Micromechanical Modeling of the Role of Inclusions in High Cycle Fatigue Damage Initiation and Short Crack Growth

This presentation was made at CAASE18, The Conference on Advancing Analysis & Simulation in Engineering. CAASE18 brought together the leading visionaries, developers, and practitioners of CAE-related technologies in an open forum, to share experiences, discuss relevant trends, discover common themes, and explore future issues.

Resource Abstract

Multiscale microstructural and micromechanical modeling has arisen as a candidate to improve upon the classical methodologies for evaluation of fatigue crack initiation and propagation, both with respect to improving our understanding of the fundamental material deformation and damage processes as well as in establishing more accurate design rules for engineering purposes. By exploiting methodologies of multiscale materials modeling it is envisioned that engineering material properties can be directly computed based on microstructural scale analysis of single crystal plasticity and damage evolution. The models can be then further used to simulate the various dependencies affiliated with fatigue damage arising from material microstructure, such as the effects of stress triaxiality, compressive loading and overall complex stress states. The overall goal of these efforts is the general decrease in empirism, inaccuracy and affiliated uncertainty in the fatigue modeling and design chain.
Current work utilizes a novel crystal plasticity coupled damage model to evaluate inclusion to steel microstructure interactions with the objective of better understanding and quantifying the role inclusions play with respect to nucleation and growth of microstructure scale fatigue cracks. The approach is microstructural, i.e. material characteristics such as microstructural morphologies, individual phases and inclusions are included explicitly in the numerical finite element models and the subsequent behavior with respect to single crystal deformation and initiation of fatigue damage can be directly witnessed. A micromechanical model where crystal plasticity and damage are directly coupled is employed in the analysis. As such, the appearance of material damage during cyclic loading at microstructural cleavage planes can be observed based on single crystal slip as well as interactions arising from the stress-strain states of the inclusion and the metallic microstructure.
A case study is carried out for primarily martensitic quenched and tempered steel for machine construction. The mechanisms of deformation during cyclic loading and the role of differing loading ratios are assessed along with implications with respect to fatigue damage. The role of inclusion properties and its size relative to the martensitic microstructure are addressed and discussed. Damage evolution in relation to inclusion characteristics is found to be in line with classical empirical criteria utilized in pursuing validation of the material models and the computational methodology. The results suggest potential ways of exploiting multiscale materials modeling in design of fatigue resistant microstructures, optimization of material solutions and in improved fatigue design of products and components.

Document Details

AuthorFrondelius. T
Date 5th June 2018
OrganisationWartsila Finland Oy


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