Composite Materials Research Progress

Damage Variables in Impact Testing of Composite Laminates 251
perforation (Figure 13), the DD data show an initial decrease thus suggesting a reduction in
the percentage of impact energy that the laminate is able to absorb. For the thicker laminate
(GVP90_12.31), this initial reduction is quite significant, going from a percentage of energy
absorption of about 85% in the first impact to a quite stable value of about 70% in subsequent
tests. Visual observation of the laminate after each impact pointed out that in the first few
impacts the impactor indents the laminate and that the size of this indentation does not
significantly change in subsequent tests. Existence of an initial localized damage that does not
appear to significantly grow in subsequent tests is also what is conveyed by the DuI as well as
the DI data, which keep to a constant low level throughout the test.
DD, DI
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
DD DI
1 4 7 10 13 16 19 22 25 28 31 34 37 40
Impact Number
Figure 13a. Comparison between DD and DI data in repeated impact tests performed on CE90m_4.00
laminates. Impact energy: 24.5 J.
DD, DI
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
DD DI
1 4 7 10 13 16 19 22 25 28 31 34 37 40
Impact Number
Figure 13b. Comparison between DD and DI data in repeated impact tests performed on GVP90_12.31
laminates. Impact energy: 24.5 J.