Engineering Diffractometer - User Info
Compressive Yielding of Tungsten Fiber Reinforced
Bulk Metallic Glass Matrix Composites
Bjørn Clausen 1,
Seung-Yub Lee 1, Ersan Üstündag 1,
C. Can Aydiner 1, R. Dale Conner 1 and
Mark A. M. Bourke 2 (submitted to Scripta Mater. 2003)
In-situ uniaxial compression tests were
conducted on four tungsten fiber reinforced bulk metallic glass
(BMG) matrix composites using neutron diffraction. These
composites possess impressive mechanical properties including
yield strengths over 2 GPa and fracture strains of nearly 10%. The high atomic weights of both W and
the BMG preclude the use of any other diffraction techniques. The experiments were conducted on the
SMARTS instrument at LANSCE. The
diffraction data were interpreted with a finite element model. The neutron diffraction data allowed the
determination of the in-situ constitutive
behavior of both phases. Both
phases were seen to obey the von Mises yield criterion.
The fibers were observed to yield first
and then transfer load to the matrix. The
residual stresses due to thermal expansion mismatch between
the two phases (also measured with neutron diffraction) were
found to control the initiation of yielding in the fibers.
Current
work at Caltech involves the development of an advanced micromechanics
model to describe the generation of multiple shear bands in
the matrix as well as analysis of neutron diffraction data
from other BMG composites with Mo, Ta and steel fibers, and in-situ-formed
dendritic precipitates.
Figure 1. Comparison
of finite element model calculations ("as-received" and "in-situ") of the early yielding
with the longitudinal macroscopic stress-strain curves for
a 60% W/BMG composite obtained from an extensometer. The
FEM employed two versions of the W constitutive behavior:
(i) data from tests on free (as-received) fibers, and (i)in-situ stress-strain plot inferred from
neutron experiments on composites. The
significant difference between the two model plots proves
the need to perform in-situ experiments to deduce the exact
constitutive behavior of phases in a composite.
1 Department
of Materials Science, California Institute of Technology, Pasadena,
CA 91125;
2 Materials
Science and Technology Division, Los Alamos National Laboratory,
Los Alamos, NM 87545
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