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Bulk-metallic glasses (BMGs) or amorphous metals are metallic
alloys which are produced by rapid quenching of liquid metals to
prevent crystallization. Therefore BMGs lack long-range order and
crystalline structure associated with conventional metallic alloys,
and thus it is void of dislocations and crystalline defects which
weaken conventional metals. Currently, BMGs are finding increased
use in the MEMS, structural, military, luxury and sporting goods
industries.
Typically, the processing of BMGs into component products take
place at temperatures within the
supercooled liquid region
where the metallic glasses can flow very easily and achieve large
deformations at relatively high deformation rates without
fracturing. Hence, a reliable constitutive model and robust
computational procedure are required to aid in the design process of
components manufactured out of metallic glasses at high homologous
temperatures.
In this seminar, we will describe our recently developed
finite-deformation-based and thermo-mechanically-coupled
constitutive model for amorphous metals (Thamburaja and Ekambaram,
2007). Central to the derivation of the constitutive model is the
use of basic thermodynamics principles and the theory of micro-force
balance (Fried and Gurtin, 1994). The constitutive model is then
implemented in the ABAQUS/Explicit (2007) finite-element program by
writing a user-material subroutine.
Our constitutive model and its numerical implementation are then
verified to the simple compression experiments of Lu et al. (2003)
conducted on a Vitreloy-1 Zr-based BMG under a variety of
deformation rates and test temperatures within the supercooled
liquid region. The stress-strain response from these aforementioned
experiments are well-reproduced by our constitutive model and
finite-element simulations. In particular, we show that a more
accurate description of the bulk-metallic glass' stress-strain
behavior is obtained by taking into account the variation of the
temperature field within the test specimen during the deformation
process.
Finally, we also show the ability of our constitutive model and
numerical simulation in accurately predicting the orientation of
failure/fracture planes for metallic glasses tested at temperatures
within the supercooled liquid region under simple compression.
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