Week - 4 - crash box simulation

Aim:

In this Challenge we have to perform a stimulation of crash box it s is quit similar like car crash, but in these case instead of car we have taken an rectangular box which moves to an certain velocity and get crashed into a rigid wall
Crush box is one of the components in automotive which absorb the crash energy. At the time of impact the crash box will rebounces to absorb impact loads and minimize the kinetic energy. In frontal collision the crash box will play a major role to absorb energy by collapsing than the other body parts.

In LS DYNA is used as a solver. For different material models they determine displacement and energy absorption. For a particular model,find out results at different thickness and velocities.The results are plotted for 3 cases which are different material model, various thickness and velocities. Square and rectangular cross sections absorb lower energy than the other cross sections..

The meshed model is imported to LS DYNA solver for analysis, the analysis carried out in two parameter first one is changing two different thicknesses those are 1.2mm,1.5mm. crash box design Corrugated and plane design with the initial velocity is as 13.85mm/ms.

Procedure:

create the section id for the material by clicking section in keyword manager and select the element as shell with thickness 1.2mm.

create the node set id in entity creation

After defining the sections , open the part tab in the key-word manager assingining rigid_wall in front of crash box with 10mm away.

Assign the material id for the parts in the model,for phone as *MAT_PIECEWISE_LINEAR_PLASTICITY.here i assign RO=7.330e-06,E=222.00000,PR=0.3000000,SIGY=0.2900000.

create the part in keyword manager and assign the section id and mat card what we create before.

Creating the intial velocity click keyword manager and select the velocity now give the velocity for the rectangular box. create the node set id for which the elements to be in velocity,in the negative x direction with 13.85mm/ms,so it get crash on the rigid wall

create the output file by clicking the database and select the binary d3 plot and also create outfile by clicking Database>ASCII_option>select the glstat and RCFORC,RWFORC,SECFORC,SLEOUT.

Next in control card select the termination for animation time for the model

After the automatic contact ,the box element are self contact during crashing (Automatic sibgke surface) here it was not required to define the master surface or node ,here in this case i defined the slave part ,because here we considered the crashbox itself is master and slave..

Results:

Plot the results of kinetic energy, internal energy, total energy and von misses stress, displacement. From these results validate which parameter is absorbing more energy and resist the stress with the same velocity with respect to time.

Von misses stress

Maximum vonmises peak is 2.900E-01
Minimum value is 0.000E+00

Effective plastic strain

Maximum effective plastic strain peak is 4.972e-02
Minimum value is 0.000E+00

Lower plastic strain

Maximum vonmises peak is 4.776E-02
Minimum value is 0.000E+00

We know that thickness will help to increase the stiffness. More stiffness will results to lower stress values.
BUt in these type of analysis we have look into how the failure occursand what kind of deformation happen during thr crash bar impacts the rigidwall .
The figure indicates ma and min stress values.
For more thickness the area of wall hits the rwall at a very low compared to less thickness ,but more stress are applied at the frontal part of the crash tube .
The crashpoint of the view is more thickness , rigidity and stiffness,From the above we have conclude that stress of 1.5mm thk is quit better than the 1.2 mm thk crashbox.

Plot thegraph of kinetic energy, internal energy, total energy and sliding energy with respect to time.

Plot a graph using crush tube impacted by some velocity by a rigid wall ,effective plastic strain vs time graph

crossectional force

Cross-sectional force 1.2mm

Acceleration occurs during crash box impacted towards rigid wall at some velocity while it impact the rigid wall it get rebounces ,it provide more shocks .

The stress results are plotted in hyper works and graphs are plotted in ls post procesing. Kinetic energy and internal energy graphs are plotted with respect to time.
 When the thickness is increased simultaneously stress is increased and stiffness also increases.
 When the surface area increases the stress is decreased.
The stress results and energy graphs are plotted for corrugated and plane design with respect to two thicknesses.

COMPARISON OF RESULTS
1. Stress results of corrugated design and Plane design.
2. Stress results in between Thicknesses.
3. Corrugated design Energy graphs with their Thickness.
4. Plane design Energy graphs with their Thickness.

The stress values vary with their thickness and design, plane design stress values are more than the corrugated design due to minimum surface area compares with corrugated design. When the surface area increases the stress will be decreased. The stress values are increased when the thickness of the component will be increased and stiffness also increases. The 1.2 mm thickness crash box will absorb optimum stress compare to 1.5mm. If stiffness is increase the more shocks will be produced, due to shocks occupant will be injured so that the crash box should absorb optimum stress.

Conclusion

The work carried out on the design and crash analysis of the crush box by using LS DYNA software. By comparing above results corrugated design is better than plane design because it absorbs low stress when compared to it. While considering thickness factor, 1.2 mm thickness absorbs optimum stress to other thicknesses (1.5mm). By the various stress values of thickness and from energy factor as observed from the graph it suggests that 1.2mm thickness yield satisfactory results.