Week - 4 - Crash Box Simulation

CRASH TEST ON A RECTANGULAR CHANNEL

AIM:

• To simulate a crash test for a crash box with varying thickness under initial velocity using Ls-dyna should satisfy under two situations such as ,

1. Box crashes on the rigid wall and rebounces completely.
2. Box buckles and folds in axial direction so as to come in self contact.

• To run the another simulation by increasing the thickness of the crashbox from 1.2 to 1.5mm.

OBJECTIVE :

1. To create the simulation file (input file ) from the given K format type of file.
2. To create the material card.
3. To create a section card for thickness 1.2mm
4. To assign material and section card to the part.
5. To define a rigid wall.
6. To assign initial velocity of the crash box.
7. To create a cross section.
8. To define a contact interface.
9. To assign control termination card.
10. To create a contact interface between rigid wall and crash box.
11. To define the output database as both binary D3 plot and ASCII.
12. To checkup the model of1.2 mm thickness and run the simulation.
13. To create a section card for thickness 1.5mm
14. To run the simulation for model thickness 1.5mm

OUTPUT DELIVERABLES:

1. To create the Input .k file and output files (d3plot, glstat, sleout, rcforc)
2. To perform the animation of the final simulation.
3. To perform Cross-sectional force generated in the middle of the crashbox (along its length)
4. To plot the Acceleration of a node in the middle of the crashbox (along its length)
5. To perform Maximum directional stress and strain along the length of the crashbox (X strain, Y strain etc)
6. To plot of all energies (total, internal, kinetic, hourglass, sliding)
7. To compare the accelerations and stress/strain plots of 1.2/1.5mm crashboxes.

DATA BASE:

ASSUMPTION AND INFORMATION:

1. The crashbox should crash into a rigidwall created using *RIGIDWALL_ keyword.
2. Material for the crashbox is steel.
3. The simulation needs to be started using elastic material to verify its correctness and later a nonlinear material card data will be provided.
4. Thickness of the crashbox is 1.2mm.
5. Initial velocity for the crashbox should be around 50 kmph.
6. The units system to be used is gm-mm-ms.

SOFTWARE USED:

Solver tool - LS-Prepost 4.7.17 and LS-Run 1.0.100838

PROCEDURAL STEPS:

STEP 1 : Import the file

1. imported the K format type of crash test file using LS-Prepost software.
2. File > Import > LS-Dyna keyword file > browsed to selected the K type of file > imported it.

STEP 2 : Check the keywords

1. In order to check the keywords contained in the file we have to follow the below step
2. Side bar > model and part > keyword manager > checked the model.
3. Only shell elements presented in the model.Accordingh to analysis shell elements only needed.

Step 3 : To check duplicate elements.

1. In order to check duplicate elements by firstly check the nodes the following steps.
2. Sidebar > element tools > check duplicates > selected nodes by area > Zero-duplicate nodes had been showed.

Step 4 : To create the material card.

1. To assign the material card for box by the following steps.
2. Side bar > model and part > keyword manager > MAT > all > selected the required materials for the crash box.
3. For crash box has assigned the material is 001 ELASTIC .
4. Created new ID is 1 and give title is crashbox_material and specified the values as gg-mm-ms unit system
5. This is Material Type 1. This is an isotropic hypoelastic material and is available for beam, shell, and solid elements in LS-DYNA.

Where,

Ro- density of the steel is 7.85 x 10⁻³ gm /mm³.

E- youngs modulus of the steel is 210 x 10³ gm / mm ms².

PR- poissons ratio of the steel is 0.3.

Step 5 : To create the section card of thickness 1.2mm

1. In this section element formulation ,integration rule , nodal thickness and cross sectional properties are defined.
2. Created the section shell for crashbox.
3. Side bar > model and part > keyword manager >all > section >specified the thickness value is 1.2mm > created the new SECIDs for crashbox.

Where,

ELFORM is Element formulation.

SHRF is Shear correction factor which scales the transverse shear stress.

NIP is Number of through thickness integration points.

Step 6: To assign material card and section card to the crashbox.

