Application of coupled brittle–ductile model to study correlation between Charpy energy and fracture toughness values

• Published in: Engineering fracture mechanics 1999-05, Vol.63 (1), p.57-80
• Main Authors: Folch, L.C.A., Burdekin, F.M.
• Format: Article
• Language: English
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/S0013-7944(99)00009-0

A coupled brittle–ductile fracture local approach model has been developed to predict either Charpy energy or fracture toughness and to investigate conditions for correlations between them. A modification to the Beremin model has been introduced to assess failure in individual elements and make it compatible with the Lemaitre model for implementation as a user subroutine for the program ABAQUS. A probabilistic based fracture criterion was introduced to monitor the damage within individual elements by either cleavage or ductile tearing. The fracture toughness and Charpy energy for a nuclear industry steel BPL A508 were determined for the transition temperature range using finite element analyses with three-dimensional solid elements for both the standard 25 mm SE(B) three-point bend specimen and the Charpy 45° V-notch specimen. Prescribed failure probabilities of 0.05, 0.5 and 0.95 were imposed as critical values to predict the scatter of fracture toughness experimental data. The evaluation of constraint, equivalent plastic strain and maximum principal stress amongst other parameters gave the basis for comparison of the response of the two geometries. Critical values of fracture stress in the modified Beremin model for cleavage fracture and of the Lemaitre damage parameter for ductile fracture were calibrated from experimental fracture toughness data. These same critical values were then used in the analysis of the Charpy specimens, including allowance for strain rate effects, and good agreement found between predicted and experimental energy absorption values. The only conditions where the maximum constraint and equivalent plastic strain in the two specimen geometries were found to match were at the temperature for 28 J energy absorption in the Charpy impact energy and that for fracture toughness, KIC, of 100 MPa-m1/2 for the BPL A508 steel. This may be an important factor in the correlation between Charpy and fracture toughness tests proposed by Wallin.