Eventos Anais de eventos
COBEM 2019
25th International Congress of Mechanical Engineering
Correlation of Charpy Impact Energy and Fracture Toughness for Low Alloy Structural Steel Welds
Submission Author:
Claudio Ruggieri , SP , Brazil
Co-Authors:
Kleber Eduardo Bianchi, Vitor Scarabeli Barbosa, Paulo Fernandes, Claudio Ruggieri
Presenter: Vitor Scarabeli Barbosa
doi://10.26678/ABCM.COBEM2019.COB2019-0444
Abstract
Several flaw assessment methodologies, such BS7910 and API 579, among others, rely on the direct application of macroscopic measurements of fracture toughness derived from laboratory testing of conventional fracture specimens containing deep, through cracks, to characterize the essentially stress-controlled failure by a transgranular cleavage mechanism. A widely procedure to estimate fracture toughness values which enter directly into those defect assessment methodologies for repair decisions and life-extension programmes of in-service structural components is to adopt empirical correlations between fracture toughness and Charpy impact energy. However, despite the undoubted simplicity and advantages of these empirical correlations, there are significant differences between a Charpy V-notch (CVN) test and fracture toughness test conducted on a much larger precracked fracture specimens. Moreover, most of the correlation formulas were developed for specific materials and may not describe adequately changes in microstructure and mechanical properties due to differences in heat treatment, production process, different heats of the same steel and microalloying content. Another important issue not properly addressed is that the majority of these correlations were developed with limited data, so that no information was provided on the statistical scatter and associated probability function properties for the measured fracture toughness values. All these aspects underline the potential uncertainties and unreliability of CVN energy correlation with fracture toughness data. Motivated by these observations, this work addresses an experimental investigation of the cleavage fracture behavior for ASTM A572 Grade 50 steel welds fabricated by different welding processes. A primary purpose of this study is to examine a correlation approach to evaluate fracture toughness values of steel welds based on Charpy V-notch (CVN) impact energy data thereby enlarging existing relationships between fracture toughness and CVN energy. Fracture toughness testing conducted on three-point bend SE(B) specimens having a weld centerline notch provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc, for the steel welds, including the baseplate material, which are then converted to corresponding KJc-values. Conventional Charpy tests produce further experimental data which serve to characterize the ductile-to-brittle transition of the tested steel welds and the CVN energy correlation with fracture toughness data derived from conventional correlation formulas. A statistical analysis based on the Master Curve approach conducted on the experimentally measured fracture toughness data provides the reference temperature for the tested materials from which improved estimates of fracture toughness based on CVN energy can be made. The results show that either direct fracture toughness correlations with CVN energy and fracture toughness estimates based on the Master Curve methodology appear suitable to characterize fracture resistance of the tested steel welds.
Keywords
fracture toughness, Charpy energy, J integral, reference temperature, steel weld, SE(B) specimen
