mdnastran r3 training 133b course notes

Part Number: MDNA*R3*Z*Z*Z*SM-NAS133-B-NT Copyright2009 MSC.Software CorporationMarch 2009

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NAS133-b Course Notes

Introduction to Contact Analysiswith MD Nastran

March 2009

2

Copyright2009 MSC.Software Corporation

Legal Information

MSC.Software Corporation reserves the right to make changes in specifications and other information contained in thisdocument without prior notice. The concepts, methods, and examples presented in this text are for illustrative andeducational purposes only, and are not intended to be exhaustive or to apply to any particular engineering problem ordesign. MSC.Software Corporation assumes no liability or responsibility to any person or company for direct or indirectdamages resulting from the use of any information contained herein.

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Section Page

1.0 Getting Started

Objectives ………………………………………………………………………………………………. 1-2

Introduction to Contact Analysis ………………………………………………………………………………... 1-5

Case Study 1 - Contact Analysis of Two Deformable Bodies ……………………………………………….. 1-11

Contact Body Definition ………………………………………………………………………………………….. 1-18

Job Setup ………………………………………………………………………………………………………….. 1-30

Workshop 1 – Solid-to-Shell Contact

2.0 Contact Basics

Contact Detection ………………………………………………………………………………………………… 2-5

Contact Search Options …………………………………………………………………………………………. 2-30

Case Study 2 – Contact Search Examples ……………………………………………………………………. 2-34

Workshop 2 – Solid-to-Solid Contact

3.0 Glued Contact

Glued Contact …………………………………….......................................................................................... 3-2

Case Study 3 – Modal Analysis with Glued Contact …………………………………………………………. 3-9

Workshop 3 – Shell Edge-to-Edge Glued Contact

4.0 Additional Contact Topics

Contact Separation Control …………………………………………………………………………….............. 4-2

Quadratic Contact ………………………………………………………………………………………………… 4-5

Bolt Preload ……………………………………………………………………………………………………….. 4-9

Workshop 4 – Bolted Joint Analysis

CONTENTS

4


NAS133-b, Section 1, March 2009Copyright2009 MSC.Software Corporation S1-1

SECTION 1

GETTING STARTED


SEMINAR OBJECTIVES

● At the end of this seminar, you will understand the basiccontact capabilities in MD Nastran and be able to:

● Identify structural analysis problems that can benefit from contactmodeling

●Set up a basic contact job, including contact bodies, contactparameters, contact tables, and contact search algorithms

●Select an appropriate Nastran solution sequence to handle the job

● Interrogate and evaluate the contact analysis results


SOFTWARE VERSIONS

● The lecture notes and workshops are based on thefollowing software versions:● MD Nastran R3● Patran 2008r2


GETTING STARTED

● Introduction to Contact Analysis● Case Study 1● Contact Body Definition● Job Setup● Workshop 1 - Solid-to-Shell Contact


Introduction to Contact Analysis


What is Contact Analysis?

● Contact analysis is the analysisof contact bodies (deformableor rigid) interacting with eachother

● Contact analysis types● Touching Contact●Glued Contact

Glued Contact

Touching Contact


Contact Analysis Examples● Solid-to-solid contact examples

Interference Fit

Lug-Clevis-PinPreloaded Bolted JointGlued Assembly


Contact Analysis Examples (cont.)

● Shell-to-shell contact examples

Edge-to-edge glued contact

Edge-to-edge contact

Face to face contact


Contact Analysis Examples (cont.)

