Journal articles on the topic 'Toughening techniques'
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1
Clarke, D. R., and B. Schwartz. "Transformation toughening of glass ceramics." Journal of Materials Research 2, no. 6 (December 1987): 801–4. http://dx.doi.org/10.1557/jmr.1987.0801.
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The utilization of transformation toughening has hitherto been restricted to increasing the fracture resistance of polycrystalline ceramic materials. Although a number of investigators have attempted to extend the concept to toughening glasses and glass ceramics with tetragonal zirconia, no successful reports have been published. It is argued that the approaches employed are inevitably limited primarily because they do not take into account the necessity of nucleating the tetragonal-to-monoclinic transformation away from the crack tip itself. By concentrating on the nucleation event and using standard ceramic processing techniques, it has been demonstated that transformation toughening can be used to increase the toughness of glass-ceramic materials, and this approach is illustrated by increasing the fracture toughness of a cordierite glass ceramic.
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Shah, S. P., and C. Ouyang. "Toughening Mechanisms in Quasi-Brittle Materials." Journal of Engineering Materials and Technology 115, no. 3 (July 1, 1993): 300–307. http://dx.doi.org/10.1115/1.2904222.
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Fracture processes in cement-based materials are characterized by a large-scale fracture process zone, localization of deformation, and strain softening. Many studies have been conducted to understand the toughening mechanisms of such quasi-brittle materials and to theoretically model their nonlinear response. This paper summarizes two innovative experimental techniques which are being developed at the ACBM Center to better define the fracture process zone in cement-based materials. A brief summary is also given of two types of theoretical approaches which attempt to simulate some of the observed nonlinear fracture response of these materials.
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Gunnison, Katie E., Mehmet Sarikaya, and Ilhan A. Aksay. "Toughening mechanisms in abalone shell." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 196–97. http://dx.doi.org/10.1017/s0424820100174114.
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Abalone shell (Haliotis Rufescens) is a naturally ocurring ceramic/polymer composite material. The system displays a unique laminated structure of calcium carbonate (aragonite) crystals in a matrix of biological macromolecules. The CaCO3 crystals and the organic matrix are arranged in a miniature “brick and mortar” structure referred to as nacre. Figure 1 is a TEM bright field micrograph illustrating the high degree of order observed in this microstructure.Although the nacre region of the shell is more than 95% CaCO3 by volume, the natural matrix material and the arrangement of the microstructure lead to a substantial increase in the observed mechanical properties. Mechanical tests performed on the nacre region show a fifty-fold increase over that of pure bulk CaCO3 (Fig. 2), which also compares with other ceramic and cermet systems.Vickers microhardness testing was performed on samples polished for optical microscopy. Crack propagation features were observed by standard SEM techniques and analyzed in an attempt to identify the possible toughening mechanisms that are operating in the nacre structure. The cracks generally travel by a tortuous path, often displaying microcracks and crack branching. However, these mechanisms alone are not sufficient to account for the observed mechanical properties.
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McCoy, M. A. "Crystallization of MgO • Al2 • SiO2 • ZrO2 glasses." Proceedings, annual meeting, Electron Microscopy Society of America 44 (August 1986): 440–41. http://dx.doi.org/10.1017/s0424820100143778.
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Transformation toughening by ZrO2 inclusions in various ceramic matrices has led to improved mechanical properties in these materials. Although the processing of these materials usually involves standard ceramic powder processing techniques, an alternate method of producing ZrO2 particles involves the devtrification of a ZrO2-containing glass. In this study the effects of glass composition (ZrO2 concentration) and heat treatment on the morphology of the crystallization products in a MgO•Al2•SiO2•ZrO2 glass was investigated.
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Llanes. "In-Depth Understanding of Fatigue Micromechanisms in Cemented Carbides: Implications for Optimal Microstructural Tailoring." Metals 9, no. 9 (August 23, 2019): 924. http://dx.doi.org/10.3390/met9090924.
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The fatigue mechanics and mechanisms of cemented carbides (composites usually referred to as hardmetals) are reviewed. The influence of microstructure on strength lessening and subcritical crack growth for these ceramic-metal materials when subjected to cyclic loads are highlighted. The simultaneous role of the ductile metallic binder as a toughening and fatigue-susceptible agent for hardmetals results in a tradeoff between properties measured under monotonic and cyclic loading: fracture strength and toughness on one hand, as compared to fatigue strength and crack growth resistance on the other one. Toughness/fatigue–microstructure correlations are analyzed and rationalized on the basis of specific crack–microstructure interactions, documented by the effective implementation of advanced characterization techniques. As a result, it is concluded that the fatigue sensitivity of cemented carbides may be reduced if either toughening mechanisms beyond ductile ligament bridging, such as crack deflection, are operative, or strain localization within the binder is suppressed. In this regard, grades exhibiting metallic binders of a complex chemical nature and/or distinct microstructural assemblages are proposed as options for effective microstructural tailoring of these materials.
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Tatarko, Peter, Štefánia Lojanová, Ján Dusza, and Pavol Šajgalík. "Fracture Toughness of Si3N4 Based Ceramics with Rare-Earth Oxide Sintering Additives." Key Engineering Materials 409 (March 2009): 377–81. http://dx.doi.org/10.4028/www.scientific.net/kem.409.377.
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Fracture toughness of hot-pressed silicon nitride and Si3N4+SiC nanocomposites prepared with different rare-earth oxides (La2O3, Sm2O3, Y2O3, Yb2O3, Lu2O3) sintering additives have been investigated by Chevron Notched Beam, Indentation Strength and Indentation Fracture techniques. The fracture toughness values of composites were lower due to the finer microstructures and the lack of toughening mechanisms. In the Si3N4 with higher aspect ratio (Lu or Yb additives) crack deflection occurred more frequently compared to the Si3N4 doped with La or Y, which was responsible for the higher fracture toughness.
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Jervis, T. R., J.-P. Hirvonen, M. Nastasi, and H. Kung. "Tribology and mechanical properties of excimer laser-processed Ti–Si3N4 surfaces." Journal of Materials Research 10, no. 8 (August 1995): 1857–60. http://dx.doi.org/10.1557/jmr.1995.1857.
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Titanium films were mixed, using excimer laser radiation, into the surface of bulk Si3N4 materials. The tribological and mechanical properties of these surfaces were then evaluated using pin-on-disk and nanoindenter techniques, respectively. Reduced friction and a change in the wear mechanism that resulted in a more benign failure mode were observed. These results are interpreted as resulting from the establishment of a transfer film, changes in the compliance of the surface which reduces instantaneous stresses in the surface, and toughening of the surface, all results of the laser process.
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Zhang, Kai, Jing Hui Fan, and Yan Ma. "Preparation of Impact Resistance Epoxy Resin Encapsulating Materials." Applied Mechanics and Materials 327 (June 2013): 18–22. http://dx.doi.org/10.4028/www.scientific.net/amm.327.18.
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According to research requests of encapsulating materials used in anti-impact precision electron apparatus parts, the materials system was designed on the relation of mechanics performance and techniques properties. Then epoxy resin E-51 was toughening modified with a kind of self-synthesized polyester epoxy resin which had liquid crystal groups. The results showed that the optimized epoxy resin encapsulating materials has high compression strength and favorable operating properties. The impact strength of prepared epoxy resin encapsulating materials increased 4.0 times, and the gel time at room temperature was over 100 minutes.
