Simulated delaminations in thermal NDT standards and the concept of thermally equivalent defects

Abstract

In the thermal nondestructive testing (TNDT) of composite panels NDT standards (reference panels) are used to validate TNDT procedures and to verify the effectiveness of data processing algorithms. Most composite NDT standards use Teflon implants to simulate delaminations in composite panels.

3D numerical modeling has been used to evaluate the temperature versus time behavior of Teflon/foamed polypropylene implants and FBHs to determine how the parameters of implants (dimension, thickness, number of layers) or FBHs (dimension and depth) can be optimized to provide the best possible representations of real delaminations.

An ongoing question in the TNDT “community” has been “How well do Teflon implants and FBHs represent real delaminations?”

This paper will answer this question and provide recommendations.

Following the numerical modeling, composite test panels with simulated delaminations were fabricated, they were tested by TNDT, and the results were evaluated and compared.

The concept of thermally equivalent defects is introduced. A thermally equivalent defect is an FBH or Teflon/foamed polypropylene implant that accurately represent the temperature versus time performance of a real delamination, even though the simulated defect may not be the same diameter or depth of the real delamination.