ANSYS Bracket Tutorial

ANSYS Bracket Tutorial

Note: the following tutorial has been created by,

Thomas Olofsson Ph.D

Structural Engineering

Luleå University of Technology

Sweden

The document was originally found in:

http://orion1.anl.luth.se/kurser/datorstod/ansys/

Introduction

The ANSYS program is a computer program for finite element analysis and design. The program

is used to find out how a given design (e.g., a machine component) works under operating

conditions. The ANSYS program can also be used to calculate the optimal design for given

operating conditions using the design optimization feature.

The ANSYS program is a multi-purpose program, meaning that you can use it for almost any

type of finite element analysis in virtually any industry - automobiles, aerospace, railways,

machinery, electronics, sporting goods, power generation, power transmission, and

biomechanics, to mention just a few. "Multi-purpose" also refers to the fact that the program can

be used in all disciplines of engineering - structural, mechanical, electrical, electromagnetic,

electronic, thermal, fluid, and biomedical. The ANSYS program is also used as an educational

tool in universities and other academic institutions.

ANSYS software is available on many types of computers - PCs (personal computers),

workstations, minicomputers, superminis, mainframes, super mainframes, etc. Several operating

systems are supported, as are a multitude of graphics devices.

http://www.ansys.com/

Starting ANSYS

In the HP-lab under UNIX environment start ansys with the commands:

1. module add ansys51 2. ansys51 -g -j jobname (jobname is the filename your work is saved in. DON'T START

ANSYS NOW!)

In the PC-lab start ansys by double-clicking on the ansys icon on the desktop.

About the Graphical User Interface (GUI)

ANSYS GUI

A total of six windows are opened when you start ANSYS.

Utility Menu (top) - contains functions that are available throughout the ANSYS session,

such as file controls, selections, graphic controls and parameters. You also exit the

ANSYS program from the File pull down menu.

Main Menu (bottom left) - Contains the primary ANSYS functions, organized by

preprocessor, solution, general postprocessor, design optimizer.

Toolbar (middle right) - Contains push buttons that execute commonly used ANSYS

commands. More push buttons can be added.

Input Window (middle left)- Shows program prompt messages and allow you to type in

commands directly

Graphic Window (bottom right)- A window where graphics are shown and graphical

picking are made.

Output Window (not shown here) - Shows text output from the program, such as listing

of data etc. It is usually positioned behind the other windows and can de put to the front

when necessary.

Graphical picking

Many functions use graphical picking - using the mouse to identify model entities and coordinate

locations. The two most common types of graphical picking are:

locational picking - coordinates of a new point are located

retrieval picking - identifying a certain entity such as a line, key point etc

Whenever you use graphical picking a picking menu appears:

Fig. 2 Locate pick menu to the left and retriev pick menu to the right.

The Function title on the top of the menu identifies the function being performed, in this

example defining keypoints (location picking) / deleting key points (retrival picking).

Pick mode allows you to pick or unpick a location or entity. You can use either these toggle

buttons or the right mouse button to switch between pick or unpick mode. The mouse pointer is

an up arrow for picking and a down arrow for unpicking. For retrieval picking, you can also have

the option to select from single, box, circle and polygon mode.With single pick mode each click

picks an entity. With the other three modes, press and drag the mouse to enclose a set of entities

in a box, circle or polygon.

Next the Pick status is shown, nr of picked items "Count". The Picked data in the case of

location picking shows the coordinates. For retrival picking, this entry shows the entity nr. You

can see this data by pressing and dragging the mouse in the graphics area. This allows you to

preview the information before releasing the mouse button and picking the item.

Sometimes the required data is easier entered from the keyboard in the Input Window , e.g

coordinates can be easier to enter directly . The Keyboard entry options you can choose

between WP (working plane) or Global coordinates. For retrival picking you can enter a List of

entity numbers or a Range of numbers from the keyboard in the Input Window.

On the bottom of the pick menu you have the action buttons:

OK - Applies the picked items to execute the function and close the picking menu.

Apply - Applies the picked items to execute the function but does not close the picking

menu. Youc can either use this button or the middle button on the mouse (HP). For

Windows 95 users (two mouse button) the middle button is simulated by pressing shift

key and right mouse button simultaneously.

Reset - Unpicks all picked entities and restore the pick menu and the graphic area to their

state at the last apply.

Cancel - Cancels the function and close the picking menu.

Pick All - Picks all entities, (retrieval picking).

Help - Help for the function being applied.

