Abaqus 6 8 Analysis 5

Abaqus Analysis Users Manual

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Abaqus Analysis

Users Manual

Volume V

Version 6.8

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Legal NoticesCAUTION: This documentation is intended for qualied users who will exercise sound engineering judgment and expertise in the use of the Abaqus Software. The Abaqus Software is inherently complex, and the examples and procedures in this documentation are not intended to be exhaustive or to apply to any particular situation. Users are cautioned to satisfy themselves as to the accuracy and results of their analyses. Dassault Systmes and its subsidiaries, including Dassault Systmes Simulia Corp., shall not be responsible for the accuracy or usefulness of any analysis performed using the Abaqus Software or the procedures, examples, or explanations in this documentation. Dassault Systmes and its subsidiaries shall not be responsible for the consequences of any errors or omissions that may appear in this documentation. DASSAULT SYSTMES AND ITS SUBSIDIARIES DISCLAIM ALL EXPRESS OR IMPLIED REPRESENTATIONS AND WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OF THE CONTENTS OF THIS DOCUMENTATION. IN NO EVENT SHALL DASSAULT SYSTMES, ITS SUBSIDIARIES, OR THEIR THIRD-PARTY PROVIDERS BE LIABLE FOR ANY INDIRECT, INCIDENTAL, PUNITIVE, SPECIAL, OR CONSEQUENTIAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS PROFITS, BUSINESS INTERRUPTION, OR LOSS OF BUSINESS INFORMATION) EVEN IF DASSAULT SYSTMES OR ITS SUBSIDIARY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. The Abaqus Software is available only under license from Dassault Systmes or its subsidiary and may be used or reproduced only in accordance with the terms of such license. This documentation and the software described in this documentation are subject to change without prior notice. No part of this documentation may be reproduced or distributed in any form without prior written permission of Dassault Systmes or its subsidiary. Export and re-export of the Abaqus Software and this documentation is subject to United States and other export control regulations. Each user is responsible for compliance with applicable export regulations. The Abaqus Software is a product of Dassault Systmes Simulia Corp., Providence, RI, USA. Dassault Systmes, 2008 Printed in the United States of America. U.S. GOVERNMENT USERS: The Abaqus Software and its documentation are commercial items, specically commercial computer software and commercial computer software documentation and, consistent with FAR 12.212 and DFARS 227.7202, as applicable, are provided with restricted rights in accordance with license terms. Abaqus, the 3DS logo, SIMULIA, and CATIA are trademarks or registered trademarks of Dassault Systmes or its subsidiaries in the United States and/or other countries. Other company, product, and service names may be trademarks or service marks of their respective owners. For additional information concerning trademarks, copyrights, and licenses, see the Legal Notices in the Abaqus Version 6.8 Release Notes and the notices at: http://www.simulia.com/products/products_legal.html.

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PrefaceThis section lists various resources that are available for help with using Abaqus.Support

Both technical engineering support (for problems with creating a model or performing an analysis) and systems support (for installation, licensing, and hardware-related problems) for Abaqus are offered through a network of local support ofces. Contact information is listed in the front of each Abaqus manual.SIMULIA Online Support System

The SIMULIA Online Support System (SOSS) has a knowledge database of SIMULIA Answers. The SIMULIA Answers are solutions to questions that we have had to answer or guidelines on how to use Abaqus. You can also submit new requests for support in the SOSS. All support incidents are tracked in the SOSS. If you are contacting us by means outside the SOSS to discuss an existing support problem and you know the incident number, please mention it so that we can consult the database to see what the latest action has been. To use the SOSS, you need to register with the system. Visit the My Support page at www.simulia.com for instructions on how to register. Many questions about Abaqus can also be answered by visiting the Products page and the Support page at www.simulia.com.Anonymous ftp site

Useful documents are maintained on an anonymous ftp account on the computer ftp.simulia.com. Login as user anonymous, and type your e-mail address as your password.Training

All ofces offer regularly scheduled public training classes. We also provide training seminars at customer sites. All training classes and seminars include workshops to provide as much practical experience with Abaqus as possible. For a schedule and descriptions of available classes, see www.simulia.com or call your local representative.Feedback

We welcome any suggestions for improvements to Abaqus software, the support program, or documentation. We will ensure that any enhancement requests you make are considered for future releases. If you wish to make a suggestion about the service or products, refer to www.simulia.com. Complaints should be addressed by contacting your local ofce or through www.simulia.com.

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CONTENTS

Contents Volume I

PART I1. Introduction Introduction

INTRODUCTION, SPATIAL MODELING, AND EXECUTION

Introduction: generalAbaqus syntax and conventions

1.1.1 1.2.1 1.2.2 1.3.1 1.4.1

Input syntax rules ConventionsDefining an Abaqus model

Dening a model in AbaqusParametric modeling

Parametric input2. Spatial Modeling Defining nodes

Node denition Parametric shape variation Nodal thicknesses Normal denitions at nodes Transformed coordinate systemsDefining elements

2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.3.1 2.3.2 2.3.3 2.3.4

Element denition Element foundations Dening reinforcement Dening rebar as an element property OrientationsDefining surfaces

Surfaces: overview Dening element-based surfaces Dening node-based surfaces Dening analytical rigid surfaces

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Dening Eulerian surfaces Operating on surfacesDefining rigid bodies

2.3.5 2.3.6 2.4.1 2.5.1 2.6.1 2.7.1 2.8.1 2.9.1 2.10.1

Rigid body denitionDefining integrated output sections

Integrated output section denitionDefining nonstructural mass

Nonstructural mass denitionDefining distributions

Distribution denitionDefining display bodies

Display body denitionDefining an assembly

Dening an assemblyDefining matrices

Dening matrices3. Execution Procedures Execution procedures: overview

Execution procedure for Abaqus: overviewExecution procedures

3.1.1 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 3.2.9 3.2.10 3.2.11 3.2.12 3.2.13 3.2.14 3.2.15

Execution procedure for obtaining information Execution procedure for Abaqus/Standard and Abaqus/Explicit Execution procedure for Abaqus/CAE Execution procedure for Abaqus/Viewer Execution procedure for Python Execution procedure for parametric studies Execution procedure for Abaqus HTML documentation Execution procedure for licensing utilities Execution procedure for ASCII translation of results (.fil) les Execution procedure for joining results (.fil) les Execution procedure for querying the keyword/problem database Execution procedure for fetching sample input les Execution procedure for making user-dened executables and subroutines Execution procedure for input le and output database upgrade utility Execution procedure for generating output database reports

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Execution procedure for joining output database (.odb) les from restarted analyses Execution procedure for combining output from substructures Execution procedure for network output database le connector Execution procedure for xed format conversion utility Execution procedure for translating NASTRAN bulk data les to Abaqus input les Execution procedure for translating Abaqus input les to NASTRAN bulk data les Execution procedure for translating PAM-CRASH input les to partial Abaqus input les Execution procedure for translating RADIOSS input les to partial Abaqus input les Execution procedure for translating Abaqus output database les to NASTRAN Output2 results les Execution procedure for exchanging Abaqus data with ZAERO Execution procedure for encrypting and decrypting Abaqus input data Execution procedures for job execution controlEnvironment file settings

3.2.16 3.2.17 3.2.18 3.2.19 3.2.20 3.2.21 3.2.22 3.2.23 3.2.24 3.2.25 3.2.26 3.2.27 3.3.1 3.4.1 3.5.1 3.6.1

Using the Abaqus environment settingsManaging memory and disk resources

Managing memory and disk use in AbaqusFile extension definitions

File extensions used by AbaqusFORTRAN unit numbers

FORTRAN unit numbers used by Abaqus

PART II4. Output Output

OUTPUT

Output Output to the data and results les Output to the output databaseOutput variables

4.1.1 4.1.2 4.1.3 4.2.1 4.2.2 4.3.1

Abaqus/Standard output variable identiers Abaqus/Explicit output variable identiersThe postprocessing calculator

The postprocessing calculator

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5.

