Nominated by Yale University as an outstanding Ph.D. thesis
Investigates microstructure-property relationships in bulk metallic glasses using a novel quantitative approach by which influence of the second phase features on mechanical properties can be independently and systematically analyzed
Provides insight to a wide range of problems including complex microstructural architectures, stochastic foam designs found in nature, as well as flaw tolerance and sensitivity studies of different classes of materials
Dr. Baran Sarac received his B.S. degree in metallurgical and materials engineering and mechanical engineering from Middle East Technical University, Ankara, Turkey. He has completed his masters and doctorate degree in the Department of Mechanical Engineering and Materials Science at Yale University, New Haven, CT, under the mentorship of Prof. Jan Schroers. He worked successively as a postdoctorate researcher in Helmholtz Zentrum Geesthacht for one year, and has recently embarked on his new position at Leibniz Institute, IFW Dresden with the same title on mechanical and functional characterization of smart alloy systems. His other research interests include structural design, thermoplastic forming, in-situ testing and morphological characterization of advanced cellular structures, as well as numerical simulations of superplastic materials via finite element analysis.
Through his studies at Yale University, Dr. Sarac has been entitled to several esteemed awards, including 2013 Yale University Harding Bliss Prize owing to his contributions to further the intellectual life of the Yale School of Engineering & Applied Science, Pierre W. Hoge fellowship (between 2008-2009), and 2012 Materials Research Society Fall Best Poster Award. His publications have appeared in peer reviewed international journals such as Nature Communications, Advanced Functional Materials, Acta Materialia, Materials Letters,illegalscripta Materialia, and Journal of Microelectromechanical systems (IEEE), where he was concomitantly involved in federal research projects of DARPA and US Department of Energy.
This thesis consists of an in-depth study of investigating microstructure-property relationships in bulk metallic glasses using a novel quantitative approach by which influence of the second phase features on mechanical properties can be independently and systematically analyzed. The author evaluates and optimizes the elastic and plastic deformation, as well as the overall toughness of cellular honeycombs under in-plane compression and porous heterostructures under uniaxial tension. The study reveals three major deformation zones in cellular metallic glass structures, where deformation changes from collective buckling showing non-linear elasticity to localized failure exhibiting a brittle-like deformation, and finally to global sudden failure with negligible plasticity as the length to thickness ratio of the ligaments increases. The author found that spacing and size of the pores, the pore configuration within the matrix, and the overall width of the sample determines the extent of deformation, where the optimized values are attained for pore diameter to spacing ratio of one with AB type pore stacking.
1.General Introduction 1.1 Motivation and Scope of Complex Materials 1.2 An Overview of Metallic Glasses 1.3 Processing of Metallic Glasses 1.4 Mechanical Property Enhancement in MG Composites 1.5 References 2. Fabrication Methods of MG Artificial Microstructures 2.1 Metallic Glass Alloy Synthesis 2.2 Silicon Mold Fabrication 2.3 Fabrication Methods of Artificial Microstructures 2.4 Conclusions 2.5 References 3. Structural Characterization of Metallic Glasses 3.1 Formability Test 3.2 Thermal Analysis 3.3 Structural Analysis 3.4 Bend Test 3.4 Conclusions 3.5 References 4. Artificial Microstructure Approach 4.1 Objectives 4.2 Periodic Cellular Structures of Metallic Glasses 4.2.1 MG Cellular Structure Sample 4.2.2 In-Plane Compression Test 4.2.3 Euler Buckling Instability 4.2.4 Results and Discussion 4.2.4.1 Deformation Regions of MG Cellular Structures 4.2.4.2 Manipulation of Geometry 4.2.4.3 Cellular Structures of Different Materials 4.2.4.4 Energy Absorption Capacity 4.2.4.5 Microstructural Optimization 4.2.4.6 Embrittlement of MGs 4.2.4.7 Comparison with Numerical Simulations 4.2.4.8 Mechanical Characterization under Uniaxial Tension 4.2.4.9 Mechanical Characterization at Different Orientations 4.2.5 General Findings & Conclusions 4.3 Toughening Mechanisms in Metallic Glasses 4.3.1 Uniaxial Tensile Test 4.3.1.1 Effect of Pore Size 4.3.1.2 Effect of Morphology 4.3.1.3 Effect of Pore Spacing 4.3.1.4 Effect of Pore Shape 4.3.1.5 Effect of Material Type 4.3.1.6 Effect of Pore Number 4.3.1.7 Effect of Electroplating 4.3.1.8 Microscopic Analysis of the Deformation Mechanism 4.3.1.9 Mechanical Property Optimization through d/s 4.3.1.10 Comparison with Numerical and Empirical Models 4.3.1.11 Effect of Isothermal Annealing on Mechanical Properties 4.3.2 Investigation of MG Composites Using FEM Analysis 4.3.3 General Findings & Conclusions 4.4 References 5. General Conclusions and Outlook 5.1 General Conclusions 116 5.2 Push the Limit: 3D Metallic Glass Structures 5.3 Multiple Material Artificial Microstructures 5.4 Non-Periodic Cellular Structures & Flaw Tolerance 5.5 Algorithmic Topological Optimization 5.6 Fracture Toughness in MG Heterostructures 5.7 Other Application Fields of MG Heterostructures 5.8 References.
General Introduction.- Fabrication Methods of MG Artificial Microstructures.- Structural Characterization of Metallic Glasses.- Artificial Microstructure Approach.- General Conclusions and Outlook.
Dr. Baran Sarac received his B.S. degree in metallurgical and materials engineering and mechanical engineering from Middle East Technical University, Ankara, Turkey. He has completed his masters and doctorate degree in the Department of Mechanical Engineering and Materials Science at Yale University, New Haven, CT, under the mentorship of Prof. Jan Schroers. He worked successively as a postdoctorate researcher in Helmholtz Zentrum Geesthacht for one year, and has recently embarked on his new position at Leibniz Institute, IFW Dresden with the same title on mechanical and functional characterization of smart alloy systems. His other research interests include structural design, thermoplastic forming, in-situ testing and morphological characterization of advanced cellular structures, as well as numerical simulations of superplastic materials via finite element analysis.
Through his studies at Yale University, Dr. Sarac has been entitled to several esteemed awards, including 2013 Yale University Harding Bliss Prize owing to his contributions to further the intellectual life of the Yale School of Engineering & Applied Science, Pierre W. Hoge fellowship (between 2008-2009), and 2012 Materials Research Society Fall Best Poster Award. His publications have appeared in peer reviewed international journals such as Nature Communications, Advanced Functional Materials, Acta Materialia, Materials Letters,illegalscripta Materialia, and Journal of Microelectromechanical systems (IEEE), where he was concomitantly involved in federal research projects of DARPA and US Department of Energy.