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Xu, Yun Yun, Tao Zhang, Zhen Rong Lin, Shan Dan Zhou, and Xin Xu. "Advances in Research of Carbon Fiber Reinforced Composite Materials." Advanced Materials Research 332-334 (September 2011): 1607–10. http://dx.doi.org/10.4028/www.scientific.net/amr.332-334.1607.
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Carbon fibers combine low weight and exceptional mechanical properties,making them ideal reinforcements forpolymer composite materials. An attempt has been made to review and analyze the development and problems made during last few decades in the field of carbon fiber reinforced polyamide composites. The recent advance of research, structure and property, the advanced techniques were summarized in this paper. In accordance with the hot spots of the research, the interface behavior, reinforcement and toughening of this type of material were expounded specially. Finally, the prospect and development of this composite were analyzed.
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Zhao, Hong Ping, Robert Kwok Yiu Li, and Xi Qiao Feng. "Experimental Investigation of Interlaminar Fracture Toughness of CFRP Composites with Different Stitching Patterns." Key Engineering Materials 297-300 (November 2005): 189–94. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.189.
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Through-thickness stitching is one of the most effective techniques to improve the delamination resistance of composite laminates. The effects of two different stitching patterns on the mode-I interlaminar fracture toughness of unidirectional carbon fiber reinforced plastics (CFRP) are examined experimentally in the present paper by using the double cantilever beam (DCB) test method. It is found that the zigzag stitching pattern results in a better toughening effect than the straight line pattern, and that the stitching density also has a considerable influence on the mode-I fracture toughness.
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Schmier, Stefanie, Naoe Hosoda, and Thomas Speck. "Hierarchical Structure of the Cocos nucifera (Coconut) Endocarp: Functional Morphology and its Influence on Fracture Toughness." Molecules 25, no. 1 (January 6, 2020): 223. http://dx.doi.org/10.3390/molecules25010223.
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In recent years, the biomimetic potential of lignified or partially lignified fruit pericarps has moved into focus. For the transfer of functional principles into biomimetic applications, a profound understanding of the structural composition of the role models is important. The aim of this study was to qualitatively analyze and visualize the functional morphology of the coconut endocarp on several hierarchical levels, and to use these findings for a more precise evaluation of the toughening mechanisms in the endocarp. Eight hierarchical levels of the ripe coconut fruit were identified using different imaging techniques, including light and scanning electron microscopy as well as micro-computer-tomography. These range from the organ level of the fruit (H0) to the molecular composition (H7) of the endocarp components. A special focus was laid on the hierarchical levels of the endocarp (H3–H6). This investigation confirmed that all hierarchical levels influence the crack development in different ways and thus contribute to the pronounced fracture toughness of the coconut endocarp. By providing relevant morphological parameters at each hierarchical level with the associated toughening mechanisms, this lays the basis for transferring those properties into biomimetic technical applications.
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Konnola, Raneesh, and Kuruvilla Joseph. "Polymer Grafted Multi-Walled Carbon Nanotube as a Novel Toughening Agent for Epoxy System." Materials Science Forum 830-831 (September 2015): 577–80. http://dx.doi.org/10.4028/www.scientific.net/msf.830-831.577.
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Hydroxyl terminated poly (ethersulfone) was used to modify the surface of multi-walled carbon nanotube (MWCNT). The grafting reaction was confirmed by different characterization techniques such as Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and Transmission Electron Microscope. Epoxy nanocomposites using the modified fillers were prepared. The fracture toughness of the system was examined and compared with MWCNT-epoxy nanocomposite.
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Li, J., X. S. Zhang, and P. Song. "Toughening mechanism and thermal shock resistance of ZrO2(3Y)/Fe28at-%Al composites evaluated by indentation techniques." Advances in Applied Ceramics 113, no. 7 (July 11, 2014): 404–10. http://dx.doi.org/10.1179/1743676114y.0000000183.
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Yang, J.-M., Steven T. J. Chen, S. M. Jeng, R. B. Thayer, and J.-F. LeCoustaouec. "Processing and mechanical behavior of SiC fiber-reinforced Si3N4 composites." Journal of Materials Research 6, no. 9 (September 1991): 1926–36. http://dx.doi.org/10.1557/jmr.1991.1926.
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The interfacial properties and mechanical behavior of the SCS-6/Si3N4 composites fabricated by hot pressing from powder lay-up and tape lay-up techniques were studied. Interfacial shear strength and frictional stress were measured using an indentation test. Fracture toughness and work-of-fracture were measured using a three-point bending test on a chevron-notched specimen. The influence of interfacial shear strength on the toughening mechanisms and crack propagation behavior were investigated. The results indicate that the processing routes and fiber orientation will affect the interfacial properties, which in turn have a significant influence on mechanical properties.
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Huang, Kai Jin. "Synthesis of Al2O3/AlB12/Al Composite Ceramic Powders by Pulsed Nd:YAG Laser Igniting Method and a Study of their Mechanical Properties." Applied Mechanics and Materials 26-28 (June 2010): 919–24. http://dx.doi.org/10.4028/www.scientific.net/amm.26-28.919.
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Based on the combined toughening principle, pure Al2O3/AlB12/Al composite ceramic powders have been synthesized using pulsed Nd:YAG laser igniting method. This method starts from Al and B2O3 powder mixtures, after which Al2O3/AlB12/AlN composite ceramics were fabricated by hot-press sintering at 1600°C for 2h under the protection of a N2 atmosphere. XRD and SEM techniques were used to characterize the phases and morphologies of the powders and the ceramics. The bending strength and the fracture toughness of the ceramics were measured by the three-point bending method and the indentation fracture method, respectively. The results show that the pure Al2O3/AlB12/Al composite ceramic powders can be successfully synthesized by pulsed Nd:YAG laser igniting method because the adiabatic temperature of Al-B2O3 system is more than 1800K. Al2O3 and AlB12 phases were formed by the liquid-liquid reaction mechanism and the liquid-solid reaction mechanism, respectively. The bending strength and the fracture toughness of the Al2O3/AlB12/AlN composite ceramics were 525.86MPa and 5.68MPa.m1/2, respectively. These values are 50.25% and 42% greater than those of the pure Al2O3 ceramic (350MPa and 4MPa.m1/2) due to the reinforcing and toughening in-situ formation of small AlN particles.
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Huang, Kai Jin, Li Yan, Hua Min Kou, and Chang Sheng Xie. "Synthesis of Al2O3/AlB12/Al Composite Ceramic Powders by a New Laser-Induction Complex Heating Method and a Study of their Mechanical Properties." Applied Mechanics and Materials 29-32 (August 2010): 596–601. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.596.
