Miahkyi O. Immunity increasing of thermal flaw detection in sandwich and pipelines

This article deals with the way of increasing the noise immunity of thermal flaw detection of honeycomb constructions and pipelines by reducing interference in thermal non-destructive testing for both by selecting the monitoring signal-to-interference ratio, and by the further computer processing of the experimental data obtained. The modern state of thermal non-destructive testing is noted. Honeycomb constructions are the most widely used materials in modern aviation and space technology. The need is stressed to employ honeycomb constructions due to their quality control. Honeycomb constructions are the basis for the housing of practically all products of this sector where reliability of all parts meets the increased requirements. It is known that to detect the defects of detection cutoff type is promising to apply thermal flaw detection. We know that a number of industrial fields and agricultural industry use pipelines. In order to identify manufacture quality and pipelines extent of wear is better to apply thermal flaw detection. However, in comparison with other methods of non-destructive control, the use of thermal control is connected with a number of factors which complicate its application. The main problems of application of thermal non-destructive control are both the existence of a large quantity of noises and interferences of different nature and the fact that the thermal flaw detection is conducted, as a rule, not under optimum regimes, which substantially worsens detectability of flaws and limits reliability of control results. Therefore, increase in the efficiency and reliability of thermal flaw detection, based on in-depth analysis of the processes of detecting defects and development of the principles of optimization of both the procedure of control and subsequent processing of the obtained information, is an important and relevant task. Thermophysical models of multilayered honeycomb constructions and pipelines are proposed. The calculations of optimum thermal non-destructive control (TNC) regimes were carried out as the object of control (OC) of the thermophysical model. A multilayer plate was chosen as a model of honeycomb constructions. It is adequately reflects actual design of the honeycomb structures, which consists carbon plastic skin between the two layers of which the honeycomb plastic is placed. Calculations by the thermophysical model were performed by the cylindrical coordinate system where r is the radial coordinate; z is the vertical coordinate, φ is the angular coordinate. A number of interferences such as the inhomogeneities of the sample surface emissivity and the “edge effect” are modeled separately. For effective suppression of interferences, they were divided into two groups: the first one which includes the inhomogeneities of the emissivity of the OC surface and additive interferences, taking into account its properties suppressing the control mode and the second group which includes multiplicative interferences which are eliminated by successively filtering the obtained thermograms. Calculations by the thermophysical model were performed by two methods such as the finite-difference procedure and finite elements method and after that they were also compared to the data obtained as a result of the experiment on several different samples. We also carried out experimental studies on the pressure of the steam cooling system of the South Ukrainian NPP. On their basis, it can be concluded that the use of methods of thermal non-destructive testing is one of the most promising areas. During the shooting within the operating conditions of the pressure steam lines system, the presence of an additive noise caused by the illumination by external radiation sources was also detected. To suppress these noises, a number of filters were developed, as well as the sequence of their application to significantly reduce the level of noise during TNC, thereby increasing the sensitivity of thermal flaw detection to detect defects of the "non - glue" type in honeycomb structures-the size of the threshold defect is reduced from 6 mm to 3 mm, and the reliability of their detection increased by 17 -20%, which creates all the prerequisites for the production of a visual method of defect identification to move to an automated, based on the relevant technical means.