Advanced Nondestructive Evaluation I

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Authors: Yong Hak Huh, Philip Park, Dong Jin Kim, Jun Hyub Park
Abstract: Fatigue crack propagation behavior under cyclic tensile or torsional loading with biaxial static loads has been investigated. Two different biaxial loading systems, i.e. cyclic tensile loading with static torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular specimens. The crack propagation was measured by two crack gages mounted near the notch and crack opening level was measured by unloading compliance method. The directions of the fatigue crack propagated under respective biaxial loading conditions were examined and the growth rates were evaluated by using several cyclic parameters, including equivalent stress intensity factor range, Keff, crack tip opening displacement range, CTD, minimum strain energy density factor range, Smin. Furthermore, the growth rates were evaluated by effective cyclic parameters considering crack closure. It was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no influence on the propagation directions of the cracks. Furthermore, it was shown that the fatigue crack growth rates under biaixial faigue loading were well expressed by using the cyclic fatigue parameters, Keq,eff, CTDeff, Smin,eff considering crack closure effect.
Authors: Nam Su Huh, Yoon Suk Chang, Young Jin Kim
Abstract: The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3-D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, both single and combined loadings are considered. Being based on detailed 3-D FE limit analysis, the present solutions are believed to be valuable information for structural integrity assessment of cracked pipes.
Authors: Tetsuya Nemoto, Hiroyuki Matsuura, Masahiro Nakano, Akira Shimamoto
Abstract: The effect of hydrolysis of polycarbonate on tensile behavior were investigated. The specimens were exposed in a chamber at constant room temperature and water for 300 hours, and measurements were made on the variation of weight and tensile properties. In addition, the increase and decrease of the carbonate part was measured with an ultraviolet spectroscopy. The results are as follows: It was confirmed that it was effective to the examination of the influence of the diffusion of water with an overlay castfilm. It has been understood to the diffusion of water from the surface layer has diffused at the same time by about 6μm, and it has diffused gradually when it is deeper than 6μm. The change in the tensile behavior by the hydrolysis was able to be confirmed by observing the carbonate part of the polycarbonate. It became clear, the break strain has decreased because the carbonate part is taken apart by the hydrolysis. Afterwards, the break strain steadies by constructing a bridge, and the yield stress increases.
Authors: Dong Ho Choi, Hang Yong Choi, Sang Hwan Chung, Hoon Yoo
Abstract: The strain energy density factor approach under mixed-mode condition is used for the prediction of crack propagation in the orthotropic steel deck specimen, which is similar to that of existing suspension bridges. Stress intensity factor approach is used to compare with strain energy density factor approach for the fatigue crack growth analysis. The stress intensity factors are computed by numerical extrapolation using cracked models for the different crack length. The study shows that the fatigue crack propagation under mixed-mode condition is slower than that under mode I only. Parametric studies on the initial crack length, critical crack length and parameters related to crack growth equations are performed to show the influence of these parameters on the fatigue life.
Authors: Bo Young Lee, Hyung Kook Jin, Dae Hwan An, Jae Sung Kim, Duck Hee Ryu, Joon Hyun Lee
Abstract: Damages in nuclear facilities during the operation of the Reactor Coolant System (RCS) are caused by cyclic loadings due to mechanical or thermal fatigue. Therefore, the development of an integrated technology including fabrication of standard specimens and their practical usage is needed to enhance the reliability of nondestructive testing for surge lines or main feed water lines. In this study, thermal fatigue cracks on STS 304 plates (t = 6mm) and tubes (O.D = 89.7mm. t = 7.7mm) for performance demonstration inspection were fabricated for the Reactor Coolant System (RCS) in nuclear power plants. In case of plates, cyclic thermal changes, from 20 to 450, were loaded on the V-notched specimens under tensile stressed conditions. The applied tensile stress was 1,700MPa at the notch portion. In the case of tubes, cyclic thermal changes, from 35 to 355, were applied on the V-notched specimens under compressive stressed conditions. In the case of plates, the initial crack was generated at 17,000 cycles and the depth of crack was 2.54mm at 22,000 cycles. Unlike the plates, in the case of tubes, the initial crack formed at 14,000 cycles and the crack penetrated the tube at 25,000 cycles. In this paper, shapes and fractographies of fabricated thermal fatigue cracks, and the used cyclic thermal loads are presented.
