Reinforced Carbon-Carbon Panels Research Articles

On the Use of the Transient Hot-Strip Method for Measuring the Thermal Conductivity of High-Conducting Thin Bars

The thermal conductivity of thin, high-conducting ceramic bars—commonly used in mechanical tensile testing—is measured using a variant of the short transient hot-strip technique. As with similar contact transient methods, the influence from the thermal contact resistance between the sensor and the sample is accurately recorded and filtered out from the analysis—a specific advantage that enables sensitive measurements of the bulk properties of the sample material. The present concept requires sensors that are square in shape with one side having the same width as the bar to be studied. As long as this requirement is fulfilled, the particular size of the thin bar can be selected at will. This paper presents an application where the present technique is applied to study structural changes or degradation in reinforced carbon–carbon (RCC) bars exposed to thermal cycling. Simultaneously, tensile testing and monitoring of mass loss are conducted. The results indicate that the present approach may be utilized as a non-destructive quality control instrument to monitor local structural changes in RCC panels.

Materials analysis: A key to unlocking the mystery of the Columbia tragedy

Materials analyses of key forensic evidence helped unlock the mystery of the loss of space shuttle Columbia that disintegrated February 1, 2003 while returning from a 16-day research mission. Following an intensive four-month recovery effort by federal, state, and local emergency management and law officials, Columbia debris was collected, catalogued, and reassembled at the Kennedy Space Center. Engineers and scientists from the Materials and Processes (M&P) team formed by NASA supported Columbia reconstruction efforts, provided factual data through analysis, and conducted experiments to validate the root cause of the accident. Fracture surfaces and thermal effects of selected airframe debris were assessed, and process flows for both nondestructive and destructive sampling and evaluation of debris were developed. The team also assessed left hand (LH) airframe components that were believed to be associated with a structural breach of Columbia. Analytical data collected by the M&P team showed that a significant thermal event occurred at the left wing leading edge in the proximity of LH reinforced carbon carbon (RCC) panels 8 and 9. The analysis also showed exposure to temperatures in excess of 1,649°C, which would severely degrade the support structure, tiles, and RCC panel materials. The integrated failure analysis of wing leading edge debris and deposits strongly supported the hypothesis that a breach occurred at LH RCC panel 8.