The goal of this research work is to further the understanding of crystal plasticity,
particularly at reduced structural and material length scales. Fundamental
understanding of plasticity is central to various challenges facing design and manufacturing
of materials for structural and electronic device applications. The development
of microstructurally tailored advanced metallic materials with enhanced mechanical
properties that can withstand extremes in stress, strain, and temperature, will aid
in increasing the efficiency of power generating systems by allowing them to work
at higher temperatures and pressures. High specific strength materials can lead to
low fuel consumption in transport vehicles. Experiments have shown that enhanced
mechanical properties can be obtained in materials by constraining their size, microstructure
(e.g. grain size), or both for various applications. For the successful
design of these materials, it is necessary to have a thorough understanding of the influence
of different length scales and evolving microstructure on the overall behavior.
In this study, distinction is made between the effect of structural and material
length scale on the mechanical behavior of materials. A length scale associated with
an underlying physical mechanism influencing the mechanical behavior can overlap
with either structural length scales or material length scales. If it overlaps with structural
length scales, then the material is said to be dimensionally constrained. On the other hand, if it overlaps with material length scales, for example grain size, then the
material is said to be microstructurally constrained. The objectives of this research
work are: (1) to investigate scale and size effects due to dimensional constraints; (2)
to investigate size effects due to microstructural constraints; and (3) to develop a size
dependent hardening model through coarse graining of dislocation dynamics.
A discrete dislocation dynamics (DDD) framework where the scale of analysis is
intermediate between a fully discretized (e.g. atomistic) and fully continuum is used
for this study. This mesoscale tool allows to address all the stated objectives of this
study within a single framework. Within this framework, the effect of structural and
the material length scales are naturally accounted for in the simulations and need not
be specified in an ad hoc manner, as in some continuum models. It holds the promise
of connecting the evolution of the defect microstructure to the effective response of
the crystal. Further, it provides useful information to develop physically motivated
continuum models to model size effects in materials.
The contributions of this study are: (a) provides a new interpretation of mechanical
size effect due to only dimensional constraint using DDD; (b) a development of
an experimentally validated DDD simulation methodology to model Cu micropillars;
(c) a coarse graining technique using DDD to develop a phenomenological model to
capture size effect on strain hardening; and (d) a development of a DDD framework
for polycrystals to investigate grain size effect on yield strength and strain hardening.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7776 |
| Date | 2010 May 1900 |
| Creators | Padubidri Janardhanachar, Guruprasad |
| Contributors | Benzerga, Amine |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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