ABAQUS-FEAII_lec1

8/3/2019 ABAQUS-FEAII_lec1

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Lecture 1: Abaqus, meshing and other things

Finite Element Analysis II

Todays Lecturer: Johan ClausenDepartment of Civil Engineering

Email: [email protected]


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Finite Element Analysis II 2

Finite Element Analysis II

Lectures: Jesper Winther Strdahl and Johan Clausen

The finite element method for structural and solid mechanics

Derivation for stiffness matrices for different elements

Programming of beam and membrane elements (skiveelementer in Danish)

(Re-?) introduction to Abaqus: Meshing and modelling techniques

As usual course information can be found on

\\files.civil.aau.dk\i5jcc\public_html\7sem_finite_element\Finite_element_v2.htm. The

webpage is currently under revision. An e-mail will be sent to you in the event of a

change to the webpage that affects the downloadable items (slides, programs) or the

information regarding the material you have to read before each lecture.


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Todays lecture: Abaqus, meshing and other things

Modelling of a simple structure in Abaqus

Meshing

Element types

The meshs significance on the stress field

How to model plasticity and other non-linear phenomena

3D meshing


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Abaqus

A general purpose commercial finite element code

Can model many types of problems linear and non-linear

Structural, heat, flow, conduction, magnetism, dynamic....

The users own materials, elements, etc. can be programmed into Abaqus

Conclusion: VERY versatile and market leader in advanced FE-analysis (mostly in academia)

Drawback 1: Somewhat harder to learn to use compared to other commercial FE-programs

Drawback 2: Commercial licenses are very expensive (Cowi has one license in Denmark)


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Plane element types

Rods and beams (Danish: stnger og bjlker)

Triangular and quadrilateral membrane elements (Danish: skiveelementer)


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Three-dimensional element types

Three-dimensional rods and beams

Plate elements

Combined plate and membrane element

Three-dimensional solid (tetrahedral, hexahedral, wedge)

And many more...


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Modelling a simple plane structure with membrane elements

The material is steel with E= 0.21 106 MPa and = 0.3


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Modelling a simple plane structure with membrane elements Step 1

Start Abaqus and click Create Model Database


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Double click Part and fill out the dialogue box Click continue when the box is filled out


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Click the Create lines connected button The lines can be drawn by mouse clicks or

by typing in the coordinates as shown

Sketch the part by typing the coordinates

given in slide 7

The window can be adapted to the object

any time by clicking Auto Fit View.

When finished click the Create lines

connected button again and click done-


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The part SteelThing can be seen in the modeltree by clicking the expansion +

The options under SteelThing can be seen by

expanding the model tree

Go into the mesh-mode by double-clicking

mesh (Empty)


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The Mesh menu buttons (only some are explained)

Mesh seeds: Specification of

mesh nodes on the boundaries. Is

used to control mesh density.

Mesh controls. Controls the

mathematical algorithm used

to divide the structure into

triangles and quadrilaterals

Create an element mesh

Specify the element type. For example:

Structural or heat conduction.

Linear or 2nd degree shape functions.

Integration point rule (Gauss order)


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Open the menu in the seed button by pressing the lower right corner of the button

The different buttons are:

1. Seed part: Used for seeding the entire part

2. Seed Edge by Number: Give the number of elements

on a specific edge

3. Seed Edge by Size: Set the element size on an edge

4. Seed Edge biased: The distance between the nodes

change over the edge

5. The last two buttons are for deleting seeds

1 2 3 4 5

Click Seed Edge by Number (2)


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Select the edges and set the appropriate number as shown 2 elements

2 elements

1 element

Type the number here


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Press assign mesh controls Select the options as shown in the dialogue box

Click ok


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Press Assign element type Select the options as shown in the

dialogue box. Remenber to untick the

Reduced integration check box

Press OK


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Press Mesh Part Press yes under the drawing area

You should now see the depicted

mesh


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Double click on the Materials flag in themodel tree

Enter the name Steel in the Name field

Under Mechanical, select Elasticity and

Elastic


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Fill in the properties fields and press ok

Important: Abaqus does not check units

in any way! As the dimensions of our model

was entered in mm the all stress terms (e.g.

Eand loads) must be entered in MPa to be

dimensionally consistent.

