An Estimation of Error-Free Frequency Response Function from Impact Hammer Testing

The spectrum of impulse response signal from the impact hammer testing is widely used to obtain the frequency response function (FRF). However the FRFs obtained from the impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed by the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer testing are transient and damped, they are undoubtedly non-periodic. It is inevitable that the signals acquired for limited recording time should cause several errors. This paper makes clear the relation between the errors in the FRF and the length of the recording time. A new method is suggested to reduce the errors in the FRF in this paper. Several numerical examples involving 1-dof models are considered to elucidate the properties of the errors and the validity of the proposed method.