Experimental Analysis of Frequency-Dependent Ultrasonic Attenuation and Velocity in Additively Manufactured Polymers

Ultrasonic velocity and attenuation in non-metallic materials such as polymers exhibit strong frequency-dependent behavior, unlike the largely frequency-independent attenuation observed in metals, which limits penetration depth and measurement resolution in non-destructive evaluation (NDE). This study investigates the frequency-dependent ultrasonic velocity and attenuation characteristics of additively manufactured polymer materials by evaluating four attenuation coefficients—standard time-domain exponential fitting, frequency-domain exponential fitting, Welch-based frequency-domain exponential fitting, and frequency-dependent attenuation at the nominal transducer frequency—and two velocity measures: standard constant longitudinal velocity and frequency-dependent velocity. Eight fused-deposition-modeled polymer samples were fabricated with varying nozzle temperatures (195°C and 205°C), nozzle diameters (0.4 mm and 0.6 mm), and raster angles (25° and 50°). Results show that higher nozzle temperatures and larger nozzle diameters reduce attenuation and increase ultrasonic velocity by improving interlayer bonding, reducing porosity, and enhancing material homogeneity. Statistical analysis using Minitab identified 205°C and a 0.6 mm nozzle diameter as the optimal combination for minimizing attenuation and maximizing velocity in NDE applications, while lower temperatures, smaller diameters, and 50° raster angles were more suitable for sound-absorption and damping applications. The proposed frequency-dependent characterization methodology was validated using standard samples and established literature data, providing a systematic framework for evaluating acoustic properties in additively manufactured polymers and bridging the gap between conventional frequency-independent approaches and advanced signal-processing-based techniques.