3D Ultrasonic Evaluation of Porosity Detection in Carbon Fiber Reinforced Polymer Composites: Effects of Backscattering and Back Reflection

Abstract

3D ultrasonic C-scan inspections at 50 MHz were conducted to detect porosity in carbon fiber–reinforced polymer (CFRP) composites fabricated under vacuum pressures of 0, −330, and −686 mm Hg, resulting in porosity levels of 7.1%, 6.4%, and 5.8%, respectively. In specimens fabricated at 0 mm Hg, porosity levels of approximately 6–8% were detected near the surface layers, whereas deeper regions exhibited lower detected porosity values of approximately 2–4%. The ability to detect internal porosity decreased with increasing laminate depth because of ultrasonic signal attenuation caused by backscattering and back reflection at fiber–matrix interfaces. The measured porosity percentages from the top to bottom layers were 8.07%, 3.29%, 3.16%, 2.63%, 3.87%, 2.27%, 2.40%, and 5.51%, in sequence. These results revealed fluctuations in ultrasonic detectability at greater depths, reflecting the complex interaction between ultrasonic wave propagation, material anisotropy, and internal microstructural features. Overall, the results demonstrate that 3D ultrasonic imaging is an effective non-destructive evaluation (NDE) technique for surface and near-surface porosity characterization, although its sensitivity decreases in deeper and highly attenuated laminate regions.