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Metal and Polymer Foam Hybrid Materials: Design, Fabrication and Analysis

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Metal and Polymer Foam Hybrid Materials: Design, Fabrication and Analysis METAL AND POLYMER FOAM HYBRID MATERIALS: DESIGN, FABRICATION AND ANALYSIS by Julianna E. Campbell A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Materials Science and Engineering University of Toronto Copyright © 2009 by Julianna E. Campbell Abstract METAL AND POLYMER FOAM HYBRID MATERIALS: DESIGN, FABRICATION AND ANALYSIS Julianna E. Campbell Master of Applied Science Graduate Department of Materials Science and Engineering University of Toronto 2009 Two novel hybrid materials for use in sandwich cores of structural materials are designed, manufactured and mechanically tested. Each material is a hybrid of metal and polymer foam. One set of hybrids is fabricated using an aluminium micro-truss filled with varying densities of polyurethane foam. Increases up to 120% in stiffness, 372% in strength, 740% in resilience and 106% in impact energy over the aluminium micro-truss are obtained from compression and impact testing. Furthermore, the stiffness of these hybrids can be tailored according to the density of the polyurethane foam. Another set of hybrids is fabricated using a rapid prototyped ABS polymer truss that is foamed and electroplated with nanocrystalline nickel. Increases up to 1525% in stiffness, 1165% in strength and 650% in energy absorption over the foamed ABS truss are obtained. Furthermore, the gain in strength, stiffness and energy absorption outweigh the gain in density in these hybrid materials. ii Acknowledgements This work could not have been completed without the help and support of many col- leagues and friends. First and foremost I would like to thank my supervisors, Dr. Hani Naguib and Dr. Glenn Hibbard. Their guidance and support was invaluable throughout the course of this research. Further thanks goes to the Hybrid Materials group, especially to Marc Suralvo for helping with the electroplating of the ABS trusses, to Ian Stewart for helping to fabricate the aluminium PCMs and to Brandon Bouwhuis and Eral Bele for their help with the inelastic buckling models. A special thanks also to those in the SAPL group: Linus Leung, Christine Chan, Aaron Price, Reza Rizvi, Eunji In, Choonghee Jo, Joe McRae, Jack Chang, Dina Badawy and all of the summer students for their support, help and advice, and most importantly for making this experience enjoyable. To my parents, Ian and Linda, sisters, Katie and Laura, brothers-in-law, Roland and Bryan and many friends who have been waiting for me to finish school for many years now - I think this is it - thanks for your support through all of the years! Most of all I would like to thank my husband, Scott. I am forever grateful for his endless patience and support throughout this process and for all of his help with my research and latex. Without him, this thesis would never have been completed. iii Contents 1 Materials to Fill the High-Strength, Low-Density Void 1 1.1 Materials Selection Charts: Looking at Materials Space . 2 1.2 Hybrid Materials that Fill the Empty Space in Materials Selection Charts 4 1.3 Objective of Thesis . 7 1.4 Overview of Thesis . 9 1.5 Conclusion: Developing Hybrid Materials to Fill Materials Space . 10 2 Structural Materials: Sandwich Structures 11 2.1 Sandwich Structures . 11 2.2 Lattice Sandwich Core Materials . 13 2.2.1 Polymer Foams: Bending-dominated cellular materials . 14 2.2.2 Periodic Cellular Metal Micro-Trusses: Stretch-dominated lattice materials . 16 2.3 Hybrid Materials . 19 2.3.1 Polymer Foam Matrix Hybrid Materials . 19 2.3.2 Plated Hybrid Materials . 20 2.4 Conclusion: Current Hybrid Materials Missing the Low-Density Advan- tage of Foam . 22 3 Pyramidal PCM and Polyurethane Hybrid Materials 23 3.1 Materials and Sample Manufacture . 23 iv Contents 3.2 Experimental Method and Mechanical Testing . 26 3.2.1 Compression Testing of PCM, PU Foam and Hybrid Materials . 27 3.2.2 Impact Testing of PCM, PU Foam and Hybrid Materials . 27 3.3 Results of Mechanical Testing . 29 3.3.1 Stiffness of PCM, PU Foam and Hybrid Materials . 31 3.3.2 Strength of PCM, PU Foam and Hybrid Materials . 36 3.3.3 Resilience of PCM, PU Foam and Hybrid Materials . 40 3.3.4 Impact Resistance of PCM, PU Foam and Hybrid Materials . 41 3.4 Conclusion: PCM/PU Foam Hybrid Materials Offer Advantages Over Constituent Parts . 49 4 Rapid prototyped ABS Truss Cores Plated with Nanocrystalline Nickel 50 4.1 Sample Development and Manufacture . 50 4.1.1 Rapid Prototyping the ABS trusses . 51 4.1.2 Batch Foaming of the ABS Trusses . 51 4.1.3 Electroplating of ABS Trusses . 59 4.1.4 Summary . 