Simulation of Ballistic Impact on Composite Panels

Ballistic impact on composite panels is studied in this work both experimentally and computationally. The purpose was to develop computational methods to analyze a high speed jet engine fragment impacting on composite targets. 12 inch by 12 inch laminated panels with 8, 16, and 32 plies and the standard +-45, 0 /90 degree stacking sequences were considered. With the nominal ply thickness of 0.0075 inches, the corresponding panel thicknesses were 0.06, 0.125 and 0.25 inches. The panels were mounted on a heavy steel frame and spherical and cylindrical projectiles were shot against composite plates. Several shots with varying impact speeds were fired against each panel thickness. The impact damage was observed, and the initial and exit speeds were measured. The ballistic tests indicated that the amount of energy absorbed during impact by a target is nearly constant showing only a slight increase with increasing initial energy. The amount of energy absorbed per ply increases only slightly for the thicker samples. In addition, the tests showed that the cylindrical projectiles required a larger amount of energy to penetrate the composite panels than did the spherical projectiles LS-DYNA® was used to simulate the tests. The panels were modeled with 8-node solid elements. *MAT_COMPOSITE_DMG_MSC (162) was used to model the orthotropic ply material. This model can be used to model progressive failure of composites with unidirectional and woven fabric fibers. One layer of solid elements was used through the thickness of each ply and several mesh densities were studied. A new Cohesive Contact formulation *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_TIEBREAK (and ONE WAY TIEBREAK) made available as a “DYCOSS” option was defined between each ply to model delaminations. The cohesive contact - DYCOSS option 9 has been developed during this work. This delamination modeling feature is based on fracture mechanics and requires fracture toughness inputs for the composite material. Option 9 has both the power law and BK-law to account for Mode I and Mode II interaction and allows for a better definition of the constitutive laws. The main advantages of cohesive contact are that it allows the user to toggle very easily between ordinary tie-break based delamination models and cohesive contact models and there is no need for separate cohesive elements in the model. Good overall agreement was found between computations and testing.