APPLICATION OF FRACTURE MECHANICS TO CHOOSE THE RATIONAL VARIENTS OF DESIGN ELEMENTS IN SOLID PROPELLANT ROCKET MOTOR GRAINS
To provide the mechanical capacity of solid propellant rocket motor (SPRM) it is used the unloading high tension and deformation areas in grain due to the design elements. In spite of use such powerful methods of structural analysis of stress-strain state in complex SPRM grains as finite element method (FEM) the numerical methods stay still approximate. Accurate estimation of stress-strain state of real constructions in tension areas depends on calculator experience. In this connection to increase efficiency of calculations and to improve their assurance the algorithms are developed which allow use methods of singular boundary value problems analysis in common with methods structural analysis. This technique is based on joint use of FEM with fracture mechanics methods. United analysis is achieved by solution joining in the area where the solutions made by FEM are without doubt. The technique efficiency is demonstrated by the example of case-grain bonding analysis at thermo-force loading in SPRM. Evaluation of stress-strain state in the field of unloading cup according to the degree of case-grain bonding is carried out by direct and energy methods of fracture mechanics. The calculation of energy release rates shows that the 0.4 part of case-grain dome unloading is the most dangerous. When the grain is partly unloaded the dynamic delamination is possible in the field of unloading cup. The extent of delamination is predicted in pattern of energy release rate. The least level of stress-strain state is realized in the field of unloading cup at complete case-grain dome unloading. At 3 strips scheme of case-grain bonding the part of bonding with the angle ~18° is the most rational. Under such conditions in the case of force delamination near unloading cup the dynamic development of delamination is not expected. Condition of delamination advance is continuous increase of loading.