Composite Materials Research Progress

Damage Evaluation and Residual Strength Prediction of CFRP Laminates … 171
the test because the energy stored in the material tends to its limit and the AE cumulate
energy (Ea) increases due to the progression of material damage.
When a significant internal material failure happens there is an instantaneous release of
the stored energy that produces an AE event with a high energy content. This fact is
highlighted by the sudden drops of the function f(x) that can be described by functions of type
II: PII(x).
In figure 3 are reported some examples of combinations of parts of the function f(x), and
in particular in figure 3a it possible to note three trends of type I (PI,1, PI,3 and PI,2)
respectively connected by two functions of type II (PII,1 and PII,2).
f
f
f
PI,1
Displacement
PI,4
Displacement
Displacement
S1+
PI,5
S1-
PI,2
PIII,
PII,1
S2+
S2-
1 PIV,1
PIV,2
PI,3
PII,2
PII,3 PII,4
Figure 3. Examples of compositions of the basic function describing common parts of the function f.
PII,5
A
B
C