Advanced Nondestructive Evaluation I

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Authors: Jun Hyub Park, Yun Jae Kim, Man Sik Myung, Chang Seung Lee, Sung Hoon Choa, Nam Sup Choi
Abstract: This paper describes a novel test procedure, new structure of specimen easy to manipulate, align and grip a thin-film and test machine for a tensile and fatigue test. For the proposed specimen, the surroundings of the specimen including the side support strips except for six bridges are etched during the fabrication of the specimen, which in turn makes it possible to cut off easily the specimen from the wafer by minimizing a damage to the test film and also possible to produce the specimen in mass production. For the present specimen, a small hole is made at the grip end and using a small pin for setting the specimen onto the tester, the setting process and alignment of specimen is much easier, compared to the specimen proposed by Sharpe et al. To gain confidence in reliability of testing results, pre-test using the Al-3%Ti is performed, which is widely used in the RF switch and other MEMS devices. Tensile tests are performed, from which tensile strengths of the Al-3%Ti are measured as 343±16.22MPa at 200μm width and 1.1μm thickness.
Authors: In Pil Kang, Jong Won Lee, Gyeong Rak Choi, Joo Yung Jung, Sung Ho Hwang, Yeon Sun Choi, Kwang Joon Yoon, Mark J. Schulz
Abstract: This paper introduces a new sensor design based on a carbon nanotube structural neuron for structural health monitoring applications. The carbon nanotube neuron is a thin and narrow polymer film sensor that is bonded or deposited onto a structure. The electrochemical impedance (resistance and capacitance) of the neuron changes due to deterioration of the structure where the neuron is located. A network of the long carbon nanotube neurons can form a structural neural system to provide large area coverage and an assurance of the operational health of a structure without the need for actuators and complex wave propagation analyses that are used with other SHM methods. The neural system can also reduce the cost of health monitoring by using biomimetic signal processing to minimize the number of channels of data acquisition needed to detect damage. The carbon nanotube neuron is lightweight and easily applied to the structural surface, and there is no stress concentration, no piezoelectrics, no amplifier, and no storage of high frequency waveforms. The carbon nanotube neuron is expected to find applications in detecting damage and corrosion in large complex structures including composite and metallic aircraft and rotorcraft, bridges, and almost any type of structure with almost no penalty to the structure.
Authors: Yong Rae Roh, Don Young Kim, Seung Han Yang, Seung Hee Park, Chung Bang Yun
Abstract: This paper presents a non-destructive evaluation (NDE) technique for detecting damages on a jointed steel plate on the basis of the time of flight and wavelet coefficient, obtained from wavelet transforms of Lamb wave signals. Probabilistic neural networks (PNNs) and support vector machines (SVMs) were applied for pattern classification. In this study, the applicability of the PNNs and SVMs was investigated for the damages in and out of the Lamb wave path. It has been found that the present methods are very efficient in detecting the damages simulated by the loose bolts on the jointed steel plate.
Authors: Dong Hoon Kang, Chang Sun Hong, Chun Gon Kim
Abstract: Because of their good multiplexing capabilities, fiber Bragg grating (FBG) sensors are being studied more actively than any of other fiber optic sensors. The application fields of FBG sensors have been mainly focused on composite materials through embedding rather than through surface attachments. However, there are many limitations on the embedding of FBG sensors into composite materials because of the birefringence that is induced when FBG sensors are not embedded parallel to the reinforcing fibers. This study investigates the fabrication of FBG sensors that have various grating lengths, good multiplexing capabilities, better stability from birefringence, and ease in production. The signal characteristics of FBG sensors are also verified through the cure monitoring of two composite laminates.
Authors: Byung Young Moon, H. K. Kang, Kwon Son, S.W. Chung
Abstract: Anterior cruciate ligament(ACL) is liable to a major injury that often results in a functional impairment requiring surgical reconstruction. The success of reconstruction depends on such factors as attachment positions, initial tension of ligament and surgical methods of fixation. The purpose of this study is to find isometric positions of the substitute during flexion/extension. A threedimensional knee model was constructed from CT images and was used to simulate length change during knee flexion/extension. The results showed that minimum length changes were 1.9~5.8 mm(average 3.6±1.4 mm). The proposed method can be utilized and applied to optimal reconstruction for ACL deficient knee.