If we had entered the dimensions in m

the stress terms should have been in Pa.

If in doubt, always use the basic SI-units,

then you never go wrong. (i.e. length in m,

force in N, stress in Pa, and so on)


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Double click the Sections flag in the model tree Type in the name in the dialogue box

Select settings as shown and press continue

In the Edit Section dialogue select steel as the

material and press OK


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Double click the Sections Assignment flag in the model tree (in the SteelThing expanded menu) Select the part in the drawing window and click Done


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Assign the SteelSection and click ok


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Expand the Assembly flag in the model tree and double click in Instances

Select the SteelThing part and click ok


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Expand the Steps flag in the model tree. You can now see that there is only one step defined, Initial

Double click on Steps

Fill in the dialogue box as shown

Click continue

You have now created the step in which the load is

applied. The initial step is always present and is always the

first step.


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Fill in the dialogue box as shown and press OK

If, later on, you are going to

include large displacements in youcalculations, this is where you do

it, by setting Nlgeom to on

Also, if you are to perform non-

linear analyses you should enter

the Incrementation flag and

change the settings found here


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Double click on the Loads flag in the model tree

Fill in the dialogue box as shown and press Continue.

Note that we select a Pressure load and not a

line load. The line load is used for beam

elements

Note that the load is applied in the LoadStep

step and not in the Inititial step.


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Select the top edge of the structure and

press Done

Fill in the dialogue box as shown and

press OK

Note that pressure is given as a

negative number. This is due to the fact

that a positive pressure always acts

towardsthe surface on which it is applied.


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An array of arrows representing the pressure

load can now be seen


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Double click on the BC flag on the model tree

(BC is an abreviation of Boundary Conditions)

Select Displacement/Rotation and fill in the

dialogue box as shown.

Click Continue.


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Select the lower edge and press Done


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As the edge is free to move in the horizontal (x)

direction but supported in the vertical (y) directon

only tick the box U2

Press OK


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Expand the BCs flag. the Vertical support condition should now be visible

Double click on the BCs flag once more to

create the horizontal support

Fill in the dialogue box as shown and press

Continue.


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Select the lower left corner of the structure and press Done


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Constrain the corner in the horizontal direction and press OK


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Double click on the Jobs flag to create a calculation job Fill in the dialogue box as shown

Click Continue


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If you like you can fill in a description Then click OK

By expanding the Job flag you

should now see your job


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To submit a job for calculation right click on the job name Choose Submit

If a dialogue box appears, click OK

Your job is now being calculated


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You can now see that your job is running To monitor you job while running right click on the job name and select Monitor

A dialogue box appears where you can monitor your job.

You can close the box by pressing Dismiss


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To go to the post-processing unit to see the results right click on the job name Select Results


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Press the Plot contours on deformed shape button

This will show the von Mises Stress contours on

the deformed structure.

To view other stresses select the field Output

option in the main tool bar. Here you can select the

result that you want to plot.


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To find out the node number and itsdisplacement click the Tool- drop down

menu

Select Query

In the Query dialogue box select

Node

Click on the node on the inside corner(denoted A on slide 7)

You can now see the node number and

the nodal displacement

Note the node number

Repeat with node B on slide 7 and

note the displacement. You will need it for

comparison later.


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To find out the exact stress value of a point select Query in menu Tools

Select Probe values in the dialogue box


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Tick the boxes as shown and move the cursor to where you want to see the von Mises stress

Note the values of the

stress at point A from slide

no. 7 (the indside corner).

You will need this value later

in the lecture.

Here you need the node

number that you noted

earlier, in order to know

which of the displayed

stress values belongs to the

corner node.


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Different meshing techniques

Demonstrated by lecturer

Exercise: Try to mesh the structure with different mesh techniques and different elements

(triangular, quadrilateral, linear shape functions, 2nd degree shape functions). For each mesh note

the von Mises stress of point A and the displacement of point B. Do they differ in each case?


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Non-linear analyses

von Mises plasticity

Large displacements


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Analysis of a shell structure

The load is a uniform pressure load The holes are centrally placed circles with a radius of 10 mm

The shell thickness is 2 mm


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Use of symmetry

We make use of symmetry to reduce the number of elements


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Thank you for your attention

ABAQUS-FEAII_lec1

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