Damage quantification in composites using self-heating based vibrothermography and dedicated image processing

The self-heating based vibrothermography (SHVT) is a promising non-destructive testing (NDT) technique for polymer-matrix composites, which is based on inducing resonant vibrations of a tested structure. Vibrations serve as a thermal excitation for NDT inspection due to the hysteretic heating of a polymer matrix, known as the self-heating effect. In previous studies, it was validated that the controlled self-heating temperature rise ensures proper thermal excitation of tested composite structures and has a non-destructive and non-invasive character for such structures. It was shown that the increase in temperature usually below 5°C from the ambient temperature is enough to provide appropriate thermal excitation of a tested structure for identifying structural damage. The following study focuses on methods for processing of thermographic images acquired from NDT inspections using SHVT to enable accurate quantification of damage. The results of inspections of two-dimensional glass fiber-reinforced composite specimens with introduced artificial damage were used for a case study to quantify the damage and assess the accuracy of the determination of its spatial position and characteristic dimensions. The results of the processing demonstrated significant enhancement in identification of the introduced damage and allowed its precise quantification, which creates a potential for practical applications, especially during inspection of structures with single-side access or in the cases where external thermal excitation typical for most of classical thermographic techniques cannot be applied.