MSE Special Seminar: Ms Andrea Nicolas, The driving forces behind corrosion growth and cracking

Abstract

The service life of aluminum alloy structures is markedly lower when galvanic corrosion is present due to early crack initiation at localized pitting, with the likelihood of cracking being higher at pits spanning several microns. To understand the joint effect that the mechanical and chemical behavior of AA7050-T7451 have on the evolution of corrosion prior, during, and after its transition to cracking, the microstructure, constituent particles, mechanical strains, mechanical stresses and the corrosion morphology were experimentally characterized and computationally modeled at the micrometer level using high-resolution methods. The material was corroded under both mechanically loaded and unloaded conditions under different corrosion intervals to properly capture the evolution of corrosion before, during, and after particle fallout. For the events prior to cracking, statistical cross-correlations between the mechanical state of the material and the corrosion morphology were performed to understand the mechanisms driving corrosion at its various stages. For the cracking event and its subsequent growth, the joint analysis of strains and stresses obtained from 3D crystal plasticity models were used to calculate Fatigue Indicator Parameters (FIPs) that can quantitatively give an insight of the major mechanisms driving crack initiation and growth on pre-corroded materials. It is concluded that both corrosion growth and its transition to cracking is a multivariable event jointly driven by the local chemistry and the micromechanics in the material.

Bio

Andrea is a research assistant at the Advanced Computational Materials and Experimental Evaluation (ACME) Laboratory in the School of Aeronautics and Astronautics at Purdue University, under the advice of Professor Michael Sangid, expected to complete her PhD in May 2019. In her research, she looks at the integrated evolution of corrosion and its transition to cracking on aerospace-grade materials from both a mechanical and chemical point of view, where her expertise in high-resolution characterizations, large scale simulations, and big data statistics allow for a more holistic overview of the events driving material failure. She is the recipient of the Bilsland Dissertation Fellowship, which provides support to outstanding PhD candidates in their final year of doctoral degree completion. Prior to entering graduate school Andrea worked at Industria de Turbopropulsores, a Spanish company owned by Rolls Royce and Sener, where she was in the structural analysis team working on the development and production of aircraft turbine components subjected to severe working conditions.