Abstract:
This paper details the critical role of Finite Element Analysis (FEA) using the software LS-DYNA in the investigation of the Space Shuttle Columbia accident and also presents a comprehensive investigation into the seismic stability of the soil-concrete interface in composite dams using the NIKE3D computer code. In the Columbia investigation, after foam from the external tank struck the left wing, an Impact Analysis Team was formed to determine the severity of the damage. A significant challenge was the lack of material property data for the foam and the wing's Reinforced Carbon-Carbon (RCC) at the high impact rates and specific atmospheric conditions of the event. The team developed complex, non-linear material models accounting for strain-rate effects and brittle failure through physical testing. A detailed finite element model of the wing's leading edge, consisting of over 400 individual parts, was created to provide pre-test predictions that guided physical impact tests, showing excellent correlation between simulated high strain and actual damage. In the dam stability research, the NIKE3D code was selected for its robust interface formulation capable of modeling the complex, nonlinear behavior of slippage, debonding, and rebonding under seismic loads. To validate this FEA approach, the NIKE3D code was calibrated against dynamic centrifuge test data from a retaining wall model, with the numerical analysis showing excellent agreement with the physical test results. The study involved extensive 2-D and 3-D parametric finite element analyses on dam models of varying heights to assess how geometric parameters affect interface performance. These analyses used both a nonlinear Ramberg-Osgood model and a linear elastic model to evaluate the impact of the soil model choice, revealing a significant difference between 2-D and 3-D results and highlighting the necessity of 3-D modeling for an accurate assessment.
