Abstract: A method of stress relieving metal parts that includes the steps of applying mechanical cyclic vibration energy to a part over a test frequency range while monitoring the damping effects of energy flowing into the part as a function of frequency. A plurality of orders of harmonic vibration absorption peaks are identified, each consisting of a plurality of vibration absorption resonant peaks, employing a vibration transducer having a response that is dampened to distinguish the harmonic peaks from the resonant peaks. A sub-harmonic stress relief frequency is identified as a function of such frequency response and the composition of the part in question, and mechanical cyclic vibration energy is applied to the part for an extended time period at the sub-harmonic frequency so identified.