Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: From Cyclic Plastic Localization and Accumulation to Crack Nucleation and Propagation
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing 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: Garrett Pataky, Clemson University; Ashley Spear, University of Utah; Antonios Kontsos, Drexel University; Brian Wisner, Ohio University; J.C. Stinville, University of Illinois Urbana-Champaign

Wednesday 8:30 AM
March 17, 2021
Room: RM 34
Location: TMS2021 Virtual

Session Chair: Jean-Charles Stinville, University of California - Santa Barbara


8:30 AM  
Fatigue and Dwell-fatigue Crack Initiation at (0001) Twist Boundaries in Ti Alloys : Cyril Lavogiez1; Jean-Charles Stinville2; Tresa Pollock2; Paraskevas Kontis3; Valéry Valle4; Patrick Villechaise1; Samuel Hemery5; 1ISAE-ENSMA; 2University of California Santa Barbara; 3MPIE; 4Université de Poitiers; 5Institute Prime - Ensma
    Crack initiation sites were characterized in Ti-6Al-4V submitted to fatigue and dwell-fatigue loadings. Statistically relevant data revealed that crack formation proceeds along localized slip at (0001) twist boundaries. Results from prior research have been revisited to confirm the broad relevance of this mechanism. In order to understand the role of these boundaries in the local deformation pattern eventually leading to cracking, in situ SEM tensile tests combined with EBSD were used to monitor the onset of slip activity and strain localization was characterized using high resolution DIC. Further information about the underlying mechanism and the role of these specific boundaries was provided through detailed characterization at crack initiation sites using TEM and APT.

8:50 AM  
Multi-scale Analysis of Fatigue Damage in Welded Lean Duplex Stainless Steel Components: Ayoub Elmoutaouakkil1; Anna Fraczkiewicz1; Alexandre Gay2; Jacques Stolarz1; 1Emse; 2e.l.m. Leblanc
     The purpose of the study is to investigate fatigue damage mechanisms of welded assemblies, from full-scale engineering structures to laboratory-scale components analyzed at microstructure level. In that respect, assessments of full-scale tank performance have allowed the comparison of fatigue strength of welded structures to that of its base metal. Hence, the extent of effect of welds’ material and notch effect on fatigue behavior was pointed out. Further examination of the relative potency of material and notch effect, weld-scale tests were conducted on model specimens, with geometrical and microstructural characteristics similar to that of full-scale tanks. It was demonstrated that crack initiation is the responsible damage mechanism and that failure location is more sensitive to microstructural effects than geometrical one. Furthermore, microstructure-scale analyses have confirmed that cyclic plastic activity preferentially occur within the ferrite phase, which is presumably softer than the austenitic one.

9:10 AM  Invited
Tracking Crystal-scale Cyclic Plasticity in Inconel 718 Using High Energy X-rays: Dalton Shadle1; Kelly Nygren2; Matthew Miller1; 1Cornell University; 2Cornell High Energy Synchrotron Source
    Fatigue crack initiation in ductile polycrystals during low cycle fatigue conditions depends strongly on the plastic strain history experienced by each crystal. In this work, a High Energy X-ray Diffraction Microscopy (HEDM) experiment conducted at the FAST beamline at the Cornell High Energy Synchrotron Source (CHESS) was used to quantify the evolving 3D stress state and intragrain lattice orientation of each crystal within a deforming Inconel 718 sample subjected to fully reversed cyclic loading. Correlation of the orientation distributions to the aspects of the evolving stress states - such as stress triaxiality – is used to understand the potential for crack initiation. Connections to crystal plasticity simulations are discussed.

9:30 AM  
Plastic Localization in Solid Solution and Precipitation Strengthened Inconel 718 and Its Effect on VHCF Properties: Alice Cervellon1; Damien Texier2; Marie Agathe Charpagne1; Chris Torbet1; Valéry Valle3; Jean Charles Stinville1; Tresa Pollock1; 1University of California Santa Barbara; 2Institut Clément Ader; 3Institut Pprime
    Fatigue crack nucleation in Ni-based superalloys with minimal metallurgical defects is governed by plastic strain localization in the form of microscopic fatigue shear bands near specific twin boundaries. This mechanism is observed to play a crucial role in determining fatigue life in the VHCF regime. The intensity of cyclic plastic localization, that depends on the precipitate structure of the alloy, strongly affects crack nucleation in the VHCF regime. The intensity of plastic localization has been measured by high resolution digital image correlation in a solid solution and precipitation strengthened variants of Inconel 718, and correlated to VHCF life. Both plastic localization and slip irreversibility are observed to be greatly increased by the presence of precipitates. As a consequence, a reduction in fatigue life is observed in the precipitation strengthened Inconel 718 in comparison to its solid solution version.

