Em2004 270

Material Point Method Simulations of Fragmenting Cylinders

Biswajit BanerjeeDepartment of Mechanical Engineering

University of Utah

17th ASCE Engineering Mechanics Conference, 2004

Outline

• Scenario

• Material Point Method (MPM)

• Approach

• Validation

• Simulations of fragmentation

Scenario

What happens to the container ?

Simulation Requirements

• Fire-container interaction

• Large deformations

• Strain-rate/temperature dependence

• Failure due to void growth/shear bands

The Material Point Method (MPM)(Sulsky et al.,1994)

Why MPM ?

• Tightly-coupled fluid-structure interaction.

• No mesh entanglement.• Convenient contact

framework.• Mesh generation trivial.• Easily parallelized.• No tensile instabilities.

• First-order accuracy.• High particle density for

tension dominated problems.

• Computationally more expensive than FEM.

Advantages Disadvantages

Stress update

• Hypoelastic-plastic material• Corotational formulation (Maudlin & Schiferl,1996)

• Semi-implicit (Nemat-Nasser & Chung, 1992)

• Stress tensor split into isotropic/deviatoric

• Radial return plasticity

• State dependent elastic moduli, melting temperature

Plasticity modeling

• Isotropic stress using Mie-Gruneisen Equation of State.

• Deviatoric stress :• Flow stress : Johnson-Cook, Mechanical Threshold

Stress, Steinberg-Cochran-Guinan• Yield function : von Mises, Gurson-Tvergaard-

Needleman, Rousselier

• Temperature rise due to plastic dissipation• Associated flow rule

Damage/Failure modeling

• Damage models:• Void nucleation/growth (strain-based)• Porosity evolution (strain-based)• Scalar damage evolution: Johnson-Cook/Hancock-

MacKenzie

• Failure• Melt temperature exceeded• Modified TEPLA model (Addessio and Johnson, 1988)

• Drucker stability postulate• Loss of hyperbolicity (Acoustic tensor)

Fracture Simulation

• Particle mass is removed.

• Particle stress is set to zero.

• Particle converted into a new material that interacts with the rest of the body via contact.

Validation: Plasticity Models

6061-T6 Aluminum EFC Copper

JC MTS SCG JC MTS SCG

635 K 194 m/s

655 K 354 m/s

718 K 188 m/s

727 K 211 m/s

Validation: Mesh dependence

OFHC Copper298 K 177 m/sMTS

6061-T6 Al655 K 354 m/sJC

1,200,000 cells151,000 cells18,900 cells

735,000 cells91,800 cells11,500 cells

Validation: Penetration/Failure

Validation: Penetration/Failure

160,000 cells 1,280,000 cells

Validation: Erosion Algorithm

Validation: Impact

Validation: Impact Results

Validation: 2D Fragmentation

Validation: 2D Fragmentation

Gurson-Tvergaard-Needleman yield, Drucker stability, Acoustic tensor, Gaussian porosity, fragments match Grady equation, gases with ICE-CFD code.

JC (steel), ViscoScram (PBX 9501)

MTS (steel), ViscoScram (PBX 9501)

Simulations: 3D Fragmentation

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Simulation: Container in Fire

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Questions ?