The Effects of the Adhesively Bonded Repair Patch on the Dynamic Response of the Composite Beam Under a Harmonic Peeling Load

The dynamic response of an adhesively patched repaired composite beam under a harmonic peeling load was obtained theoretically and experimentally. In the theoretical part, dynamic responses of the repaired composite beams were obtained by modeling the parent beam as the Euler-Bernouli beam and the repaired patch as the Euler-Bernouli beam supported on a viscoelastic foundation, which resist both peeling and shear stresses. Both axial and transverse displacements were considered in deriving the coupled equations of motion. The effects of the adhesive loss factor, as well as its elastic modulus on the vibrational behavior of the repaired composite beams were investigated theoretically. In addition, finite element modal analyses were performed to justify the results of the proposed theoretical model. In the experimental part, unidirectional fiberglass reinforced epoxy composite specimens with various repaired patch length, thickness and material properties were manufactured. The patch section was either the fiberglass epoxy or E-glass fiber reinforced composites with various ply sequences. Patches were bonded to the composite beam using an epoxy. The system response was measured by the hammer test technique using a non-contact laser vibrometer. The resonant frequencies and damping ratio of the specimens were evaluated from the dynamic response of the composite beam and the results were compared to that of the theoretical and finite element analyses. The results showed that the dynamic response of the repaired composite depended on the adhesive elastic modulus. For the composite repaired with a high adhesive elastic modulus, the beam may act as a classical Euler-Bernouli composite beam. For the composite patched with a low elastic modulus adhesive, the first resonant frequency of the system may decrease up to 22%. In contrast, the natural frequencies may not significantly change having used adhesive with a high elastic modulus.