Authors: Byung Young Moon, Chun Tae Lee, Kwon Son, S.W. Chung
Abstract: This study developed and evaluated a shoe cushioning system to reduce impact force patterns during running. The shoe cushioning system is composed with a polyurethane pocket, which contains water and porous grains to absorb the force against the weight inside the pocket. Load-displacement curves for the shoe cushioning system were obtained from an instrumented testing machine and the results were compared with various pockets that have air, water or grains. Mechanical testing showed that the pocket with 5 g particles was the best for the shoe cushioning system. This founding will be helpful to designing the shoe.
Authors: Jae Hwan Kim, Sung Ryul Yun, Chun Suk Song
Abstract: Cellulose-based Electro-Active Paper (EAPap) has been studied as an attractive electroactive polymer material for artificial muscles due to its low cost, availability, lightweight, large displacement output, low actuation voltage and low power consumption. However, the force output of EAPap is small since paper is so flexible that the bending stiffness is low. In this paper, the cellulose based EAPap material is enhanced by using carbon nanotubes with cellulose paper. Coating of multi-walled carbon nanotubes mixed with polyaniline on EAPap as well as MWNT dispersion in the paper are tried to enhance the force output of the EAPap. The coating process of MWNT/PANI on the EAPap and the dispersion of MWNT in the cellulose paper are explained. The performance of the hybrid EAPap actuators is evaluated in terms of tip displacement, blocking force and electrical power consumption. The power output and the actuator efficiency are improved.
Authors: Seung Hee Park, Sohaib Ahmad, Chung Bang Yun, Yong Rae Roh
Abstract: This paper presents a feasibility study of an impedance-based damage detection technique using PZT (Lead-Zirconate-Titanate) patches for real-time health monitoring of concrete structures. The PZT patches are used to detect progressive surface damage on a plain concrete beam. Both experimental and analytical studies are carried out. For damage quantification, root-mean square deviations (RMSD) before and after damage are used as a damage indicator.
Authors: Jin Kyung Lee, Young Chul Park, Sang Ll Lee, Joon Hyun Lee, Jong Baek Lee
Abstract: Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite (MMC). TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress using shape memory effect in the matrix. A hot press method was used to create the optimal condition for the fabrication of shape memory alloy (SMA) composite. The bonding effect between the matrix and the reinforcement within the SMA composite was strengthened by the cold rolling. The fabricated composite by these processes can be applied as a part of the aircraft, and this part is operated under severe flying condition such as low temperature and high pressure. In this study, an acoustic emission technique was used to quantify the microscopic damage behavior of cold rolled TiNi/Al6061 SMA composite at low temperature condition. The results showed that the tensile strength of the TiNi/Al6061 SMA composite increased with the TiNi reinforcement at low temperature condition, but the strength for the specimen subjected to the cold rolling decreased. AE parameters of AE counts, amplitude and energy were useful to evaluate the microscopic damage behavior of the composite.
Authors: Kug Kwan Chang, In Kyu Rhee, Young Sook Roh
Abstract: There have been very few research results available for high cycle fatigue properties of SMAs. In many of the devices designed to exploit the effect of fatigue loadings, the specimen is subjected to only several thousand thermal or loading cycles. Therefore, the stability of the alloy under applied loading with high cycle fatigue becomes an important issue. Moreover, there has not been any fatigue testing in compression for SMAs. The behavior of SMAs under tension and compression may be different, which is very important for many special applications of SMAs. The present study focus on the high cycle fatigue of SMAs under compression. A new surface monitoring technique for micro-deformation and micro-strain analysis, called IIMT, is introduced. IIMT is used for monitoring the performance of SMAs under high cycle stress loading in compression. The stress-strain curves and shape memory strain output at various loading cycles were obtained, which provide valuable information for design and applications of SMAs.

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