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M. Gonzales and N. N. Thadhani
of the breakout shock wave. Interferometry or stress gage-based measurement
techniques average the response over the probe area as well as the temporal
resolution of the sensor. Recent work by Kang et al. [44] attempts to address these
limitations by introducing CdTe quantum dots directly into the microstructure of the
heterogeneous material.
In situ sensing is a challenge because local interaction between the sensor
material and the local microstructure can change the character of the shock wave
and bias the true nature of the interaction. However, these sensors are small enough
that this interference is minimized. Furthermore, these sensors provide a pressureinduced blueshift which can be normalized. Laser-driven flyer impact experiments
on CdTe quantum dots embedded in glass show a well-defined blueshift in the
photoluminescent emission spectra [44]. These blueshifts correspond strongly with
the peak shock pressure and are indicators of the peak stress, up to a maximum
at around 6 GPa. Optical microcavity structures [66] also show promise as insitu pressure sensors taking advantage of the pressure-sensitive spectral shift in
Al 2 O 3 optical microcavity lamellar composites. This is a truly exciting work
which merits further consideration, as in situ pressure and TOA data would be
invaluable to validating and informing meso-scale shock compression simulations
of heterogeneous materials.
4 Summary and Conclusions: Where Can ICMSE Continue
to Provide Value in Understanding Dynamic Behavior of
Heterogeneous Materials?
This chapter discussed some of the challenges in understanding the dynamic behavior of heterogeneous materials. The difficulties stem from the multiple length and
time scales involved in the processes and how the microstructural effects interplay
with the bulk response. Experimental challenges exist in probing the ultrafast
response of heterogeneous and particulate materials under shock compression, and
isolating the effects of individual phenomena at every length scale is a challenge
that has yet to be conquered. Experiments probing the response tend to smear the
meso-scale effects, but strides are continually being made to address this by the
community.
With the continued refinement of experimental techniques, ultrafast imaging,
synchrotron radiation sources, laser shock technologies, and improvements in
ultrafast diagnostics, the method developers will have a wealth of information to
refine their models and simulation capabilities. Numerical simulation remains a
powerful tool to help assess the nature of the complex shock compression event.
In this regard, ICMSE has proven to be an invaluable tool in helping to
explore the sources of chemical reactivity in intermetallic-forming powder mixtures.
Microstructure-based simulations provided a possible explanation for the interesting
observations of both optimal stoichiometries leading to enhanced chemical reactivity, as well as the dispersed wave mechanics inherent to the reactive powder mixture.
M. Gonzales and N. N. Thadhani
of the breakout shock wave. Interferometry or stress gage-based measurement
techniques average the response over the probe area as well as the temporal
resolution of the sensor. Recent work by Kang et al. [44] attempts to address these
limitations by introducing CdTe quantum dots directly into the microstructure of the
heterogeneous material.
In situ sensing is a challenge because local interaction between the sensor
material and the local microstructure can change the character of the shock wave
and bias the true nature of the interaction. However, these sensors are small enough
that this interference is minimized. Furthermore, these sensors provide a pressureinduced blueshift which can be normalized. Laser-driven flyer impact experiments
on CdTe quantum dots embedded in glass show a well-defined blueshift in the
photoluminescent emission spectra [44]. These blueshifts correspond strongly with
the peak shock pressure and are indicators of the peak stress, up to a maximum
at around 6 GPa. Optical microcavity structures [66] also show promise as insitu pressure sensors taking advantage of the pressure-sensitive spectral shift in
Al 2 O 3 optical microcavity lamellar composites. This is a truly exciting work
which merits further consideration, as in situ pressure and TOA data would be
invaluable to validating and informing meso-scale shock compression simulations
of heterogeneous materials.
4 Summary and Conclusions: Where Can ICMSE Continue
to Provide Value in Understanding Dynamic Behavior of
Heterogeneous Materials?
This chapter discussed some of the challenges in understanding the dynamic behavior of heterogeneous materials. The difficulties stem from the multiple length and
time scales involved in the processes and how the microstructural effects interplay
with the bulk response. Experimental challenges exist in probing the ultrafast
response of heterogeneous and particulate materials under shock compression, and
isolating the effects of individual phenomena at every length scale is a challenge
that has yet to be conquered. Experiments probing the response tend to smear the
meso-scale effects, but strides are continually being made to address this by the
community.
With the continued refinement of experimental techniques, ultrafast imaging,
synchrotron radiation sources, laser shock technologies, and improvements in
ultrafast diagnostics, the method developers will have a wealth of information to
refine their models and simulation capabilities. Numerical simulation remains a
powerful tool to help assess the nature of the complex shock compression event.
In this regard, ICMSE has proven to be an invaluable tool in helping to
explore the sources of chemical reactivity in intermetallic-forming powder mixtures.
Microstructure-based simulations provided a possible explanation for the interesting
observations of both optimal stoichiometries leading to enhanced chemical reactivity, as well as the dispersed wave mechanics inherent to the reactive powder mixture.