This paper on "Fail-Safe Analysis of a Bolted Joint on a Solid Rocket Motor Nozzle" was presented at the NAFEMS World Congress on Effective Engineering Analysis - 25-28 April 1999, Newport, Rhode Island, USA.

Abstract

In order to meet design requirements. bolted joints in a Reusable Solid Rocket Motor (RSRM) nozzle must retain structural integrity. even if a single bolt fails. Finite Element Analysis using ABAQUS/Standard demonstrated compliance with this requirement. Techniques developed to model the nozzle are applicable to a variety of applications.
Although the overall cylindrical shape of the RSRM nozzle is conducive to axisymmetric modeling, capturing the behavior of individual bolts required three-dimensional (3D) analysis. A 10^o section of a joint was modeled in 3D and the remainder of the nozzle was modeled axisymmetrically. The axisymmetric and 3D portions of the model were coupled using constraint equations. The axisymmetric material properties and loading were modified to integrate with the 10^o analysis.
The 10^o joint section contains three housings. two half-inch bolts, two three quarter-inch bolts, two bond-lines, and two phenolic rings. The model has significant amounts of contact between housing flanges, bolts and housings, and orientated gap elements at the bolt threads. Additionally, tied contact was imposed with the adhesive. Tied contact constrains dissimilar meshes together, allowing rapid transitions in mesh refinement and is particularly useful for long thin adhesive bonds.
The analysis progressed in two stages. First, the bolt preload was applied using pre-tensioned sections in the bolt shank. Second, the maximum expected operating pressure was applied to the phenolic surface. The joint must remain intact and seal against exhaust gasses. Therefore, of primary interest is the loading on the intact bolts and the contact at the seal surfaces.