● Shell-to-solid contact examples

Face-to-face contact

Edge-to-face glued contact


Contact Analysis Examples (cont.)● Beam contact examples

Beam-to-beam contact

Beam-to-solid glued contact


Case Study 1

Contact Analysis of TwoDeformable Bodies


Case Study 1

● Two parts with different mesh densities


Case Study 1

●Initial Pass: No Contactdefinition

●Parts don’t see each other

●Parts pass through each other

●Second Pass: Add Contactbody definition

●Parts now contact each other

No Contact

Contact added


Case Study 1

● No more issues with point-to-point GAP elements inSOL 106

● Matching meshes● GRID-by-GRID definition● Open/closed orientation coordinate system● Open/closed stiffness ratios


Case Study 1

●Easy contact body setup:


Case Study 1

● Comprehensive contact resultsplots:

●Contact status

●Contact normal stress

●Contact normal force


Case Study 1

● Summary of Case Study

● Studied contact between two partswith dissimilar meshes

● Demonstrated easy contact setup

● Solved the problem in Linear StaticSOL 101

● Plotted contact normal stress and forceto gain insight into load path andcontact status


Contact Body Definition


● Contact bodies can be deformable or rigid

● Deformable bodies will be covered in this class

● Rigid bodies will be covered in the Advanced ContactAnalysis class

Contact Body Types

Rigid die block

Rigid tool

Deformable part


● A deformable body is a collection of finite elements

● A deformable body must contain elements of the same class:

● Linear shell CTRIA3/CQUAD4

● Quadratic shell CTRIA6/CQUAD8

● Linear solid CHEXA/CPENTA/CTETRA

● Quadratic solid CHEXA/CPENTA/CTETRA

● Beams CBAR/CBEAM/CROD

Definition of Deformable Bodies


● Each deformable body consists of one or more finite elements

● Nodes or elements must belong to no more than one deformable body

● A deformable body does not need to completely correspond with aphysical body:

Definition of Deformable Bodies (cont.)

v

deformable contact body


On the other hand be careful with a subset of elements

Definition of Deformable Bodies (cont.)

Limited number ofelements definedin contact body

Local normal vectorto the outer boundarymay be completelywrong


Definition of Deformable Bodies (cont.)● All deformable bodies can come in contact with each other,

including self-contact● Nastran automatically figures out the free faces as potential

contact surfaces● Nastran also automatically accounts for shell thicknesses

t1t2


Creating a Deformable BodyFrom the Patran Loads/BCs menu:

1. Create / Contact / ElementUniform

2. Select "Deformable Body"


Creating a Deformable Body (cont.)

On "Select Application Region"form:

3. Select elements based ongeometry, elements, orproperty to create adeformable body

or

or


● BCBODY – Flexible or Rigid Contact Body


● Contact Body Nastran entries:

● BSURF – Defines a contact body by Element IDs(Referenced by BSID in BCBODY)


Creating a Deformable Body (cont.)● Sample Nastran input file:

DEFORM or RIGID

List ofelements



● Property-based Nastran entry:

(Referenced by BSID in BCBODY)BCPROP – Defines a contact body by Element Property



● Sample Nastran input file:

BCPROP


Job Setup


Choosing a Solution Sequence

● Contact analysis is supported in both SOL 400 and 101●Use SOL 400 for general nonlinear contact analysis

●Use SOL 101 for “linear” contact analysis where●Contact is the only nonlinearity present

●No material nonlinearity is present

●No geometric nonlinearity is present

● For example, Case Study 1 presented an analysis of twocontacting cantilevered plates using SOL 101●SOL 101 is a good starting point

●But if the computed displacements are large, or material plasticityneeds to be modeled, then SOL 400 should be used instead of SOL101


Choosing a Solution Sequence (cont.)

● Permanent Glue is a special type of contact●Designed to join 2 dissimilar meshes

●Available for SOL 101, 103, 105, 107, 108, 109, 110, 111, 112,and 200

●Will be covered later in section 3


Selecting Results Output Format

● The traditional Nastran results are available in both XDB andMASTER/DBALL

● Contact analysis results are only available inMASTER/DBALL

● Do the following when setting up a contact analysis job●Set SCR=NO and specify NASTRAN SYSTEM(316)=19 to generate

MASTER and DBALL files suitable for contact results post processing

●Alternatively set SCR=POST

● If restart is required, specify NASTRAN SYSTEM(316)=7


Requesting for Output

● Traditional Nastran results such as displacement and stressare requested as usual in the Case Control Section

● To obtain contact results such as contact normal force andcontact normal stress, specify the following in the CaseControl Section● BOUTPUT=ALL

● Following slides show how to use Patran to set up the contactanalysis job


Choose a Solution Sequence● From the Patran Analysis menu:

1. Analyze / Entire Model / Full Run

2. Select “Solution Type"


Choose a Solution Sequence(cont.)

