Hydrodynamic Ram Analysis Of All-Composite Wing Box




			HYDRODYNAMIC RAM ANALYSIS OF ALL-COMPOSITE WING BOX Ronald L. Hinrichsen, NCSA/UIUC William Baron, AFRL/VAS This file is available for download in *.pdf* format. Click here Research Objectives: To use state of the art nonlinear dynamic explicit time integration finite element codes (LSDYNA3D and MSC/DYTRAN) to predict the hydrodynamic ram damage resulting from the detonation of a 30mm High Explosive Incendiary (HEI) threat within an all-composite fluid-filled wing box. To evaluate the predictions made by the two codes and make recommendations for their improvement. To evaluate methodologies for effectively handling the failure initiation and progression within the domain of the all-composite structure, including the skins, spar and rib webs, and spar and rib caps (joints). Methodology: The methodology of this research was to model the explosion and fluid using the Eulerian perspective while the structure was modeled using the Lagrangian perspective; the coupling attained through the Arbitrary Lagrangian Eulerian (ALE) and Coupled Euler Lagrange techniques. Predicted fluid pressures and structural strains (as functions of time and distance from the detonation center) were compared with those quantities attained via experimentation. *Figure 1. Experimental Set Up* Results: Both the LSDYNA3D and MSC/DYTRAN codes were found to be effective in predicting the fluid pressures and impulses as functions of time and distance from the detonation. The use of fluid elements on the order of 1/2 inch in each dimension were found to be optimum in this regard. Although the peak pressures were consistently under estimated, the impulses were found to be nearly identical with the experimental values up to distances of 100 cm from the detonation. Both the LSDYNA3D and MSC/DYTRAN codes were found to be effective in predicting the structural strains as functions of distance and time up to 0.0025 seconds after detonation. The MSC/DYTRAN code was restricted to the ALE technique for the fluid-structure coupling. The distortion of the fluid elements in the vicinity of the spar webs in the second bay removed from the detonation was found to be the limiting reason for why the analysis could not be extended past 0.0025 seconds. The most promising coupling technique was the CEL method used within the LSDYNA3D code. Because element distortion of the fluid is not encountered in this technique, it is possible to extend the analysis beyond 0.0025 seconds. Further research is needed to determine the optimum fluid mesh size to ensure that momentum is properly transferred from the fluid to the structure. The present LSDYNA3D code incorporates a single integration point. This is a limitation which also needs to be further investigated. Significance: This research is significant as it points the way to an effective and efficient method for designing all-composite fluid-filled wing structures under the imposition of hydrodynamic ram loads resulting from detonations occurring within the fluid domain. This research is also significant as it outlines a methodology for investigation of detonations occurring within commercial aircraft. *Figure 2. Structural Model With Stress Contours* *Figure 3. Fluid Model With Pressure Isosurfaces* *Figure 4. Comparison Of Gross Damage (Side View)* *Figure 5. Comparison Of Gross Damage (Front View)* *Figure 6. Comparison Of Pressure Pulse At 40 cm From Detonation* *Figure 7. Comparison Of Peak Pressure At Distance From Detonation* *Figure 8. Comparison Of Scaled Impulse At Distance From Detonation* *Figure 9. Comparison Of Strains On Spar Web*