Title: Modeling Microstructurally Small Fatigue Crack Nucleation in Al7075 Speaker: David Littlewood, Ph.D. Department of Mechanical, Aerospace, and Nuclear Engineering Date/Time: Wednesday, 9 July 2008, 10:00AM Location: CSRI/90 (NM) Brief Abstract: The microstructurally small crack growth regime represents 50-80% of total fatigue life and is responsible for the bulk of uncertainty in fatigue life estimation. The DARPA Structural Integrity Prognosis System (SIPS) project is concerned with improving fatigue life prediction for Al7075-T651 using a geometric approach for simulating the incubation, nucleation, and propagation stages of microstructurally small crack growth. In this talk, I will describe our current efforts in simulating the nucleation stage of crack formation that consists of damage accumulation in the neighborhood of cracked Al7Cu2Fe particle inclusions. To capture damage evolution, metrics based on stress and crystallographic slip have been integrated into a three-dimensional elasto-viscoplastic finite element formulation. The corresponding software implementation was designed for use on large-scale parallel computing systems, including the IBM BlueGene system at Rensselaer's Computational Center for Nanotechnology Innovations (CCNI). I will present initial results comparing model predictions to a series of fatigue experiments. The polycrystal models in these simulations were constructed from orientation imaging microscopy data, allowing for direct comparison of experimental observations and model predictions. Lattice orientation in the vicinity of cracked particle inclusions is shown to have a strong influence on fatigue crack nucleation. CSRI POC: John Aidun, (505) 844-1209 |