1. Modelling and Simulation for dent/deformation removal Henry Tan Tuesday, 24/2/09

2. Collapse of a Plate r: radius of collapsed area R: radius of the pressurized area h: thickness pressure p Material regarded as rigid/perfect plastic: R r Critical pulling pressure to cause plate collapse Critical pulling force to generate collapse collapsed area Collapse refers to loss of the load- carrying capacity of a component

3. Rigid / Perfect-Plastic Material rigid/perfect plastic Test data for a steel elastic/linear-hardening

4. Sample 1: Twist-A-Dent Twist the turning knob until the dent pops. pulling bridge Ads from Ding King: Dent Repair Tool

5. Sample 1: Calculations Thickness: h = 1.5mm Yield stress: Force needed to generate plastic collapse: Radius of pulling bridge support Pressure on the bridge support during collapsing

6. Vacuum pressure to lift the dent to it's normal position Sample 2: Pulling

7. Sample 2: Force Balance of the Puller Pumping force Pulling force Pressure exerted by the dent to the puller

8. Finite Element Method: Elements and Nodes Meshing: to create elements and nodes Nodes: to save information Element: to Interpolate information Tetrahedron element

9. System Equations: Establishing and Solving Solving equations: nonlinear equations (involving plasticity) Build up system equations: Approach 1: Force balance equations for each node Approach 2: Minimize the potential energy of the system

10. FEM Output for Design Output: (deformation field, stress field) Using output for design guidance

11. As a FEM User 1. Geometry 2. Materials 4. Load (increasing)3. Boundary conditions Inputs for FEM processing (pre-processing)

12. Initial Residual Stresses, Damaged Material Initial residual stresses and damaged material properties are unknown. Denting process needed to generate the stresses and materials before pulling. Dynamic denting (compared with static pulling/recovering) needs to be considered.