Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: Fatigue Characterization Using Advanced Experimental Methods in 2D and 3D
Sponsored by: TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Garrett Pataky, Clemson University; Ashley Spear, University of Utah; Jean-Briac le Graverend, Texas A&M University; Antonios Kontsos, Drexel University; Brian Wisner, Ohio University
Monday 8:00 AM
February 24, 2020
Room: 11A
Location: San Diego Convention Ctr
Session Chair: Antonios Kontsos, Drexel University
8:00 AM Invited
Fatigue Damage Initiation in Nickel Superalloys by Slip Localization and Redistribution: J.C. Stinville1; Patrick Callahan2; M. P. Echlin1; Marie-Agathe Charpagne1; A.T. Polonsky1; Valery Valle3; I.J. Beyerlein1; T. M. Pollock1; 1University of California, Santa Barbara; 2Naval Research Laboratory; 3Institut P' - UPR 3346, CNRS - Université de Poitiers - ENSMA
Fatigue crack initiation is governed by the early localization of plasticity during cyclic loading and the transition from plastic localization to damage. High-resolution digital image correlation (HR-DIC) is used to measure the early localization of strain and then Tribeam tomography of the same region captures the sub-surface 3D microstructures that govern damage accumulation. These advanced experimental techniques are used to elucidate the processes that lead to crack initiation during low cycle fatigue at room temperature for nickel base superalloys. A slip redistribution mechanism is observed during the first fatigue cycle, where a complex evolution of the distribution of strain localization near specific twin boundaries occurs. The slip redistribution is present prior to the formation of persistent slip bands and ultimately leads to crack nucleation.
8:20 AM
Multiscale Analysis of Fatigue Crack Initiation in Stainless Steel 316L: Pragna Bhaskar1; Josh Kacher1; 1Georgia Tech
Twin and high angle grain boundaries are known to play important roles in crack initiation processes during cyclic loading in ductile FCC materials such as stainless steel 316L. However, little is known of the developing dislocation state leading up to crack formation. To study the evolving deformation state at twin and grain boundaries, a multiscale characterization approach combining electron backscatter diffraction (EBSD)-based geometrically necessary dislocation density measurements with site specific transmission electron microscopy (TEM) analysis was applied at interrupted stages of fatigue loading. In this approach, EBSD data are used to generate a statistical understanding of how microstructure characteristics such as grain size and grain boundary characteristics influence dislocation accumulation and to guide site selection for TEM analysis. Results will be discussed in terms of crack formation mechanisms at grain and twin boundaries and how boundary characteristics influence dislocation accumulation patterns.
8:40 AM
Unraveling Cyclic Deformation Mechanisms of a Precipitate-strengthened Magnesium Alloy using In-situ Neutron Diffraction: Di Xie1; Zongyang Lyu1; Ke An2; Yan Chen2; Peter Liaw1; Yanfei Gao1; 1the University of Tennessee; 2Oak Ridge National Laboratory
The accelerated adoption of magnesium alloys as structural components in the automobile and aerospace industry is driven by their unique properties. However, very limited works have been done for the plasticity and fatigue mechanisms of magnesium alloys. The alternate twinning and detwinning behavior in a precipitation-strengthened magnesium alloy was investigated using in situ neutron diffraction during the cyclic deformation along the extrusion direction at constant strain amplitude of +/-1% at room temperature. The connection between the macroscopic behavior and the microscopic response during cyclic deformation at the grain level was established. Meanwhile, the effect of precipitates on the fatigue behavior of magnesium alloy using in situ neutron diffraction method has been studied, which may have profound guiding significance for the application and design of next-generation structural materials.
9:00 AM
Fatigue Behavior and Modeling of PEEK Polymer under Uniaxial and Multiaxial Loadings: Rakish Shrestha1; Jutima Simsiriwong2; Nima Shamsaei1; 1Auburn University; 2University of North Florida
Engineering thermoplastics are being extensively used in aerospace, automotive, and bio-medical industries as a lightweight alternative for manufacturing structural components that are subjected to cyclic loading. As a result, the understanding of fatigue behavior of polymeric materials, especially under various realistic cyclic loading conditions, need to be fully obtained. In this study, the fatigue resistance of polyether ether ketone (PEEK), an engineering thermoplastic, is investigated under various strain-controlled loading conditions. These include (I) uniaxial fatigue tests with and without mean strains, (II) uniaxial fatigue tests with variable amplitude loadings, and (III) multiaxial fatigue tests. Deformation behavior for PEEK polymer under different loading conditions is discussed using both macroscopic and microscopic analyses. A damage parameter capable of correlating the fatigue life obtained from various loading conditions is also proposed.
9:20 AM
Experimental-numerical Analysis of the Correlation Between the Stress & Strain Fields Induced by the Graphite Particles and the Crack Nucleation and Propagation Path in Ductile Cast Iron: Tito Andriollo1; Yubin Zhang1; Søren Fæster1; Jesper Hattel1; Varvara Kouznetsova2; 1Technical University of Denmark; 2Eindhoven University of Technology
Accurate prediction of the fatigue properties of ductile cast iron components is crucial in sectors like transport and energy production. So far, mainly empirical methods have been used to correlate the primary microstructural parameters, i.e. size and distribution of the graphite particles, to the crack nucleation and growth rate under cyclic loading. To attempt a micro-mechanical interpretation, a 3D finite element model of the region surrounding the crack tip in a compact tension specimen is created. The model consists of an internal region where the microstructure reconstructed with computed tomography – matrix plus graphite particles – is discretized and a homogenized external region where displacement boundary conditions measured via digital image correlation are applied. The results reveal the existence of a correlation between the crack nucleation site and the plastic strain accumulated during each cycle. In addition, a weaker correlation between crack propagation direction and maximum principal stress is found.
