Restored pseudo heat flux (RPHF) algorithm for carbon fibre composite defect detection using thermography under uneven heating

Abstract

Carbon fibre composite materials are widely used in high-value, high-profit applications – such as aerospace manufacturing and shipbuilding – due to their low density, high mechanical strength, and flexibility. However, existing techniques for non-destructive evaluation of composite materials are limited and not robust. Thermography has been demonstrated to be a promising technology; however, thermal diffusion and uncontrolled uneven heating considerably degrade its capacity to detect thin planar defects in carbon fibre composites. In this study, we have developed a method, restored pseudo heat flux (RPHF), for addressing this problem. Unlike many existing methods, RPHF does not require prior knowledge about defect depth. A numerical simulation was developed, and three sets of experiments were performed using a layered sample. Results suggest that in comparison with other existing methods, RPHF does not require an accurate value for its input, thermal diffusivity. It provides a good approximation to heat flux distribution and significantly improves the detection capability of thermography when compared to several existing methods.

Keywords:

• Time-resolved thermography
• inverse heat conduction
• Fourier transform

Acknowledgement

The authors sincerely appreciate suggestions and information on carbon fibre parts manufacturing and characterization by Dr. Terry Creasy. The authors also sincerely appreciate American Durafilm (http://www.americandurafilm.com/about-american-durafilm/) for providing free FEP and TEFP film for use in simulating defects.