Workshop N

7

Bolt Pretension

Compressed Gasket

The pretension feature of ANSYS is useful for creating, managing, and loading structures having multiple pretensioned bolts. This feature was introduced in version 5.6 but has been upgraded to enhance bolt pretension modeling. In the example below 3 bolts are used to attach a stiff plate to a gasket. The bolts are then sequentially tightened to 10,000 pounds each, compressing the gasket. The problem starts by loading a database file which contains an idealized 2D model of the bolt/gasket sequence shown below. In the file the bolts, plate, and gasket have been modeled and meshed with beam, solid, and contact elements included. Material properties and boundary constraints are already defined.

Brief Instructions

1. Start ANSYS 5.7 with the default jobname (file).

2. Resume the database file Pretension.db1

3. Create Pretension sections at each of the bolts.

4. Apply 10,000-pound pretension loads to the 3 bolts. Use 0.1% of force for behavior before loading. After an initial untensioned load step, load and lock in sequence: Bolt 1 first (load in step 2, lock in step 3), Bolt2 2nd, Bolt 3 last.

5. A solution/postprocessing script has been prepared to set up and solve the 5 load steps. Click Read input from PT_util.dat.

Detailed Instructions

6. Start ANSYS 5.7 with the default jobname (file).

7. Resume the database file Pretension.db1

Click on:

- Utility Menu > File > Resume from...

Pretension.db1

[OK]

8. Create pretension sections at each of the bolts. Click on:

Main Menu > Preprocessor > Sections > Pretensn Mesh > Picked Elements

( Select two elements at the center of the vertical beam, elements to be separated (shown right). [APPLY]

( Pick node on separation plane (node between two chosen elements). [OK]

( SECID = 1 ( NAME = bolt1 ( KDIR = Y-axis, then [APPLY]

Repeat above for bolt2

( SECID = 2 ( NAME = bolt2 ( KDIR = Y-axis, then [APPLY]Repeat same procedure for bolt3

( SECID = 3 ( NAME = bolt3 ( KDIR = Y-axis, then [OK]When completed, the plot in ANSYS graphics window should look like:

4. Apply 10,000-pound pretension loads to the 3 bolts. To prevent sectioned bolts from behaving as unconstrained free bodies, use 0.1% of force for behavior before load.

Click on:

- Main Menu > Preprocessor > Loads > Apply > Sections > 1 Pretensn Sectn

( Select 1 bolt1

[OK]

( KINIT = 0.1% of force

( FDVALUE = 10000

( LSLOAD = 2

( LSLOCK = 3

[APPLY]Repeat above for bolt2

( Select 2 bolt2

[OK]

( KINIT = 0.1% of force

( FDVALUE = 10000

( LSLOAD = 3

( LSLOCK = 4

[APPLY]

Repeat same procedure for bolt3

( Select 3 bolt3

[OK]

( KINIT = 0.1% of force

( FDVALUE = 10000

( LSLOAD = 4 ( LSLOCK = 5

[OK]

9. Read input file to solve model

Click on:

- Utility Menu > File > Read input from

PT_util.dat

[OK]

This input file is set up to solve 5 load steps. (The first load step is run prior to pretensioning any bolts, to capture the initial configuration for display animation purposes.) The input file then animates the results (Animate > Over Results).

Note that the bolt pretension forces and locking displacements are not specified in this input file -- the program automatically applies these effects in the correct load step, in accordance with your earlier SLOAD input.

A listing of file PT_util.dat follows:

/SOLU

ANTYPE,0

NLGEOM,1 ! large displacement effects in plate & gasket

NCNV,2,0,0,0,0

RESCONTRL,DEFINE,ALL,LAST,5

/com,step 1 - establish contact

outres,all,last

nsub,1,1,1

solve

/com,step 2 - tighten bolt 1

outres,all,none

outres,all,-4

nsub,4,10,4

solve

/com,step 3 - lock bolt 1, tighten bolt 2

solve

/com,step 4 - lock bolt 2, tighten bolt 3

solve

/com,step 5 - lock bolt 3

nsub,1,1,1

solve

FINISH

/post1

set,last

FLST,5,52,1,ORDE,8

FITEM,5,1

FITEM,5,-9

FITEM,5,82

FITEM,5,-98

FITEM,5,235

FITEM,5,-251

FITEM,5,388

FITEM,5,-396

NSEL,U, , ,P51X

/PSF,DEFA, ,1,0,1

/PBF,DEFA, ,1

/PIC,DEFA, ,1

/PSYMB,CS,0

/PSYMB,NDIR,0

/PSYMB,ESYS,0

/PSYMB,LDIV,-1

/PSYMB,LDIR,0

/PSYMB,ADIR,0

/PSYMB,ECON,0

/PSYMB,XNODE,0

/PSYMB,DOT,1

/PSYMB,PCONV,

/PSYMB,LAYR,0

/PSYMB,FBCS,0

/PBC,NFOR, ,0,,,,

/PBC,NMOM, ,0,,,,

/PBC,RFOR, ,2,,,,

/PBC,RMOM, ,0,,,,

/PBC,PATH, ,0,,,,

/triad,lbot

/RGB,INDEX,100,100,100, 0

/RGB,INDEX, 80, 80, 80,13

/RGB,INDEX, 60, 60, 60,14

/RGB,INDEX, 0, 0, 0,15

PLDISP,2

/user

ANDATA,0.5, ,2,1,14,1,0,1

Soft Gasket

Stiff Plate

EMBED PBrush

Bolt 3

Bolt 2

Bolt 1

EMBED PBrush

EMBED PBrush

Select two elements at central node

EMBED PBrush

Note stars at central nodes

EMBED PBrush

7-2ANSYS 5.7 New Features Workshop Supplement

ANSYS 5.7 New Features Workshop Supplement7-1