In most cases, the delamination of the conventional composite was extensive and the damage was too severe to establish a meaningful correlation between the damage area and indentation.
Since the TTU results showed that the damage of the toughened composite specimens was more or less rectangular or circular, a linear dimension could be related to the damage area.
Figure 9 shows that the CAI's are plotted as a function of damage area for the toughened and conventional composites after impact by the two impactors, respectively.
The CAI's for the untoughened composite apparently fell onto a smooth curve, but they were much lower than those of the toughened composite at the same impact damage area.
As a result, the CAI's of the toughened composite could be described as a rather simplistic function of impact energy, In addition, to exclude possible effects of inaccuracy in impact energy delivered by different impactor, the CAI's of the toughened composite could be conveniently correlated to the damage area, with the CAI's exhibiting a monotonous decrease with the linear dimension of the damage areas.
The extent of damage as represented by the magnitude of damage areas was calculated from the TTU results.