9:40 AM Break
10:00 AM
Microstructure-sensitive Evaluation of the Cyclic Behavior of Additively Manufactured Metals
: Emine Tekerek1; Brian Wisner2; Antonios Kontsos1; 1Drexel University; 2Ohio University
Progress in metal additive manufacturing (AM) methods enables the production of novel metallic parts. The resulting metals are dependent on the input material, manufacturing processing methods, and post-manufacturing treatments. Both the microstructure and mechanical properties of AM-produced metals differ from those achieved using traditional manufacturing methods. Consequently, the need to link the microstructures from AM methods with the mechanical response presents an important qualifying step towards the acceptance of such materials in engineering applications. The cyclic behavior of AM manufactured Ti-6Al-4V and AlSi10Mg specimens is studied using microstructure-sensitive nondestructive evaluation methods coupled with in-situ mechanical testing and Electron Back Scatter Diffraction measurements. Further, pre- and post-test X-ray micro-computer tomography and surface profilometry were used to characterize porosity levels and surface roughness. The combination of these methods revealed the role of microstructural characteristics on the initiation and development of localized cyclic damage which was related to the manufacturing and processing parameters.
10:20 AM
In-situ Characterization and Modelling of Cyclic Deformation in Rare-earth Magnesium Alloys: Duncan Greeley1; Mohammadreza Yaghoobi1; Darren Pagan2; Veera Sundararaghavan1; John Allison1; 1University of Michigan; 2Cornell High Energy Synchrotron Source
Rare-earth magnesium alloys are attractive materials for lightweighting due to their low density and high strength-to-weight ratio. In structural transportation applications, fatigue damage is a primary concern and understanding underlying deformation mechanisms is essential for accurate prediction of component life. In this study, cyclic deformation in Mg-2.4wt.%Nd was tracked in-situ utilizing High Energy X-Ray Diffraction Microscopy (HEDM) at the Cornell High Energy Synchrotron Source (CHESS). Full-volume unloaded grain morphology and local orientation were measured with near-field HEDM. Evolution of grain-by-grain slip system activity and twinning in a single displacement-controlled, fully-reversed loading cycle was characterized with far-field HEDM for the Mg-Nd alloy in as-extruded and solution heat treated conditions. Cyclic strain evolution was modelled using PRISMS-Plasticity, an open-source, parallel 3-D crystal plasticity finite element software package, and the dataset is publicly published in the Center for Predictive Integrated Materials Science (PRISMS) Materials Commons data repository.
10:40 AM Cancelled
Capturing the Spatial Field of Deformation Ahead of a Fatigue Crack in Hydrogen-charged 316L Stainless Steel using High Energy X-ray Diffraction: Kelly Nygren1; Daniel Banco2; Akihide Nagao3; Shuai Wang4; Eric Miller2; Darren Pagan1; 1Cornell High Energy Synchrotron Source; 2Tufts University; 3JFE Steel Corporation; 4Southern University of Science and Technology
To capture the plastic deformation field ahead of a fatigue crack, high energy X-ray diffraction is combined with a new, dictionary-based data reduction algorithm. The data processing algorithm enables new quantitative analyses of defect content in the bulk of cold-worked alloys to be performed. The utility of this new data processing method is demonstrated with a study of hydrogen-pre-charged 316L stainless steel to elucidate the role of hydrogen on the development of plasticity ahead of a fatigue crack – an important factor for understanding hydrogen-enhanced fatigue crack growth. Hydrogen is found to dramatically change the defect generation ahead of the crack. The data is interpreted with complementary electron microscopy studies for determining the effective plastic zone size. The application of this technique for in situ fatigue crack growth studies will be discussed.
11:00 AM
Characterization of Fatigue Mechanisms in Nickel Microbeams: Alejandro Barrios1; Ebiakpo Kakandar2; Xavier Maeder3; Gustavo Castelluccio2; Olivier Pierron1; 1Georgia Institute of Technology; 2Cranfield University; 3Empa, Swiss Federal Laboratories for Materials Science and Technology
This work presents two small-scale fatigue testing techniques to characterize the nanoscale crack nucleation and propagation mechanisms in electroplated Ni microbeams under bending. The microbeams were subjected to in-situ SEM high cycle and low cycle fatigue loading conditions. In the high cycle regime, crack nucleation and propagation are caused by the formation of voids that likely nucleate from the condensation of vacancies. However, in the low cycle regime, the crack propagation follows the conventional mechanisms of crack tip stress intensification. To gain further insight into the transition between these fatigue regimes, a 3D microstructural characterization of the fatigued microbeam is obtained by performing electron backscatter diffraction (EBSD) tomographies with Focused Ion Beam (FIB). In addition, finite element modeling with 3D crystal plasticity are coupled with experimental results to provide further understanding of the influence of the microstructure in the fatigue mechanisms.