3. For SOL 101, select LINEAR STATIC


Choose a Solution Sequence(cont.)3. For SOL 400

• Select IMPLICIT NONLINEAR• Click on Solution Parameters…• Select SOL 400 Run


Select Results Output Format4. For either SOL 101 or 400

• Select Solution Parameters…• Select Results Output Format…• Select MASTER/DBALL


Request for Output5. On the Subcases form

• Select Output Requests…• Select Contact Results


Workshop 1

Solid-to-Shell Contact


Workshop 1

● Perform an end-to-end contact analysis with MD Nastran● Gain familiarity with the Patran contact analysis GUI


Workshop 1

● Please go to the Seminar Workbook where you willfind step-by-step instructions for this workshop


SECTION 2

CONTACT BASICS


Contact Basics

● Contact Detection● Contact Search Options● Case Study 2 - Contact Search Examples● Workshop 2 - Solid-to-Solid Contact


Approaching a Contact Analysis

● The contact analysis case study 1 and workshop 1 in theprevious section reached convergence quickly with plausibleresults using all program defaults. But real-world contactproblems often will require more user intervention.

● Recall that linear finite element analysis is characterized bya linear force-displacement relationship. The system oflinear equations produce a unique solution.

● In contrast, contact analysis is a nonlinear analysis and isan incremental and iterative process, and does notguarantee a unique solution.


Approaching a Contact Analysis (cont.)● This section will help you tackle real-world contact problems

by showing you

●How contact detection works

●How to use contact analysis parameters

● It is strongly recommended that tests on small models beperformed first to gain experience before you tackle largecomplex contact models.


Contact Detection


Contact Detection● The user defines bodies (deformable or rigid) which are

potential candidates for contact during the analysis

● Grid points and segments defining the boundary of thedeformable bodies are automatically determined

● The contact algorithm automatically detects grid pointsentering contact and generates the appropriate constraintsto ensure no penetration occurs

● Two contact detection algorithms are available in Nastran

● Node-to-Patch contact

● Beam-to-Beam contact


Node-to-Patch Contact Detection

● Following contact examples use the node-to-patch contactalgorithm

Solid to solid contact

Shell surface to surfacecontact

Shell edge to edge glue

Shell edge to solid glue

Shell edge to surface glue

Solid to Shell contact

Beam to solid glue

Beam to shell glue


Beam-to-Beam Contact Detection

● Following contact examples use the beam-to-beam contactalgorithm

Shell edge to edge contact Beam to beam contact


Node-to-Patch Contact● Node-to-Patch contact

● A node from one body comes into contact with a patch on a secondbody.

● The touching node is the slave. It is located on the contacting body.● The touched patch is the master. It is located on the contacted body.● When contact is detected, a contact constraint is imposed. The

touching node becomes the tied node. Nodes on the patch becomethe retained nodes.

Touching (contacting) Node - Slave

Touched (Contacted) Patch - Master


Node-to-Patch Contact Example

● A contact analysis of two solid deformable bodies is used toillustrate how the contact algorithm works

A

View A

Slave

Master


Possible Contact Situations

Master

distance tolerance

2

2) Node outside element patch, inside distance tolerance

3

3) Node inside element patch, inside distance tolerance

4

4) Node inside element patch, outside distance tolerance

Slave

1

1) Node outside element patch, outside distance tolerance

View A


1) Node outside element patch, outsidedistance tolerance

● Bodies are not in contact● Contacting node remains in current position


2) Node outside element patch, insidedistance tolerance

● A multipoint constraint is imposed in order to close the gapbetween the contacting node and the patch

