Fracture Toughness Characterization for Heat-Affected Zones of Welded Highway Bridge Steels

Abstract

The work described herein examines the fracture toughness and impact energy absorption in the heat-affected zone (HAZ) of modern bridge steels. Performed under the National Cooperative Highway Research Program (NCHRP) Project 10-95A, the aim of the research was to recommend toughness requirements for the HAZ of welded bridge steels. Testing and analysis of modern grades of bridge steels was conducted as part of this study. This included Vickers hardness testing, Charpy V-Notch impact testing, and rigorous elastic-plastic fracture toughness testing from the base metal, weld metal, and throughout the HAZ. To date, the experimental program carried out is the largest single fracture toughness database assembled. Analysis of fracture toughness results includes the application of the master curve methodology to statistically characterize the fracture behavior in the lower transition region. Additionally, failure assessment diagrams were utilized to present fracture toughness results in terms of critical flaw sizes. Correlations between Charpy V-Notch impact energy and fracture toughness, which form the basis for current material specifications, were also examined. To identify the critical welding parameters, comparisons were made between fracture performance and welding parameters of both new and historic data.