Papers by Keyword: Bend Strength

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Authors: Ján Dusza, Lucia Hegedűsová, Monika Kašiarová, Erika Csehová
Abstract: The paper deals with the determination of the characteristic strength and as well as the Weibull moduli and of the Si3N4+SiC micro/nanocomposite determined by the four-point bending test and the contact test using opposite spheres both applied to specimens of different size, respectively. Material failure in the bending and contact modes is caused by the presence of processing defects as fracture origins, and by the formation of cone cracks, respectively, where a stable growth of the cone cracks initiated during contact loading is assumed to be a reason of , . A microstructural analysis of the processing flaws, and a mathematical analysis of the propagation of the cone cracks regarding different dimensions of a specimen are also presented.
Authors: Ján Dusza, Monika Kašiarová, Lucia Hegedűsová, Miroslav Hnatko, Pavol Šajgalík
Abstract: Bending and contact strength of a carbon derived in-situ reinforced Si3N4-SiC micro/nanocomposite have been investigated. Four-point bending strength was measured using specimens with different effective volume and Weibull statistical analysis has been used for characterization of the strength values in the form of characteristic strength and Weibull modulus. The characteristic strength values of the investigated composite were σ0 = 675 MPa and σ0 = 832 MPa with the Weibull modulus of 6,4 and 8,6 for the specimens with effective volume 15,9 mm3 and 1,28 mm3 respectively. Contact strength of the investigated material was carried out using sphere on sphere and roller on roller methods and the obtained results are σ0S = 1997 MPa, σ0R = 1242 MPa, and mS = 17,1 mR = 6. Fracture origins in the specimens with effective volume of 15.9 mm3 tested in four-point bending were surface and volume located technological defects with dimensions from 10 μm to 180 μm, mainly in the form of clusters of pores and large SiC grains. Fracture mirror sizes were measured and the mirror constant was calculated. Fracture origins in the specimens with effective volume of 1.28 mm3 tested in four-point bending were surface (subsurface) defects with the same type as for the specimens with a higher effective volume. The fracture during the contact strength test „roller/roller“ has been initiated under the surface of the specimens and during the contact strength test „sphere/sphere“ by creation and growth of the cone cracks to critical size.
Authors: Ki Woo Nam, B.G. Ahn, M.K. Kim, C.S. Son, Jin Wook Kim, Seok Hwan Ahn
Abstract: The optimized conditions of pressureless sintering were investigated in order to obtain the bending strength and the elastic wave signal of Al2O3 composite ceramics for textiles machinery. As sintering conditions, a temperature range from 1400°C to 1700°C and time from 30 minutes to 150 minutes were applied. Three-point bending tests were conducted on the sintered materials to obtain the strength property. From the test results, the optimum sintering condition was 1600°C, 100 minutes. Al2O3 composite ceramics showed that the elastic wave signal characteristics had a regular correlativity between the optimum sintering temperature and time as well as the maximum bending strength.
Authors: Meng Kao Yeh, Chia Min Lin
Abstract: Composite materials, having advantages of high specific strength, high specific stiffness, are used in many applications, such as musical instrument, acoustical tile, fire wall, sports equipment, aerospace and vehicle industries. Composite products in the form of sandwich structures are specifically useful in recent years. In this paper, the bending strength of sandwich structure made by graphite/epoxy face laminates and core material made by multi-walled carbon nanotubes (MWNTs) reinforced polymer was investigated experimentally. In experiment, the three-point bending test was performed to measure the bending properties of sandwich beams. The influences of fiber orientation in the face laminates and MWNTs content in polymer reinforced nanocomposite core material on the bending strength of sandwich beams were discussed in this paper. The failure mechanism of sandwich beams with various fiber orientations in the face laminates was also discussed.
Authors: Yu Ping Zeng, Naoki Kondo, Kiyoshi Hirao, Hideki Kita, Tatsuki Ohji, Shuzo Kanzaki
Abstract: Silicon nitride ceramics was prepared by tape casting nonaqueous ceramic slurries, laminating the green ceramic tapes, and gas pressure sintering in nitrogen atmosphere. Lu2O3 and SiO2 were used as the sintering additives, and 3 wt.% β-Si3N4 seed was added to enhance β-Si3N4 grain growth unidirectionally. The seeded and tape-cast Si3N4 showed very good high temperature bending strength at 1500oC, when the stress applied along with the grain alignment direction. This was attributable to the formation of a high melting point grain boundary phase and the fibrous Si3N4 grains alignment. After exposure in air at 1500oC for up to 100 h, the oxidation products formed on the Si3N4 surface consist of Lu2Si2O7 and SiO2. The bending strength of the oxidized and tape-cast Si3N4 was degradation, the strength decrease was associated with the formation of new defects on the surface and the interface between the oxide layer and the Si3N4 bulk.
Authors: S. Shinzato, Takashi Nakamura, Koji Goto, Tadashi Kokubo
Abstract: A new bioactive bone cement (cGBC) consisting of crystallized MgO-CaO-SiO2-P2O5 glass beads and high-molecular-weight polymethyl methacrylate (hPMMA) has been developed to overcome the degradation seen with a previously reported cement (GBC) consisting of MgO-CaO-SiO2-P2O5-CaF2 glass beads and hPMMA. The purpose of the present study was to evaluate the degradation of cGBC using an in vivo aging test, and to compare the degradation of cGBC with that of GBC. Hardened rectangular specimens (20x4x3mm) were prepared from both cements. Their initial bending strengths were measured using the three-point bending method. GBC and cGBC specimens were then implanted into the dorsal subcutaneous tissue of rats, removed after 6 or 12 months, and tested for bending strength. The initial bending strengths (MPa) of GBC and cGBC were 141.9±1.8 and 144.4±2.4, respectively, while at 6 months they were 109.1±2.6 and 114.1±4.9, and at 12 months they were 109.1±3.2 and 113.1±3.3, respectively. Although the difference in initial bending strengths was not significant, the bending strength of cGBC was significantly higher than that of GBC at 6 and 12 months, indicating that cGBC is more resistant to cement degradation. The bending strengths of both GBC and cGBC decreased significantly from 0 to 6 months but did not change significantly thereafter. Thus, degradation of cGBC and GBC does not appear to continue after 6 months. We believe that cGBC and GBC are strong enough for use under weight-bearing conditions and that their mechanical strength (especially that of cGBC) is retained in vivo.
Authors: Wen Bin Sun, Wei Zhong He, Yang Jiang
Abstract: For the analysis and design of RC structures, there is a fundamental assumption that the strain in an embedded reinforcing bar is the same as that in the surrounding concrete. Therefore, bond forces must be developed on the interface between concrete and steel, such as to prevent significant slip from occurring at the interface. An end anchorage may be considered reliable if the bar is embedded in to concrete a prescribed distance known as the development length of the bar. If in the beam the actual extended length of a bar is equal to or greater than this required development length, no premature bond failure will occur. Research has indicated that the development length was influenced by tensile strength of concrete, surface and diameter of bar, cover distance, bar spacing, transverse reinforcement, and other factors. Current design methods in different countries’ Codes, attentions are directed toward providing adequate length of embedment, which will ensure development of the full strength of the bar.
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