ANSYS Bracket Tutorial
-
Upload
rakeshsakote -
Category
Documents
-
view
99 -
download
7
Transcript of 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.
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
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
Main menu: Preprocessor - Modeling - Create - Areas - Circle - Solid Circle
Pick center point (left mouse button) at WP polar system (0,0).
Move the mouse to 0.025 radius and click left mouse button
OK to close picking menu
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:
Main menu: Preprocessor - Modeling - Create - Areas - Circle - Solid Circle
Pick center point (left mouse button) at WP polar system (0,0).
Move the mouse to 0.0125 radius and click left mouse button
OK to close picking menu
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
Main menu: Preprocessor - Modeling - Create - Areas - Circle - Solid Circle
Pick center point (left mouse button) at WP polar system (0,0).
Move the mouse to 0.0125 radius and click left mouse button
OK to close picking menu
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).