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[en] There are many different mathematical models that can be used to evaluate ah inspection system's Probability of Detection (PoD). Each model has a unique feature, These features can make one model more appropriate than another model. There are more than 12 commonly used PoD models used in NDT and each model has its own unique mathematical form. This article introduces each model and compares them to reveal their unique features. PoD is typically rather heavily explained using mathematics, but understanding the mathematics to a very deep level is not required to generate a good PoD curve. Computers take care of the heavy math. Having an understanding of the differences between model types is essential for creating a PoD that actually represents the inspection situation. This is the main reason behind having a selection of models. (author)
[en] The Probability of Detection (PoD) is a very useful aspect of an inspection. It is a measure of an inspection system and/or personnel's detection capabilities. The PoD can be used to quantify improvements to an inspection, as well as personnel performance changes. Although the PoD can be a useful NDT tool, it is not used extensively. This is mainly due to the complex mathematics behind the model. Evaluating a PoD has specific NDT requirements, as well as statistical requirements. (author)
[en] All NDT inspections use models. The number and type of models will vary between inspections. A qualified inspection will use a PoD model to evaluate detection capabilities. All techniques have some degree of calibration. Some calibration processes generate curves that are simple models. Parameters are the building blocks of models. Models can be generated to understand what happens to the results of an inspection when parameters change. Not all parameter variation will cause a decrease in a system's detection capability. For example, an increase in an indication's length will likely increase the chance of detection. Each variable or parameter involved in an inspection has natural variations. These variations will affect an inspection with different degrees. Evaluating when a change is significant becomes an important aspect in developing sound inspection techniques. This article addresses several techniques used to determine significance in changes between measurements. (author)
[en] A probe that can examine a ferromagnetic heat-exchanger finned tube with a curved part is proposed in this paper. The distortion in the electromagnetic field due to the existence of flaws and tube support plate (TSP) was measured using an active-type excitation coil, a bobbin-type Hall sensor array, and a passive-type pick-up coil. The active-type excitation coil could recognize the existence and location of flaws. The Hall sensor array could recognize the existence, location, and distribution of flaws. The passive-type pick-up coil could recognize the position of TSP, which was used as a landmark. The effectiveness and TSP-recognition ability of the proposed probe were verified using a finned-tube specimen made of STS 439 with various types of artificial defects
[en] A fairly new method of manufacturing components - additive manufacturing could send shock waves through the manufacturing industry in the near future. Additive manufacturing is a process where objects are built by adding layer -upon-layer of material, whether the material is plastic, metal, concrete, or other materials. This is different from current manufacturing (subtractive manufacturing), as an object is typically made as a blank form and subsequently reshaped in the manufacturing processes such as machining, forging, etc. The process behind additive manufacturing is fairly simple: 3-D modeling software is used to create a blueprint. That blueprint is then used to create a component using different methods and materials. The object is then created layer-by-layer until completed.
[en] In this paper, we describe the non-destructive testing method for alumina ceramic-aluminum laminates using pulsed terahertz waves and their defect visualization technique. The test specimen was fabricated by bonding an alumina ceramic and an aluminum plate using an epoxy adhesive. The lower part of the alumina ceramic- aluminum laminates was fixed, and then, the bending test was performed to generate the crack of alumina ceramic and delamination. For defect inspection, terahertz time domain spectroscopy based on a photoconductive antenna and a motorized x-y stage were used to acquire the data. The terahertz wave was incident on the surface of the test specimen at an angle of 45 degrees. A-scan, B-scan, and C-scan are performed by processing the terahertz waveform in the time and frequency domains. As a result, we successfully visualized the pores generated by the adhesion of alumina ceramics and the aluminum plate, and the artificial cracking and the delamination
[en] Full-text: Acoustic Emission (AE) technique, a passive non-destructive testing (NDT) method has been widely used to monitor running state of pressure vessel. One of the factors that affect the performance of AE is the attenuation of AE signal. Attenuation characteristics of AE signals mainly affected by propagation distance. Attenuation refers to the decrease in amplitude that occurs as a wave travels through a medium. The measurement of the wave attenuation shall be performed if no documented data base for the structure. The wave attenuation is important for the maximum sensor distance and the possibility to re-calculate the peak amplitude to the point of origin. The attenuation affects the characteristics of wave propagation in determining the wave velocity used critically for source location computation, for potential numerical adjustment, and for numerical assessment of the computed results. In this project, the two most commonly used AE parameters, energy and amplitude, were studied to reveal the corresponding AE wave attenuation. The behavior of acoustic waves produced and the attenuation of AE signals from pencil lead breaks were studied. (author)
[en] This paper presents a fiber Bragg gating (FBG) sensor that can be surface mounted for simultaneous strain and temperature measurements. By embedding a conventional FBG sensor in a composite laminate, local birefringence is introduced, which causes the bandwidth of the FBG spectrum to vary with strain as well as temperature. As such, temperature and strain can be simultaneously determined from two FBG spectral parameters, i.e. the spectral bandwidth and the Bragg wavelength. Techniques for improving the spectrum of the FBG-composite sensor and for inversely determining the strain and temperature from the measured FBG spectral parameters are discussed. Thermal–mechanical testing of the FBG-composite sensor was carried out to validate the sensor performance. The measurement errors, within one standard deviation, for the strain and temperature measurements were found to be ±62 με and ±1.94 °C, respectively. (paper)
[en] A high energy X-ray generator based on a linear electron accelerator is required to penetrate a thick steel plates of 10 cm or more. Most of a high energy X-ray non-destructive inspection systems used in Korea are imported products. And X-ray inspection system with energies greater than 10 MeV is under strict control of international trade, so it is having difficulties in expansion and maintenance of the existing system. Therefore, in order to use X-ray generator having an energy of 10 MeV or more, we have to develop our own system The high energy X-ray inspection system consists of an X-ray generator based on linear electron accelerator, beam collimators, sample transportation and detector. We have developed a 15 MeV X-ray generator based on S-band linear electron accelerator. The maximum sample size for 2-D images is up to 1 meter, and the 3-D image sample size is up to 0.3 meter. It is expected that non-destructive testing of various samples including heavy industry and nuclear power field will be possible using the developed system.
[en] Currently, thin plate-type materials are widely used as structural materials in various industries. Defects in such a thin plate cause destruction of the structure, resulting in human and material damage. The ultrasonic inspection technique is the most widely used non-destructive inspection method to detect such defects. However, it is difficult to detect micro defects in a thin plate with thickness ≤ 5mm and analyze their signals. In this study, electromagnetic acoustic transducer-based resonant ultrasonic spectroscopy was applied to detect micro defects. Through finite element analysis, the change of the resonance frequency and output voltage depending on the presence or absence of defects was determined, and a test specimen was fabricated by incorporating fine defects to an actual aluminum plate. Our results indicate that it is possible to identify the presence of micro defects using this technique and to recognize the scanned image by changing the resonance frequency and output voltage