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Based on the combined toughening principle, pure Al2O3/AlB12/Al composite ceramic powders have been synthesized using a new laser-induction complex heating method. This method starts from Al and B2O3 powder mixtures, after which Al2O3/AlB12/AlN composite ceramics were fabricated by hot-press sintering at 1600°C for 2h under the protection of a N2 atmosphere. XRD and SEM techniques were used to characterize the phases and morphologies of the powders and the ceramics. The bending strength and the fracture toughness of the ceramics were measured by the three-point bending method and the indentation fracture method, respectively. The results show that the pure Al2O3/AlB12/Al composite ceramic powders can be successfully synthesized by this new laser-induction complex heating method because the adiabatic temperature of Al-B2O3 system is more than 1800K. Al2O3 and AlB12 phases were formed by the liquid-liquid reaction mechanism and the liquid-solid reaction mechanism, respectively. The bending strength and the fracture toughness of the Al2O3/AlB12/AlN composite ceramics were 551.44MPa and 6.04MPa.m1/2, respectively. These values are 57.55% and 51% greater than those of the pure Al2O3 ceramic (350MPa and 4MPa.m1/2) due to the reinforcing and toughening in-situ formation of small AlN particles.
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Gigante, Vito, Luca Bosi, Paola Parlanti, Mauro Gemmi, Laura Aliotta, and Andrea Lazzeri. "Analysis of the Damage Mechanism around the Crack Tip for Two Rubber-Toughened PLA-Based Blends." Polymers 13, no. 22 (November 22, 2021): 4053. http://dx.doi.org/10.3390/polym13224053.
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The toughening mechanisms of poly(lactic acid; PLA) blended with two different elastomers, namely poly (butylene adipate-co-terephtalate; PBAT) and polyolefin elastomers with grafted glycidyl methacrylate (POE-g-GMA), at 10 and 20 wt.%, were investigated. Tensile and Charpy impact tests showed a general improvement in the performance of the PLA. The morphology of the dispersed phases showed that PBAT is in the form of spheres while POE-g-GMA has a dual sphere/fibre morphology. To correlate the micromechanical deformation mechanism with the macroscopical mechanical behaviour, the analysis of the subcritical crack tip damaged zone of double-notched specimens subjected to a four-point bending test (according to the single-edge double-notch four-point bend (SEDN-4PB) technique) was carried out using several microscopic techniques (SEM, polarized TOM and TEM). The damage was mainly generated by shear yielding deformation although voids associated with dilatational bands were observed.
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Palaniyappan, Saravanan, Maik Trautmann, Yiran Mao, Johann Riesch, Parikshith Gowda, Nick Rudolph, Jan Willem Coenen, Rudolf Neu, and Guntram Wagner. "Yttria-Coated Tungsten Fibers for Use in Tungsten Fiber-Reinforced Composites: A Comparative Study on PVD vs. CVD Routes." Coatings 11, no. 9 (September 16, 2021): 1128. http://dx.doi.org/10.3390/coatings11091128.
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Tungsten fiber-reinforced tungsten (Wf/W) composites are being developed to improve the intrinsic brittleness of tungsten. In these composites, engineered fiber/matrix interfaces are crucial in order to realize toughening mechanisms. For such a purpose, yttria (Y2O3), being one of the suitable interface materials, could be realized through different coating techniques. In this study, the deposition of thin films of yttria on a 150 µm tungsten wire by physical and chemical vapor deposition (PVD and CVD) techniques is comparatively investigated. Although fabrication of yttria is feasible through both CVD and PVD routes, certain coating conditions such as temperature, growth rate, oxidation of Wf, etc., decide the qualitative nature of a coating to a particular extent. In the case of PVD, the oxidation of Wf is highly reduced compared to the WO3 formation in high-temperature CVD coating processes. Yttria-coated tungsten fibers are examined comprehensively to characterize their microstructure, phase, and chemical composition using SEM, XRD, and Raman spectroscopy techniques, respectively.
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Kumar, Ajay, and Rajesh Ghosh. "A review on experimental and numerical investigations of cortical bone fracture." Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 236, no. 3 (January 8, 2022): 297–319. http://dx.doi.org/10.1177/09544119211070347.
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This paper comprehensively reviews the various experimental and numerical techniques, which were considered to determine the fracture characteristics of the cortical bone. This study also provides some recommendations along with the critical review, which would be beneficial for future research of fracture analysis of cortical bone. Cortical bone fractures due to sports activities, climbing, running, and engagement in transport or industrial accidents. Individuals having different diseases are also at high risk of cortical bone fracture. It has been observed that osteon orientation influences cortical bone fracture toughness and fracture mechanisms. Apart from this, recent studies indicate that fracture parameters of cortical bone also depend on many factors such as age, sex, temperature, osteoporosis, orientation, location, loading condition, strain rate, and storage facility, etc. The cortical bone regains its fracture toughness due to various toughening mechanisms. Owing to these factors, several experimental, clinical, and numerical investigations have been carried out to determine the fracture parameters of the cortical bone. Cortical bone is the dense outer surface of the bone and contributes to 80%–82% of the skeleton mass. Cortical bone experiences load far exceeding body weight due to muscle contraction and the dynamics of motion. It is very important to know the fracture pattern, direction of fracture, location of the fracture, and toughening mechanism of cortical bone. A basic understanding of the different factors that affect the fracture parameters and fracture mechanisms of the cortical bone is necessary to prevent the failure and fracture of cortical bone. This review has summarized the advancement considered in the various experimental techniques and numerical methods to get complete information about the fracture mechanisms of cortical bone.
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Ikeda, Junji, Giuseppe Pezzotti, and Takefumi Nakanishi. "Phase Stability of Zirconia Toughened Alumina Composite for Artificial Joints." Key Engineering Materials 309-311 (May 2006): 1243–46. http://dx.doi.org/10.4028/www.scientific.net/kem.309-311.1243.
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The phase stability under aqueous condition and changes in the wear region after the Pin-on-Flat wear testing were evaluated using Raman and fluorescence spectroscopy techniques and X-ray diffractometry for a newly developed zirconia toughened alumina (JMM-ZTA). This study suggests that JMM-ZTA is a highly stable material under aqueous environment in the human body and has a high wear resistance in Pin-on-Flat wear tests. This results from a transformation toughening mechanism operative in JMM-ZTA. Therefore, JMM-ZTA appears to have a possibility to improve the performance of monolithic alumina as a material for hip and knee joint prostheses.
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Smith, A. P., H. Ade, R. J. Spontak, and C. C. Koch. "Morphological and Chemical Characterization of a Mechanically Alloyed Rubber Toughened PMMA With X-Ray Spectromicroscopy." Microscopy and Microanalysis 4, S2 (July 1998): 142–43. http://dx.doi.org/10.1017/s1431927600020833.
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Rubber toughening was first developed about seventy years ago as a method of increasing the impact resistance of brittle glassy polymers. Since that time, a wide variety of techniques have been developed to produce discrete dispersions of rubber within a glassy polymer matrix. We are exploring a new route to rubber-toughen polymer through the non-equilibrium process of mechanical alloying (high-energy ball milling). Here we have blended poly(methyl methacrylate) (PMMA) with polyisoprene (PI) (see the insets in Fig. 1 for chemical structures) and have characterized the resultant blends with Scanning Transmission X-ray Microscopy (STXM) in order to obtain chemical, as well as morphological, information about the blends.The STXM technique utilizes tuneable soft x-rays that are focused with a diffraction zoneplate to a microprobe of 45 nm full width at half maximum. Thin sections of the sample are placed at the microprobe and the transmitted photon intensity is measured.
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Charles, Andrew, and Andrew Rider. "Triblock Copolymer Toughening of a Carbon Fibre-Reinforced Epoxy Composite for Bonded Repair." Polymers 10, no. 8 (August 8, 2018): 888. http://dx.doi.org/10.3390/polym10080888.