● Remains in contact if normal tensile force is less thanseparation force


● A multipoint constraint is imposed to resolve thepenetration of the contacting node into the patch

3) Node inside element patch, insidedistance tolerance


4) Node inside element patch, outsidedistance tolerance

● Node penetrated● Increment will be recycled with modified step● Important: If this situation occurs at beginning of

analysis, contact will not be found


Contact Constraint for 2D (plane stress, plane strain,and axisymmetric) Elements

● Set up tying relation:A = 1/2 (1-A) B + 1/2 (1+A) C – d

with:displacement component in local y direction

(normal to segment BC)natural coordinate along segment BC

y‘Slave

Master

A

B

C

dx

y


Contact Constraint for 3D (solid and shell) Elements● Set up tying relation:

wA = 1/4 (1-A) (1-A) wB + 1/4 (1+A) (1-A) wC

+1/4 (1+A) (1+A) wD +1/4 (1-A) (1+A) wE – d

with:wdisplacement component in local z direction, corresponding to the normal ofsegment BCDE

natural coordinates on segment BCDE

B

C

D

E

Ad

Slave node

MasterPatch

B(-1,-1)

E(-1,1)

C(1,-1)

D(1,1)


Distance Tolerance●The size of the contact tolerance has a significant impact on

the computational costs and the accuracy of the solution

●Contact tolerance too small:●Detection of contact is difficult, leading to higher costs

●More nodes are likely to be considered penetrating leading to increasein increment splitting, therefore, increasing the computational costs

●Contact tolerance too large:●Nodes are considered in contact prematurely, resulting in a loss of

accuracy

●Nodes might “penetrate” the surface by a large amount


●Measured normal to the contacted body

●May be user-defined

●By default, this tolerance is evaluated from:●1/20x “smallest element edge“ for continuum elements

●1/4x “smallest thickness“ for beam and shell elements

●This distance tolerance is specified by the ERRORparameter in Nastran.

Distance Tolerance (cont.)

= ERROR

= ERROR


●By default, the contact tolerance is biased to the inside by a factor of 0.9*●Can be changed within the range of bias factor 0 BIAS 1 (default: 0.9)*

● Improves accuracy since the distance below which a node comes intocontact is reduced

●Reduces increment splitting since the distance to cause penetration isincreased

●The default/recommended value is BIAS = 0.9 for most contact analyses●For frictional problems, set BIAS = 0.99 to get improved results

disttol

disttol(1-BIAS) . disttol

(1+BIAS) . disttol

Bias Factor

No Bias With Bias

* For glued contact, the default Bias is 0.0

Inside Master

Outside MasterMasterSurface


Specify Distance Tolerance and Bias Factor

●From the Patran Analysis menu:


Specify Distance Tolerance and Bias Factor● Specify the distance tolerance and bias in the Patran form● Leaving the Distance Tolerance field blank tells Nastran to use the

default computed value● Leaving the Bias field blank tells Nastran to use the default value


● BCPARA – Contact Parameters

Specify Distance Tolerance and Bias Factor

● Nastran entry:

● ERROR and BIAS can also be specified for specific contact pairs using theBCTABLE entry. BCTABLE is covered later in the seminar.


Contact Detection for Shells

● Shell elements can have contact at their top, bottom, andmid-plane

● By default, contact is checked for both top and bottom

● The user can specify other options using the COPT parameter

● Shell elements should be oriented consistently


●COPT is defined as

COPT = A + 10 . B + 1000 . C

●A – the outside of solid elements in the body= 1: the outside will be in the contact description (default)

●B (flexible bodies) – the outside of shell elements in thebody

= 1: top and bottom can contact, thickness included (default)= 2: only bottom can contact, thickness included= 3: only bottom can contact, thickness ignored= 4: only top can contact, thickness included= 5: only top can contact, thickness ignored= 6: top and bottom can contact, thickness ignored

Contact Parameter COPT


●B (rigid bodies) – rigid surface= 1: the rigid surface can contact (default)

●C (flexible bodies) – the edges of the body= 1: only the beam edges can contact (default)

= 10: only the free and hard shell edges can contact

= 11: beam edges and free and hard shell edges can contact

Free edges

Hard edges

Contact Parameter COPT (cont.)


