Nondestructive Evaluation for Engineered Residual Stress Verification

Over the last six years, the Air Force Research Laboratory has pursued the development, refinement, and validation of a nondestructive evaluation (NDE) capability to determine if residual stresses were present after a cold expansion (Cx) process. Multiple NDE-based techniques have been evaluated, ultimately leading to the down-selection of two techniques, one eddy current based and one ultrasonic-based. These two techniques have been subjected to rigorous testing to evaluate their sensitivity to confounding factors through an extensive test matrix. This was followed by additional refinement of the two techniques. The initial capabilities were focused on straight, open holes in aluminum and has recently been expanded to filled and countersunk holes, as well as titanium and steel alloys. Demonstrations of the NDE techniques have been performed in the lab using test coupons and parts extracted from aircraft, as well as in US Air Force depots on aircraft to highlight the potential ease of eventual transition operational.

This presentation describes the outcome of these efforts, plus the remaining tasks that must be accomplished before full implementation can be realized.