Use of several thermal analysis techniques to study the cracking of a nitrile butadiene rubber (NBR) insulator on the booster separation motor (BSM) of the space shuttle

摘要

Two different vendor rubbler formulations have been used to produce the silica-filled NBR insulators for the BSM of each of the two Solid Rocket Boosters (SRBs) on the space shuttle. Each cured insulator is bonded to the BSM aluminum aft closure with an epoxy adhesive, and some of the curved areas in the rubber may have significant residual stresses. A number of recently bonded NBR insulators have shown fine surface cracks, and stressed insulator areas may be aging at a faster rate than the unstressed areas, thus hastening the surface cracking. Thermal analysis data on both vendor insulators by DMA through a temperature/frequency sweep from 24 to 74 °C have shown a higher flexural storage modulus and Arrhenius activation energy for the stressed area than for the unstressed area. Other thermal analysis techniques are being used to study the insulator surface versus bulk interior for better understanding of this anomaly.