continuous irradiation. The simulation profile was consistent with the experimental one. Additionally, the stress produced by the laser ablation was 3500–9000 MPa, which exceeded the tensile stress (350–500 MPa), and fracturing and micro-cracks occurred. Laser damage analysis was performed via COMSOL Multiphysics to predict laser damage morphology, and validate the 3D surface profiler and scanning electron microscope results.
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Tan, Zheng Lin, Mou Cheng Wu, Jie Li i Qing Zhang Wang. "Decay Mechanism of the Chestnut Stored in Low Temperature". Advanced Materials Research 554-556 (lipiec 2012): 1337–45. http://dx.doi.org/10.4028/www.scientific.net/amr.554-556.1337.
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Based on the determination of physiological indexes of chestnut stored in the refrigerator, i.e. SOD (Superoxidize dismutase), CAT (Catalase), MDA (Malondialdehyde), Vc (Vitamin C) and GSH (Glutathione), damage rate and decay rate, by Factor Analysis and Canonical Correration Analysis, decay mechanism of the chestnut is that leaking of electrons results the formation of O2., which promote the SOD activity and Vc content; O2. damages mitochondrial membrane, its electrons transfer to H2O and then form H2O2 which damages the membrane, finally result in chestnut decay. By Comparison of the membrane and the mitochondrion in electron microscope photos of chestnut cell, this conclusion is also proved.
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Xu, Zehao, Xiangjun Liu i Lixi Liang. "Numerical Investigation of Hydraulic Fracture Propagation Morphology in the Conglomerate Reservoir". Geofluids 2022 (23.07.2022): 1–22. http://dx.doi.org/10.1155/2022/6811300.
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The random distribution of gravels makes the conglomerate reservoir highly heterogeneous. A stress concentration occurs at the gravel-matrix interfaces owing to the embedded gravel and affects the local mechanical response significantly, making it difficult to control and predict hydraulic fracture (HF) propagation. The mechanism of HF propagation in conglomerate reservoirs remains unclear; thus, it is difficult to effectively design and treat hydraulic fracturing. Based on the global pore-pressure cohesive zone element (GPPCZ) model method, a two-dimensional (2D) fracture propagation model with flow-stress-damage (FSD) coupling was established to investigate HF nucleation, propagation, and coalescence in conglomerate reservoirs. This model was experimentally verified, and fractal theory was introduced to quantify the complexity of fracture morphology. The microscale interactions of the gravel, matrix, and interface have been taken into consideration during simulating HF propagation accurately in macroscale. The influence of the mechanical properties of gravel, matrix, matrix-gravel interface, and reservoir stress distribution state, on HF morphology (HF length, stimulated reservoir square, and HF complexity morphology), was investigated. Finally, the main factors affecting fracture propagation were analyzed. It was revealed that the difference between the mechanical properties of the gravel and the matrix in the conglomerate rock will affect the geometry of HF to varying degrees. The local behavior of fracture propagation is obviously dominated by the elastic modulus, tensile strength, and the strength for the matrix-gravel interface. However, the propagation of HF at the whole scale is mainly dominated by the horizontal stress state, including the minimum horizontal stress and horizontal stress difference. In addition, the difference in horizontal stress significantly affects the fracturing patterns (deflection, bifurcation, and penetration) when HF encounters gravel. In this study, a simulation method of HF propagation in conglomerate reservoirs is introduced, and the results provide theoretical support for the prediction of HF propagation morphology and plan design of hydraulic fracturing in conglomerate reservoirs.
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Krajcinovic, D., i A. Rinaldi. "Statistical Damage Mechanics— Part I: Theory". Journal of Applied Mechanics 72, nr 1 (1.01.2005): 76–85. http://dx.doi.org/10.1115/1.1825434.
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Statistical damage mechanics in this work establishes the connection between damaged random heterogeneous micromaterial and the system macroparameter. Renormalization group theory provides the bridge from the microscale to the macroscale. Delaunay lattices, which simulate and capture the role of the disordered microstructure in damage process, substitute a polycrystal specimen assuming that microcracks are grain-boundaries cracks. The macroparameters of the system, in the form of algebraic functions, are obtained applying the Family–Vicsek scaling relation on simulation data.
