Advanced Instrumentation and Measurements for Early Nondestructive Evaluation of Damage and Defects in Aerostructures and Aging Aircraft
Final rept. 1 Apr 93-30 Jun 98
NORTHWESTERN UNIV EVANSTON IL
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This report details the KU part of an AFOSR sponsored VanderbiltNorthwestern University Research Initiative URI project. The project was divided into several tasks. New laser based ultrasonic techniques were developed including a Sagnac interferometer. This interferometer is a common-path device that is robust enough to be operated in the field. An adaptive heterodyne interferometer using photorefractive recording media was also developed for detecting ultrasound on rough surfaces. In another task, self-focusing ultrasonic arrays were devised capable of automatically focusing on surface breaking and interior flaws. Measurement models for characterizing this device were validated through direct interferometric measurements. Also, a fall-field dynamic holographic interferometer was developed for disbond detection with high spatial resolution. This device allows for real-time automatic frequency scanning of an adhesively-bonded composite structure in order to make visible any underlying disbonded regions. In addition, this report describes the application and results of nondestructive evaluation E and other methods to the detection and characterization of the integrity of composite materials and the evaluation of the effectiveness and reliability of composite repairs for aging aircraft. Real-time NDE methods were developed and applied to composite laminates under monotonic loading to failure. Results from ultrasonic, acoustic emission AE and matrix cracking measurements were correlated with the macroscopic response of the material and its degradation. The effectiveness of composite patches in controlling damage propagation in a cracked aluminum substrate under fatigue conditions was also investigated by means of ultrasonic and acousto-ultrasonic methods.
- Test Facilities, Equipment and Methods