The influence of fatigue cracks on the modal vibration response of composite sandwich beams

This paper summarizes finite element and experimental studies of the effect of fatigue cracks on the vibration characteristics of composite sandwich beams. The natural frequencies and corresponding vibration modes of a free-free sandwich beam having three distinct fatigue crack forms were predicted using a two-dimensional finite element analysis (FEA). In this analysis, the free and forced vibration responses of the sandwich beams were studied, and the shifts in the peaks of the frequency response due to crack forms were examined. Four point bending and vibration tests were conducted on sandwich beams with carbon/epoxy laminated composite faces and foam core to verify the finite element results and to obtain data for modeling. Agreement between predictions of the model and experimental observations is good.