Dynamic characteristics of disbonds in honeycomb structures

The use of the mechanical impedance method for nondestructive testing and analysis of honeycomb structures is described. This technique is frequently used in aircraft maintenance to test the bond or disbond of honeycomb structures. The mechanical impedance instruments, MIA 3000, Versiscan and VP 200, are used for the testing. In the analysis, a defect area of honeycomb structure was modelled as a spring, mass and damping system, so that its resonance frequency is unique to the structure. According to theory and experimental observation, the resonance frequency of a disbond area is lower than that of the perfect bond area. Therefore this resonance frequency may be used to examine the bonding of structures for disbond areas. By using different test frequencies, different amplitudes or phases of impedance can be determined. It is found that with low test frequency, disbond areas can be clearly shown by the amplitude variation. However, if the test frequency is higher than the resonance frequency of the perfect bond area, the amplitude or phase of impedance cannot effectively show a disbond. It has also been found that if the test frequency is slightly lower than the resonance frequency of the perfect bond area, the impedance phase is the best indicator of the defect area. © 1994.