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Epoxy resins are the most widely used systems for structural composite applications; however, they lack fracture toughness, impact strength and peel strength due to high cross-linking densities. Use of conventional toughening agents to combat this can lead to reductions in mechanical, thermal and processability properties desirable for bonded composite applications. In this work, an asymmetric triblock copolymer of poly(styrene)–b–poly(butadiene)–b–poly(methylmethacrylate) was used to modify an epoxy resin system, with the materials processed using both vacuum bag and positive pressure curing techniques. Interlaminar fracture toughness testing showed improvements in initiation fracture toughness of up to 88%, accompanied by a 6 °C increase in glass transition temperature and manageable reductions in gel-time. Shear testing resulted in a 121% increase in ultimate shear strain with only an 8% reduction in shear strength. Performance improvements were attributed to nano-structuring within the toughened resin system, giving rise to matrix cavitation and dissipation of crack front strain energy upon loading.
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Pu, Pengpeng, and Tijun Chen. "Nanostructured Metals with an Excellent Synergy of Strength and Ductility: A Review." Materials 15, no. 19 (September 23, 2022): 6617. http://dx.doi.org/10.3390/ma15196617.
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Nanocrystalline metals developed based on fine grain strengthening always have an excellent strength, but are accompanied by a drop in ductility. In the past 20 years, substantial efforts have been dedicated to design new microstructures and develop the corresponding processing technologies in order to solve this problem. In this article, the novel nanostructures designed for simultaneously achieving high strength and high ductility developed in recent years, including bimodal grain size distribution nanostructure, nanotwinned structure, hierarchical nanotwinned structure, gradient nanostructure, and supra-nano-dual-phase nanostructure, are reviewed. Based on a comprehensive understanding of the simultaneously strengthening and toughening mechanisms, the microstructures and corresponding processing techniques are mainly discussed, and the related prospects that may be emphasized in the future are proposed.
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Liu, Huanrong, Zehui Jiang, Benhua Fei, Chungyun Hse, and Zhengjun Sun. "Tensile behaviour and fracture mechanism of moso bamboo (Phyllostachys pubescens)." Holzforschung 69, no. 1 (January 1, 2015): 47–52. http://dx.doi.org/10.1515/hf-2013-0220.
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Abstract The present work is aiming at the elucidation of the tensile behaviour and fracture performance of moso bamboo (Phyllostachys pubescens Mazei ex H. de Lebaie) by means of digital speckle correlation method (DSCM) and microscopic techniques. Results indicated that fibres play a major role in longitudinal tension and impeding crack radial propagation. Hybrid I-II failure mode was observed, i.e., crack opening (in tensile stress) and shear sliding (in shear stress). According to microscopic fracture characteristics, fibres extraction and stretching, filament formation in parenchyma with fibres bridging, interface debonding and the helix fracture of fibres happened in tension, which created more interfaces and dissipated more energy. The graded composite structure of bamboo provides intrinsic and extrinsic toughening mechanisms which contribute to improved toughness and physical properties.
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Nawa, Masahiro, Kiyotaka Yamada, and Giuseppe Pezzotti. "Microscopic Mechanisms behind the Toughening Behavior of Ceria Stabilized Tetragonal Zirconia/Alumina Nanocomposite for Biomedical Applications." Key Engineering Materials 361-363 (November 2007): 813–16. http://dx.doi.org/10.4028/www.scientific.net/kem.361-363.813.
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With elongation of average human life, problem such as bone embrittlement and osteoporosis call for quick solution and the expectation for artificial biomaterials heightens. Many ceramics widely used as artificial biomaterials are limited by their poor reliability characteristics. A CeO2 stabilized tetragonal zirconia polycrystalline (Ce-TZP) matrix incorporating nanometer sized Al2O3 particles within the zirconia grains (Ce-TZP/Al2O3) was recently developed. This material experienced significant improvements in both fracture toughness and strength above the standard mechanical performance of monolithic zirconia. In this paper, we performed a macro/microscopic fracture mechanics assessment of this developed Ce-TZP/Al2O3 nanocomposite, in comparison with a 3 mol% Y-TZP according to advanced in situ confocal Raman spectroscopy techniques.
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Zhang, Yu Yuan, Quan Li Li, and Hai Ming Wong. "Cell-Free Biomimetic Mineralization Strategies to Regenerate the Enamel Microstructure." Crystals 11, no. 11 (November 12, 2021): 1385. http://dx.doi.org/10.3390/cryst11111385.
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The distinct architecture of native enamel gives it its exquisite appearance and excellent intrinsic-extrinsic fracture toughening properties. However, damage to the enamel is irreversible. At present, the clinical treatment for enamel lesion is an invasive method; besides, its limitations, caused by the chemical and physical difference between restorative materials and dental hard tissue, makes the restorative effects far from ideal. With more investigations on the mechanism of amelogenesis, biomimetic mineralization techniques for enamel regeneration have been well developed, which hold great promise as a non-invasive strategy for enamel restoration. This review disclosed the chemical and physical mechanism of amelogenesis; meanwhile, it overviewed and summarized studies involving the regeneration of enamel microstructure in cell-free biomineralization approaches, which could bring new prospects for resolving the challenges in enamel regeneration.
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Alexander, K. B., H. T. Lin, and P. F. Becher. "The role of EM studies on the development of ceramic composites." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 1 (August 1992): 150–51. http://dx.doi.org/10.1017/s0424820100121156.
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Advances in the development of ceramics and ceramic composites rely on an understanding of the mechanisms which contribute to the formation of desired microstructural features or control the mechanical response of the material. For example, in silicon nitride, careful control of the liquid phase composition and growth conditions permits the development of elongated grains which provide in-situ reinforcement of the material. Electron microscopy studies have aided in understanding the solution-reprecipitation process which controls the growth of silicon nitride as well as the role of the liquid phase on this process. The composition and thickness of the residual glass phase at the grain boundaries and triple points are important for both the toughening and creep response of the material and can only be realistically analyzed by high resolution analytical and electron imaging techniques.
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Wang, Xiong, Sheng Hu, Yi Guo, Guangquan Li, and Renwei Xu. "Toughened High-Flow Polypropylene with Polyolefin-Based Elastomers." Polymers 11, no. 12 (December 1, 2019): 1976. http://dx.doi.org/10.3390/polym11121976.
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Polyolefin is the most widely used and versatile commodity polymer. In this work, three types of polyolefin-based elastomers (PBEs) were adopted to toughen a high-flow polypropylene to improve its overall performance. The chain microstructures of these PBEs, including ethylene/1-octene (E/O) random copolymer from Dow Chemical′s polyolefin elastomer (POE), olefin block copolymers (OBCs) of E/O from Dow, and ethylene/propylene random copolymer from ExxonMobil’s propylene-based elastomer, were elucidated by GPC, 13C NMR, TREF, and DSC techniques. The mechanical, thermal and optical properties, and morphology analysis of the PP/PBE blends were also studied to investigate the toughening mechanism of these PBEs. The results showed that all three types of PBEs can effectively improve the Izod impact strength of the PP/PBE blends by the addition of the rubber compositions, at the cost of the stiffness. PBE-1 and PBE-2 were found to have a great stiffness–toughness balance with about 1700 MPa of flexural modulus, about 110 °C of HDT and 3.6 kJ/m2 of impact strength on the prepared PP/PBE blends by forming separated rubber phase and refined spherulite crystals. As a result, the OBC with alternating hard and soft segments could achieve a similar toughening effect as the E/P random copolymer. Surprisingly, no obvious rubber phase separation was observed in the PP/PBE-4 blend, which might be due to the good compatibility of the E/P random chains with the isotactic PP; therefore, the PP/PBE blend obtains great toughness performance and optical transparency with the highest Izod impact strength of 4.2 kJ/m2 and excellent transparency.
