Articoli di riviste: "INCREASED TOUGHNESS"

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Ruan, Shiling, John J. Lannutti, Stan Prybyla e Robert R. Seghi. "Increased fracture toughness in nanoporous silica–polyimide matrix composites". Journal of Materials Research 16, n. 7 (luglio 2001): 1975–81. http://dx.doi.org/10.1557/jmr.2001.0270.

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Silica–polyimide nanocomposites were prepared by hot-pressing mixtures of polyimide and highly porous silica powder. The silica powder was produced using a sol-gel process that generates pores as small as 15 Å. The effects of loading, cure, and post-cure temperature on fracture toughness were investigated. The addition of silica particles improved the fracture toughness from 0.5 to a maximum of 1.9 MPa m0.5. However, fracture toughness dropped at silica weight percentages ≥30%. The cure and post-curing temperatures have a strong influence on toughness; post-curing exposure ≥400 °C reduced toughness. Transmission electron microscopy examination of the fracture surfaces indicated that the toughness improvements may occur at the nanometer scale due to crack pinning and branching induced by the nanoporous silica particles.

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Lee, S. M., E. Pippel, U. Gosele, C. Dresbach, Y. Qin, C. V. Chandran, T. Brauniger, G. Hause e M. Knez. "Greatly Increased Toughness of Infiltrated Spider Silk". Science 324, n. 5926 (24 aprile 2009): 488–92. http://dx.doi.org/10.1126/science.1168162.

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Konrad, Jean-Marie, e Julie Cummings. "Fracture toughness of frozen base and subbase soils in pavement". Canadian Geotechnical Journal 38, n. 5 (1 ottobre 2001): 967–81. http://dx.doi.org/10.1139/t01-032.

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Temperature distribution in the pavement structure, moisture distribution in granular soils, modulus of the asphalt concrete, and fracture toughness of material in the pavement structure strongly influence the propagation and spacing of thermal contraction cracks. Fracture toughness was determined for frozen sand (subbase layer) and frozen crushed stone (base layer) by adapting established fracture mechanics test procedures recommended in American Society for Testing and Materials standard test method E399-83 for metals. It was established that fracture toughness increases with decreasing temperature and increasing volumetric ice content. For a temperature of 5°C, the fracture toughness of frozen crushed stone increased almost linearly from 0.05 to 0.40 MPa·m0.5 when the volumetric ice content increased from 6 to 14%. For frozen sand, the fracture toughness KIC in a wedge-opening mode increased from 0.04 to 0.70 MPa·m0.5 when the volumetric ice content increased from 8 to 28%. It was also established that the fracture toughness of frozen soil decreases with decreasing soil average grain size according to a logarithmic law.Key words: fracture, toughness, experimental, frozen, granular soil, pavement.

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Van Niekerk, Anna Maria Susanna, e Hester E. Roets. "The Psycho-Educational Practice of Mental Toughness in Dealing with Trauma". International Journal of Psychological Studies 9, n. 4 (20 novembre 2017): 83. http://dx.doi.org/10.5539/ijps.v9n4p83.

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This study investigated whether an intervention program, which was developed within the psycho-educational field, could support traumatized people to increase their mental toughness. This program is based on the four components of mental toughness, namely control, challenge, commitment and confidence. A valid and reliable psychometric instrument, the Mental Toughness Questionnaire 48 (MTQ48), has been successfully used in both the corporate and sports psychology world to determine people’s mental toughness but has never before been tested in supporting traumatised people. Many corresponding aspects between mental toughness and trauma were discovered and used to compile a psycho-educational intervention program to support traumatized persons to develop increased mental toughness. An action research design was employed, where both qualitative as well as quantitative methods were used. Eight traumatized people participated in the research. The results of the study indicated that seven of the eight participants’ overall mental toughness increased after the intervention program, and four of the eight participants’ mental toughness components increased. All respondents indicated that they could better deal and cope with their trauma. The conclusion could be drawn that the psycho-educational intervention program, which was based on enhancing mental toughness, was successful in supporting the traumatised participants to increase their mental toughness.

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Wang, Wenke, Yang Guo, Yuanbo Li e Zhengning Li. "Fracture Toughness of Different Region Materials from a Dissimilar Metal Welded Joint in Steam Turbine Rotor". Coatings 12, n. 2 (29 gennaio 2022): 174. http://dx.doi.org/10.3390/coatings12020174.

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This study systematically evaluated the fracture toughness of a CrMoV/NiCrMoV dissimilar metal welded joint (DMWJ) with buttering layer technology in a steam turbine rotor. The fracture resistance curves and parameters of base metals (BM-1 and BM-2), weld metal (WM), buttering layer (BL), and heat-affected zones (HAZ-1 and HAZ-2) in the welded joint were all obtained. The characteristic microstructures, carbides, and fracture surfaces were observed by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed a different fracture toughness of each region in the DMWJ. The BM-1 showed a brittle fracture mode, mainly related to the directional needle-shaped carbide M3C. However, HAZ-1, BL, WM, HAZ-2, and BM-2 illustrated ductile fracture mode. The tempered microstructure and dispersed carbides increased the toughness of each material. Except for BM-1, the ductile fracture toughnesses of BL and WM were low in DMWJ due to coarse spherical carbide M7C3. The fracture toughness in the middle of HAZs was higher than that of the corresponding BMs owing to the fine tempered martensite and bainite. The fracture toughness along DMWJ appeared uneven. In sum, these findings look promising for the accurate integrity evaluation of DMWJs.

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Park, Sang Dae, Mitsugu Todo e Kazuo Arakawa. "Effect of Annealing on Fracture Mechanism of Biodegradable Poly(lactic acid)". Key Engineering Materials 261-263 (aprile 2004): 105–10. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.105.

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Effect of annealing on the fracture behavior of poly(lactic acid) (PLA) was investigated. Fracture toughness of PLA samples prepared under different annealing conditions was measured under static and dynamic loadings. Microstructure and crack growth behavior were characterized by polarizing microscopy (POM). Crystallinity was determined by DSC analysis. Fracture surface morphology was also studied by scanning electron microscopy. It was shown that the static fracture toughness increased with increase of crystallinity, while the dynamic toughness increased as crystallinity increased. POM exhibited that craze formation played an important role in the fracture mechanism of amorphous samples. Macroscopic fracture toughness and microscopic crack growth mechanism were correlated on the basis of these experimental results, and effect of annealing on the toughness and mechanism were discussed.

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Mutoh, Y., N. Miyahara, K. Yamaishi e T. Oikawa. "High Temperature Fracture Toughness in Silicon Nitride and Sialon". Journal of Engineering Materials and Technology 115, n. 3 (1 luglio 1993): 268–72. http://dx.doi.org/10.1115/1.2904217.

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Fracture Toughness of HIP-sintered silicon nitride decreased with increasing temperature up to 1200°C. The brittle-to-ductile transition was observed in the temperature range from 1200°C to 1275°C: the fracture toughness rapidly increased in the transition region. Above the transition temperature, the fracture toughness decreased with increasing temperature. Fracture toughness of sialon increased with increasing temperature. Transition of fracture mechanism was observed in sialon around 1300°C. The differences of temperature dependence of fracture toughness between two materials are interpreted in terms of the effects of grain-boundary glass phase on fracture.