●COPT can be defined on the BCBODY entry.

●COPT can also be defined on the BCTABLE entry. COPTdefinitions in BCTABLE overrides COPT definitions inBCBODY.

●The implementation of COPT in BCBODY and BCTABLEare describe in following pages.



● COPTB in BCBODY



● BCTABLE●COPTS / COPTM as the default for all contact pairs●COPTS1 / COPTM1 for a contact pair



Contact Search Options


Contact Detection Search Logic

● The contact detection default search logic is calledDouble-Sided Search

● First the lower-ID body is checked against the higher-ID body forcontact. If contact is found, contact constraints are created.

● Next the higher-ID body is checked against the lower-ID bodyand additional contact constraints are created without conflictingwith the existing constraints.

● The Double-Sided Search works well for bodies withsimilar mesh densities and similiar material properties


Contact Detection Search Logic (cont.)

● If there is a large difference in material propertiesbetween two contact bodies, the softer one should bedefined as the slave body.

● If there is a large difference in mesh density between twocontact bodies, the body with the finer mesh should bedefined as the slave body.

● Additional contact detection search logics are availableto handle these situations. This is defined using thecontact table entry BCTABLE.


Contact Detection Search Logic (cont.)● Contact detection search options are selected by the ISEARCH

parameter in BCTABLE

● ISEARCH=0 (default) Double-sided search● First the lower-ID body is checked against the higher-ID body for contact. If

contact is found, contact constraints are created.● Next the higher-ID body is checked against the lower-ID body and additional

contact constraints are created without conflicting with the existing constraints.● ISEARCH=1 Single-sided search

● Search order is from slave to master● Slave and master are defined in the contact table

● ISEARCH=2 Automatic● Search order is from the body with smaller average element edge size to body with

larger average element edge size. The search is single sided.


Case Study 2

Contact Search Examples


Case Study 2A – ISEARCH=0

● ISEARCH=0, Double-Sided Search

● Program default

● Works well for bodies with similar mesh densities

● This case study illustrates that this search logic does not workwell when bodies with very different mesh densities are incontact

Note: In Patran you can not control the BCBODY ID. The ID’s areassigned automatically as contact bodies are created.


● First search from body 1 to 2:u3 = u3(u5, u6)

Case Study 2AISEARCH=0, Doubled-Sided Search

body 1 body 2

1

72

6

5

4

3

● Then search from body 2 to 1:u4 = u4(u1, u3)u5 = u5(u1, u3)u6 = u6(u3, u2)u7 = u7(u3, u2)

● This illustrates the wrong body numbering

Skipped, sincenode 3 hasalready been usedas a dependentnode

dependent

independent


● First search from body 1 to 2:u4 = u4(u1, u3)u5 = u5(u1, u3)u6 = u6(u3, u2)u7 = u7(u3, u2)

● Then search from body 2 to 1:u3 = u3(u5,u6)

Skipped, but okay!

Case Study 2AISEARCH=0, Doubled-Sided Search

● This illustrates the correct body numbering

body 2 body 1

1

72

6

5

4

3


Case Study 2B – ISEARCH=1

● ISEARCH=1, Single-Sided Search

● Use this option for bodies with different mesh densities

● User assigns slave and master to a pair of contact bodies

● The body with the finer mesh should be defined as the slave

● The search is performed from the slave to the master


● Search from Slave to Master:u3 = u3(u5, u6)

Case Study 2BISEARCH=1, Single-Sided Search

● Slave has the coarser mesh. Wrong choice.

dependent

independent

Slave Master

1

72

6

5

4

3


● Search from Slave to Master:u4 = u4(u1, u3)u5 = u5(u1, u3)u6 = u6(u3, u2)u7 = u7(u3, u2)

Case Study 2BISEARCH=1, Single-Sided Search

● Slave has the finer mesh. Correct choice.

