Session: CS-21-01 Constraint Effects on C&S

Paper Number: 123672

123672 - Consideration of Constraint Effect in Fracture Mechanics Assessment for a Vessel Low Alloy Steel 

Defect assessment methodology for nuclear components rarely account for positive effects such as loss of constraint even though it is well known and not discussed. Local approach models for brittle failure do consider implicitly this effect and take benefits of several decades of practice in R&D programs.

Numerous fracture tests have been performed by EDF and Framatome on various specimen’s geometry extracted from a 18 MND 5 ferritic steel plate, in the brittle-to-ductile transition regime. C(T) with various thicknesses, SEN(T), SEN(B), and non-standard specimens have been tested. This database has been recently updated with SEN(T) tests performed in the lower shelf of the transition domain.

This work highlights a robust identification of a Beremin model’s parameters which allows to predict constraint effect with minor consequences of the choices of the model formulation (classic model, consideration of stress threshold…) and on m parameter on the final interpretation. Results demonstrate constraint effects, resulting in shifting KIC values of most specimens to higher values than those obtained on C(T) specimens and the capability of the local approach models to predict the experimental results.

A methodology is proposed to consider constraint effect in Engineering Fracture Mechanics Assessment without considering any probability of failure or statistical approach :

- Local approach is used to determine the K-σw relationship of various defects geometries,

- These relationships allow transferring K values calculated by global approach into equivalent K values on C(T)-1T specimens, considering C(T)-1T specimens as the reference ones on which is determined the toughness on the brittle-to-ductile transition domain.

Presenting Author: Jules Louerat FRAMATOME

Presenting Author Biography: Jules Louerat is a mechanical engineer, fracture mechanics expert, working in Framatome La Défense in the Steam Generators design department for 10 years.

Authors:

Jules Louerat FRAMATOME
Olivier Ancelet Framatome
Stephane Marie Framatome
Stephane Chapuliot EDF
Anna Dahl EDF