PSI - Issue 65

Akhmetkhanov R. S. et al. / Procedia Structural Integrity 65 (2024) 6–10 Akhmetkhanov R. S. / Structural Integrity Procedia 00 (2024) 000–000

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1. Introduction

Even the strongest metal structures can be subjected to deformation under severe impacts. This can lead to serious consequences, including loss of mechanical properties of the material, compromised component integrity and even failure of the entire structure. During impact, metal is subjected to mechanical stress, which can cause various types of deformation. When deforming the material (plastic) there are local zones of material temperature increase, which can be used to determine the local heterogeneity of the mechanical properties of the material. This is the basis for thermal diagnostics. This is the basis for thermal diagnostics, for example, as shown in the works of authors Nesteruk D.A., Vavilov V.P. (2007) and Moiseychik A.E., Moiseychik E.A. (2014). The method of thermal control is widely used for diagnostics of materials and technical systems, for estimation of physical properties of materials. And the analysis of shock loading of composite materials are given, for example, in the works of authors U. Galietti, D. Palumbo(2010), Rajic N., Rowlands D.(2013), Robinson A. F., Dulieu-Barton J. M., Quinn S. and etc.(2009) and Daiki Shiozawa, Takahide Sakagami, Yu Nakamura and etc.(2017). Impacts can cause the formation of cracks and microcracks in the material. This leads to a decrease in its strength and fatigue resistance. Cracks can occur both in the area of direct contact with the impact load and in remote locations due to impact energy transfer. In general, impacts can have a significant effect on the strength and structure of a material, changing its physical and mechanical properties. To statistical data were used to evaluate the peculiarity of the thermal fields, multi-fractal spectra, Minkowski connectivity and distribution of n (number of zones) of size r (average radius) with the same level of deformation (clusters). The multi-fractal spectra are related to the type of these distributions. The Minkowski connectivity is defined by a function μ ( z ), which quantifies the connectivity of the of the image in terms of the values of temperature 2. Main results

Nw N b N 

,





where – N denotes the total number of pixels, N w denotes the number of continuous sets of "white" pixels (clusters at a certain level z of coloration of the image – levels of image colorization in gray scale). Pixels that are below the threshold are called "black" pixels. Finally, N b denotes the number of continuous sets of black pixels. For the temperature field, "white" pixels have a higher temperature than "black" pixels. Let's consider the thermogram when an impact is applied to a plate made of composite material. Localized impact effects of impact in the form of thermal field and their differences can be seen in Figure 1. The white point is the place of the impact.

Fig. 1. Thermograms of the thermal field at impacts: (a) material without defect; (b) material with defect, h, l - overall dimensions of the plate.