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Yin, Hong Feng, e Lin Lin Lu. "Effect of Processing Condition on the Microstructure and Mechanical Properties of Ti₃SiC₂/SiC Composites". Materials Science Forum 658 (luglio 2010): 352–55. http://dx.doi.org/10.4028/www.scientific.net/msf.658.352.

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Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effect of processing condition on the microstructure and mechanical properties of the composites were investigated. The results showed that: (1) Hot-pressing temperature influenced the phase constituent of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. (2) The flexural strength and fracture toughness of composites increased when the content of SiC was increased. When the SiC content was 30wt% the flexural strength and fracture toughness of Ti3SiC2/SiC composite were 371MPa and 6.9MPa•m1/2 respectively. However, when the content of SiC reached 50wt%, the flexural strength and fracture toughness of composites decreased due to high porosity in the composites. (3) The flexural strength and fracture toughness of composites increased with the particle size of SiC added in composites. (4) Ti3SiC2/SiC composites were non-brittle at room temperature.

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Wang, Xiao Xiang, Wei Qi Wang, Wei Qing Li, Feng Li Li e Yu Lan Yang. "The Effect of Heat Treatment System on Mechanical Properties of Titanium Alloy BTi-6554". Materials Science Forum 618-619 (aprile 2009): 177–80. http://dx.doi.org/10.4028/www.scientific.net/msf.618-619.177.

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The effects of solution and aging treatment on the mechanical properties of BTi-6554 alloy titanium were investigated. The results showed: As to βsolution and aging treatment, the increase of fracture toughness is quite conspicuous as the solution temperature was raised, but the change of strength and plasticity is not obvious; As to (α+β) solution and aging treatment, the decline of fracture toughness and plasticity is quite conspicuous as the solution temperature increased, but the strength increased. The strength of (α+β) solution and aging treatment is higher than that of βsolution and aging treatment, but the fracture toughness is relatively lower. As the aging temperature increased, the strength of the alloy gradually decreased, but the plasticity and fracture toughness gradually improved and the improvement of fracture toughness is quite conspicuous. A better combination of strength-toughness-ductibility could be obtained under the heat treatment as solution at 900~930 oC and aging treatment at 560~590 oC.

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Bisht, Neeraj, e Prakash Chandra Gope. "Effect of rice husk (treated/untreated) and rice husk ash on fracture toughness of epoxy bio-composite". Journal of the Mechanical Behavior of Materials 29, n. 1 (1 gennaio 2020): 177–85. http://dx.doi.org/10.1515/jmbm-2020-0018.

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Abstract Present work studies the effect of particle reinforcement on fracture toughness of bio-composites. The filler used has been taken as rice husk. Epoxy resin has been taken as matrix material. Composites with varying filler loading of 10, 20, 30 and 40 wt.% were fabricated. The fracture toughness was seen to be increasing with increase in filler loading. However beyond 20% there was a decrease in fracture toughness with increase in filler loading. The effect of fibre treatment on toughness was also observed. Rice husk fibres pre-treated with NaOH were used. It was observed that fracture toughness further improved due to treatment. The increase in fracture toughness was significant. Fracture toughness increased from 1.072 to 2.7465 MPa√mm for 20% reinforcement and after treatment it increased to 2.876 MPa√mm. It was observed that concentration of treatment media also affects the fracture toughness. Further the effect of hybridization was observed by addition of rice husk ash as a secondary reinforcement. The fracture toughness of the resulting composites was remarkably higher than that of pure epoxy.

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Wang, Pengfei, Zhaodong Li, Guobiao Lin, Shitong Zhou, Caifu Yang e Qilong Yong. "Influence of Vanadium on the Microstructure and Mechanical Properties of Medium-Carbon Steels for Wheels". Metals 8, n. 12 (23 novembre 2018): 978. http://dx.doi.org/10.3390/met8120978.

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Steels used for high-speed train wheels require a combination of high strength, toughness, and wear resistance. In 0.54% C-0.9% Si wheel steel, the addition of 0.075 or 0.12 wt % V can refine grains and increase the ferrite content and toughness, although the influence on the microstructure and toughness is complex and poorly understood. We investigated the effect of 0.03, 0.12, and 0.23 wt % V on the microstructure and mechanical properties of medium-carbon steels (0.54% C-0.9% Si) for train wheels. As the V content increased, the precipitation strengthening increased, whereas the grain refinement initially increased, and then it remained unchanged. The increase in strength and hardness was mainly due to V(C,N) precipitation strengthening. Increasing the V content to 0.12 wt % refined the austenite grain size and pearlite block size, and increased the density of high-angle ferrite boundaries and ferrite volume fraction. The grain refinement improved the impact toughness. However, the impact toughness then reduced as the V content was increased to 0.23 wt %, because grain refinement did not further increase, whereas precipitation strengthening and ferrite hardening occurred.

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Yu, Kui, Srikkanth Balasubramanian, Helda Pahlavani, Mohammad J. Mirzaali, Amir A. Zadpoor e Marie-Eve Aubin-Tam. "Spiral Honeycomb Microstructured Bacterial Cellulose for Increased Strength and Toughness". ACS Applied Materials & Interfaces 12, n. 45 (28 ottobre 2020): 50748–55. http://dx.doi.org/10.1021/acsami.0c15886.

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Kendall, K., N. McN Alford, S. R. Tan e J. D. Birchall. "Influence of toughness on Weibull modulus of ceramic bending strength". Journal of Materials Research 1, n. 1 (febbraio 1986): 120–23. http://dx.doi.org/10.1557/jmr.1986.0120.

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It is demonstrated both theoretically and experimentally that fracture toughness does not directly influence the Weibull modulus of ceramic bending strength for materials that obey the Griffith criterion for crack propagation. Weibull modulus remains unchanged as toughness is increased. However, toughness variations with crack length do affect the Weibull modulus. Thus materials that display R-curve behavior or Dugdale character give an increased Weibull modulus and appear more reliable.

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Qu, Wen Qing, Min Yuan Song, Jun Shan Yao e Hai Yun Zhao. "Effect of Temperature and Heat Treatment Status on the Ductile Fracture Toughness of 2219 Aluminum Alloy". Materials Science Forum 689 (giugno 2011): 302–7. http://dx.doi.org/10.4028/www.scientific.net/msf.689.302.

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Through measurement of fracture toughness of 2219 aluminum alloy three-point bend specimen and observation of fracture surface and microstructure at different temperature, the influences of temperature and heat treatment status on the fracture toughness of 2219 aluminum alloy are discussed. The results show that temperature has an important influence on the fracture toughness of 2219 aluminum alloy. Compared with fracture toughness in room temperature, the fracture toughness is increased by 36% at low temperature. Heat treatment status also affects fracture toughness greatly, and fracture toughness in the T62 state is better than that in the T87 state. In conclusion, the reason why enhancement of fracture toughness of 2219 aluminum alloy at low temperature appearance is concluded.

