UT image analysis

• From the UT images, it can be seen that the damage develops along the interfaces between layers having different orientations 

• Delamination extension increases with increasing distance (depth) from impact surface, resulting in the hat-shaped configuration of delamination damage

• The UT analysis also reveals an absence of delamination in a small zone directly below the impactor-material surface contact point

• The last UT image represents the in-plane projection of the damage developed at different depths in the whole laminate thickness

• By comparing the UT images for quadriaxial and for biaxial NCF specimens impacted under the same testing conditions, it can be seen that the internal damage is always larger for quadriaxial laminates