Abstract USAF structures operate under more rigorous requirements than their commercial counterparts. Consequently, harsh environmental conditions in combat zones and aging fleets are of paramount concern. In light of these issues, extra low interstitial grade titanium-alloys present excellent corrosion resistance, and are lightweight, making them attractive materials for expanded use in USAF applications to improve aircraft structure components. However, the material fatigue strength of these alloys is significantly affected by variation in internal microstructural. For example, fatigue crack initiation and early growth that account for about 2/3 of the total life depends strongly on the grain boundaries (GBs), and other defects. Hence, the objective of this 3-year research project is to qualitatively and quantitatively map the relationship between GB characters or precipitate coherencies and material cohesive strengths with crack initiation and short-crack growth (SCG) mechanisms of Ti-6Al-4V-alloys. To achieve this objective, the technical approach consists of multiple tasks aimed at (i) quantify crack initiation mechanics in HCP materials based on the energetics of twin boundary- and GB-dislocation interactions; (ii) quantify appropriate nonlocal cohesive zone models (nCMZ) using an atomistic method, for single crystal, various GB and interfaces; (iii) develop an extended-finite element with a crystal plasticity model, a crack initiation criterion, nCZMs, and a wavelet time scaling method to study SCG mechanisms; and (iv) verifying the quantitative relationship between the crack plane twist/tilt angle and resistance to crack growth by studying crack growth from a fine notch with different twist angles relative to the primary slip plane in a coarse grain. The proposed work will advance the design technology (models for the digital twin concept) for more fatigue resistant alloys and the methodology for more accurate life prediction of key metallic components in engineering systems and directly respond to rigorous and evolving USAF needs for lightweight, strong, and reliable materials.
|Effective start/end date||3/15/13 → 3/14/16|
- DOD-USAF-AFRL: Air Force Office of Scientific Research (AFOSR): $346,371.00