Modeling thermal shrinkage of tire cords and its application in FE analysis of Post Cure Inflation

Abstract

Thermal shrinkage in polymeric tire cords greatly influences tire dimensions and performance. In order to reduce the undesirable effects of this phenomenon, the Post Cure Inflation (PCI) process is used as a step in tire manufacturing. Finite element analysis of such a complex process requires the consideration of thermal shrinkage, creep, and change in material stiffness for both the cords and the rubber materials. This work focuses on the development of a tire cord material model, which accounts for thermal shrinkage and its related effects. A thermomechanical finite strain rebar element is formulated to enable the representation of the cords within the tire geometry. The proposed cord material distinguishes recoverable from unrecoverable shrinkage to allow a more general description of different types of polymeric cords. A temperature, stress and time dependent thermal shrinkage evolution law is introduced. Moreover, mechanical creep and stiffness variations due to temperature change and shrinkage are considered. The developed formulation is validated against several experimental data obtained for tire cords. Curing and PCI process of a tire segment are also simulated to investigate the effect of thermal shrinkage on the resulting tire dimensions.