Terminal Ballistics of Composite Panels and Verification of Finite Element Analysis

Abstract

Composite materials are becoming more prevalent in a wider range of applications due to the inherent advantages afforded by their strength to weight ratio over more traditional engineering materials such as metals. As such, composite materials are being exposed to a wider range of operating environments. The aerospace sector has utilized composite materials for several decades to also benefit from the weight savings such as increased fuel efficiency and vehicle range. These operating environments for aerospace vehicles are hostile where fragments or projectiles can either penetrate or perforate the composite material fuselage potentially damaging critical electronic and control components and leading to catastrophic vehicle failure. Significant research efforts have been made towards modeling the impact phenomena to develop the energy absorption capabilities of the composite materials through the use of several different approaches including empirical correlation through experimental testing, analytical methods, and numerical methods. The research utilized both experimental and Finite Element methods to establish the energy absorption capabilities of carbon fiber/epoxy laminate composite panels of different thicknesses to the impact of a blunt-faced cylindrical 316 Stainless Steel projectile at different angles of obliquity. A total of 4 test matrices were performed which includes 0°, 30°, and 45° obliquity at 0.08” panel thickness, and 0° obliquity at 0.18” panel thickness. An experimental accelerator was developed to accelerate the projectile to prescribed velocities or energy levels. The impacting and residual velocities were measured using a high speed video camera. The experimental data was used to create a correlation between impacting and residual velocity for each of the test matrices. iii At high strain rates and upon the initiation of damage, composite materials exhibit a softening behavior where the stiffness and rigidity of the composite are reduced successively as damage propagates. The material model utilized in the Finite Element model is an orthotropic model with progressive damage using a variation of Hashin’s failure criteria. The damage model is based on the Matzenmiller (MLT) damage approach and uses damage softening parameters. Since current experimental methods can yield a wide range of values for the damage softening parameters, a parametric study was performed to calibrate the parameters using the experimental velocity correlation of the 0° obliquity, 0.08” panel thickness test matrix. The calibrated material model was then used to model the other three test matrices. The Finite Element model robustness was validated for the extrapolated cases and was in good agreement with the experimental data.