Inspection benchmarking of Fiber Reinforced Polymers produced by Additive Manufacturing

The production of Polymer Matrix Composites (PMCs) through Additive Manufacturing (AM) presents new defects, and the detection of these is crucial for proper functioning. Non-destructive testing (NDT) techniques such as terahertz (THz), air-coupled ultrasounds, and active thermography are fast, automatable, non-invasive, and noncontact inspection methods. The aim of this study is to investigate the use of NDT techniques for detecting defects in PMCs produced by AM. Six samples were produced using polylactic acid (PLA) as the base material and reinforced with continuous fibers of Kevlar, glass, and carbon. Two types of samples were created: one with a full-thickness reinforcement defect in a specific area and the other with a partial reinforcement defect, with a layer of fibers missing in the same area. The samples were then tested using three NDT techniques: THz, non-contact ultrasonic, and active thermography. The results showed that THz was only able to detect the defect in the carbon fiber sample with full-thickness reinforcement, ultrasonic testing was able to detect the defects in Kevlar and carbon fiber samples with missing three layers of fibers, and active thermography was the most reliable technique, detecting all samples with missing three layers of fibers as well as partial reinforcement defects.