Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: Advanced Experimental Characterization of Microstructurally Driven Fatigue Behavior
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
Tuesday 2:00 PM
March 16, 2021
Room: RM 34
Location: TMS2021 Virtual
Session Chair: Garrett Pataky, Clemson University
2:00 PM Invited
Microstructure and Fatigue Damage Evolution in Additive-manufactured Metals Using Enhanced Measurement Techniques and Modeling Approaches: Mustafa Awd1; Frank Walther1; Ali Fatemi2; 1TU Dortmund University; 2University of Memphis
Process-induced microstructures can have a high impact on the fatigue strength of engineering materials. Advanced materials testing builds the base for the design and manufacturing of reliable, high-performance products for various technical applications. Modern analytical and intermittent testing strategies with applied enhanced measurement techniques, i.e., physical instrumentation of testing specimens during loading, allows the characterization of process-structure-property relationships in various fatigue damage stages. In-situ mechanical testing in analytical devices like micro-computed tomography (µ-CT) enables the immediate correlation of material’s reactions with the applied loading conditions. The focus of this study lies in the characterization of fatigue damage evolution and progression before failure depending on environmental as well as material specific microstructural characteristics. Measurement-based fatigue damage tracking during testing of SLM aluminum alloys revealed the interaction between porosity and microstructure under loading in the very high-cycle fatigue (VHCF) regime. The grain boundary strengthening of the microstructure increased VHCF strength by 33%.
2:20 PM
Low Cycle Fatigue Behavior of an Optimally Produced
Additive Manufactured Aluminum Alloy: Emine Tekerek1; Vignesh Perumal1; Darren Beckett2; Scott Halliday3; Antonios Kontsos1; 1Drexel University; 2Sigma Labs; 3Navajo Technical University
The mechanical behavior of AM metals depends on their microstructures which are affected by the melt-pool geometry in laser-based methods. Such melt pool effects are defined by the used laser properties including speed and power. In this context, this talk focuses on exploring linkages between microstructures produced by the rapid AM solidification process and the low-cyclic fatigue behavior of a common AM aluminum alloy. Thermomechanical simulations are first used to define geometries which have been optimized for thermal effects. In addition, melt pool measurements are performed to establish a correlation between print parameters and manufacturing conditions. To investigate the fatigue behavior, cyclic loading inside the Scanning Electron Microscope coupled with in situ Digital Image Correlation, Acoustic Emission and microscopic investigation is used to investigate the specific role of porosity and second-phase particles. The results are coupled with solidification studies at the TEM level, as well as micro-computer tomography data.
2:40 PM
Investigation of the Fatigue Crack Behavior of 304 Stainless Steels Using Synchrotron X-ray Tomography: Ryan Schoell1; Li Xi1; Harvey West1; Zeev Shayer2; Djamel Kaoumi1; 1North Carolina State University; 2Colorado School of Mines
The fatigue crack behavior of three variations of 304 stainless steel including, commercial 304, 304H (high carbon) and 304L (low carbon) was studied using synchrotron x-ray tomography and diffraction. Fatigue cracks were developed using four-point bending on notched specimens. Smaller single-edged crack specimens were then extracted and subjected to synchrotron x-rays. X-ray tomography based on attenuation contrast showed the formation of fatigue voids in all samples. Some micro voids were elongated in a specific direction. The number density of microvoids was measured in all three samples. Scanning electron microscopy (SEM) of the as-received materials revealed elongated and spherical precipitates/inclusions. X-ray diffraction (XRD) revealed the formation of deformation induced α’-martensite and ε-martensite around the crack. The microstructure found through SEM and XRD was correlated with the crack tomography to understand the differences and similarities in fatigue crack behavior observed in the three materials.
3:00 PM
Long Range Internal Stress Assessment Using Convergent Beam Electron Diffraction and Dislocation Dipole Height in Cyclically Deformed Copper Single Crystals: Roya Ermagan1; Maxime Sauzay2; Michael Kassner1; 1University of Southern California; 2CEA Paris-Saclay
Understanding Long Range Internal Stresses (LRIS) is critical for explaining the basis of the Bauschinger effect, spring-back in metal forming, and plastic deformation in cyclically deformed metals. Few studies have assessed LRIS in cyclically deformed single crystals in single-slip while there are no such studies in multiple-slip. Here, we report on LRIS in a cyclically deformed copper single crystal in multiple-slip via two methods: 1- Lattice parameter determination using Convergent Beam Electron Diffraction (CBED) and 2- Measuring the maximum dipole heights. TEM micrographs show a labyrinth dislocation microstructure with high dislocation density walls and low dislocation density channels. Lattice parameters and dipole heights were assessed in the channels and walls of the labyrinth structure. Lattice parameters obtained were almost identical near the walls and in the channels. The maximum dipole heights were also approximately independent of location. Thus, a homogenous stress state within the heterogeneous dislocation structure is suggested.