File Output Format Accessing the results file

Accessing the results le: overview Results le output format Accessing the results le information Utility routines for accessing the results leOI.1 OI.2 Abaqus/Standard Output Variable Index Abaqus/Explicit Output Variable Index

5.1.1 5.1.2 5.1.3 5.1.4

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Volume II

PART III6. Analysis Procedures Introduction

ANALYSIS PROCEDURES, SOLUTION, AND CONTROL

Procedures: overview General and linear perturbation procedures Multiple load case analysis Direct linear equation solver Iterative linear equation solver Static stress/displacement analysis Static stress analysis procedures: overview Static stress analysis Eigenvalue buckling prediction Unstable collapse and postbuckling analysis Quasi-static analysis Direct cyclic analysis Low-cycle fatigue analysis using the direct cyclic approach Dynamic stress/displacement analysis Dynamic analysis procedures: overview Implicit dynamic analysis using direct integration Explicit dynamic analysis Direct-solution steady-state dynamic analysis Natural frequency extraction Complex eigenvalue extraction Transient modal dynamic analysis Mode-based steady-state dynamic analysis Subspace-based steady-state dynamic analysis Response spectrum analysis Random response analysis Steady-state transport analysis Steady-state transport analysis Heat transfer and thermal-stress analysis Heat transfer analysis procedures: overview Uncoupled heat transfer analysis Sequentially coupled thermal-stress analysis

6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.2.6 6.2.7 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6 6.3.7 6.3.8 6.3.9 6.3.10 6.3.11 6.4.1 6.5.1 6.5.2 6.5.3

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Fully coupled thermal-stress analysis Adiabatic analysisElectrical analysis

6.5.4 6.5.5

Electrical analysis procedures: overview Coupled thermal-electrical analysis Piezoelectric analysisCoupled pore fluid flow and stress analysis

6.6.1 6.6.2 6.6.3

Coupled pore uid diffusion and stress analysis Geostatic stress stateMass diffusion analysis

6.7.1 6.7.2

Mass diffusion analysisAcoustic and shock analysis

6.8.1

Acoustic, shock, and coupled acoustic-structural analysisAbaqus/Aqua analysis

6.9.1

Abaqus/Aqua analysisAnnealing

6.10.1

Annealing procedure7. Analysis Solution and Control Solving nonlinear problems

6.11.1

Solving nonlinear problems Contact iterationsAnalysis convergence controls

7.1.1 7.1.2

Convergence and time integration criteria: overview Commonly used control parameters Convergence criteria for nonlinear problems Time integration accuracy in transient problems

7.2.1 7.2.2 7.2.3 7.2.4

PART IV8. Analysis Techniques: Introduction

ANALYSIS TECHNIQUES

Analysis techniques: overview

8.1.1

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9.

Analysis Continuation Techniques Restarting an analysis

Restarting an analysisImporting and transferring results

9.1.1 9.2.1 9.2.2 9.2.3 9.2.4

Transferring results between Abaqus analyses: overview Transferring results between Abaqus/Explicit and Abaqus/Standard Transferring results from one Abaqus/Standard analysis to another Transferring results from one Abaqus/Explicit analysis to another10. Modeling Abstractions Substructuring

Using substructures Dening substructuresSubmodeling

10.1.1 10.1.2 10.2.1 10.2.2 10.2.3 10.3.1 10.4.1 10.4.2 10.4.3 10.5.1

Submodeling: overview Node-based submodeling Surface-based submodelingGenerating global matrices

Generating global matrices Symmetric model generation Transferring results from a symmetric mesh or a partial three-dimensional mesh to a full three-dimensional mesh Analysis of models that exhibit cyclic symmetryMeshed beam cross-sections

Symmetric model generation, results transfer, and analysis of cyclic symmetry models

Meshed beam cross-sections11. Special-Purpose Techniques Inertia relief

Inertia reliefMesh modification or replacement

11.1.1 11.2.1 11.3.1

Element and contact pair removal and reactivationGeometric imperfections

Introducing a geometric imperfection into a model

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Fracture mechanics

Fracture mechanics: overview Contour integral evaluation Crack propagation analysisHydrostatic fluid modeling

11.4.1 11.4.2 11.4.3

Modeling uid-lled cavitiesSurface-based fluid modeling

11.5.1

Surface-based uid cavities: overview Dening uid cavities Dening uid exchange Dening inatorsMass scaling

11.6.1 11.6.2 11.6.3 11.6.4

Mass scalingSteady-state detection

11.7.1

Steady-state detectionParallel execution

11.8.1

Parallel execution in Abaqus Parallel execution in Abaqus/Standard Parallel execution in Abaqus/Explicit12. Adaptivity Techniques Adaptivity techniques: overview

11.9.1 11.9.2 11.9.3

Adaptivity techniquesALE adaptive meshing

12.1.1

ALE adaptive meshing: overview Dening ALE adaptive mesh domains in Abaqus/Explicit ALE adaptive meshing and remapping in Abaqus/Explicit Modeling techniques for Eulerian adaptive mesh domains in Abaqus/Explicit Output and diagnostics for ALE adaptive meshing in Abaqus/Explicit Dening ALE adaptive mesh domains in Abaqus/Standard ALE adaptive meshing and remapping in Abaqus/StandardAdaptive remeshing

12.2.1 12.2.2 12.2.3 12.2.4 12.2.5 12.2.6 12.2.7

Adaptive remeshing: overview Error indicators Solution-based mesh sizing

12.3.1 12.3.2 12.3.3

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Analysis continuation after mesh replacement

Mesh-to-mesh solution mapping13. Eulerian Analysis

12.4.1

Eulerian analysis14. Extending Abaqus Analysis Functionality Co-simulation

13.1.1

Co-simulation: overview Preparing an Abaqus analysis for co-simulationUser subroutines and utilities

14.1.1 14.1.2 14.2.1 14.2.2 14.2.3

User subroutines: overview Available user subroutines Available utility routines15. Design Sensitivity Analysis

Design sensitivity analysis16. Parametric Studies Scripting parametric studies

15.1.1

Scripting parametric studiesParametric studies: commands

16.1.1 16.2.1 16.2.2 16.2.3 16.2.4 16.2.5 16.2.6 16.2.7 16.2.8 16.2.9 16.2.10

aStudy.combine(): Combine parameter samples for parametric studies aStudy.constrain(): Constrain parameter value combinations in parametric studies aStudy.dene(): Dene parameters for parametric studies aStudy.execute(): Execute the analysis of parametric study designs aStudy.gather(): Gather the results of a parametric study aStudy.generate(): Generate the analysis job data for a parametric study aStudy.output(): Specify the source of parametric study results aStudy=ParStudy(): Create a parametric study aStudy.report(): Report parametric study results aStudy.sample(): Sample parameters for parametric studies

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CONTENTS

Volume III

PART V17. Materials: Introduction Introduction

MATERIALS

Material library: overview Material data denition Combining material behaviorsGeneral properties

17.1.1 17.1.2 17.1.3

Density18. Elastic Mechanical Properties Overview

17.2.1

Elastic behavior: overviewLinear elasticity

18.1.1

Linear elastic behavior No compression or no tension Plane stress orthotropic failure measuresPorous elasticity

18.2.1 18.2.2 18.2.3

Elastic behavior of porous materialsHypoelasticity

18.3.1

Hypoelastic behaviorHyperelasticity

18.4.1

Hyperelastic behavior of rubberlike materials Hyperelastic behavior in elastomeric foams Anisotropic hyperelastic behaviorStress softening in elastomers

18.5.1 18.5.2 18.5.3

Mullins effect in rubberlike materials Energy dissipation in elastomeric foamsViscoelasticity

18.6.1 18.6.2

Time domain viscoelasticity Frequency domain viscoelasticity

18.7.1 18.7.2

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Hysteresis

Hysteresis in elastomersEquations of state

18.8.1

Equation of state19. Inelastic Mechanical Properties Overview

18.9.1

Inelastic behaviorMetal plasticity

19.1.1

Classical metal plasticity Models for metals subjected to cyclic loading Rate-dependent yield Rate-dependent plasticity: creep and swelling Annealing or melting Anisotropic yield/creep Johnson-Cook plasticity Dynamic failure models Porous metal plasticity Cast iron plasticity Two-layer viscoplasticity ORNL Oak Ridge National Laboratory constitutive model Deformation plasticityOther plasticity models

19.2.1 19.2.2 19.2.3 19.2.4 19.2.5 19.2.6 19.2.7 19.2.8 19.2.9 19.2.10 19.2.11 19.2.12 19.2.13

Extended Drucker-Prager models Modied Drucker-Prager/Cap model Mohr-Coulomb plasticity Critical state (clay) plasticity model Crushable foam plasticity modelsFabric materials

