PHOTOGRAMMETRIC SURFACE RECESSION MEASUREMENTS ON ABLATIVE SAMPLES OF VARIOUS SHAPE

Kurzfassung

Results from plasma wind tunnel testing of a lightweight carbon phenolic ablative material are presented. The tests were carried out in a high-enthalpy subsonic flow at a condition corresponding to the Hayabusa re-entry condition in 78 km altitude. The samples were produced from ZURAM which is a carbon-fiber structure impregnated with phenolic resin. The focus of the investigation was on the measurement method of the recession. Stereoscopic photogrammetry was applied to reconstruct the sample surface in three-dimensional space over the testing time. Two cameras were used to capture images simultaneously. Using a three-step process the sample surface for each image pair was reconstructed and the recession between the image pairs was calculated. The recession resolution is in the range of 45 µm. The advantage of the method is that the time-resolved in-situ surface recession measurement gives insight into the local recession distribution over the sample surface. This means that recession differences due to the sample geometry or due to material inhomogeneities can be identified. In order to verify this, samples were prepared that include distinct geometric features which influence the recession. Starting with a flat surface cylinder, samples with a rounded surface were prepared as well as a cone-sphere sample and one with a defined indentation in the form of a half-sphere. The temporally and locally resolved recession was successfully measured and related to the sample geometric features.