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Ultrasonic characterization of the complex Young’s modulus of polymer parts fabricated with microstereolithography

Clinton B. Morris (Department of Mechanical Engineering, University of Texas at Austin, Texas, Texas, USA)
John M. Cormack (Applied Research Laboratories and Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, USA)
Mark F. Hamilton (Applied Research Laboratories and Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, USA)
Michael R. Haberman (Applied Research Laboratories and Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, USA)
Carolyn C. Seepersad (Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas, USA)

Rapid Prototyping Journal

ISSN: 1355-2546

Article publication date: 8 October 2018

Issue publication date: 18 October 2018

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Abstract

Purpose

Microstereolithography is capable of producing millimeter-scale polymer parts having micron-scale features. Material properties of the cured polymers can vary depending on build parameters such as exposure. Current techniques for determining the material properties of these polymers are limited to static measurements via micro/nanoindentation, leaving the dynamic response undetermined. The purpose of this paper is to demonstrate a method to measure the dynamic response of additively manufactured parts to infer the dynamic modulus of the material in the ultrasonic range.

Design/methodology/approach

Frequency-dependent material parameters, such as the complex Young’s modulus, have been determined for other relaxing materials by measuring the wave speed and attenuation of an ultrasonic pulse traveling through the materials. This work uses laser Doppler velocimetry to measure propagating ultrasonic waves in a solid cylindrical waveguide produced using microstereolithography to determine the frequency-dependent material parameters of the polymer. Because the ultrasonic wavelength is comparable with the part size, a model that accounts for both geometric and viscoelastic dispersive effects is used to determine the material properties using experimental data.

Findings

The dynamic modulus in the ultrasonic range of 0.4-1.3 MHz was determined for a microstereolithography part. Results were corroborated by using the same experimental method for an acrylic part with known properties and by evaluating the natural frequency and storage modulus of the same microstereolithography part with a shaker table experiment.

Originality/value

The paper demonstrates a method for determining the dynamic modulus of additively manufactured parts, including relatively small parts fabricated with microstereolithography.

Keywords

Citation

Morris, C.B., Cormack, J.M., Hamilton, M.F., Haberman, M.R. and Seepersad, C.C. (2018), "Ultrasonic characterization of the complex Young’s modulus of polymer parts fabricated with microstereolithography", Rapid Prototyping Journal, Vol. 24 No. 7, pp. 1193-1202. https://doi.org/10.1108/RPJ-01-2018-0011

Publisher

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Emerald Publishing Limited

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