LASER VIBROMETRY AND STRAIN GAGE MEASUREMENTS OF THERMOSONIC ACTIVATION

摘要

Work in Thermosonics (Vibration Thermography) has demonstrated the ability to make cracks in metals, delamination in composites and disbonds visible to Infrared Thermography. A basic question of what energy levels are needed to "activate" the discontinuities remains as an impediment to a universal understanding and use of the technique. A specific strain gage configuration to measure only differential movement between the sides of a crack was compared with laser vibrometry measurements of the surface movement and crack infrared emittance levels of simple samples. Measurements were made to measure the effect of varying some of the operating parameters and the relationship of the measurements to crack visibility.