FATIGUE AND FRACTURE OF THIN METALLIC FOILS WITH AEROSPACE APPLICATIONS A Thesis Presented to The Academic Faculty by Leslie E. Lamberson In Partial Fulfillment of the Requirements for the Degree Master of Science School of Aerospace Engineering Georgia Institute of Technology May 2006 FATIGUE AND FRACTURE OF THIN METALLIC FOILS WITH AEROSPACE APPLICATIONS Approved by: Dr. Erian A. Armanios, Advisor School of Aerospace Engineering Georgia Institute of Technology Dr. David L. McDowell School of Mechanical Engineering Georgia Institute of Technology Dr. Massimo Ruzzene School of Aerospace Engineering Georgia Institute of Technology Date Approved: 03/31/2006 To my dad ACKNOWLEDGEMENTS I extend my most sincere gratitude to the members of my thesis committee for their guidance and mentorship. Special thanks particularly to my thesis advisor, Dr. Erian Armanios, for his unconditional support of my research efforts, as well as Dr. Massimo Ruzzene and Dr. David McDowell for their patience, professionalism, and gracious assistance. My deepest appreciation goes to my family: Mom, Dad, Aunt Jo Anne, and my brother, Jonathan. Special thanks to Professor Arthur Hoadley at Western Michigan University for introducing me to aeronautical engineering, as well as Professor Ann Marie Sastry at the University of Michigan for being an amazing role model and mentor throughout my studies. I also warmly acknowledge my Lockheed Martin Aeronautics mentors: Lee, Scott, Mike, Terry, and the rest of the Advanced Development Programs team in Forth Worth for their kind support of my graduate career. I extend a special heartfelt thank you to Amy, Adele, Lil, and Wendy, as well as Sandy and Mimi from WIE for helping me through some rough nights and stressful times; and to Frank for always being there to greet me at the door. Lastly, to the numerous artists who kept my creative side alive: Ms. Arthur, Mr. Estner, Peter, Judy, Christian, Gay, Margo, and Carol – thank you for the dance. Generous financial support from the Georgia Institute of Technology NASA Space Grant Consortium and the Zonta International Amelia Earhart Fellowship are gratefully acknowledged. The thesis topic suggestion and experimental configuration to test foils was supplied by Dr. John Holmes at the Georgia Institute of Technology. iv TABLE OF CONTENTS Page ACKNOWLEDGEMENTS iv LIST OF TABLES vii LIST OF FIGURES viii LIST OF SYMBOLS AND ABBREVIATIONS x SUMMARY xii CHAPTER 1 INTRODUCTION 1 2 BACKGROUND AND LITERATURE REVIEW 3 2.1 TPS Historical Perspective 3 2.2 Types of TPS 4 2.3 Ceramic versus Metallic TPS 11 2.4 Parametric Studies on Metallic TPS 13 2.5 Additional Thin Foil Fatigue and Fracture Applications 17 3 METALLIC FOIL FATIGUE AND FRACTURE 21 3.1 TPS Relevance 21 3.2 Thin Metallic Foil Research 21 3.3 Research Objective 22 3.4 Experimental Procedure 23 3.5 Fracture Toughness Tests 29 3.6 Fatigue Tests 30 3.7 Data Analysis 31 4 EXPERIMENTAL RESULTS 32 4.1 Fracture Toughness 32 4.2 Fatigue Crack Growth 36 v 5 CONCLUDING REMARKS 49 5.1. Conclusions 49 5.2 Recommendations 50 APPENDIX A: Tensile Testing Raw Data 52 APPENDIX B: Fracture Toughness Raw Data 60 APPENDIX C: Fatigue Testing Raw Data 75 APPENDIX D: Additional SEM Micrographs 90 REFERENCES 95 v i LIST OF TABLES Page Table 2.1: Potential benefits and challenges of metallic versus ceramic TPS 12 Table 2.2: Weight and cost considerations of metallic versus ceramic