Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: From Plastic Localization to Damage Nucleation and Propagation
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: J.C. Stinville, University of Illinois Urbana-Champaign; Garrett Pataky, Clemson University; Ashley Spear, University of Utah; Antonios Kontsos, Drexel University; Brian Wisner, Ohio University; Orion Kafka, National Institute Of Standards And Technology
Monday 8:30 AM
February 28, 2022
Room: 254B
Location: Anaheim Convention Center
Session Chair: Jean-Charles Stinville, University of Illinois Urbana-Champaign
8:30 AM Invited
On the Relevant Scale Related to Fatigue Crack Initiation in Different Metallic Alloys: Patrick Villechaise1; Jonathan Cormier1; Samuel Hemery1; 1Institut Pprime
A way to improve metallic alloys against fatigue crack initiation is to apply thermo mechanical treatments in order to achieve a well-adapted metallurgical microstructure. To propose relevant metallurgical solutions, one needs first to identify the mechanisms governing the early stages of fatigue damage in relation with the microplasticity and the microstructure. The plastic localization within slip bands and the interactions with microstructural elements like grain/twin boundaries or other interfaces are often at the root of crack initiation. Lots of studies aim to identify the very local microstructure at the origin of cracks using the most advanced techniques for analyzing the role of crystallography, chemistry and 3D morphology. However the finest scale is not always the only one that has to be considered. This question will be discussed based on results obtained on different FCC (steels, Ni-based superalloys) and HCP (/ and -metastable Ti alloys) alloys.
9:00 AM Invited
Role of Cyclic Strain Localization in Fatigue Crack Initiation and Growth: Jaroslav Polak1; Veronika Mazanova2; Tomáš Babinský1; Milan Heczko2; 1Institute of Physics of Materials ASCR; 2CEMAS, Ohio State University
Cyclic strain localization in crystalline materials represents the important aspect in the early evolution of the fatigue damage. Recent results on polycrystalline copper, 316L austenitic steel, Sanicro 25 superaustenitic steel and René 41 superalloy were studied. AFM and SEM with the FIB cuttings are reported to show the true evolution of the persistent slip markings (PSMs). TEM and STEM studies of the foils prepared using FIB from the surface reveal the dislocation structure of persistent slip bands (PSBs) and the relation to the PSMs on the surface. The general model of localized cyclic plastic straining within PSBs and formation of the surface relief is proposed. Substantial role is played by point defects which are continuously produced within PSBs. Migration of point defects leads to mass redistribution and formation characteristic PSMs in the form of extrusions and intrusions. Crack-like intrusions induce localized slip-unslip leading to crack initiation and stage I growth.
9:30 AM
Influence of Compressive Hold Times In Dwell-fatigue of Alloy 718: Melanie Bordas-Czaplicki1; Jonathan Cormier2; Patrick Villechaise2; Vincent Roue3; 1Safran Aircraft Engines - ENSMA - Institut Pprime - UPR CNRS 3346; 2Institut Pprime; 3Safran Aircraft Engines
The impact of hold times in tension and/or compression has been investigated in DA718 Inconel alloy. All tests were carried out at 650 °C, in stress-controlled mode, trapezoidal waveform at Rσ=-1 and 10 s hold times at maximum and/or minimum stress. Compared to pure tensile dwell-fatigue tests, compression drastically reduced the fatigue life and alloy’s ductility independently of the tension hold time. The evolution of maximum and minimum of plastic strain followed the same trend for each condition. Crack initiation from surface non-metallic particles and mixed micro-propagation has been systematically observed. Damage mechanisms were studied through interrupted tests by following crack initiation on the gauge length thanks to a SEM. Initiation at particles appeared at the first cycles for each waveform. It has been observed an interaction between environment and delta phase at grain boundaries followed by crack initiation.
