Detection of delamination in carbon-fibre-reinforced polymers with lock-in thermography

Attention of this paper is devoted to testing and evaluation of carbon-fibre-reinforced polymer specimens with lock-in thermography. Several specimens were prepared by a vacuum infusion technique using a low-viscosity epoxy system; delaminated areas were simulated by the insertion of thin Kapton (R) diskettes at a given depth through the thickness. Artificial defects had different shapes (circular or elliptical) and dimensions. Inserts were located at different depths and, in some cases, by overlapping more than one Kapton (R)-shaped layer (i.e. two or more concentric discs, each of different diameter). A preliminary test campaign was performed by differential scanning calorimetry and rheometry to find optimal processing parameters to achieve fully cured state of matrix and to avoid the formation of defects in accordance with aerospace standards for composites manufacturing. Specimens were non-destructively inspected with optical lock-in thermography; results were presented in terms of phase images. All inserts were discovered and also well outlined under difficult conditions such as in the case of thin overlapped foils.