Multi-scale computational modeling of the effects of defects and microstructural anomalies on mechanical response of parts resulting from additive manufacturing
Restricted (Penn State Only)
- Author:
- Jiang, Panwei
- Graduate Program:
- Materials Science and Engineering (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 10, 2024
- Committee Members:
- John Mauro, Program Head/Chair
Saurabh Basu, Chair & Dissertation Advisor
Todd Palmer, Major Field Member
Darren Pagan, Major Field Member
Amrita Basak, Outside Unit Member
Ed De Meter, Outside Field Member - Keywords:
- Crystal plasticity model
Fatigue Indicator Parameter
DAMASK
Microstructure-sensitive
Lattice strutcture
Gibson-Ashby model
Texture
Grain morphology - Abstract:
- The mechanical response of metallic parts is governed by their microstructural attributes. Process-induced defects such as pores, surface roughness, and anomalous (heterogeneous) microstructures can complicate this response. Understanding these effects is crucial for designing trustworthy performance-critical parts. However, the stochastic nature of microstrucure attributes, and process defects makes empirical delineation of these effects costly. Herein, the overarching goal of this research is to understand how defects and anomalous microstructure features affect the performance of materials and structures resulting from additive manufacturing. The methodology involves establishing microstructure-specific, and macro-structure-specific computational simulation pipelines so that these effects can be delineated. The effect of anomalous microstructure features on the fatigue of Ti alloy Ti6Al4V was studied. Herein, the effects arising from crystallographic textures, and grain morphologies were analyzed in two microstructures from the study that exhibited good, and poor performance in empirical fatigue life characterizations. This was done using numerical simulations wherein pseudo measures of the propensity of a microstructure to fail by fatigue loading were extracted. It was seen that grain morphology plays a significant role in governing these pseudo measures, and some origins of this effect were explored. The effect of porosity defects on the elastic response of lattice structures was delineated. Traditional approaches to delineate such effects have relied on the Gibson-Ashby model, wherein the effect of defects, as well as the elastic response of the originally designed structure are encapsulated within the same relationship. However, this approach does not enable one to parameterize the isolated effect of changes to the original design, or defect density. This is important from the prespective of design as it enables a designer to create structures that are resilient against unexpected process defects. Herein, a multiplicative change to the Gibson-Ashby model is proposed that accounts for porosity and surface roughness defects. The implications of this modeling approach are studied with respect to simple body-centered-cubic lattice structures that can be produced by additive manufacturing.