60 4.2 Experimental Method and Mechanical Testing . 60 4.3 Results of Mechanical Testing . 62 4.3.1 Mechanical Properties of Foamed and Plated ABS Trusses . 67 4.3.2 Effects of Foaming and Plating . 71 4.3.3 Buckling Analysis of Plated ABS Trusses . 80 4.4 Summary . 84 5 Conclusions and Future Work 85 References 89 v List of Figures 1.1 Typical material selection chart . 3 1.2 Hybrid materials are a combination of two or more existing materials . 4 1.3 Four main types of hybrid materials . 6 1.4 Materials selection chart of Young's modulus versus density . 8 2.1 Examples of sandwich structures . 12 2.2 Example of honeycomb . 13 2.3 Examples of periodic cellular metal (PCM) micro-trusses . 17 3.1 Manufacturing the pyramidal PCMs . 24 3.2 Schematic of the mold used to create the hybrid materials . 25 3.3 Pyramidal PCM, PU foam and hybrid samples . 27 3.4 Gardner impact tester . 28 3.5 Representative stress-strain curves - high density . 30 3.6 Representative stress-strain curves - low density . 30 3.7 Comparison of stiffness for pyramidal PCM, polyurethane foam and hybrids 32 3.8 Comparison of stiffness and density for the PCM, foams and hybrids . 34 3.9 Comparison of hybrid stiffness and foam stiffness . 35 3.10 Comparison of strength for pyramidal PCM, polyurethane foam and hybrids 36 3.11 Comparison of strength and density for the PCM, foams and hybrids . 37 3.12 Comparison of the strength of the polyurethane foam samples found ex- perimentally and using Menges model . 39 vi List of Figures 3.13 Comparison of the strength of the hybrid samples found experimentally and using Menges model . 39 3.14 Comparison of resilience for pyramidal PCM, polyurethane foam and hybrids 40 3.15 Comparison of resilience and density for the PCM, foams and hybrids . 41 3.16 Damage profile for the pyramidal PCM . 42 3.17 Damage profile for the PU foams . 43 3.18 Damage profile for the PCM/PU foam hybrids . 43 3.19 Comparison of impact failure modes for the PCM, foams and hybrids . 45 3.20 Comparison of impact energy for crack formation in the PU foam samples 46 3.21 Comparison of impact energy for pyramidal PCM and hybrids . 47 3.22 Comparison of impact energy of the hybrid versus the sum of its parts (the PCM and PU foam) . 47 3.23 Comparison of impact energy and density . 48 4.1 Schematic diagram of fused deposition modeling (FDM) process . 52 4.2 CAD drawing of polymer truss . 53 4.3 Rapid prototyped polymer truss sample . 54 4.4 SEM micrograph of the cross-section of the ABS truss . 54 4.5 Photo of rapid prototyped ABS trusses . 56 4.6 Percentage of volume expansion of rapid prototyped ABS trusses versus foaming temperature . 56 4.7 Micrographs of the foamed structure of the rapid prototyped ABS trusses 57 4.8 Nanocrystalline nickel plated ABS truss . 59 4.9 Failure of ABS trusses due to edge effects . 61 4.10 Restriction plate used during compression testing to eliminate edge effects 61 4.11 Representative stress-strain curves where strain is calculated using both the total truss height and the core height . 62 4.12 Representative stress-strain curves for the unplated ABS trusses . 63 4.13 Representative stress-strain curves for the plated ABS trusses . 63 vii List of Figures 4.14 Comparison of representative stress/strain plot and derivative/strain plot for plated samples foamed at 85 ◦C ..................... 65 4.15 Comparison of representative stress/strain plot and derivative/strain plot for unplated samples foamed at 85 ◦C.................... 66 4.16 Fracture at the node joint of the plated ABS truss at peak strength . 67 4.17 Representative stress-strain curves of the plated and unplated rapid pro- totyped ABS trusses . 68 4.18 Mechanical properties of the nano-Ni plated and unplated ABS trusses . 70 4.19 Material selection charts for mechanical properties of the nano-Ni plated and unplated ABS trusses . 72 4.20 Decreasing trends in specific stiffness, specific strength and specific energy absorption of the foamed ABS trusses . 73 4.21 Comparison of the strength of the ABS foam trusses found experimentally and using the Gibson/Ashby model . 75 4.22 Relative ratios for mechanical properties of the foamed ABS trusses . 77 4.23 Relative ratios for mechanical properties of the nano-Ni plated and un- plated ABS trusses . 79 4.24 Comparison of the theoretical and experimental force per strut versus the cross-sectional area of the core for pinned (k=1) end conditions . 82 4.25 Comparison of the theoretical and experimental strength versus the cross- sectional area of the core for pinned (k=1) end conditions . 82 4.26 Comparison of hybrid strength with previous studies . 83 5.1 Materials selection chart with PCM/PU foam and ABS/nanoNi hybrid materials . 88 viii List of Tables 3.1 Nine different sample types .
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