TPS 12 Table 3.1: Room temperature mechanical properties of Al-Mg (97/3) foil 28 Table 3.2: Summary of fracture toughness precracking data for Al-Mg foils 30 Table 4.1: Summary of fracture toughness values 33 Table 4.2: Various materials fracture toughness values 33 Table 4.3: Cyclic plastic zone size calculations for 30 µm thick foil 39 Table 4.4: Cyclic plastic zone size calculations for 100 µm and 250 µm thick foil 40 Table 4.5: Fatigue test conditions and Paris relation constants for 30 µm thick foil 47 Table 4.6: Fatigue test conditions, Paris relation constants for 100 µm, 250 µm thick foil 47 vi i LIST OF FIGURES Page Figure 2.1: X-33 reusable launch vehicle with metallic TPS 4 Figure 2.2: Lotus diagram of optimum TPS design factors 5 Figure 2.3: AFRSI schematic 6 Figure 2.4: TABI schematic 6 Figure 2.5: LI-900 schematic 7 Figure 2.6: AETB schematic 8 Figure 2.7: TIMW schematic 9 Figure 2.8: SA/HC schematic 9 Figure 2.9: SA/HC2 schematic 10 Figure 2.10: TI/HC schematic 10 Figure 2.11: AMCH schematic 11 Figure 2.12: ARMOR TPS panel, outer surface` 14 Figure 2.13: Upper and lower range foil gauge thickness for engineering applications 17 Figure 3.1: Schematic of experimental setup 23 Figure 3.2: Experimental setup, hemispherical bearing schematic 24 Figure 3.3: Specimen geometry 26 Figure 3.4: Room temperature stress-strain response, 30 µm thick foil 27 Figure 3.5: Room temperature stress-strain response, 100 µm and 250 µm thick foil 27 Figure 3.6: Setup of experimental procedure, close up of hemispherical bearing 29 Figure 4.1: Load-displacement curve, orientation effect for 30 µm thick foil 34 Figure 4.2: Load-displacement curve, size effect for 30 µm, 100 µm and 250 µm thick foil 34 Figure 4.3: Schematic dependence of fracture toughness on thickness 36 Figure 4.4: Crack length vs. cycles for 250 µm thick foil 37 Figure 4.5: Crack length vs. cycles for 100 µm thick foil 37 vi ii Figure 4.6: Crack length vs. cycles for 30 µm thick foil 38 Figure 4.7: Comparison of crack lengths and cycles for 30 µm and 100 µm thick foil 38 Figure 4.8: Fatigue crack growth for 250 µm thick foil at 70 MPa 41 Figure 4.9: Fatigue crack growth for 100 µm thick foil at 90 MPa 41 Figure 4.10: Fatigue crack growth for 100 µm thick foil at 120 MPa 42 Figure 4.11: Fatigue crack growth for 100 µm thick foil at 160 MPa 42 Figure 4.12: Fatigue crack growth for 30 µm thick foil at 120 MPa 43 Figure 4.13: Fatigue crack growth for 30 µm thick foil at 160 MPa 43 Figure 4.14: Fatigue crack growth for all foil thicknesses examined 44 Figure 4.15: SEM micrograph of 250 µm thick foil 45 Figure 4.16: SEM micrographs of near and far from notch fracture surfaces, 100 µm 45 Figure 4.17: SEM micrographs of near and far from notch fracture surfaces, 30 µm 46 Figure 4.18: Photomicrography of crack arresting, 250 µm thick foil at 70 MPa 48 ix NOMENCLATURE LIST OF SYMBOLS α length ratio (half specimen width by half crack length) C Paris relation constant da/dN cyclic crack growth rate K stress intensity factor K fracture toughness (critical stress intensity factor) Ic ∆K stress intensity factor range ∆K threshold region th m fatigue crack growth rate exponent N cycles to failure T r cyclic plastic zone size y R stress ratio (minimum/maximum) R2 constant of correlation σ minimum stress min σ maximum stress max σ yield strength y x multiplying factor X magnifying factor Y geometry correction factor x