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Casaroli, Andrea, Marco Virginio Boniardi, Barbara Rivolta, Riccardo Gerosa i Francesco Iacoviello. "Metallurgical Failure Analysis of Closed Water Circuit Containing Molybdate-Based Inhibitor". Metals 13, nr 4 (6.04.2023): 723. http://dx.doi.org/10.3390/met13040723.
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In this work, two industrial heating/cooling circuits are compared. One of the two systems failed in a short time showing severe corrosion damage and a through thickness crack close to one of the welds. The main difference between the circuits is the presence of a sodium molybdate-based corrosion inhibitor in the damaged one. The addition of these substances is very frequent in such applications, and they generally work very well in preventing serious corrosion attacks. Nevertheless, the technical literature reports other cases in which systems working with fluids containing such inhibitors failed prematurely. The authors performed a failure analysis of the damaged circuit focusing their attention on the regions where fluid leaks were observed because of through thickness cracks. This damage was located close to the pipe–flange weld. These zones were investigated by visual examination, radiographic and scanning electron microscope (SEM) analyses, metallographic observations by light optical microscope (LOM), Vickers micro-hardness tests and optical emission spectroscopy (OES) chemical analysis. The failure was related to the presence of severe pitting and crevice corrosion in the welded areas with the final activation of a further critical corrosion mechanism, i.e., stress corrosion cracking (SCC). In order to explain the shorter working life of the failed system, a physical model of the corrosion mechanisms acting on the two circuits was proposed.
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Newaz, G. M., i Ke Zhang. "Inelastic Response of Off-Axis MMC Lamina". Journal of Engineering Materials and Technology 120, nr 2 (1.04.1998): 163–69. http://dx.doi.org/10.1115/1.2807006.
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Damage evolution and failure characteristics were investigated for a 10 deg off-axis SiC/It unidirectional metal matrix composite (MMC) lamina subjected to monotonic loading. A replica technique was used to monitor sequential damage evolution under monotonic loading for the 10 deg MMC lamina. The replicas were then examined under a Scanning Electron Microscope (SEM). Characteristic debonding along the fiber—a dominant damage mechanism, matrix plasticity in the form of slip bands and fiber cracks were observed at various strain levels and were rationalized based on the state of stress in the off-axis lamina. This investigation provides an insight into the off-axis material response for MMC lamina and associated damage mechanisms and can guide mechanism-based multiaxial constitutive model and failure criteria development.
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Dascomb, S. D., i D. G. Howitt. "Mechanism for radiation damage in borosilicate glasses". Proceedings, annual meeting, Electron Microscopy Society of America 49 (sierpień 1991): 1128–29. http://dx.doi.org/10.1017/s0424820100089950.
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Oxygen bubble formation has been observed in sodasilicate glasses during irradiation. Although the irradiation always produces a consistent microstructure of oxygen microbubbles and an amorphous phase decomposition, there is a substantial difference between the rate at which the damage occurs. When a sample has been previously gamma irradiated, the damage occurs at much greater rates when compared to in situ irradiation in the electron microscope. It has been suggested that it is not the radiation damage rate that is responsible for this behavior but rather the presence of an electric fieldFigure 1 illustrates the microstructure found in a sodasilicate glasses showing the characteristic bubble formation on the perimeter of the area illuminated by the beam and the phase separation within the interior.
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Yang, Hai Dong, N. Liu, Z. Ding, Z. G. Zhu i C. G. Zhang. "Wear Behavior of PCBN Tool in High Speed Turning TC4". Advanced Materials Research 426 (styczeń 2012): 344–47. http://dx.doi.org/10.4028/www.scientific.net/amr.426.344.
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PCBN tools were used for the turning of TC4. The cutting behavior and wear mechanisms were examined by means of the microscope, SEM and EDS analyses. The results have shown that ,the forms of the tool wear are mainly the rake face wear, flank wear, tip damage ,flaking and tipping; while the wear mechanism are mainly adhesion wear ,diffusion wear, machine wear and oxidation wear.