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Zhao, Qing Xin, Zhao Yang Liu, Jin Rui Zhang e Ran Ran Zhao. "Research on Impact Behavior of Reactive Powder Concrete". Advanced Materials Research 150-151 (ottobre 2010): 779–82. http://dx.doi.org/10.4028/www.scientific.net/amr.150-151.779.

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By means of the three-point bending impact equipment, with the measurement of ultrasonic velocity, the impact behavior and damage evolution of reactive powder concrete (RPC) with 0, 1%, 2% and 3% volume fraction of steel fiber were tested. The results showed that steel fiber significantly improved the compressive strength, flexural strength, flexural toughness and impact toughness of RPC matrix. The compressive strength, flexural strength, flexural toughness of RPC with 3% steel fiber increased by 40.1%, 102.1%, and 37.4 times than that of plain concrete, respectively, and simultaneously, the impact toughness of RPC with 3% steel fiber was 93.2 times higher than that with 1% steel fiber. RPC with 2% and 3% steel fiber dosage both had relatively high compressive strength, flexural strength and flexural toughness; however, compared with the sample with 2% steel fiber dosage, the impact toughness of RPC with 3% steel fiber dosage increased by more than 10 times. Therefore, taking economy and applicability into consideration, if we mainly emphasis on the compressive strength, flexural strength and flexural toughness, RPC with 2% steel fiber is optimal. While if impact toughness is critical, RPC with 3% steel fiber would be the best choice.

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Park, Sun Hyo, In Young Ryu, Won Jun Lee, Dae Joon Kim, Jung Suk Han e Myung Hyun Lee. "Sinterbility and Mechanical Properties of Zirconia Nanoparticles Prepared by Hydrothermal Process". Solid State Phenomena 124-126 (giugno 2007): 1293–96. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.1293.

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A hydrothermal method has been used to produce nanoparticles of 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP) with high fracture toughness. The effects of reaction temperature and pH on crystallite size and sintered density, and the influence of Nb2O5 addition into 3Y-TZP on toughness have been investigated. The particle size increased with increasing the processing parameters and the influence of temperature was more significant than pH. The density of nanosized 3Y-TZP increased with increasing pH up to 9 and then decreased abruptly with further increase. The density increased slightly with the reaction temperature up to 140°C and then changed little with increasing temperature. The toughness increased in proportional to the Nb2O5 content. After sintering for 1 h at 1270°C, the highest relative density of 98% was obtained from nanoparticles of about 17 nm, prepared at 200°C and pH 9, and the toughness of 3Y-TZP was increased from 2.5 to 8.3 MPam1/2 by addition of 1.2 mol% Nb2O5.

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Kim, Ki-Hong, Won-Beom Lee, Tae-Hwan Kim e Seok-Won Son. "Microstructure and Fracture Toughness of Nitrided D2 Steels Using Potential-Controlled Nitriding". Metals 12, n. 1 (11 gennaio 2022): 139. http://dx.doi.org/10.3390/met12010139.

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Potential-controlled nitriding is an effective technique for enhancing the life of steel molds and dies by improving their surface hardness and toughness against fatigue damage. In this study, the effect of the nitriding potential on the microstructure and fracture toughness of nitrided AISI D2 steels was investigated. The nitrided layers were characterized by microhardness measurements, optical microscopy, and scanning electron microscopy, and their phases were identified by X-ray and electron backscatter diffraction. As the nitriding potential increased to 2.0 atm−1/2, an increase in the surface hardness and fracture toughness was observed with the growth of the compound layer. However, both the surface hardness and the fracture toughness decreased at the higher nitriding potential of 5.0 atm−1/2 owing to the increased porosity in the compound layers, which mainly consist of the ε (Fe2–3N) phase. Additionally, by observing crack growth behavior, the fracture toughness was analyzed considering the material characteristics of the diffusion and compound layers. The fracture toughness was influenced by the location of the initial Palmqvist cracks due to the localized plastic deformation of the diffusion layer and increased crack length due to the porous compound layer.

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Feng, Hu, Gang Chen, Danying Gao, Kunpeng Zhao e Chong Zhang. "Mechanical Properties of Steel Fiber-Reinforced Magnesium Phosphate Cement Mortar". Advances in Civil Engineering 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/3978318.

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A new cement-based mortar with high early strength and toughness was developed by adding micro steel fibers (MSF) in magnesium phosphate cement (MPC) mortar. The compressive and flexural tests were carried out to investigate the effect of curing time, MSF volume fraction, sand-cement mass ratio, and water-cement mass ratio on the strength and flexural toughness of MSF-reinforced MPC mortar (MSFRMM). Also, the flexural toughness and ductility of MSFRMM were evaluated according to ASTM C1609. The results of this study showed that the addition of MSF from 0% to 1.6% by volume significantly improved the compressive strength of MSFRMM. The MSFRMM showed high early strength, especially during the first 3 days. The addition of MSFs changed the flexural failure mode of MPC-based mortar from brittleness to ductility, and the flexural toughness of MSFRMM remarkably increased with the increase of MSF volume fraction from 0% to 1.6%. The toughness and ductility of MSFRMM slightly increased with the increase of the dosage of cement. The toughness and ductility of MSFRMM increased with the decrease of the water-cement mass ratio due to the improved density of the mortar caused by the reduction of water.

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Zhou, Ze Yu, Xiang Xiao, Kang Du, Cheng Liu, Dan Lv e Xin Yu Lv. "Effect of Extrusion Temperature on Microstructure and Mechanical Properties of 7A36 Aluminum Alloy". Materials Science Forum 993 (maggio 2020): 108–15. http://dx.doi.org/10.4028/www.scientific.net/msf.993.108.

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The microstructure, texture distribution, tensile property and fracture toughness of 7A36 aluminum alloy profile were investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), tensile and toughness tests, respectively. The results show that when extrusion temperature increased from 410 °C to 430 °C, the second phase grew and the intensity of aging state alloy increased. With the extrusion temperature increased, the fracture toughness and elongation increased firstly and the decreased. The fracture toughness KICcan reach to 46.47 MPa·m1/2 at 420 °C. The extruded and final state of the 7A36 profile was dominated by the textured texture (Brass, S, and Copper), accompanied by a small amount of recrystallized type texture (Cube and Goss). As the extrusion temperature increased, the hard deformation texture increased, resulting in an increase in strength. The increase of extrusion temperature led to the increase of dynamic recrystallization fraction. The dynamic recrystallization fraction of the extruded state was 2.26 % when extrusion temperature was 430 °C. The change in KIC performance is the combined result of re-crystallization, second phase and texture.

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Kinloch, A. J., A. C. Taylor, M. Techapaitoon, W. S. Teo e S. Sprenger. "From matrix nano- and micro-phase tougheners to composite macro-properties". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, n. 2071 (13 luglio 2016): 20150275. http://dx.doi.org/10.1098/rsta.2015.0275.