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Tamas-Benyei, Peter, Eniko Bitay, Hajime Kishi, Satoshi Matsuda, and Tibor Czigany. "Toughening of Epoxy Resin: The Effect of Water Jet Milling on Worn Tire Rubber Particles." Polymers 11, no. 3 (March 20, 2019): 529. http://dx.doi.org/10.3390/polym11030529.
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In this work a cycloaliphatic amine-cured epoxy (EP) resin was modified by micron-scale rubber particles (RP). Nominal RP, in sizes of 200 and 600 µm respectively, were produced using worn truck tires and ultra-high-pressure water jet cutting. The RP were dispersed into the EP resin using different mixing techniques (mechanical, magnetic, and ultrasonic stirring) prior to the introduction of the amine hardener. The dispersion of the RP was studied using optical light microscopy. A longer mixing time reduced the mean size of the particles in the EP compounds. Static (tensile and flexural), dynamic (unnotched Charpy impact), and fracture mechanical (fracture toughness and strain-energy release rate) properties were determined. The incorporation of the RP decreased the stiffness and strength values of the modified EPs. In contrast, the irregular and rough surface of the RP resulted in improved toughness. The fracture toughness and strain-energy release rate were enhanced up to 18% owing to the incorporation of 1% by weight (wt%) RP. This was traced to the effects of crack pinning and crack deflection. Considerably higher improvement (i.e., up to 130%) was found for the unnotched Charpy impact energy. This was attributed to multiple cracking associated with RP-bridging prior to final fracture.
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Hattar, K., J. Han, M. T. A. Saif, and I. M. Robertson. "In situ Transmission Electron Microscopy Observations of Toughening Mechanisms in Ultra-fine Grained Columnar Aluminum Thin Films." Journal of Materials Research 20, no. 7 (July 1, 2005): 1869–77. http://dx.doi.org/10.1557/jmr.2005.0233.
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A unique straining device, fabricated using microlithographic techniques, has been developed to permit real-time investigation in the transmission electron microscope (TEM) of the deformation and failure mechanisms in ultrafine-grained aluminum. The tensile specimen is a freestanding thin film with a columnar microstructure that has a uniform cross-section (100 × 0.125 μm) and a gauge length of 300 μm. In situ TEM straining experiments show the fracture mode is intergranular with no accompanying general plasticity. Propagating cracks were halted at large grains, and crack blunting occurred through grain-boundary-mediated processes. The blunting process was accompanied by dislocation emission and deformation twinning in the grain responsible for arresting the crack. Voids or microcracks nucleated and grew on grain boundaries ahead of the arrested crack, and crack advance occurred through linkage of the microcracks and the primary crack.
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Xin, Hai. "Double-Network Tough Hydrogels: A Brief Review on Achievements and Challenges." Gels 8, no. 4 (April 18, 2022): 247. http://dx.doi.org/10.3390/gels8040247.
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This brief review attempts to summarize research advances in the mechanical toughness and structures of double-network (DN) hydrogels. The focus is to provide a critical and concise discussion on the toughening mechanisms, damage recoverability, stress relaxation, and biomedical applications of tough DN hydrogel systems. Both conventional DN hydrogel with two covalently cross-linked networks and novel DN systems consisting of physical and reversible cross-links are discussed and compared. Covalently cross-linked hydrogels are tough but damage-irreversible. Physically cross-linked hydrogels are damage-recoverable but exhibit mechanical instability, as reflected by stress relaxation tests. This remains one significant challenge to be addressed by future research studies to realize the load-sustaining applications proposed for tough hydrogels. With their special structure and superior mechanical properties, DN hydrogels have great potential for biomedical applications, and many DN systems are now fabricated with 3D printing techniques.
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Xiao, Xuan, Shi Qiang Lu, Xian Juan Dong, Ming Gang Huang, and Jun Wei Liu. "The Effect of Titanium Addition on Microstructure and Properties of Laves Phase Cr2Nb Alloy Synthesized by Hot Pressing." Advanced Materials Research 328-330 (September 2011): 1102–8. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1102.
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The composite materials with a nominal composition of Cr2Nb-24wt.%Ti were fabricated by mechanical alloying followed by hot pressing. The microstructures and properties were investigated on the composites contained with Laves phase prepared through 20 hours mechanical alloying of chromium, niobium and titanium elemental powders and hot pressing at 1250°C for half an hour. The results indicate that the near full-dense Laves phase Cr2(Nb,Ti) based alloy with homogeneous composition and microstructure is obtained by mechanical alloying and hot pressing techniques. The dispersed soft second phase Nb solid solutions with the fine grain size less than 1μm are distributed uniformly on the matrix. The sample has a relative density of 99%, fracture toughness of 5.32MPa•m1/2 and compress strength of 2080MPa. Due to the effect of fine-grain and alloying addition, the toughening of the Cr2(Nb,Ti) based alloy has been fully realized.
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Guo, Zhenping, Lei Wang, Cheng Wang, and Qiuliang Li. "Effects of Zirconium and Yttrium Oxide on Mechanical and Oxidation Properties of Mo–3Si–1B–1Zr–1Y2O3 (wt.%) Alloy." Coatings 10, no. 9 (August 28, 2020): 833. http://dx.doi.org/10.3390/coatings10090833.
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Mo–3Si–1B alloys with zirconium (1 wt.%) and yttrium oxide (1 wt.%) additives were fabricated by vibrating sintering techniques. The doped Mo–3Si–1B alloys consisted mainly of α-Mo, Mo3Si, and Mo5SiB2 (T2) phases. It was found that the grains were reduced, and the intermetallics particles were dispersed more homogeneously after the addition of Zr and Y2O3. The optimization in microstructure induced corresponding improvements in both fracture toughness and oxidation resistance. The predominant strengthening mechanisms were fine-grain strengthening and particle dispersion strengthening. In addition, fracture toughness test showed that the additions could improve the toughness of Mo–3Si–1B alloys, for which the toughening mechanism involved a crack trapping by α-Mo phases and extensive small second phase particles in the alloys. What should be paid attention to is the satisfactory oxidation resistance, both at medium-low temperature (800 °C) and high temperature (1200 °C) with doped additives.
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Shadangi, Yagnesh, Vikas Shivam, Kausik Chattopadhyay, and Nilay Krishna Mukhopadhyay. "Powder Metallurgical Processing of Sn-Reinforced Al-Cu-Fe Quasicrystals: Structure, Microstructure and Toughening Behavior." Journal of Manufacturing and Materials Processing 6, no. 3 (May 31, 2022): 60. http://dx.doi.org/10.3390/jmmp6030060.
