Nonlinear acoustics techniques were used to measure fatigue in turbine blades in a power generation plant. The measurements were made in the field using a reference based measurement technique, and a reference sample previously measured in the laboratory. The acoustic nonlinearity parameter showed significant increase with fatigue in the blades, as indicated by service age and areas of increased stress. The technique shows promise for effectively measuring fatigue in field applications and predicting subsequent failures. Hinton, Yolanda L. and Na, Jeong K. and Yost, William T. and Kessel, Gregory L. Langley Research Center NASA/TM-2000-210303, NAS 1.15:210303, ARL-TR-2244, L-17972...