Thèse de doctorat en Mécanique
Sous la direction de Andrei Constantinescu.
Soutenue en 2015
Classify amongst the family of highly filled elastomer, solid propellant is used in the solid propulsion media. In order to guarantee the integrity of the structure, the behavior of solid propellant must be highlighted. Solid propellant behavior is viscoelastic, but present several non-linearities due to his high volume fraction of filler. This study focuses on the impact of the prestrain on the viscoelastic properties. The objective here is to characterize this impact, model it, implement it into a numerical code and investigate this influence on the response of a complete motor under dynamic solicitations. To do this, the work is divided in several parts. First, the microstructure of the propellant is studied in order to determine the microscopic causes of the macroscopic non-linearities. Then viscoelastic properties are characterized, both into the time or frequency domain, using uni axial and bi axial solicitations. To perform bi axial tests, a bi axial traction device is developed. A base on the experimental results, a continuous model is identified to describe the viscoelastic properties as a function of the prestrain. This model is discretized, in order to be implemented into a constitutive law, which permits to give a relation between strain and stress into the material. The constitutive law is traduced into a finite element code, in order to perform computation. Simulations are done on a numerical model of a solid propulsion motor. The properties of the propellant are alternatively modeled by a linear viscoelastic and non-linear viscoelastic (developed in this study) model. The two responses of the complete structure under dynamic solicitations are then compared, to prove it is important to take into account the non-linear influence of the prestrain, and the necessity to exactly model the propellant behavior. In a similar way, future works could investigate the non-linearity induced by the dynamic part of the strain on the viscoelastic properties.
Nonlinear viscoelastic modeling of a highly filled elastomer under multiaxial loading
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