Determining the Complex Young’s Modulus of Polymer Materials Fabricated with Microstereolithography C. Morris*, J. M. Cormack*†, M. F. Hamilton*†, M. R. Haberman*†, C. C. Seepersad* *Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712 †Applied Research Laboratories, The University of Texas at Austin, Austin, TX 78758 Abstract 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 time and laser power. Current techniques for determining the material properties of these polymers are limited to static measurements via micro/nanoindentation, leaving the dynamic response undetermined. 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 method is now applied to determine the frequency-dependent material parameters of polymers manufactured using microstereolithography. Because the ultrasonic wavelength is comparable to the part size, a model that accounts for both geometric and viscoelastic effects is used to determine the material properties using experimental data. Introduction Parts produced by additive manufacturing (AM) are increasingly utilized for applications such as energy absorbing honeycomb structures, prosthetic limbs, and shock isolation systems where the response of the material to dynamic loading must be considered [1, 2, 3]. Due to the geometric design freedom introduced by AM, parts can achieve mechanical performance levels previously unattainable by other manufacturing technologies [4]. Successful prediction of the mechanical performance of parts made from AM processes requires accurate mechanical modeling which, in turn, requires precise knowledge of rate-dependent material properties of the as-built parts. The frequency dependent modulus that relates the stress developed in the material due to a dynamically applied strain is one such property. The material property describing this relationship is known as the dynamic modulus, which is frequency dependent and expressed as a complex quantity that accounts for both storage and loss of mechanical energy. The modulus of low-loss elastic materials like metals is approximately rate independent for most applications, and can therefore be described with static elastic moduli. The static Young’s modulus for the uniaxial loading case is one such property that can be measured through quasi-static tensile or three point bending tests. If the material exhibits viscoelastic behavior, the mathematical description of the frequency dependent storage and loss moduli require a more generalized constitutive model [5], the parameters of which must be obtained experimentally. When a viscoelastic material is dynamically loaded, some of the imparted strain energy is stored elastically within the material while some of the energy is dissipated. The amount of 426 Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference
Determining the Complex Young’s Modulus of Polymer Materials Fabricated with Microstereolithography
Jun 21, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
