Composite Materials Research Progress

Damage Evaluation and Residual Strength Prediction of CFRP Laminates … 187
It has to be noticed that building up the diagram in figure 13 the Elastic modulus values
have been associated to the mean values of the strain range that have been used to discretize
the stress-strain curve.
Using the calculated values of the Elastic modulus it was also estimated the values of the
damage by means of its conventional definition: D = 1- E(s)/E0, where E0 is the Young
modulus of the undamaged material.
In Table 4 are summarized the strain intervals, low-strain and up-strain, that have been
used to discretize the stress-strain curves of all specimens for each type of laminates, the
corresponding strain mean value to which the estimated Elastic modulus and Damage values
are associated.
Stress (MPa)
2500
2000
1500
1000
500
0
0
0 0.0025 0.005 0.0075 0.01 0.0125 0.015 0.0175 0.02
Strain
Stress - Strain Model
Damage
Figure 14. Discretized stress-strain curve and Damage according to the key-drops analysis.
The information summarized in Table 4 can be usefully implemented in FEA software to
model the considered composite laminate progressive failure behaviour.
In figure 15 are graphically represented the Elastic modulus and the Damage values
plotted considering as strain values the mean values reported in Table 4
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Damage