Health Monitoring
Resistance Based Composite Health Monitoring
Monitoring Composite structures present a unique structural health-monitoring problem. Damage can occur during manufacture and usage that is not easily detectable, and it can significantly weaken the structure. The U.S. Army's fleet of helicopters operates in extreme conditions. The rigors of this environment present a unique challenge to monitor the health of the helicopter's composite structural components. Midé has developed a novel method that uses the measured electrical resistances of a composite structure only along the edges of the structure to monitor its health and provide a means for damage detection. The major advantages of the proposed innovation are that it is practical, minimizes wiring/cabling, and does not require any additional sensors to be embedded within the composite. Not embedding sensors in the composite maintains the strength and integrity of the structure and reduces cost.
Below is an example node pattern is shown where the only nodes that require access are the outer, red numbered nodes.
Midé has developed a patented algorithm (US Patent 6,802,216) that determined all the leg resistances using only the resistances measured between the boundary nodes. The patent describes the algorithm in detail. The ability to measure all resistances of the grid without having access to the internal nodes significantly reduces the number of connections and wires needed to monitor the health of the composite.
Midé has verified this technology is feasible on composite samples, as well as on full-scale composite parts of a Comanche helicopter. The algorithm was used to monitor the health of a small scale test article. In these tests, a twelve-boundary node grid was assumed. This grid had twenty-two legs or resistances. The algorithm predicted the resistances in for the undamaged or healthy structure. The conclusion was that the method was able to report damage when the surface area of the damaged area exceeded 0.1% of the total surface area of the composite. A newer version of the electronics already built and used on the full-scale test article reduced this limit substantially.
A.Small test article showing how the wires are routed around the boundary of the composite. Note that during manufacturing copper tabs were embedded between the plies. B. Photograph of a composite helicopter Comanche door with its inherent grid overlaid on the photo. Test results of this door have demonstrated the technology is capable of determining the location and extent of damage.
For more information:
Please contact Attila (Products), or call: 781-306-0609 x225