PASSIVE HEALTH MONITORING COUPLED WITH FULL-FIELD ACTIVE INSPECTION OF MULTI-LAYERED COMPOSITE ARMOR STRUCTURES

This paper presents the results of implementing vibration based damage detection techniques for in situ monitoring and offline nondestructive evaluation of composite armor materials. It is shown that exogenous impact forces can be passively detected, located, and quantified for specimens that were fabricated using woven S-2 glass, elastomer, and carbon fiber sandwich simulated multi-layered armor. Damaging impact energies are applied to test specimens and the passively measured frequency response of the armor is used to update the dynamic model of the specimen and subsequently estimate the level of damage incurred. The forced response of the material at the damaged region is investigated. It is shown that the material damping and stiffness in the damaged region exhibit nonlinearities. A laser Doppler vibrometer is also utilized to show that nonlinear frequency modulation techniques are useful for damage inspection.