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Abstract The residual effect of thermally and mechanically loaded polyurea samples was investigated in this study using terahertz time-domain spectroscopy (THz-TDS). Samples of different thicknesses were submerged in liquid nitrogen and allowed to reach cryogenic isothermal conditions while another set of samples were extracted from quasi-statically loaded strips. All samples were interrogated using THz-TDS since terahertz waves exhibit non-ionizing, nondestructive interactions with polymers. The time-domain terahertz signals were used to extract the optical and electrical properties as a function of sample thickness and loading conditions. The residual effect was prominent in the mechanically loaded samples compared to a nearly negligible presence in thermally loaded polyurea. On average, the results of the thermally loaded samples were subtle when compared to the virgin samples, whereas samples that were mechanically stretched showed a considerable difference in the characteristics of the time-domain signals. For example, the peak amplitude in the time-domain signal of the stretched thick sample showed a 9% difference from that of the virgin sample, whereas the thermally loaded sample saw only a 4.9% difference. Spectral analysis reported the frequency-dependent, complex refractive index of virgin and loaded polyurea as a function of thickness and spectral peaks associated with fundamental vibrational modes of the polyurea structure. The disappearance of three spectral peaks, 0.56 THz, 0.76 THz, and 0.95 THz, elucidated the residual effect of the mechanically loaded samples. In general, terahertz spectroscopy was shown to be a promising tool for future in situ and in operando investigations of field-dependent polymer responses.
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Spectro‐Microscopic Characterization of Elastomers Subjected to Laser‐Induced Shock Waves
Abstract The core of this research is separated into three domains, the ultrahigh strain rate response of elastomeric polymers, laser‐induced shock waves , and terahertz time‐domain spectroscopy (THz‐TDS). Elastomers, e.g., polyurea, constitute an advance class of materials suitable for many applications, specifically in high impact loading scenarios, thus, a laser‐induced shock wave (LSW) experimental technique is used to investigate the mechanical response of shock‐loaded polyurea. LSW can submit samples to a strain rate exceeding 106s−1at low strains, enabling determination of material intrinsic failure modes. The large deformation induced during shock loading may alter the macromolecule structure, which can only be detected spectroscopically. Therefore, this research incorporated terahertz bulk spectroscopy to detect and report molecular conformational changes. Microscopy techniques were also used to elucidate changes in the microscale properties, morphology, and topography. The interpretation of the results explicated brittle failure in terms of partial and total spallation and, remarkably, ductile failure leading to plastic deformation, including plastic bulging and adiabatic shearing, not previously associated with LSW technique. Furthermore, spectral changes found in the terahertz regime substantiated the validity of terahertz spectroscopy in elucidating the underlying mechanism associated with the impact mitigating properties of dynamically loaded polyurea.
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- Award ID(s):
- 1925539
- PAR ID:
- 10363003
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Materials and Engineering
- Volume:
- 307
- Issue:
- 2
- ISSN:
- 1438-7492
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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