Master Slave

1

72

6

5

4

3


Case Study 2C – ISEARCH=2

● ISEARCH=2, Automatic

● Search order is from the body with smaller average elementedge size to body with larger average element edge size.

● The search is single sided.

● This option works well when the mesh density within each bodyis fairly uniform.


● Search from Fine mesh to Coarse mesh:u4 = u4(u1, u3)u5 = u5(u1, u3)u6 = u6(u3, u2)u7 = u7(u3, u2)

Case Study 2CISEARCH=2, Automatic

● The program automatically determines slave and master based on averageelement size

CoarseMesh

Fine Mesh

1

72

6

5

4

3


Case Study 2D – Optimized Contact

● Set ISEARCH=0 and ISTYP=2

● This is called the Optimized Contact

● Also known as double-sided search with optimized contactconstraints

● Designed for self contact (body A contacting body A) or body Aand body B contacting at multiple places and the mesh size atthese places are different.

● The Program creates optimized constraints based on materialstiffness and mesh densities. The decision is based on contactregions, not contact bodies.

● Must set ISEARCH=0 and ISTYP=2. If ISEARCH≠0, then ISTYPis ignored.


Case Study 2DISEARCH=0 and ISTYP=2, Optimized Contact● Examples of where optimized contact could be utilized


Specify Contact Search Order

●From the Patran Analysis menu:


Specify Contact Search Order (cont.)● The Patran contact table is a matrix of size ncbody x ncbody where

ncbody = number of contact bodies● The contact bodies are listed alphabetically down the left-hand column.


Specify Contact Search Order (cont.)● Clicking in a cell will cycle it through T (touching), G (glued), and blank

(no contact).


Specify Contact Search Order (cont.)● For example, click in the diagonal cells three times each to deactivate

self contact


Specify Contact Search Order (cont.)● In this example, the web has a finer mesh and the skin has a coarser

mesh, and the two are in contact.● Instead of the default search algorithm, the user wants to set ISEARCH=1

with the web as the slave, and skin as the master.● In the left-hand column of the matrix, the skin is listed above the web.

This makes the skin the 1st body, and the web the 2nd body.

1st body

2nd body

above

web

skin


Specify Contact Search Order (cont.)● Click in the cell as shown, and select 2nd1st since the user wants to

search from 2nd body to 1st body, i.e. searching from web to skin.


● BCTABLE – Contact Table

Specify Contact Search Order (cont.)

● Nastran entry created:

ISEARCH=1


Specify Contact Search Order (cont.)

● Important note:● ID numbers shown in Patran contact table do not correspond to

BCBODY ID numbers in Nastran input file.


Workshop 2

Solid-to-Solid Contact


Workshop 2● Learn to handle contact bodies with different mesh densities● Learn to set up a contact search from a fine-mesh body to a coarse-

mesh body

Correct searchoption

Wrong searchoption


Workshop 2



SECTION 3

GLUED CONTACT


Glued Contact

● SOL 400 and 101 support the general glued contactcapability

● Simulates a glued joint

● Bodies don’t have to be initially in contact. They can come incontact during the analysis and become glued.

● After being glued together, bodies can separate again or stayglued based on user-specified criteria.

● Just like touching contact, the general glued contact utilizes thenonlinear solver which is an incremental and iterative process.


Glued Contact (cont.)

● Permanent Glued Contact is a special case of gluedcontact

●Designed to help users quickly assemble components withdissimilar meshes

●Available in SOL 101, 103, 105, 107, 108, 109, 110, 111, 112,and 200.

●A linear solution. Permanent contact constraint MPC equationsare used. No nonlinear increments or iterations involved.


●BCTABLE – IGLUE parameter

Setting up Glued Contact


● BCTABLE – IGLUE parameter● 0 – no gluing

● 1 - Activates the glue option. In the glue option, all degrees-of- freedom of the contactnodes are tied in case of deformable-deformable contact once the node comes incontact. The relative tangential motion of a contact node is zero in case of deformable-rigid contact. The node will be projected onto the contact body.