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The present work deals with powder metallurgical processing of Sn-reinforced Al-Cu-Fe icosahedral quasicrystalline (IQC) composites processed through mechanical milling (MM) followed by hot pressing and pressureless sintering. The structure, microstructure and toughening behavior of the nanocomposite powders and bulk samples were investigated through X-ray diffraction (XRD), optical metallography (OM), scanning electron microscopy (SEM) and indentation techniques. The XRD pattern suggested the coexistence of IQC and λ-Al13Fe4 (mC102; a = 1.549 nm, b = 0.808 nm, c = 1.248 nm) and B2-type Al (Cu, Fe) (cP2; a = 0.29 nm) crystalline phases in milled as well as sintered samples. The face-centered icosahedral (FCI) ordering was persistent even after 40 h of milling and sintering. The structural transformation during MM influences the indentation behavior of IQC-Sn nanocomposite powders, and the microhardness was found to be in the range of ~5.3 to 7.3 GPa. Further, efforts were made to study the indentation behavior of IQC-Sn composite prepared by pressureless sintering and hot pressing. The fracture toughness of the IQC-10Sn hot-pressed sample was found to be ~1.92 MPa.√m, which is ~22% higher than that of the as-cast and annealed IQC. The enhancement in the fracture toughness resulted mainly from the inhibition of cracks by Sn reinforcement particles. This suggests that powder metallurgical processing can produce the IQC-Sn composite with an optimal combination of microhardness and fracture toughness.
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Sun, Wei, Fei Yang, Fan Tao Kong, Xiao Peng Wang, and Yu Yong Chen. "Microstructure and Fracture Toughness of a TiAl/Ti Laminated Composite." Applied Mechanics and Materials 884 (August 2018): 29–35. http://dx.doi.org/10.4028/www.scientific.net/amm.884.29.
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In this paper, the TiAl/Ti laminated (MIL) composite was fabricated via hot-pack rolling of the as-forged Ti-43Al-9V-0.3Y (at.%) plates and commercial Ti6Al4V (wt.%) sheet at 1250°C and then annealed at 90°C for 6 hours. The composite was analyzed by XRD and SEM techniques, respectively. Results showed that the interface between Ti and TiAl in the composite was consisted of four different microstructure areas and the phase constitutions for each area were: area 1: acicular β-Ti and α2 phase; area 2: acicular α2 phase; area 3: acicular α2 phase and B2 matrix; and area 4: acicular γ, α2 phase and B2 matrix. The fracture toughness of the TiAl/Ti MIL composite was tested, showing that the KIC value was about 38.35MPa·m1/2 at room temperature and higher than that of the pure Ti-43Al-9V-0.3Y alloy, which had a value of about 24.72 MPa·m1/2. The possible toughening mechanism for the TiAl/Ti MIL composite was discussed.
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Beithou, Nabil. "Workplace Violence on Physicians and Nurses: Causes and Pre-Violence Suggested Solutions." Journal of Biomedical Research & Environmental Sciences 3, no. 7 (July 2022): 848–51. http://dx.doi.org/10.37871/jbres1523.
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One of the important occupational health problems is violence. Violence is more prevalent among physicians and nurses in psychiatric and emergency departments in Jordan public hospitals. Causes of this phenomenon are associated with different causatives such as hospitals facilities (including beds, medication, oxygen… etc.), hospital staff, ministry of health and patients with their families. In this work violence on physicians and nurses in Jordan hospitals is analyzed based on the causes of violence. Solutions are searched upon the causatives of these actions not only on education, training and toughening punishment. Results of this work showed that 58.3 % of violence is due to hospital facilities and staff, 25% government actions and 17.7 % due to patients and their families. This work suggests investing more in healthcare institutions, provide more skilled staff, introduce a management procedure following incidents, preventive policies and improving health institutional facilities by applying programs for medicine inventory control, human factors and management techniques.
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Chen, Si-Ming, Huai-Ling Gao, Yin-Bo Zhu, Hong-Bin Yao, Li-Bo Mao, Qi-Yun Song, Jun Xia, et al. "Biomimetic twisted plywood structural materials." National Science Review 5, no. 5 (July 30, 2018): 703–14. http://dx.doi.org/10.1093/nsr/nwy080.
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Abstract Biomimetic designs based on micro/nanoscale manipulation and scalable fabrication are expected to develop new-style strong, tough structural materials. Although the mimicking of nacre-like ‘brick-and-mortar’ structure is well studied, many highly ordered natural architectures comprising 1D micro/nanoscale building blocks still elude imitation owing to the scarcity of efficient manipulation techniques for micro/nanostructural control in practical bulk counterparts. Herein, inspired by natural twisted plywood structures with fascinating damage tolerance, biomimetic bulk materials that closely resemble natural hierarchical structures and toughening mechanisms are successfully fabricated through a programmed and scalable bottom-up assembly strategy. By accurately engineering the arrangement of 1D mineral micro/nanofibers in biopolymer matrix on the multiscale, the resultant composites display optimal mechanical performance, superior to many natural, biomimetic and engineering materials. The design strategy allows for precise micro/nanostructural control at the macroscopic 3D level and can be easily extended to other materials systems, opening up an avenue for many more micro/nanofiber-based biomimetic designs.
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Periasamy, Kailashbalan, Everson Kandare, Raj Das, Maryam Darouie, and Akbar A. Khatibi. "Interfacial Engineering Methods in Thermoplastic Composites: An Overview." Polymers 15, no. 2 (January 12, 2023): 415. http://dx.doi.org/10.3390/polym15020415.
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The paper critically analyzed different interfacial enhancing methods used in thermoplastic composites. Although the absence of cross-linked polymer chains and chemical bonds on solidification enables the thermoplastics to be remelted, it creates weak interfacial adhesion between fibre reinforcements and the thermoplastic matrix. The weak fibre-matrix interface bonding reduces the efficiency with which the applied load can be transferred between these composite constituents, causing the composite to fail prematurely. Their need for high-temperature processing, poor compatibility with other polymer matrices, and relatively high viscosity render thermoplastics challenging when used to manufacture composite laminates. Therefore, various methods, including nanoparticles, changing the polarity of the fibre surface by plasma etching, chemical treatment with ozone, or an oxidative attack at the fibre surface, have been applied to improve the fibre/matrix bonding in thermoplastic composites. The fabrication steps followed in these techniques, their progress in research, and the associated toughening mechanisms are comprehensively discussed in this paper. The effect of different fibre-matrix interfacial enhancement methods on the mechanical properties of thermoplastic composites is also deliberated.
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Cho, Johann, and Aldo Roberto Boccaccini. "Ceramic and Glass Matrix Composites Containing Carbon Nanotubes." Materials Science Forum 606 (October 2008): 61–77. http://dx.doi.org/10.4028/www.scientific.net/msf.606.61.
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Carbon nanotubes (CNTs) are promising reinforcing elements for structural composites due to their remarkable mechanical properties. The impressive electrical and thermal properties of this new form of carbon also make CNTs containing composites ideal candidates for multifunctional applications. In the past decade, researchers have investigated CNTs as toughening inclusions to overcome the intrinsic brittleness of ceramics and glasses. Although there are numerous investigations available in the literature, a significant progress has not occurred or it has been rather slow compared to advances in the field of CNT/polymer matrix composites. This paper reviews current trends in research and development efforts on the use of CNTs for fabrication of ceramic and glass matrix composite materials. The review includes a summary of key issues related to the optimisation of CNT-based composites and an overview of investigations dealing with processing techniques developed to optimise dispersion quality, interfaces and density. The mechanical properties of as-produced composites are discussed and a comprehensive comparison of data available for different matrix materials is presented. Finally, the potential applications of the resulting CNT/inorganic matrix composites and the scope for future developments in the field are highlighted.