19.3.1 19.3.2 19.3.3 19.3.4 19.3.5

Fabric material behaviorJointed materials

19.4.1

Jointed material modelConcrete

19.5.1

Concrete smeared cracking Cracking model for concrete Concrete damaged plasticity

19.6.1 19.6.2 19.6.3

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Permanent set in rubberlike materials

Permanent set in rubberlike materials20. Progressive Damage and Failure Progressive damage and failure: overview

19.7.1

Progressive damage and failureDamage and failure for ductile metals

20.1.1 20.2.1 20.2.2 20.2.3 20.3.1 20.3.2 20.3.3 20.4.1 20.4.2 20.4.3

Damage and failure for ductile metals: overview Damage initiation for ductile metals Damage evolution and element removal for ductile metalsDamage and failure for fiber-reinforced composites

Damage and failure for ber-reinforced composites: overview Damage initiation for ber-reinforced composites Damage evolution and element removal for ber-reinforced compositesDamage and failure for ductile materials in low-cycle fatigue analysis

Damage and failure for ductile materials in low-cycle fatigue analysis: overview Damage initiation for ductile materials in low-cycle fatigue Damage evolution for ductile materials in low-cycle fatigue21. Other Material Properties Mechanical properties

Material damping Thermal expansionHeat transfer properties

21.1.1 21.1.2 21.2.1 21.2.2 21.2.3 21.2.4 21.3.1 21.4.1 21.5.1 21.5.2

Thermal properties: overview Conductivity Specic heat Latent heatAcoustic properties

Acoustic mediumHydrostatic fluid properties

Hydrostatic uid modelsMass diffusion properties

Diffusivity Solubility

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Electrical properties

Electrical conductivity Piezoelectric behaviorPore fluid flow properties

21.6.1 21.6.2 21.7.1 21.7.2 21.7.3 21.7.4 21.7.5 21.7.6 21.8.1 21.8.2

Pore uid ow properties Permeability Porous bulk moduli Sorption Swelling gel Moisture swellingUser materials

User-dened mechanical material behavior User-dened thermal material behavior

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CONTENTS

Volume IV

PART VI22. Elements: Introduction

ELEMENTS

Element library: overview Choosing the elements dimensionality Choosing the appropriate element for an analysis type Section controls23. Continuum Elements General-purpose continuum elements

22.1.1 22.1.2 22.1.3 22.1.4

Solid (continuum) elements One-dimensional solid (link) element library Two-dimensional solid element library Three-dimensional solid element library Cylindrical solid element library Axisymmetric solid element library Axisymmetric solid elements with nonlinear, asymmetric deformationInfinite elements

23.1.1 23.1.2 23.1.3 23.1.4 23.1.5 23.1.6 23.1.7 23.2.1 23.2.2 23.3.1 23.3.2

Innite elements Innite element libraryWarping elements

Warping elements Warping element library24. Structural Elements Membrane elements

Membrane elements General membrane element library Cylindrical membrane element library Axisymmetric membrane element libraryTruss elements

24.1.1 24.1.2 24.1.3 24.1.4 24.2.1 24.2.2 24.3.1

Truss elements Truss element libraryBeam elements

Beam modeling: overview

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Choosing a beam cross-section Choosing a beam element Beam element cross-section orientation Beam section behavior Using a beam section integrated during the analysis to dene the section behavior Using a general beam section to dene the section behavior Beam element library Beam cross-section libraryFrame elements

24.3.2 24.3.3 24.3.4 24.3.5 24.3.6 24.3.7 24.3.8 24.3.9

Frame elements Frame section behavior Frame element libraryElbow elements

24.4.1 24.4.2 24.4.3

Pipes and pipebends with deforming cross-sections: elbow elements Elbow element libraryShell elements

24.5.1 24.5.2

Shell elements: overview Choosing a shell element Dening the initial geometry of conventional shell elements Shell section behavior Using a shell section integrated during the analysis to dene the section behavior Using a general shell section to dene the section behavior Three-dimensional conventional shell element library Continuum shell element library Axisymmetric shell element library Axisymmetric shell elements with nonlinear, asymmetric deformation25. Inertial, Rigid, and Capacitance Elements Point mass elements

24.6.1 24.6.2 24.6.3 24.6.4 24.6.5 24.6.6 24.6.7 24.6.8 24.6.9 24.6.10

Point masses Mass element libraryRotary inertia elements

25.1.1 25.1.2

Rotary inertia Rotary inertia element libraryRigid elements

25.2.1 25.2.2

Rigid elements Rigid element library

25.3.1 25.3.2

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Capacitance elements

Point capacitance Capacitance element library26. Connector Elements Connector elements

25.4.1 25.4.2

Connectors: overview Connector elements Connector actuation Connector element library Connection-type libraryConnector element behavior

26.1.1 26.1.2 26.1.3 26.1.4 26.1.5

Connector behavior Connector elastic behavior Connector damping behavior Connector functions for coupled behavior Connector friction behavior Connector plastic behavior Connector damage behavior Connector stops and locks Connector failure behavior Connector uniaxial behavior27. Special-Purpose Elements Spring elements

26.2.1 26.2.2 26.2.3 26.2.4 26.2.5 26.2.6 26.2.7 26.2.8 26.2.9 26.2.10

Springs Spring element libraryDashpot elements

27.1.1 27.1.2

Dashpots Dashpot element libraryFlexible joint elements

27.2.1 27.2.2

Flexible joint element Flexible joint element libraryDistributing coupling elements

27.3.1 27.3.2

Distributing coupling elements Distributing coupling element library

27.4.1 27.4.2

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Cohesive elements

Cohesive elements: overview Choosing a cohesive element Modeling with cohesive elements Dening the cohesive elements initial geometry Dening the constitutive response of cohesive elements using a continuum approach Dening the constitutive response of cohesive elements using a traction-separation description Dening the constitutive response of uid within the cohesive element gap Two-dimensional cohesive element library Three-dimensional cohesive element library Axisymmetric cohesive element libraryGasket elements

27.5.1 27.5.2 27.5.3 27.5.4 27.5.5 27.5.6 27.5.7 27.5.8 27.5.9 27.5.10

Gasket elements: overview Choosing a gasket element Including gasket elements in a model Dening the gasket elements initial geometry Dening the gasket behavior using a material model Dening the gasket behavior directly using a gasket behavior model Two-dimensional gasket element library Three-dimensional gasket element library Axisymmetric gasket element librarySurface elements

27.6.1 27.6.2 27.6.3 27.6.4 27.6.5 27.6.6 27.6.7 27.6.8 27.6.9 27.7.1 27.7.2 27.7.3 27.7.4

Surface elements General surface element library Cylindrical surface element library Axisymmetric surface element libraryHydrostatic fluid elements

Hydrostatic uid elements Hydrostatic uid element library Fluid link elements Hydrostatic uid link libraryTube support elements

27.8.1 27.8.2 27.8.3 27.8.4

Tube support elements Tube support element libraryLine spring elements

27.9.1 27.9.2 27.10.1 27.10.2

Line spring elements for modeling part-through cracks in shells Line spring element library

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Elastic-plastic joints

Elastic-plastic joints Elastic-plastic joint element libraryDrag chain elements

27.11.1 27.11.2 27.12.1 27.12.2 27.13.1 27.13.2 27.14.1 27.14.2 27.15.1 27.15.2 27.16.1 27.16.2

Drag chains Drag chain element libraryPipe-soil elements

Pipe-soil interaction elements Pipe-soil interaction element libraryAcoustic interface elements

Acoustic interface elements Acoustic interface element libraryEulerian elements

Eulerian elements Eulerian element libraryUser-defined elements

User-dened elements User-dened element libraryEI.1 EI.2 Abaqus/Standard Element Index Abaqus/Explicit Element Index

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CONTENTS

Volume V

PART VII28. Prescribed Conditions Overview

PRESCRIBED CONDITIONS

Prescribed conditions: overview Amplitude curvesInitial conditions

28.1.1 28.1.2 28.2.1 28.3.1 28.4.1 28.4.2 28.4.3 28.4.4 28.4.5 28.4.6 28.5.1 28.6.1

Initial conditionsBoundary conditions

Boundary conditionsLoads

Applying loads: overview Concentrated loads Distributed loads Thermal loads Acoustic and shock loads Pore uid owPrescribed assembly loads