9:50 AM
Cyclic Plasticity and Fatigue Properties of Ultra-high Strength CrCoNi Medium-entropy Alloy with Heterogeneous Partially Recrystallized Microstructure: Milan Heczko1; Veronika Mazánová1; Connor Slone2; Ivo Kuběna3; Jiří Tobiáš3; Tomáš Kruml3; Easo George4; Maryam Ghazisaeidi1; Jaroslav Polák3; Michael Mills1; 1The Ohio State University; 2Exponent, Inc.; 3Institute of Physics of Materials CAS; 4Oak Ridge National Laboratory
The effect of tunable partially recrystallized (PRX) heterostructures on the cyclic plasticity and overall fatigue performance of equiatomic CrCoNi was investigated. After specific processing steps of cold-rolling and heat-treatment the alloy was subjected to strain-controlled low cycle fatigue tests at room temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated. The evolution of the internal critical stresses and the effective saturated stress during cyclic loading was analyzed using a generalized statistical theory of the hysteresis loop. The deformation substructure was studied by atomic resolution electron microscopy and correlated with the cyclic response. EBSD and SEM-FIB were used to identify mechanisms leading to fatigue crack initiation and growth. It is revealed that CrCoNi alloy with PRX microstructure exhibits ultra-high monotonic and cyclic strength and extraordinary fracture toughness while preserving good ductility and resistance to cyclic plastic deformation.
10:10 AM Break
10:25 AM
Role of Twins on Localization of Cyclic Strain and Fatigue Crack Initiation in CrCoNi Medium-entropy Alloy: Veronika Mazanova1; Mulaine Shih1; Milan Heczko1; Connor E. Slone2; Easo George3; Jaroslav Polak4; Maryam Ghazisaeidi1; Michael J. Mills1; 1The Ohio State University; 2Exponent; 3Oak Ridge National Laboratory; 4Institute of Physics of Materials CAS
Mechanical properties and mechanism related to monotonic deformation has been thoroughly studied in MPEs. However, there remains a lack of knowledge about the fatigue behavior and associated mechanisms. In the current work, attention is focused on the localization of cyclic strain in the equiatomic CrCoNi alloy in fully recrystallized microstructural state. Although the alloy is characterized by high fraction of annealing twin boundaries, the early fatigue-induced surface relief is found to occur preferentially along thin deformation twins. The effect of twin size on the preferential localization of cyclic strain and fatigue crack initiation was studied using a sophisticated experimental workflow designed to extract information from the surface and the bulk of tested material by SEM, EBSD, ECCI, FIB and HR-STEM. Experimental results are complemented by atomistic modeling of the local stress states in association with different twin sizes under an applied load.
10:45 AM
Enhancing Fatigue Crack Growth Resistance of High Strength Aluminum Alloys Reinforced by Shape Memory Alloy: Nelson Affonseca Netto1; Lv Zhao2; Eric Charkaluk3; Aude Simar1; 1Institute of Mechanics, Materials and Civil Engineering, Université Catholique de Louvain, Louvain la Neuve, Belgium; 2Department of Mechanics, School of Aerospace Engineering, Huazhong University of Science and Technology, Wuhan, China; 3Laboratoire de Mécanique des Solides, CNRS, École Polytechnique, Palaiseau, France
In the framework of metal matrix composites (MMCs), shape memory alloys (SMAs), when serving as reinforcements, provide a possibility to tune cracking mechanisms due to their shape memory effect (SME). The SME is used to introduce local internal stresses in the vicinity of the reinforcements, attracting or repelling the propagating crack, therefore leading to fracture path deviation and enhancing resistance to crack growth. In the present work, nitinol (NiTi) particles were used as particulate reinforcements for Al7075 and the composites have been manufactured via friction stir processing (FSP) to prove the aforementioned concept. According to fatigue crack propagation tests, the Al7075/NiTi composites present lower fatigue crack growth rate compared to the FSPed Al7075 reference material as well as the Al7075/NiTi composites without internal stresses. Digital image correlation (DIC) analysis allows for an understanding of the plasticity and damage mechanism at the crack tip during its propagation.
11:05 AM
Crack Initiation and Growth Behavior of Additively Manufactured Contemporary Aluminum Alloys: Surface Roughness, Micro-/Defect-structure, and Build Orientation: Pooriya Nezhadfar1; Muztahid Muhammad1; Mikyle Paul1; Spencer Thompson2; Ankit Saharan2; Nam Phan3; Nima Shamsaei1; 1Auburn University; 2EOS GmbH; 3Naval Air Systems Command
Aluminum alloys are one of the prominent materials for additive manufacturing (AM), and much effort has been devoted to developing novel, high-strength aluminum alloys. However, the fatigue performance of these alloys needs to be thoroughly investigated before being deployed in critical load-bearing applications. It is well known that surface roughness, micro-/defect-structure, and build orientation can affect AM materials' different stages of fatigue behavior, including their crack initiation and growth. Accordingly, this study investigates the crack initiation and growth behavior of six aluminum alloys in different surface conditions and build orientations fabricated via a laser beam powder bed fusion (LB-PBF) AM process. The role of surface roughness and micro-/defect-structure on the crack initiation behavior of these alloys is investigated. In addition, the effect of build orientation on micro-/defect-structure, and consequently, on fatigue crack initiation and growth behavior of these alloys are addressed, and anisotropy in fatigue behavior is discussed.