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Zika, T., I. C. Gebeshuber, F. Buschbeck, G. Preisinger i M. Gröschl. "Surface analysis on rolling bearings after exposure to defined electric stress". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 223, nr 5 (18.03.2009): 787–97. http://dx.doi.org/10.1243/13506501jet538.
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This article gives an overview about classical and frequency converter-induced spurious bearing currents in induction machines and discusses typical damage patterns caused by the current passage. To investigate on the electric damage mechanisms, test bearings are operated in a test rig and exposed to specific (classical low-frequency, and high-frequency) bearing currents. The induced damages to the surfaces are analysed visually and with the help of an atomic force microscope, and compared for the different electric regimes applied. Further, the electrically damaged bearing surfaces are characterized by standard roughness parameters. The surface structure observable on certain test bearings shows good correlation to the structure found with a bearing that had failed in the field under similar electric conditions. One of the investigated electric regimes applying high-frequency currents proved capable of generating fluting patterns - as found in real applications - on the test rig. The experiments also indicate that high-frequency bearing currents, although in total dissipating less energy, are more dangerous to a bearing than continuous current flow. The presented method gives a good starting point for further investigation on electric current damage in bearings, especially regarding high-frequency bearing currents, and on bearing/grease lifetime under specific electric regimes.
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Ren, Chunlei, Amna Siddique, Baozhong Sun i Bohong Gu. "Differences of transverse impact damages in 3D angle-interlock woven composites between warp and weft directions". International Journal of Damage Mechanics 28, nr 8 (2.01.2019): 1203–27. http://dx.doi.org/10.1177/1056789518823053.
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Transverse impact damages of 3D angle-interlock woven composites have been tested at split Hopkinson pressure bar along warp and weft directions respectively. The impact deformation and damages were photographed with a high-speed camera. A finite element analyses model was established at mesostructure level to unveil the inner yarn, resin damages, and stress distributions. There are significant differences of yarn breakages and interface damage between the two directions. From finite element analysis simulations and scanning electron microscope photographs, we found the warp yarns were in kink band deformation and shear damage, while the weft yarns were in compressive failure and had smooth fractography. The warp yarns which run through-thickness directions impede transverse impact crack propagations in resins and lead to high delamination resistances. The straight weft yarns impart high stiffness and strength to in-plane directions.
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He, Huan Ju, Ling Feng Zhang i Shao Zhe Li. "Dynamic Compressive Behavior and Damage Mechanism of Magnesium Alloy". Advanced Materials Research 1120-1121 (lipiec 2015): 1124–28. http://dx.doi.org/10.4028/www.scientific.net/amr.1120-1121.1124.
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The dynamic compression test was carried out for the AZ91 Magnesium alloy of as-cast and aging state with a split Hopkinson pressure bar, and the dynamic behavior has been investigated. Finally the fracture surface of samples at the different strain rates was analyzed by scanning electron microscope (SEM). The results show that compared with the as-cast AZ91, it is more impressible for the solid solution and age-treatment AZ91 at the similar strong strain rates, while the stress-strain curve has the duality of positive and negative effects as the variation of strain rate.
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KONIECZNY, Jarosław. "DESTRUCTION MECHANISMS OF CU-ETP COPPER GUIDES FOR SECTIONAL INSULATORS OF RAILWAY TRACTION". Scientific Journal of Silesian University of Technology. Series Transport 113 (1.12.2021): 101–13. http://dx.doi.org/10.20858/sjsutst.2021.113.8.
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This article presents the results of a research on the operational damage to sectional insulator guides made of hard electrolytic copper Cu-ETP (Electrolytic Tough Pitch Copper). The guides were used on various rail routes, in real conditions, on which the trains ran at maximum speeds between 40 and 120 km/h for periods of 6 or 12 months. The microstructure of the surface, the working layer of the guide, which contacts the graphite plate of the current collector and the cross-section of the guide in the place where it was damaged was examined using the Olympus light microscope. The analysis of the chemical composition in the EDS micro-regions was performed using the Zeiss Supra 53 scanning electron microscope (SEM), while the qualitative X-ray phase analysis was performed with the use of the Panalytical X'Pert diffractometer. Scratches and deformations of the surface layer characteristic of the phenomenon of friction caused by the current collector were observed in the microstructure of the damaged parts of the guides of section insulators. The effect of a very intense oxidation process was also observed, as well as the effects of an electric arc, which according to the author, is the factor that has the most destructive effect on the condition of the guides.
