Biharmonic (two-frequency) load frequencies influence on mechanical behavior of solid propellant simulator

This work is devoted to the engineering unit development for stress-strain state assesses of the viscoelastic structures in aerospace engineering under some biharmonic (two-frequency) loads. Uniaxial monoharmonic (one-frequency) tests of low-modulus viscoelastic polymer composite were conducted under different values of pre-static deformation and initial phase shift angle, as well as uniaxial biharmonic (two-frequency) tests under different values of first (low-frequency) and second (high-frequency) harmonics frequencies. The complex modulus method was used to describe the behavior of viscoelastic material under harmonic loads. Material dynamic deformation properties were determined by a specially developed method. The method allows determining the dynamic modulus and loss angle of the first and the second harmonics. A relative frequency factor was offered for the study of the effect of biharmonic load frequencies on the behavior of viscoelastic material. The method of experiment results under boundary values of frequencies ratio of the first and second harmonics was offered. This approach allows us to determine the behavior of viscoelastic materials under monoharmonic loads in the biharmonic formulation of the problem. Dependencies of the dynamic modulus and the loss angle of the second harmonic on frequencies ratio of the first and second harmonics were shown. It has been found that the initial phase shift change does not impact viscoelastic materials behavior. A mathematical model describing material behavior under different values of frequencies was proposed. This model allows us to describe, with a sufficient accuracy, the material behavior under any frequencies ratio. Biharmonic tests are more preferable for determining the dependence of the dynamic modulus on pre-static deformation than monoharmonic tests under pre-static deformation changing.