● 2 - Activates a special glue option to insure that there is no relative tangential andnormal displacement when a node comes into contact. An existing initial gap or overlapbetween the node and the contacted body will not be removed, as the node will not beprojected onto the contacted body. To maintain an initial gap, ERROR should be set toa value slightly larger than the physical gap.

● 3 - Insures full moment carrying glue when shells contact. The node will be projectedonto the contacted body.

● 4 - Insures full moment carrying glue when shells contact. The node will not beprojected onto the contact body and an existing initial gap or overlap between the nodeand the contacted body will not be removed, as the node will not be projected onto thecontacted body.

● In SOLs 101 and 400, if contact is initially not true set NLGLUE on BCPARA to 1

● For SOL 400 with a mixture of glued and non-glued bodies, BCPARA,0,NLGLUE,1 must beused

Setting up Glued Contact (cont.)


●Users can select nodes of the contact body to doregular contact instead of glued contact●This option is normally used for crack analysis where

the grids along the crack are not glued but all other gridson a contact body have glued contact

●Input via UNGLUE bulkdata card referenced byBCTABLE or UNGLUE case control commands

Deactivate Glued Contact


●A glued contact can be broken with or without abreaking criterion. Controlled via JGLUE onBCTABLE:●0 – glued contact nodes will stay in contact. Default.●1 – to invoke the standard separation behavior●2 – breaking glued with a breaking criterion

Breaking Glued Contact


●BKGL, keyword for breaking glued:●BGST, maximum tangential stress (default=0.0)●BGSN, maximum normal stress (default=0.0)●BGM, the first exponent (default=2.0)●BGN, the second exponent (default=2.0)

Breaking Glued Contact (cont.)

n

BGSN

BGN

+ 1.0t

BGST

BGM

>


Case Study 3Modal Analysis with Glued Contact


Case Study 3● Analyze the shrouded vanes shown below

● This is MD User’s Guide Application Example 25● Hub and vanes are meshed with Tet10 elements● Shroud is meshed with Hex8 elements● Glue the two bodies together and compute the first 10 free-free

modes

Hex8 – Tet10 doublecurved interface

Coarser mesh

Finer mesh


Case Study 3● Import the Nastran deck nug_25_1_mesh_only.dat● Create two contact bodies


Case Study 3● Set up the contact table


Case Study 3● Set the cell to “G” to set IGLUE=1● We want the Shroud (finer mesh) as slave, and Hub_and_Vanes (coarser mesh) as master.● Select 2nd1st. This sets ISEARCH=1 with the correct slave and master body definitions.


Case Study 3● Set ICOORD=1. This specifies stress-free initial contact

which modifies the coordinates of the nodes in contact toclose gaps and penetrations between the two bodies.

● This is an important step to improve clean rigid-bodymodes and help the model pass the grounding check. Italso ensures no artificial stresses are induced.


Case Study 3● Set up a SOL 103 normal modes analysis and request for

the first 10 modes.


Case Study 3● Review the BCTABLE entry.

ISEARCH=1

ICOORD=1

ERROR=default

● Important: BIAS is not specified, which defaults to 0.0 for glued contact.


Case Study 3● Review normal modes results:

● 6 clean rigid-body modes

1st flexible mode 1,130 Hz


Workshop 3

Shell Edge-to-Edge Glued Contact


Workshop 3● Learn to create a shell edge-to-edge glued contact with moment transfer

capability


Workshop 3



SECTION 4ADDITIONAL CONTACT TOPICS


Contact Separation Control●The default contact separation control is based on force● If the solution has converged, a check is performed on

the normal force acting on the nodes in contact

●Fn Fseparation: Node remains contacting●Fn > Fseparation: Node is allowed to separate

Fn

A


Contact Separation Control (cont.)●The user can specify a separation force or use the default

value●By default, the separation force Fseparation equals the

maximum residual forceF

x

F1

x1

F2

x2x2‘ x2‘‘

residual force


Contact Separation Control (cont.)

