Impact Damage Characterization of Composites Download Poster The objective of this study is to characterize and develop a model-based understanding and real time monitoring of impact damage in composite laminates subject to low velocity impact We first characterize the laminate properties using lamb waves. Impact tests were carried out in an instrumented drop weight test frame. The tests are monitored by an array of ultrasonic sensors placed on the specimen surface. The sensors pick up signals generated by the impact as well as by the damage initiated within the specimen. We are exploring the nature of these signals and the failure modes of the composites with the ultimate intent of understanding their sequential interrelationship. Wave based analysis of the acoustic signals, and post impact damage evaluation both by ultrasonic and destructive means are also performed. A series of tests have been performed on cross-ply laminates of AS4/3502 and IM7/8551-7 materials of different thickness and real-time impact and acoustic emission data have been collected. Typical load-energy curves, AE signals, C-Scan images and microstructure of damage in the laminates are shown.

Instron/Dynatup Impact Tester and Madhu C-Scan and B-Scans of the Damaged Areas Acoustic Emission Signal

Load and Energy versus Time Curves

Impact Damage in a Cross-Ply Graphite/Epoxy Composite

Inspection of Damaged Composites by Laser-Based Ultrasound (LBU) Laser Based Ultrasound (LBU) is a remote nondestructive inspection technique that combines the capabilities of ultrasonics for the detection, location and sizing of flaws in a material, with the capabilities of optics. The technique in based on the use of a pulsed laser for the generation of ultrasonic waves that propagate inside the material and on the detection of these waves with a second laser coupled to an optical interferometer. In collaboration with Dr. Andy McKie at Rockwell Science Center, we are developing techniques to detect impact damage in composite plates using LBU. The research involves modeling laser generation of ultrasound in composites, the propagation of laser- generated ultrasound in the composite plates, their interaction with hidden flaws, and the interaction of the resulting wave with the confocal Fabry-Perót interferometer. The waveforms calculated using our model will be compared with experiments for model verification.

Schematic of the Laser-Based Ultrasound Experimental Set-up Laser Generated Lamb Waves Detected by Confocal Fabry-Perot Interferometer

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