Dynamics of Dwell Fatigue in Microtextured Titanium Alloys.
Abstract
Improved prediction of the behavior of structural materials under the complex loading conditions encountered in naval ship and aircraft components is critical to ensure reliable, long-term performance and to guide the design of new materials along high controlled processing paths. However, a major challenge for structural materials is the strong dependence of the intrinsic plasticdeformation processes on material structure, with important features at the nanoscale, microscale and mm-scale in most classes of metallic materials. Slip processes under monotonic and cyclic loading are typically highly heterogeneous, propagating through complex microstructure dominatednetworks, ultimately resulting in local cracking and failure. The predictive challenge is all the more difficult in structural titanium alloys since (i) deformation is a time-dependent dynamic process at ambient temperature, (ii) the alloys display complex microstructure features at both the microscopic and mesoscopic scale, (iii) multiple deformation mechanisms exist at roomtemperature, including deformation twinning, slip and grain boundary sliding and (iv) cyclic properties exhibit some undesirable and not well understood dependencies on loading waveform and microtexture..The overarching goals of this proposed research program are to (1) integrate and extend emerging experimental techniques that reveal the dynamics and 3D spatial evolution of the deformation processes that occur during monotonic and cyclic deformation of microtextured titanium, (2) use the experimental information to critically evaluate and further develop models for yielding and fatigue and (3) to make models and 3D data broadly available to the Navy and its suppliers for usein life prediction or for development of improved processing paths. Of particular interest are the dynamics of the deformation processes that contribute to premature dwell fatigue failures in microtextured titanium alloys and the discovery and acquisition of the representative microstructural volume elements relevant to the cyclic loading process. At the mesoscale (~m to mm) protocols for acquisition, segmentation and analysis of 3D TriBeam datasets of model andcommercial titanium alloys will be developed. These datasets will provide new insights on the microstructural networks that enhance local deformation and will complement dynamic topotomographic synchrotron-based experiments at the same scale. At finer lengthscales (nm to ~m), new Heaviside digital image correlation (H-DIC) approaches will be deployed to acquire high spatial resolution quantitative measurements of deformation processes at the scale individual phases and grains. Newly developed in-situ transmission scanning electron microscopy (TSEM) straining approaches will provide complementary dynamic information on time-dependent dislocation and twinning processes at this scale. Information from this unique set of experimental techniques will provide critical input for, and validation of, the predictions of crystal plasticity,viscoplastic FFT (fast Fourier transform) and analytical models for deformation and crack initiation under cyclic loading conditions.Anticipated outcomes of the research include: (i) new insights and quantitative information on time-dependent deformation mechanisms in microtextured titanium alloys (ii) three dimensional information on structure and deformation dynamics from the nm to meso lengthscales (iii) 3D datasets and model outputs openly available to the naval community and its suppliers for continueddevelopment of predictive tools for the behavior of titanium alloys in aircraft and ship applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 24, 2019
- Source ID
- N000141912129
Entities
People
- Tresa M. Pollock
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara