Acoustic emission monitoring was used during tensile tests of low-carbon structural steels to determine the physical characteristics of the acoustic emission phenomena. Results indicate that acoustic emissions are caused by micro-plastic deformation processes (i.e., dislocation motion).

A series of axial-fatigue tests was performed on several types of structural steels, some of which had extensive service in bridges. There was no apparent relation between specimen load histories and subsequent performance in fatigue tests. Tensile tests of specimens subjected to extensive fatigue testing, at stresses below the yield strength of the material, revealed no major difference in mechanical properties or acoustic emission response due to their fatigue histories.

Further tests revealed that acoustic emission testing in the frequency range of 100-300 kHz has the physical capability of detecting cracks on large structural steel members. This may prove beneficial for the comprehensive nondestructive evaluation of steel bridges.

Report Date


Report Number

No. 497

Digital Object Identifier



Accepted for publication by the Transportation Research Board.