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In this paper, firstly, the morphology and toughness of a range of bulk epoxy polymers, which incorporate a second phase of well-dispersed silica nanoparticles and/or rubber microparticles, have been determined. Secondly, the macro-properties of natural-fibre reinforced-plastic (NFRP) composites based upon these epoxy polymers have been ascertained, using (i) unidirectional flax fibres or (ii) regenerated-cellulose fibres in the architecture of a plain-woven fabric. Thirdly, the toughening mechanisms which are induced in these materials by the presence of the silica nanoparticles, the rubber microparticles and the natural fibres have been identified. Finally, the values of the toughness of the bulk epoxy polymers and corresponding NFRPs have been quantitatively modelled. The increased toughness recorded for the bulk epoxy polymer due to the presence of the silica nanoparticles and/or rubber microparticles was indeed typically transferred to the NFRP composites when using such epoxies as the matrices for the fibres. Thus, the important role that may be played by modifications to the epoxy matrices in order to increase the toughness of the composites was very clearly demonstrated by these results. However, notwithstanding, the toughening mechanisms induced by the fibres were essentially responsible for the very high toughnesses of the NFRP composites, compared with the bulk epoxy polymers. The modelling studies successfully predicted the values of toughness of the bulk epoxy polymers and of the NFRP composites. These studies also quantified the extent to which each toughening mechanism, induced by the second-phase nano- and microparticles and the natural fibres, contributed to the overall values of toughness of the materials. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

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Yenigun, Burak, Muhammad Salman Chaudhry, Elli Gkouti e Aleksander Czekanski. "Characterization of Mode I and Mode II Interlaminar Fracture Toughness in CNT-Enhanced CFRP under Various Temperature and Loading Rates". Nanomaterials 13, n. 11 (25 maggio 2023): 1729. http://dx.doi.org/10.3390/nano13111729.

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This study investigates the influence of temperature and loading rate on the Mode I and Mode II interlaminar fracture behavior of carbon-nanotubes-enhanced carbon-fiber-reinforced polymer (CNT-CFRP). CNT-induced toughening of the epoxy matrix is characterized by producing CFRP with varying loading of CNT areal density. CNT-CFRP samples were subjected to varying loading rates and testing temperatures. Fracture surfaces of CNT-CFRP were analyzed using scanning electron microscopy (SEM) imaging. Mode I and Mode II interlaminar fracture toughness increased with increasing amount of CNT to an optimum value of 1 g/m2, then decreased at higher CNT amounts. Moreover, it was found that CNT-CFRP fracture toughness increased linearly with the loading rate in Mode I and Mode II. On the other hand, different responses to changing temperature were observed; Mode I fracture toughness increased when elevating the temperature, while Mode II fracture toughness increased with increasing up to room temperature and decreased at higher temperatures.

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Singh, D., e D. K. Shetty. "Microstructural Effects on Fracture Toughness of Polycrystalline Ceramics in Combined Mode I and Mode II Loading". Journal of Engineering for Gas Turbines and Power 111, n. 1 (1 gennaio 1989): 174–80. http://dx.doi.org/10.1115/1.3240220.

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Fracture toughness of polycrystalline alumina and ceria partially stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion were the main sources of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

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Liu, Jingwu, Jian Sun, Shitong Wei e Shanping Lu. "The Effect of Nickel Contents on the Microstructure Evolution and Toughness of 800 MPa Grade Low Carbon Bainite Deposited Metal". Crystals 11, n. 6 (21 giugno 2021): 709. http://dx.doi.org/10.3390/cryst11060709.

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In this work, three deposited metals with different nickel (Ni) contents were produced by active gas metal arc welding (GMAW) in order to explore the influence of Ni on the microstructure evolution and toughness of 800 MPa grade low carbon bainite deposited metal. The results showed that microstructure of the deposited metals mainly consisted of lath bainite, lath martensite, coalesced bainite (CB), and retained austenite (RA), and that the toughness was closely related to two factors: CB and RA. RA in deposited metal could improve the toughness, while the CB would deteriorate the toughness of deposited metal. As the Ni content increased, a large amount of CB was generated in the deposited metals. The RA content increased from 1.5% to 5.7% with the content of Ni increasing from 5.5% to 6.5%. However, the RA content did not increase when the Ni content increased from 6.5% to 7.5%. Additionally, the smallest control unit of toughness in 800 MPa grade low carbon bainite deposited metals is the Bain Packet (BP) from the perspective of crystallography characteristics. This work provided a reference for the chemical composition design of 800 MPa grade steel welding consumables and showed that the toughness of the deposited metal could be improved effectively by increasing the RA content while suppressing the formation of CB.

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Safiuddin, Md, George Abdel-Sayed e Nataliya Hearn. "Flexural and Impact Behaviors of Mortar Composite Including Carbon Fibers". Materials 15, n. 5 (23 febbraio 2022): 1657. http://dx.doi.org/10.3390/ma15051657.

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This study investigated the flexural and impact performances of mortar composite made with carbon fibers (MCCF). Four mortar composites (MCCF1, MCCF2, MCCF3, and MCCF4) were produced, using 1%, 2%, 3%, and 4% carbon fibers by volume, respectively. Another mortar composite without any carbon fibers (MCCF0) was prepared for its use as a control mix. The freshly mixed mortar composites were tested for inverted slump cone flow time to ensure they had an adequate workability to cast test specimens under vibration. In addition, all fresh mortar composites were examined for density and air content. The hardened mortar composites were tested for their first-crack flexural strength, ultimate flexural strength, first-crack impact resistance, and ultimate impact resistance. Moreover, the first-crack flexural toughness, ultimate flexural toughness, first-crack impact toughness, and ultimate impact toughness were determined for all hardened mortar composites. The correlations among the hardened properties of the mortar composites were also sought. Finally, the optimum fiber content was defined from the overall test results and considering the costs of the mortar composites. The test results showed that the workability and density of the fresh mortar composite decreased, whereas its air content increased due to the inclusion of carbon fibers. However, MCCF3 possessed the highest density and lowest air content among all MCCF mixes. It also had a higher workability than MCCF4. In the hardened state, the first-crack flexural strength and impact resistance, as well as the ultimate flexural strength and impact resistance of mortar composite, increased significantly with the increasing volume content of carbon fibers. In addition, the first-crack flexural toughness, ultimate flexural toughness, first-crack impact toughness, and ultimate impact toughness increased greatly with the higher volume content of carbon fibers. Strong correlations between the flexural strength and impact resistance, and between the flexural toughness and impact toughness of the mortar composites, were observed. Above all, excellent flexural strength, flexural toughness, impact resistance, and impact toughness values were observed for MCCF4 (4% carbon fibers). The 28-day ultimate flexural strength and impact resistance of MCCF4 increased by 4.6 MPa and 134 blows, respectively, as compared to MCCF0. Moreover, the 28-day ultimate flexural toughness and ultimate impact toughness values of MCCF4 were higher than that of MCCF0, by 3739.7 N-mm and 2703.3 J, respectively. However, MCCF3 (3% carbon fibers) also exhibited a good performance under flexural and impact loadings. Based on the costs of all mortar composites and their performances in both fresh and hardened states, MCCF3 was derived as the best mortar mix. This implies that 3% carbon fibers can be defined as the optimum fiber content in the context of the present study.

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25

Xu, Fang, Ming Kai Zhou, Wei Guo Shen e Bei Xing Li. "Study on the Toughness Performance of Polypropylene Fiber and SBR Polymer Latex Modified Cement Mortar". Advanced Materials Research 79-82 (agosto 2009): 1751–54. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.1751.