9:50 AM  
Microstructural and Mechanical Evolution of Aluminum 7075-T6 during Non-reversible Fatigue Loading: Joseph Indeck1; Gabriel Demeneghi1; Jason Mayeur1; Cyril Williams2; Kavan Hazeli1; 1The University of Alabama in Huntsville; 2U.S. Army Research Laboratory
    This work details microstructural changes, and their effect on subsequent mechanical properties, of aluminum 7075-T6 during non-reversible fatigue loading. Experiments on aluminum 7075-T6 at different tensile mean stresses were interrupted at 25% and 75% of the fatigue life. Scanning electron microscopy, electron backscatter diffraction, and Vickers microhardness were used to quantify changes in the microstructure of the fatigued material. Cracking of larger sized iron inclusions and an increase in voids was observed in the subsurface material due to fatigue. An increase in the total amount of voids correlated to mechanical property changes of the post-fatigued material. Quasi-static strength of the material at specific fatigue life ratios was seen to decrease as the mean stress was increased whereas dynamic strength remained constant. The presented results establish that the subsequent post-fatigue mechanical properties of aluminum 7075-T6 is dependent on both the mean stress level and the subsequent loading strain rate.

10:10 AM  
Effect of Microtexture on Minimum Dwell Fatigue Life of Ti-6Al-4V: Sushant Jha1; Daniel Sparkman2; James Larsen2; Reji John2; Adam Pilchak2; 1University of Dayton Research Institute; 2US Air Force Research Laboratory
    Near-alpha and alpha+beta titanium alloys exhibit significant debit in life under dwell fatigue loading compared to cyclic fatigue when containing microtextured regions (MTRs). The debit in life has been attributed to early initiation and faster small-crack growth through suitably oriented MTRs, via a faceted crack growth mechanism. In addition to size, density of similarly oriented grains, and crystallographic orientation, the spatial distribution of suitably oriented MTRs is a key factor affecting the distribution in dwell fatigue life. A probabilistic model that captures the effect of spatial distribution of MTRs along with other key MTR variables on the distribution in life was developed. In order to account for the spatial distribution of MTRs, a pluri-Gaussian random field model was used to generate statistically representative instantiations of MTR microstructure. The effect of MTR variables on debit in minimum dwell fatigue life was studied and compared to experimental results.

10:30 AM  
On the Role of Annealing Twin Boundaries in the Cyclic Plastic Strain Localization and the Fatigue Crack Initiation in Equiatomic CrCoNi Medium-entropy Alloy: Veronika Mazanova1; Milan Heczko1; Connor Slone1; Ivo Kubena2; Easo George3; Maryam Ghazisaeidi1; Tomas Kruml2; Jaroslav Polak2; Michael Mills1; 1The Ohio State University; 2Institute of Physics of Materials CAS; 3Oak Ridge National Laboratory
    Equiatomic CrCoNi alloy was cold-rolled and heat-treated to produce a fully recrystallized microstructure with average grain size 25 microns and annealing twin boundary (TB) fraction of 0.3. The alloy with this microstructural state combines good cyclic strength with superior resistance to cyclic plastic deformation. Among the mechanisms leading to the extraordinary performance of CrCoNi, the significant role of the TBs in the fatigue crack initiation and growth is revealed. Three different types of interactions between TBs and bands of localized cyclic slip (PSB) are studied: (1) slip transmission across TBs, (2) localization of the cyclic slip along the twin plane, and (3) PSBs impinging on the TBs. Origins of TB-PSB interactions are studied by correlative microscopy based on electron backscatter diffraction, focused ion beam, and transmission electron microscopy. The significance of different TB/matrix configurations is discussed in relation to the fatigue crack initiation and the overall fatigue resistance.

10:50 AM Reminder ... A joint session, "Microstructure-based Fatigue Studies on Additive-Manufactured Materials," will be held on Wednesday at 2 p.m. EDT in conjunction with the Additive Manufacturing Fatigue and Fracture V: Processing-Structure-Property Investigations and Application to Qualification symposium.