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Timothy, Jithender J., Alexander Haynack, Thomas Kränkel i Christoph Gehlen. "What Is the Internal Pressure That Initiates Damage in Cementitious Materials during Freezing and Thawing? A Micromechanical Analysis". Applied Mechanics 3, nr 4 (5.11.2022): 1288–98. http://dx.doi.org/10.3390/applmech3040074.
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Damage induced by repetitive freezing and thawing processes is one of the critical factors that affect concrete durability in cold climates. This deterioration process manifests as surface scaling and internal damage. The damage processes are governed by physicochemical mechanisms that are active across multiple scales. In this contribution, we present a novel multiscale theoretical framework for estimating the critical pressure required for microcrack initiation during freezing and thawing of cementitious mortar. Continuum micromechanics and fracture mechanics is used to model the phenomena of microcrack initiation and growth. Damage at the microscale is upscaled to the level of the specimen using multilevel homogenization. The critical pressure is estimated using poromechanics at the microscopic scale. A theoretical analysis shows that in the frozen state, the material can resist higher pressures. As a consequence, the material is more susceptible to damage during thawing. The micromechanical predictions are within the range of the predictions obtained by electrokinetic theory.
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Schembre, J. M., i A. R. Kovscek. "Mechanism of Formation Damage at Elevated Temperature". Journal of Energy Resources Technology 127, nr 3 (16.03.2005): 171–80. http://dx.doi.org/10.1115/1.1924398.
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The pore and grain surface of reservoir rocks often has clay and other fine material attached onto pore walls. It has been long recognized that brine salinity and pH are key factors affecting the attractive forces between pore surfaces and fines. If mobilized particles are assembled in sufficient quantities, they obstruct pore throats and reduce the permeability of the formation. There is anecdotal evidence of substantial fines migration during steam injection enhanced oil recovery operations. As of yet, the mechanism of fines release with temperature is unexplained. The Derjaguin, Landau, Verwey, and Overbeek theory of colloidal stability is used in conjunction with laboratory, core-scale experiments to demonstrate that high temperature, alkaline pH, and low salinity (typical characteristics of steam condensate) are sufficient to induce fines mobilization. Temperature is a key variable in calculations of fines stability. Hot-water floods are performed in Berea sandstone at temperatures ranging from 20°C to 200°C. Permeability reduction is observed with temperature increase and fines mobilization occurs repeatably at a particular temperature that varies with solution pH and ionic strength. A scanning electron microscope is used to analyze composition of the effluent samples collected during experiments. It confirms the production of fine clay material. On the practical side, this study provides design criteria for steam injection operations so as to control fines production.
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Todo, Mitsugu, Yoshihiro Fukuya, Seiya Hagihara i Kazuo Arakawa. "Finite Element Modeling of Damage Formation in Rubber-Toughened Polymer". Key Engineering Materials 297-300 (listopad 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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Tsivolas, Eleftherios, Leonidas N. Gergidis i Alkiviadis S. Paipetis. "Prediction of damage mechanisms of cross-ply composite materials using novel non-linear multiscale methodologies". Modelling and Simulation in Materials Science and Engineering 29, nr 8 (10.11.2021): 085015. http://dx.doi.org/10.1088/1361-651x/ac325d.
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Abstract In the present work, a novel multiscale material methodology is applied to a finite element mesh of a cross-ply composite material in tension in order to study the progressive damage and failure of the material at multiple scales by combining damage evolution models and failure criteria in microscale and cohesive zone modeling in macroscale. The micromechanics user material (Umat) developed follows a nonlinear version of the Mori–Tanaka theory and is coupled with mesoscale damage model. The concept of this user material is to dehomogenize-localize the strain tensor at each integration point for each time increment using Eshelby’s theories and strain concentration tensors. This material implementation allows the researcher to analyze results at two scales in the post processing stage, both for the composite material and the constituents for each time increment. It is observed that in the multiscale model the results are closer to the experimental measurements and even more damage mechanisms can be predicted, such as matrix damage and fiber failure. The developed multiscale methodology is advantageous since the constituents can follow different material models, with many failure criteria. It is also capable of predicting stresses, strains, plastic strains and more analysis variables not only in the macroscale-homogeneous level but also in microscale constituent-wise level.
