The Presidential Panel investigating the January 28, 1986 Challenger explosion determined that the loss of the Challenger was caused by destruction of seals (O-rings) that are intended to prevent hot gases from leaking through the joints between segments of the Solid Rocket Motor during propellant burn. The Commission recommended a number of corrective actions beyond the O-ring joint redesign.
One element that had exhibited distress in post-flight examinations and was evaluated for redesign was the solid rocket motor nozzle liner. Thermostructural analysis of the nozzle liner is a complex engineering problem because the unique, advanced composite material decomposes internally and ablates at the hot surface that is exposed to the pressures, velocities, chemistry, and extreme temperatures (approaching 4500 ºF) of the rocket motor exhaust flow stream.
The internal temperatures, stresses, and failure modes of the liner under these extreme conditions of space flight launches needed to be better understood. Exponent engineers developed a finite element code named “FANTASTIC” (Failure Analysis Nonlinear Thermal and Structural Integrated Code) to perform coupled structural and thermal analysis of a three-dimensional anisotropic inelastic material system that changes loading, dimensions, and material properties with time. The code became a valuable tool for assessing the integrity of the rocket motor nozzle composite material design as well as other structural elements.