Damage Detection in Thick-Walled Composites Using Surface Mounted Piezoelectric Elements
Abstract
The goal of the Phase 1 SBIR project described in this report was to develop a free vibration method for nondestructive evaluation of thick-walled composites. The governing principle of the free vibration method is that the frequency spectrum generated by a given object has the specificity of a fingerprint. Accordingly, if the boundary conditions, material properties, or geometry of the object are changed, some or all of the natural frequencies will change. Dramatic shifts have been observed in the natural vibrational frequencies of thin composite plates with the introduction of delaminations or other interply modifications; these observations provided the motivation for the present project in which the method was extended to thick plates. In our version of the free vibration method, the composite is excited into vibration by a single mechanical pulse and the vibrational behavior is monitored by removable surface- bonded piezoelectric polymer film elements. When bonded to the surface of the composite, the piezoelectric film acts like a strain gage, except that it requires no external power source and generates signals far greater than those of a traditional amplified strain gage. The great sensitivity of the piezoelectric polymer film sensors and the simplicity of the overall test configuration makes this version of the method attractive for in-plant or in-field nondestructive evaluation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 15, 1997
- Accession Number
- ADA358460