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Mikkelsen, L. P. "Observations of microscale tensile fatigue damage mechanisms of composite materials for wind turbine blades". IOP Conference Series: Materials Science and Engineering 388 (19.07.2018): 012006. http://dx.doi.org/10.1088/1757-899x/388/1/012006.
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Ali, M. S., P. A. S. Reed, S. Syngellakis, Andrew J. Moffat i Carl Perrin. "Microstructural Factors Affecting Fatigue Initiation in Various Al Based Bearing Alloys". Materials Science Forum 519-521 (lipiec 2006): 1071–76. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.1071.
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Microscale fatigue damage mechanisms in various Al-Sn-Si based bearing alloys used as linings of plain automotive bearings are reported. Extensive work on previously developed alloys has concluded that secondary phase particles such as Sn and Si are potential fatigue initiation sites with a complex combination of various particle geometry parameters. A newly developed alloy contains a number of complex widely scattered intermetallics with much finer and fewer Sn and Si particles. This alloy system appears to be more resistant to initiate microscale fatigue damage compared to the previous systems.
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Tüzün, Pervin, Ömer Faruk Kadı, Fikret Yıldız, Ramiz Hamid i Humbat Nasibov. "A Laser Damage Threshold for Microscope Glass Slides". Photonics 10, nr 9 (24.08.2023): 967. http://dx.doi.org/10.3390/photonics10090967.
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Laser-based light sources have fostered innovative developments in biomedical and biosensor fields. However, laser-induced damage to optical components is a limitation for designing and implementing highly sensitive biosensors, necessitating the development and characterization of suitable optical components. Microscope glass slides are among the most extensively used optical units in this field. This study investigated the laser-induced damage threshold (LIDT) of high-quality microscope glass slides obtained from three different vendors. An S-on-1 protocol following the ISO 21254 series standards was adopted to ensure a meaningful comparative analysis. Multiple laser pulses at a constant fluence (at the three laser wavelengths most widely used in biosensors) were used for LIDT tests. An automated test bench was developed and employed to minimize the influence of human factors on the test results. The fatigue damage mechanism was observed in all the samples. The findings revealed good consistency among LIDT values within and across batches from the same vendor. However, a notable discrepancy was observed when comparing the results of slides obtained from different vendors, with threshold values differing by up to two-fold. This study emphasizes the need to carefully consider the glass material source when selecting microscope glass slides for laser-sensitive applications.
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Nguyen, Ba Nghiep, Brian J. Tucker i Mohammad A. Khaleel. "A Mechanistic Approach to Matrix Cracking Coupled with Fiber–Matrix Debonding in Short-Fiber Composites". Journal of Engineering Materials and Technology 127, nr 3 (22.03.2005): 337–50. http://dx.doi.org/10.1115/1.1924565.
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A micro–macro mechanistic approach to damage in short-fiber composites is developed in this paper. At the microscale, a reference aligned fiber composite is considered for the analysis of the damage mechanisms such as matrix cracking and fiber–matrix debonding using the modified Mori–Tanaka model. The associated damage variables are defined, and the stiffness reduction law dependent on these variables is established. The stiffness of a random fiber composite containing random matrix microcracks and imperfect interfaces is then obtained from that of the reference composite, which is averaged over all possible orientations and weighted by an orientation distribution function. The macroscopic response is determined using a continuum damage mechanics approach and finite element analysis. Final failure resulting from saturation of matrix microcracks, fiber pull-out and breakage is modeled by a vanishing element technique. The model is validated using the experimental results found in literature as well as the results obtained for a random chopped fiber glass–vinyl ester system. Acoustic emission techniques were used to quantify the amount and type of damage during quasi-static testing.
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Wenling Chen, i Fasuo Zhao. "Analysis of Creep Damage Mechanism of Mica Quartz Schist Based on Microscope Image". Journal of Convergence Information Technology 8, nr 9 (15.05.2013): 37–43. http://dx.doi.org/10.4156/jcit.vol8.issue9.5.
