Aerospace, Ultrasonic Testing
Use of Carbon Fiber–Reinforced Polylactic Acid Print Specimens to Control Porosity for Air-Coupled Ultrasound Reference Experiments
ABSTRACT
To improve nondestructive evaluation (NDE) techniques for porous composite materials, reference specimens with representative porosity conditions are needed, along with validated ultrasonic NDE models sensitive to varying porosity. Carbon fiber–reinforced polylactic acid (CF/PLA) 3D print specimens are proposed as a low-cost solution. CF/PLA specimens were manufactured with controlled geometry and infill level to serve as an analog of naturally occurring porosity. The effects of infill level, infill shape, and specimen thickness on air-coupled ultrasonic testing (ACUT) through-transmission frequency responses were studied experimentally. Serial sectioning with microscopy and contact ultrasound were used to verify porosity and material properties. Modes increase in frequency as percent infill increases or specimen thickness decreases. Changes in mode amplitude are influenced by complex transducer behavior. Infill shape also affects trends. Control of geometry and porosity in printed specimens is imperfect but sufficient for reference specimens. CF/PLA specimens show potential as reference standards for controlled porosity and benchmarks for models.
KEYWORDS: air-coupled ultrasound, porous composites, surrogate materials, pore morphology, pore volume fraction, carbon fiber–reinforced polylactic acid
