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Multiscale Behavior of Fused Deposition Additively Manufactured Thermoplastic Cellular Materials Kaitlynn Melissa Conway Clemson University, [email protected]

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Multiscale Behavior of Fused Deposition Additively Manufactured Thermoplastic Cellular Materials Kaitlynn Melissa Conway Clemson University, Kconwa2@Clemson.Edu Clemson University TigerPrints All Theses Theses 8-2018 Multiscale Behavior of Fused Deposition Additively Manufactured Thermoplastic Cellular Materials Kaitlynn Melissa Conway Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_theses Recommended Citation Conway, Kaitlynn Melissa, "Multiscale Behavior of Fused Deposition Additively Manufactured Thermoplastic Cellular Materials" (2018). All Theses. 2954. https://tigerprints.clemson.edu/all_theses/2954 This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. MULTISCALE BEHAVIOR OF FUSED DEPOSITION ADDITIVELY MANUFACTURED THERMOPLASTIC CELLULAR MATERIALS A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Master of Science Mechanical Engineering by Kaitlynn Melissa Conway August 2018 Accepted by: Dr. Garrett J. Pataky: Thesis Advisor, Committee Chair Dr. Joshua D. Summers Dr. Huijuan Zhao Abstract Cellular materials are known for being lightweight as well as deforming in unique ways. Cellular materials have become more viable due to additive manufacturing (AM). AM cellular materials are easier to fabricate compared to traditional cellular materials and AM cellular materials are not as limited in geometry as traditional fabrication methods were. AM materials were studied in this paper in a two-phase approach. Phase 1 focused on the global mechanical properties of AM cellular materials. Phase 2 focused on the crazing of AM thermoplastic glassy polymers and how additive manufacturing affects the behavior or cellular materials. Because cellular materials do not have a consistent cross sectional area throughout the material, there is not a standard cross sectional area to use for property calculations. The author introduced an effective area for in-plane loading that normalized cellular materials by the amount of area present to allow accurate, direct comparisons between cellular materials of different unit cell geometries, unit cell dimensions, cellular materials of different stock material and comparisons between cellular material and solid materials. Strains calculated from DIC displacement measurements were used to validate the behavior observed using the effective area compared to how the cellular material was actually deforming. It was observed that the AM honeycomb material crazed at the plastic hinges that formed. Crazing was studied in AM acrylonitrile butadiene styrene (ABS) and extruded ABS to compare how crazing behavior differed in AM materials versus extruded materials. Extruded ABS crazes were thin with an average width of 10 m and appeared simultaneously throughout the cross section of a dog bone specimen when theµ macro crazing threshold stress was reached. AM ABS ii crazes were an order of magnitude wider with an average width of 100 m and appeared at one or two locations when the macro crazing threshold stress was reached.µ Further crazing spread from the original craze locations as the material was further strained. Using DIC to detect macro crazing in AM ABS dog bone specimens and MicroCT scans to locate voids in the specimens, crazing was discovered to initiate in the large voids inherent in the AM process. Understanding how AM thermoplastics deform is critical for the development of using AM thermoplastic cellular materials. iii Acknowledgements I would like to first thank my advisor Dr. Garrett J. Pataky for pushing me to become a better researcher. His high standards have taught me the importance of quality work, as well as the importance of quality when presenting my work. I also would like to acknowledge his endless patience when I ruined specimens, broke equipment and made the same mistakes countless times in a row. I would like to thank Dr. Joshua D. Summers and Dr. Huijuan Jane Zhao for agreeing to be on my committee and meeting with me throughout my time here to discuss my research. Your assistance and patience is incredibly appreciated. I would like to thank my family for their continuous love and support, as well as for introducing me to my love affair with science. My parents have always encouraged me to be curious and ask questions. They are always interested to hear about my research and classes and have encouraged me throughout my education. I would like to thank my sister for being someone I can laugh with and never farther than one text away. I would like to thank Clemson University, the Clemson Mechanical Engineering Department, all of my professors, all of the welcoming people and all of the friends I have made during my time here. I would especially like to thank my office mates of Office 125, who have made my time here so much more enjoyable: Vivic Harrinanan, Lauren Carter, Jody Bartanus, Jacob Biddlecom, Matt Williams, Mitra Shabani, Cameron Abarotin and Diana Burden. iv I would like to especially thank my undergraduate alma mater, LeTourneau University, not only for providing me with such a solid foundation in mechanical engineering, but also for showing me what it means to use your vocation for the glory of God. I would like to thank the Sonoco Institute of Packaging Design and Graphics and the Department of Food, Nutrition and Packaging Science for use of their 3D printers and CNC table. I would like to thank W. Aaron Snyder for his continuous patience and willingness to help me while printing hundreds of specimens, as well as assisting with the varied assortment of tasks I recruited him for. When I first introduced myself and asked to use his 3D printer, I never dreamed he would become one of my closest friends. I would also like to thank Travis Pruitt and the Godley-Snell building for use of their MicroCT scanner. v Table of Contents Abstract ............................................................................................................................................ ii Acknowledgements ........................................................................................................................ iv List of Figures ................................................................................................................................ viii List of Tables .................................................................................................................................... x Chapter 1. Motivation of Additively Manufactured Cellular Materials .......................................... 1 Chapter 2. Literature Review .......................................................................................................... 5 2.1 Fused Deposition Additive Manufacturing ............................................................................. 5 2.2 Thermoplastics used in Fused Deposition Additive Manufacturing ....................................... 6 2.2.1 Poly (Lactic Acid) ............................................................................................................. 6 2.2.2 Acrylonitrile Butadiene Styrene ..................................................................................... 6 2.3 Crazing .................................................................................................................................... 7 2.3.1 Prediction of Micro Craze Initiation ............................................................................. 10 2.4 Cellular Materials.................................................................................................................. 11 Chapter 3. Phase 1: Global Properties and Local Mechanisms of Additively Manufactured Cellular Materials .................................................................................................................... 15 3.1. Methods and Materials ....................................................................................................... 15 3.2 Calculation of Effective Area ................................................................................................ 17 3.2.1 Footprint Area .............................................................................................................. 18 3.2.2 Column Area ................................................................................................................. 18 3.2.3 Effective Area ............................................................................................................... 18 3.3. Results ................................................................................................................................. 19 3.3.1 Honeycomb Cell Behavior ............................................................................................ 20 3.3.2 Brick Cell Behavior ........................................................................................................ 23 3.4. Discussion ............................................................................................................................ 25 3.4.1 Comparison of Area Methods ...................................................................................... 25 3.4.2 Mechanical Behavior using the Effective Area Method ............................................... 27 3.5 Conclusions ........................................................................................................................... 32 vi Chapter 4. Phase two: Deformation of Additively Manufactured Acrylonitrile Butadiene
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