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Guldan, V. V., O. N. Sulima, and A. A. Sukhotin. "Legal Aspects of Participation of a Psychologist as a Specialist in Enforcement of Court Decisions in Parenting Cases (Part I)." Psychology and Law 8, no. 2 (2018): 125–37. http://dx.doi.org/10.17759/psylaw.2018080210.
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The article provides an analysis of scientific sources, normative legal acts, instructive letters of Federal Bailiffs Service of Russia, the position of judges and practices on the execution of enforcement documents related with upbringing of children. A psychologist with the legal status of specialist is to be involved in this category of enforcement proceedings. Based on analysis, problems associated with the imperfection of separate legal norms were identified, as well as Insufficiently thought-over legal design of specialist status in enforcement proceedings were found. The authors make proposals on expanding the list of rights and toughening the responsibility of specialist in enforcement proceedings, as well as the proposal to provide a psychologist with right of making an acquaintance with the conclusion made by a forensic psychological or complex forensic psycho-psychiatric expertise. Based on the position of the judges and the absence of prohibition in carrying out of a special study made by a specialist in the enforcement proceedings, and the existing task for psychologist to evaluate psychological condition of a child, the authors conclude that the psychologist has the right to conduct a psychodiagnostic examination using scientific methods and techniques. The proposed measures to improve the legal norms are aimed to ensure a possibility of full and correct execution of adjudications on legal disputes related with upbringing of a child.
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Koberstein, J. T. "Polymer Surfaces and Interfaces." MRS Bulletin 21, no. 1 (January 1996): 16–18. http://dx.doi.org/10.1557/s0883769400035089.
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Since their commercialization in the late 1940s, applications for synthetic polymers have grown at an extraordinary rate, to the point where polymers are now ubiquitous in our society. The demands placed upon polymer performance have paralleled the growth in applications and has driven the development of sophisticated multiconstituent polymer formulations with many outstanding physical and mechanical properties. Many applications require that a polymeric material be attached to or in contact with another material. In some cases, such as the classic nonstick fry pan, as well as lubrication and release paper, it is desirable to create surfaces that do not interact with the material in contact. On the other hand, in applications such as rubber toughening of blends, filled or fiber-reinforced polymers, and coatings, dissimilar materials must adhere to each other if high performance is to be obtained. While the majority of the research and development efforts to date have centered on optimizing bulk properties, the focus is now shifting toward the development of polymer systems with controlled surface and interfacial properties.The recent flurry of activity in polymer interfacial science can be traced to the simultaneous emergence of three factors: a strong commercial need to control the surface properties of advanced multicomponent polymer systems, the availability of sophisticated theoretical methods for studying polymer surface and interphase problems, and the devel opment of new characterization techniques capable of investigating molecular level structure at polymer interphases. The seven articles that comprise this issue provide an overview of basic polymer interface science by discussing some of the current advances in polymer interface theory, by presenting many of the new techniques available for polymer interphase characterization, and by illustrating some of the interesting and challenging problems associated with their applications.
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Crossley, Glen A., and Simon A. M. Hesp. "New Class of Reactive Polymer Modifiers for Asphalt: Mitigation of Low-Temperature Damage." Transportation Research Record: Journal of the Transportation Research Board 1728, no. 1 (January 2000): 68–74. http://dx.doi.org/10.3141/1728-10.
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Results from the low-temperature performance evaluation of a new class of reactive polymer modifiers designed to improve binder-aggregate adhesion in asphalt concrete are discussed. A living free radical polymerization process was used to prepare polyisoprene (PI) with short blocks of reactive silane-functional monomer at one end of the polymer chain. Performance was evaluated with the thermal stress restrained specimen test at a cooling rate of-10°C/h. The results obtained were compared with those for unmodified and styrene-butadiene (SB)-modified mixes. When added at 3 and 6 percent by weight of the binder, SB reduced the fracture temperature of the asphalt concrete by 6°C and 9°C, respectively. Similar results were obtained with the reactive polymers. However, although all the SB-modified samples failed in a catastrophic mode, none of the samples containing the silane-functional PI did. It is hypothesized that these polymers toughened the asphalt to an extent that cracks were only able to grow in a stable mode as opposed to an unstable mode or that localized yielding occurred. The method for obtaining the desired toughening effect is flexible; lower-cost monomers, such as butadiene, and more common polymerization methods, such as emulsion or anionic polymerization techniques, could be used equally well to produce polymers with similar or better performance characteristics. An added benefit is that the tested polymers were able to improve the stripping resistance of the mix significantly.
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Frigan, Chevalier, Zhang, and Spies. "Is a Zirconia Dental Implant Safe When It Is Available on the Market?" Ceramics 2, no. 4 (October 12, 2019): 568–77. http://dx.doi.org/10.3390/ceramics2040044.
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The market share of zirconia (ZrO2) dental implants is steadily increasing. This material comprises a polymorphous character with three temperature-dependent crystalline structures, namely monoclinic (m), tetragonal (t) and cubic (c) phases. Special attention is given to the tetragonal phase when maintained in a metastable state at room temperature. Metastable tetragonal grains allow for the beneficial phenomenon of Phase Transformation Toughening (PTT), resulting in a high fracture resistance, but may lead to an undesired surface transformation to the monoclinic phase in a humid environment (low-temperature degradation, LTD, often referred to as ‘ageing’). Today, the clinical safety of zirconia dental implants by means of long-term stability is being addressed by two international ISO standards. These standards impose different experimental setups concerning the dynamic fatigue resistance of the final product (ISO 14801) or the ageing behavior of a standardized sample (ISO 13356) separately. However, when evaluating zirconia dental implants pre-clinically, oral environmental conditions should be simulated to the extent possible by combining a hydrothermal treatment and dynamic fatigue. For failure analysis, phase transformation might be quantified by non-destructive techniques, such as X-Ray Diffraction (XRD) or Raman spectroscopy, whereas Scanning Electron Microscopy (SEM) of cross-sections or Focused Ion Beam (FIB) sections might be used for visualization of the monoclinic layer growth in depth. Finally, a minimum load should be defined for static loading to fracture. The purpose of this communication is to contribute to the current discussion on how to optimize the aforementioned standards in order to guarantee clinical safety for the patients.
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Pan, Huang Hsing. "An Overall Approach for Microcrack and Inhomogeneity Toughening in Brittle Solids." Journal of Mechanics 15, no. 2 (June 1999): 57–68. http://dx.doi.org/10.1017/s1727719100000332.
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ABSTRACTBased on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.
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Tannous, Katia, Aline Gallo De Mitri, and Vadim Mizonov. "EXPERIMENTAL STUDY OF FLUID DYNAMIC BEHAVIOR OF BIOMASS PARTICLES IN FLUIDIZED BEDS: A REVIEW." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 61, no. 9-10 (October 22, 2018): 4–14. http://dx.doi.org/10.6060/ivkkt.20186109-10.5895.
