SIF Distributions in Cracked Photoelastic Rocket Motor Models; Preliminary Studies.

摘要

It Is generally believed that motor grain design criteria which or treats a part through crack in the fin of a rocket motor as an edge crack extending through the length of the motor is a conservative approach to the problem. Some estimates suggest a margin of safety of about 1.5 is achieved in doing so. In an attempt to improve cost effectiveness and efficiency, an experimental effort has been undertaken to obtain stress intensity factors (SIF) at critical locations around the border of part through cracks in motor grain fins to compare with the design criteria using photoelastic models and a method of analysis developed by the first author 1 (Appendix A). The frozen stress photoelastic method is used and a new material employing amine type hardeners is used which may produce surface effects in the initial casting but appears far superior to other materials in other respects. Two-dimensional experimental studies at AFRL-Edwards AFB suggest that cracks tend to initiate at the locus along the fin tip, where the main tip radius coalesces with a much smaller corner radius. However, some manufacturers report cracks initiating on the axis of symmetry of the fin, possibly due to defects collected there during the casting process.