Ductile Fracture Behavior of a Nickel-Based Superalloy and Thermally- Induced Strain Behavior of an Aluminum Alloy THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Jarrod Lee Smith, B.S. Graduate Program in Mechanical Engineering The Ohio State University 2015 Master's Examination Committee: Dr. Amos Gilat, Advisor Dr. Brian Harper Copyright by Jarrod Lee Smith 2015 Abstract The objective of this research is to generate experimental data that can be used to calibrate and validate constitutive models for plastic deformation and failure that are implemented in numerical simulations. In the first part of the research, tension tests are conducted at elevated temperatures on notched and unnotched thin flat specimens made of a nickel-based superalloy. The geometry of each sample is designed to induce various states of stress inherent in original jet engine components. Three-dimensional Digital Image Coorelation (3D-DIC) is used to measure the full-field deformations. The results of these tests show the setup is successful in capturing displacements and strains on the surface of each sample at elevated temperatures for ductile materials. The force versus displacement curves reveal that the nickel-based superalloy being tested exhibits thermal softening and serrated flow due to strain localizations at elevated temperatures. The second part of the research introduces a method to characterize the thermally induced strain behavior of a 6000 series aluminum alloy during the car manufacturing process. To simulate the stamping process, dogbone and rectangular strip specimens are subject to uniaxial and bending strains. A method for measuring strains on the surface of specimens during bend tests is established. Following deformation, specimens are subjected to thermal heating cycles that simulate the paint-bake cycle. The thermally ii induced strains during the heating cycle are measured for the each of the specimens. In addition, the material properties and thermal buckling behavior of the aluminum at various temperatures are investigated. The results show that specimens subject to different bending strains display elevated coefficients of thermal expansion and residual strain after being rendered to a heating cycle. The measurements from the material property and thermal buckling testing can be used to calibrate a thermally dependent material model. iii This document is dedicated to my closest friends, my family, and the memory of my mother. iv Acknowledgments Several people have helped me during my life to get to this point and I would like to take the time to thank them now. First I’d like to thank my parents Mike and Marsha whose inspiration, love, and courage throughout my life and academic career has made this possible. To my sisters Shanna and Maryssa: your guidance, love, and resilience throughout all the pitfalls and peaks of our lives has been a beacon for me to follow. To my closest friends- Bryan Middlebrooks, Patrick Burr, Lucy Leard, Michael Heit, and Jon Bentley- your friendship, support and advice has been exemplary. My Advisor, Professor Amos Gilat has been both an inspiration and incribly supportive throughout my time here and it has been a pleasure to work with him. Dr. Jeremy Seidt has been a tremendous mentor for me in and out of the laboratory and I’m eternally grateful for all of his help and guidance over the past few years. I would also like to thank Dr. Brian Harper for taking the time to serve as my thesis defense committee member. This research was funded by Pratt and Whitney and the Honda Research and Development Americas. Thanks to Mike Hribernik and Kon Haake at Pratt and Whitney for their advice and support over the completion of the research. Thanks to Ryan Hahnlen for their support in this project as well. v Lastly, I would like to thank my fellow students and colleagues from the Dynamic Materials of Mechanics Laboratory: Jeremiah Hammer, Kevin Gardner, Tim Liutkus, and Aaron Reesa. These researchers have been an important part in my experience not only through providing insight in our discussions but also through their friendship. vi Vita 2008................................................................Xenia High School 2012................................................................B.S. Mechanical Engineering The Ohio State University 2012- present .................................................Graduate Research Associate, Dynamic Mechanics of Materials Laboratory, Department of Mechanical and Aerospace Engineering, The Ohio State University Fields of Study Major Field: Mechanical Engineering vii Table of Contents Abstract ............................................................................................................................... ii Acknowledgments............................................................................................................... v Vita .................................................................................................................................... vii Fields of Study .................................................................................................................. vii Table of Contents ............................................................................................................. viii List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xii Chapter 1: Introduction ................................................................................................... 1 Chapter 2: Ductile Behavior of a Nickel-based Superalloy at Elevated Temperature ... 5 2.1 Motivation & Objectives .......................................................................................... 5 2.2 Literature Review ...................................................................................................... 7 2.2.1 Ductile Fracture .................................................................................................. 7 2.2.2 Nickel-Based Superalloys ................................................................................. 11 2.2.3 Elevated Temperature 3D DIC ......................................................................... 12 2.3 Experimental Procedures and Techniques .............................................................. 14 viii 2.3.1 Specimen Design .............................................................................................. 14 2.3.2 Elevated Temperature Experiments .................................................................. 15 2.3.3 3D-DIC Measurements ..................................................................................... 20 2.4 Results & Discussion .............................................................................................. 24 2.4.1 Smooth Uniaxial Test Series ............................................................................ 24 2.4.2 Varied Geometry Test Series ............................................................................ 25 2.4.3 Elevated Temperature Effects on Varied Geometry Test Series ...................... 26 2.4.4 Serrated Flow Effects for Varied Geometry Test Series .................................. 27 2.4.4 Fracture Locus for Varied Geometry Test Series ............................................. 32 2.5 Summary & Conclusions ........................................................................................ 34 Chapter 3: Thermally Induced Strains of a 6000 Series Aluminum Alloy.................. 36 3.1 Motivation & Objectives ......................................................................................... 36 3.2 Literature Study ....................................................................................................... 37 3.2.1 Paint-Bake Response ........................................................................................ 37 3.2.2 Thermal Buckling ............................................................................................. 39 3.3 Experimental Procedures & Techniques ................................................................. 41 3.3.1 Tension Tests .................................................................................................... 41 3.3.2 Bend Testing ..................................................................................................... 45 3.3.3 Thermal Cycling ............................................................................................... 49 ix 3.4 Results & Discussion .............................................................................................. 56 3.4.1 Initial Strain Testing ......................................................................................... 56 3.4.2 Material Property Test Series ........................................................................... 58 3.4.3 Thermal Cycle Testing ..................................................................................... 62 3.5 Summary & Conclusions ........................................................................................ 72 Appendix A: Full Experimental Results - Ductile Fracture of Nickel-Based Superalloy 74 A.1 Force versus displacement curves .......................................................................... 75 A.2 True stress versus true strain