A STUDY ON THE NONDESTRUCTIVE EVALUATION OF CARBON/CARBON BRAKE DISKS USING ULTRASONICS Kwang-Hee 1m and David K. Hsu Center for NDE Iowa State University 1915 Scholl Road, Ames, IA 500 II Hyunjo Jeong School of Mechanical Engineering Pusan National University San 30, Changjon-Dong, Kumjeong-Gu, Pusan, 609-735, Korea INTRODUCTION Owing to the advantage of very large strength-to-weight and stiffitess-to-weight ratios, composite materials are attractive for a wide range of applications. Increasingly, more and more high perfonnance engineering structures are being built with critical structural components made from composite materials. Especially, carbon/carbon (C/C) composites are one of the few materials that are suitable for structural applications at high temperature environments. One such application is an aircraft brake disk. As compared to stccl brakes, carbon/carbon brakes are lighter by about 40% and last twice as long in tenns of the number of landings per overhaul [I]. Aircraft brake manufactures are therefore making brake disks and rotors out of carbon/carbon composites [2,3]. Aircraft brakes are critical components that serve multiple functions: they are the friction member, the heat sink elements, and the structural elements. To ensure product quality and structural integrity, nondestructive evaluation (NDE) methods [4, 5] are needed for inspecting carbon/carbon brake disks and rotors. Ultrasonic testing is capable of revealing material inhomogeneity and internal defects. More importantly, the velocity of ultrasonic waves is related to the elastic stiffitess of the material in a direct relationship. In this work, several ultrasonic ND E techniques were applied in the evaluation of a developmental C/C brake disk. Through-transmission C-scans in an immersion setup based on both the amplitude and time-of-flight of the transmitted ultrasonic pulse were used for qualitative assessment of the material homogeneity in the plane of the disk. Ultrasonic velocity of longitudinal waves propagating in the thickness direction was measured at selected locations using elastomer-faced dry-coupling transducers. To correlate ultrasonic velocity with density variation and microstructures, a series of specimens were cut out along a radial direction for density measurement and microscopy. Ultrasonic pulse echo C-scans were used for detecting material anomalies near the surface of the disk. Finally, ultrasonic velocity and C-scan in the in-plane directions were measured to obtain the influence of fabric, chopped fiber and void for the six cut-out pieces ofa C/C disk. Review of Progress in Quantitative Nondestructive Evaluation. Vol. 18 Edited by Thompson and Chimenti. Kluwer AcademiclPlenum Publishers, 1999 2235 brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Digital Repository @ Iowa State University