Determination of the Specific Fracture Energy of the Material under Shear Deformation
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DETERMINATION OF THE SPECIFIC FRACTURE ENERGY OF THE MATERIAL UNDER SHEAR DEFORMATION R. О. Shyshkovskyi
UDC 539.319
We present a procedure for the evaluation of the strain and fracture energy of the material under the conditions of shear deformation based on the application of the method of digital image correlation. The established characteristics are used to determine the stress-strain state and service life of drill columns and shafts of hydraulic turbine in bending and torsion. Keywords: torsion, shear, specific fracture energy, local deformation, method of digital image correlation.
Introduction In order to substantiate the period of safe operation and residual service life of structural elements intended for long-term operation, it is necessary to take into account the influence of all factors on the behavior of the mechanical characteristics of the material. In this case, it is also important to know the actual stress-strain state formed under the action of complex operating loads. Thus, to determine the residual service life of the shafts of hydraulic turbines and drill columns under operating conditions, it is necessary to analyze the current energy state (energy losses) of the material according to the changes in the deformation processes on the surface with the help of contemporary methods of deformation monitoring [1, 2] (finite-element, cellular-automata, opticaldigital, etc.). Note that, in order to determine the residual service life of equipment under the conditions of complex loading, it is customary to use the characteristics of strength and durability of the material obtained in the course of fracture tests under the conditions of uniaxial tension [3, 4]. However, drill columns, turbine shafts, and the rolls of rolling mills are subjected to the combined action of tensile and torsional deformations. The accumulation of defects in the material under operating loads depends on the force scheme of deformation. In these cases, it is necessary to correctly determine the characteristics of strength both under tension and under torsion, as well as under their joint action. A procedure for the evaluation of the strain and fracture energy of a local volume of the material in tension was developed in [3, 5]. The proposed procedure is based on the construction of complete equilibrium diagrams under the conditions of torsion with determination of true strains in local volumes and stresses by the method of digital image correlation (DIC) [5]. The values of true strains and stresses are used to determine the specific fracture energy in torsion as an invariant strength characteristic of the material under the conditions of shear. Procedure of Investigations We tested cylindrical specimens for their specific fracture energy in torsion by using a special device installed in an EUS-20 universal tensile-testing machine [5]. We used continuous cylindrical specimens (Fig. 1). “Lviv Polytechnic Institute” National University, Lviv, Ukraine; e-mail: [email protected]. Translated from Fizyko-Khimichna Mekha
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