Papers by Keyword: Fracture Strength

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Authors: Kazuki Tajima, Hae Jin Hwang, Mutsuo Sando, Koichi Niihara
Authors: Kazuki Tajima, Hae Jin Hwang, Mutsuo Sando, Koichi Niihara
Authors: Hajime Miyazawa, Katsuyoshi Hotta, Hiroyuki Shimizu, Mitsuaki Morita, Haruo Hirose
Abstract: In the study of the application of a laser technique on the bulk of press formed Bi system, the authors have reported that a superconductive layer can be obtained underneath the laser melted layer. In a continuing series of this study, this paper deals with the mechanical properties of the bulk laser treated. Superconductive powder of Bi system, 2223 phase was pressed to form a disk specimen of 2 mm thick and 10 mm at 29 MPa to 196 MPa. Then a CO2 laser beam of output power 6 W to 9 W was scanned linearly in air to melt the surface of the specimen to be subjected to the evaluation of hardness and fracture strength. The experimental results showed that the values of microvickers hardness of superconductive layer and melted layer are 135 and 105 respectively while that of the specimen as press formed is as low as 45. The fracture strength of the laser treated specimen was increased to 34 N from 15 N. The mechanical properties obtained deserve non sensitive handling in a practical use of the treated bulk.
Authors: Wen Bo Luo, Chu Hong Wang, Xiu Liu, Qiang Shen
Abstract: The influence of physical aging on mechanical properties of glassy polymers was investigated in this paper. After annealing above Tg to release the previous thermal and stress history, the polymethyl methacrylate (PMMA) samples were quenched to 27°C, aged for various times (ta), and were then stretched at the same temperature by two ways: (1) step stresses with four different magnitudes varying from 15MPa to 30MPa; (2) constant rate stretch up to fracture. The physical aging effect was monitored by measuring the initial instantaneous elastic modulus (E) and the fracture strength (σf) from the stress-strain curves as a function of ta up to 1368h. It is shown that both E and σf of the material increase with aging time and approach to their asymptotic values, which satisfy the KWW rule, while the isochronous creep compliance decreases with log ta in a linear manner within the aging time range considered in this paper.
Authors: Yong Hwan Kim, S.I. Kwun
Abstract: The microstructural changes and the relations between mechanical properties and additive powder with various brazing temperatures and times were investigated. The IN738 and BNi-3 alloy powders were used as an additive and filler metal powders for the brazing process. The wide-gap brazing process was carried out in a vacuum of 2×10-5 torr. The wide-gap region brazed with 60wt.% IN738 additive powder had a microstructure consisting of IN738 additive, and binary eutectic of Ni3B-Ni, and (Cr, W)B. As the brazing temperature and time were increased, the size of IN738 additive powder increased to 181µm, which decreased the amount of low strength Ni3B-Ni eutectic structure, thereby increasing the fracture strength of the wide-gap brazed region. Cracks in the brazed region were observed to propagate through the Ni3B-Ni structure, which lowered the fracture strength of the wide-gap brazed region.
Authors: Jian Bo Ji, Jian Tong
Abstract: The effects of different concentrations of the mixed solution, different test temperature conditions for corrosion rate of 316L stainless steel wires by using the weight loss method, discussion on fracture strength of 316L stainless steel wires changes after corrosion. The results showed that the higher the concentrations of the mixed solution, test temperature, the larger corrosion rate of 316L stainless steel wires, the smaller fracture strength of 316L stainless steel wires. During the test, the surface of 316L stainless steel wires occurred passivation. Though Cl- of the mixed solution didnt take direct part in the reaction, it prompted passive film rupture, accelerated the corrosion rate of 316L stainless steel wires. Meanwhile, the stress-strain curve of 316L stainless steel wires after corrosion no obvious yield phenomenon, showing the form of brittle fracture. And test temperature factors on the corrosion rate of 316L stainless steel wires and mechanical properties of the most obvious effect.
Authors: Wataru Nakao, Sang Kee Lee, Masahiro Yokouchi, Koji Takahashi, Kotoji Ando
Abstract: For improving fracture toughness as well as endowing with excellent self-crack-healing ability, mullite/SiC particles /SiC whiskers multi-composites were developed. Crack-healing ability and the mechanical properties of the specimens were investigated. Mullite/ 20 vol% SiC whiskers, mullite/ 25 vol% SiC whiskers and mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles composites can completely heal the pre-crack of 100 ım in surface length by heat-treatment at 1300 oC for 2 h in air. However, not completeness of the strength recovery was caused for mullite/ 15 vol% SiC whiskers composite by crack-healing. In spite of the same SiC content, the crack-healing ability of mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles composite is superior to that of mullite/ 25 vol% SiC whiskers composite. Admixing with SiC whisker was effective for improvement in fracture toughness. Additionally, the fracture toughness was not reduced by admixing with SiC particles.
Authors: Shoji Kamiya, Hideki Sekine
Abstract: Apparent fracture strength of notched fiber-reinforced composite laminates depends on the notch tip radius even if it is evaluated in terms of the local parameters such as the stresses at a notch tip or the stress intensity factors. Although numbers of phenomenological explanations have been made, this phenomenon has not yet been physically clear enough. In order to elucidate its key mechanism, our interest is here focused on the interlaminar crack extension from a notch tip in cross-ply laminates subjected to mode-I loading. We find a stochastically expected upper bound of interlaminar crack length due to the probabilistic breakage process of fibers in load-bearing laminas inside the delaminated zone. This upper bound, i.e., the critical length of interlaminar crack, is inherent to the laminate and corresponds to its notched strength. The well-known variation in apparent fracture strength of notched fiber-reinforced composite laminates with respect to the notch tip radius is clearly explained as the scale effect of this constant critical length in different displacement distributions ahead of notch tips of different radii.
Authors: Kohei Morishita, S. Ochiai, H. Okuda, Toshihiro Ishikawa, M. Sato
Abstract: For description of the mechanical performance of SiC/SiC composites and for safety design for practical use, it is needed to reveal the degradation mechanism especially of fiber under the oxygen atmosphere. In the present work, the fracture behavior and microstructure of the polycrystalline silicon carbide fiber exposed in air at 1173-1873 K for 20 and 3.6 ks were studied with monofilament tensile test, microstructure observation and fracture toughness determination test using newly developed FIB(focused-ion-beam)-method.
Authors: Chun Hong Chen, Satoshi Ishiguro, Sawao Honda, Hideo Awaji
Abstract: Based on the FGM concept, laminated alumina tube with a tailored porosity gradient along the radial direction has been successfully fabricated by the lamination method in the centrifugal molding technique. Experiments were performed with colloidally processed alumina powder and pore-former agent. The powder mixture was made into slurry in water media and the tubes were cast using a stainless steel mold. The porosity profile was designed with the presence of PMMA particles as pore-former agent and the nature of porosity was investigated by microstructure observations. The bimodal pore structure of the tubes was constructed from large spherical pores about 10 μm formed by burning-out the pore-former agent and small sub-micron pores caused by the lower sintering temperature. The fracture behavior of porous tubes with tailored porosity gradient was investigated using the O-ring compression testing. The failure behavior was divided into two types depending on the pore-former agent. The air permeability and fracture behavior were independent of the lamination process. The influence of the porosity gradient on the fracture strength was investigated and the results showed there was a reduction in fracture strength with increase in the laminate number, and the minimum strength was found in continuous graded tubes.
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