Nondestructive thermographic evaluation of thermal diffusivity in additively manufactured fiber-reinforced composites using low-cost cooling: an early-stage analysis

Abstract

This work explores a low-cost, non-destructive method for estimating in-plane thermal diffusivity in fiber-reinforced polymer composites manufactured through additive processes. The method relies on localized surface cooling—rather than conventional heating—using a commercially available freezing spray, and thermal acquisition is performed through a compact microbolometric infrared sensor. This setup offers a practical and accessible alternative to more complex systems typically based on laser excitation or high-power heat sources. Two composite materials with different reinforcement strategies were analyzed: one reinforced with continuous carbon fibers, the other with short fibers, manufactured through a layer-by-layer additive process. The main objective of this study is to assess whether such a simple thermal stimulus can reliably detect direction-dependent variations in thermal diffusivity and highlight possible in- plane anisotropy, which often arises in additively manufactured composites due to fiber orientation and process-induced architecture. Although the specimens were subjected to controlled low-energy impact, this investigation is limited to evaluating thermal transport properties as a first step within a broader research effort to develop quantitative and low- cost thermographic methods for damage assessment. Results show that the cooling-based approach can reveal subtle differences in thermal response: the continuous-fiber composite exhibited modest anisotropy, while the short-fiber specimen appeared nearly isotropic. The method's simplicity, low cost, and non-invasive nature make it highly attractive for laboratory characterization and in-field diagnostics, especially where traditional heating techniques may be unsuitable or impractical.