• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.47-52
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• 2011

It is well known that stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates because the layup of composite laminates influences their properties. Ultrasonic NDE of composite laminates is often based on the backwall echoes of the sample. A pair of such transducers was mounted in a holder in a nose-to-nose fashion to be used as a scanning probe on composites. Miniature potted angle beam transducers were used (Rayleigh waves in steel) on solid laminates of composites. Experiments were performed to understand the behavior of the transducers and the nature of the waves generated in the composite (mode, wave speed, angle of refraction). C-scan images of flaws and impact damage were then produced by combining the pitch-catch probe with a portable manual scanner known as the Generic Scanner ("GenScan"). The pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to fiber orientation of the CFRP composites, including low level porosity, ply waviness, and cracks. Therefore, it is found that the experimentally Rayleigh wave variation of pitch-catch ultrasonic signal was consistent with numerical results and one-side ultrasonic measurement might be very useful to detect the defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.5 no.1
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• pp.34-47
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• 1985

The developing country, KOREA where does not possess the natural resources for traditional energy such as oil and gas, so. The nuclear energy is the most single reliable source available for closing the energy gap. For these reason, It is inavoidable to construct the nuclear power plant and to develop technology related nuclear energy. The rate of operation in large nuclear power facilities depends upon the performance of work system through design and construction, and also the applied technology. Especially, it is the most important element that safety and reliability in operation of nuclear power plant. In view of this aspects, Nuclear power plant is performed severe examinations during preservice and inservice inspection. This study provide an automation of analysis for volumetric examination which is required to nuclear power plant components. It is composed as follows: I. Introduction II. Inservice Inspection of Nuclear Power Plant ${\ast}$ General Requirement. ${\ast}$ Principle and Methods of Ultrasonic Test. ${\ast}$ Study of Flaw Evaluation and Design of Classifying Formula for Flaws. III. Design of Automation for Flaw Evaluation. IV. An Example V. Conclusion In this theory, It is classifying the flaws, the formula of classifying flaws and the design of automation that is the main important point. As motioned the above, Owing to such as automatic design, more time could be allocated to practical test than that of evaluation of defects, Protecting against subjective bias tester by himself and miscalculation by dint of various process of computation. For the more, adopting this method would be used to more retaining for many test data and comparative evaluating during successive inspection intervals. Inspite of limitation for testing method and required application to test components, it provide useful application to flow evaluation for volumetric examination. Owing to the characteristics of nuclear power plant that is highly skill intensive industry and has huze system, the more notice should be concentrated as follows. Establishing rational operation plan, developing various technology, and making the newly designed system for undeveloped sector.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.2
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• pp.40-47
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• 1993

Composites composed of a precipitation harden 2124 alloy matrix reinforced by SiC whiskers, which are fabricated by powder metallugy, are suscepttible to fatigue damage due to the pile-up of moving dislocation and the microcrack initiation along SiC-Al interfaces, especially at the external surfaces of a body. The initial process, such as pile-up of dislocation or microcrack, that corresponds to the stage I during fatigue failure process are too small to be detected and characterized by conventional ultrasonic technique. This paper describes the applicability of an acoustic microscope with Line-Focus-Beam(LFB) lens of 225MHz to evaluate fatigue damage of SiC whiskers reinforced Al alloy. The specimens which were 6.6mm thick, 13mm wide, and 105mm long in the gage section were fatigued in tension-tension under load control. The velocity of leaky surface and leaky pseudosurface acoustic waves are obtained by FFT analysis technique from V(z) curve which is a record of output of piezoelectric transducer. These results are discussed with the change of number of fatigue cycles. The result obtained by acoustic microscope is compared with that by ultrasonic technique generated at 5MHz with conventional surface wave transducers.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.142-148
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• 2012

This study presents the assessment results of adhesive properties on the interface between a silicon wafer and nano-scale polymer thin film pattern through UAFM images by using the contact resonance frequency of the cantilever. For the experiment, we varied surface treatment processes for the silicon wafer and fabricated a 300nm polymer thin film pattern through lithography. Images from the optical microscope were used to compare the produced test specimens for adhesive condition and the critical load value from the nano scratch test was used to verify the adhesive condition of the nano pattern. Each test specimen resulted in a $1{\mu}m{\times}1{\mu}m$ surface image and subsurface adhesive image. Adhesive condition was evaluated by image contrast differences on the interface according to the changing amplitudes and phases of contact resonance frequency.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.47-52
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• 2011

An electromagnetic acoustic transducer(EMAT) is a non-contact transducer which can transmit the ultrasonic guided waves into specimens without couplant. And it can easily generate specific guided waves such as SH(shear horizontal) or Lamb waves by altering the design of coil and magnet. In this study, the SH wave, which is generated by EMAT, has been applied to estimate the thickness-reduction in a steel plate. Especially, the interesting feature of the dispersive behavior in selected wave modes is used to detect the thickness-reduction. Experimental results show that the reduction-level can be quantified by the measurement of the group velocity of the wave which passes though the thinning area.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.424-430
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• 2000

In order to develop an ultrasonic evaluation method for properties degradation of high temperature materials, a number of Cr-Mo-V steel samples were heat-treated and their damage mechanism was examined. Ultrasonic parameters such as velocity, attenuation, and more recently developed nonlinear acoustic parameter were measured. The nonlinear acoustic parameter was found to be most sensitive to material degradation mainly attributed to the precipitation of impurities in grain boundaries. When compared to the electrical resistivity results, the nonlinear parameters showed similar behavior. There existed a relatively good correlation between the nonlinear parameter and the fracture appearance transition temperature (FATT) obtained by Charpy V-notch impact test. Based on the relationship between the FATT and the fracture toughness ($K_{IC}$), correlation between the nonlinear parameter and $K_{IC}$ was established.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.291-298
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• 1995

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter $d/{\lambda}$; where d is transducer or defect size and ${\lambda}$ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the $d/{\lambda}$ is greater than 1.5, measured directivities almost agreed with the theoretical one.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.118-125
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• 2014

As the earth's current global warming has caused elevation of sea water temperature, size of storms is foreseen to increase and consequently large damages on port facilities are to be expected. In addition, due to the improved processing efficiency of port cargo volume and increasing necessity for construction of eco-friendly port, demands for various forms of port facilities are anticipated. In this study, two kinds of nondestructive evaluation (NDE) techniques (rebound hardness and ultrasonic pulse velocity methods) are investigated for the effective maintenance of smart green harbor system. A new methodology to estimate the underwater concrete strengths is proposed and its feasibility is verified throughout a series of experimental works.

• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.5-10
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• 2012

In this study, carbon steel (A53) is used as the material for the pipes in a marine plant and ship industry. Welds are necessary to join the carbon steel, and the effect of this welding on the properties of the carbon steel has been studied by many researchers. In this study, the dynamic behavior of welded carbon steel was studied using an acoustic emission (AE) technique, which is a nondestructive test. There are numerous AE parameters that can be used to analyze the damage behavior of carbon steel by external loading. The AE parameters of energy, cumulative count, amplitude, and AE event were used, and each parameter was differentiated according to the degree of damage to the carbon steel. The energy showed a high level at the elastic range of the load curve, while the amplitude had the highest value at the hardening region. The cumulative count showed a growth tendency similar to the loading curve. In addition, an ultrasonic technique and hardness test were applied to evaluate the mechanical properties according to the base zone, HAZ region, and weld zone of the weld specimen. The velocity and attenuation ratio showed little change between zones, and an evaluation of the ultrasonic waves on each zone of the specimen was found to be a useful method to clarify the mechanical properties of the carbon steel.