Damage Tolerance Approach to SRM Composite Cases

Abstract

An innovative FEM-based methodology for the investigation of damage tolerance behavior of a composite cases for Solid Rocket Motor is presented. The work has been developed in the frame of Vega Program. The aim of this program is to design and qualify a small Launch Vehicle capable to put in orbit payload of 1.5 tons. In view of the industrialization phase of the Vega SRM composite cases, damage tolerance aspect became a relevant issue to assure product quality. Among the several kinds of damages that can affect composite case structures delaminations are the most dangerous and can lead in very fast way to a premature collapse of the structures, in particular under compressive load. The delaminations can rise up during the manufacturing process of composite panels or they can arise as a consequence of impact with foreign objects. In this work, a numerical methodology has been developed to take into account the fundamental phenomena that rule on the behaviour of composite panels containing both trough-the-width and embedded delaminations. The aim was to define the acceptable damage level of the solid rocket composite cases developed within the Vega program frame. The developed numerical tool has been based on the finite elements code MARC 2001. Such a code, already capable to perform a complete non-linear analysis in case of geometric nonlinearity (large displacements and rotations), has been suitable used to evaluate by means the Modified Virtual Crack Closure Technique (MVCCT) the Energy Release Rate (ERR) that is the governing fracture mechanics parameter of the delamination on set growth.