Authors: Jong Ho Park, Joon Hyun Lee, Gyeong Chul Seo, Sang Woo Choi
Abstract: In carbon steel pipes of nuclear power plants, local wall thinning may result from erosion-corrosion or flow-accelerated corrosion(FAC) damage. Local wall thinning is one of the major causes for the structural fracture of these pipes. Therefore, assessment of local wall thinning due to corrosion is an important issue in nondestructive evaluation for the integrity of nuclear power plants. In this study, laser-generated ultrasound technique was employed to evaluate local wall thinning due to corrosion. Guided waves were generated in the thermoelastic regime using a Q-switched pulsed Nd:YAG laser with a linear slit array. . In this paper, time-frequency analysis of ultrasonic waveforms using wavelet transform allowed the identification of generated guided wave modes by comparison with the theoretical dispersion curves. Modes conversion and group velocity were employed to detect thickness reduction.
Authors: Won Geun Yi, Min Rae Lee, Joon Hyun Lee, Sang Woo Choi, Bo Young Lee
Abstract: Pipelines of nuclear power plants undergo high pressure and temperature. Thermal stratification typically occurs in the surge line and the main feed water lines by flow and this stratification will initiate and propagate thermal fatigue cracks. This may cause rupture and leakage and it is a serious problem to nuclear power plants operation. Therefore it is very important to detect and measure thermal fatigue cracks. In this study, thermal fatigue cracks were generated in austenitic stainless steel specimens by a thermal cycle in notched pipes and weld jointed pipes. Ultrasonic techniques were used to evaluate the thermal fatigue crack depth. When ultrasonic waves propagate from an angle beam probe to thermal fatigue cracks, waves are reflected and diffracted. Crack depth was evaluated by the reflected signals from back wall and diffracted signals from the crack tip, but diffracted signals were too weak to detect so the reflected signals were more useful. The TOFD and dB drop methods were used in this study. The TOFD method is uses a time delay of diffracted signal from the crack tip. The dB drop method is an application of an amplitude decreasing rate by a probe moving distance.
Authors: You Tang Li, Zhi Yuan Rui, Chang Feng Yan
Abstract: A uniform model, in which the crack, V-notch, U-notch and arc are described as breach uniformly, is put forward in this paper. The tip radius, depth and field angle of breach are regarded as the parameter of annularly breached bar. The stress field and displacement field near the tip of the annularly breached bar under bending, in which takes fα(a/b) as its descriptive parameter, was given. All forms of breaches according to the change of tip radius, depth and field angle were discussed. The effects of parameters on fα(a/b) in bending were analyzed. The criteria for the safety design and fracture design both of which on fα(a/b) were obtained. The results not only can be applied widely to anti-fracture design but also be used for reference in anti-fatigued design in product lifecycle management.
Authors: You Tang Li, Ping Ma, Chang Feng Yan
Abstract: The anti-fatigued design is an important field in product lifecycle management. A uniform criterion of annularly breached spindle was put forward in this paper. The crack, V-notch, U-notch and arc were described as breach uniformly according to the tip radius, depth and field angle of breach in the method. The connection between sharp V-notch and crack, between V-notch and U-notch has been set up. We fuse the fatigue fracture theory and life prediction techniques together on the design technology of lifecycle safety guarantee of mechanical structures. The relationship between life and detectability of the breached spindle system was discussed to provide useful guidance for practical applications. The criterion for the safety design and fracture design both of which on fα was obtained. The criterion of annular breached spindle under torsion was obtained at first and then the effects of bending to lifecycle of spindle were analyzed.
Authors: Krishnan Balasubramaniam, B.V. Soma Sekhar, J. Vishnu Vardan, C.V. Krishnamurthy
Abstract: Structural Health Monitoring (SHM) of aircrafts is of great relevance in the present age aircraft industry. The present study demonstrates three techniques that have the potential for the SHM of multi-layered composite structures. The first technique is based on multi-transmitter-multireceiver (MTMR) technique with tomographic methods used for data reconstruction. In the MTMR, the possibility of SHM using algebraic reconstruction techniques (ART) for tomographic imaging with Lamb wave data measured in realistic materials is examined. Defects (through holes and low velocity impact delaminations) were synthetic and have been chosen to simulate impact damage in composite plates. The second technique is a single-transmitter-multi-receiver (STMR) technique that is more compact and uses reconstruction techniques that are analogous to synthetic aperture techniques. The reconstruction algorithm uses summation of the phase shifted signals to image the location of defects, portions of the plate edges, and any reflectors from inherent structural features of the component. The third technique involves a linear array of sensors across a stiffener for the detection of disbanded regions.

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