Challenge

Week - 4 - Crash Box Simulation

AIM: To simulate crash a crash test simulation of crash box impacting a rigid wall in LS Dyna.

Objective

To create a rigid wall in LS-Dyna
Apply initial velocity of 50 kmph to the crash box.
Run the simulation and compare results of crash box having thickness 1.2 mm and 1.5 mm respectively.
The unit system followed is gm-mm-ms
Plot the cross-sectional force generated in the middle of the crash box.

Modelling Rigid wall

Rigid walls mimic surfaces or volumes that are frequently used to represent stiffer structures that are either stationary or in motion.
A stationary planar rigid wall is created ahead of the frontal portion of the crash box by selecting a node on the edge, Select planar option and Geo-Vector >> 1n+NL
Now translate the rigid wall to some distance in the direction of the velocity of crash box.
The crash box is made to hit the stiffer rigid wall at an impact velocity of 13.88 mm/ms.

Initial velocity

Before creating the initial velocity keyword, we must create node set (NSID) for all the shell elements of the crash box.
Go to Create Entity >> Under Set Data >> create a new SET_NODEby selecting all the elements of the box.
Now assign that NSID in the initial velocity as shown below
50 kmph = 13.89 mm/ms

Shell card Selection

Shell section card is required to define section properties for shell elements.
Go to Keyword Manager
Select section >> shell >> section ID and title.
Choose Element Formulation value in ELFORM as 2 (Belytschko-Tsay type elements).
Mention the thickness of the shell elements as 1.2 mm for one simulation and then 1.5 mm for the other simulation.

Material Card

For crash box, we will assign the material as steel which is a non-linear characteristic material.
Go to Keyword Manager
Select MAT >> 024-PIECEWISE_LINEAR_PLASTICITY material card. Give it a material ID and title.
As we are using gm-mm-ms unit system, we will provide the characteristic values of steel as follows:

Hourglass can be defined using HGID. This keyword is used to reduce or control hourglass energy during the simulation.
Go to Keyword Manager and select the values as shown below.

Contact Card

Contact card can be used to define self-contact for crash box as the crash box elements can have contact between themselves after the deformation. Therefore, define AUTOMATIC_SINGLE_SURFACE contact with coefficient of friction 0.2as shown below.

Ship work like this
in your own course.