Tut #2 LSDyna: Impact Analysis

9093 Tut#2: LSDyna Impact Analysis, page 1

Engineering 9093 – Ice Class Ship Structures

Tut #2

LSDyna: Impact Analysis By C. Daley

Overview

For a general introduction of LSDyna™ see Tut. #1. Unlike most finite element

programs LSDyna can easily model unrestrained bodies, such as a sphere flying at and

striking a plate. In this lab we will model that situation.

Learning Objectives

The lab builds on the LSDyna features learned in Lab#1. In this lab we will model

unrestrained motion (rigid body motion). We will model the plate as steel, but the

sphere as a special body called a "rigid body". We will not apply a force to either of

the two bodies. Instead we will apply an initial velocity to the rigid sphere. We will

specify a contact model which will allow us to model the contact that will occur

between the sphere and the plate. Without a contact model the sphere would just fly

through the plate. The plate will be modeled as elasto-plastic and will dent when

struck by the sphere. The sphere cannot dent. A few shortcuts for displaying and

hiding model features will also be shown.

LSDYNA Model #2 – Ball Impacting Plate

Step 1: describe and sketch the problem:

In this second example we will model a rigid sphere impacting a steel plate. The

problem is sketched below.


The problem description is as follows:

Geometry- Plate: 0.30 x .30 m (elasto-plastic) , Sphere: 0.05m radius (rigid),

Load: is the result of contact at impact

Supports: the plate edge is fixed, sphere is moving.

Material: Steel, with E = 200e9 Pa (2e11 N/m2), y = 3e8 Pa, Et= 1e9 Pa

Units: N, m, Pa, s

Step 2: estimate expected results (analytically):

How can this be done ?

Step 3: open LS-PrePost

1) First, Open LS-PrePost which should be on the desktop, with Icon or

Step 4: Directly create the FE model (nodes and element mesh)

1) Click the element and mesh button: . which opens up a new set of icons for

meshing.

2) Click the shape mesher button: . which opens a dialog window to directly create

a mesh.

In the Entity box at the top, select: 4N_Shell and fill in the 4 corner coordinates, the

number of divisions (elements) in x and y, and the Target Name, so it looks like this:


When you click on , a trial mesh is created. If it looks ok, press

and . At this point you should have a window that looks like:

1) To create the sphere, click the shape mesher button: . which opens a dialog window to

directly create a mesh. Select Sphere_Solid, make the Radius 0.05, the Density 6, the z

position 0.06 and the Target Name Ball, as shown below. press Create, Accept and Done.


The window should look like:

Note: LSDyna has automatically created 2 parts, and has colored part 1 red and part 2

blue. Each part has nodes and elements but does not yet have the other properties they

need.

Step 5: Define the material properties

1) Click the model and part button: which will bring up a new set of icons.

2) Click the keyword manager button: which opens a dialog window to directly create

keywords (Note: LS-Dyna files are called .k files because they are essentially a list of keyword

commands).

At this point the model option is selected, and there are 3 categories of keyword

already there (element, node and part). Note that there are 1768 elements, along with the 1940

nodes and 2 parts. Select the option and the window will display all the possible keywords:


1) Click on the + to the left of MAT to open the material options:

2) Select and then click on near the top of the

window. A Keyword Input Form will open to allow input of the properties for this

material model:

3) click on NewID and fill in the form so that it look like this;


then press and then press . This material model describes elasto-

plastic behavior in steel. This is similar to the bilinear-kinematic material property

that can be specified in ANSYS.

4) Now Select and then click on near the top of the window. A

Keyword Input Form will open to allow input of the properties for this material model:

5) click on NewID and fill in the form so that it look like this;

then press and then press . This material model is used for rigid

materials, though it has the density of steel.

Step 6: Define the section properties

1) In LSDyna the section properties contain information about the element parameters

and the type of physics employed. In the Keyword Manager window, scroll down

until you see the Section keyword. Click on the + and then select SHELL


2) Click on near the top of the window. A Keyword Input Form will

open to allow input of the properties for this section model. Click on NewID and

fill in the form as follows:

The form shows that the plate elements will have a thickness of 0.0030 m (3mm), that

there are 5 integration points through the thickness (NIP=5) and the shear factor is

0.833.

then press and then press . After pressing Accept, you will see

in the right hand space of the form. (Don't worry if the SECID number

is different).

3) Now we need a SOLID section for the elements in the sphere. Under the SECTION

Keyword, scroll down and select SOLID

4) Click on near the top of the window. A Keyword Input Form will

open to allow input of the properties for this section model. click on NewID and

fill in the form as follows:

The form only needs a TITLE. There is no other data to enter.

then press and then press .


Step 7: Apply the material and section properties to the model (to the 'Part')

1) In the Keyword Manager window, select the Part Keyword, press + and select Part:

Then press . A Keyword Input Form will open. There are 2 parts

defined, but the section and material information are not yet linked to the parts (there are

zeros under SECID and MID); .

2) Note that the 2 parts are listed in the upper right area of the form:

This means that you are editing the Plate.

