Detection of delamination in composite beams using frequency deviations due to concentrated mass loading

Modern composite structures are usually designed to withstand mass loading. The effects of delamination due to concentrated mass loading with respect to modal frequency variations in composite beams have been investigated in the present work numerically and experimentally. A noticeable delamination-induced modal frequency deviation has been observed when a concentrated mass loading is imposed at pre-defined sections of the delaminated composite beams compared to the intact (reference) composite beams. For delaminations of only 10% of the length of a composite beam, modal frequency deviations of about 20% were observed numerically and experimentally. Further investigations of different delamination configurations show that the modal frequency deviations are dependent on the longitudinal location as well as the interlayer positions of the defects. Higher frequency deviations are observed when delamination approaches the clamped boundary of a composite beam. The results suggest that the frequency curve deviations have a local or global characteristic depending on whether the delamination occurs at the near surface or the mid-plane of the composite beam, respectively. Consequently, the frequency curves can be employed as NDT tool for delamination identification and localisation.