Sometimes when the "hot spot" of two or more items are coincident you might pick more than

one item in retrieval picking. Ansys will bring up a multiple entities dialog where you can cycle

through the overlapping entities by a Next and Previous button until the desired entity is

highlighted. Press OK to select that entity.

FEM analysis of a corner bracket

(vinkeljärn) - Uppgift 3

This is an example of a simple static analysis of the corner bracket shown below. The objective

is to control if the bracket will yield under loading. This is a typical ANSYS analysis procedure.

Input data

The dimensions of the corner bracket is given below. The bracket is made of steel with a

Young's modulus of E=205 GPa (GPa = 109 N/m

2) and the Poisson's ratio of 0.27 and a yield

stress, including a safety factor, of 400 MPa.

Corner bracket

The upper left hole is constrained around it's entire circumference. The lower right-hand hole is

loaded by pin with a total force of 10 kN. The force is approximately distributed along the

contact as a tapered pressure varying linearly along the lower half of the circumference, see

below. The global coordinate system have been chosen to be in the center of the upper left-hand

hole.

Boundary conditions

We will assume plane state of stress, (plane stress is a state of stress in which the normal and

shear stress perpendicular to the plane is assumed to be zero). We will use solid modelling and

automatically mesh it with nodes and elements.

Summary

The steps in any Finite Element solution can be divided in three phases:

Preprocessing - define the model suchs as mesh, loads and boundary condition

Solution - assembling and solving the system of equation

Postprocessing - extracting relevant result from the solution

Preprocessing Steps

1. Specify jobname and title.

2. Set preferences

3. Define element types and options

4. Define real constants

5. Define material properties

6. Define the model starting with two rectangles

7. Change plot controls and replot

8. Change working plane (WP) to polar and create first circle

9. Move the WP and create second circle

10. Add areas (rectangles and circles)

11. Create line fillet

12. Create area fillet

13. Add remaining areas together

14. Create first bolt hole

15. Move WP and create second bolt hole

16. Subtract the holes from the bracket

17. Mesh the area

Solution steps

18. Apply displacement constraint

19. Apply pressure load

20. Solve

Postprocessing steps

21. Enter the general postprocessor

22. Plot deformed shape

23. Plot the von Mises equivalent stress

24. List reactions at constrained nodes

25. Exit the ANSYS program

http://www.mece.ualberta.ca/Tutorials/ansys/sweden/ansys.html#Pre

http://www.mece.ualberta.ca/Tutorials/ansys/sweden/ansys.html#Solv

http://www.mece.ualberta.ca/Tutorials/ansys/sweden/ansys.html#Post

Preprocessing

1 Specify jobname and title

The jobname determines the name of the file your job is stored under. You specify the jobname

when you start ANSYS, i.e. from an xterm window write:

> module add ansys51

> ansys51 -g -j uppgift3

After a while the ANSYS GUI:s will appear on the screen. You can also change the job name

later from the Utility meny:

Utility menu: File - Change Jobname…

Enter uppgift3 and click on OK

Next define the title of your job

Utility menu: File - Change Title…

Enter Corner bracket - Exersize 1 and click on OK

2 Set preferences

The preferences dialog allows you to set the desired engineering discipline for context filtering

of menu choices. By turning on the structural filtering completely surpresses thermal,

electromagnetic and fluid menu topics.

Main menu: Preferences

Select the the Structural will show and click OK

3. Define element types and options

In any FEM analysis you need to select an appropriate element type for your analysis. ANSYS

have many different types of element (2-D, 3-D, line elements suchs as bars, beam etc). Many

types have additional element options to specify the element behavior, element results and

printout option, etc.

We will use only one element type, PLANE82 which is a 2-D, quadratic structural higher order

element. The element have 8 nodes (4 corner nodes and 4 midside nodes) and have quadratic

approximation of the displacement field (higher order shape function). Using higher order

elements we can use a coarser mesh to get the same accuracy compared to lower order element

(liner shape fucntion).

We also need to specify plane stress with thickness as an option for PLANE 82, the thickness

will be defined as a real constant in the next step.

Main menu: Preprocessor - Element Type - Add/Edit/Delete..

Add.. an element type

Select Structural Solid family Quad 8 node 82 element and press OK

In the element type dialog now select options… to specify

Plane stress w/thk (with thickness)

OK to close the Element type options dialog

Close the Element type dialog

4. Defining real constants

For element types whos geometry is not fully defined by its node location, real constants

provide additional geometry information. Real constants are tied to the element e.g cross-

sectional properties for beam elements, shell thickness for shell elements etc. You can have

multiple sets of real constants only if multiple element types are used in the analysis. In our case

we will define the thickness of the PLANE82 element.

