Crack identification in beam from dynamic responses

A time domain method is proposed in which the parameters of a crack in a structural member are identified from strain or displacement measurements. The crack is modeled as a discrete open crack represented mathematically by the Dirac delta function. The dynamic responses are calculated basing on modal superposition. In the inverse analysis, optimization technique coupled with regularization on the solution is used to identify the crack(s). The formulation for identification is further extended to the case of multiple cracks. A general orthogonal polynomial function is used to generate the derivatives of the strain or displacement time responses to eliminate the error due to measurement noise. Computation simulations with sinusoidal and impulsive excitations on a beam with a single crack or multiple cracks show that the method is effective for identifying the crack parameters with accuracy. The proposed identification algorithm was also verified experimentally from impact hammer tests on a beam with a single crack.