• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.405-414
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• 2009

This paper proposed a methodology based on ultrasonic diffraction technique to inspect the depth of a crack initiated from a notch of CT specimen by fatigue test, and its usefulness was verified by experiments. Especially, in order to identify accurately the diffractive waves from the crack tip in the situation where there are extra diffractive elements such as a notch, we have tried imaging by transducer scan and analyzed the propagation path of diffracted wave. Two specimens with and without a crack were experimented. Higher frequency and larger refractive angle of transducer showed a tendency to decrease the error in the measurements, and the measured crack depth showed an error less than 0.38 mm in case of 4 MHz $60^{\circ}-60^{\circ}$. The proposed methodology is applicable to weak diffractive sources, and so that it would be useful to inspect micro cracks and for their depth sizing.

• Journal of Korean Medical classics
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• v.34 no.2
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• pp.85-94
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• 2021

Objectives : Pulse diagnosis is one of the main diagnostic methods of Korean Medicine that understands the patient's condition and illness by reading changes in the patient's pulse, which is described in terms of pulse condition While they are described in detail in medical texts, it is difficult to grasp their true nature, as the written descriptions fail to do justice to the experience of pulse taking it tries to convey. As a way to approach pulse condition the effect of the body's tension on the radial vein was measured using an ultrasonic device, after which the measured changes and how they could be reflected in pulse condition were studied. In other words, changes in the radial vein following induced tension were analyzed. Methods : 1) The thickness of the subject's radial vein was measured using a linear probe of an ultrasonic device[LOGIQ 5 Basic, GE, USA]. 2) Fatigue level was increased through artificial stimulation using the Gripmeter[ks-301, Lavisen, Korea]. 3) Thickness of the radial vein post tension induction was measured. 4) The results were analyzed with the Tukey test or paired t-test as post hoc tests. Results : Thickness of the radial vein of the subject pre- and post- Gripmeter stimulation decreased with significance. Conclusions : Constriction of the radial vein that happened after tension induction could be linked to the Tight Pulse[緊脈] that is related to patterns of contraction and pulling.

• Advanced Composite Materials
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• v.18 no.1
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• pp.43-59
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• 2009

The current study assessed the effect of a bolt hole on tensile fatigue properties of CFRP laminates. Two specimens, i.e. $[(0/90)_3]S$, $[(0/45/90/-45)_2]_S$, were analyzed using a finite element method and were experimentally tested for cases, both with and without a hole, whose diameter corresponded to 0.12 times the specimen width. Delamination positions predicted by a 3-dimensional static finite element analysis were matched well to those observed by an ultrasonic imaging system in the middle of fatigue test. A hole whose diameter corresponds to 0.12 times the specimen width caused the fatigue strength to decrease by 9% and 11% under 5 Hz loading frequency, and by 22% and 25% under 10 Hz loading frequency for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively. Because the decrease in sectional area due to the hole was normalized in calculation of the tensile strength, a stress concentration around the hole is believed to induce the strength degradation of fatigue specimens. From the finite element analyses, the stress concentration factor around a hole was expected as 8.8 and 9.5 for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively.

• Advanced Composite Materials
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• v.16 no.2
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• pp.151-166
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• 2007

High-cycle fatigue characteristics of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates [-45/0/45/90]s up to $10^8$ cycles were investigated. To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz, since it is difficult to investigate the fatigue characteristics in high-cycle at 5 Hz. Then, the damage behavior of the specimen was observed with a microscope, soft X-ray photography and a 3D ultrasonic inspection system. In this study, to evaluate quantitative characteristics of both transverse crack propagation and delamination growth in the high-cycle region, the energy release rate associated with damage growth in the width direction was calculated. Transverse crack propagation and delamination growth in the width direction were evaluated based on a modified Paris law approach. The results revealed that transverse crack propagation delayed under the test conditions of less than ${\sigma}_{max}/{\sigma}_b$ = 0.3 of the applied stress level.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.52-58
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• 2000

