L.M.Gelman, S.V.Gorpinich
Vibroacoustical free oscillation method for nondestructive testing of cracks

Acoustic bulletin, Vol. 2 4, (1999) p.13-22
Theoretical and experimental consideration of the free oscillation method for vibroacoustical diagnostics of the fatigue cracks is presented. New generalizations of a decrement of oscillations for nonlinear systems are proposed. For the first time the expression for decrement of the free oscillation of a nonlinear one-mass system with crack has been received. Systematized investigations of dependencies of the decrement from the relative crack size are carried out. For the first time it was shown that with the increase of a crack in controlled object there are possible both the increase and the decrease of decrement. Also, it was shown that the dependence of a decrement from the crack size is controlled by dependence of the attenuation assymetry factor from the relative crack size. The decrement was investigated for cases of the frequency-dependent and frequency-independent external and internal frictional forces. The experimental results with titanium compressor blades of aircraft gas turbine engine match with the theoretical ones. The obtained results are of general nature, and can be used for diagnostics of objects described by a nonlinear one-mass model.
vibroacoustic method, crack nondestructive testing, the attenuation decrement