Cepstrum-Based Deconvolution of Ultrasonic Pulse-Echo Signals from Laminated Composite Materials

A transform-domain ultrasonic pulse-echo signal processing technique was developed to determine the locations of delaminations in thin composite laminates. It was shown in this study that complex and magnitude cepstra can be used as effective tools for detecting reflected echoes and reconstructing high-resolution images. The scheme was experimentally verified by detecting the echo arrival times with respect to the front face, using a broadband focused immersion transducer. Introduction Composite materials generally offer significant practical and potential advantages over conventional materials in many critical structural components. The ever expanding structural applications of composites expose themselves to various environmental and loading conditions, causing higher probability of induced damage in the material. Thin laminated composites are usually susceptible to transverse loads. The mismatch in bending stiffnesses between the layers introduce large inter-laminar shear stresses even for quasi-isotropic laminates. As a result, inter-laminar delaminations may occur, which are detrimental to the performance of the structure. Dynamic loads such as low velocity transverse impact loading may also introduce similar damage which may act as nuclei of future structural failure (ASTM-STP568, 1974). Consequently, it is necessary to detect and characterize such defects nondestructively in an early stage of damage growth. 1Esther and Harold E. Edgerton Assistant Professor, Department of Civil and Environmental Engineering, Room 1-272, Massachusetts Institute of Technology, Cambridge, MA 02139, [email protected] 2Graduate Student, [email protected]