Advances in Fracture and Failure Prevention

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Authors: Jae Yeol Kim, Young Tae Yoo, Kyung Seok Song, Chang Hyun Kim, Dong Jo Yang
Abstract: The purpose of this research is stability estimation of plant structure through classification and recognition about welding flaw in SWP(Spiral Welding Pipe). And, In this research, we used nondestructive test based on ultrasonic test as inspection method, and made up inspection robot in order to control of ultrasonic probe on the SWP surface, and programmed to signal processing code and pattern classifying code by user made programming code. Inspection robot is simply constructed as 2-axes because of welding bead with fixed pitch. So, inspection of welding part can be possible as composition of inspection part for tracking on welding line. For evaluation of flaw signal is reflected on welding flaw, user-made program codes are composed of signal processing and Bayesian classifier and perceptron neural network and back-propagation neural network. And then, we confirmed to superiority of neural network method compared with Bayesian classifier for classification and recognition rate. According to this result, we selected back-propagation neural network as classification and recognition method about the system of SWP stability Estimation[2]. Through this process, we proved efficiency on the system of SWP stability Estimation, and constructed on the base of the system of SWP stability Estimation for the application in industrial fields.
Authors: Cong Xin Chen, Cai Hua Liu
Authors: Yun Hae Kim, Y.J. Son, B.H. Woo, C.W. Bae, S.M. Kim, Ryuichiro Ebara
Abstract: Cavitation-erosion is a hydrodynamic phenomenon that results in the formation and collapse of vapor bubbles in a liquid. Cavitation damage is encountered in a wide variety of fluid handling machinery and over a broad range of liquid pressures and temperatures. In this study, cavitation damage was investigated by using the piezoelectric vibrator with 20kHz, 50μm to cavity generation apparatus. At the first cavitation test, coated composite material specimens appear to generating the low bubbles due to damping vibration. This study is mainly compared with cavitation test (ASTM G 32) and modified cavitation test. And it is also concerned with phenomenon of cavitation-erosion on the several materials. In order to compare the both test methods, cavitaion weight loss and rate of the several materials in fresh-water and sea-water measured and observed with digital camera.
Authors: H. Kumano, H. Soyama, Masumi Saka
Abstract: Damage for gettering can be introduced by a high speed submerged water jet with cavitation, i.e., a cavitating jet, into a silicon wafer. Gettering is an important technique for removing unwanted impurities from the surface of the silicon wafer that is active device region. Metal contaminations diffuse in bulk of the wafer and adhere to the defects through the thermal treatments in semiconductor processes. If the damage was intentionally introduced into the silicon wafer, these contaminations can be gathered within the intended region. Consequently, the surface of the wafer can be kept free from impurities. The method presented here utilizes cavitation impacts to introduce the damage for gettering. By using cavitation impacts, the damage can be introduced without the use of particles which form sources of contamination during farther wafer handling, as in shot blasting that is a popular technique. The cavitation impacts caused by a cavitating jet were used since the intensity of cavitation impacts can easily be controlled by controlling hydraulic parameters. The gettering effect of the damage introduced by the cavitating jet was already confirmed, but the detail information of the introduced damage has not been obtained. After applying thermal treatment to the wafer treated by the cavitating jet, there are Oxidation-induced stacking faults (OSF) which would be gettering sites. However, the source of OSF is not yet confirmed. In this paper, the damage on the silicon wafer surface introduced by the cavitating jet for gettering is observed to evaluate the source of OSF.
Authors: H. Kumano, H. Soyama, Masumi Saka
Abstract: A novel gettering method using cavitation impacts is presented. Gettering is very important technique for IC manufacturing. Silicon wafers used as a substrate for semiconductors are often exposed to contamination during the device processes. If crystal defects are intentionally introduced into back-side of silicon wafer, metal impurities such as Cu and Fe in the wafer are trapped in the defects and gather into the region during heat cycles. As a result, the zone near the surface of the wafer that is used as active device region is kept off unwanted impurities. This technique is called gettering. In this paper, to introduce backside damage, which is one of the gettering techniques, cavitation impacts are utilized. Cavitation bubbles produce high-pressure impacts upon collapsing. The suitable damage can be introduced by controlling the intensity of cavitation impacts. The high speed submerged water jet with cavitation, i.e., a cavitating jet, was used to cause cavitation impacts. The cavitating jet can introduce backside damage without the use of particles, as in shot blasting that is popular technique. In order to confirm the gettering effectiveness of the damage introduced by a cavitating jet, an experimental study was carried out. The silicon wafer treated by the cavitating jet was intentionally contaminated with solution of Cu(NO3)2. The wafer was then thermally treated. The surface was observed after etching that makes defects on the surface observable. On the surface of the wafer having no gettering effectiveness, defects which were induced by contamination are observed. If the wafer has gettering effectiveness, defects are not observed on the surface. Gettering effectiveness of the damage introduced by the cavitating jet was shown.
