Lsdyna_demo

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Setting up Explosive Blast Loads in LS-DYNA

LS-DYNA has many special features that can be used for modeling automobile airbags, seat belts,

simulating crash tests with dummies, metal forming and many more. One of the very useful features is

the ability to simulate the detonation of an explosive and the loading caused by it. LS-DYNA allows users

to simulate blasts using Brode function or an airblast function that provides pressure loads due to

explosives in conventional weapons. In this example we will take the plate used in previous examples

and subject it to pressure load due to blast.

Building the Model:

1. To create the model click on page 7 in the main menu and select the Mesh tab to open theMeshing interface. Let the entity remain Box_Solid and select Box. Enter the co-ordinates of the

end points of the diagonal as 0, 0, 0 and 1.0, 1.0, 0.02. Enter the mesh density as Vx: 20, Vy: 20

& Vz: 2. Click Create and then Accept. Press Done to clear the dynamic interface area.

2. To define the material properties open page 3 and click on the *Mat tab. From the Group bydrop-down menu select All. Scroll down and select 003-PLASTIC_KINEMATIC and press Edit. In

the Title enter Aluminum. You can click on NewID or type in the material identification MID as

1. The density RO is 2700 (kg/m3), Youngs Modulus E is 69e+09 (Pa), Poissons Ratio PR is 0.3,

Yield stress SIGY is 2.25e+08 (Pa) and tangent modulus ETAN is 6.33e+08 (Pa). Press Accept,

then Done.

3. Now click on the *Section tab, select SOLID and press Edit. Enter the Section ID SECID as 1.Entering the title is optional. For this problem we will use the default constant stress solid

element. Press Accept, then Done.

4. To assign the material properties and the element definitions to the model press the *Part tab.Select PART (1) and press Edit. You can change the title to Plate. Enter SECID and MID as 1. Click

Accept, then Done.

5. Change the Title displayed on the screen and also in the keyword file by going to page 4 andpressing he *Title tab. Select & Edit [*]TITLE (1). Change the title to Blast Loading of an

Aluminum Plate. Press Accept then Done.

6. Save the model by selecting File>Save Keyword from the pull down Menu. Enter the filename asBlast.k and press Save.

Loads & Boundary Conditions:

1. To select the surface segments on which the pressure load will be applied go to page 5. Click onthe Set Data interface SetD tab. Scroll down to SET_SEGM on the drop down list and select theCreate button. Enter Set ID SID as 1. In the interface area below the rendering hot buttons click

Area to select segments lying within the picked area and select ByElem to pick segments by

element. Set the model into front view (ZY) using the rendering hot button. Left click and drag

the mouse so that only the top horizontal edge lies completely within the box (your box should

end above the line that lies between the two layers of elements). Rotate the model around and


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check if all the element faces on the top surface (400) have been selected. Click Apply, then

Done in the Set Data interface area on the right.

2. To define the blast load go back to page 3 and press the *Load tab. Select Blast and press Edit.Press NewID and enter charge mass WGT as 10. Enter the coordinates of point of explosion as

(0.5, 0.5, 0.5). Enter the time-zero of explosion TBO as 1.00e-04. Change the type of burst ISURF

to 2 for airburst.

3. Now to apply the load select the *Load tab. Select SEGMENT_SET from the list and press Edit.Enter the Segment Set ID SSID as 1. For blast you are required to enter the Load Curve ID LCID as

-2. Click Draw to visualize the load vectors on the nodes. Click ResForm button in the interface

area below the rendering hot buttons to restore the dialog window. Press Accept, then Done.

4. Blast requires you to define at least two load curves even though they may remainunreferenced. Press the *Define tab and select to Edit CURVE from the list. Enter the Load

Curve ID LCID as 1. Insert the default abscissa, A1 and ordinate O1 values which correspond to

time and load respectively. Insert the next set of values as 1 & 1. Click Accept then Add and

repeat the same for LCID 2. Click Accept then Done.

5. To select the nodes on the bottom edges of the plate which will be fixed go back to page 5.Select the Single Point Constraint Data interface Spc tab. Select Create and Set. Enter the node

set ID NSID as 1 or alternatively press NewID. In the interface area below the rendering hot

buttons select by edge ByEdge and then select to propagate the selection Prop. Click on any

edge of the bottom face (do not click on a node) to select all the nodes belonging to that edge.

Click on the other three edges in a similar fashion to select all the edges to be fixed. In the

interface area on the right select the X, Y & Z translational degrees of freedom to be

constrained. Click Apply and Done.

Defining Solution & Output Parameters

1. Click on the *Control tab, select TERMINATION and press Edit. Enter the termination timeENDTIM as 0.015 Secs. Select Accept then press Done.

2. Select HOURGLASS from the list to Edit. Change the default hourglass viscosity type IHQto 4 forthe stiffness form of Flanagan-Belytschko integration. Press Accept, then Done.

3. To calculate the energies select ENERGY from the list to Edit. Change the hourglass energycalculation option HGEN to 2 to include hourglass energy in the energy balance.

4. To specify the output database to be written click on the *Dbase tab. Select BINARY_D3PLOTfrom the list and press Edit. Enter the time interval between complete output states DT as

0.0001. Click Accept, then Done.

5. Select BINARY_D3THDT and click Edit. Enter the time interval between outputs of time historydata DT as 0.015. Select Accept then press Done.6. Click on ASCII_option then Edit. Select BNDOUT, GLSTAT, MATSUM & SPCFORC and enter the

output interval in the field below as 0.005 for each of them. Press Accept, then Done.

Save the keyword file again.


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Solution & Postprocessing

1. To solve the current keyword file first copy it to your hammer account. To run LS-DYNA type inlsdyna I= Blast.k and press Enter.

2. To look at the results copy your result files back onto your computer and start LS-PREPOST. Clickon File>Open>Binary Plot in the pull down Menu and select d3plot and press OK.

3. Entities of interest whose fringe plots may be plotted are pressure, von Mises stress and z-displacement.

4. Click on the tab Find. Select Node, enter 662 in the field and click Find. Press the History tab andselect Nodal. From the list select Z-displacement and press Plot. The plot window has a lot of

tools that allow you to operate on the curve before you save a plot. Press Close to close the

window. Note the delay in setting off of the charge of 0.0001 sec.

Questions, comments? Contact: [email protected]

Documents

Lsdyna_demo