Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 100554

100554 - Impact of Infill and Shell Design Features on Compression Stiffness in Material Extrusion of Thermoplastic Urethane 

Thermoplastic polyurethane (TPU) filaments exhibit extreme elastic properties under an applied stress. In this work, material extrusion is used to create TPU test specimens under varied structural design conditions to evaluate how changes in structure affect the stiffness of material extrusion parts. The goal is to demonstrate that structural strength and stiffness within material extrusion printed TPU can be tuned and altered for specific applications depending on the number of outer shells, the infill percentage, and infill pattern. In this study, a full factorial design of experiments methodology was employed to provide a systematic method for experimentally analyzing the influence and effect of the three design factors on compressive strength and modulus of elasticity. Based on the data collected from this experiment, a statistical regression model was presented that can be used to predict rigidity in TPU parts manufactured through material extrusion. Based on the results of the initial model, additional investigations were carried out to further understand methods to predict rigidity. In the first supplemental investigation, additional test specimens were created to investigate the assumed linearity of response between 10% and 30% infill percentages. The next experiment was designed to analyze the impact of TPU hardness with commercially available TPU, red Polyflex® with a durometer of 95 Shore A, compared to the lava Ninjaflex® with a durometer of 85 Shore A used in the initial investigation. The primary experiment followed a procedure derived from the ASTM testing standard D575 – 91 Rubber Properties in Compression in which all test pieces were cubes. To investigate the effect of corners, an additional experiment was conducted with cylinders that had equal cross-sectional areas to the cubes.  Two final experimental investigations were conducted into the effects of infill line intersections in both cube and cylinder shaped parts. It was found that shore hardness and infill percentage had the largest impact with respect to stiffness but that all factors were significant and the only interaction not significant at α = 0.05 was the two-factor interaction of infill pattern and number of external shells. Increasing infill density from 10% to 30% and increasing TPU material hardness from 85 A to 95 A provided similar increases in stiffness constant and compressive strength between 85% and 100%. Exterior corners were found to provide additional stiffness as they essentially act as thicker columns in the perimeter of the parts with increased significance at lower infill densities. Increasing internal infill intersections was most impactful at low compression displacements with multi-axial grid constraints yielding twice a high compressive strength than single-axial line constraints.

Presenting Author: Ryan Van Domelen University of St. Thomas

Presenting Author Biography: Ryan Van Domelen is a Senior, majoring in Mechanical Engineering, at the University of St. Thomas in Saint Paul, Minnesota and will graduate this December. Ryan won the American Mathematical Association of Two-Year Colleges (AMATYC) student research league, placing first in the nation, and recently completed NASA&#39;s Proposal Writing and Evaluation Experience. He will also be first author on a paper being submitted to the Manufacturing Science &amp; Engineering Conference (MSEC) 2023. <br/><br/>Ryan has a keen interest in researching how additive manufacturing can be utilized in combustion engines. Specifically, he would like to investigate how additively manufactured microstructures in cooling channels can be use to manipulate turbulence and improve heat transfer. He will be applying to Mechanical and Aerospace Engineering PhD programs to begin graduate studies fall of 2023.

Authors:

Ryan Van Domelen University of St. Thomas
John Wentz University of St. Thomas
Duy Le University of St. Thomas
Andrew Broman University of St. Thomas
Sandra Hawley University of St. Thomas