Authors: X.L. Yue, S. Nishida, Nobusuke Hattori, K. Nakano, Wen Xian Sun
Abstract: The current investigation involves fabrication and characterization of Al MMCs reinforced with stainless steel fiber (SSF). Hot isotatic pressing (HIP), an effective metallurgical technology for producing well-consolidated products with strong interface bonding and reduced fabrication defects, was employed to fabricate the composites. A variety of processing conditions were investigated to determine their effect on microstructure and properties of the composites. To arrange the fiber orientation, a secondary treatment of rotary swaging was carried out on the specimens and the effect of rotary swaging was discussed. The experimental results reveal that processing conditions closely related to properties of the obtained composites. Severe interface reaction takes place at high processing temperature and thick interface reaction layer forms around reinforcing fibers, which reducing interface bonding strength, hence tensile properties of the composites.
Authors: Hong Gun Kim, Sung Mo Yang, Hong Gil Noh, Dong Joo Lee
Abstract: An investigation of composite mechanics to investigate stress transfer mechanism accurately, a modification of the conventional shear lag model was attempted by taking fiber end effects into account in discontinuous composite materials. It was found that the major shortcoming of conventional shear lag theory is not being able to provide sufficiently accurate strengthening predictions in elastic regime when the fiber aspect ratio is very small. The reason is due to its neglect of stress transfer across the fiber ends and the stress concentrations that exist in the matrix regions near the fiber ends. To overcome this shortcoming, a more simplified shear lag model introducing the stress concentration factor which is a function of several variables, such as the modulus ratio, the fiber volume fraction, the fiber aspect ratio, is proposed. It is found that the modulus ratio is the most essential parameter among them. Thus, the stress concentration factor is expressed as a function of modulus ratio in the derivation. It is also found that the proposed model gives a good agreement with finite element results and has the capability to correctly predict the variations of the internal quanitities.
Authors: Dong Joo Lee, In Seop Lee
Abstract: The hygrothermal degradation of glass fiber/nylon composite was investigated after aged at 25°C, 50°C, 75°C and 100°C up to 1 month of total exposure in aqueous solution. The effects of moisture absorption and thermal aging on mechanical properties are compared as functions of temperature, fiber volume and concentration of sodium chloride. The amount of water absorption increases when the aging temperature is increased and the concentration of NaCl is lowered. In general, the mechanical properties decrease with amount of water absorption. The degradation rate of various mechanical properties is different depending on the temperature, fiber volume and the concentration of NaCl. The diffusion mechanisms of water in short-fiber reinforced nylon are discussed as functions of fiber volume, molding conditions and concentration of sodium chloride.
Authors: T. Yamamoto, H. Takeda, Hiizu Hyakutake
Abstract: The validity of the idea of severity near the notch root of notched FRP plates is investigated experimentally. The investigation was accomplished by obtaining experimental data on the static and cyclic loading tests for notched plates of a glass fiber-reinforced polypropylene (GF/PP). To evaluate the damage near the notch root, we measured the luminance distributions by means of a luminance-measuring technique using a CCD camera. The experimental results for the static loading tests show that the configuration and the area of damaged zone near the notch root were determined by both the maximum elastic stress at the notch root, σmax and notch-root radius ρ. The maximum elastic stress at fracture, σmax,c is governed by the notch-root radius ρ and it is independent of notch depth. The number of loading cycles to fatigue damage initiation is determined by both the σmax and ρ. These experimental results confirm the validity of the failure criterion in static load and the fatigue failure criterion based on the idea of severity near the notch root.
Authors: Sheng Wu Wang, Hisatoshi Hirai, Tatsuo Tabaru, A. Kitahara, Hideto Ueno
Abstract: Nb base in-situ composites with the base composition of Nb-5Mo-2W-18Si were prepared by conventional arc-melting and induction heating floating zone melting followed by directional solidification. To investigate the effect of HfC addition, Nb was replaced with 0, 1 and 2 mol% HfC. The in-situ composites predominantly have an eutectic microstructure consisting of Nb solid solution (NbSS) and (Nb,Mo,W))5Si3 (5-3 silicide). The strength at 1470 K and 1670 K increases without fracture toughness decreasing, with increasing the HfC content. Directional solidification also improves the strength at the high temperature. The slip band under the shearing stress occurs in the NbSS during plastic deformation, which contributes to suppress microcrack propagation. It seems that HfC addition reinforces the bonding strength at grain boundary or NbSS/5-3 silicide interface.

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