Advanced Nondestructive Evaluation I

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Authors: Taku Shimomura, Akira Shimamoto
Abstract: Polymer materials are used in the structural members such as aircraft, ship, automobiles in order to enlarge and lighten the machinery and structures. In such the machinery and structures, the complex destruction phenomena are generating by the deterioration of use conditions of the polymer materials. And the materials are placed under biaxial or multi-axial stress conditions rather than uni-axial stress conditions due to their complicated structures. To understand the basic deformation behaviours and the features in destruction process under multi-axial stress conditions is more important in the reliability and the accident prevention plan. To help overcome this problem, the authors have developed a hydraulic high-speed biaxial loading test device. In this study, we had comparative study for the values of the dimensionless stress intensity factors, F values by the photoelastic and caustics methods to clarify deformation behaviours and characteristics of polymer materials under biaxial stress conditions.
Authors: Tadashi Asahina, Insu Jeon, Kiyotaka Katou, Tsutomu Sonoda
Abstract: The cell-structure of highly porous aluminum material prepared by melt foaming technology was investigated under deformation with fine-focus X-ray 3D-CT to make clear the development target porous material for automobile industries with improved reliability. It was confirmed that structures with more fine, more uniform and exclusion peculiar anisotropic pores would make improved mechanical properties of the material.
Authors: Jong Sub Lee, Gye Chun Cho, Eun Soo Hong
Abstract: An electrical needle-size probe is developed to effectively assess one-dimensional spatial variability of laboratory soil specimens in high resolution. A calibration procedure is also presented to determine resistance from the measured complex impedance. The capability of the developed electrical needle probes to resolve interfaces and spatial variability is explored using sand specimens prepared by various conditions. The complex impedance is measured 0.2~0.5 mm for every specimen. Results show that the coefficient of variation increases as the size of the probe reaches the size of the particle while a very large ratio of probe size to grain size would decrease the detectability of local soil variations due to averaging effects and smoothening. The attainable spatial resolution depends on the needle diameter: submillimetric resolution is typically achieved in laboratory applications and it can be scaled for field applications. The local electrical parameters permit one to infer the soil porosity and the electrolyte conductivity.
Authors: Gye Chun Cho, Jong Sub Lee
Abstract: The purposes of this study are to analyze post liquefaction shear strength and to explore the potential use of wave-based techniques to monitor liquefaction and post liquefaction response. The first part presents a detailed analysis of triaxial test results to identify robust strength criteria. The second part documents experimental data on the characterization of liquefaction events with P-wave reflection imaging and S-wave trans-illumination techniques. The relevance of multiple coexisting temporal and spatial scales is highlighted. The following results are obtained: 1) the post liquefaction shear strength can be estimated within the framework of critical state soil mechanic; 2) the P-wave reflection images obtained before and after liquefaction represent the depression of the soil-water interface; 3) excess pore pressure migration from liquefied deep layers may cause zero-effective stress in dilative shallow layers. P-wave reflection is a valuable tool to monitor the evolution of subsurface structures and S-wave trans-illumination technique can be used to yield a comprehensive picture of the spatial evolution of liquefaction.
Authors: Nguyen Duc Thanh, Gye Chun Cho, Young Jong Sim, Seok Won Lee
Abstract: This study proposes a tomography-based method for evaluating grouting performance after injection. Tomography is a convenient approach for solving the boundary measurement inverse problem of capturing discrete pixels and synthesizing these pixels into a unified image. Four arrays of eight electrodes are installed into large triaxial cell specimens to simulate in-situ crosshole resistivity testing. Sand is used as a base material and a wet cement mixture is grouted into the specimens. Electromagnetic waves are used as a means of accumulating the physical properties of the specimens. Each measured electrical resistivity is considered as a discrete signal. The electrical resistivity distribution is calculated and optimized through an iterative modified least-squares inversion based on a forward solution of Coulomb and Gauss’s law equations. Results show that the electrical properties of an injected grout material and its location and size can be effectively estimated from a series of resistance measurements.