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In this paper, polypropylene fiber and SBR polymer latex are added into cement mortar to improve the toughness. Using two flexural toughness test methods of ASTM-C1018 and JSCE-SF4, the ratio of compressive strength to flexural strength (σC/σF for short) and flexural toughness index are used to evaluate the toughness of the cement mortar. The experimental results show that, comparing to the control cement mortar sample, when the SBR polymer mass percent of 20% and the polypropylene fiber volume percent of 1.0%, the σC/σF is 2.17, reduced by 59.2%, the ASTM toughness index I5, I10, I30 is 2.86, 2.95, 3.16 respectively, increased by 63.4%, 58.6%, 68.1% respectively, the JCI toughness index is 13.1, increased by 258%. Based on the SEM, adding SBR-polymer into cement mortar can form the polymer transition layer between the interfaces of polypropylene fibers and cement matrix, from XRD test, SBR polymer latex has no significant influence on the cement hydration after 7d curing. This research provides some useful references for the application of this new material.

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26

Kwon, Soon Chul, Tadaharu Adachi, Wakako Araki e Akihiko Yamaji. "Effect of Particle Size on Fracture Toughness of Spherical-Silica Particle Filled Epoxy Composites". Key Engineering Materials 297-300 (novembre 2005): 207–12. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.207.

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We investigated the particle size effects on the fracture toughness of epoxy resin composites reinforced with spherical-silica particles. The silica particles had different mean particle diameters of between 1.56 and 0.24µm and were filled with bisphenol A-type epoxy resin under different mixture ratios of small and large particles and a constant volume fraction for all particles of 0.30. As the content with the added smaller particle increased, the viscosity of each composite before curing remarkably increased. We conducted the single edge notched bending test (SENB) to measure the mode I fracture toughness of each composite. The fracture surface with the small particle content exhibited more rough areas than the surface with larger particles. The fracture toughness increased below the small particle content of 0.8 and saturated above it. Therefore, near the small particle content of 0.8, the composite had a relatively low viscosity and a high fracture toughness.

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27

Ural, Ani, e Deepak Vashishth. "Effects of Intracortical Porosity on Fracture Toughness in Aging Human Bone: A μCT-Based Cohesive Finite Element Study". Journal of Biomechanical Engineering 129, n. 5 (9 febbraio 2007): 625–31. http://dx.doi.org/10.1115/1.2768377.

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The extent to which increased intracortical porosity affects the fracture properties of aging and osteoporotic bone is unknown. Here, we report the development and application of a microcomputed tomography based finite element approach that allows determining the effects of intracortical porosity on bone fracture by blocking all other age-related changes in bone. Previously tested compact tension specimens from human tibiae were scanned using microcomputed tomography and converted to finite element meshes containing three-dimensional cohesive finite elements in the direction of the crack growth. Simulations were run incorporating age-related increase in intracortical porosity but keeping cohesive parameters representing other age-related effects constant. Additional simulations were performed with reduced cohesive parameters. The results showed a 6% decrease in initiation toughness and a 62% decrease in propagation toughness with a 4% increase in porosity. The reduction in toughnesses became even more pronounced when other age-related effects in addition to porosity were introduced. The initiation and propagation toughness decreased by 51% and 83%, respectively, with the combined effect of 4% increase in porosity and decrease in the cohesive properties reflecting other age-related changes in bone. These results show that intracortical porosity is a significant contributor to the fracture toughness of the cortical bone and that the combination of computational modeling with advanced imaging improves the prediction of the fracture properties of the aged and the osteoporotic cortical bone.

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28

Kuang, Jia Cai, Hong Lei Wang, Xin Gui Zhou e Ying Jun Deng. "Fracture Toughness of CNTs/AlN Ceramics Tested by Indentation". Advanced Materials Research 177 (dicembre 2010): 151–53. http://dx.doi.org/10.4028/www.scientific.net/amr.177.151.

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CNTs/AlN ceramics were fabricated by hot-pressing sintering process. The fracture toughness was measured by indentation method. The morphologies of indentation cracks were analyzed by SEM. The results show that the facture toughness of AlN was slightly improved because appreciate toughening mechanisms such as CNTs pull-out, crack bridging and deflect operate in CNTs/AlN. In addition, the facture toughness of CNTs/AlN increased with increasing CNTs content up to 3wt%. Then, the fracture toughness decrease when the CNTs content is 4wt%.

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29

Zheng, Xu, Yi Yang, Jianguo Tang, Baoshuai Han, Yanjin Xu, Yuansong Zeng e Yong Zhang. "Influence of Retrogression Time on the Fatigue Crack Growth Behavior of a Modified AA7475 Aluminum Alloy". Materials 16, n. 7 (29 marzo 2023): 2733. http://dx.doi.org/10.3390/ma16072733.

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This paper investigates the effect of retrogression time on the fatigue crack growth of a modified AA7475 aluminum alloy. Tests including tensile strength, fracture toughness, and fatigue limits were performed to understand the changes in properties with different retrogression procedures at 180 °C. The microstructure was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The findings indicated that as the retrogression time increased, the yield strength decreased from 508 MPa to 461 MPa, whereas the fracture toughness increased from 48 MPa√m to 63.5 MPa√m. The highest fracture toughness of 63.5 MPa√m was seen after 5 h of retrogression. The measured diameter of η’ precipitates increased from 6.13 nm at the retrogression 1 h condition to 6.50 nm at the retrogression 5 h condition. Prolonged retrogression also increased the chance of crack initiation, with slower crack growth rate in the long transverse direction compared to the longitudinal direction. An empirical relationship was established between fracture toughness and the volume fraction of age-hardening precipitates, with increasing number density of precipitates seen with increasing retrogression time.

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30

Hart, Kevin R., Ryan M. Dunn, Jennifer M. Sietins, Clara M. Hofmeister Mock, Michael E. Mackay e Eric D. Wetzel. "Increased fracture toughness of additively manufactured amorphous thermoplastics via thermal annealing". Polymer 144 (maggio 2018): 192–204. http://dx.doi.org/10.1016/j.polymer.2018.04.024.

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31

Taheri, Morteza, Seyed Farshid Kashani-Bozorg, Hamid Reza Teymouri, Amir Hossein Fallah-Morad, Rohallah Panahi Liavoli e Amirreza Davar. "Characterization of fracture behavior of a nickel-based using Charpy instrumented in different conditions of heat treatment and evaluation temperatures". Engineering Research Express 3, n. 4 (22 ottobre 2021): 045010. http://dx.doi.org/10.1088/2631-8695/ac2f54.

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Abstract Since gas turbine blades work in acute conditions, the study of their mechanical behavior, including impact, is one of the most important tasks recommended. The aim of this study was to investigate the impact behavior of IN738 superalloy welded by pulsed laser under different heat treatment conditions and different temperatures. The results of this study showed that the lowest fracture toughness was related to the specimens that were welded under casting conditions. This was due to the formation of liquation cracks during welding and due to the reaction between the (Ti,Ta)C carbide, γ-γ′ eutectic, and γ′ phase with the superalloy matrix. As the test temperature increased from ambient temperature to 600 °C, the impact toughness increased. This is attributed to the free presence of dislocations, which causes ductile behavior in the alloy. As the temperature increased further to 770 °C, the fracture toughness increased due to the increased strength of the superalloy yield due to locking of dislocations. At temperatures above 770 °C, the toughness of the superalloy was reduced again due to the decrease in strength due to the passage of dislocations through the obstacles.