1. Already assigned the material card and section card for crashbox, now we have to assigned the both cards to their respective crashbox part.
2. Inorder to create the crash box part by the following steps.
3. Side bar > model and part > keyword manager >model > part > assigned the MID and SECID cards to crashbox part.

Step 7: To define a rigid wall.

1. The RIGIDWALL provides a easy way to define a contact between a rigid surface and nodal points of a deformable body, called slave nodes.
2. A rigid wall is defined by a surface type and a group of slave nodes.
3. Each wall can be fixed or moving. A rigid wall is a kinematic condition.So a rigid wall is created ahead of crash box. So that crash box should crash into a rigid wall created. And rigid wall should create at some distance from crash box, because crash box have to move with some initial velocity. Also, we have to take care about rigid wall normal vector direction. It should be facing crash box. In order to create rigid wall by the following steps.
4. Sidebar > model and part > create entity > rigidwall > create > cheked 1n+NL option > selected the one node > check Global and XL > rigidwall created.
5. Then we have to move the rigidwall from crashbox by the distance of 15mm by the following steps
6. At the same time > uncheked 1n+NL option >checked translate option > specified the distance is 15mm > rigidwall created 15 mm distance from the crashbox.and also make sure vector normals of the crashbox and rigidwall opposite to each other.so thats only the crashbox rebounces after strike. if vector normals of the crashbox and rigidwall is parallel to each other , crashbox penetrated through the rigid wall thats not needed for the analysis.

Step 7: To assign initial velocity to the crashbox.

1. To provide initial velocity to the crashbox by the following steps.
2. Sidebar > model > create entity > initial > velocity > pick by part > provide initial velocity in x direction as 13.88 mm/ms >done.

Step 8 : To create a cross section

1. The purpose of creating cross section is to define a cross section for resultant forces written to ASCII file secforc.
2. So we have to create cross section at middle of crash box in order to get values of forces along the length of the crash box.
3. In order to create cross section we have to following the below steps.
4. Sidebar > model and part > create entity > database > create > checked plane > cheked 1n+NL option > selected the node > check Nx > apply and done.

Step 9 : To define a contact interface

1. The keyword *CONTACT provides a way of treating interaction between disjoint parts.
2. Now we have to define contact interface. Before defining contact card, first we have to create set data segment, in which we will create segment for crash box (in which we will select those elements which are going to interact during simulation).
3. Define a set of segments with optional identical or unique attributes. For three-dimensional geometries, a segment can be triangular or quadrilateral. For two dimensional geometries, a segment is a line defined by two nodes and the GENERAL option does not apply.
4. In order to create set of segments we have to following the below steps.
5. Side bar > model and part > create entity > set data > *SET_SEG > selected the elements by part > apply and done

1. In order to create contact card, we have to select contact automatic single surface for crash box. In which slave is crash box.
2. In order to create contact card for the following steps.
3. Sidebar > model and part > keyword manager > contact > AUTOMATIC_SINGLE _SURFACE > assigned slave set segment id > aceept and done.

Step 10 : To define control card.

(1) To create control energy card.

1. The purpose of creating control energy card, provide controls for energy dissipation options.
2. In order to assign control energy card we have to following the below steps.
3. Sidebar > model and part > keyword manager > control > ENERGY >set HGEN as 2 > accept and done.

Where,

HGEN Hourglass energy calculation option.

RWEN Rigidwall energy dissipation.

SLNTEN Sliding interface energy dissipation option.

RYLEN Rayleigh energy dissipation option (damping energy dissipation):

IRGEN Initial reference geometry energy option.

(2) To create control hourglass card.

1. We use the reduced integration point formulation method which introduce the hourglass energy in the simulation.
2. To reduce hourglass energy, it is necessary to enable the hourglass card in the energy card from keyword card and enable hourglass card from control keyword.
3. In order to assign control hourglass card we have to following the below steps.
4. Sidebar > model and part > keyword manager > control > HOURGLASS > set default values > accept and done.

IHQ - Default hourglass control type.

QH - Default hourglass coefficient.

(3) To create control termination card

1. The main purpose of control termination card is to stop the job.
2. In order to assign the control termination card by the following steps.
3. Side bar > model and part > keyword manager > control > termination > specify termination time is 5ms > aceept and done.