Prescribed assembly loadsPredefined fields

Predened elds

PART VIII29. Constraints Overview

CONSTRAINTS

Kinematic constraints: overviewMulti-point constraints

29.1.1 29.2.1 29.2.2 29.2.3

Linear constraint equations General multi-point constraints Kinematic coupling constraints

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CONTENTS

Surface-based constraints

Mesh tie constraints Coupling constraints Shell-to-solid coupling Mesh-independent fastenersEmbedded elements

29.3.1 29.3.2 29.3.3 29.3.4 29.4.1 29.5.1 29.6.1

Embedded elementsElement end release

Element end releaseOverconstraint checks

Overconstraint checks

PART IX30. Defining Contact Interactions Overview

INTERACTIONS

Contact interaction analysis: overviewDefining contact pairs in Abaqus/Standard

30.1.1 30.2.1 30.2.2 30.2.3 30.2.4 30.2.5 30.2.6 30.2.7 30.2.8 30.2.9 30.2.10 30.2.11 30.2.12 30.2.13 30.2.14 30.3.1 30.3.2

Dening contact pairs in Abaqus/Standard Contact formulations in Abaqus/Standard Contact constraint enforcement methods in Abaqus/Standard Modeling contact interference ts in Abaqus/Standard Adjusting initial surface positions and specifying initial clearances in Abaqus/Standard contact pairs Smoothing contact surfaces in Abaqus/Standard Removing/reactivating Abaqus/Standard contact pairs Dening tied contact in Abaqus/Standard Extending master surfaces and slide lines Contact modeling if substructures are present Contact modeling if asymmetric-axisymmetric elements are present Contact diagnostics in an Abaqus/Standard analysis Common difculties associated with contact modeling in Abaqus/Standard Adjusting contact controls in Abaqus/StandardDefining general contact in Abaqus/Explicit

Dening general contact interactions in Abaqus/Explicit Assigning surface properties for general contact in Abaqus/Explicit

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CONTENTS

Assigning contact properties for general contact in Abaqus/Explicit Contact formulation for general contact in Abaqus/Explicit Resolving initial overclosures and specifying initial clearances for general contact in Abaqus/Explicit Contact controls for general contact in Abaqus/ExplicitDefining contact pairs in Abaqus/Explicit

30.3.3 30.3.4 30.3.5 30.3.6

Dening contact pairs in Abaqus/Explicit Assigning surface properties for contact pairs in Abaqus/Explicit Assigning contact properties for contact pairs in Abaqus/Explicit Contact formulations for contact pairs in Abaqus/Explicit Adjusting initial surface positions and specifying initial clearances for contact pairs in Abaqus/Explicit Common difculties associated with contact modeling using contact pairs in Abaqus/Explicit31. Contact Property Models Mechanical contact properties

30.4.1 30.4.2 30.4.3 30.4.4 30.4.5 30.4.6

Mechanical contact properties: overview Contact pressure-overclosure relationships Contact damping Contact blockage Frictional behavior User-dened interfacial constitutive behavior Pressure penetration loading Interaction of debonded surfaces Breakable bonds Surface-based cohesive behaviorThermal contact properties

31.1.1 31.1.2 31.1.3 31.1.4 31.1.5 31.1.6 31.1.7 31.1.8 31.1.9 31.1.10

Thermal contact propertiesElectrical contact properties

31.2.1

Electrical contact propertiesPore fluid contact properties

31.3.1

Pore uid contact properties32. Contact Elements in Abaqus/Standard Contact modeling with elements

31.4.1

Contact modeling with elements

32.1.1

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CONTENTS

Gap contact elements

Gap contact elements Gap element libraryTube-to-tube contact elements

32.2.1 32.2.2 32.3.1 32.3.2 32.4.1 32.4.2 32.5.1 32.5.2

Tube-to-tube contact elements Tube-to-tube contact element librarySlide line contact elements

Slide line contact elements Axisymmetric slide line element libraryRigid surface contact elements

Rigid surface contact elements Axisymmetric rigid surface contact element library33. Defining Cavity Radiation in Abaqus/Standard

Cavity radiation

33.1.1

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Part VII: Prescribed ConditionsChapter 28, Prescribed Conditions

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28.Overview

Prescribed Conditions28.1 28.2 28.3 28.4 28.5 28.6

Initial conditions Boundary conditions Loads Prescribed assembly loads Predened elds

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OVERVIEW

28.1

Overview

Prescribed conditions: overview, Section 28.1.1 Amplitude curves, Section 28.1.2

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28.1.1

PRESCRIBED CONDITIONS: OVERVIEW

The following types of external conditions can be prescribed in an Abaqus model:

Initial conditions: Nonzero initial conditions can be dened for many variables, as described in Initial conditions, Section 28.2.1. Boundary conditions: Boundary conditions are used to prescribe values of basic solution variables: displacements and rotations in stress/displacement analysis, temperature in heat transfer or coupled thermal-stress analysis, electrical potential in coupled thermal-electrical analysis, pore pressure in soils analysis, acoustic pressure in acoustic analysis, etc. Boundary conditions can be dened as described in Boundary conditions, Section 28.3.1. Loads:

Many types of loading are available, depending on the analysis procedure. Applying loads: overview, Section 28.4.1, gives an overview of loading in Abaqus. Load types specic to one analysis procedure are described in the appropriate procedure section in Part III, Analysis Procedures, Solution, and Control. General loads, which can be applied in multiple analysis types, are described in: Concentrated loads, Section 28.4.2 Distributed loads, Section 28.4.3 Thermal loads, Section 28.4.4 Acoustic and shock loads, Section 28.4.5 Pore uid ow, Section 28.4.6

Prescribed assembly loads:

Pre-tension sections can be dened in Abaqus/Standard to prescribe assembly loads in bolts or any other type of fastener. Pre-tension sections are described in Prescribed assembly loads, Section 28.5.1.

Connector loads and motions: Connector elements can be used to dene complex mechanical connections between parts, including actuation with prescribed loads or motions. Connector elements are described in Connectors: overview, Section 26.1.1. Predefined fields: Predened elds are time-dependent, non-solution-dependent elds that exist over the spatial domain of the model. Temperature is the most commonly dened eld. Predened elds are described in Predened elds, Section 28.6.1.

Amplitude variations

Complex time- or frequency-dependent boundary conditions, loads, and predened elds can be specied by referring to an amplitude curve in the prescribed condition denition. Amplitude curves are explained in Amplitude curves, Section 28.1.2. In Abaqus/Standard if no amplitude is referenced from the boundary condition, loading, or predened eld denition, the total magnitude can be applied instantaneously at the start of the step and remain constant throughout the step (a step variation) or it can vary linearly over the step from the value at the end of the previous step (or from zero at the start of the analysis) to the magnitude given

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28.1.11 EMail:[email protected]



(a ramp variation). You choose the type of variation when you dene the step; the default variation depends on the procedure chosen, as shown in Procedures: overview, Section 6.1.1. In Abaqus/Explicit if no amplitude is referenced from the boundary condition or loading denition, the total value will be applied instantaneously at the start of the step and will remain constant throughout the step (a step variation), although Abaqus/Explicit does not admit jumps in displacement (see Boundary conditions, Section 28.3.1). If no amplitude is referenced from a predened eld denition, the total magnitude will vary linearly over the step from the value at the end of the previous step (or from zero at the start of the analysis) to the magnitude given (a ramp variation). When boundary conditions are removed (see Boundary conditions, Section 28.3.1), the boundary condition (displacement or rotation constraint in stress/displacement analysis) is converted to an applied conjugate ux (force or moment in stress/displacement analysis) at the beginning of the step. This ux magnitude is set to zero with a step or ramp variation depending on the procedure chosen, as discussed in Procedures: overview, Section 6.1.1. Similarly, when loads and predened elds are removed, the load is set to zero and the predened eld is set to its initial value. In Abaqus/Standard the variation of many prescribed conditions can be dened in user subroutines. In this case the magnitude of the variable can vary in any way with position and time. The magnitude variation for prescribing and removing conditions must be specied in the subroutine (see User subroutines and utilities, Section 14.2).Applying boundary conditions and loads in a local coordinate system

You can dene a local coordinate system at a node as described in Transformed coordinate systems, Section 2.1.5. Then, all input data for concentrated force and moment loading and for displacement and rotation boundary conditions are given in the local system.Loads and predefined fields available for various procedures

