Toshimitsu Ishii

On the NDT and E for the diagnosis of defects using infrared thermography

The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defects depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.

On the proposal of quantitative temperature measurement by using three-color technique combined with several infrared sensors having different detection wavelength bands

Abstract We developed the previous infrared sensing technique, the two-color technique, to establish further a more general technique to measure the temperature quantitatively under near-ambient conditions. The quantitative temperature measurement, three-color technique, was newly proposed by combining three kinds of infrared radiometers having different detection wavelength bands. The measurement can also be done by adding three infrared filters to one infrared radiometer. The radiometers have a selective detection wavelength band of several μm in width which is in the range of 2–13 μ m. The method was confirmed using numerical simulation to allow a parametric study of how the result varies for different values of emissivity corresponding to the respective infrared radiometers. An experimental investigation was also performed to evaluate the measurement error and the adaptability of the technique. As this technique has a feature that can perform quantitative temperature measurement for objective surfaces at each picture element without presuming any emissivity, reflectivity and ambient conditions, there is a possibility that the technique will be useful for various medical or engineering disciplines.

Infrared radiation properties of the carbon–carbon composite and their application to nondestructive detection of its defects

Abstract Infrared radiation properties and surface characteristics of C/C composites and graphites were examined at temperatures in the range of 293–373 K from the viewpoint of the nondestructive detection of defects in these materials. The radiation temperature of specimen surface and its variation were quantitatively evaluated on the basis of true specimen temperature, ambient temperature, emissivity and radiosity coefficient to obtain data applicable to the thermographic detection of defects. It was found that the larger the pore size and roughness of specimen, the larger the variation of data points. Graphite specimens with different artificial flaws 1–10 mm in diameter and 1–8 mm in depth were examined by thermography, and the minimum difference in radiation temperature at a defect to be detected was obtained with regard to the flaw size.

Proposal of quantitative temperature measurement using two-color technique combined with several infrared radiometers having different detection wavelength bands

Infrared thermography has been widely used to visualize a two-dimensional temperature field for various engineering applications. However, in general, conventional infrared thermography cannot directly be applied to quantitative temperature measurement on glossy metal surfaces under near-ambient conditions, because of the severe influ- ence of the reflected energy incident from the surroundings on the mea- surement. When it is necessary to measure the temperature quantita- tively, an appropriate calibration involving complicated procedures must be performed. In this paper, therefore, a new technique of measuring temperature is proposed for near-ambient conditions, by combining si- multaneously several infrared radiometers having different detection wavelength bands to enable a two-color technique, which does not re- quire any temperature calibrations. The sensors concerned have a se- lective wavelength band of several micrometers in width in the range of 2 to 13 mm. The applicability of the method, including a series of proposed equations, has been confirmed by an investigation; the numerical simu- lation presented merely allows a parametric study of how the result var- ies for different values of emissivity corresponding to a pair of infrared radiometers. An experimental investigation is also performed to estimate or correct the measurement error pertaining to the present technique. This technique has the feature that a two-dimensional temperature field can be evaluated quantitatively, nondestructively, and simultaneously at each picture element without presuming any emissivity and reflectivity, even though the object has a complicated shape; so that it may be useful in various medical or engineering applications.

Evaluation methods of NETD and MRTD for IR camera by using FLIR collimator

An application of infrared radiometer or IR camera has been widely spread in many industries for these twenty years, because of its convenience to use, wide measuring range by remote sensing, and visual survey due to thermal image. In this IR method it is very useful to detect invisible surface and internal flaws. Conventional IR makers are accustomed to use NETD as the resolution characteristics of IR camera, but general customers using IR camera cannot evaluate the minimum detectable size of measuring object, if they cannot evaluate MRTD. The study of the quantitative evaluation to clarify the relation between NETD and MRTD is very little. This paper represents evaluation methods of NETD and MRTD, and their quantitative relation by using collimator FLIR testing.

Study on the Visual Detection of Defects in Divertor Structures for the Fusion Reactor by Means of Infrared Radiometer(Influence of Heating Methods on Visual Detection).

Our previous study indicated that infrared radiometry was suitable for nondestructive testing of joints in divertor structures for a fusion reactor. Radiation temperature difference between an unbrazed tile and a brazed one was clearly observed when the model divertor was heated using a halogen lamp. This paper describes the influence of three different heating methods on thermal images of model divertor that contain improperly bonded are as in the joint, in order to obtain information about the most appropriate heating method. Model divertors, which consist of carbon-carbon(C/C) composite tiles brazed to a Cu heat sink with different brazed areas, were heated using the halogen lamp, high temperature gas, or warm water. It was confirmed that the temperature difference between brazed and unbrazed areas could be detected by infrared radiometry and that the smallest unbrazed area was detected when warm water was used.

Measurement of radiosity coefficient by means of an infrared radiometer.

An infrared radiometer has been used for measuring and visualizing the radiation temperature distribution of a surface in many fields. Measured radiation energy by the radiometer is a summation of an emitted radiation and a reflection, which is called a radiosity flux. The present paper shows the characteristics of the radiosity of tested materials. The infrared sensor in used to measure the erosion rate of the graphite by ion beam injection and the temperature distribution of a cutter.