Conclusions
In the present work, the stiffness reduction of a quasi-isotropic CFRP
laminate obtained by automated fibre placement innovative process was
studied by means of a thermographic approach.
A total of ten specimens were tested at four different stress levels,
50-60-65-70% of UTS, and monitored by using infrared thermal camera.
The analysis of thermal signal provided the thermoelastic signal used as
metrics for evaluating stiffness degradation. At the same
cycles-to-total cycles ratio, thermoelastic data were compared to the
data of the extensometer that provided averaged stress/strain data in
the gage length of the sample.
Specific processing algorithms were used to extract the mechanical and
thermal metrics.
The major outcome of the present research is represented by the
modelling of the stiffness degradation by using thermoelastic data.
The other results achieved by performing present research are:
- A demonstration of the capability of the thermoelastic signal to
provide local information and making possible the quantitative
estimation of the damage in the material.
- A demonstration of narrow correlation between mechanical and thermal
behaviour
- A qualitative major capability of the thermoelastic metrics for
describing mechanical properties variations
This approach is useful also because it can be adopted to estimate
stiffness degradation on in-situ applications on operating components
where stress state and damage behaviour are unknown and where the
extensometer cannot be used.