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32

Jayesh, S., e Jacob Elias. "Experimental Investigations on Impact Toughness and Shear Strength of Novel Lead Free Solder Alloy Sn-1Cu-1Ni-XAg". Powder Metallurgy Progress 19, n. 2 (1 dicembre 2019): 90–96. http://dx.doi.org/10.1515/pmp-2019-0009.

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Abstract (sommario):

AbstractLead is known to be banned in alloy making, highlighting toxicity concerns and environmental legislations. Researchers and scholars around the globe were in immediate search of new lead free solder alloys which could potentially replace the old Sn-Pb alloy. In this comprehensive study, shear strength and impact toughness tests were conducted on Sn-1Cu-1Ni when different amounts of Ag (0.25, 0.5, 0.75 1 % by wt.) is added. Shear strength test is tested using micro force test system. Impact toughness test is analyzed using Charpy impact test set up by calculating the energy difference before and after impact. The study reveals that, Ultimate shear stress increased from 19 MPa to 21.3 MPa. Yield strength increased from 27.4 MPa to 29.7 Mpa. Impact toughness of the alloys increased from 9.4 J to 10.1 J. Thus, Sn-1Cu-1Ni-1Ag is found to have improved shear strength and impact toughness than Sn-1Cu-1Ni.

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33

Takayama, Tetsuo, Mitsugu Todo e Kazuo Arakawa. "Relationship between Fracture Mechanism and Microstructure in PLA/PCL Polymer Blends". Key Engineering Materials 353-358 (settembre 2007): 1169–72. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.1169.

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Abstract (sommario):

PLA/PCL and PLA/PCL/LTI blends were developed to improve the fracture properties of biodegradable PLA. LTI was blended to improve the miscibility of PLA and PCL. It was shown that the fracture toughness values were dramatically increased due to LTI addition. SEM results also exhibited that PCL spherulites decreases due to LTI addition and therefore, void formation is reduced and local stress concentration is suppressed, resulting in the improvement of the toughness values. The improved miscibility is also closely related to the enhancement of ductile deformation; as a result, the fracture toughness is increased.

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34

Zhao, Jing Song, Yi Feng, Nan Nan Chen, Fan Yan Chen, Jie Chen, Xue Bin Zhang, Xiao Bing Pan, Jing Tu e Xiao Ping Ouyang. "Fabrication and Mechanical Properties of Alumina—CNTs Composites". Applied Mechanics and Materials 66-68 (luglio 2011): 1390–96. http://dx.doi.org/10.4028/www.scientific.net/amm.66-68.1390.

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The transmutation target of nuclear waste material has been fabrication by a powder metallurgy method by using Alumina as the matrix and CNTs as reinforcement. The effect of different nanotube contents on the fracture toughness and the bending strength was investigation. The results showed the fracture toughness and the bending strength of composites increased with increasing CNTs mass fraction when the content of CNTs was less than 1.5%. However, when the contents of CNTs greater than 1.5%, the fracture toughness and the bending strength of composites decreased as the content of CNTs increased. Possible mechanisms are discussed in detail in the paper.

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35

You, Min, Chun Zhi Mei, Wen Jun Liu, Jing Rong Hu e Ling Wu. "Effect of Alkali on the Impact Toughness of Adhesively Bonded Joints". Applied Mechanics and Materials 166-169 (maggio 2012): 1904–7. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.1904.

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Abstract (sommario):

The effect of the temperature and immersed time of the alkali solution on the impact toughness of the adhesively bonded steel single lap joint under impact loading is studied using the experimental method. The results obtained show that the impact toughness of the specimen increased when the immersed time increased then it decreased as it beyond 3 days. When the immersed time is longer than 72 h, the higher the temperature is, the lower the impact toughness of the joint. The moisture absorption of the adhesive layer with the immersed time was also investigated and it was found that there is a relationship to the impact toughness of the adhesively bonded single lap joint. The epoxy adhesive layer was analyzed with FT-IR and it was found that the hydroxyl enhanced and bonding strength may increase after 72 h immersed in alkali solution.

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36

Xue, Xiao Huai, Song Nian Lou, Bainian Qian e Shaofei Yu. "Development of the SAW Wire for High Strength TMCP Steel". Materials Science Forum 475-479 (gennaio 2005): 269–72. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.269.

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Abstract (sommario):

The wire for high strength and toughness TMCP steels of submerged arc welding was developed. The low carbon and micro-alloying with Ti-B system was adopted to obtain the acicular ferrite dominated deposited metals. Experimental results show that the carbon equivalent (Pcm) should be higher than 0.17, which can ensure the high strength and high toughness of the deposited metals. In the alloy system, Oxygen and Nitrogen contents, micro-alloyed elements (C, Mn) and its mixture ratio are the key factors that affect the deposited metals toughness. With increasing C, Mn content, the acicular ferrite is increased and toughness is improved. Oxygen and Nitrogen are deleterious to the toughness of deposited metals.

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37

Yan, Han, Di Zhao, Tongfu Qi, Xuesong Leng e Kuijun Fu. "Relationship of the Microstructure and Toughness of the Coarse Grain Heat-Affected Zone of TiNbV Microalloyed Steels Based on Electron Backscatter Diffraction Analysis". Journal of Materials Engineering and Performance 31, n. 1 (7 ottobre 2021): 201–10. http://dx.doi.org/10.1007/s11665-021-06140-1.

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Abstract (sommario):

AbstractThe microstructure evolution and impact toughness of the coarse grain heat-affected zone (CGHAZ) of TiNbV microalloyed steels were investigated by using a thermal simulation test. The samples were treated with various simulated welding thermal cycles. The phase constituents and grain sizes were analyzed by using electron backscatter diffraction analysis. The microstructure of the CGHAZ of the treated samples consisted of ferrite, acicular ferrite, pearlite, and bainite. The samples have a higher impact toughness under a lower welding heat input. This is because the microstructure of the CGHAZ is dominated by the higher volume fraction of the high-angle grain boundaries of acicular ferrites. The presence of bainite and coarsening grains are two key factors deteriorating the toughness of the CGHAZ of TiNbV microalloyed steels. The volume fraction of bainite sharply increased as the welding heat input increased, leading to a decrease in the impact toughness of the CGHAZ. For a higher welding heat input, both the severe coarsening of the grain size and a higher bainite content would result in poor impact toughness.

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38

Sikder, Bablu, e Abhijit Chanda. "Effect of Annealing on Fracture Toughness Evaluation of Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃₋_δ (BSCF) at Different Temperatures". Applied Mechanics and Materials 592-594 (luglio 2014): 816–20. http://dx.doi.org/10.4028/www.scientific.net/amm.592-594.816.

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Abstract (sommario):

An experimental study on the fracture toughness of BSCF samples were conducted at room temperature as well as elevated temperatures (upto 800°C). The results showed a typical variation of fracture toughness and fracture stress with temperature. It decreased upto 600°C and then increased to reach a comparatively higher value at 800°C. Without annealing the samples showed comparatively higher fracture toughness because of the presence of compressive residual stress.

