Date of Award
Santa Clara : Santa Clara University, 2022.
Doctor of Philosophy (PhD)
With the prevalence of carbon fiber reinforced polymers (CFRPs) in aerospace platforms, there is a need to better understand radiative heat transport through the material. A laboratory experiment was constructed and a computational zonal Monte Carlo (ZMC) model developed to quantify and understand the laser scattering properties of CFRPs. The ZMC model builds off of the zonal method (ZM)—developed by Hottel et al. and expanded by researchers such as Yuen et al.—by incorporating Monte Carlo techniques into the ZM. The ZMC method is superior in efficiency to the ZM and alternative ray tracing methods, which enables larger mediums of exchange to be analyzed.
A laser experiment was constructed using a commercial off-the shelf 1.26 kW ytterbium fiber laser (run at 70 W in this thesis) with customized optics to focus the beam into a vacuum chamber, as well as photodiodes, thermocouples, an IR camera and pyrometer for temperature, reflection and transmissivity measurements. Transmission data were analyzed using the ZMC method to determine CFRP albedo and extinction coefficients, which can be utilized for platform-level aerospace models to predict heat transfer more accurately through CFRP structures. Specifically, these optical properties can be read into multi-physics tools such as COMSOL to better predict radiation scattering through CFRP.
Matching laser radiation scattering to CFRP test data has not been done before and provides validation to optical property predictions. The effects of nodal, substrate and detector plane sizing, as well as laser beam parameters, were also studied and optimized when matching albedo and extinction coefficient predictions from the ZMC method to experimental test data.
Average albedo values for IM7/977-3 CFRP using the anchored ZMC method are 0.78 and 0.81 with one-ply and two-ply samples, respectively, having standard deviations of 0.11 and 0.09. Extinction coefficient predictions are 109.4 and 93.8 cm-1 with standard deviations of 28.3 and 18.8 cm-1 for one-ply and two-ply samples. When these optical properties are incorporated into multi-physic models and scaled up to larger aerospace platforms, this increased radiation transport accuracy will lead to a better understanding of laser-material interactions and burn-through times.
Shepard, Steven P., "Experimentation and Modeling of Laser Radiation Scattering Through Carbon Fiber Reinforced Polymers" (2022). Engineering Ph.D. Theses. 43.