Press the black dot to the right of SECID, and you see the following window open;

Select and press Done. When you do the SECID is updated. Click on the

black dot to the right of MID and select and press Done.

then press in the Keyword Input Form ( Don't press ) . We now have to

apply the properties to the solid elements of the sphere.

3) Select the Ball part listed in the upper right area of the form:

This means that you are editing the Ball.

Press the black dot to the right of SECID, and you see the following window open;

Select and Press Done. When you do the SECID is updated. Click on the

black dot to the right of MID and select and press Done.

Now press and now press . We now have a finite element model with

material and section properties.

Note - You have to the new information for each part prior to moving on to the

next part, else the info will be lost.


Step 8: Apply boundary conditions (fix the edges of the plate)

Rather than using the Keyword Manager window, we will use a special tool to create the

boundary conditions (an app called Entity Creation) :

The Model and Part button already selected:

Click on the Create Entity button. This will bring us an Entity Creation form.

Select the + Boundary and then select Spc :

Now change to Create mode by selecting

Make sure the Set option selected and all 6 degrees of freedom selected:

Now you need to select the nodes at the left end of the model. A Sel. Nodes dialog box

should be open: with Pick selected:

As a quick way to select all the edges of the plate, change the view to Edge Line Mode by

pressing at the bottom of the main LSDyna window. This will change the view so

that you only see the edges. Now in the Sel. Nodes dialog box press the

button. Now all boundary nodes are selected and the screen should look like;


Now in the Entity Creation form you can hit : You should see that a new

node set has been created: Now hit to close the Entity Creation form. You should change the view back to Shaded Element Mode by hitting

.

Step 9: Apply a velocity to the ball.

This activity can also be done with Create Entity feature. With the Create Entity form

open, select Velocity under Initial

Make sure the create option is selected.

Enter -20 in the Vz box.

Now you need to select all the nodes in the ball. The Sel.Nodes window is open. Select the

ByPart option:


and click on the sphere in the main window. All the nodes in the sphere will be highlighted:

Now hit in the Entity Creation window and you will see a long list of nodes.

Now Click

Hint : you can turn the viewing of velocity vectors and boundary conditions on or off by selecting

in the Entity Creation window and All or None in the Entity Selection window.


Step 10: Specify the Contact model.

We will use the simplest form of contact modeling. In the Keyword Manager, select Contact

and then select the AUTOMATIC_SINGLE _SURFACE option. Hit and see the

form. Just select NewID and fill in the Title with "Contact Model"

Now press and now press .

Step 11: Specify the duration of the simulation.

Return to the Keyword Manager and select

Scroll down to find and then click

Put 0.01 in the ENDTIM box :

hit and

Step 12: Specify output frequency.

LSDyna will solve the problem with a very short timestep. There would likely be far

too much output if you were to look at all the data for every solution timestep. Instead

you can specify the frequency of the output. Return to the Keyword Manager and

select the DATABASE and BINARY_D3PLOT Keywords. and then click

Specify an output timestep for the pot data of 0.0001 seconds (0.10ms)

hit and

In the Keyword Manager window hit to close it

Step 13: Save the .k file

Under the File menu select the Save Keyword As command and save the file as

Plate_Ball1.k in its own folder (to keep the output files all in one place)

Note - you will have to type Plate_Ball1.k , as LSPrePost will not automatically add

the .k extension.


Step 14: Run the LS-Dyna Analysis

1) Click on the LS-Dyna Manager Program , which opens the window.:

In the top menu, select Solver and select Start LS-Dyna Analysis. Next you see the

input screen. Use the Browse button to select the Plate_Ball1.k file. By default the

same folder as the .k file is in will be the folder where the output is sent.

When the .k file is selected, press the RUN button. A winow will pop up showing the

computation steps. When finished is should say Normal termination :


Step 15: Examine results of the LS-Dyna Analysis

1) Re-Open LS-PrePost.

2) From the File Menu, Select Open and LS-Dyna Binary Plot. 3) In the same folder as the .k file should be a file called d3plot - open it. Now you

should see the screen as shown below.

You can hit the Play button to annimate the bar over the .001 second of analysis.

To see more data, hit the Post button , then hit the Fringe Component

select Plastic Strain and , and the plot will become:

Now you will see the animated stresses. You can select Static under the Fringe Range

button to keep a constant range of stress during the animation.


Self Study Exercises: Student:______________

For each of these exercises, be prepared to show the instructor your results if asked.

Exercise #1 – Change the model initial shape . Open the d3plot file, then re-open the .k

file. Animate the results until there is a dent in the plate, and stop the animation. Save a

version of the .k file in a new folder (call the file Impact2.k ). Now close all and re-open the

Impact2.k file in LS-PrePost.

What is different?

In LSDyna run the new Impact2.k file and then review the results in LSPrePost.

What has happened?

Ex#1 Initials of Instructor_________

Exercise #2 – Redo the analysis starting with the ball as elasto-plastic (ie not rigid).with

a strength of 5 MPa.

What is different?

Ex#2 Initials of Instructor_________

Tut #2 LSDyna: Impact Analysis

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Transcript of Tut #2 LSDyna: Impact Analysis