In this paper it is shown that natural frequency and antiresonant
frequency shifts induced by structural damage in an axially
vibrating rod contain information on certain generalized Fourier
coefficients of the stiffness variation caused by the degradation.
This property is used to define a reconstruction procedure based
on iterative updating of the undamaged configuration. The results
of numerical simulations on rods with localized or diffuse damages
are in good agreement with the theory, provided that mean
frequency and antiresonant frequency shifts are bigger than
modelling/measurement errors. Experimental results obtained on
cracked steel rods showed that, in the inverse problem solution,
noise and modelling errors on antiresonances are usually strongly amplified
with respect to cases in which frequency data are used.
