Thermal Ablation Experiments of Carbon Phenolic and SiC-Coated Carbon Composite Materials Using a High-Velocity Oxygen-Fuel Torch

Abstract

For future spacecraft TPS (heat shield) applications, ablation experiments of carbon phenolic material specimens with two lamination angles (0° and 30°) and two specially designed SiC-coated carbon–carbon composite specimens (with either cork or graphite base) were conducted using an HVOF material ablation test facility. The heat flux test conditions ranged from 3.25 to 11.5 MW/m2, corresponding to an interplanetary sample return re-entry heat flux trajectory. A two-color pyrometer, an IR camera, and thermocouples (at three internal locations) were used to measure the specimen temperature responses. At the 11.5 MW/m2 heat flux test condition, the 30° carbon phenolic specimen’s maximum surface temperature value is approximately 2327 K, which is approximately 250 K higher than the corresponding value of the SiC-coated specimen with a graphite base. The 30° carbon phenolic specimen’s recession value is approximately 44-fold greater, and the internal temperature values are approximately 1.5-fold lower than the corresponding values of the SiC-coated specimen with a graphite base. This indicates that increased surface ablation and a higher surface temperature relatively reduced heat transfer to the 30° carbon phenolic specimen’s interior, leading to lower internal temperature values compared to those of the SiC-coated specimen with a graphite base. During the tests, a phenomenon of periodic explosions occurred on the 0° carbon phenolic specimen surfaces. The 30° carbon phenolic material is considered more suitable for TPS applications due to its lower internal temperatures, as well as the absence of abnormal material behavior as observed in the 0° carbon phenolic material.

Arc-Jet Tests of Carbon–Phenolic-Based Ablative Materials for Spacecraft Heat Shield Applications

“…The internal temperatures of the SP-30-1 specimen at the 35 mm and 45 mm locations were below the design limit of 453.15 K (i.e., 180 °C), whereas the internal temperature at the 25 mm location increased very slightly above the design limit, by approximately 20 K, after the end of the exposure time, i.e., during the cool-off period. The trends shown by the internal temperatures of the SP-30-1 specimen during the cool-off period are nearly flat, which is contrary to the trends shown by the carbon–phenolic specimens in our previous study [ 16 ], where internal temperatures tended to rise during the cool-off periods. This represents a significant improvement.…”

“…Then, using the measured C p and thermal diffusivity values, the thermal conductivity ( κ ) of the silica–phenolic was determined using Equation (1) (where is material density). The values for C p , thermal diffusivity, and thermal conductivity of the 30° carbon–phenolic material, i.e., the recession layer used in this study, up to 773.15 K (i.e., 500 °C) are provided in our previous study [ 16 ]. The values for thermal conductivity of the Cork P50 material up to 523.15 K (i.e., 250 °C) can be found in [ 38 ].…”

“…The actual specimen photographs are shown in Figures 10 and 15. Each of the smaller size specimens had a stagnation surface diameter, i.e., the surface that was exposed to the test flow, of 30 mm, and these specimens were re-purposed from our earlier study [ 16 ] for preliminary investigations at the stationary test condition. The objective of the stationary tests was to evaluate whether the combination of recession and insulating layers could withstand an intermediate heat flux test condition between the minimum and maximum values used in the transient test condition.…”

“…Each thermocouple slot was 1.2 mm in diameter, and each specimen’s three thermocouple slots were machined in a straight line in the space between two bolts, the center slot being the 45 mm slot. This straight-line arrangement of thermocouples was adopted due to engineering constraints imposed by the usage of bolts, whereas a coaxial arrangement of thermocouples was used in our previous study [ 16 ]. The distance between each thermocouple slot’s center was 3 mm.…”

“…In our previous study [ 16 ], we conducted a preliminary investigation of carbon–phenolic materials with two lamination angles (0° and 30°) and two specially designed SiC-coated carbon–carbon composite specimens (with either cork or graphite base) using an HVOF (high-velocity oxygen fuel) material ablation test facility. In that previous study, the heat flux test conditions were selected to correspond with a re-entry heat flux trajectory of an interplanetary sample return spacecraft, and the values ranged from 3.25 to 11.5 MW/m 2 .…”