Table 28.1.11 Loads and predefined fields Added mass (concentrated and distributed) Base motion

Available loads and predened elds. Procedures Abaqus/Aqua eigenfrequency extraction analysis (Natural frequency extraction, Section 6.3.5) Procedures based on eigenmodes: Transient modal dynamic analysis, Section 6.3.7 Mode-based steady-state dynamic analysis, Section 6.3.8 Response spectrum analysis, Section 6.3.10 Random response analysis, Section 6.3.11

Boundary condition with a nonzero prescribed boundary

All procedures except those based on eigenmodes

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Loads and predefined fields Connector motion Connector load Cross-correlation property Current density (concentrated and distributed) Electric charge (concentrated and distributed) Equivalent pressure stress Film coefcient and associated sink temperature Fluid ux Fluid mass ow rate Flux (concentrated and distributed) Force and moment (concentrated and distributed) Incident wave loading

Procedures All relevant procedures except modal extraction, buckling, those based on eigenmodes, and direct steady-state dynamics Random response analysis, Section 6.3.11 Coupled thermal-electrical analysis, Section 6.6.2 Piezoelectric analysis, Section 6.6.3 Mass diffusion analysis, Section 6.8.1 All procedures involving temperature degrees of freedom Analysis involving hydrostatic uid elements Analysis involving convective heat transfer elements All procedures involving temperature degrees of freedom Mass diffusion analysis, Section 6.8.1 All procedures with displacement degrees of freedom except response spectrum Direct-integration dynamic analysis (Implicit dynamic analysis using direct integration, Section 6.3.2) involving solid and/or uid elements undergoing shock loading All procedures except those based on eigenmodes Coupled pore uid diffusion and stress analysis, Section 6.7.1 All procedures involving the use of substructures All procedures except adiabatic analysis, mode-based procedures, and procedures involving temperature degrees of freedom

Predened eld variable Seepage coefcient and associated sink pore pressure Distributed seepage ow Substructure load Temperature as a predened eld

With the exception of concentrated added mass and distributed added mass, no loads can be applied in eigenfrequency extraction analysis.

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AMPLITUDE CURVES

28.1.2

AMPLITUDE CURVES

Products: Abaqus/Standard References

Abaqus/Explicit

Abaqus/CAE

Prescribed conditions: overview, Section 28.1.1 *AMPLITUDE Chapter 40, The Amplitude toolset, of the Abaqus/CAE Users Manual

Overview

An amplitude curve:

allows arbitrary time (or frequency) variations of load, displacement, and other prescribed variables to be given throughout a step (using step time) or throughout the analysis (using total time); can be dened as a mathematical function (such as a sinusoidal variation), as a series of values at points in time (such as a digitized acceleration-time record from an earthquake), as a user-customized denition via user subroutines, or, in Abaqus/Standard, as values calculated based on a solution-dependent variable (such as the maximum creep strain rate in a superplastic forming problem); and can be referred to by name by any number of boundary conditions, loads, and predened elds.

Amplitude curves

By default, the values of loads, boundary conditions, and predened elds either change linearly with time throughout the step (ramp function) or they are applied immediately and remain constant throughout the step (step function)see Procedures: overview, Section 6.1.1. Many problems require a more elaborate denition, however. For example, different amplitude curves can be used to specify time variations for different loadings. One common example is the combination of thermal and mechanical load transients: usually the temperatures and mechanical loads have different time variations during the step. Different amplitude curves can be used to specify each of these time variations. Other examples include dynamic analysis under earthquake loading, where an amplitude curve can be used to specify the variation of acceleration with time, and underwater shock analysis, where an amplitude curve is used to specify the incident pressure prole. Amplitudes are dened as model data (i.e., they are not step dependent). Each amplitude curve must be named; this name is then referred to from the load, boundary condition, or predened eld denition (see Prescribed conditions: overview, Section 28.1.1).Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name Load or Interaction module: Create Amplitude: Name: name

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AMPLITUDE CURVES

Defining the time period

Each amplitude curve is a function of time or, for the steady-state dynamics procedure, a function of frequency (see Direct-solution steady-state dynamic analysis, Section 6.3.4, and Mode-based steadystate dynamic analysis, Section 6.3.8). Amplitudes dened as functions of time can be given in terms of step time (default) or in terms of total time. These time measures are dened in Conventions, Section 1.2.2.Input File Usage:

Use one of the following options: *AMPLITUDE, NAME=name, TIME=STEP TIME (default) *AMPLITUDE, NAME=name, TIME=TOTAL TIME Load or Interaction module: Create Amplitude: any type: Time span: Step time or Total time

Abaqus/CAE Usage:

Continuation of an amplitude reference in subsequent steps

If a boundary condition, load, or predened eld refers to an amplitude curve and the prescribed condition is not redened in subsequent steps, the following rules apply:

If the associated amplitude was given in terms of total time, the prescribed condition continues to follow the amplitude denition. If no associated amplitude was given or if the amplitude was given in terms of step time, the prescribed condition remains constant at the magnitude associated with the end of the previous step.

Specifying relative or absolute data

You can choose between specifying relative or absolute magnitudes for an amplitude curve.Relative data

By default, you give the amplitude magnitude as a multiple (fraction) of the reference magnitude given in the prescribed condition denition. This method is especially useful when the same variation applies to different load types.Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, VALUE=RELATIVE Amplitude magnitudes are always relative in Abaqus/CAE.

Absolute data

Alternatively, you can give absolute magnitudes directly. When this method is used, the values given in the prescribed condition denitions will be ignored. Absolute amplitude values should generally not be used to dene temperatures for nodes attached to beam or shell elements as values at the reference surface together with the gradient or gradients across the section (default cross-section denition; see Using a beam section integrated during the analysis to dene the section behavior, Section 24.3.6, and Using a shell section integrated during the analysis to

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AMPLITUDE CURVES

dene the section behavior, Section 24.6.5). Because the values given in the temperature eld denition are ignored, the absolute amplitude value will be used to dene both the temperature and the gradient.Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, VALUE=ABSOLUTE Absolute amplitude magnitudes are not supported in Abaqus/CAE.

Defining the amplitude data

The variation of an amplitude with time can be specied in several ways. The variation of an amplitude with frequency can be given only in tabular or equally spaced form.Defining tabular data

Choose the tabular denition method (default) to dene the amplitude curve as a table of values at convenient points on the time scale. Abaqus interpolates linearly between these values, as needed. By default in Abaqus/Standard, if the time derivatives of the function must be computed, some smoothing is applied at the time points where the time derivatives are discontinuous. In contrast, in Abaqus/Explicit no default smoothing is applied (other than the inherent smoothing associated with a nite time increment). You can modify the default smoothing values (smoothing is discussed in more detail below, under the heading Using an amplitude denition with boundary conditions); alternatively, a smooth step amplitude curve can be dened (see Dening smooth step data below). If the amplitude varies rapidlyas with the ground acceleration in an earthquake, for exampleyou must ensure that the time increment used in the analysis is small enough to pick up the amplitude variation accurately since Abaqus will sample the amplitude denition only at the times corresponding to the increments being used. If the analysis time in a step is less than the earliest time for which data exist in the table, Abaqus applies the earliest value in the table for all step times less than the earliest tabulated time. Similarly, if the analysis continues for step times past the last time for which data are dened in the table, the last value in the table is applied for all subsequent time. Several examples of tabular input are shown in Figure 28.1.21.Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, DEFINITION=TABULAR Load or Interaction module: Create Amplitude: Tabular

Defining equally spaced data

Choose the equally spaced denition method to give a list of amplitude values at xed time intervals beginning at a specied value of time. Abaqus interpolates linearly between each time interval. You must specify the xed time (or frequency) interval at which the amplitude data will be given, . You can also specify the time (or lowest frequency) at which the rst amplitude is given, ; the default is =0.0. If the analysis time in a step is less than the earliest time for which data exist in the table, Abaqus applies the earliest value in the table for all step times less than the earliest tabulated time. Similarly, if the analysis continues for step times past the last time for which data are dened in the table, the last value in the table is applied for all subsequent time.

