<p>Raman spectroscopy is a molecular spectroscopy technique
that uses monochromatic light to provide a fingerprint to identify structural
components and chemical composition. Depending on the changes in the unit-cell
parameters and volume under the application of stress and temperature, the
Raman spectrum undergoes changes in the wavenumber of Raman-active modes that
allow identification of sample characteristics. Due to the various advantage of
mechanical Raman spectroscopy (MRS), the use of this technique in the
characterization and modeling of chemical changes under stress and temperature
have gained popularity. </p>
<p> Quantitative
information regarding the local behavior of interfaces in an inhomogeneous
material during shock loading is limited due to challenges associated with time
and spatial resolution. Recently, we have extended the use of MRS to
high-strain rate experiments to capture the local thermomechanical response of
mock energetic material and obtain material properties during shock wave
propagation. This was achieved by developing a novel method for <i>in‑situ</i>
measurement of the thermo‑mechanical response from mock energetic materials in
a time‑resolved manner with 5 ns resolution providing an estimation on local
pressure, temperature, strain rate, and local shock viscosity. The results show
the solid to liquid phase transition of sucrose under shock compression. The
viscous behavior of the binder was also characterized through measurement of
shock viscosity at strain rates higher than 10<sup>6</sup>/s using microsphere
impact experiments.</p>
<p> This
technique was further extended to perform Raman spectral imaging over a
microscale domain of the sample with a nano-second resolution. This was
achieved by developing a laser-array Raman spectral imaging technique where
simultaneous deconvolution of Raman spectra over the sample domain was achieved
and Raman spectral image was reconstructed on post-processing. We developed a
Raman spectral imaging system using a laser array and analysis was performed
over the interface of sucrose crystals bonded using an epoxy binder. This study
provides the Raman spectra over the microstructure domain which enabled the
detection of localized melting under shock compression. The distribution of
shock pressure and temperature over the microstructure was obtained using
mechanical Raman analysis. The study shows the effects of an actual interface
on the propagation of shock waves where a higher dissipation of shock energy
was observed compared to an ideal interface. This increase in shock dissipation
is accompanied by a decrease in both the maximum temperature, as well as the
maximum pressure within the microstructure during shock wave propagation.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/19342028 |
| Date | 11 March 2022 |
| Creators | Abhijeet Dhiman (5930609) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/MICRO-SCALE_THERMO-MECHANICAL_RESPONSE_OF_SHOCK_COMPRESSED_MOCK_ENERGETIC_MATERIAL_AT_NANO-SECOND_TIME_RESOLUTION/19342028 |
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