Evaluation of Residual Stresses due to Spherical Impact using LS – DYNA Jason Fayer MANE-6980 ENGINEERING PROJECT Spring 2010

Introduction/Background  Objective of Project Create an alternate solution for predicting residual stresses in dents. The solution will be using LS-DYNA to provide a cost effective and repeatable solution.  Background Information In the aerospace industry, components are often damaged due to dents during the assembly process and during the components life cycle due to FOD. When the fatigue life is evaluated in thin components, the ultra conservative assumption that the dent can be modeled as a through crack is used to calculate crack propagation. If realistic stresses can be simulated with LS-DYNA, a more realistic cycle evaluation can be provided, thus providing significant cost savings.  Expected Project Outcome Obtain residual stresses in a component due to a dent from a spherical impact simulated in LS – DYNA. The residual stresses can then be used to evaluate crack growth and fatigue life

Methodology/Approach Review Background Material Perform Analysis to match experimental data observed in “The Residual Stress State Due to a Spherical Hard-Body Impact” by B.L. Boyce  Perform analytical calculations  Create Ball and Plate model  Apply Material Properties, Boundary conditions, contact parameters, etc.  Perform explicit simulation in LS-DYNA by applying velocity to ball Debug Accordingly  Perform explicit / implicit Analysis in LS-DYNA by applying springback simulation to analysis Debug Accordingly to match experimental results Compare experimental results, analytical results, and numerical results Record residual stress, strain, displacement, and run-time (cost) Make conclusions If time permits, compare crack growth prediction of plate with:  Through crack  Residual Stress

Problem Description Dials to Turn  Mesh Density  Material Properties Strain Rates Failure strains (to possibly match high velocity impacts)  Simulation Formulations Explicit analysis Implicit Seamless springback simulation Implicit dynain springback simulation  Contact Parameters Contact Type Contact stiffness Dampening  Element types  Time Steps

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