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Decease of natural resources and increase of price of fossil fuels at growing energy consumption, toughening of ecological standards and necessity of the increase of the level of energetics diversification motivates mankind to more wide usage of renewable energy resources including the solid fuel of biological origin. The potential of biofuel usage is rather considerable because the energy equivalent of the biomass harvest on the land exceeds the worldwide energy consumption several times as much. The biomass application as a renewable fuel is already a reality worldwide with the development of policies and technologies that turn viable the transformation of biomass into energy. The aims of this work is to present a literature experimental review on the studies concerning to the use of fluidized beds taking into account their design and scale-up. Initially, the usual solid particle terminology and some important biomass properties are presented. A brief description of conversion technologies and the fluidization phenomena are introduced, followed by an explanation of the different experimental techniques. The characteristic velocities (initial, apparent, of segregation, and complete) are discussed based on different biomass properties, as well as a number of empirical correlations for these velocities are described. Finally, some considerations are made about characteristic bed porosities (apparent and complete) and bed expansion. Based on the literature analysis, an improvement has been done on the understanding of the biomass fluidization phenomena, however, further research is needed to comprehend the effect of biomass characteristics on the bed operational parameters, besides more accurate and general correlations must be developed to improve these technologies.
For citation:
Tannous K., De Mitri A.G., Mizonov V. Experimental study of fluid dynamic behavior of biomassparticles in fluidized beds: a review. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 4-14
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Rożniata, E. "The Microstructures and Energy Dispersive Spectroscopy Analysis of a Hypoeutectoid Steels With 1% Cr." Archives of Metallurgy and Materials 58, no. 4 (December 1, 2013): 1253–59. http://dx.doi.org/10.2478/amm-2013-0144.
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Abstract The results of a microstructure, Energy Dispersive Spectroscopy analysis and hardness investigations of the hypoeutectoid steels with 1% Cr, imitating by its chemical composition toughening steels, are presented in the paper. Dilatometric tests were performed using L78R.I.T.A dilatometer of the German company LINSEIS. Using dilatometer the changes of elongation (Δl) of the samples with dimensions φ 3X10mm as a function of temperature (T) were registered. Obtained heating curves were used to precisely determine the critical temperatures (critical points) for the tested steels, while the differentiation of obtained cooling curves allowed to precisely define the temperatures of the beginning and the end of particular transition to draw two CCT diagrams. The analysis of the chemical composition of the phases present in the studied steels for different cooling rates were performed using an electron microprobe (X-ray microanalyzer). In this study a point, linear and a fixed area analysis techniques were used. After placing the samples tested steels in the chamber and the achievement of appropriate vacuum, spots for analysis were identified and the EDS analysis (Energy Dispersive Spectroscopy) was performed. EDS analyzes were performed using Nova NanoSEM 450 scanning electron transmission microscope. Developed CCT diagrams in accordance with the Rose and Wever classification are of type IV, which means that the diffusional transformations are separated by a stability range of the undercooled austenite and have the shape of the letter ”C”. The hardenability of tested steels is similar, but molybdenum acts much more effectively than nickel. Molybdenum occupies the I-st place among the effectiveness of alloying elements for the steels designed for low tempering, where the ”background” of other elements is weak. For both tested hypoeutectoid steels an EDS analysis revealed the precipitation of alloyed cementite at the grain boundaries. Chromium, as a ferrite creative element, quite strongly diffuses into the grain boundaries. It is visible with the change of chromium distribution along pearlite/ferrite grains boundaries.
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Li, Xiaoyan, Wenjing Zhang, Shiwei Zhai, Shawei Tang, Xiaoqin Zhou, Dengguang Yu, and Xia Wang. "Investigation into the toughening mechanism of epoxy reinforced with multi-wall carbon nanotubes." e-Polymers 15, no. 5 (September 1, 2015): 335–43. http://dx.doi.org/10.1515/epoly-2015-0143.
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AbstractThis study reports the reinforcement and fracture toughening mechanism of pristine multi-walled carbon nanotubes (MWCNTs) on epoxy matrix. The tensile strength and fracture energy (GIC) of the epoxy polymer increased simultaneously upon the addition of a small amount of MWCNTs. The fracture surfaces of single-edge-notch three-point bending test specimens were analysed by scanning electron microscopy, and the double-notch four-point bending technique was used to investigate the fracture process by transmission electron microscopy, respectively. MWCNT pull-out and subsequent plastic void growth were found; meanwhile, fracture of MWCNTs was observed along the crack propagation path. The theoretical model of shearing band initiated by the stress concentrations around the MWCNTs is the dominant toughening mechanism. While the crack bridging of MWCNTs and the plastic void growth of epoxy also have a toughening effect.
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Sharifi, M., C. W. Jang, C. F. Abrams, and G. R. Palmese. "Toughened epoxy polymers via rearrangement of network topology." J. Mater. Chem. A 2, no. 38 (2014): 16071–82. http://dx.doi.org/10.1039/c4ta03051f.
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A new toughening mechanism for thermosetting polymers is shown. The technique involves manipulation of polymer network topology allowing the glassy material to deform under loading without rupturing covalent bonds.
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Gholizadeh, Ali, Hasan Mansouri, Ali Nikbakht, Hamed Saghafi, and Mohamad Fotouhi. "Applying Acoustic Emission Technique for Detecting Various Damages Occurred in PCL Nanomodified Composite Laminates." Polymers 13, no. 21 (October 26, 2021): 3680. http://dx.doi.org/10.3390/polym13213680.
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Interleaving composite laminates by nanofibers is a well-known method of increasing interlaminar fracture toughness. Among many possibilities, polycaprolactone (PCL) nanofibers is one of the best choices for toughening composite laminates. The influence of PCL on delamination mode of failure is considered before. However, the effect of PCL on other damage modes, such as fiber breakage and matrix cracking, is yet to be studied. In this study, the acoustic emission (AE) technique is applied to determine the effect of toughening composite laminates by PCL nanofibers on matrix cracking, fiber/matrix debonding, and fiber breakage failure mechanisms. For this purpose, mode I and mode II fracture tests are conducted on modified and non-modified glass/epoxy laminates. Three different methods, i.e., peak frequency, wavelet transform, and sentry function, are utilized for analyzing the recorded AE data from mode I test. The results show that applying PCL nanofibers not only increases the mode I critical strain energy release rate by about 38%, but also decreases different failure mechanisms by between 75 and 94%.
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Xu, Chong Hai, M. D. Yi, Z. Y. Jiang, J. J. Zhang, and G. C. Xiao. "Preparation of an Advanced Al2O3 Based Nanocomposite Ceramic Die Material." Materials Science Forum 628-629 (August 2009): 465–70. http://dx.doi.org/10.4028/www.scientific.net/msf.628-629.465.
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Through the incorporation of nano sized Titanium Carbonitride powders into the Al2O3 matrix, an advanced Al2O3/Ti(C7N3) nanocomposite ceramic die material was fabricated by vacuum hot pressing technique. Effects of the content of nano Ti(C7N3) on the microstructure and mechanical properties of the nanocomposite ceramic die material were investigated. It indicates that both flexural strength and fracture toughness were increased noticeably compared with the pure micrometer sized alumina ceramic. Toughening mechanisms of the ceramic composite were also analyzed. It reveals that the intragranular/intergranular microstructures and the resulted transgranular/intergranular fracture modes are the main causes for the reinforcing and toughening of the nanocomposite ceramic die material.