Assessment of the 3D ply-by-ply fiber structure in impacted CFRP by means of planar Ultrasound Computed Tomography (pU-CT)

Abstract

The manufacturing process of fiber reinforced polymer laminates could induce local distortions from the nominal fiber architecture. Further, low-velocity impact events may induce additional changes in the fiber architecture, due to local plasticity and delamination formation. These deviations could have a significant effect on the structural performance of composites. This study presents a planar ultrasound computed tomography (pU-CT) technique to reconstruct the local fiber architecture of impacted CFRP laminates. The proposed pU-CT technique employs a pulse-echo scanning modality, and the 3D reconstruction process consists of three subsequent analysis steps: Step 1: Extraction of front- and rear surfaces, delamination interfaces, and interply interfaces. Step 2: Estimation of the out-of-plane ply orientation. Step 3: Extraction of the in-plane fiber direction. The developed pU-CT technique is experimentally demonstrated on an impacted 24-layer CFRP laminate with a stacking sequence [45/0/−45/90]3S. The obtained 3D reconstruction result reveals that the impact event introduced a complex delamination cluster, as well as local plasticity resulting in distorted out-of-plane ply orientation. The in-plane fiber angles remain unaffected and closely match the nominal quasi-isotropic stacking sequence. It is anticipated that the pU-CT method could complement X-ray computed tomography measurements for the inspection of (damaged) CFRP laminates with sizeable dimensions.