Polymer Testing (May 2022)
Stiffness and damping behavior of 3D printed specimens
Abstract
In this work, we analyzed a variety of metrics derived from Laser Doppler Vibrometry (LDV) characterization of 3D printed rectangular prisms. The metrics of interest were natural frequencies and amplitudes of first and second bending vibration modes, equivalent elastic moduli, damping ratios and areas of transmissibility functions. To explore the influence of printing process parameters on the dynamical behavior and, therefore, on the aforementioned metrics, 48 different combinations were considered, including build orientation, raster angle, nozzle temperature, print speed and layer height as relevant parameters. Thus, 96 polylactic acid (PLA) rectangular prisms were fabricated and LDV characterization was carried out. Based on the equivalent elastic modulus metrics, it was possible to corroborate the influence of printing process parameters on the mechanical performance, being raster angle, build orientation and nozzle temperature the most influential parameters. Likewise, the analysis of damping ratios served to assess the degree of interfilament bonding of 3D printed rectangular prisms. Thus, rectangular prims that exhibited high damping ratios also showed evident lack of adhesion between deposited filaments. Low damping ratios and, therefore, superior interfilament bonding was connected with on edge build orientation, high nozzle temperature (220 °C) and low print speed (60 mm/s) for specimens fabricated using 0° as raster angle. The analyses of areas of transmissibility functions and amplitudes of vibration modes also confirmed a better transmission of excitation (i.e., larger areas and higher amplitudes) for optimally fabricated parts, that is, specimens featuring relatively high equivalent elastic moduli and low damping ratios. Moreover, the application of Classical Laminate Theory to establish the relationships between elastic modulus and damping ratio with raster angle confirmed low temperature (200 °C) and high print speed (120 mm/s) resulted in low elastic modulus a high damping ratios and, therefore, poor interfilament bonding. The present findings confirm LDV is a powerful technique in the characterization of additively manufactured products, being able to discriminate different mechanical behaviors as well as the degree of interfilament bonding. Despite of their simplicity, the metrics derived from LDV characterization represent an attractive tool for both research and industrial applications.
