Microdefect identification in polymers by mapping depth-resolved phase-difference distributions using optical coherence tomography

A novel method for the identification of microdefects in transparent or semi-transparent polymers and polymer composites is established, which maps the depth-resolved phase-difference distribution during polymer deformation using optical coherence tomography (OCT), and detects internal microdefects using the defect-induced phase-difference-distribution anomalies. For validation, epoxy resin, silicone rubber and glass fiber-reinforced resin matrix composite samples with internal defects with different dimensions were measured by using a line-field spectral-domain OCT system. Small defects, which could not be observed from the cross-sectional images, were identified from the measured phase-difference distributions; fibers and microdefects of a similar size in the polymer composites were distinguished using the proposed novel method. The proposed method can be employed, not only for polymers and polymer composites, but also for other transparent and semi-transparent materials such as glass and ceramic.