Phenomena and Material Property Requirements for a Combined Structural and Thermal Ablation Model
Start Date
1-3-2011 9:40 AM
Description
The primary physical response phenomena associated with ablative insulators are discussed in this presentation. Ablative insulators are typically heated by radiation and convection at an exposed surface. As regions within the insulator increase in temperature the material decomposes (pyrolizes), and a pyrolysis front progresses into the insulator leaving behind a layer of charred material. Pyrolysis gases are generated as the material chars, and these gases flow through and exchange energy with the porous char structure. Meanwhile, erosion of the surface material can occur due to chemical and mechanical interaction with the boundary flow. Thermal modeling approaches used to simulate these phenomena are discussed in this presentation with a focus on the in-depth material response. In addition to thermal modeling, structural modeling is often required for accurate assessment of phenomena such as pocketing, ply-lifting, wedge-outs, and delaminations, all of which can dramatically affect the thermal protection ability of an ablative insulator. Structural material responses are integrally tied to thermal responses. For example, the moduli can be dependent on the degree-of-char, which is integrally tied to the thermal history. In addition, material stiffness and capabilities have been shown to be tied to the amount of moisture present in the material, which is also tied to the thermal response. Structural behavior is also influenced by pressures in the material (calculated with thermal codes), and pressure magnitudes are highly dependent on structural loading (calculated with structural codes). Conjugate models are therefore required for accurate simulation of the thermal and structural behavior of ablative insulators. This presentation outlines areas where this coupling is required and describes associated property requirements.
Phenomena and Material Property Requirements for a Combined Structural and Thermal Ablation Model
The primary physical response phenomena associated with ablative insulators are discussed in this presentation. Ablative insulators are typically heated by radiation and convection at an exposed surface. As regions within the insulator increase in temperature the material decomposes (pyrolizes), and a pyrolysis front progresses into the insulator leaving behind a layer of charred material. Pyrolysis gases are generated as the material chars, and these gases flow through and exchange energy with the porous char structure. Meanwhile, erosion of the surface material can occur due to chemical and mechanical interaction with the boundary flow. Thermal modeling approaches used to simulate these phenomena are discussed in this presentation with a focus on the in-depth material response. In addition to thermal modeling, structural modeling is often required for accurate assessment of phenomena such as pocketing, ply-lifting, wedge-outs, and delaminations, all of which can dramatically affect the thermal protection ability of an ablative insulator. Structural material responses are integrally tied to thermal responses. For example, the moduli can be dependent on the degree-of-char, which is integrally tied to the thermal history. In addition, material stiffness and capabilities have been shown to be tied to the amount of moisture present in the material, which is also tied to the thermal response. Structural behavior is also influenced by pressures in the material (calculated with thermal codes), and pressure magnitudes are highly dependent on structural loading (calculated with structural codes). Conjugate models are therefore required for accurate simulation of the thermal and structural behavior of ablative insulators. This presentation outlines areas where this coupling is required and describes associated property requirements.