Application of Shearography Techniques for Vibration Characterization and Damage Detection in Sandwich Structures

Abstract : The paper presents a new Electronic Shearography (ES) system for Structural Health Monitoring and damage detection, where a huge step in sensitivity has been accomplished compared to earlier shearography systems. Debondings and delaminations in sandwich panels can be detected from a distance of several meters. We are able to detect changes in the surface of a few nanometers even in noisy environments. The test setup and measurement routine are fast and easy. Todays technology demonstrator covers test-areas from sq cm to about 0.5 sq m but with further development larger test areas can be achieved. The measurements can be done by static loading or by dynamic excitation. By static loading one measures deformations in the surface after loading by heat or pressure. The dynamic excitation is done by vibrating the test object and record the vibration pattern. When a damaged area is loaded statically, or excited dynamically it may react differently than undamaged areas, the damage detection is based on finding something that stands out from the rest of the measurement. It is usually easy to see the damage even for the untrained eye. The system is also ideal for difficult geometries such as corners and curved objects because of the easy excitation and measurement method. Examples from both static and vibrational measurements on composite materials are included in the paper. The tests are done with a technology demonstrator developed by Optonor AS [1].