UNIVERSITY OF

ILLINOIS

URBANA-CHAMPAIGN

Stinville Research Group

Materials Science and Engineering

NEWS ABOUT US

Cyclic Slip Accumulation in Structural Metals

Our research team has made a breakthrough in understanding the micro-mechanisms that contribute to fatigue damage under tension-tension loading. These findings are detailed in our recent publication in the journal Acta Materialia. The paper, authored by R.L. Black, D. Anjaria, J. Genée, V. Valle, and J. C. Stinville, is titled “Micro-Strain and Cyclic Slip Accumulation in a Polycrystalline Nickel-Based Superalloy” .

The study challenges the commonly belief that direct or indirect slip transmission at grain boundaries is the primary factor influencing macroscopic behavior. Our research reveals that when slip transmission is inhibited, the grain boundary can undergo localized shearing. This shearing leads to the development of local compressive stresses during tensile load, which in turn cause cyclic irreversibility during cycling, even under tension-tension loading. This insight opens up new avenues for understanding and potentially mitigating fatigue damage in materials.

This work provides a comprehensive characterization and analysis of deformation and fatigue damage mechanisms in a nickel-based superalloy during ambient temperature fatigue and points to a fundamental deformation mechanism that results in the onset of crack nucleation. Strain and slip irreversibility are investigated at the nanometer scale using high-resolution digital image correlation and high-resolution electron backscatter diffraction, highlighting distinct deformation mechanisms contributing to crack nucleation. It is observed during early fatigue cycling at relatively low applied stress, the formation of intense slip events that induce grain boundary shearing. This results in intense micro-scale strain in the neighboring grains, producing localized plasticity and stresses. Such stresses facilitate fatigue extrusion-intrusion mechanisms during subsequent cycling, resulting in preferred crack nucleation. Finally, the configurations within the microstructure that promote such deformation and damage mechanisms sequence are highlighted

 

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