Session: Track 1-1B: Rail

Paper Number: 132096

132096 - Fatigue Crack Growth Rate Material Characterization of Targeted Microstructures of Welded Rail 

Rail and joint integrity are some of the most important factors affecting safety of rail transport in the US and worldwide. Extensive research has recently been completed addressing the integrity and inspection interval for modern head-hardened rails, in reference to legacy rails. However, joints between these rails have received limited attention. Addressing this gap in knowledge is the main objective of a project currently being undertaken by Tuskegee University, Edison Welding Institute (EWI) and Thornton Tomasetti (TT) and sponsored by the Federal Railroad Administration (FRA).

Two processes are primarily used in joining rail together, flash-butt welding and thermite welding. While these processes are well understood, their effects on the fatigue and wear behavior of the rail steels within the joint as well as overall rail integrity, requires detailed analysis. Each process creates unique microstructures that deviate from that of the base material for rail, causing the need for characterization of the specific microstructures created from each process. These unique microstructures can have different properties, specifically when it comes to fracture toughness, fatigue crack growth rate (FCGR), and wear; hence flaw detection, inspection intervals, and replacement schedules must be handled differently for rail joints. A more defined knowledge of these mechanical properties including fatigue damage tolerance will allow for improved modelling and inspection planning at the welded joints.

The current project has prepared samples of welded rails, joined by flash-butt welding and thermite welding. Metallographic analysis and a suite of mechanical tests were conducted on the weld metal, the heat affected zone (HAZ) and the base rail material for comparison. Mechanical testing included uniaxial tension, fracture toughness and fatigue crack growth rate (FCGR) tests. Data from the FCGR tests have been used to determine the parameters for crack growth rate equations, which have been applied in a fatigue crack growth life evaluation methodology initially developed at The National Transportation Systems Center (Volpe).  Subsequent modifications to the methodology have been introduced by TT, as part of the rail integrity effort sponsored by the FRA, to estimate probabilistic fatigue crack growth life.  Moreover, probabilistic analyses have been carried out to estimate the slow crack growth or propagation life of welded rail joints containing a detail fracture. The results of the testing program and the probabilistic analyses allow comparisons to be made with the base rail material to assess the effects of welding on the life of the rails.

This presentation summarizes the work undertaken to date and the preliminary results of this ongoing research project.

Presenting Author: Pawel Woelke Thornton Tomasetti

Presenting Author Biography: Pawel Woelke co-leads the Applied Science Practice at Thornton Tomasetti and is responsible for tackling the most challenging engineering problems in automotive, rail, shipping and other industries. He specializes in assessment of characterization of extreme loading conditions such as explosion, fire, impact etc. and their effects on structures, materials and mechanical systems. Pawel has also contributed to and led a number of vulnerability studies for critical infrastructure in the New York metropolitan area, including bridges, tunnels, buildings, storage facilities and retaining walls, as well as elements of non-load-bearing building envelope.
Over the last several years, Pawel has been focusing on decarbonization efforts and enabling energy transition through improving safety of the energy storage systems, hydrogen, nuclear reactors and facilities, carbon dioxide transportation and storage and other hazardous materials.

Authors:

Peter Taylor Thornton Tomasetti
Pawel Woelke Thornton Tomasetti
Bill Mohr Edison Welding Institute
David Jeong Independent Consultant