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39

Zhou, Min, Lin Xiu Du, Xiang Hua Liu e Kai Zhang. "Phase Transformation and Properties under Different Quenching Mediums of a X120 Pipeline Steel". Advanced Materials Research 152-153 (ottobre 2010): 408–12. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.408.

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Abstract (sommario):

The microstructure, CVN toughness and micro-hardness of an X120 pipeline steel were investigated by metalloscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) etc. It showed that the microstructure evolved from lathe martensite, lathe bainite to granular bainite and polygonal ferrite, the size of M-A islands increased. With cooling velocity increasing, the CVN toughness at -20 was fluctuating, and reaching its peak in the steel cooled in oil had the best toughness, while the steel cooled in furnace was brittle at -20 . With cooling velocity decreasing, the micro-hardness of the steel decreased, whereas, the micro-hardness of the steel cooled in furnace increased slightly.

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40

Bang, Kook Soo, Woo Yeol Kim, Chan Park, Young Ho Ahn e Jong Bong Lee. "Effects of Nitrogen on Weld Metal Microstructure and Toughness in Submerged Arc Welding". Materials Science Forum 539-543 (marzo 2007): 3906–11. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3906.

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Abstract (sommario):

The effects of nitrogen content on weld metal impact toughness in submerged arc welding were investigated and interpreted in terms of microstructural changes and solid solution hardening. The weld metal impact toughness in as-welded condition decreased with increasing nitrogen content from 110 to 200 ppm. The weld metal microstructure changed with increasing nitrogen content; ferrite with second phase increased at the expense of tough acicular ferrite. In addition to microstructural changes, the microhardness of acicular ferrite increased gradually with the nitrogen content. Therefore, the loss of impact toughness can be attributed to a combination of the effects of microstructural changes and solid solution hardening.

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41

Taştan, Zarife. "Mental Toughness and Motivational Climate of Volleyball Players". Pakistan Journal of Medical and Health Sciences 15, n. 11 (30 novembre 2021): 3321–24. http://dx.doi.org/10.53350/pjmhs2115113321.

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Abstract (sommario):

Background: Sports psychology focuses on the analysis of various psychological variables and cognitive processes that affect athletes' performance and focuses on improving their cognitive abilities to maximize efficiency. Aim: The aim of this research is to determine the relationship between mental toughness and motivational climate in licensed volleyball players studying in Coaching Education departments. Methods: In this study, the relational screening model was used to determine the relationship between mental toughness and motivational climate in licensed volleyball players studying in Coaching Education departments. Results: it was concluded that the performance climate levels of licensed volleyball players studying in coaching education departments increased as their level of confidence increased, and decreased as their constancy and control levels increased. Again, as a result of the analysis, it was observed that the variables of confidence, constancy and control had a significant role in predicting the performance climate of licensed volleyball players. Conclusion: it can be said that mental toughness predicts motivational climate in licensed volleyball players who study in coaching education departments. Keywords: Mastery Climate, Performance Climate, Mental Toughness, Coaching Education Students, Motivational Climate.

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42

Fei, Yu Huan, Chuan Zhen Huang, Han Lian Liu e Bin Zou. "Mechanical Properties of Al₂O₃-TiN Nanocomposite Ceramic Tool Materials". Key Engineering Materials 499 (gennaio 2012): 108–13. http://dx.doi.org/10.4028/www.scientific.net/kem.499.108.

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Abstract (sommario):

Al2O3-TiN nanocomposite ceramic tool materials were fabricated by hot-pressing technique and the mechanical properties were measured. Mechanical properties such as room temperature flexural strength, Vickers hardness and fracture toughness were measured through three-point bending test and Vickers indentation. The effects of the content of nano-scale TiN, sintering temperature and holding time on the mechanical properties were investigated. The results shows that the addition of nano-scale TiN can improve the mechanical properties of alumina ceramics. Both the flexural strength and the fracture toughness first increased then decreased with an increment in the content of nano-scale TiN. Both the Vickers hardness and the fracture toughness increased with an increment in the sintering temperature. The flexural strength increased with an increment in the holding time, while the fracture toughness decreased with an increment in the holding time. The composites with only nano-scale TiN have the highest Vickers hardness for the holding time of 30min, while the hardness of the composites with nano-scale TiN and micro-scale TiN decreased with an increment in the holding time.

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43

Liu, Cheng Jun, Ya He Huang, Hong Liang Liu e Mao Fa Jiang. "Effects and Mechanisms of Niobium on the Fracture Toughness of Heavy Rail Steel". Advanced Materials Research 163-167 (dicembre 2010): 110–16. http://dx.doi.org/10.4028/www.scientific.net/amr.163-167.110.

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Abstract (sommario):

Heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects and mechanisms of niobium on the fracture toughness of heavy rail steel were investigated. In addition, the appropriate range of niobium content for heavy rail steel was determined. With the niobium content increasing, both the austenite grain size and pearlite laminae distance of heavy rail steel were decreased gradually at first and then increased rapidly. When the niobium content was low, the precipitates containing niobium predominantly appeared in the cementite, which improved the toughness of heavy rail steel by fining the austenite grain size and pearlite laminae distance; when the niobium content > 0.024%, the fine dispersed precipitates containing niobium mainly occurred in the ferrite, which improved the toughness of heavy rail steel by pining dislocations and inhibiting crack growth; with the niobium content increasing, both the quantity and size of precipitates containing niobium were increased gradually; when the niobium content > 0.073%, most precipitates containing niobium could not pin dislocations and inhibit crack growth because the particles size was too big, thus the fracture toughness of heavy rail steel was bad. So the optimum range of the niobium content could improve the fracture toughness of heavy rail steel. In the present study, when the niobium content was about 0.053%, the fracture toughness of heavy rail steel was the best. The maximum plane-strain fracture toughness was 49.88 MPam1/2.

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44

Sembokuya, Hideki, Masaki Hojo e Kiyoshi Kemmochi. "Mode I Interlaminar Fracture Toughness of Organic Fiber Reinforced Plastics". Advanced Composites Letters 6, n. 3 (maggio 1997): 096369359700600. http://dx.doi.org/10.1177/096369359700600302.

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Abstract (sommario):

Mode I Interlaminar fracture behaviors of organic (aramid and polyarylate) fiber reinforced plastics were investigated. The values of interlaminar fracture toughness increased with the increase of crack length. The increase of intrelaminar fracture toughness was due to the fiber bridging between crack surfaces.

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45

Madrigal, Leilani. "The Development of a Behavior Checklist for Mentally Tough Behaviors in Volleyball". Sport Psychologist 34, n. 3 (1 settembre 2020): 177–86. http://dx.doi.org/10.1123/tsp.2019-0159.

