Challenge

Week - 4 - Crash Box Simulation

BBhoomireddy Narasimha Reddy27 Sept 2021

Aim:

To create a fullfilled simulation file for the crash analysis of the given model by having two different thicknesses of 1.2mm and 1.5mm from the

given FE model and produce the following outputs.

Outputs:-

- Input .k file and output files (d3plot, glstat, sleout, rcforc)

- Animation of the final simulation

- Cross-sectional force generated in the middle of the crashbox (along its length)

- Acceleration plot of a node in the middle of the crashbox (along its length)

- Maximum directional stress and strain along the length of the crashbox (X strain, Y strain etc)

- Plot of all energies (total, internal, kinetic, hourglass, sliding)

- Compare the accelerations and stress/strain plots of 1.2/1.5mm crashboxes.

Procedure:

1.Firstly open the LS-Dyna software and import the .k file of the model given us above.

2.Now the part is defined by assigning the section properties and material properties.

3.For creating a section solid, Go to

keyword manager>SECTION>SHELL.

The section properties of crash box are assigned as shell element with 1.2 mm thickness and ELFORM=2, Belytschko-Tsay element formulation.

4.Material properties:

The crash box is assigned with steel material with following parameters as shown in table.

Steel material properties Value

Mass Density [gm/mm ] 7.85e-3

Young’s Modulus [MPa] 210e3

Poisson's ratio 0.3

Yield stress [MPa] 355

Tangent modulus [MPa] 1.3e3

5.Now create a material card for assigning to the crash box by going into the

Keyword manager>MAT>024 PIECEWISE_LINEAR_PLASTICITY.

6.Now add a hourglass card for the model from going into the

Keyword manager> HOURGLASS.

Viscous hourglass control is recommended for problems deforming with high velocities i.e, Hourglass control type=IHQ=2, Flanagan-Belytschko

viscous form.

7.Now assign all the three cards that created above to the part in the given FE model as shown in the below fig.

Keyword manager>PART

8.Now set a intial velocity as the value of 13.88 mm/ms which is applies in the negative x-direction as shown in the below fig.

Create Entity>Initial>Velocity>cre

9.Now create a rigid wall infront of the crash box as shown in the below fig.

Create Entity>Rigidwall>cre>Planar>1n+NL

The rigid wall is created at a distance of 10mm away from the crash box.

10.Now create a contacts as shown in the below fig.

Keyword manager>CONTACT>AUTOMATIC_SINGLE_SURFACE

11.CONTROL FUNCTION:

Keyword manager>CONTROL>ENERGY

The control energy function is enabled for computing the hourglass energy, stonewall energy and sliding energy.

Keyword manager>CONTROL>TERMINATION

12.DATABASE OPTION:

Keyword manager>DATABASE>BINARY_D3PLOT

The time step value of 0.02 ms is given for the BINARY_D3PLOT and in the DATABASE_ASCII option for GLSAT, MATSUM, NODOUT, RCFORC,

RWFORC,SECFORC and SLEOUT.

Keyword manager>DATABASE>EXTENT_BINARY

Keyword manager>DATABASE>HISTORY_NODE

Keyword manager>DATABASE>CROSS_SECTION_PLANE

DATABASE_CROSS_SECTION_PLANE card is used to compute the sectional force of the crash box.

Normal Termination:

RESULTS:

The D3plot output file is opened in LS-PrePost using option File>open>LS-Dyna binary plot.

The animation of Von-Mises stress and Effective plastic strain for 1.2 mm and 1.5mm thick crash box is as shown below.

v-m stress animation contour of 1.2 mm thick crash box

v-m stress animation contour of 1.5 mm thick crash box

Effective plastic strain contour of 1.2 mm thick crash box

Effective plastic strain contour of 1.5 mm thick crash box

ACCELERATION PLOT OF A NODE IN THE MIDDLE OF THE CRASH BOX

Fig(a), shows the x-acceleration plot of node 5789 for a crash box having 1.2 mm thickness

Fig(b), shows the x-acceleration plot of node 5862 for a crash box having 1.5 mm thickness

From figures (a) & (b), it is observed that the deacceleration occurs during the impact at 1.5ms and it is evident the crash box having a thickness of 1.5 mm thickness deaccelerated at a faster rate than the crash box having the thickness of 1.2mm. This is due to increases in the thickness of the

crash box increases the deacceleration rate in a faster manner during the impact. After, the impact rebounce happens, and the crash box accelerates and deaccelerates until the end time.

MAXIMUM DIRECTIONAL STRESS :

Fig (a) shows the Maximum directional stress in the x-direction for the crash box having 1.2 mm thickness

Fig (b) shows the Maximum directional stress in the x-direction for the crash box having 1.5mm thickness

From, the above figures (a) & (b), it is observed that the maximum directional stress for the crash box with a thickness of 1.5 mm having x stress value of 399.519 MPa is lower than the crash box with a thickness of 1.2mm which has (219.383 MPa). The value of stress in the crash box with a

thickness of 1.5mm reduced since there is an increase in the thickness which also increases the cross-section. As we, know that the increase in cross-section area decreases the stress value.

Fig (a) shows the Maximum directional stress in the Y-direction for the crash box having 1.2 mm thickness

Fig (b) shows the Maximum directional stress in the Y-direction for the crash box having 1.5 mm thickness

From, the above figures (a) & (b), it is observed that the maximum directional stress for the crash box with a thickness of 1.5 mm having a Y stress value of 127.7 MPa is lower than the crash box with a thickness of 1.2mm which has (240.969). The value of stress in the crash box with a

thickness of 1.5mm reduced since there is an increase in the thickness which also increases the cross-section. As we, know that the increase in cross-section area decreases the stress value.

MAXIMUM DIRECTIONAL STRAIN (X & Y)

Fig (a) shows the Maximum directional strain in the X-direction for the crash box having 1.2 mm thickness

Fig (b) shows the Maximum directional strain in the x direction for the crash box having 1.5 mm thickness

From, Fig (a) and (b), it is observed that the x strain of both crash boxes is almost the same since there is only a slight change in the thickness for the crash boxes.

Fig (a) shows the Maximum directional strain in the Y direction for the crash box having 1.2 mm thickness

Fig (b) shows the Maximum directional strain in the Y direction for the crash box having 1.5 mm thickness

From, Fig (a) and (b), it is observed that the Y strain of both crash boxes is almost the same since there is only a slight change in the thickness for the crash boxes.

PLOT OF ALL ENERGIES:

Fig (a) , represents, GLSTAT DATA Plot for the crash box (1.2mm thickness)

Fig(b), represents GLSTAT DATA Plot for the crash box (1.2mm thickness)

STRESS PLOT:

Fig(a), represents the Effective (v-m) of the crash box having 1.2 mm thickness

Fig(b), represents the Effective (v-m) of the crash box having 1.5 mm thickness

STRAIN PLOT

Fig(a), represents the effective plastic strain plot of the crash box having 1.2 mm thickness

Fig(a), represents the effective plastic strain plot of the crash box having 1.5 mm thickness

CONCLUSION:

Thus, the crash test for the crash box is simulated with different crash box thickness, along with the given material properties, boundary

conditions, and required output data are delivered, plotted, and compared successfully.

Week - 4 - Crash Box Simulation

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in your own course.

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Ship work like thisin your own course.

Talk to a career counsellor

Ship work like this
in your own course.