Characterizing and Inspecting for Progressive Epoxy Debonding in Bonded Insulated Rail Joints

Document Type

Journal Article

Publication Date


Subject Area

infrastructure - track, mode - rail


Tracks, Railroad tracks, Rail joints, Insulated joints, Inspection, Epoxy coatings, Debonding


Progressive epoxy debonding is a common factor in many failures of bonded, insulated joints (IJs) in heavy axle load railroad service. This paper describes a study in which IJs with different amounts of debonding were visually inspected and measured and then disassembled. The shape and area of the debonded region for each IJ was quantified and variability between joints recorded. Because of some degree of ambiguity in the visual appearance of the interior surfaces, two different criteria for identifying the boundaries of the debonded region are described and applied. Debonding usually extends farther along the upper and lower portions of the rail–joint bar interface, resulting in a V- or U-shaped debonded region. Additionally, debonding tends to be more extensive on one end of the joint than the other, although it appears that debonding is generally about equal on the field and gage sides. The total debonded area was compared with several linear measurements of damage to the externally visible top edge of the epoxy–insulator layer—the part that is available for inspection in an in-service IJ. There is a strong correlation between the total debonded area in the joint and the total extent of damaged (missing or loose) top insulator edge. The debonded area can be estimated visually, with 80% confidence, to within 12,000 to 28,000 mm², depending on which criteria are used to define the debonded region.