Viscoelastic analyses of launch vehicle components

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175464

Chi, J K; Lin, S R ^[1]

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1. Aerospace Corporation, Los Angeles, CA (United States)

Current analysis techniques for solid rocket propellant, and insulation used in space launch vehicles, have several shortcomings. The simplest linear elastic analysis method ignores the inherent viscoelastic behavior of these materials entirely. The relaxation modulus method commonly used to simulate time-dependent effects ignores the past loading history, while the rigorous viscoelastic finite-element analysis is often expensive and impractical. The response of viscoelastic materials is often characterized by the time-dependent relaxation moduli obtained from uniaxial relaxation tests. Since the relaxation moduli are functions of elapsed time, the viscoelastic analysis is not only dependent on the current stress or strain state but also the full loading history. As a preliminary step towards developing a procedure which will yield reasonably conservative results for analyzing the structural response of solid rocket motors, an equivalent-modulus approach was developed. To demonstrate its application, a viscoelastic thick-walled cylindrical material, confined by a stiff steel case and under an internal pressure condition, was analyzed using (1) the equivalent-modulus elastic quasi-static method, (2) an exact viscoelastic closed-form solution, and (3) the viscoelastic finite-element program. A combination of two springs and one viscous damper is used to represent the viscoelastic material with parameters obtained from stress-relaxation tests. The equivalent modulus is derived based on an accumulated quasi-static stress/strain state. The exact closed-form solution is obtained by the Laplace Transform method. The ABAQUS program is then used for the viscoelastic finite-element solution, where the loading-rate dependent moduli is represented by a Prony series expansion of the relaxation modulus. Additional analyses were performed for two space launch solid rocket motors for the purpose of comparing results from the equivalent-modulus approach and the ABAQUS program.

• OSTI ID: 175464
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
A CODES
ELASTICITY
PROPELLANTS
RELAXATION
SERIES EXPANSION
SPACE VEHICLES
STEELS
STRAIN RATE
STRAINS
STRESS RELAXATION
TIME DEPENDENCE