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TsAGI Science Journal

ISSN Print: 1948-2590
ISSN Online: 1948-2604

TsAGI Science Journal

DOI: 10.1615/TsAGISciJ.v46.i7.60
pages 687-714

INVESTIGATION OF CRACK PROPAGATION PROCESS BY MEASUREMENTS OF LOCAL DEFORMATION RESPONSE: I. ACTUAL STRESS FIELD

Svyatoslav Igorevich Eleonskii
Central Aerohydrodynamic Institute (TsAGI), 1 Zhukovsky Str., Zhukovsky, 140180, Moscow Region, Russia
Igor Nikolaevich Odintsev
Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASh RAN), 4 M. Kharitonyevskiy Pereulok, Moscow, 101990, Russian Federation
Vladimir Sergeevich Pisarev
Central Aerohydrodynamic Institute (TsAGI) 1, Zhukovsky str., Zhukovsky, 140180, Moscow region, Russia
Andrei Vladimirovich Chernov
Central Aerohydrodynamic Institute (TsAGI) 1, Zhukovsky str., Zhukovsky, 140180, Moscow region, Russia

ABSTRACT

This work consists of two parts. The first part includes detailed consideration of theoretical foundations of a modified version of the crack compliance method. On this basis, a new experimental method of determining the fracture mechanics parameters is developed and verified. The proposed approach is based on the joint application of the crack compliance method and the optical interference measurements of a local deformation response to a small increment of the crack length. The experimental information represents the values of the in-plane displacement components, which are derived by electronic speckle interferometry at the crack tip vicinity. The mathematical relationships required for the transformation of the initial data to the sought values of the fracture mechanics parameters are presented. It is shown that the values of the stress intensity factor (SIF) and the so-called T-stress can be obtained by determining the first four coefficients of an asymptotic Williams' series. Measurement of the absolute values of the tangential displacement components at reference points located on the line of the crack length increment is the key element of the developed approach. In addition, the availability of high-quality interference fringe patterns that reflect only the deformation displacements without the influence of rigid displacements is a reliable indicator of the real stress state in the vicinity of the crack tip. These facts indicate that in order to interpret the initial experimental data it is not required to use complicated mathematical (numerical) models containing all of the geometrical parameters of the investigated object and the conditions of the external loading. The accuracy analysis of the proposed approach involves comparing the SIF and T-stress values for the edge and central crack in thin plates with similar results to finite-element modeling and analytical solutions, respectively.