Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling: Multi-Mechanical Interactions during Extreme Environment Fatigue Loading
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
Wednesday 8:30 AM
March 2, 2022
Room: 254B
Location: Anaheim Convention Center
Session Chair: Brian Wisner, Ohio University
8:30 AM Invited
Damage Manifestation in Hydrogen-assisted Fatigue: Matthew Connolly1; May Martin1; Robert Amaro2; Peter Bradley1; Damian Lauria1; Jun-Sang Park3; Zack Buck1; Andrew Slifka1; 1National Institute of Standards and Technology; 2Advanced Materials Testing & Technologies; 3Argonne National Laboratory
To make reliable predictions of a structure’s lifetime, it is necessary to know the amount of damage the material undergoes during a typical service cycle and the cumulative damage the material can withstand prior to failure. The amount of damage is most often described by a single parameter, e.g. the stress-intensity factor in fatigue crack growth or strain-amplitude in strain-life testing. However, not all damage processes are equal. For equivalent plastic strain levels, damage may occur by void nucleation and coalescence, dislocation generation and movement, or grain separation and rotation. Similarly, hydrogen can affect whether, and how, mechanical loading translates to damage. Here we present simultaneous High Energy X-ray Diffraction (HEXRD) and Small-Angle X-ray Scattering (SAXS) measurements during fatiguing of steel in air and in hydrogen which demonstrate the differences in damage manifestation during hydrogen-assisted and unassisted fatigue.
8:50 AM
Spatial and Temporal Slip Heterogeneity in Ti–7Al as a Function of Oxygen Content and Crystallographic Ordering: Felicity Worsnop1; Rachel Lim2; Darren Pagan2; Joel Bernier3; Yilun Xu1; Thomas McAuliffe1; David Rugg4; Fionn Dunne1; David Dye1; 1Imperial College London; 2Pennsylvania State University; 3Lawrence Livermore National Laboratory; 4Rolls-Royce plc
Time-dependent, spatially heterogeneous slip is central to the performance of titanium alloys in aero engine applications, exemplified by the cold dwell fatigue phenomenon. Slip localisation in the hcp α phase is influenced by interstitial oxygen content and by crystallographic ordering of aluminium to form Ti3Al α2. The effects of these solutes on slip avalanching (i.e. time intermittency) are not well established. Model alloys Ti–7Al–0.05O and Ti–7Al–0.25O (wt.%) were produced in disordered and ordered states to isolate these factors. In situ high-energy X-ray diffraction microscopy was performed during creep loading, revealing the time-dependent behaviour on the slip systems of hundreds of grains in each polycrystalline specimen. Dislocation configurations after deformation were characterised in TEM. Our experiments demonstrate that, despite their similar effects in promoting spatial localisation of slip, oxygen and α2 have notably dissimilar effects on the time intermittency of slip in α titanium.
9:10 AM
Model the Initiation of Hot
Cracking during Laser Welding of Al6061: Guannan Tang1; Anthony Rollett1; 1Carnegie Mellon University
Hot cracking as one of the major defects in additive manufacturing is notoriously present during the printing of commercial Al6061. This study seeks to quantitatively understand the initiation of hot cracking in this process. In this work, we used a coupled approach between a Lattice Boltzmann method and a Cellular Automaton model to simulate the thermal history of the melting process and microstructure of the fusion zone. The evolution of the thermal stress and strain field were calculated based on those simulations, using a fast-Fourier-Transforms based method. Those results together allow us to compute the solidification shrinkage, thermal deformation and liquid back-feed at the scale of grain boundary. By finding positions where solidification shrinkage and thermal deformation exceeds the compensation by liquid back-feed, a hot cracking propensity map of all the grain boundaries can be extracted. Those will give a quantitative identification to the initiation of hot cracking.
9:30 AM
Atomic Mechanism of Near Threshold Fatigue Crack Growth in Vacuum: Mingjie Zhao1; Wenjia Gu1; Derek Warner1; 1Cornell University
Structural failures resulting from prolonged low-amplitude loading are particularly problematic. Over the past century a succession of mechanisms have been hypothesized, as experimental validation has remained out of reach. Thanks to the progression of computational resources and a new implementation of a concurrent multiscale method, we have been able to assess the validity of long-hypothesized material separation mechanisms thought to control near-threshold fatigue crack growth in vacuum, and reconcile reports of crack growth in atomistic simulations at loading amplitudes below experimental crack growth thresholds. We find that sustained fatigue crack growth in vacuum requires emitted dislocations to change slip planes prior to their reabsorption into the crack on the opposite side of the loading cycle. This provides a mechanistic foundation to relate fatigue crack growth tendency to fundamental material properties, e.g. stacking fault energies and elastic moduli, opening the door for improved prognosis and design of novel fatigue resistance alloys.