Unintended consequences: Assessing thermo-mechanical changes in vinyl nitrile foam due to micro-computed X-ray tomographic imaging

Abstract

Micro-computed X-ray tomography (μCT) is a volumetric imaging tool used to quantify the internal structure of materials. μCT imaging with mechanical testing (in situ μCT) helps visualize strain-induced structural changes and develop structure-property relationships. However, the effects on thermophysical properties of radiation exposure during in situ μCT imaging are seldom addressed, despite potential radiation sensitivity in elastomers. This work quantifies the radiation dosage effect on thermo-, chemical-, and mechanical-properties for a vinyl nitrile-based foam. Material properties were measured after (0, 1, 2, and 3)days at (8.1±0.9)kGy/d. Morphological characteristics were investigated via scanning electron microscopy. Thermal transitions were assessed using differential scanning calorimetry. Viscoelasticity was measured with dynamic mechanical analysis over a range from -30°C to 60°C. Higher dose lead to stiffening and increased dissipation. Chemical structure was assessed with Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy. Soxhlet extraction was used to measure gel content. In summary, substantial changes occur in thermophysical properties, which may confound structure-property measurements. However, this also provides a modification pathway. Quantitation and calibration of the properties changes informed a finite element user material for material designers to explore tunablity and design optimization for impact protection engineers.

Keywords

• X-ray modification
• Radiation damage
• Polymer foam
• Impact protection
• X-ray micro-computed tomography