Non-linear vibroacoustical free oscillation method for crack detection andevaluation

The free-oscillation method with decrement as a feature for vibroacoustical diagnostics of cracks is considered. For the first time theoretical bases of decrement usage for free-oscillation diagnosis method of cracks are deve loped. Three new generalizations of decrement of oscillations for non-linea r systems are proposed. New expression of decrement of considered non-linea r system is received. The above-mentioned system describes in detail the fa tigue crack. Systematised investigations of decrement dependencies from the relative crack size and model natural frequency are carried out for cases of frequency-dependent and frequency-independent external and internal fric tion forces. For the first time the possibility of decrement increasing and decreasing with increment of the relative crack size is shown theoreticall y. The method adaptation is proposed. Estimate of testing detail natural fr equency is proposed to be used as a measured interfering parameter for meth od adaptation. Experimental results with titanium compressor blade of aircr aft gas turbine engine match the theoretical prognosis. The received result s are new, general and can be used for diagnostics of objects described by non-linear one-mass model. (C) 2000 Academic Press.