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AMPLITUDE CURVES

Amplitude Table: a. Uniformly increasing load 1.0 Relative load magnitude 0.0 1.0 0.0 Time period 1.0 Time Relative load

0.0 1.0

b. Uniformly decreasing load Relative 1.0 load magnitude 0.0 1.0 1.0 0.0

0.0

Time period c. Variable load

1.0

Relative 1.0 load magnitude

0.0 0.4 0.6 0.8 1.0 Time period 1.0

0.0 1.2 0.5 0.5 0.0

0.0

Figure 28.1.21

Tabular amplitude denition examples.

Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, DEFINITION=EQUALLY SPACED, FIXED INTERVAL= , BEGIN= Load or Interaction module: Create Amplitude: Equally spaced: Fixed interval: The time (or lowest frequency) at which the rst amplitude is given, indicated in the rst table cell. , is

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AMPLITUDE CURVES

Defining periodic data

Choose the periodic denition method to dene the amplitude, a, as a Fourier series: for for where , N, , , , and , input is shown in Figure 28.1.22.Input File Usage: Abaqus/CAE Usage:0.60

, are user-dened constants. An example of this form of

*AMPLITUDE, NAME=name, DEFINITION=PERIODIC Load or Interaction module: Create Amplitude: Periodic

0.40

0.20

a0.00

0.20

0.40

0.00

0.10

0.20

0.30 Time

0.40

0.50

p

p = 0.2s a = A 0 + [A n cos n(tt 0) + B n sin n(tt 0)]n=1 N

for t t 0 for t < t 0

a = A0 with N = 2, = 31.416 rad/s, t 0 = 0.1614 s A 0= 0, A 1 = 0.227, B 1 = 0.0, A 2 = 0.413, B 2 = 0.0

Figure 28.1.22

Periodic amplitude denition example.

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AMPLITUDE CURVES

Defining modulated data

Choose the modulated denition method to dene the amplitude, a, as for for where , A, , Figure 28.1.23.Input File Usage: Abaqus/CAE Usage:

, and

are user-dened constants. An example of this form of input is shown in *AMPLITUDE, NAME=name, DEFINITION=MODULATED Load or Interaction module: Create Amplitude: Modulated

3

2

a 1

0

-1 0 1 2 3 4 5 Time 6 7 8 9 10 -1 ( x 10 )

a = A 0 + A sin 1 (tt 0) sin 2 (tt 0) a = A0 with A 0= 1.0, A = 2.0, 1 = 10,

for t > t 0 for t t 0

2 = 20, t 0 = .2

Figure 28.1.23

Modulated amplitude denition example.

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AMPLITUDE CURVES

Defining exponential decay

Choose the exponential decay denition method to dene the amplitude, a, as for for where , A, , and Figure 28.1.24.Input File Usage: Abaqus/CAE Usage:

are user-dened constants. An example of this form of input is shown in *AMPLITUDE, NAME=name, DEFINITION=DECAY Load or Interaction module: Create Amplitude: Decay

5

4

3 a 2

1

0 0 1 2 3 4 5 Time 6 7 8 9 10 ( x 10 -1)

a = A0 + A exp [(tt0) / td] a = A0 with A0 = 0.0, A = 5.0,

for t t0 for t < t0

t0 = 0.2,

td = 0.2

Figure 28.1.24

Exponential decay amplitude denition example.

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AMPLITUDE CURVES

Defining smooth step data

Choose the smooth step denition method to dene the amplitude, a, between two consecutive data points and as for where . The above function is such that at , at , and the rst and second derivatives of a are zero at and . This denition is intended to ramp up or down smoothly from one amplitude value to another. The amplitude, a, is dened such that for for where and are the rst and last data points, respectively. Examples of this form of input are shown in Figure 28.1.25 and Figure 28.1.26. This denition cannot be used to interpolate smoothly between a set of data points; i.e., this denition cannot be used to do curve tting.Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, DEFINITION=SMOOTH STEP Load or Interaction module: Create Amplitude: Smooth step

Defining a solution-dependent amplitude for superplastic forming analysis

Abaqus/Standard can calculate amplitude values based on a solution-dependent variable. Choose the solution-dependent denition method to create a solution-dependent amplitude curve. The data consist of an initial value, a minimum value, and a maximum value. The amplitude starts with the initial value and is then modied based on the progress of the solution, subject to the minimum and maximum values. The maximum value is typically the controlling mechanism used to end the analysis. This method is used with creep strain rate control for superplastic forming analysis (see Rate-dependent plasticity: creep and swelling, Section 19.2.4).Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, DEFINITION=SOLUTION DEPENDENT Load or Interaction module: Create Amplitude: Solution dependent

Defining the bubble load amplitude for an underwater explosion

Two interfaces are available in Abaqus for applying incident wave loads (see Incident wave loading due to external sources in Acoustic and shock loads, Section 28.4.5). For either interface bubble dynamics can be described using a model internal to Abaqus. A description of this built-in mechanical model and the parameters that dene the bubble behavior are discussed in Dening bubble loading for spherical incident wave loading in Acoustic and shock loads, Section 28.4.5. The related theoretical details are described in Loading due to an incident dilatational wave eld, Section 6.3.1 of the Abaqus Theory Manual.

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AMPLITUDE CURVES

1.0

a

0.1 Time

t0 = 0.0

A0 = 0.0

t1 = 0.1

A1 = 1.0

a = A0 for t t0 = A0 + (A1 A0) 3 (10 15 + 6 2) for t0 < t < t1 = A1 for t t1 where = t t0 t1 t 0

Figure 28.1.25

Smooth step amplitude denition example with two data points.

The preferred interface for incident wave loading due to an underwater explosion species bubble dynamics using the UNDEX charge property denition (see Dening bubble loading for spherical incident wave loading in Acoustic and shock loads, Section 28.4.5). The alternative interface for incident wave loading, which will be removed in a subsequent release of Abaqus, uses the bubble denition described in this section to dene bubble load amplitude curves. An example of the bubble amplitude denition with the following input data is shown in Figure 28.1.27.

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AMPLITUDE CURVES

(t3, A3)

(t4, A4)

(t2, A2) a (t5, A5) (t1, A1) (t6, A6)

(t0, A0)

Time

t0 = 0.0 t4 = 0.4

A0 = 0.1 A4 = 0.5

t1 = 0.1 t5 = 0.5

A1 = 0.1 A5 = 0.2

t2 = 0.2 t6 = 0.8

A2 = 0.3 A6 = 0.2

t3 = 0.3

A3 = 0.5

a = A0 for t t0 = A6 for t t6 Amplitude, a, between any two consecutive data points (ti, Ai) and (ti+1, Ai+1) is a = Ai + (Ai+1 Ai) 3 (10 15 + 6 2) where = t ti ti+1 ti

Figure 28.1.26Input File Usage: Abaqus/CAE Usage:

Smooth step amplitude denition example with multiple data points. *AMPLITUDE, NAME=name, DEFINITION=BUBBLE Bubble amplitudes are not supported in Abaqus/CAE. However, bubble loading for an underwater explosion is supported in the Interaction module using the UNDEX charge property denition.

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AMPLITUDE CURVES

(a)Figure 28.1.27

(b)

Bubble amplitude denition example: (a) radius of bubble and (b) depth of bubble center under uid surface.

Defining an amplitude via a user subroutine

Choose the user denition method to dene the amplitude curve via coding in user subroutine UAMP (Abaqus/Standard) or VUAMP (Abaqus/Explicit). You dene the value of the amplitude function in time and, optionally, the values of the derivatives and integrals for the function sought to be implemented as outlined in UAMP, Section 1.1.18 of the Abaqus User Subroutines Reference Manual, and VUAMP, Section 1.2.5 of the Abaqus User Subroutines Reference Manual. You can use an arbitrary number of state variables that can be updated independently for each amplitude denition. Moreover, solution-dependent sensors can be used to dene the user-customized amplitude. The sensors can be identied via their name, and two utilities allow for the extraction of the current sensor value inside the user subroutine (see Obtaining sensor information, Section 2.1.14 of the Abaqus User Subroutines Reference Manual). Simple control/logical models can be implemented using this feature as illustrated in Crank mechanism, Section 4.1.2 of the Abaqus Example Problems Manual.Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, DEFINITION=USER, VARIABLES=n Load or Interaction module: Create Amplitude: User: Number of variables: n

