539.421

переривчасте руйнування
тонколистові метали
діаграми стрибкоподібного росту тріщин
залежності вимірюваних змінних від часу
характерні стани тріщини
discontinuous failure
shit metals
step-wise crack grows diagrams
time dependence of the measured variables
characteristic crack states

Розроблено методику експериментального дослідження стрибкоподібного росту наскрізної тріщини в листових металах. Встановлено, що пружно-пластичне руйнування тонколистового алюмінієвого сплаву в умовах загальної текучості являє собою процес переривчастої зміни поздовжніх і поперечних розмірів порожнини тріщини. Запропонований новий підхід до опрацювання та інтерпретації даних про переривчасте руйнування зразків з центральним отвором при одновісному розтягу, що базується на аналізі діаграм зміни параметрів експерименту в часі. Розглянуто процедуру отримання мінімально необхідного набору даних, що дозволяє визначати характерні стани стрибкоподібно зростаючої тріщини. Показано, яким чином результати даної роботи можуть бути використані при оцінюванні руйнування високонавантажених деталей, що містять відносно короткі наскрізні вирізи.
The paper is devoted to the development of procedure for obtaining, processing and interpreting of the initial data on step-wise propagation of the through crack in the rectangular plate with a central opening under uniaxial tension. It is assumed that use of this procedure makes it possible to evaluate (separately) the local effects, which deal with to the crack propagation within the fracture development zone, and the effects, which deal with to the global plastic deformation of the specimen in question. The primary problems on the way to such procedure are the following: 1) Decision on configuration and dimensions of the specimen having an initial stress concentrator, which enables one to obtain the experimental diagrams with a sufficiently extended region of the step-wise growth of the crack; 2) Determination of the loading rate range that is consistent with quasi-static development of the specimen fracture process; 3) Determination of the minimally required set of initial data and their presentation, which simplifies the analysis of experimental data and, simultaneously, enhances their accuracy; 4) Determination of specific states for the crack tip region and justification of the field of possible practical use of the results. It was found that the preferred configuration of the specimen for investigation on discontinuous fracture is the rectangular plate, which undergoes fracture under conditions close to those for transverse plane strain. A circular hole with a relatively smaller diameter of 2r0 is situated in the center of the plate with a ratio of 2H0 (height) to 2W0 (width) which equals 0,1. It is shown that with velocity of the active grip which equals or is less than 0,001 mm/sec, the experimental diagrams covering sufficiently extended regions of discontinuous fracture. The analysis of the time dependences of the registered variables demonstrates that each crack step can be described using six specific conditions for its tip region. Among them there are such conditions, which can be used in solution of two basic problems that are important from the practical point of view. The paper presents the results of tests and their ways of use in the estimation of fracture of highly loaded components with relatively short through cracks.

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