Critical Distance Default Values for Structural Steels and a Simple Formulation to Estimate the Apparent Fracture Toughness in U-Notched Conditions

Sergio Cicero,Juan Fuentes,Virginia Madrazo,Pablo González,Isabela Procopio

doi:10.3390/met8110871

Sergio Cicero, Juan Fuentes + Show 3 more

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https://doi.org/10.3390/met8110871

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Journal: Metals	Publication Date: Oct 24, 2018
Citations: 7	License type: CC BY 4.0

Affiliation: Universidad de Cantabria, Centro Tecnológico del Mar

Abstract

The structural integrity assessment of components containing notch-type defects has been the subject of extensive research in the last few decades. The assumption that notches behave as cracks is generally too conservative, making it necessary to develop assessment methodologies that consider the specific nature of notches, providing accurate safe predictions of failure loads or defect sizes. Among the different theories or models that have been developed to address this issue the Theory of Critical Distances (TCD) is one of the most widely applied and extended. This theory is actually a group of methodologies that have in common the use of the material toughness and a length parameter that depends on the material (the critical distance; L). This length parameter requires calibration in those situations where there is a certain non-linear behavior on the micro or the macro scale. This calibration process constitutes the main practical barrier for an extensive use of the TCD in structural steels. The main purpose of this paper is to provide, through a set of proposed default values, a simple methodology to accurately estimate both the critical distance of structural steels and the corresponding apparent fracture toughness predictions derived from the TCD.

Highlights

There are numerous situations where the defects responsible for structural failure are not cracks
If defects are blunt, it may be overly conservative to assume that they behave like sharp cracks and, to apply sharp crack analysis methodologies generally based on Fracture Mechanics
The aim of this paper has been to provide a simple accurate methodology to estimate both the critical distance of structural steels and the corresponding apparent fracture toughness predictions derived from the Theory of Critical Distances, and, from the Line Method

Summary

Introduction

There are numerous situations where the defects responsible for structural failure are not cracks (i.e., sharp defects whose tip radius tends to zero). If defects are blunt (e.g., notches), it may be overly conservative to assume that they behave like sharp cracks and, to apply sharp crack analysis methodologies generally based on Fracture Mechanics. For brittle failure situations in cracked components, in which linear-elastic behavior is dominant, fracture mechanics establishes that fracture occurs when the applied stress intensity factor (K) is equal to the material fracture toughness (Kmat ): K = Kmat (1). Notches subject components to less severe stress fields at the defect tip, resulting in an apparent higher material fracture resistance (often referred to as apparent fracture toughness). If this is not taken into account in the analysis, Equation (1) often proves to be overly conservative.

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