A model of debonding instability for solid propellant rocket motor: Part II — Unequal longitudinal and transverse stress rate

Considered in Part I was the debonding instability of a three-layered composite system made of steel, adhesive and rubber which models the situation in a solid-fuel rocket motor. Under the condition of a uniform stress rate of 0.75 ksi/s applied to the longitudinal and transverse direction, severe inhomogeneity of the material response were found in regions next to the adhesive/rubber interface. This led to the prediction of a macrocrack about 5 × 10⁻³ in. after an elapsed time of one second and sudden fracture over a length of 1.88 in. at eight seconds after loading.This is Part II of the work that examines the influence of load transients on interface failure. As unequal stress rate state is assumed where loading in the transverse direction is removed causing a more severe disturbance in the longitudinal direction even though the same stress rate of 0.75 ksi/s is maintained. A slightly bent crack of the order of 10⁻³ in. is predicted to initiate near the adhesive/rubber interface; it led to the onset of fracture over a length of 1.60 in. at four seconds. Onset of instability is predicted to occur at a much earlier state.