Advanced Materials Research Vols. 26-28

Abstract: For the high quality of wheel, the railway wheel has standardized such as UIC, KS, and JIS code but the chemical composition, the mechanical property and the hardness is merely requested. Although the standard of railway wheel has sustained, the damages of railway wheel have been occurred in service running. Because of wheel damage with spalling, shelling and thermal crack, the maintenance cost for the railway wheel has increased. In order to reduce wheel damage, it is necessary to reinforce the standard of railway wheel. In present study, the fracture mechanics characteristics of railway wheel such as threshold stress intensive factor, fracture toughness and impact energy depended on temperature have tested. The result shows that the standard of railway wheel has to supplement fracture toughness and impact energy depended on low temperature in order to reduce the wheel damage.

Abstract: The objective of this study is to estimate the feasibility of advanced nondestructive method(X-ray diffraction, AE(acoustic emission) and BN(barkhausen noise)measurement application for fatigue life evaluation of the high-temperature pipeline steel such as main steam pipe etc. in power plant. In this study, various nondestructive tests using various types of specimen simulated low cycle fatigue damage were performed in order to analyze fatigue properties when fatigue damage conditions become various stages such as 1/4, 1/2 and 3/4 of fatigue life, respectively. As a result of X-ray diffraction tests for specimens simulated fatigue damages, we conformed that the variation of the full width at half maximum intensity decreased in proportion to the increase of fatigue life ratio. And also, AE and BN signal due to fatigue damage has linear relationship with fatigue life ratio algebraically. From this relationship, it was suggested that direct expectation of the life consumption rate was feasible.

Abstract: Some methods of enhancing oil-gas pipeline magnetic flux leakage (MFL) detection technique are introduced in the paper. Some man-made defects or imperfections on the pipe surface are detected via the axial magnetization inspection vehicle along the pipeline. The magnetic dipole model of corrosion defect is stated and the important interference factors on magnetic flux leakage are analyzed. Finite element method is used to analyze and simulate normal defects on pipe surface, which can attribute to get natural defect MFL signal. The influence of benign pipeline artifacts (valves, welds, tees, flanges, etc.), pipe material and pipe wall, vehicle velocity, defect dimensions and interaction among defects, and so on are studied in detail. The magnetic flux leakage contour images or indication extraction maps are given and presented. These interference factors are compensated and solved. These approaches and results applied in the paper are contributed to the feature extraction and indication of pipeline abnormality. The results suggest that these approaches and conclusions are significantly effective for the pipeline magnetic flux leakage inspection.

Abstract: The μ-via in microelectronic substrate should have multiple purposes, one of them is to allow to the path of signal or current from electronic devices. The micro void can be easily formed in μ-via because μ-vias are filled with a screen printing process and the size of via is small. The residual void has been known as crack initiation of copper layer during a reliability test. The solder resist filling process and the behavior of a residual void in μ-vias were investigated. The void extraction process was very effective comparing with the conventional process to remove a residual void. As extracted with 1.5 atm for more than 30 sec, the residual void in μ-BVH was perfectly eliminated.

Abstract: Various damage index (DI) algorithms of detecting changes such as a loosen bolt and a delamination development in a composite structure were examined using ultrasonic Lamb waves generated by embedded piezoelectric active sensors. The DI is a single value that is a function of response signal’s attenuation due to any damage or changes in a structure. Various DI algorithms such as active damage interrogation (ADI), time domain root men square (RMS), short time Fourier Transform (STFT) and time reversal (TR) were discussed. For experimental validation, a composite stiffened panel was used, and loosen bolt damage and low-velocity- impact damage were tested. In order to pitch and catch Lamb waves, surface mounted PZTs (lead zirconate titanate) were used. According to the DI algorithms, appropriate ultrasonic guided Lamb waves were selected for actuators. Each set of DI algorithm and drive signal showed different characteristics to detect the damage.

Abstract: Inconel alloy such as alloy 600 and alloy 690 is widely used as the steam generator tube materials in the nuclear power plants. The impact fretting wear tests were performed to investigate wear mechanism between tube alloy and 409 stainless steel tube support plates in the simulated steam generator operating conditions, pressure of 15MPa, high temperature water of 290°C and low dissolved oxygen(<10 ppb). From investigation of wear test specimens by the SEM and EDS analysis, hammer imprint, which is known to be an actual damaged wear pattern, has been observed on the worn surface, and fretting wear mechanism was investigated. Wear progression of impact-fretting wear also has been examined. It was observed that titanium rich phase contributes to the formation of voids and cracks in sub-layer of fretting wear damage by impact fretting wear.

Abstract: The high-pressure crystallized bisphenol-A polycarbonate (BAPC) and BAPC / dioctyl phthalate (DOP) blend samples were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results showed that the rate of the crystallization of BAPC could be greatly increased by the introduction of DOP at high pressure. Morphologies of spherulites of BAPC with different characteristics were observed during the investigation, including ellipsoids ascribed to the liquid-liquid phase separation via spinodal decomposition, sheaf-like and spherical features corresponded to the different stages of spherulitic growth, and stereo-open forms with a three-dimensional structure. The disclosed entities, some of which have potentials in functional applications, may promote the understanding of the formation process and mechanism of polymer spherulites.

Abstract: It is known that the phase-decomposition process of 60/40 Cu-Zn alloy is so-called the bainitic transformation, and decomposition of α-phase from the β’-phase is as follow: β’ → α9R → αfcc. In this work,decomposition of α-phase from the β’ single phase of Cu-40.26at.%Zn alloy has been investigated by high-resolution transmission electron microscopy (HRTEM) to understand the phase transformation of this alloy. Especially, striations in the α-phase has been focused on the special feature for the change of the structure and hardening of this alloy during annealing. The result of a comparison between this alloy and the Si added alloy is also reported.

Abstract: A low impurity magnesium alloy has bean prepared. Deformation behavior in cold-rolling and corrosion behavior of the alloy were compared with those of a commercial alloy. The specimens were cold-rolled at room temperature with reduction rates of 0~80 %. Transmission electron microscopic observations on the cold-rolled specimens were carried out. In the case of the low impurity magnesium alloy, recrystallization easily occurred. Analyses of microstructures in the deformed specimens were carried out by means of EBSP, and the recrystallization phenomena have been discussed. Another effect of lowering the impurities is to improve a corrosion resistance with changing the corrosion morphology.