mechanical nonlin 13.0 ws 06a creep

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Customer Training Material

or s op

Stress Relaxation

Structural Nonlinearities

WS6A-1ANSYS, Inc. Proprietary

2010 ANSYS, Inc. All rights reserved.Release 13.0

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ANSYS Mechanical Structural Nonlinearities

Customer Training MaterialWorkshop 6A: Stress Relaxation

Goal

Predict rate dependent stress relaxation of structure using an implicit time

hardening implicit creep model.

Model Description

C-Clamp assembly consisting of a

C-Clamp

tetrahedral elements to represent

the clamp and a line body meshed

with beam elements to represent

the bolt

Bolt tied to the clamp body via

fixed joints at each end.

Bolt

Rate dependent structural steel for

clamp

High strength rate independent



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steel for bolt


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Customer Training Material Workshop 6A: Stress Relaxation

Model Description (contd)

Materials:

Bolt: Rate independent structural steel

Clamp: Rate dependent structural steel that relaxes according to the following

Modified Time Hardening formula:

1

1

432

+

=

+

C

etC

cr

Where: C1 = 2e-10, C2=1, C3=1.5, C4 = 0, metric units (N, mm)

Load specifications:

10,000N bolt pretension loading for 150 seconds



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Customer Training MaterialWorkshop 6A: Stress Relaxation

Steps to Follow:

Restore Archive browse for file W6a-creep.wbpz

Save as

File name: W6a-creep

*



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The project Schematic should look like the

picture to the right.

From this Schematic, you can see that Engineering

defined (green check marks). It remains to define the rate dependent creep

material properties, set up and run the FE model in

ec an ca

Hi hli ht the En ineerin Data Cell and o en b

clicking on the Right Mouse Button (RMB)=>Edit.

Verify that the units are in Metric(Tonne,mm,..)

system. If not, fix this by clicking on

, ,..



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Define the creep material model

Highlight the Default Structural

Steel material and RMB=>Duplicate

to create a se arate material model.

Rename this new material Creep

With the new Creep material

,

and insert a Modified Time

Hardening creep model from the

Creep folder.

The Engineering Data page should

now look as shown



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Define the creep material model (contd)

Set the Reference Length Unit to mm

Using the constant values from page WS6A-3 fill in the data table accordingly



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e urn o e ro ec c ema c

Refresh project

Double click on the Model ell to open the FE Model Mechanical

Session) (or RMB=>Edit)



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Once inside the Mechanical application, verify the working unit system

Unit > Metric (mm,kg,N,s,mV,mA)

Open the folders beneath the model branch to become familiar with the

- .

Expand Geometry branch and note the two different body types (solid body forthe clamp, line body for the bolt).

Expand the Connections branch and note the two fixed joints designed to connect

the ends of the bolt to the faces of the clamp by way of constraint equations

automatically. The pinball is sized to represent the extent of bolt head and nut

interface with the clamped surfaces.



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Highlight the Solid body representing the clamp and change material

assignment to the Creep model



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Loads and Boundary conditions.

The back face of the clamp body is fixed.

A bolt pretension load is applied to the line body over two load steps

load

LS2 locks the adjustment into the bolt via constraint equations .



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Highlight the Analysis Settings branch,set number of load steps to 2 and

define the Solution Control specifications as shown for each load step.

Note:

-

with the Creep Effects turned Off. LS2 activates the creep calculation (end time =150 s) over several substeps,

allowing bisections if/when creep strain exceeds 10 times the elastic strain.



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Execute the solve

This run should converge without trouble,

but might take a few minutes depending on

hardware.

Note the development in creep strain as

indicated by nonzero values reported for

creep ratio in the solver output during the

.

After Solution is complete, Post process

results (displacement, stress, strain,etc)

Insert Equivalent Creep Strain

Notice how the Equivalent Creep Strain

increases (as expected) over time, while the

the structure relaxes.

Animate various results over time to confirm

these effects.



December 2010

mechanical nonlin 13.0 ws 06a creep

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