Main menu: Preprocessor - Real Constant…

Add a real set

OK for PLANE82

Enter 0.01 for THK ( 10 mm thickness)

You can also try the help button before you press OK and close the dialog box.

Information about the PLANE82 element are presented in a help window. To exit the

help window select File and Exit

Press Close to finish the definition of the real constant dialog

5. Define material properties

Material properties such as Young's modulus, Poisson's ratio or density are independent of the

geometry. Although they are not necessary tied to the element the material properties are listed

for each element type. Depending on the application the material properties can be linear,

nonlinear, anisotropic, temperature dependent etc. As with element type and real constants you

can have multiple material sets (to correspond to different materials) within one analysis. Each

set is given a reference number.

For this analysis we only have one isotropic linear elastic material (Young's modulus and

Poisson's ratio) . Furthermore we will neglect the density.

Main menu: Preprocessor - Material Props - Constant - Isotropic

OK to define material set 1

Enter 205.e9 for EX (Young's modulus)

Enter 0.27 for NUXY (Poisson's ratio)

Press OK to define and close material set 1

We will now save the what we have done so far. The database in memory will be saved to a file

uppgift3.db. The file will be your jobname with the extension db. You should save your work

on regular intervalls so if a mistake is made, the model can be restored from tha last saved state.

Toolbar: SAVE_DB

6. Define rectangles

There are several ways to create the model in ANSYS. In this example we will create the model

with simple geometric shapes called primitives and automatically mesh the final model. A

rectangle primitive consists of the following entities: an area, four lines and four keypoints.

The bracket can be built from two rectangles, two circles and two holes. Combining theses

primitives we get our bracket, but first we will start with the two rectangles. The global origin

we choose to set in the center of the upper left-hand hole.

Main menu: Preprocessor - Modeling - Create - Areas - Rectangle - By dimensions

Enter 0, 0.15, -0.025, 0.025 for X1,X2,Y1 and Y2 (Tab key between entries)

Apply to define the first rectangle

Enter 0.1, 0.15, -0.025, -0.075 for X1,X2,Y1 and Y2 for the second rectangle

OK to define the second rectangle and close the dialog

You should now have two rectangles in the same color drawn in the Graphic window.

7. Change plot controls and replot

To clearly distinguish between the areas just created we will turn on the area numbers and color

control is turned on. This is done from the utility menu:

Utility menu: PlotCtrls - Numbering

Turn on area numbering and press OK to close and replot

Toolbar: SAVE_DB

8 Change working plane to polar and create first circle

The next step is to create the half circles on the ends of rectangles. We will actually create full

circles and the add them to the rectangles (step 10). We will also make use of the working plane

(WP). The working plane is a 2D coordinate system (cartesian or polar) with an origin, a snap

increment and a display grid. By default the origin coincide with the global origin.

Before we begin we have to zoom out within the graphic window to see more of our created

circles. For this we use the Pan, Zoom, Rotate dialog box. We will also display the WP origin.

Utility menu: PlotCtrls - Pan, Zoom, Rotate

Click on the small dot (.) to zoom out

Let the Pan, Zoom, Rotate dialog be open you'll need it later

Utility menu: Workplane - Display Working Plane (toggle on)

The WP origin will now be visible on top of the global origin. Next, change the WP to polar,

snap on, snap increment and display grid spacing to 0.005, the polar radius to 0.025 and the

tolerance to 0.001.

Utility menu: Workplane - WP settings

Set the parameters according to the display and click OK when finished

The next step is to create the first circle using the picking function in ANSYS. You can at this

point use the Pan,Zoom,Rotate dialog to zoom in the polar WP coordinate system. Use the big

dot to zoom in and the to pan.

Main menu: Preprocessor - Modeling - Create - Areas - Circle - Solid Circle

Pick center point (left mouse button) at WP polar system (0,0). (Note the message in the

Input window)

Move the mouse to 0.025 radius and click left mouse button

OK to close picking menu

9 Move working plane and create second circle

First we will move the WP origin to the center of the other circle. Then we will create the other

circle in the same manner as the first one. The simplest way to move the WP without entering the

number offset is to pick the average of two keypoints at the lower end of the other rectangle.

