3.2 Material Models

Training Manual 00141915 Aug 2000

3.2-1

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.73.2 Material Models

• Material enhancements in ANSYS 5.7 include:

A. Material Definition GUI

B. Hyperelasticity

C. Metal Plasticity

D. Viscoplasticity

E. User Material Subroutine for 18x Elements


3.2-2

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.7Material Models

A. Material Definition GUI

• New GUI for material model definition

– Applicable to all linear and nonlinear materials (except ANSYS/LS-DYNA and FLOTRAN fluids)

– Logical tree structure sorted by discipline and behavior

– Associates all properties (MP’s and TB’s) for a material model, which is treated as a single entity


3.2-3

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.7Material Models

… Material Definition GUI

• Definition and editing of models

– Intuitive definition of complex relationships (combination models)

– Dynamic interface, e.g., {stress vs. strain} vs. temperature

• Provides a framework for future expansion

– Experimental data input

– Support for external material database (XML, proprietary…)


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.7Material Models


All models in database

All available materials grouped by discipline

• Models and disciplines


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.7Material Models


Expanded folder shows material model contents

Materials are grouped by behavior

• Subgroupings


3.2-7

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.7Material Models

B. Hyperelasticity

Background:

• Existing (5.6) mixed U-P elements (56, 58, 74, 158) have limited application

– Assumed not incompressible

– Pressure is NOT a DOF (eliminated before solution)

– Penalty based formulation causes problems

– Input via• TB,MOONEY,mat,ntemp,npts

• Material property dialogs


3.2-8

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.7Material Models

… Hyperelasticity

New in ANSYS 5.7:

• Mixed U-P formulation added to all 18x family of elements (except beams which are naturally excluded).

– Poisson’s ratio of 0.5 allowed (incompressible)

– Compressible and incompressible parts are two separate formulations

– Lagrange multipliers for Pressure DOF

– Includes all relevant stress states

– Input via:• New TB,HYPER option*

• New material definition GUI

*TB,BOYCE has been moved to TB,HYPER


3.2-9

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.7Material Models

… Hyperelasticity

• New formulation also offers more hyperelastic material models:

– Mooney-Rivlin

– Ogden

– Neohookean

– Polynomial

– Arruda-Boyce

– User hyperelasticity


3.2-10

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.7Material Models

...Hyperelasticity

• Example: Axisymmetric plug using Ogden model


3.2-11

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.7Material Models

...Hyperelasticity

• Example: Cook membrane problem using Mooney material


3.2-12

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.7Material Models

C. Metal Plasticity

• ANSYS 5.7 represents a significant change in the philosophy of material implementation: Keep material behavior separate from element technology.

– Allows complex behavior to be simulated by combining simple behaviors

– Easier to maintain existing material models and add new ones

• New plasticity model: Hill type anisotropy


3.2-13

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.7Material Models

...Metal Plasticity

Hill type Anisotropy

• Must be combined with another form of plasticity such as bilinear isotropic hardening

• 6 input constants define the ratio of the yield value in each orthogonal direction to that specified on the hardening model.

• Elastic portion of model may be isotropic or orthotropic


3.2-14

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.7Material Models

...Metal Plasticity

• Example - uniformly loaded stainless steel plate with constant pressure

BISO only BISO with Hill anisotropy


3.2-15

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.7Material Models

… Metal Plasticity

• Plasticity options available in 5.7:

– Isotropic hardening laws

– Kinematic hardening laws

– Anisotropic plasticity

– Viscoplasticity

– User material


3.2-16

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.7Material Models

D. Viscoplasticity

• Types of viscoplasticity in ANSYS 5.7:

– Creep• Implicit Creep

• Explicit Creep

• usercreep for implicit and usercr for explicit

– TB,ANAND for 106, 107 and 108 only

– TB,RATE for 18x elements• Peryzna

• Peirce

– User Material for 18x elements


3.2-17

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.7Material Models

… Viscoplasticity

• BISO only


3.2-18

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.7Material Models

… Viscoplasticity

• BISO plus Perzyna


3.2-19

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.7Material Models

… Viscoplasticity

• BISO plus Peirce


3.2-20

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.7Material Models

E. User Material

• Why User Material?

– Not all materials can be included• some material behavior proprietary

• need to apply limited resources to general behavior

– Gives users the ability to create custom material behavior

• Subroutine usermat*, which was beta at 5.6, is now released.

– Note: Some differences exist between beta and released versions. 5.6 users should re-create user material at 5.7.

*Not to be confused with USERPL, USERCR, etc


3.2-21

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.7Material Models

… User Material

• Subroutine usermat

– For 18x elements only, i.e, only structural analyses at the present time

– User must specify both linear and nonlinear properties

– Requires relink of ANSYS (use ANSCUSTOM script)

– Demonstration routine includes BISO plasticity

Documents

3.2 Material Models