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Abstract (sommario):

Mental toughness is a factor related to performance, better coping, and increased confidence. There has been a growing trend toward assessing mental toughness behaviorally. The purpose of this paper was to develop a behavioral assessment of mental toughness in volleyball. Following a five-stage process to develop a systematic observation instrument, the current study identified 10 mental toughness behaviors in volleyball, specifically, six behaviors occurring during a play and four behaviors after a play (i.e., when a point is scored from the opposing team). Furthermore, eight behaviors represent mentally tough actions, while two behaviors represent mentally weak actions. The results indicate that the behavioral checklist is a reliable systematic observation instrument. Coaches and certified mental performance consultants can benefit from using this checklist by discussing mental toughness and behaviors corresponding to mental toughness during game play, and then have a quantifiable way to track behaviors with individuals and volleyball teams.

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46

Slyker, Leigh, e Lawrence Bonassar. "Alginate Conjugation Increases Toughness in Auricular Chondrocyte Seeded Collagen Hydrogels". Bioengineering 10, n. 9 (4 settembre 2023): 1037. http://dx.doi.org/10.3390/bioengineering10091037.

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Abstract (sommario):

Current auricular cartilage replacements for pediatric microtia fail to address the need for long-term integration and neocartilage formation. While collagen hydrogels have been successful in fostering neocartilage formation, the toughness and extensibility of these materials do not match that of native tissue. This study used the N-terminal functionalization of collagen with alginate oligomers to improve toughness and extensibility through metal–ion complexation. Alginate conjugation was confirmed via FTIR spectroscopy. The retention of native collagen fibrillar structure, thermal gelation, and helical conformation in functionalized gels was confirmed via scanning electron microscopy, oscillatory shear rheology, and circular dichroism spectroscopy, respectively. Alginate–calcium complexation enabled a more than two-fold increase in modulus and work density in functionalized collagen with the addition of 50 mM CaCl2, whereas unmodified collagen decreased in both modulus and work density with increasing calcium concentration. Additionally, the extensibility of alginate-functionalized collagen was increased at 25 and 50 mM CaCl2. Following 2-week culture with auricular chondrocytes, alginate-functionalization had no effect on the cytocompatibility of collagen gels, with no effects on cell density, and increased glycosaminoglycan deposition. Custom MATLAB video analysis was then used to quantify fracture toughness, which was more than 5-fold higher following culture in functionalized collagen and almost three-fold higher in unmodified collagen.

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47

Chotěborský, R., P. Hrabě e A. Kabutey. "Change of mechanical properties in substrate during rewelding deposit". Research in Agricultural Engineering 57, No. 3 (22 settembre 2011): 105–9. http://dx.doi.org/10.17221/36/2010-rae.

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Abstract (sommario):

A study was carried out to examine the influence of rewelding deposit of structural low carbon steel and also the changes which occur in heat-affected zone and subcritical zone during rewelding. Optical metallography, microhardness Vickers method and Charpy impact test were employed to analyze these differences. The results show that rewelding deposit increased the heat-affected zone and fine coarse grain heat-affected zone and also has influence on impact toughness of substrate and their microhardness. Again, it was found that rewelding increased the fine coarse grain heat-affected zone. This effect resulted in increasing impact toughness in the heat-affected zone. However, submicroscopic change in substrate ferrite showed decreasing impact toughness.

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48

Shin, Yong-Chul, e Seung-Mo Kim. "Enhancement of the Interlaminar Fracture Toughness of a Carbon-Fiber-Reinforced Polymer Using Interleaved Carbon Nanotube Buckypaper". Applied Sciences 11, n. 15 (24 luglio 2021): 6821. http://dx.doi.org/10.3390/app11156821.

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In this study, a carbon nanotube (CNT) buckypaper was interleaved in a carbon-fiber-reinforced polymer (CFRP) composite to improve the interlaminar fracture toughness. Interleaving the film of a laminate-type composite poses the risk of deteriorating the in-plane mechanical properties. Therefore, the in-plane shear modulus and shear strength were measured prior to estimating the interlaminar fracture toughness. To evaluate the effect of the buckypaper on the interlaminar fracture toughness of the CFRP, double cantilever beam (DCB) and end notch flexure (ENF) tests were conducted for mode I and mode II delamination, respectively. No significant change was observed for the in-plane shear modulus due to the buckypaper interleaving and the shear strength decreased by 4%. However, the interlaminar fracture toughness of the CFRP increased significantly. Moreover, the mode II interlaminar fracture toughness of the CFRP increased by 45.9%. Optical micrographs of the cross-section of the CFRPs were obtained to compare the microstructures of the specimens with and without buckypaper interleaving. The fracture surfaces obtained after the DCB and ENF tests were examined using a scanning electron microscope to identify the toughening mechanism of the buckypaper-interleaved CFRP.

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49

Guo, Wei, Zicheng Zheng, Wei Li, Hao Li, Fankun Zeng e Huajie Mao. "The Cellular Structure and Toughness of Hydrogenated Styrene-Butadiene Block Copolymer Reinforced Polypropylene Foams". Polymers 15, n. 6 (17 marzo 2023): 1503. http://dx.doi.org/10.3390/polym15061503.

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Polypropylene nanocomposites containing varying amounts of Styrene-ethylene-butadiene-styrene block copolymer (SEBS) were prepared through the supercritical nitrogen microcellular injection-molding process. Maleic anhydride (MAH)-grafted polypropylene (PP-g-MAH) copolymers were used as compatibilizers. The influence of SEBS content on the cell structure and toughness of the SEBS/PP composites was investigated. Upon the addition of SEBS, the differential scanning calorimeter tests revealed that the grain size of the composites decreased, and their toughness increased. The results of the rheological behavior tests showed that the melt viscosity of the composite increased, playing a role in enhancing the cell structure. With the addition of 20 wt% SEBS, the cell diameter decreased from 157 to 66.7 μm, leading to an improvement in the mechanical properties. Compared to pure PP material, the impact toughness of the composites rose by 410% with 20 wt% of SEBS. Microstructure images of the impact section displayed evident plastic deformation, effectively absorbing energy and improving the material’s toughness. Furthermore, the composites exhibited a significant increase in toughness in the tensile test, with the foamed material’s elongation at break being 960% higher than that of pure PP foamed material when the SEBS content was 20%.

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50

Bedse, R. D., J. K. Sonber, K. Sairam, T. S. R. Ch Murthy e R. C. Hubli. "Processing and Characterization of CrB2-Based Novel Composites". High Temperature Materials and Processes 34, n. 7 (13 gennaio 2015): 683–87. http://dx.doi.org/10.1515/htmp-2014-0084.

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Abstract This paper presents the results of investigations carried out on processing and characterization of CrB2-based novel composites. Niobium metal powder was used as additive to form new composites. Hardness and fracture toughness of chromium boride increased by addition of niobium. CrB2 composites were prepared by addition of 2.5, 10 and 20 wt.% Nb. Density of higher than 95% ρ th was achieved in all the samples. Hot pressed samples were analyzed to contain reaction products of NbB2, Cr2B3 and Cr3B4 phases along with CrB2. Hardness of CrB2 composite was increased from 18.46 GPa to 21.89 GPa by increasing the Nb content from 2.5 to 10 wt.%. Fracture toughness of composites prepared by addition of 2.5 and 10% was measured as 3.11 and 3.38 MPa.m1/2 respectively. Addition of 20% Nb resulted in increased fracture toughness of 4.32 MPa.m1/2 .

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