3:20 PM
Correlation between Cyclic Plastic Deformations and Strength Mismatches in Ni-Steel Dissimilar Joints under Isothermal Low-cycle Fatigue Tests: Shutong Zhang1; Sebastian Romo1; Rafael Arthur Giorjao1; Antonio Ramirez1; 1Ohio State University
Welding repairs technologies have been widely adopted to restore the damages of large pressure vessels like coke drums that endure severe cyclic loading conditions. However, due to the intrinsic mismatching strengths and microstructures, the fatigue life of dissimilar repair joints is significantly compromised by the concentrations of plastic deformations at susceptible regions. Correlating plastic deformations with localized strength mismatches and constraining effect can contribute to the accurate prediction of susceptible regions and fatigue life of the joints. In this study, the low-cycle fatigue behaviors of Ni-Steel dissimilar joints are evaluated using digital image correlation (DIC), which is an in-situ technique to characterize the strain distributions in mesoscale level. Local strength mismatches at weld transition characterized by micro-hardness indentations are correlated with plastic deformations analysis. Energy-base criteria is further proposed to predict the fatigue life of stress-concentrated areas and hence to predict the fatigue life of joints.
3:40 PM
High and Very High Cycle Fatigue Behavior of Additively Manufactured 17-4 PH Stainless Steel: The Effect of Shielding Gas: Pooriya Nezhadfar1; Jade Welsh2; Jutima Simsiriwong2; Shuai Shao1; Nima Shamsaei1; 1Auburn University; 2University of North Florida
Shielding gas is one of the process parameters that can affect the heat transfer and solidification during the layer-wise additive manufacturing (AM) processes, which may be influential in altering the microstructure and porosity of the fabricated part. This study deals with the effect of shielding gas type (N2 vs. Ar) on the microstructure and mechanical properties of 17-4 PH stainless steel (SS) fabricated through laser beam powder bed fusion (LB-PBF) AM process. Fatigue resistance of the material is evaluated in the high and very high cycle regimes. Due to the microstructural differences, particularly refined micro-/defect-structure, fatigue performance of N2-shielded specimens is expected to be superior to that of Ar-shielded counterparts in the high cycle regime. The effect of cyclic strain rate on the fatigue behavior of specimens manufactured under N2 and Ar atmospheres, with different microstructure and porosity levels, will be also discussed.
4:00 PM
An In-situ Analysis on the Fatigue Damage in Martensitic Spring Steel: Anna Wildeis1; Matthias Thimm1; Robert Brandt1; Hans-Jürgen Christ1; Claus-Peter Fritzen1; 1University of Siegen
In the high cycle fatigue regime, crack initiation and short crack propagation can account for up to 90% of the fatigue life, which is an important motivation for studying these fatigue stages. However, the underlying mechanisms for short crack propagation in a martensitic spring steel are still not clear, especially if residual stresses must be taken into account. This investigation aims at the investigation of short crack propagation in a martensitic spring steel by means of in-situ fatigue tests in a confocal laser microscope and additional electron back-scattered diffraction analyses to link the local crystallographic orientation of the hierarchical martensitic microstructure with the short crack propagation behaviour. In order to determine the effect of residual stresses, samples are tested with and without prior shot peening treatments. Furthermore, the adaptation of a short crack model based on the boundary element method to the results obtained is presented.
4:20 PM
Post-fatigue Study of SLM Ti64 Medical Implant by 3D Correlative Microscopy: Bartlomiej Winiarski1; Matteo Benedetti2; Philip Withers3; 1Thermo Fisher Scientific; 2University of Trento; 3The University of Manchester
Open-porous Ti64 scaffolds are attractive in the field of biomedical implants, since these show reduced stress-shielding and improved osseointegration. Mechanical properties and geometric characteristics of implant scaffolds are tailored to match that of a patient’s bone by using of CAD and FE analysis. Later implants are produced by means of various additive manufacturing routes. In a previous study, the results of fatigue and quasi-static tests of hot isostatic pressed (HIP) Ti64 scaffold were compared with FE calculations based on the as-designed geometry of a regular cubic cellular scaffold and on the as-built geometry reconstructed from μCT scans.The current study investigates the fatigued and fractured HIPed Ti64 cubic cellular scaffold (from the previous study) using a 3D correlative multi-scale, multi-modal tomography and microscopy (CMT) framework. The CMT workflow combines advantages of imaging, analytical and metrological capabilities of various instruments and cross-platform correlative holder kit: helical μCT, Plasma_FIB-SEM, Laser_PFIB-SEM and TEM.