●The user can also specify separation control based on stress● Stress-based separation control eliminates the influence of

elements size● The contact normal stress used in stress-based separation

control can be calculated in two ways:●Divide the contact normal force by the equivalent nodal area●Use extrapolated and averaged integration point stresses

●For quadratic elements, the extrapolated and averagedintegration point stress should be used

● The separation stress can be specified as an absolute valueor a relative value


Quadratic Contact

● Quadratic Elements in Contact

● It is well known that a uniformdistributed load applied to the faceof a quadratic element results inequivalent nodal loads withoscillating signs

● Therefore unlike contact with linearelements, separation in quadraticelements cannot be based oncontact normal forces

●Stress-based separation controlmust be used for quadraticelements

Non-intuitive signs of forces


Quadratic Contact (cont.)

● When quadratic elements are in contact, followingcontrols are available for mid-side nodes:

● For SOL 600, use the LINQUAD parameter in BCPARA

●By default, mid-side nodes are not considered in contact. This isknown as linear contact.

●Setting LINQUAD = -1 tells the program to consider mid-side nodesin contact. This is known as quadratic contact.

● For all other MD Nastran solution sequences, the LINQUADparameter is not recognized

●Quadratic contact is on by default

●Mid-side nodes are always considered in contact


Specify Contact Separation Control●Contact separation control is specified by the IBSEP

parameter on the BCPARA entry.


●BCPARA / IBSEP – separation control flag (default=0)● 0 – separation if the contact pulling force exceeds FNTOL (input in

BCPARA or BCTABLE. Default: maximum residual force in thecomplete model).

● 1 – separation if the contact pulling fake stress (pulling force dividedby its nodal area) exceeds FNTOL (default: maximum stress at areaction node in the model times the convergence tolerance).

● 2 – separation if the contact pulling stress (from extrapolating andaveraging integration point values) exceeds FNTOL (like 1)

● 3 – separation if the contact pulling fake stress exceeds FNTOL(default=0.1) times the maximum contact stress in the model

● 4 – separation if the contact pulling stress exceeds FNTOL(default=0.1) times the maximum contact stress in the model

●Note: For quadratic contact, only options 2 or 4 should be used.

Contact Separation Control (cont.)


● Bolt preload in MD Nastran is doneusing the automated bolt preloadtool in Patran

● The tool automatically splits the boltand generates the required MPCequations

● The preload can be specified eitheras a force or a displacement

Bolt Preload


Bolt Preload (cont.)


RBE and MPC in Contact Surfaces

● In MD Nastran, dependent RBE nodes should not be allowed to come incontact. Also dependent MPC nodes should not be allowed to come incontact.

● For example, in bolt preload modeling, do not allow the bolt MPC’dnodes to come in contact with the bolt hole. Also do not allow self-contact of the bolt body. Please see MD User’s Guide ApplicationExample 23 for details on the modeling techniques required toaccomplish this.


Workshop 4

Bolted Joint Analysis


Workshop 4● Learn to set up a SOL 400 job with multiple load steps and load

increment control● Perform a bolt preload analysis with quadratic contact


Workshop 4



Review Seminar Objectives

Seminar Objectives:● Understand the basic contact capabilities in MD Nastran and

be able to:● Identify structural analysis problems that can benefit from contact

modeling●Set up a basic contact job, including contact bodies, contact

parameters, contact tables, and contact search algorithms

●Select an appropriate Nastran solution sequence to handle the job● Interrogate and evaluate the contact analysis results


Next Seminar● Due to time constraints, this seminar only covered the basics of MD

Nastran contact analysis● Additional important contact topics will be covered in the one-day

Advanced Contact Analysis Seminar● Rigid contact body● Beam-to-beam contact

● Shell edge-to-edge contact

● Interference fit● How to read contact diagnostics in output file

● Initial stress-free contact

● Treatment of faceted mesh● Treatment of corners

● Chatter suppression

● Stabilizing springs● Friction

mdnastran r3 training 133b course notes

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