Numerical and experimental investigations of practical issues in the use of wave propagation for damage identification

Shankar Sundararaman, Purdue University

Abstract

Wave propagation-based methods are being used increasingly for damage assessment in structural components in a laboratory setting. However, there are a number of practical issues that must be addressed to transition wave propagation-based methods from the laboratory into field applications. A suite of feature extraction techniques have been developed to investigate if the effects of material damage in structural components can be detected and located using an active sensing approach. In this study, damage is defined as a local change in impedance, which can be identified by comparing the response signatures from baseline and damaged states. Damage in the form of mass, score, notch, fiber breakage and dents are successfully detected and located using the time-frequency and spatio-temporal approaches described in this work. A numerical simulation methodology known as the local interaction simulation approach (LISA) was adapted for studying guided waves and their interaction with material damage. The LISA model provided a test bed for examining different diagnostic algorithms while providing full field measurement and avoiding test-to-test variability issues prevalent in experimental analysis. Material characterization studies are carried out using a two-dimensional Fourier transform to identify the elastic properties of a welded specimen. Statistical methods in conjunction with time-frequency analyses including discrete Fourier transforms, discrete wavelet transforms, local coherences, spatial embedding and analysis of variance are used to account for experimental variability and detect damage in homogeneous and heterogeneous structural components. A collocated piezoelectric sensor array in conjunction with a spatio-temporal beamforming approach is used to locate damaged regions in flat plates, curved plates and cylinders. A comparison of the LISA results with experimental data shows definite correlations indicating that the proposed experimental methods do provide a means for accurately and reliably identifying the presence of damage in a structural component. A sequence of vibro-acoustic experiments are carried out to identify the influence of operational low frequency excitation on the response to damage mechanisms in structural components. Additionally, the influences of sources of variability from test to test and across specimens were also investigated.

Degree

Ph.D.

Advisors

Adams, Purdue University.

Subject Area

Mechanical engineering

COinS