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Estimation of the Subcritical Growth Period for a Through Crack of High-Temperature Creep in a Two-Layer Plate
Abstract
The procedure for energy approach-based estimation of the subcritical growth period for a high-temperature creep crack in a two-layer plate is proposed. The validity of the procedure is illustrated by the example of central crack extension in the plate.
We develop computational models aimed at the determination of the residual service life of two-layer plates with systems of cracks under long-term static loads at high temperatures. The models are based on the first law of thermodynamics of energy balance for the components and rates of their changes in a metallic two-layer body containing macrocracks and subjected to the action of long-term tension and high-temperature fields. We consider periodic and doubly periodic systems of cracks.
The issues related to renewal of worn-out parts of a rolling stock with the layered coatings are considered in the article. In developing a mathematical model of wearing a multilayer material as an object of rheology certain assumptions, which enable using the methods of mechanics and mechanics of continuous medium, are done.
In order to determine the K-value of the complex cracked bodies within the accuracy of practical use, a new experimental method was proposed based on the brittle fracturing of epoxy resin. By comparing the experimentally determined K-value of a standard specimen with the calculated value, the accuracy of the proposed method was first checked. Then, the K-value determination tests of a specimen with cracks of different length in both sides of the specimen surface and a specimen having a semicircular part-through crack were carried out. Through the experiments, it is shown that the proposed method is practical and useful in determining the K-value of the cracked bodies. © 1982, The Society of Materials Science, Japan. All rights reserved.
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A multilayer composite material consisting of a soft, ductile and hard, strong component possesses, at a high level of hardness, much higher impact and tensile strengths compared with a single-layer material. A greater improvement in impact strength is exhibited by a system whose soft component, other things being equal, is more ductile. A better combination of mechanical properties is attainable in a MLC produced by the metallurgical process. The increase in impact strength is apparently due to the inhibition of crack propagation in the ductile component of a MLC and to an increase in the strength of the hard component associated with the small thickness of its layers.
Recent studies of the mechanics of elastic-plastic and fully plastic crack growth suggest that such parameters as the J-integral and the crack tip opening displacement can, under certain conditions, be used to correlate the initiation and early increments of the ductile tearing mode of crack growth. In this paper, the line-spring model of Rice and Levy is extended to estimate the J-integral and crack tip opening displacement for some surface crack geometries in plates and shells. Good agreement with related solutions is obtained while using orders of magnitude less computing time.
Abstract— Crack growth rate data are presented from a range of fully reversed displacement-controlled fatigue and creep-Fatigue tests and from static load-controlled creep crack growth tests on aged 321 stainless steel (parent and simulated HAZ) at 650 ° C. In the creep fatigue tests, constant displacement tensile hold periods of 12–192 h were used. Crack growth rates comprised both cyclic and dwell period contributions. Cyclic growth contributions are described by a Paris-type law and give faster crack growth rates than those associated with pure fatigue tests. Dwell period contributions are described by the C* parameter. The total cyclic crack growth rates are given by summing the cyclic and dwell period contributions. Estimates of C* using a reference stress approach together with the appropriate stress relaxation creep data are shown to correlate well with experimentally measured C* values. Crack growth rates during static load-controlled tests correlate well with C*. Good agreement is obtained between crack growth rates during the static tests and those produced during the hold period of the creep-fatigue tests.
We propose a mathematical model for the analysis of subcritical growth of high-temperature creep cracks in metallic plates.
The model is based on the first law of thermodynamics on the energy balance and the balance of rates of changes in the energies
in a metallic plate containing a macrocrack stretched by a long-term static load under the action of a high-temperature field,
which creates favorable conditions for steady-state creep in the process zone near the crack tip. We deduce an equation for
the description of the process of propagation of high-temperature creep cracks. This equation equipped with the corresponding
initial and final conditions is regarded as a mathematical model for the evaluation of the period of subcritical growth of
hightemperature creep cracks in metallic plates. The validity of the model is experimentally checked.
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- M É Chaplya
- N M Gvozdyuk
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