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AMPLITUDE CURVES

Using an amplitude definition with boundary conditions

When an amplitude curve is used to prescribe a variable of the model as a boundary condition (by referring to the amplitude from the boundary condition denition), the rst and second time derivatives of the variable may also be needed. For example, the time history of a displacement can be dened for a direct integration dynamic analysis step by an amplitude variation; in this case Abaqus must compute the corresponding velocity and acceleration. When the displacement time history is dened by a piecewise linear amplitude variation (tabular or equally spaced amplitude denition), the corresponding velocity is piecewise constant and the acceleration may be innite at the end of each time interval given in the amplitude denition table, as shown in Figure 28.1.28(a). This behavior is unreasonable. (In Abaqus/Explicit time derivatives of amplitude curves are typically based on nite differences, such as , so there is some inherent smoothing associated with the time discretization.) You can modify the piecewise linear displacement variation into a combination of piecewise linear and piecewise quadratic variations through smoothing. Smoothing ensures that the velocity varies continuously during the time period of the amplitude denition and that the acceleration no longer has singularity points, as illustrated in Figure 28.1.28(b). When the velocity time history is dened by a piecewise linear amplitude variation, the corresponding acceleration is piecewise constant. Smoothing can be used to modify the piecewise linear velocity variation into a combination of piecewise linear and piecewise quadratic variations. Smoothing ensures that the acceleration varies continuously during the time period of the amplitude denition. You specify t, the fraction of the time interval before and after each time point during which the piecewise linear time variation is to be replaced by a smooth quadratic time variation. The default in Abaqus/Standard is t=0.25; the default in Abaqus/Explicit is t=0.0. The allowable range is 0.0 t 0.5. A value of 0.05 is suggested for amplitude denitions that contain large time intervals to avoid severe deviation from the specied denition. In Abaqus/Explicit if a displacement jump is specied using an amplitude curve (i.e., the beginning displacement dened using the amplitude function does not correspond to the displacement at that time), this displacement jump will be ignored. Displacement boundary conditions are enforced in Abaqus/Explicit in an incremental manner using the slope of the amplitude curve. To avoid the noisy solution that may result in Abaqus/Explicit when smoothing is not used, it is better to specify the velocity history of a node rather than the displacement history (see Boundary conditions, Section 28.3.1). When an amplitude denition is used with prescribed conditions that do not require the evaluation of time derivatives (for example, concentrated loads, distributed loads, temperature elds, etc., or a static analysis), the use of smoothing is ignored. When the displacement time history is dened using a smooth-step amplitude curve, the velocity and acceleration will be zero at every data point specied, although the average velocity and acceleration may well be nonzero. Hence, this amplitude denition should be used only to dene a (smooth) step function.Input File Usage:

Use either of the following options: *AMPLITUDE, NAME=name, DEFINITION=TABULAR, SMOOTH=t

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AMPLITUDE CURVES

= Smooth Value x Minimum (tu u

1

,t2)

t1 t2 time

time

u

u

time

time

u

u

time

time

(a) without smoothing

(b) with smoothing

Figure 28.1.28

Piecewise linear displacement denitions.

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AMPLITUDE CURVES

*AMPLITUDE, NAME=name, DEFINITION=EQUALLY SPACED, SMOOTH=tAbaqus/CAE Usage:

Load or Interaction module: Create Amplitude: choose Tabular or Equally spaced: Smoothing: Specify: t

Using an amplitude definition with secondary base motion in modal dynamics

When an amplitude curve is used to prescribe a variable of the model as a secondary base motion in a modal dynamics procedure (by referring to the amplitude from the base motion denition during a modal dynamic procedure), the rst or second time derivatives of the variable may also be needed. For example, the time history of a displacement can be dened for secondary base motion in a modal dynamics procedure. In this case Abaqus must compute the corresponding acceleration. The modal dynamics procedure uses an exact solution for the response to a piecewise linear force. Accordingly, secondary base motion denitions are applied as piecewise linear acceleration histories. When displacement-type or velocity-type base motions are used to dene displacement or velocity time histories and an amplitude variation using the tabular, equally spaced, periodic, modulated, or exponential decay denitions is used, an algorithmic acceleration is computed based on the tabular data (the amplitude data evaluated at the time values used in the modal dynamics procedure). At the end of any time increment where the amplitude curve is linear over that increment, linear over the previous increment, and the slopes of the amplitude variations over the two increments are equal, this algorithmic acceleration reproduces the exact displacement and velocity for displacement time histories or the exact velocity for velocity time histories. When the displacement time history is dened using a smooth-step amplitude curve, the velocity and acceleration will be zero at every data point specied, although the average velocity and acceleration may well be nonzero. Hence, this amplitude denition should be used only to dene a (smooth) step function.Defining multiple amplitude curves

You can dene any number of amplitude curves and refer to them from any load, boundary condition, or predened eld denition. For example, one amplitude curve can be used to specify the velocity of a set of nodes, while another amplitude curve can be used to specify the magnitude of a pressure load on the body. If the velocity and the pressure both follow the same time history, however, they can both refer to the same amplitude curve. There is one exception in Abaqus/Standard: only one solution-dependent amplitude (used for superplastic forming) can be active during each step.Scaling and shifting amplitude curves

You can scale and shift both time and magnitude when dening an amplitude. This can be helpful for example when your amplitude data need to be converted to a different unit system or when you reuse existing amplitude data to dene similar amplitude curves. If both scaling and shifting are applied at the same time, the amplitude values are rst scaled and then shifted. The amplitude shifting and scaling can be applied to all amplitude denition types except for solution dependent and bubble.

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AMPLITUDE CURVES

Input File Usage: Abaqus/CAE Usage:

*AMPLITUDE, NAME=name, SHIFTX=shiftx_value, SHIFTY=shifty_value, SCALEX=scalex_value, SCALEY=scaley_value The scaling and shifting of amplitude curves is not supported in Abaqus/CAE.

Reading the data from an alternate file

The data for an amplitude curve can be contained in a separate le.Input File Usage:

*AMPLITUDE, NAME=name, INPUT=le_name If the INPUT parameter is omitted, it is assumed that the data lines follow the keyword line. Load or Interaction module: Create Amplitude: any type: click mouse button 3 while holding the cursor over the data table, and select Read from File

Abaqus/CAE Usage:

Baseline correction in Abaqus/Standard

When an amplitude denition is used to dene an acceleration history in the time domain (a seismic record of an earthquake, for example), the integration of the acceleration record through time may result in a relatively large displacement at the end of the event. This behavior typically occurs because of instrumentation errors or a sampling frequency that is not sufcient to capture the actual acceleration history. In Abaqus/Standard it is possible to compensate for it by using baseline correction. The baseline correction method allows an acceleration history to be modied to minimize the overall drift of the displacement obtained from the time integration of the given acceleration. It is relevant only with tabular or equally spaced amplitude denitions. Baseline correction can be dened only when the amplitude is referenced as an acceleration boundary condition during a direct-integration dynamic analysis or as an acceleration base motion in modal dynamics.Input File Usage:

Use both of the following options to include baseline correction: *AMPLITUDE, DEFINITION=TABULAR or EQUALLY SPACED *BASELINE CORRECTION The *BASELINE CORRECTION option must appear immediately following the data lines of the *AMPLITUDE option.

Abaqus/CAE Usage:

Load or Interaction module: Create Amplitude: choose Tabular or Equally spaced: Baseline Correction

Effects of baseline correction

The acceleration is modied by adding a quadratic variation of acceleration in time to the acceleration denition. The quadratic variation is chosen to minimize the mean squared velocity during each correction interval. Separate quadratic variations can be added for different correction intervals within the amplitude denition by dening the correction intervals. Alternatively, the entire amplitude history can be used as a single correction interval.

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AMPLITUDE CURVES

The use of more correction intervals provides tighter control over any drift in the displacement at the expense of more modication of the given acceleration trace. In either case, the modication begins with the start of the amplitude variation and with the assumption that the initial velocity at that time is zero. The baseline correction technique is described in detail in Baseline correction of accelerograms, Section 6.1.2 of the Abaqus Theory Manual.

