Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-9-2009 Non-Destructive Evaluation of Aerospace Composites Jeremy D. Johnson Follow this and additional works at: https://scholar.afit.edu/etd Part of the Materials Science and Engineering Commons, and the Structures and Materials Commons Recommended Citation Johnson, Jeremy D., "Non-Destructive Evaluation of Aerospace Composites" (2009). Theses and Dissertations. 2450. https://scholar.afit.edu/etd/2450 This Thesis is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. NON-DESTRUCTIVE EVALUATION OF AEROSPACE COMPOSITES THESIS Jeremy D. Johnson, Captain, USAF AFIT/GMS/ENP/09-M02 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government. AFIT/GMS/ENP/09-M02 NON-DESTRUCTIVE EVALUATION OF AEROSPACE COMPOSITES THESIS Presented to the Faculty Department of Engineering Physics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Master of Science in Materials Science Jeremy D. Johnson, BS Captain, USAF March 2009 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED AFIT/GMS/ENP/09-M02 NON-DESTRUCTIVE EVALUATION OF AEROSPACE COMPOSITES Jeremy D. Johnson, BS Captain, USAF Approved: _______________/signed/_______________ ________________ Matthew J. Bohn (Chairman) Date _______________/signed/_______________ ________________ Nancy C. Giles (Member) Date _______________/signed/_______________ ________________ James L. Blackshire (Member) Date _______________/signed/_______________ ________________ Douglas T. Petkie (Member) Date AFIT/GMS/ENP/09-M02 Abstract Five methods of non-destructive material evaluation (NDE) were used to inspect various forms of damage commonly found in aerospace fiberglass composites: voids, edge and sub-surface delaminations, surface burning, and cracking. The images produced by X-ray, X-ray Computed Tomography, terahertz (THz) imaging, ultrasound, and flash IR thermography were analyzed for the detection of defects. Test results and analysis of each NDE method’s capabilities provide a comparison study of conventional techniques versus the emerging technology of THz imaging for the non-destructive evaluation of aerospace composite materials. A comparison guide to the five methods’ damage detection effectiveness for fiberglass composites is provided by defect type. iv Acknowledgements I would like to express my sincere thanks and appreciation to my research advisor, Lt Col Matthew Bohn, for his guidance, motivation, and exceptional laboratory prowess. His patient dedication to my learning, understanding, and achievement made an enormous impact on the outcome of this research. I would also like to thank Dr. Jim Blackshire of AFRL/RXLP for his expert guidance and for providing the materials and equipment to complete the job. I am also indebted to the NDE lab technicians Dan Laufersweiler and Dave Roberts of AFRL/RXSA as well as Dan Daniels of AFRL/RXLP for guiding my test setups and procedures with expert advice. v Table of Contents Page Abstract .............................................................................................................................. iv Acknowledgements ............................................................................................................. v Table of Contents ............................................................................................................... vi List of Figures .................................................................................................................... ix List of Tables ..................................................................................................................... xi I. Introduction .................................................................................................................... 1 1.1 Background ........................................................................................................... 1 1.2 Problem Statement ................................................................................................ 4 1.3 Research Objective ............................................................................................... 5 1.4 Experimental Approach ........................................................................................ 5 1.5 Assumptions/Limitations ...................................................................................... 6 1.6 Preview ................................................................................................................. 6 II. Theory ........................................................................................................................... 7 2.1 Aerospace Composite Materials ........................................................................... 7 2.2 Electromagnetic Radiation Scattering Effects ...................................................... 9 2.3 Radiography ........................................................................................................ 11 2.3.1 X-Ray Generation ..................................................................................... 12 2.3.2 X-Ray Propagation ................................................................................... 13 2.3.3 X-Ray Detection ....................................................................................... 14 2.4 Ultrasound ........................................................................................................... 14 2.4.1 Ultrasonic Wave Generation .................................................................... 16 2.4.2 Ultrasonic Wave Propagation ................................................................... 16 2.4.3 Ultrasonic Wave Detection ....................................................................... 17 2.5 Thermographic Inspection .................................................................................. 18 2.5.1 Thermal Front Generation ........................................................................ 18 2.5.2 Thermal Front Propagation ....................................................................... 18 2.5.3 Defect Detection ....................................................................................... 20 2.6 THz Imaging ....................................................................................................... 20 2.6.1 Pulse Generation ....................................................................................... 23 2.6.2 Pulse Propagation ..................................................................................... 24 2.6.3 Pulse Detection ......................................................................................... 25 2.6.4 THz Time Domain Spectroscopy ............................................................. 27 vi Page III. Methodology .............................................................................................................. 28 3.1 Radiography Test Methods ................................................................................. 28 3.1.1 Radiographic Setup .................................................................................. 28 3.1.2 X-ray Procedure ........................................................................................ 28 3.1.3 X-ray CT Procedure ................................................................................. 29 3.2 Ultrasound Test Methods .................................................................................... 29 3.2.1 Ultrasound Setup ...................................................................................... 29 3.2.2 Ultrasound Procedure ............................................................................... 30 3.3 Thermography Test Methods .............................................................................. 30 3.3.1 Thermographic Setup ............................................................................... 30 3.3.2 Thermography Procedure ......................................................................... 31 3.4 THz Test Methods .............................................................................................. 31 3.4.1 THz Imaging Setup ................................................................................... 31 3.4.1.1 THz Beam Optics ....................................................................... 32 3.4.1.2 Lock-in Amplifier ....................................................................... 33 3.4.2 THz Imaging Procedure ........................................................................... 33 3.4.2.1 Sample Preparation ..................................................................... 33 3.4.2.2 Biasing the Balanced Photodiodes .............................................. 33 3.4.2.3 Optical Alignment ...................................................................... 34 IV. Results and Analysis .................................................................................................