Scattering of guided waves at delaminations in composite plates

Abstract

Carbon fiber laminate composites are increasingly employed for aerospace structures as they offer advantages, such as a good strength to weight ratio. However, impact during the operation and servicing of the aircraft can lead to barely visible and difficult to detect damage. Depending on the severity of the impact, fiber and matrix breakage or delaminations can occur, reducing the load carrying capacity of the structure. Efficient nondestructive testing and structural health monitoring of composite panels can be achieved using guided ultrasonic waves propagating along the structure. The scattering of the A0 Lamb wave mode at delaminations was investigated using a full three-dimensional (3D) finite element (FE) analysis. The influence of the delamination geometry (size and depth) was systematically evaluated. In addition to the depth dependency, a significant influence of the delamination width due to sideways reflection of the guided waves within the delamination area was found. Mixed-mode defects were simulated using a combined model of delamination with localized material degradation. The guided wave scattering at cross-ply composite plates with impact damage was measured experimentally using a non-contact laser interferometer. Good agreement between experiments and FE predictions using the mixed-mode model for an approximation of the impact damage was found.

Propagation and scattering of guided waves in composite plates with defects

“…Similar wave behaviour was also observed by Sohn et al [33], where the measurement was performed on a quasiisotropic composite plate. In the FE results in a different publication [34], a similar reduction in the amplitude past the delamination area was observed, which is in agreement with this experimental measurement. Comparing both specimens, which were treated with the same 7.4 J impact energy, it can be seen that guided wave scattering in both plates is unique and such variations are expected owing to the complexity in the failure mechanism of impact damage.…”

“…2, the cross section area of the impact damage can be estimated to be about 10 × 25 mm. Comparing to the FE simulation results [34], good agreement between the experimental and simulated results was achieved. Similar wave propagation behaviour before and within the impact damage can be observed from both results.…”

An integrated numerical model for investigating guided waves in impact-damaged composite laminates

“…1). Thus, the selection of element length in the guide-wave model can be considered reasonable, since the shorter wave length of A0 wave spans more than ten elements [24,37]. In addition, a stiffnessproportional material damping coefficient equalling to 4 × 10 -8 was assigned to the guided-wave model.…”

“…It is also difficult to visualise wave propagation inside the laminates during experiments. Hence, several finite element (FE) models were proposed in [15,[18][19][20][21][22][23][24] to investigate the influence of the dominant impact damage mechanism, i.e. delamination on guided waves.…”

“…On the other hand, Leckey et al developed a 3D elastodynamic finite integration model that incorporated realistic impact-induced delamination geometries measured by X-ray computed tomography (CT) scanning [15], indicating that the realistic geometry of impact-induced delamination should be taken into account in order to improve the prediction quality of numerical models. In addition, the overall impact damage was represented by simply degrading material properties in the FE models proposed in [24,25].…”