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INITIAL CONDITIONS

28.2

Initial conditions

Initial conditions, Section 28.2.1

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28.21 EMail:[email protected]


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INITIAL CONDITIONS

28.2.1

INITIAL CONDITIONS

Products: Abaqus/Standard References

Abaqus/Explicit

Abaqus/CAE

Prescribed conditions: overview, Section 28.1.1 *INITIAL CONDITIONS Using the predened eld editors, Section 16.11 of the Abaqus/CAE Users Manual, in the online HTML version of this manual

Overview

Initial conditions are specied for particular nodes or elements, as appropriate. The data can be provided directly; in an external input le; or, in some cases, by a user subroutine or by the results or output database le from a previous Abaqus analysis. If initial conditions are not specied, all initial conditions are zero except relative density in the porous metal plasticity model, which will have the value 1.0.Specifying the type of initial condition being defined

Various types of initial conditions can be specied, depending on the analysis to be performed. Each type of initial condition is explained below, in alphabetical order.Defining initial acoustic static pressure

In Abaqus/Explicit you can dene initial acoustic static pressure values at the acoustic nodes. These values should correspond to static equilibrium and cannot be changed during the analysis. You can specify the initial acoustic static pressure at two reference locations in the model, and Abaqus/Explicit interpolates these data linearly to the acoustic nodes in the specied node set. The linear interpolation is based upon the projected position of each node onto the line dened by the two reference nodes. If the value at only one reference location is given, the initial acoustic static pressure is assumed to be uniform. The initial acoustic static pressure is used only in the evaluation of the cavitation condition (see Acoustic medium, Section 21.3.1) when the acoustic medium is capable of undergoing cavitation.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=ACOUSTIC STATIC PRESSURE Initial acoustic static pressure is not supported in Abaqus/CAE.

Defining initial normalized concentration

In Abaqus/Standard you can dene initial normalized concentration values for use with diffusion elements in mass diffusion analysis (see Mass diffusion analysis, Section 6.8.1).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=CONCENTRATION Initial normalized concentration is not supported in Abaqus/CAE.

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INITIAL CONDITIONS

Defining initially bonded contact surfaces

In Abaqus/Standard you can dene initially bonded or partially bonded contact surfaces. This type of initial condition is intended for use with the crack propagation capability (see Crack propagation analysis, Section 11.4.3). The surfaces specied have to be different; this type of initial condition cannot be used with self-contact. If the crack propagation capability is not activated, the bonded portion of the surfaces will not separate. In this case dening initially bonded contact surfaces would have the same effect as dening tied contact, which generates a permanent bond between two surfaces during the entire analysis (Dening tied contact in Abaqus/Standard, Section 30.2.8).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=CONTACT Initially bonded surfaces are not supported in Abaqus/CAE.

Defining initial values of predefined field variables

You can dene initial values of predened eld variables. The values can be changed during an analysis (see Predened elds, Section 28.6.1). You must specify the eld variable number being dened, n. Any number of eld variables can be used; each must be numbered consecutively (1, 2, 3, etc.). Repeat the initial conditions denition, with a different eld variable number, to dene initial conditions for multiple eld variables. The default is n=1. The denition of initial eld variable values must be compatible with the section denition and with adjacent elements, as explained in Predened elds, Section 28.6.1.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=FIELD, VARIABLE=n Initial predened eld variables are not supported in Abaqus/CAE.

Reading initial values of predefined field variables from a user-specified results file

You can dene initial values of predened eld variables from a particular step and increment of a results le from a previous Abaqus analysis (see Predened elds, Section 28.6.1). The previous analysis is most commonly an Abaqus/Standard heat transfer analysis. The use of the .fil le extension is optional. The part (.prt) le from the previous analysis is required to read the initial values of predened eld variables from the results le (Dening an assembly, Section 2.9.1). Both the previous model and the current model must be consistently dened in terms of an assembly of part instances.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=FIELD, VARIABLE=n, FILE=le, STEP=step, INC=inc Initial predened eld variables are not supported in Abaqus/CAE.

Defining initial fluid pressure in hydrostatic fluid elements

You can prescribe initial pressure for hydrostatic uid elements (see Modeling uid-lled cavities, Section 11.5.1).

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INITIAL CONDITIONS

Do not use this type of initial condition to dene initial conditions in porous media in Abaqus/Standard; use initial pore uid pressures instead (see below).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=FLUID PRESSURE Initial uid pressure is not supported in Abaqus/CAE.

Defining initial values of state variables for plastic hardening

You can prescribe initial equivalent plastic strain and, if relevant, the initial backstress tensor for elements that use one of the metal plasticity (Inelastic behavior, Section 19.1.1) or Drucker-Prager (Extended Drucker-Prager models, Section 19.3.1) material models. These initial quantities are intended for materials in a work hardened state; they can be dened directly or by user subroutine HARDINI. You can also prescribe initial values for the volumetric compacting plastic strain, , for elements that use the crushable foam material model with volumetric hardening (Crushable foam plasticity models, Section 19.3.5). You can also specify multiple backstresses for the nonlinear kinematic hardening model. Optionally, you can specify the kinematic shift tensor (backstress) using the full tensor format, regardless of the element type to which the initial conditions are applied.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=HARDENING, NUMBER BACKSTRESSES=n, FULL TENSOR Load module: Create Predefined Field: Step: Initial, choose Mechanical for the Category and Hardening for the Types for Selected Step; select region; Number of backstresses: n

Defining hardening parameters for rebars

In Abaqus/Standard the hardening parameters can also be dened for rebars within elements. Rebars are discussed in Dening rebar as an element property, Section 2.2.4.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=HARDENING, REBAR Load module: Create Predefined Field: Step: Initial, choose Mechanical for the Category and Hardening for the Types for Selected Step; select region; Definition: Rebar

Defining hardening parameters in user subroutine HARDINI

For complicated cases in Abaqus/Standard user subroutine HARDINI can be used to dene the initial work hardening. In this case Abaqus/Standard will call the subroutine at the start of the analysis for each material point in the model. You can then dene the initial conditions at each point as a function of coordinates, element number, etc.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=HARDENING, USER Load module: Create Predefined Field: Step: Initial, choose Mechanical for the Category and Hardening for the Types for Selected Step; select region; Definition: User-defined

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INITIAL CONDITIONS

Defining elements initially open for tangential fluid flow

You can specify the pore pressure cohesive elements that are initially open for tangential uid ow (see Dening the constitutive response of uid within the cohesive element gap, Section 27.5.7).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=INITIAL GAP Initial gap is not supported in Abaqus/CAE.

Defining initial mass flow rates in forced convection heat transfer elements

In Abaqus/Standard you can dene the initial mass ow rate through forced convection heat transfer elements. You can specify a predened mass ow rate eld to vary the value of the mass ow rate within the analysis step (see Uncoupled heat transfer analysis, Section 6.5.2).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=MASS FLOW RATE Initial mass ow rate is not supported in Abaqus/CAE.

Defining initial values of plastic strain

You can dene an initial plastic strain eld on elements that use one of the metal plasticity (Inelastic behavior, Section 19.1.1) or Drucker-Prager (Extended Drucker-Prager models, Section 19.3.1) material models. The specied plastic strain values will be applied uniformly over the element unless they are dened at each section point through the thickness in shell elements. If a local coordinate system was dened (see Orientations, Section 2.2.5), the plastic strain components must be given in the local system.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=PLASTIC STRAIN Initial plastic strain conditions are not supported in Abaqus/CAE.

Defining initial plastic strains for rebars

Initial values of stress can also be dened for rebars within elements ( see Dening rebar as an element property, Section 2.2.4).Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=PLASTIC STRAIN, REBAR Initial plastic strain conditions are not supported in Abaqus/CAE.

Defining initial pore fluid pressures in a porous medium

In Abaqus/Standard you can dene the initial pore pressure, , for nodes in a coupled pore uid diffusion/stress analysis (see Coupled pore uid diffusion and stress analysis, Section 6.7.1). The initial pore pressure can be dened either directly as an elevation-dependent function or by user subroutine UPOREP.Elevation-dependent initial pore pressures

When an elevation-dependent pore pressure is prescribed for a particular node set, the pore pressure in the vertical direction (assumed to be the z-direction in three-dimensional and axisymmetric models

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INITIAL CONDITIONS

and the y-direction in two-dimensional models) is assumed to vary linearly with this vertical coordinate. You must give two pairs of pore pressure and elevation values to dene the pore pressure distribution throughout the node set. Enter only the rst pore pressure value (omit the second pore pressure value and the elevation values) to dene a constant pore pressure distribution.Input File Usage: Abaqus/CAE Usage:

*INITIAL CONDITIONS, TYPE=PORE PRESSURE Initial pore pressure is not

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