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Murdani, Anggit, Maskuri, Profiyanti Hermin Suharti i Chobin Makabe. "Fracture Mechanism of Polypropylene-Kenaf Composite under Cyclic Loading". Advanced Materials Research 1119 (lipiec 2015): 223–28. http://dx.doi.org/10.4028/www.scientific.net/amr.1119.223.
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Mechanism of fracture of polypropylene composite reinforced by kenaf fiber under cyclic loading was investigated. Weight fraction of the composite used is 50% polypropylene and 50% kenaf fiber with random fiber orientation. Skins of composite that contains polypropylene dominant fraction are formed on both surfaces. The experiments were performed with flat specimen under cyclic flexural loading with constant displacement. Cyclic softening was detected by hysteresis loop of a local area. Deformation of the specimen was measured from the observed cycles. Fracture features were investigated using optical microscope and scanning electron microscope. The result shows that polypropylene-kenaf composite with 50%-50% fraction with random fiber orientation has complicated fracture features. The damage of the composite started from internal part. The surface crack proceeded after the internal damage. Moreover, it is discussed that some of fibers were covered by only thin matrix. The strength of specimen was determined the fracture behavior of fibers.
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D'Errico, Fabrizio, Marco Boniardi, Silvia Barella i Silvia Cincera. "Damage Mechanisms of Initiating Micro-Pitting on 42CrMo4 Hardened and Tempered Steel". Key Engineering Materials 348-349 (wrzesień 2007): 869–72. http://dx.doi.org/10.4028/www.scientific.net/kem.348-349.869.
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A deep comprehension of the damage mechanisms involved in contact fatigue should optimize material and heat treatment choice for a specific application. In this work rolling disc-on-disc contact fatigue tests have been performed on a hardened and tempered UNI EN 42CrMo4 . The adopted test method creates the best conditions in order to develop micro-pitting on disc surface. Extensive micro-fractographic examinations have been carried out, on the damaged surfaces, through a scanning electronic microscope (SEM). For this steel, loaded with Hertzian pressure of 1000 MPa, the failure mode is always micro-pitting which begins at the surface, and it is not a sub-superficial damaging. If micro-pits develop, they will coalesce in larger craters. By this way, the probability that micropitting will degenerate into sub-superficial destructive pitting is very high.
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Zhao, Yang, Bin Yang i Yao Zhang. "Experimental Research and Simulation Analysis of Lightning Ablation Damage Characteristics of Megawatt Wind Turbine Blades". Metals 11, nr 8 (6.08.2021): 1251. http://dx.doi.org/10.3390/met11081251.
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In this paper, the damage mechanism of glass fiber reinforced composite (GFRC) under lightning strike by laying and inserting copper wires in the laminate was studied. The ablation characteristics of GFRC under different lightning current components were explored. Scanning electron microscope (SEM) was used to conduct the morphology analysis at the damaged area. The results show that the high temperature induced by lightning striking leads to resin pyrolysis, glass fiber (GF) sublimation, and stress waves, which results in fiber breakage and delamination. Then, a finite element (FE) thermal-electric coupling model for predicting the lightning ablation damage of GFRC was established. The comparison between the simulation and experimental results are in good agreement, which validate the effectiveness of the proposed FE model. The relationship between the lightning ablation area and the lightning current amplitude, charge amount, and specific energy in creeping discharge and through discharge was obtained by data fitting. The whole ablation damage process was revealed by FE simulation.
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Hanan, Jay C., Geoffrey A. Swift, Ersan Üstündag, Irene J. Beyerlein, Jonathan D. Almer, Ulrich Lienert i Dean R. Haeffner. "Microscale elastic strain evolution following damage in Ti-SiC composites". Metallurgical and Materials Transactions A 33, nr 12 (grudzień 2002): 3839–45. http://dx.doi.org/10.1007/s11661-002-0256-5.
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Duan, Hongyan, Zhiming Wang i Ming Song. "Tensile properties and microstructure evolution of compacted graphite iron at elevated temperatures". International Journal of Modern Physics B 33, nr 01n03 (30.01.2019): 1940007. http://dx.doi.org/10.1142/s0217979219400071.
