Development of a Testing Device for Ablative Materials

Photo of Eric Allcorn, Sam Robinson, David Tschoepe Students: Eric Allcorn, Sam Robinson, David Tschoepe

Sponsor: The University of Texas at Austin

Date: Fall 2010

Requirements:
The ablation testing device must properly simulate the conditions that ablative materials will be exposed to in real world applications. The specific requirements include heat flux into the material of approximately 14MW/m2, material surface temperature greater than 2200°C, and fluid impact velocity greater than Mach 1. In addition, the device must fit and operate within a laboratory fume hood and facilitate the acquisition of testing data through a pyrometer and up to three thermocouples. In testing, the device must also produce a range of heat fluxes to be applied over a range of sample times.

Problem:
Ablative materials provide thermal protection by self-sacrifice and are commonly used in such applications as solid rocket motor insulation and spacecraft re-entry shielding. Testing of these materials involves exposing them to a heat source for a short period of time and measuring the resulting temperature versus time profile at different points in the material. Dr. Joseph Koo and the Materials Research Group at The University of Texas at Austin are in need of a small scale device with which to test newly developed ablative materials. The design group's task is to design, fabricate, and calibrate an ablation testing device to serve this purpose.

Solution:
The team developed a device based on an oxyacetylene torch system to produce the desired temperature and heat flux inputs. A cutting nozzle attachment is used on the torch to accelerate the flame into the sample at the desired velocity. The sample size to be tested by the device is a cylindrical shape of 12.4mm (1/2 inch) diameter with thickness ranging from 15mm to 30mm based on the specific material being tested. The oxyacetylene torch is mounted on a single-axis slide mechanism that aligns the torch with the sample while also allowing variable distance between the two. The sample is held in a brass holder and suspended by three stainless steel screws to minimize heat loss from the sample. During testing, a pyrometer is aimed at the front face of the sample to obtain a front face temperature, while up to three thermocouples can be placed on the back face or embedded into the sample (depending on the specific test being performed) to obtain the back face temperature or heat soak temperature. Data from the pyrometer and thermocouples is collected by a data acquisition card that feeds the data to a LabVIEW VI. This VI then converts the readings to temperature values, plots them over time, and exports them to a test file for further analysis.

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