Polymer based aerospace structures under high velocity impact applications; experimental, constitutive and finite element analysis

Polymethyl methacrylate (PMMA) and Polycarbonate (PC) are two famous optically clear thermoplastic polymers widely used in various aeronautical and astronatucial applications. Owing to their exceptional transparency, process shape adaptability, low density and high impact strength they find particular attention in aerospace industry where they are used to manufacture air craft canopies, windshields, impact resistant windows, visors and safety glasses. The design and manufacturing of the satisfied polymeric structures involve accurate modeling of the material behavior and detailed analysis of their service behavior under extreme loading conditions. In order to evaluate the material behavior under these loading conditions, extensive work in terms of experimental characterization and material constitutive modeling is required. A systematic research methodology including the material characterization, material constitutive modeling, constitutive model implementing and finite element prediction of mechanical behaviors is proposed in this work. The material characterization tests were performed by means of universal testing machine and Split Hopkinson pressure bar (SHPB) setup. On the basis of performed tests and using phenomenological approach, a constitutive model was proposed to successfully predict the entire deformation behavior of polymers under various loading conditions with sufficient accuracy. The model was implemented numerically by establishing a User-defined material subroutine (UMAT) in explicit Finite element (FE) solver LS-DYNA. The model successfully ascertained the dynamic behavior of PMMA based aircraft windshield and PC based astronaut helmet visor under application of high velocity projectile impact. A number of FE simulations were carried out to determine the critical impact energy, maximum deformation and stress level in these structures. The simulations results help to evaluate various design approaches to optimize the structural response prior to preliminary experimentations and therefore provide an alternative to costly and time consuming extensive experimental tests.