Fractal Dimension Using the Acoustic Infrared Thermal Method of Inspection of Non-metallic Heterogeneous Materials

Various types of heterogeneous materials and structures are widely used in mechanical engineering. The widespread distribution of such materials cannot be imagined without reliable control methods. The paper uses the acoustic, infrared thermal imaging method to control non-metallic heterogeneous materials, which allows for determining structural features in solids that exhibit the effect of mechanical hysteresis and internal friction. The research was conducted on the features of the structure of a carbon-plastic plate with dimensions of 130 × 80 × 4 mm with defects made in advance: delamination and a defect obtained from shock loading. The method is based on the phenomenon of an increase in the temperature of the surface of a heterogeneous object in the defect zone under the influence of the energy of mechanical vibrations. At the same time, the carrier of information about structural defects is the thermogram, which is recorded using infrared devices. The difficulty of evaluating anomalies of the thermal field of the investigated surface of the product made of non-metallic heterogeneous material is that the result depends on the scale of measurements (on the scanning step). Therefore, the authors suggest using the so-called fractal approach invariant to the measurement scale. The box-counting method is used to determine the fractal dimension. It is shown that this method is sensitive to equiaffine transformations. For the unambiguousness of the measurement results, it is suggested to use known methods of mathematical statistics for their processing.