Modelling and Simulation for dent/deformation removal

Henry TanTuesday, 24/2/09

Collapse of a Plate

r: radius of collapsed area

R: radius of the pressurized areah: thickness

2

2.81cr Y

hp

R

0.73r R

pressure p

Material regarded as rigid/perfect plastic:

Rr

Critical pulling pressure to cause plate collapse

2 22.81cr cr YF R p h Critical pulling force to generate collapse

collapsedarea Collapse refers to loss of the load-

carrying capacity of a component

Rigid / Perfect-Plastic Material

0

100

200

300

400

500

600

0 0.005 0.01 0.015 0.02

Strain

Str

ess

(Mpa

) rigid/perfect plastic

Test data for a steel

elastic/linear-hardening

Sample 1: Twist-A-Dent

Twist the turning knob until the dent pops.

pulling bridge

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Sample 1: Calculations

Thickness: h = 1.5mm

2

3

2.81

2.5 10 N

cr YF h

400MPaY Yield stress:

Force needed to generate plastic collapse:

Radius of pulling bridge support support 0.04mR

Pressure on the bridge support during collapsing support 2

support

3

2

2

2.5 100.25MPa

2 3.14 0.04

crFp

R

Vacuum pressure to lift the dent to it's normal position

Sample 2: Pulling

Sample 2: Force Balance of the Puller

Pumping force

Pulling force

Pressure exerted by the dent to the puller

Finite Element Method: Elements and Nodes

Meshing: to create elements and nodes

Nodes: to save information

Element: to Interpolate information

Tetrahedron element

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

FEM Output for Design

Output: (deformation field, stress field)

Using output for design guidance

As a FEM User

1. Geometry 2. Materials

4. Load (increasing)3. Boundary conditions

0

100

200

300

400

500

600

0 0.005 0.01 0.015 0.02

Strain

Str

ess

(Mpa

)

Inputs for FEM processing (pre-processing)

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.