Low density indications in radiographs of solid rocket motor nozzle ablatives

Abstract

Most Low Density Indications/Low Density Lines (LDIdLDLs) are resin rich areas which are formed during the tape wrapping and cure operation. These indications appear on the tangential radiograph exposures as dark triangles at the end of plies (LDIs) or as dark lines around individual, or groups of, plies (LDLs). LDIs have been seen within components fabricated using a spiral wrap method as well as at interfaces where a second material is applied at an angle to another material, such as in the case where an insulator is wrapped over a nozzle liner. Test specimens were extracted from three components exhibiting LDIs and LDLs: Aft Exit Cones (AECs), Forward Exit Cones (FECs) and Throat Rings (TRs) to evaluate the effect of LDIsILDLs on component integrity. Test methods employed were tensile and shear. After all the test results were evaluated, it was determined that the resin-rich areas do not result in areas that are lower in strength than that required by design criteria and, i n fact give strengths equal to that of material not containing LOIS or LOLS. It was concluded that LDIs are design and process inherent while LDLs (interlaminar indications) may, or may not, be a combination of material and process inherent. I. Background v The current production Nondestructive Evaluation (NDE) used on the Redesigned Solid Rocket Motor (RSRM) Nozzle ablative liner materials is Radiography. LDIs were observed in the Glass Cloth Phenolic (GCP), and the Carbon Cloth Phenolic (CCP) interface with the GCP. An investigation was conducted to determine to what extent the LDIs/LDLs were resin-rich areas and how these areas affected Dart intelrritv. This DaDer describes the investiGtion andthe outcokes'of the effort. The problem of LDIs and LDLs resulted from wrlting new acceptance criteria for nozzle components as part of the Space Shuttle RSRH effort. The new criteria (coupled with improved NDE equipment and techniques) focused attention on LDIs and LDLs. Initial efforts t o resolve the question of LDIs/LDLs began with characterizing the LDIs seen at the carbon to glass interface. To better understand these LDIs we began by reviewing past history for the Space Shuttle SRM nozzle. Radiograph film for Throat Inlet Rings (TIR), TR, FEC and AEC were reviewed. Although previous acceptance criteria was focused on the carbon liner (therefore NDE technique was optimized to get the best possible look at the carbon) low densities at the interface were seen and are typical of what is now being seen with improved equipment and technique. After the NDE film audit was conducted, several components were *Engineer, Nozzle/Flex Bearing Design Member, AIM d