Micromechanisms and a computational model of growth of low-temperature creep cracks in materials
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MICROMECHANISMS AND A COMPUTATIONAL MODEL OF GROWTH OF LOWTEMPERATURE CREEP CRACKS IN MATERIALS О. E. Andreikiv,1 V. R. Skal’s’kyi,2 Yu. Ya. Matviiv,3 and І. Ya. Dolins’ka2
UDC 539.375
We analyze and synthesize the results of investigations available from the literature on the micromechanisms of growth of creep cracks and, on the basis of this analysis, show that these cracks grow mainly by the initiation, increase, and coalescence of pores. This enables us to formulate a computational model for the evaluation of the period of subcritical growth of low-temperature creep cracks in structural materials. As a result, we obtain a kinetic equation of growth of these cracks in the form of dependence of the crack growth rate on the stress intensity factor. Together with the initial and the final conditions, this equation forms a computational model for the evaluation of the period of subcritical growth of lowtemperature creep cracks. Keywords: low-temperature creep, micromechanisms of propagation of creep cracks, computational model, subcritical crack growth, process zone.
To construct computational models of the fracture processes in solid bodies under the conditions of lowtemperature creep, it is, first of all, necessary to consider the micromechanisms of deformation and fracture of the materials of these bodies under long-term static loading. For numerous metallic materials, these micromechanisms have various common features. However, in some cases, these features can be different. Numerous investigations of the micromechanisms of deformation and fracture of materials (especially, of metallic materials) under long-term static loading are known from the literature. In what follows, we analyze and synthesize the results obtained in [1−7] for metallic materials and their alloys. Micromechanisms of Local Deformation and Fracture of Metals and Alloys Under the Conditions of Creep Under the conditions of long-term tension and shear of polycrystalline materials on the submicroscopic level, the researchers mainly observe the following distribution of dislocations: individual dislocations, dislocation tangles, and subgrain boundaries. In the case of creep, we observe both intragranular deformation and deformation on the grain boundaries (sliding) [1−7]. Intragranular creep deformation can be of different types, including, e.g., the deformations according to the mechanisms of single (thin) sliding, multiple sliding, and transverse sliding. In polycrystalline materials, due to the different orientations of grains, one may observe complex plastic deformation. Thus, some examples of deformation of aluminum in the course of creep at different temperatures are presented in [1] (Fig. 1). 1 2 3
Franko Lviv National University, Lviv, Ukraine; e-mail: [email protected] (corresponding author). Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Lutsk National Technical University, Lutsk, Ukraine.
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 49, No. 1, pp. 28–37, January–Februa
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