A structural health monitoring system for composite pressure vessels
Vehicles that run on compressed natural gas and hydrogen are currently being developed to reduce greenhouse gas emissions and smog. To meet the need for a safe, reliable fuel storage system, a low-cost, acoustic-ultrasonic system has been developed to detect damage in high-pressure storage cylinders made of Carbon Fiber Reinforced Polymers (CFRP). This structural health monitoring system could lead to lighter, lower cost cylinders, and improved safety in automotive applications that utilize hydrogen and natural gas.Several Non-Deconstructive Evaluation (NDE) techniques were investigated in the course of this work, and low-cost piezo-film sensors were selected to monitor the cylinder. These sensors were integrated into the carbon fiber structure, resulting in a sensor network that can be used for real-time structural health monitoring of composite cylinders. The system was operated by exciting the piezo-film sensors with an impulse and then the corresponding structural response (or signature) was measured and analyzed. This was compared to a previously measured response and evaluated for changes which can indicate failures in the tank. The analysis reduces the changes in the structural response to a single damage coefficient, which can then be used for malfunction indication and decision making in an automotive on-board microprocessor control system.The technology can be deployed at a reasonable cost, and has been designed to accurately detect damage with little or no maintenance required. Thirty cylinders were used in a test matrix to examine all possible failure mechanisms of the tanks, including: fatigue, cuts and gouges, impact and delaminations, stress rupture, heat damage, and combinations of these damage mechanisms. The damage detection system was capable of detecting damage long before a critical condition arose for all cases. However, further development and testing into larger cylinder designs and testing is still required to develop a final commercial product.
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