92
D. W. Eastman et al.
is needed to guide and benchmark corresponding models. The work presented
in this chapter was undertaken as part of the Air Force Office of Scientific
Research (AFOSR)-sponsored Center of Excellence in Integrated Materials Modeling (CEIMM), and its overall goal was to provide experimental benchmarks
and validation routes for multiscale CPFEM models of the Ni-base superalloy
René 88DT, specifically through the development of scale-specific mechanical
benchmarks by capturing the mechanical response of microtensile samples, in which
explicit measures of their microstructure can also be obtained. As part of this effort,
multiple test sample geometries were designed to characterize sample volumes
that were small enough to be modeled while still providing a true polycrystalline
response. Significant effort went into developing machining processes, and the test
equipment and techniques required for obtaining the requisite data, at the various
length scales that each of these samples represented. In addition, after observing a
size effect on yield strength, a further study was done to investigate this phenomenon
by testing samples of different sizes and elucidating mesoscale trends in the behavior
of René 88DT.
2 Background
The need to connect modeling and experiments is intrinsic to the Integrated
Computational Materials Engineering (ICME) paradigm, but the ability to do so
has been limited by the need for more computational power as well as more
detailed explicit microstructural information from experimental results. In terms
of experimentally coupling 3D microstructures with mechanical properties, earlier
efforts were limited by their simplicity. This was due not only to limitations with
the state of experimental techniques available but also the technology and ability to
process the large amounts of data necessary. Becker et al. utilized only the surface
orientation data of an Al sample to develop two finite element models: a plane
strain model and a quasi-3D model with a mesh that was only one element thick
[3]. Cheong et al. performed a similar modeling effort using experimental data
collected by Zhang for a polycrystalline sample of Al–0.5% Mg [4]. The model
utilized a finite element mesh of 35 × 31 × 3 elements on a subsection of the
sample gage and compared distributions of plastic axial strain with experimental
measurements of strain as well as the macroscopic stress–strain behavior [5]. These
studies are examples of early efforts to connect experiments and modeling; however,
the drawback of not being able to model the full 3D structure of the sample is
significant.
To avoid the need for full 3D characterization of a sample microstructure,
other investigators have focused on materials with microstructures that can be
characterized well using only 2D methods. These materials tend to have either very
coarse microstructures or columnar structures, achieved by the processing methods
used to produce the material (such as directional solidification [6], the extraction
of oligocrystals [7], or the use of heat treatments to coarsen the material [8, 9]).
D. W. Eastman et al.
is needed to guide and benchmark corresponding models. The work presented
in this chapter was undertaken as part of the Air Force Office of Scientific
Research (AFOSR)-sponsored Center of Excellence in Integrated Materials Modeling (CEIMM), and its overall goal was to provide experimental benchmarks
and validation routes for multiscale CPFEM models of the Ni-base superalloy
René 88DT, specifically through the development of scale-specific mechanical
benchmarks by capturing the mechanical response of microtensile samples, in which
explicit measures of their microstructure can also be obtained. As part of this effort,
multiple test sample geometries were designed to characterize sample volumes
that were small enough to be modeled while still providing a true polycrystalline
response. Significant effort went into developing machining processes, and the test
equipment and techniques required for obtaining the requisite data, at the various
length scales that each of these samples represented. In addition, after observing a
size effect on yield strength, a further study was done to investigate this phenomenon
by testing samples of different sizes and elucidating mesoscale trends in the behavior
of René 88DT.
2 Background
The need to connect modeling and experiments is intrinsic to the Integrated
Computational Materials Engineering (ICME) paradigm, but the ability to do so
has been limited by the need for more computational power as well as more
detailed explicit microstructural information from experimental results. In terms
of experimentally coupling 3D microstructures with mechanical properties, earlier
efforts were limited by their simplicity. This was due not only to limitations with
the state of experimental techniques available but also the technology and ability to
process the large amounts of data necessary. Becker et al. utilized only the surface
orientation data of an Al sample to develop two finite element models: a plane
strain model and a quasi-3D model with a mesh that was only one element thick
[3]. Cheong et al. performed a similar modeling effort using experimental data
collected by Zhang for a polycrystalline sample of Al–0.5% Mg [4]. The model
utilized a finite element mesh of 35 × 31 × 3 elements on a subsection of the
sample gage and compared distributions of plastic axial strain with experimental
measurements of strain as well as the macroscopic stress–strain behavior [5]. These
studies are examples of early efforts to connect experiments and modeling; however,
the drawback of not being able to model the full 3D structure of the sample is
significant.
To avoid the need for full 3D characterization of a sample microstructure,
other investigators have focused on materials with microstructures that can be
characterized well using only 2D methods. These materials tend to have either very
coarse microstructures or columnar structures, achieved by the processing methods
used to produce the material (such as directional solidification [6], the extraction
of oligocrystals [7], or the use of heat treatments to coarsen the material [8, 9]).