Active structural health monitoring of composite plates and sandwiches

Abstract

The aim of presented work is to design, assemble and test a functional system, that is able to reveal damage from impact loading. This is done by monitoring of change of spectral characteristics on a damaged structure that is caused by change of mechanical properties of mater ial or by change of structure’s geometry. Excitation and monitoring of structures was done using piezoelectric patches. Unidirectional composite plate was tested for eigenfrequencies using chirp signal. The eigenfreque ncies were compared to results from experiments with an impact hammer and consequently with results from finite element method. Same method of finding eigenfrequen- cies was used on a different unidirectional composite sp ecimen. Series of impacts wer e performed. Spectrum of eigenfrequencies was measured on undamaged plate and t hen after each impact. Measur ements of the plate with different level of damage were compared. Following e xperiments were performed on sandwich materials where more different failures may happen. Set of sandwich beams (cut out from one plate made of two outer composite layers and a foam core) was investigated and subjected to several impacts. Several samples were impacted in the same manner to get comparable results. The impact s were performed with growing impact energy.