Step 11: Define the outputdatabase

(1) To define the output database as Binary D3 plot.

1. DATABASE_BINARY_D3PLOT ensures d3 plot files which its stores stress strain contour of the entire deformed model.
2. In order to create the DATABASE_BINARY_D3PLOT by the fllowing steps.
3. Side bar > model and part > keyword manager > database > select DATABASE_BINARY_D3PLOT > provide DT value is 0.01 is a time interval
   between output states > accept & done.

(2) To define the output database as ASCII.

1. ASCII can generate different outputs such as force generated in a contact like total energy and material energy etc.
2. In which we will request output as GLSTAT, MATSUM,SECFORCE, SLEOUT, and RCFORCE.
3. In order to create the ASCII by the fllowing steps.
4. Side bar > model and part > keyword manager > database > select ASCII_option > check GLSTAT DT,SECFORCE, SLEOUT, and RCFORCE > specify all value is 0.01 > accept & done.

Where,

GLSTAT is global statistics and energies.

MATSUM is part energies

SLEOUT is sliding interface energies.

SECFORC is cross section force data.

RCFORC is resultant interface force.

Step 12 : Model checkup and run the simulation.

1. The model is checked for any errors before solving using model checker.
2. After all the errors are cleared, the drop test setup is saved and is ready to run in LS DYNA manager for solving the scenario.
3. Warnings we can ignore . once model checkis run , it will look like as shown in picture below.

STEP 13 : Run the simulation

1. Before running simulation we have to edit the K file and have to edit the KEYWORD ID, so that after simulation all files should be generated with proper format as shown.

1. To run the crashbox_test_1.2mm using LS-run by the following steps.
2. Title bar > file > run LS-dyna > runned the crashbox_test_1.2mm file > achieved normal temination. it means the model is ready for post processing.
3. During simulation run window will popup as shown in picture below,

STEP 14 : Post processing
i. In order to see simulation results , we have to open output file in LS-Prepost by the following steps.
ii. In LS-prepost -Title bar > file > open > LS -Dyna binary plot > selected the d3 plot file > visibled to see animation file.
iii. For plot the stress contour , go to sidebar > post >fringe component > selected in which results need for analysing the problem.
iv. For energy plot results , go to side bar > post > ASCII > selected in which enegy results (Glstat and Matsum) need for analysing the problem.

(1) Contour plot of vonmisses stress with 1.2mm thickness.

In order to see simulation results, we have to open output file .d3plot file in LS-PrePost.

Max Effective stress = 452.643 gm / mm ms²

(2) Cross-sectional force generated in the middle of the crashbox with 1.2 mm thickness (along its length as X-direction)

Max force value = 2.017* e+05 gm mm / ms²

Max resultant force value = 4.0056 * e+05 gm mm / ms²

(3) Acceleration plot of a node in the middle of the crashbox (along its length as X-direction).

Max acceleration at node 5130 = 6.25 * e+03 mm / ms²

(4) Plot of energies of the crashbox 1.2mm.

Max kinetic energy = 1.33 * e+05 gm mm / ms²

Max internal energy = 1.22 * e+05 gm mm / ms²

Total energy = 1.35 * e+05 gm mm / ms²

Hourglass energy = 6.73 * e+03

Damping energy = 0

(5) Plot of sliding interface energies in 1.2mm crashbox

In this simulation there is no sliding operation and interfacing occurs between the rigidwall and crashbox during simulation , so there is no chance of sliding interface energies developed. so slave energy , master energy and frictional energy is zero.

(6) Maximum directional stress and strain along the length of the crashbox 1.2mm.

(6a) Maximum directional stress along the length of the crashbox in X- direction.

Max X stress = 315 gm / mm ms²

(6b) Maximum directional Strain along the length of the crashbox in x-direction.

Max X strain residual = 1.02 * e-05

(6c) Maximum directional Strain along the length of the crashbox in Y-direction.

Max Y strain residual = 1.03 * e-05

Case(ii) Simulation of crashbox with 1.5mm thickness.

