Development of a Simplified Approach for Using the Local Approach to Fracture

Abstract

: Today there is a strong demand fibm different industries to use local fracture criteria in a simplified way. This paper presents the main results of a two years joint research project where CEA, EDF, School of Mines and IRSID were associated. A simplified method based on the Beremin models for cleavage and ductile fracture has been developed. This procedure can be used to evaluate the risk of fracture of industrial structures or to allow a rapid development of new materials. Finite element simulations were systematically performed for axisymmetrically notched tensile and precracked specimens using a parametric description of stress-strain laws. Results were presented in the form of graphs that can be used directly for measuring local fracture parameters from tests on axisymmetrically notched specimens and to predict fracture toughness. An additional parameter measuring the level of plastic constraint has been taken into account. This parameter can be easily evaluated on industrial structures. This allows a simple way of using local criteria to evaluate the safety of such structures.

Development and Use of Beremin Local Criterion for Cleavage Fracture in the Steel Industry

“…The evolution of ow/k is given as a function of the mean strain of the specimen, for various values of the parameter m. Input of strain at fracture of the specimen directly gives the relevant value of ow/k for the experiment performed. This procedure is presented in detail in another paper in this conference [6].…”

“…In order to simplify this repetitive numerical procedure, a master set of calculations has been performed. It covers all the range of materials commonly tested [4]. To obtain a universal description of the stress-strain laws, the Ludwig-Holomon formulation o=kcn was used.…”

“…Two collective research programs have highlighted the main steps of the procedure [3], [4], allowing to the proposal of guidelines for the practical implementation of the method. More details can be found in the draft procedure discussed by ESIS TC1 [5].…”

“…The main interest of this fracture mechanics specimen is that the crack front crosses a brittle zone of well defined dimensions. For a cracked specimen, the stress field ahead the crack is only function of the applied K. Using the HRR stress field, the Beremin group has established the following relation : This relation can be expressed in terms of probability of fracture, formula (6). The probability of survival of a composite structure is the product of the probability of survival of each of its components.…”