PSI - Issue 20

R.S. Akhmetkhanov / Procedia Structural Integrity 20 (2019) 218–221

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R. S. Akhmetkhanov / Structural Integrity Procedia 00 (2019) 000 – 000

process, which, in turn, depended on the presence of internal or external defects. When the thermodynamic equilibrium of an object with the environment is disturbed, an excessive temperature field arises on its surface, the nature of which allows one to obtain information about the properties of objects. There are two types of NDTs - passive and active (2015, 2009). Passive control does not need an external source of heat exposure. Active opposite, involves the heating of the object by external sources. The use of active thermal control methods makes it possible to identify defects in the internal structure of delamination (voids ) , as well as delamination and cracks oriented in the structure of a mono-layer composite material, i.e. in the plane of the reinforcement layers. Defects of the internal structure, having a deep occurrence in a layered package, are observed with a greater time delay and a reduced temperature contrast in these zones. The time from the onset of exposure to the detection of a temperature anomaly is proportional to the square of the depth of the defect. Therefore, the duration of observation of the manifestation of a product defect from the onset of a temperature transient process is proportional to the square of the depth of the defect and is inversely proportional to the coefficient of thermal diffusivity of the material used. 2. The results of an experiment on thermal non-destructive testing The difference in thermal diffusivity of inclusions and defects is the main cause of the inhomogeneity of the thermal field during cooling. For the analysis of thermograms obtained as a result of thermal control of a panel made of a composite material PI, it was decided to use a multiple-scale wavelet transform for images of thermograms. Overall dimensions of the panel - 0.7; 0.6; 0,004 m. The sample was heated to a temperature of 32 ° C and further maintained at room temperature for 30 minutes. The thermal field of the sample in the form the thermogram was recorded using the MikroScan 7600 Pro thermal imager. The thermal image of the test object necessary for analysis (Fig. 1a) was determined from the maximum value of the standard deviation, as a criterion for the maximum selection of defects and irregularities in the sample material. In Figure 1b shows a histogram of the temperature density distribution over a thermal field for an image with a maximum standard deviation of StdDev = 9.761. The range of temperature values in the thermal field after exposure was in the range from 27.3 to 28.3 ° C. Color level of pixels was in the range from 0 to 255 (8-bit representation of black and white images). Light areas of the thermal field have a higher temperature level. For the analysis of the thermal field, the ImageJ program was used. O n fig. 1c, there is clearly an area with an elevated temperature of 28.3 ° C. In Figure 1d this area is clearly marked. If there are nearby defective zones, they may look like one local zone. Therefore, it was necessary to solve the problem - is it one defect or several? Conducted research in this area of the defect by the method of acoustic control showed the presence in this area of 3 defects. Image analysis can be carried out by various procedures. In fig. 2, the image of the thermal field was presented in the form of isolines (Fig. 2a), the boundaries of regions with different temperatures (Fig. 2b) and in the form of the image carcass (Fig.2c). Border highlighting (edge highlighting) - is based on algorithms that highlight points of a digital image, in which the brightness changes significantly or there are other types of inhomogeneities. The frame of the image shows the lines (usually one pixel wide) of maximum temperatures. According to fig. 2 clearly shows that the image (Fig. 1d) contains three areas with an elevated level of the temperature field. Image 2a shows these areas with defects and their configuration. More clearly on the contour lines and boundaries. Whereas the image carcass more or less clearly shows the uniform structure of the thermogram outside the area of detected defects.