Step 1A : To create the section card of thickness 1.5 mm

1. In this section element formulation ,integration rule , nodal thickness and cross sectional properties are defined.
2. Created the section shell for crashbox.
3. Side bar > model and part > keyword manager >all > section > specified the thickness value is 1.5mm. > created the new SECIDs for crashbox.

STEP 1B : Run the simulation of Crashbox with 1.5mm

1. Before running simulation we have to edit the K file and have to edit the KEYWORD ID, and save as crashbox_test2_1.5mmso that after simulation all files should be generated with proper format as shown.

1. To run the crashbox_test_1.5mm using LS-run by the following steps.
2. Title bar > file > run LS-dyna > runned the crashbox_test2_1.5mm file > achieved normal temination. it means the model is ready for post processing.
3. During simulation run window will popup as shown in picture below,

STEP 14 : Post processing
i. In order to see simulation results , we have to open output file in LS-Prepost by the following steps.
ii. In LS-prepost -Title bar > file > open > LS -Dyna binary plot > selected the d3 plot file > visibled to see animation file.
iii. For plot the stress contour , go to sidebar > post >fringe component > selected in which results need for analysing the problem.
iv. For energy plot results , go to side bar > post > ASCII > selected in which enegy results (Glstat and Matsum) need for analysing the problem.

(1) Contour plot of vonmisses stress with 1.5mm thickness.

In order to see simulation results, we have to open output file .d3plot file in LS-PrePost.

Max Effective stress = 498.643 gm / mm ms²

(2) Cross-sectional force generated in the middle of the crashbox with 1.5 mm thickness (along its length as X-direction)

Max resultant force value = Maxval= 4 * e+05 gm mm / ms²

Max X- force value = 2 *e+05 gm mm / ms²

(3) Acceleration plot of a node in the middle of the crashbox with 1.5mm (along its length as X-direction).

Max acceleration at node 5130 as = 5.4 * e+03 mm / ms²

(4) Plot of energies of the crashbox 1.5mm.

Max kinetic energy = 1.33 * e+05 gm mm / ms²

Max internal energy = 1.22 * e+05 gm mm / ms²

Total energy = 1.35 * e+05 gm mm / ms²

Hourglass energy = 6.73 * e+03

Damping energy = 0

(5) Plot of sliding interface energies in 1.5mm crashbox

In this simulation there is no sliding operation and interfacing occurs between the rigidwall and crashbox during simulation , so there is no chance of sliding interface energies developed. so slave energy , master energy and frictional energy is zero.

(6) Maximum directional stress and strain along the length of the crashbox 1.5mm.

(5a) Maximum directional stress along the length of the crashbox in X- direction.

Max X stress = 308 gm / mm ms²

(5b) Maximum directional Strain along the length of the crashbox in X-direction.

Max X strain residual = 1.16 * e-05

(5c) Maximum directional Strain along the length of the crashbox in Y-direction.

Max Y strain residual = 0.00111249

(6) Comparison of accelerations and stress plots of 1.2/1.5mm crashboxes.

(6A) Comparison of stress plot of crashbox1.2mm / 1.5mm on node at 676

X-stress plot of 1.2 mm crashbox X-stress plot of 1.5 mm crashbox

Max stress value at element 676 in crashbox with 1.2mm= 2.81 * e+02 gm / mm ms²

Max stress value at element 676 in crashbox with 1.5mm = 2.48 * e+02 gm / mm ms²

(6A) Comparison of acceleration plot of element at 5130 in the crashbox1.2mm / 1.5mm

X-acceleration plot of 1.2 mm crashbox X-acceleration plot of 1.5 mm crashbox

Max X- acceleration at node 5130 in crashbox with1.2mm = 6.25 * e+03 mm / ms²

Max X- acceleration at node 5130 in crashbox with1.5mm = 5.4 * e+03 mm / ms²

Final simulation of crashbox

CONCLUSIONS
1. Crash box simulation has been done successfully with 1.2 mm and 1.5 mm thickness respectively.
2. All the output requests have been calculated such as von misses stress, energy plots.
3. After comparing results, we can analyses that simulation results varies as per thickness changes.