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Attention has been focused on the fatigue problem for compacted graphite iron, when detonation pressure and temperature becomes higher and higher in combustion chamber for a long time. The compacted graphite iron plays an important role in the cylinder head of diesel industry for its good combination of thermal and mechanical properties. The damage mechanisms of compacted graphite iron under fatigue loading are observed in this study by scanning electron microscope (SEM) and in situ technique at elevated temperatures. The results show that tensile strength of compacted graphite iron decreases slightly at first, then decreases dramatically with the increasing temperature, which is a common phenomenon, even of various metallic materials. For the compacted graphite iron, these two stages are mainly controlled by different transformation mechanisms: the former mechanism, slip band stage, is affected by the inhibition of dislocation movement including strain strengthening, dynamic strain aging and precipitation hardening; and the latter, boundary sliding stage, is controlled by the vacancy diffusion. The newly proposed mechanisms can provide a new clue for the optimization of cast iron design. These damage mechanisms lay the foundation for the application of the crack technology.
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Rai, Ashwin, Nithya Subramanian, Bonsung Koo i Aditi Chattopadhyay. "Multiscale damage analysis of carbon nanotube nanocomposite using a continuum damage mechanics approach". Journal of Composite Materials 51, nr 6 (28.07.2016): 847–58. http://dx.doi.org/10.1177/0021998316654304.
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A multiscale-modeling framework is presented to understand damage and failure response in carbon nanotube reinforced nanocomposites. A damage model is developed using the framework of continuum damage mechanics with a physical damage evolution equation inspired by molecular dynamics simulations. This damage formulation is applied to randomly dispersed carbon nanotube reinforced nanocomposite unit cells with periodic boundary conditions to investigate preferred sites and the tendency towards damage. The continuum model is seen as successfully capturing much of the unique nonlinear trends observed in the molecular dynamics simulations in a volume 1000 times greater than the molecular dynamics unit cell. Additionally, application of the damage model to the continuum unit cell revealed insights into the failure of carbon nanotube reinforced nanocomposites at the sub-microscale.
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Zou, Zheng Long, Xiong Duan i Chu Wen Guo. "Studied for Mechanism of that Abrasive Water Jet Cutting Metal Materials". Applied Mechanics and Materials 513-517 (luty 2014): 218–22. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.218.
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Combining with the electron microscope analysis of the morphology of incision, the mechanism of abrasive water jet cutting metal materials was carried out to explore, for the rational selection of abrasive jet cutting parameters, to extend its application to provide the basis. Study shows that the abrasive water jet cutting metal materials, the material damage mechanism is mainly to yield deformation and failure and shear of grinding damage, grooving formation is mainly caused by falling impact deformation and furrows grinding.
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Chen, Xingming, Xiaoping Liu, Haoming Luo, Linjian Long i Chuanju Liu. "Microscopic Damage to Limestone under Acidic Conditions: Phenomena and Mechanisms". Sustainability 14, nr 18 (19.09.2022): 11771. http://dx.doi.org/10.3390/su141811771.
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In an acidic environment, the mineral components in rock begin to break down. As a result, the microstructure will be damaged, and then the mechanical properties will deteriorate, which will eventually have a negative effect on engineering stability. In order to study acid damage’s effect on this kind of rock, limestone samples were acidified for 0 days, 5 days, 10 days, 15 days, and 20 days. The microstructure changes in the limestone after acidification were studied via the wave velocity test and electron microscope scanning, and the damage deterioration mechanism was revealed. The results show that the acoustic signal of acidified samples has an obvious absorption effect at high frequency, and the surface pore structure of acidified samples shows fractal characteristics. The P-wave velocity, main peak amplitude, and fractal dimension of the acidified samples did not gradually decrease with time; however, there was a short-term strengthening phenomenon during immersion, which was mainly caused by the formation of CaSO4 crystals.
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Kim, Tae Gon, Kurt Wostyn, Jin Goo Park, Paul W. Mertens i Ahmed A. Busnaina. "Pattern Collapse and Particle Removal Forces of Interest to Semiconductor Fabrication Process". Solid State Phenomena 145-146 (styczeń 2009): 47–50. http://dx.doi.org/10.4028/www.scientific.net/ssp.145-146.47.
