Static and Nonlinear Dynamic Response of a Polymer Liner Confined by a Rigid Overwrap in a Type IV Hydrogen Pressure Vessel

The mechanical response of a polymeric liner in a Type IV hydrogen pressure vessel is governed by internal gas pressure, liner stiffness, nonlinear deformation, and confinement by the composite overwrap. A reduced-order analytical model is developed to describe the static and nonlinear dynamic behavior of the liner using a single generalized radial displacement. The formulation assumes cylindrical liner geometry, isothermal gas behavior, approximately constant gas mass over the mechanical response time scale, and negligible damping. The model incorporates deformation-dependent gas pressure, nonlinear restoring characteristics, effective fluid inertia, and finite clearance between the liner and overwrap. Analytical conditions for equilibrium, stability, and saddle-node bifurcation are derived. For the linear restoring model, a first integral characterizes finite-amplitude oscillations and the conditions for contact with the overwrap. Fluid inertia affects finite-amplitude motion but not static equilibrium or infinitesimal oscillations. The analysis further shows that finite-amplitude oscillations induced by an initial velocity can produce both contraction and expansion of the liner, with the diameter becoming smaller or larger than its initial value D0. Application to a representative PA11 liner demonstrates the strong effect of overwrap confinement, which substantially reduces the radial deformation. The results distinguish static and dynamic contact conditions and provide a compact analytical framework for assessing deformation, stability, and nonlinear dynamic behavior of Type IV hydrogen vessel liners.