Modeling and Experimental Study of Thermal Equivalents of Impact Damage in Composites during the Development of Reference Samples in Thermal Testing

The concept of “thermal equivalents” of impact damage in composites, created by iteratively fitting the parameters of flat bottom hole defects, has been elaborated. In thin-walled composites, impact damage tends to be located near the surface opposite to the impact, so thermal inspection on the rear surface of the product is most effective for their detection. Detection of defects on the front surface is associated with small signal amplitudes in the region of temperature indications and requires the use of the thermal equivalent of impact damage in the form of a combination of flat bottom hole defects. On the rear surface, temperature indications of impact damage are often butterfly-shaped and characterized by a large area of defect “footprints.” Single flat-bottom flaws can serve as thermal equivalents of such defects. The proposed concept of thermal equivalents of real defects in composites is verified experimentally on a carbon fiber-reinforced plastic specimen with impact damage of 62 J energy.