Multiphysics optimization of X-ray transmittance in high-pressure, high-temperature triaxial cells: A polychromatic analysis

Abstract

High-temperature, high-pressure X-ray transparent experimental platforms are essential for investigating Thermo–Hydro–Mechanical–Chemical (THMC) processes in geoscientific and engineering applications. Their design presents a fundamental conflict: structural integrity requires thick vessel walls, whereas X-ray imaging demands minimal wall thickness to reduce attenuation. This paper presents a computational multiphysics optimization framework that integrates von Mises yield criteria, temperature-dependent material properties, and polychromatic X-ray attenuation analysis to resolve this conflict. The framework evaluates candidate vessel alloys (aluminum, titanium, steel) under realistic Bremsstrahlung spectra (120–450 kVp) and spatial thermal gradients, identifying optimal geometries that maximize transmittance while satisfying mechanical safety constraints. Aluminum alloys achieve the greatest transmittance, outperforming titanium and steel at all tube voltages evaluated. The analysis evaluates gaseous confining media. Nitrogen is recommended: it offers acceptable transmittance (69%–87%, depending on alloy and tube voltage), low cost, widespread availability, and chemical inertness under high-temperature conditions, while imposing less demanding sealing requirements than helium. System transmittance values (0.3%–0.6% at 120 kVp) are comparable to adult abdominal medical CT imaging, confirming compatibility with commercial detector technology.