Technology Digests / Residual Stress Investigation of Ultrasonic Impact Treated and Untreated Thermite Welds

TD22-004

May 1, 2022
Authors
  • Gary Fry
  • Ananyo Banerjee
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Key Findings

  • A residual stress investigation showed the presence of compressive stresses underneath the surface at web/base fillet locations for new and in-service (used) welds with ultrasonic impact treatment (UIT). Compressive stresses delay fatigue defect growth while tensile stresses have the opposite effect.
  • Both residual stress estimation methods used in this study indicated tensile stresses in the web/base fillet locations of an untreated thermite weld.
  • Transverse stresses measured by the hole drilling method were compressive for all three welds underneath the surface for both head/web and web/base fillet locations with the in-service and new UIT welds having more compressive values than the untreated welds.

Residual Stress Investigation of Ultrasonic Impact Treated and Untreated Thermite Welds

In late 2020 and early 2021, MxV Rail (formerly TTCI) collaborated with Hill Engineering to investigate residual strains and stresses in thermite welds using two different techniques—the hole drilling (HD) method and the contour method. As a part of the investigation on how ultrasonic impact treatment (UIT) assists in extending the life of thermite welds, MxV Rail did residual stress estimation in three different thermite welds: 1) a UIT treated new weld, 2) a UIT treated weld removed from the track after 165 million gross tons (MGT), and 3) an untreated new thermite weld. BACKGROUND Historically, standard thermite welds in revenue service have been a weak spot in track and typically have a shorter life span than the rail surrounding the weld, particularly on the high rail of a curve. However, thermite welding remains the most common method of field welding due to the portability of its equipment and the…