Abstract

An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect of both temperature and the plastic strain value on the crack nuclei (CN) generation rate in iron and ferritic steels is presented. It is shown how the plastic strain and temperature affect CN formation rate and, as a consequence, govern the shape of the temperature dependence of fracture toughness KJc and its scatter limits. Within the framework of the microscopic model proposed, dependences of the CN bulk density on the plastic deformation value and temperature are predicted. Convenient approximation dependences for incorporating this effect into the LA are suggested. The experimental data of reactor pressure vessel steel and cast manganese steel demonstrate that the use of these dependences enables one to predict, with sufficient accuracy, the effect of temperature on the value of fracture toughness and its scatter limits over the DBT region. It is shown that accounting for both the temperature and strain dependence of CN bulk density gives rise to the invariance of parameters of the Weibull distribution to temperature.

Highlights

  • A number of studies have attempted to solve this problem [11,12,13,14,15,16]. These works showed the need to address two key issues, namely: (i) the need to incorporate the effect of temperature and the magnitude of local plastic strain on the crack nuclei (CN) bulk density ρ; (ii) the need to account for the value of the threshold stress σth

  • The dependences of CN density described above were obtained based on the analysis of the process of CN forming at microscale. They enabled us to ascertain the fundamental regularities of the influence of temperature and plastic strain on the value of CN bulk density ρ, as well as determine the physical nature of this effect

  • The incompatibility of microplastic deformations at grain or interphase boundaries causes the crack nuclei (CN) formation. The value of this incompatibility depends on the magnitude of plastic strain and temperature

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Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A number of studies have attempted to solve this problem [11,12,13,14,15,16] These works showed the need to address two key issues, namely: (i) the need to incorporate the effect of temperature and the magnitude of local plastic strain on the CN bulk density ρ; (ii) the need to account for the value of the threshold stress σth. As for the latter, this is a methodical problem. By the example of two structural steels, the suitability of using these dependences in predicting the value of fracture toughness within the DBT region is validated

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