Evaluation of Mode II Delamination Area by Non-destructive Techniques: Accuracy and Influence on Fracture Toughness Calculation

The present work estimated the accuracy of non-destructive tests in quantifying the delaminated area in CFRP samples submitted to a 4-point end notched flexure test, to evaluate the relevance of measuring the delamination area to calculate fracture toughness in mode II, instead of of the traditional method which evaluates the delamination length visually through the sample lateral faces. In this way, IR thermography, eddy current, ultrasonic microscopy, and X-ray computed microtomography (as reference) tests were employed. A methodological sequence based on image processing algorithms was performed to calculate the values of the delaminated areas for all NDT techniques. The first two techniques did not provide a clear separation between the defective and intact zones and are strongly influenced by edge effects. The result is different for the two last tests, which demonstrated a satisfactory definition of the delamination limit region. The ultrasonic microscopy test revealed results similar to microtomography, proving to be a promising alternative for this type of measurement. In addition, the importance of using more accurate methods in calculating the crack length is emphasized, as the traditional visual measurement can be highly susceptible to errors and does not allow evaluating potential tunneling effects or an uneven delamination front.