M. Ya. Leonov (1912–1992), an Outstanding Scientist in the Field of Mechanics

Abstract

In 2002, we mark the 90th anniversary of the birth and the 10th year since the death of Mykhailo Yakovych Leonov, Academician and an outstanding scientist in the field of mechanics of deformable bodies. M. Ya. Leonov was born in Rodovyno village (Armenia) to a carpenter's family. After graduating from the Moscow Institute of Civil Engineers and the Dnipropetrovsk State University, he took post-graduate courses, defended his Candidate's Degree thesis in 1940, and, later on (in 1949), became a Doctor of Science. Since 1946 to 1962, he worked at Lviv academic research institutes and institutions of higher education. This period of his scientific activity was the most fruitful. In Lviv, M. Ya. Leonov became the founder of new directions in mechanics and one of the organizers of the Lviv school in mechanics. Since 1962, M. Ya. Leonov worked in Frunze (now Bishkek, Kirghizstan). The scientific interests of Academician Leonov covered all branches of mechanics that one way or another concern the strength and stability of solids–structural elements. The contact problem of the theory of elasticity, the nonlinear oscillations (in particular, transition over resonance) and dynamic strength of elastic systems, the twisting and bending of rods, the fracture mechanics of bodies with cracks and microstructural defects, the theory of plasticity and creep—this is a list of the main directions of his scientific activity where he obtained new fundamental results and left a rich scientific heritage. In this paper, we give a brief survey of Academician Leonov's scientific ideas and results. The central place among them is occupied by his pioneer investigations in fracture mechanics. In the paper “Development of the smallest cracks in a solid” [together with V. V. Panasyuk;Prykl. Mekh., No. 4, 391–401 (1959); for English translation, see Fiz.-Khim. Mekh. Mater., 32, No. 4, 109–118 (1996)], the following ideas have been formulated first: (i) the method of modeling of the zone of inelastic deformations near the crack tip by the jump of displacements across a cut, to the lips of which the forces are applied; (ii) the strain criterion of crack propagation: a crack begins to grow if the displacements at its tip reach the critical value δ c . The method of determining the limiting equilibrium of cracked bodies based on the concepts described above and known as the δ c -model was developed and is widely used in engineering practice in Ukraine and abroad. Under the guidance of M. Ya. Leonov, an entire cohort of well-known Ukrainian scientists emerged who successfully develop the mechanics of deformable bodies, in particular, in the field of fracture and strength of structural materials and integrity of structures.