cadfem-advanced-sealings.pdf

8/11/2019 cadfem-advanced-sealings.pdf

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Advanced Simulation of Sealings

CADFEM GmbH

Rainer Rauch

- 1 -

Recent developments in ANSYS V12 for the simulation of sealings

Element technology

Material models

Contact

Robust design and optimization


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New Element: 4 Node Tetrahedron: SOLID285

Motivation for 4-node tetrahedral elements

Current mesh generators produce triangular and tetrahedral elements reliably

Can be used to mesh very complex geometrical shapes

Element is less sensitive to distortion

Element is vital to rezoning and large deformation problems such as metal-forming

Drawbacks with 4-node tetrahedral elements

Standard displacement element is hopelessly locked by the incompressibility

Mixed displacement and pressure u/P formulation improves slightly the volumetric locking,

however

Stability is of utmost concern of mixed u/P formulation

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SOLID285: Stabilized Mixed u/P Formulation

Displacements

Hydrostatic pressure (HDSP)

Interpolation functions Linear functions for both displacements and pressures

Added to satisfy LBB condition

Introduced with enhanced strain method

Condensed out at element level

DOF: HDSP

A new DOF in ANSYS

Its energy-conjugate partner: DVOL volume change Convergence check for both is controlled by CNVTOL

ezyx uuu ),,(

),,,( puuuzyx

),,,( puuuzyx

e

1

2

3

4

),,,( puuuzyx

),,,( puuuzyx

DOFsInternal


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New Element Solid285

Poisson

Ratio Theory

Mixed u/p

enhancedTetra

Error (%) Mixed u/p Error(%)

Pure

Displacement

Error (%)

0.0000 3.7500 3.7275 0.5994 3.7274 0.6015 3.7235 0.7058

0.2500 4.4531 4.4242 0.6489 4.4237 0.6594 4.4124 0.9134

0.3000 4.5825 4.5520 0.6642 4.5513 0.6805 4.5365 1.0029

0.4900 5.0399 5.0008 0.7747 4.9701 1.3841 4.7941 4.8760

0.4990 5.0602 5.0204 0.7850 4.8935 3.2927 3.7532 25.8278

0.4999 5.0623 5.0224 0.7876 4.6940 7.2738 1.1884 76.5242

SOLID285 Regular u/P

1

2

3

4

ezyx uuu ),,(

),,,( puuu zyx

),,,( puuu zyx

e) ),,,( puuu zyx

),,,( puuu zyx

DOFsInternal

Expansion of a Thick walled cylinder under internal pressure Unstructured mesh with 10 divisions in thickness directions

Compare SOLID285 (Enhanced Tetra), regular mixed u/P and pure displacement formulations

Radial stress for v=0.4999

Analytical solutions: inner radius =-1, outer radius =0

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Tension Bending Torsion Shear

Accuracy


Efficiency


Robustness

Solid186

Solid285


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0.00

6000.00

0.00 15.00Weg [mm]

Kraft[N]

Messung:Berechnung mit Solid 285:

Computer xp64

- 2 CPUs, 3 GHz

Meshing

- 3 Min.

Analysis

- 50 min.

- 7 -

Import Mesh Regenerate Geometry Parameterize Geometry


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Linear Tets

SOLID285

SOLID187

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Element technology

Contact



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New Formulations: Bergstrm-Boyce

Bergstrm-Boyce (TB, BB) polymer viscoelasticity for current element

technologies

Elements: SOLID 185, 186, 187; SOLSH190; SHELL 208, 209, 281;

Features: pressure sensitive, combined with creep,

Combinations: isotropic damage (Ogden-

Drawback: no curve fitting available;

Benefits and Applications

Technologies: filled/unfilled elastomers; biocompatible devices; artificial

tissues.

Robustness: experimentally validated;

Physicality accounted: rate-dependence; hysteresis; symmetric stress

relaxation; (mild) Mullins effects.

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New Formulations: Mullins efect

Modified Ogden-Roxburgh (TB, CDM) isotropic damage model for current

element technologies

Elements: SOLID 185, 186, 187; SOLSH190; SHELL 208, 209, 281;

Features: isotropic cyclic softening in filled polymers (Mullins effect),Combinations: almost all nearly-, or fully incompressible isotropic

hyperelasticity models

Drawback: no curve fitting available; not applicable for foams.


Technologies: filled/unfilled elastomers; damage in biocompatible devices and

artificial tissues.

Robustness: validated;

Physicality accounted: amplitude dependent damage softening.


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Example: TB,CDM (Ogden-Roxburgh)

Objective: simulation of the cyclic, high-

pressure response of rubber sealing;

Specifics: Mullins effect and BC induced

incompressibility;

Material models: neo-Hooke with

Ogden-Roxburgh;

Element technology:

-PLANE182 (ESF).

Sealing

Steel cylinders

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Mullins effect: amplitude dependent (tangent) stiffness reduction

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

-0,05 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45

Uniaxial strain measureNo

rmalizeduniaxialstressmeasure

0,0292

0,

2

0,0458

0,

2


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Element technology

Material models

Contact


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Rigid contact in Workbench

WB now supports all types of rigid contacts

Solid, Shells and 2D; w,w/o midside nodes


Highly efficient contact simulation together with

the flexible definitions of joints and drivers


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Fluid Pressure Penetration

Modeling fluid pressure penetration

- Fluid penetrating two contact surfaces- 2D/3D surface-to-surface contact pair

- Small and large sliding contact

- Rigid-flexible and flexible-flexible contact

- Pressure progresses with contact status


- Leakage Simulation

- Easy to use with few commands

- Makes complex macros obsolete

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Element technology

Material models

Contact



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Workflow: Parameters and optimization

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geometry

material properties

b.c. from any

physics

Overview in theproject page


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Sensitivities how

big is the influence of

an Input parameter

on an Output

parameter?

Correlation matrix

Which are the best

parameters to control

the model behaviour?

Define a goal and

let Design

Exploration

optimize your

model by searching

on a response

surface

Workflow: Parameters and optimization

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cadfem-advanced-sealings.pdf

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