Estimation of the cylindrical composite shell stiffness at the initial stage of curing during deployment by internal pressure

An experimental-calculation method aimed at evaluating the stiffness properties of a cylindrical shell structure made of a composite material with a polymer matrix at the initial stage of its curing is considered. Evaluation of the stiffness composition parameters at this stage of polymerization due to the different physical state of the reinforcing elements and the binder by the methods of composite materials mechanics leads to poorly determined stiffness matrices that are not suitable for a reliable description of the mechanical behavior of the structure. The research relevance is related to the study of the manufacturing large-sized pneumatic structures technology based on compositions subjected to curing in space conditions. In the proposed method, the cylinder deployment pressure (the pressure at which the cylinder diameter assumes a nominal value) corresponding to the current binder polymerization degree is determined experimentally. The degree of polymerization is characterized by viscosity and the dynamic polymer module, measured with the viscosimeter. The structure specification as well as devices used in the experiments, instruments that fix the measured state parameters and the test procedure description are provided. The effective modulus of the cylinder’s elasticity of the material has to be corresponding to its stiffness characteristics during the loading by internal pressure to the deployment pressure. It is determined by the method of successive approximations based on a geometrically nonlinear elastic model. The deployment time is much shorter, than the total binder curing time. By comparing the experimental and calculated data, the dependence of the effective elasticity modulus on the binder curing parameters is established. The almost linear dependence of the cylinder deployment pressure on the effective modulus of elasticity is revealed. It allows to extrapolate the results of the study to the values of binder parameters that are not backed up by the experience. These results allow us to evaluate the internal pressure necessary for the deployment of composite cylindrical shells with a partially cured binder, by solving the problems of solid mechanics.