Spot welding, namely a kind of electric resisting welding has been used widely in field of automobile and aircraft industries because of easiness to apply. Specimens used in this study was a mild steel of 1.2mm thickness and the electrode was a Cu-Cr alloy of 6mm diameter. The surface sheared of specimens after testing of tensile shear was observed by SEM(scanning electron microscope) after ultrasonic cleaning for 10min., and microstructures and grain size of all specimens were measured with using of O.M.(Optical microscope). By the means of measurement and observations of tensile shear load, fatigue strength and share surface, the weldability of spot welding was evaluated. When tensile shearing testing, fracture starting point in all specimens was took place at the bond between HAZ(Heat affected zone) and nugget. With increasing in number of layers, fatigue strength was decreased. With increasing in electric current, grain size in the HAZ became more fine.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.135-139
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• 1985

A J$_{IC}$ test procedure by ultrasonic method performed to observe the crack opening behavior of fatigue precrack and detect the initiation of crack propagation of compact tension specimen in this paper. Pulse-echo method with 5 MHz transducer was used on the Cr-Mo steel quenched and tempered at 593.deg. C. We obtained the following results in the elastic-plastic fracture toughness test by ultrasonic method. Echo height is a little increased linearly and rapidly at the early stage of loading . Then it is decreased considerably, finally at the unstable crack growth stage, it is rapidly increased at an unpredictable rae. The initiation of crack propagation is supposed to be at the stage deviated from linearly decreased region and then blunted. J$_{IC}$ value(10.15-12.15 Kgf/mm) by ultrasonic method is lower than that(12.2 Kgf/mm) by R-curve method. But, it is required that the research for the more exact evaluation about correlation between echo height and the crack opening behavior of precrack tip will be continued. continued.ued.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.56-64
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• 1997

Macrostructural characteristic of the transverse cracks and fatigue behavior were studied for EH 32 TMCP 50mm thick plate welded with FACW under the variation in preheat and interpass temperatures. Transverse cracks were detected in specimen welded with preheat and interpass temperature below $30^{\circ}C$, but cracks were not detected in the specimens welded with preheat and interpass temperatures at the range of $100~120^{\circ}C$.C. The location of crack formation was found to strongly depend upon the thickness of weld layers as regard to the plate thickness.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.136-137
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• 2006

Crack initiation and short crack propagation was studied on the polished notched surfaces of Cr-Mo prealloy sintered steels with 7.35 $g.cm^{-3}$ sintered density. An ultrasonic resonance test system operating in push-pull mode at 20 kHz and R=-1 was used. It showed that crack initiation took place in several places, small cracks growing oriented to the local pore structure rather than to stress orientation. Their growth rate is markedly higher than the corresponding one of long cracks. Finally, several microcracks join to form a dominant crack.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.231-237
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• 2000

A15052/AFRP laminates were developed principally to obtain a material with good fatigue strength, in which possible cracks would grow very slowly. Weight savings of more than 30% should be attainable in practice. Also, the crack bridging fibers could still was carry a significant part of the load over the crack, thus the COD and stress intensity factor was reduced at the crack tip. A15052/ AFRP laminates consists of three thin sheets of 5052-H34 aluminum alloy and two layers of [0] unidirectional aramid fiber prepreg. The cyclic-bending moment test was investigated based on applying the five kinds of bending moments. The size of the delamination zone produced between 5052-H34 aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. In addition, the relationship between the cyclic-bending moment and the delamination zone size was studied and the effect of fiber bridging mechanism was also considered.

• Composites Research
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• v.12 no.3
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• pp.1-7
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• 1999

New hybrid composite material CPAL(Carbon Patched ALuminum alloy), an Al2024-T3 plate doubleside reinforced with carbon/epoxy laminates were made. Fatigue crack growth tests were carried out at R=0.2, 0.5 in the CPAL specimens. The retardation mechanism and behavior of fatigue crack growth were examined basing on investigation of the crack and the delamination using a X-Ray and a ultrasonic C-Scan. The fatigue crack growth rates of CPAL specimens were remarkedly retarded compared to that of the Al2024-T3 specimen. The retardations amounts of the fatigue crack growth rates get higher in $0^{\circ}$/$90^{\circ}$ CPAL specimen than in $\pm$$45^{\circ}$ CPAL specimen, and get higher at R=0.2 than at R=0.5. The retardation of fatigue crack growth rates in CPAL specimen was generated by the crack bridging mechanism, that is the behavior that the fibers in CFRP layers decrease the COD in the Al2024-T3 plate.