11:25 AM
Microstructures, Mechanical Properties, and Fatigue Damage Mechanisms in Laser Powder Bed and Conventionally Cast Al-10Si-0.4Mg Alloys: Timothy Piette1; Robert Warren1; Anthony Spangenberger1; Diana Lados1; 1Worcester Polytechnic Institute
Laser powder bed (LPB) manufactured Al-10Si-0.4Mg was studied in as-fabricated, stress relieved, T6, and HIP+T6 conditions to understand processing, post-processing, and build orientation effects on mechanical properties. Associated microstructural changes, tensile properties, and fatigue crack growth (FCG) microstructure-scale mechanisms were investigated and compared with those of the conventionally cast counterparts. Anisotropic residual stresses in the as-fabricated condition affect the FCG thresholds, resulting in differences between build orientations. Heat treatments significantly alter the microstructure, affecting the orientation dependence of the properties and changing both FCG threshold values and crack growth mechanisms at different stages. Complementary fatigue testing up to the very-high-cycle fatigue regime was performed to relate the effects of build orientation, heat treatment, surface condition, and defect morphology and distribution (evaluated using x-ray computed tomography) to fatigue life. Recommendations for microstructure and post-processing optimization and integrated design for high-integrity fatigue-critical applications will be provided and discussed.
11:45 AM
Effect of Wire Size on the Fatigue Life of Superelastic Nitinol: Parisa Shabani Nezhad1; Jacob Rusch1; John Moore1; Dinc Erdeniz2; 1Marquette University; 2University of Cincinnati
Superelastic nitinol finds a wide range of applications in the aerospace and medical industries due to its shape-recovery ability. In most of its applications, nitinol is subjected to cyclic loads within its superelastic stress-strain range. Due to the complex nature of the martensitic transformations, the existing fatigue theories do not accurately predict the nucleation and propagation of fatigue cracks in superelastic nitinol, which may endure fatigue damage that leads to structural and/or functional degradation. It has been shown that, other than the surfaces, the major fatigue crack initiation sites are the microstructural imperfections such as voids and non-metallic inclusions. Among all the factors affecting fatigue performance, the size effect has received less attention. In this research, superelastic nitinol wires with three different diameters are examined to explore the effect of wire size on the nucleation and propagation of fatigue cracks near the wire surface and around the non-metallic inclusions.
12:05 PM
Understanding the Connections Between Microstructural Features and Fatigue Crack Initiation and Propagation Properties in Medical Formulations of Ultra-high-molecular-weight-polyethylene (UHMWPE): Bethany Smith1; Qin Yu2; Lisa Pruitt1; Robert Ritchie1; Samantha Kwan1; Alex Sangster3; Jon Ell1; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory; 3Marlboro Academy
Though UHMWPE has been used in joint replacements since the 1960’s, newer processing techniques and chemical formulations are introduced regularly to improve clinical performance, creating new research opportunities in an otherwise well-studied material. This research investigates how crystallinity, inter-lamellar spacing, lamellar thickness, and amount of crosslinking affect both the fatigue crack initiation and propagation properties in multiple medical formulations of UHMWPE. To accomplish this, differential scanning calorimetry (DSC) and small-angle x-ray scattering (SAXS) techniques were implemented to characterize the microstructures of five medically-relevant UHMWPE formulations. Afterwards, CT specimens adhering to ASTM E647 were used to create da/dN vs.ΔK curves under both ΔK increasing and decreasing conditions for those same formulations. Using Paris Law constants C and m and threshold ΔK's as comparison metrics, preliminary results indicate that microstructural features that increase ΔK threshold tend to also have a negative effect on propagation properties, likely due to crosslinking impeding plastic deformation.