Authors: Jun Su Choi, Hee Hwan Ryu, In Mo Lee, Gye Chun Cho
Abstract: Geophysical prospecting using electrical resistivity is one of the principal methods for subsurface exploration. However, the majority of such application methods are restricted to coarse descriptions of underground conditions. The Q-system is commonly used as a representative rock mass classification system in modern rock engineering. In this paper, electrical resistivity is related to the Q-system through theoretical analyses. The analyses are based on Coulomb's law and Gauss' law considering electrical characteristics of constituent parameters for rock mass classification such as joint thickness, joint condition, joint spacing, intact rock strength, and RQD. The results show that there is a strong correlation between electrical resistivity and rock mass classification.
Authors: Il Han Chang, Gye Chun Cho, Joo Gong Lee, Lee Hyung Kim
Abstract: Sedimentation is one of the most basic processes in the formation of a soil structure in nature. Many studies have been performed to describe the characteristics of clay sedimentation, based on settlement and water content measurement. In addition, there have been some attempts in numerical modeling to describe soil structure formation as a whole. However, these effects still fall short in explaining the overall process of soil structure formation because some relevant properties are measured after a self-weight consolidation is completed. Furthermore some measurement techniques significantly alter soil structure. Thus, a non-destructive evaluation is necessary for the effective description of soil characteristics during the sedimentation process. In this study, a testing device is designed that continuously monitors the self-weight consolidation process of sedimentation with shear waves. Piezoelectric bender elements are installed into a testing cell to generate and receive shear waves in a small strain regime. Slurries are prepared with kaolinite-type clay and placed in the cell. Shear wave velocities are continuously measured as a function of time during the whole process of the self weight consolidation. The experimental results suggest that as clay sediment is subjected to a certain loading, the shear wave velocity increases as time increases, showing an abrupt change in log time. This abrupt change is relevant to the formation of a stable soil skeleton. It is concluded that the time-dependent variations in shear wave velocity reflect sedimentation and self weight consolidation behavior and the evolution of the effective stress increment.
Authors: Kee Joo Kim, Joo Sung Kim
Abstract: To fabricate the aluminum alloys with good drawability, the textures evolution of the AA5182 sheets after rolling and subsequent annealing was studied. The measurement of the deformation textures was carried out for the sheets with high reduction ratio and the change of the recrystallization texture was investigated after heat-treatments of the rolled sheets. Rolling without lubrication and subsequent annealing led to the formation of favorable rot-CND {001}<110> and γ-fiber ND//<111> textures in AA5182 sheets. From the results, the γ-fiber ND//<111> component well evolved during rolling at high reduction ratio. Among shear deformation textures, the γ-fiber ND//<111> was not rotated in holding time until 7,200 seconds at 350. The Monte-Carlo technique was used and could be representatively simulated textures evolution during recrystallization.
Authors: Yoshimi Hatsukade, Shinya Okuno, Kazuaki Mori, Saburo Tanaka
Abstract: This study is aimed at developing an eddy-current-based SQUID-NDE system for in-situ inspection of micro flaws on thin copper heat exchanger tubes. The system employs a high temperature superconductor (HTS-) SQUID gradiometer and a Helmholtz-coil-type inducer. As specimens, copper tubes 6.35 mm in outer diameter and 0.8 mm in thickness with artificial surface flaws of several tens μm in depth were inspected using the system. Magnetic response due to a flaw of 10 μm in depth on the tube moving at 32 m/min was successfully detected while applying an excitation field of 10 μT at 3 kHz to the tube. Numerical simulations were also conducted to evaluate how many sensors would be required for inspection around the circumference of an entire tube.
Authors: Kwang Ki Lee, Kwang Soon Lee, Tae Won Kim
Abstract: Physical vapor deposition technique has been employed to develop a thin film of OLED, and atomic force microscopy was used to investigate the boundary characteristics such as uniformity of emitting layer, roughness, and surface morphology. In order to determine the deposition characteristic which associated with the materials failure in OLED, finite element simulation, together with alternative analytical modeling has been carried out by means of island growth mechanism analysis. The boundary growth of thin film can be determined from the velocity of island boundary using simple rate equations. The results obtained are compared with experimental observation. Generally good agreement has been achieved.

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