Lessons Learned: Solid Modeling of Bolts in Contactpages.mscsoftware.com/rs/mscsoftware/images/Lessons Learned in... · Copyright © 2013 Boeing. All rights reserved. CBUSH Element

MSC Software Confidential

Copyright © 2013 Boeing. All rights reserved.


Lessons Learned:

Solid Modeling of Bolts in Contact 2013 Regional User Conference

Presented By: Tricia Carr

May 7, 2013




• Presentation will outline lessons learned and impediments to

productivity found during a bolted joint analysis study

• An in-house tool was developed to rapidly generate FE models

from simple user inputs

– Program wrote out session files (PCL code)

– Can run batch mode or from inside Patran; session file generates a FE

model

• In-house tool creates 2D (plate) or 3D (solid) models

– We'll discuss our 3D models with contact

– Both Sol 101 and Sol 400 used

Introduction

2



Some sample models

3



Models are highly regular

4



Generating session files for Sol 400 runs

5

Sol 400 is Sol 600 (MARC?)

Session file PCL commands are in

different order than Sol 101 (and

order matters)

Not as easy as Sol 101

Some options can be

turned off with one line

Other options aren't so

easy…



Example problem with Sol 400 PCL

6

• Sol 400 writes out a PSHLN1 for every PSHELL (from MARC?)

• PSHLN1 fails when MID1 is not equal MID2 (unless MID3 is specified)

• Easy enough to $ out a card—but how to remove it in PCL? Add SMALL STRAIN to

the element properties.

Getting rid of NLMOPTS

However—

You need to first

create the property,

then MODIFY it, or

SMALL STRAIN

won't "stick"



• Interference fit

– bolt modeled 0.002" larger than

hole

– ERROR used to force shank

and hole surface to mate

Contact—interference fit and axial preload

• Axial preload

– Bolt length modeled shorter

than stackup

– ERROR used to force bolt head

and washer face to mate

7



Interference Fit — making it work

8

If a model is created with

overlap between contact pairs,

set ERROR larger than the

overlap value to make

interference work



Saving a Contact Table

9

Reading bulk data into Patran…

…doesn't always get you all of your table




10

Export/Import has problems, too

…some parameters (ERROR, BIAS, CINTERF, etc) aren't exported




11

•Session file

•Excel macro

•Python script

You may want to write

your own!



"Bolt Spinning"

12

Contact problems (Sol 101 or

Sol 400) show bolts spinning

• Actual deflection is small

• Direction changes at

different load steps

Adding friction or weak

springs does not solve the

problem

Problem



13

CBUSH Element Spin Stabilization (1,2,3 stiffness)

0.03400

0.03500

0.03600

0.03700

0.03800

0.03900

0.04000

0.1 1 10 100 1000 10000

Esti

mate

d F

aste

ner

Axia

l R

ota

tio

n (

deg

)

CBUSH Element 1,2,3 Stiffness (lb/in)--Semilog X-Axis

Estimated Fastener Axial Rotation vs CBUSH Stiffness (1,2,3) (X-Semilog)

CBUSHConfig 1

No CBUSH

Tuning CBUSH stiffness within a

reasonable range does not eliminate the

‘spinning’ in fastener

2

1

Axial rotation calculated based on ∆2 measured on

outside of shank and nominal radius of shank

• Rotation= atan( ∆2 / rshank )



What is happening in the model—

14

Crude schematic of bolt in hole

Rigid body motion of bolt…

…node-to-face contact

Code pushes back

node-to-face contact

Regularity of mesh means neither solution better—

code can't "make up its mind"



MARC

15

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Explanation of SPLINE option (analytical contact)



Activating Analytical Contact

16

IDSPL 0

No spline (what we had)

IDSPL +1

Unless you specify areas to

spline with BLSEG, all surfaces

are smoothed (probably not

what you want)

IDSPL –1

Easier! Nastran splines any

angles less than 60°(default)

IDSPL on BCBODY



Model with Analytical Contact—

17

… artificial contact no longer occurs Master surface is smoothed



Analytical Contact solves "Bolt Spinning"

18

• Normally, turning smoothing

on will ALLOW a bolt to turn,

not PREVENT it

• "spinning" or "cogging" due

to unusual regularity of our

models

But why?



• Analytical Contact

– may prevent bolt 'spinning' or 'cogging'

– Seems to be caused by very regular models

– Activated by IDSPL -1 on BCBODY

• No good way to save a contact table!

– Write your own

• Read the .f06 file (always)

– for Sol 101 runs with contact:

• EXO-6 can miss the FATAL; Patran results don't list % of load applied

Lessons Learned

19



20

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Lessons Learned: Solid Modeling of Bolts in Contactpages.mscsoftware.com/rs/mscsoftware/images/Lessons Learned in... · Copyright © 2013 Boeing. All rights reserved. CBUSH Element