Utility menu: Workplane - Offset WP to - Keypoints

Pick keypoint 1 at lower left corner of rectangle

Pick keypoint 2 at lower right corner of rectangle

OK to finish picking offset WP


Pick center point (left mouse button) at WP polar system (0,0).



Toolbar: SAVE_DB

10. Add areas

We need to add the different areas together to get one continuous area. This is done with the

boolean operation: Add areas

Main menu: Preprocessor - Modeling - Operate - Boolean - Add - Areas

Click on Pick All in the Add areas dialog

OK to add all areas together

Toolbar: SAVE_DB

11. Create line fillet

We need to fill in the radius between the intersection of the two rectangles. But first we turn off

the line numbers and turn off the display of the working plane.

Utility menu: PlotCtrls - Numbering

Turn on line numbering and press OK to close and replot

Utility menu: Workplane - Display Working Plane (toggle off)

Your graphic display should now look something like:

Main menu: Preprocessor - Modeling - Create - Lines - Line Fillet

Pick line 17 and 8

Enter 0.01 (10 mm) as fillet radius

OK to create fillet and close dialog box

12. Create fillet area

The next step is to create a fillet area that can be added to the rest of the bracket. Before you

continue to create a fillet area of the lines you just creates use the Pan, Zoom, Rotate dialog

under Utility menu: PlotCtrls to zoom in the fillet radius as shown above.

Main menu: Preprocessor - Modeling - Create - Areas - Arbitrary - By Lines

Pick lines L4, L5, L1

OK to create area and close dialog

Use the Pan, Zoom, Rotate dialog again and click on Fit and plot the areas under

Utility Menu: Plot - Areas

Your plot should now look like:

Don't forget to save your work:

Toolbar: SAVE_DB

13. Add areas together

Now add the fillet area to the bracket area. Use the same procedure as in step 10.

Main menu: Preprocessor - Modeling - Operate - Boolean - Add - Areas

Click on Pick All in the Add areas dialog

OK to add all areas together

Toolbar: SAVE_DB

14. Create first bolt hole

The holes have a radius of 12.5 mm so we need to change the WP snap and display increment to

2.5mm if we want to pick the circle origin and radius when we create the holes.

Utility menu: Workplane - Display Working Plane (toggle on)

Utility menu: Workplane - WP settings

Change the snap incr and display spacing to 0.0025 and click OK when finished

Now create the first hole:





15. Move working plane and create the second bolt hole

First we move WP back to the global origin:

Utility menu: Workplane - Offset WP to - Global origin

Then we create the other hole





To view the result so far we plot all lines (plotting areas can result in that some areas hidden by

others):

Utility menu: Plot - Lines

Toolbar: SAVE_DB

16. Subtract the bolt holes from the bracket

To finalize the model we only have to subtract the bolt areas from the bracket to create holes.

Main menu: Preprocessor - Modeling - Operate - Booleans - Subtract - Areas

Pick bracket as base area from which to subtract

Apply (in picking dialog, Not OK!)

Pick both bolt holes as areas to be subtracted

OK to subtract and close the picking menu

Final model of the corner bracket

Toolbar: SAVE_DB

17. Mesh the area

We will specify a global element size to control overall mesh density:

Main Menu: Preprocessor - Meshing- Shape & Size - Global Elem Size

Type 0.01 in the SIZE Element edge length

OK to close dialog

Finish the preprocessing by meshing the bracket

Main Menu: Preprocessor - Meshing - Mesh - Areas

Pick the bracket area

OK to mesh and close the picking menu

The mesh should look something like this

Toolbar: SAVE_DB

Solution

18. Apply displacement constraints

The upper bolt hole is constrained, e.g. we have to lock the displacements (set them to zero) of

the nodes on the circumference. Since we have not explicitely defined where the nodes on the

circumference are located, (ANSYS automatically did that), we'll lock the 4 keypoints on the

circumference and tell ANSYS the all nodes located along the lines between the keypoints will

also be locked.

Main Menu: Solution - Loads - Apply - Structural - Displacement - On Keypoints

Pick the four keypoints around the upper left-hand hole

OK to complete in the picking menu

Click on All DOF (Degree Of Freedom)

Click to yes to expand displacement constraints to nodes

OK to set constraint and close dialog

Toolbar: SAVE_DB

19. Apply pressure load

We'll now apply the tapered (linearly varying) pressure to the bottom right bolt hole. In ANSYS

a hole is made of four lines defining the perimeter (omkrets). We will apply the pressure to the

two lines making up the lower part of the circle. Since the total load Fy is 10 kN we need to

calculate the maximum pressure pm in the middle of the lower half.