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The removal of particles from silicon wafers without pattern damage during fabrication process is extremely important for increasing the yield. Various physically assisted cleaning techniques such as megasonic cleaning, jet spray cleaning, and laser shock wave cleaning (LSC) have been introduced. However, most of tools show pattern damage [1]. One of the main challenges in next generation cleaning process is the particle removal without the pattern damage. As the feature size continues to decrease, the patterns are so fragile that it is hard to remove particles less than 50 nm without pattern damages. To accomplish the effective cleaning performance without the damage, the collapse force of pattern and removal force of particle should be known quantitatively. In this paper, pattern collapse forces were measured for different gate stack patterns by lateral force microscope (LFM) [2]. The particle removal mechanism of LSC was studied to find the relationship between measured collapse forces and particle removal force by LSC which has a known applied force. Finally, particle contaminated pattern wafers were cleaned by LSC with optimized process parameters to verify the relationship and to achieve the best particle removal performance without the pattern damage.
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Bo¨hm, H. J., F. G. Rammerstorfer, F. D. Fischer i T. Siegmund. "Microscale Arrangement Effects on the Thermomechanical Behavior of Advanced Two-Phase Materials". Journal of Engineering Materials and Technology 116, nr 3 (1.07.1994): 268–73. http://dx.doi.org/10.1115/1.2904285.
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Finite Element based micromechanical methods are used to study the influence of microscale phase arrangements on the overall and microscale thermomechanical properties of two advanced two-phase materials, duplex steels and unidirectional continuously reinforced metal matrix composites (MMCs). Both inclusion-matrix topologies and interwoven microgeometries are investigated for duplex steels, and the predicted macroscopic transverse elastoplastic responses are correlated with quantitative stereological descriptions of the microgeometries. For the MMCs, the emphasis is put on the influence of the fiber arrangement on the microscale residual stress states of the as-produced material and on their effects on damage mechanisms.
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Li, Chen, Feihu Zhang i Zhaokai Ma. "Study on grinding surface deformation and subsurface damage mechanism of reaction-bonded SiC ceramics". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 232, nr 11 (15.12.2016): 1986–95. http://dx.doi.org/10.1177/0954405416682282.
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In order to explore the grinding surface deformation and subsurface damage mechanism for reaction-bonded SiC ceramics, the grinding experiment for reaction-bonded SiC ceramics was carried out under the condition of different grinding depths using two different kinds of grain sizes of grinding wheel. The ground surface morphology of specimen was observed using the field emission scanning electron microscope (5000 ×), and the value of surface roughness Rz was measured by the confocal microscope, which found that there were the brittle removal region and the plastic removal region on the ground surface of reaction-bonded SiC ceramics and it could improve the ground surface quality and proportion of ductile region using the fine grinding wheel and reducing the grinding depth. The specimen was polished by the ion cross section polisher and the ground subsurface was analyzed by the field emission scanning electron microscope, which found that there were transgranular fracture, intergranular fracture, crack bifurcation, ladder-shaped crack and other phenomenon in the grinding process. And it could control the subsurface damage depth using the fine grinding wheel and reducing the grinding depth. The relationship between surface roughness and subsurface damage was analyzed based on the indentation theory, which found that the simulation results were close to the experiment results when the value of m is in the range of 1/8–1/4. When m is 0.2143 calculated by genetic algorithm, the simulation results are the best.
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Liu, Cai Ping, Qing Quan Duan i Ling Tao Mao. "Ductile Damage Evolution Analysis of Lead-Free Sn-Zn Solder Based on Meso Topography". Advanced Materials Research 152-153 (październik 2010): 1004–8. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.1004.
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Meso topography is used to examine the damage degree of lead-free Sn-Zn solder. Real-time meso topography is observed using scanning electronic microscope(SEM), which is assembled in a loading machine. The solder’s deformation and fracture is simulated using a damage accumulation process. The observed meso-structure evolutionary processes of the solder material is then analyzed according to the macro-meso combined mechanism. Some image processing technique are used. A new model of fracture mechanism and degree of damage is proposed.. that We show that the proposed meso structure evolution equations can accurately model the degree of material damage.