Strength of Materials, Vol. 51, No. 6, November, 2019 EFFECT OF SHOCK AND VIBRATION PRELOADING ON THE PARAMETERS OF TEAR DIMPLES AND THEIR CONGLOMERATES P. O. Marushchak, a,1 I. V. Konovalenko, a UDC 621.181 and M. G. Chausov b The quantitative method of evaluating the parameters of tear dimples and their conglomerates was proposed with examination of their fractographic images. The method is based on calculating the correlation coefficient distribution field of pixel intensity for compatible image areas. The 17G1S-U steel specimen fractograms produced with a REM-106I scanning electron microscope were studied. The zones of large tear dimples are shown to be characterized by strong correlation of brightness of compatible areas, which provides applying the advanced method for their detection and examination. The interrelation between image-assisted calculated dimple parameters with physico- mechanical characteristics of the material was established. Keywords: fractographic images, tear dimples, coefficient of roundness. Introduction. Research of basic deformation and fracture mechanisms for structurally nonuniform media is a currently central problem, which requires a complex approach and different methods of investigation [1]. This is also important for studying pipe steels with their microstructure oriented along the rolling direction, which influences significantly the evolution of the deformation process [2–4]. One of the approaches to evaluate the material properties under critical deformation (prefracture stage) is the method of complete diagrams, which provides simultaneous determination of its mechanical properties and crack resistance. This method is applied to studying the effect of the unsteady (non-equilibrium) dynamic process (UDP) on the fracture mechanism of 17G1S-U pipe steel. By the unsteady dynamic process is meant shock and vibration loading conditions, which are responsible for active dissipative phenomena in the material, associated with the self-organization of its structure [5]. Previously [4, 5], the structure of the material was established to transform into the unsteady state induced by such a shock effect. Its further self-organization can adversly affect pipe steel properties, in particular the crack resistance is reduced [5]. Despite a great body of accumulated experimental data, the mechanisms and major factors of the fracture surface relief formation are still a debated topic. An unambiguous physicomechanical description is lacking to represent the effect of the internal material structure, loading conditions, stress-strain state under deformation on the fracture mechanisms at macro- and microlevels. The interrelation of deformation processes on the surface and in the volume of the material would require additional investigations [6, 7]. In static tension, the fracture surfaces generate tear dimples. Thur form, size, depth are important quantitative parameters that may be employed to reconstruct the kinetics of deformation and fracture of the materials or full-scale structures [8–11]. Several research efforts [1, 2, 8, 10, 11] demonstrated the potentials of automated methods for their investigation. At the same time, the materials can differ in the dimple form, size, and morphology. Modern scanning 868 0039–2316/19/5106–0868 © 2019 Springer Science+Business Media, LLC a Ternopil Ivan Puluj National Technical University, Ternopil, Ukraine ( 1 maruschak.tu.edu@gmail.com). b National University of Life and Environmental Sciences, Kyiv, Ukraine. Translated from Problemy Prochnosti, No. 6, pp. 68 – 79, November – December, 2019. Original article submitted November 10, 2017. DOI 10.1007/s11223-020-00137-2