Application of time-reversal guided waves to field bridge testing for baseline-free damage diagnosis

Abstract

There is ongoing research at Carnegie Mellon University to develop a nondestructive evaluation technique. The uniqueness of this baseline-free diagnosis lies in that certain types of damage can be identified without direct comparison of test signals with previously stored baseline signals. By relaxing dependency on the past baseline data, false positive indications of damage, which might take place due to varying operational and environmental conditions of in-service structures, can be minimized. This baseline-free diagnosis technique is developed based on the concept of a time reversal process (TRP). According to the TRP, an input signal at an original excitation location can be reconstructed if a response signal obtained from another point is emitted back to the original point after being reversed in a time domain. Damage diagnosis lies in the premise that the time reversibility breaks down when a certain type of defect such as nonlinear damage exists along the wave propagation path. Then, the defect can be sensed by examining a reconstructed signal after the TRP. In this paper, the feasibility of the proposed NDT technique is investigated using actual test data obtained from the Buffalo Creek Bridge in Pennsylvania.