Calculating the maximum pressure

The ANSYS convention for pressure loading is that positive value represents pressure into the

surface (compressive). We need to apply the pressure in two steps first from 0 to pm at the left

side then from pm to 0 on the right lower side of the hole.

Main menu: Solution - Apply - Loads - Structural - Pressure - On Lines

Pick the line defining the bottom left part of the circle (line L6)

Apply in the picking menu

Enter 0 for VALI and 62.83e6 for VALJ

Apply in the PRES on Lines menu

Pick the line defining the bottom right part of the circle (line L7)

Apply in the picking menu

Enter 62.83e6 for VALI and 0 for VALJ

OK in the PRES on Lines menu

Pressure applied on the lower part of the circle

Toolbar: SAVE_DB

20. Solve

Main menu: Solution - Solve - Current LS

Review the information in the status window and close the window (File - Close)

OK to begin the solution in the Solve current load step dialog

Close the information dialog when the solution is done

The result of this load step problem are stored in the database and on the result file

jobname.RST. The analysis can contain multiple loadsteps but only the last solution is storde in

the database. All other solutions are stored on the result file.

Postprocessing

Postprocessing is where you review the result of the analysis. The general postprocessor is used

to review the result at one loadstep (time step). Over the entire model. The time-history

postprocessor is used to review results at specific points in the model over all time steps.

21. Enter the general postprocessor and read in the results

Main menu: General postprocessor - Read results - First Set

22. Plot the deformed shape

Main menu: General Postproc - Plot results - Deformed shape

Choose Def(ormed) - undeformed

OK

Deformed shape of loaded corner bracket

23. Plot the von Mises equivalent stress

In uniaxial (enaxlig) loading the steel yields (plasticerar) when the uniaxial stress is equal to the

yield limit. In a multiaxial state of stress the yielding starts when the stress state is equal to the

von Mises yield criteria. The equivalent stress (se) value in a multiaxial state of stress can be

calculated using:

where s1 , s2 and s3 are the principal stresses (huvudspänningar). When the equivalent stress

value reaches the yield limit the steel starts to yield.

The postprocessor in ANSYS can plot contours of the von Mises equivalent stress value which

makes it easy to spot critical areas of the steel structure.

Main menu: General Postproc - Plot results - Contour plot - Nodal Solu

Choose stress item and scroll down to select von Mises (SEQV)

OK

von Mises stress contours

To the left of the plot (not shown here) you get a color legend of stress contour values. You also

get the maximum value (SMX), the minimum value (SMN) and the maximum value with the

estimated error added (SMXB). Note! The finite element method only gives approximations of

the true stress levels. In this case one might consider to give a denser mesh especially around the

upper bolt hole where the maximum stress levels are.

Compare the SMXB value with the yield limit. Will the corner bracket yield?

To see the stress contours more clearly, we'll turn of the displayof the element mesh and make

the outline solid:

Utility menu: PlotCtrls - Edge Options

Select edges only, replot and dashed/solid

OK

24. List reaction solution

In Finite Element analysis it is essential to have checkpoints. The sum of the reaction forces in y-

direction should equal the total applied load and the sum in the x-direction should be near zero.

Main menu: General Postproc - List results - Reaction Solu

OK to list all items in the List Reaction Solution dialog

Scroll down in the PRESOL window and check the total values

When finished File-Close

There are many other options available for reviewing results in the general postprocessor. You

have now finished the analysis and we exit the program.

25. Exit the ANSYS program

When you exit the program you can save geometry and loads portion of the database (default)

OR the default and solution OR default, solution and postprocessing (i.e. save everything) OR

save nothing. We have chosen to save nothing (since we are finished).

ANSYS Toolbar: QUIT

Select Quit - No Save! in the Exit ANSYS dialog

OK

Redovisning av uppgift 3

Redovisa:

1. Största nedböjningen (DMX i nedböjningsplotten)

2. Maximala von Mises spänningarna i strukturen SMX och SMXB.

3. Vad är skillnaden mellan SMX och SMXB?

4. Var i strukturen är påkänningarna som störst?

5. Finns det risk att stålet börjar flyta?

6. Summa reaktionskrafter i x och y-led (Total Fx, Fy i listningen av reaction forces).

Documents

ANSYS Bracket Tutorial