Week - 4 - crash box simulation

OBJECTIVE

A crashbox is a highly energy absorbing structure that crashes application of loads and reduces impact on other components nearby.a fully fledges crash box is highly sophisticated design but in this case we will go with rectangular channel which can through of as the most simple crashbox.

PROCEDURE

The given file .k can be opened through Ls-Prepost selecting it as a keywordfile.the unit system followed for unit consistency is gm-mm-ms.here the analysis carried out in two parameter.first one is changing two different thickness those are 12mm and 1.5 mm and all the pre processing setting are same. firstly create the shell element thickness from the keyword manager.then assigned property.the crash box made up of steel material with initial elastic property and prolonged to have plastic non-linear effct.MAT24 is used.the crash box is made to hit the stiffened rigid wall at an impact velocity 13.88 m/s.

CASE-1 : 1.2 mm thickness

MATERIAL

MAT_24 is used for the simulation with the basic input parameter values of density ,youngs modulus and poisssons ratio.

SECTION CREATION

Shell formation so we assign the elform=2 and the thickness =1.2mm.

RIGID WALL

The stationary plannar rigid wall is created head of the frontal portion of the crash box at an aproximation distance.C reate entity > rigid wall and choosing aproximate node and palne.

rigid wall infront of crash box 10 mm away.

INITIAL VELOCITY

For initial_velocity card is used to apply from the crash box in the direction of impact .the intial velocity 13.88 is applied in the -X direction

CONTACT

Automatic contact was created as the box elements are getting self contact during crashing (automatic single surface)here it was not needed to define the master surface or node only the defined the slave part is because the crash box itself is master slave.

SET CROSSECTIONAL FORCES

The sectional force at the mid of crash box created.we first defined set and the element set of parallel series connecting those nodes.after creating these two database cross section was created for capturing the force during crushing.

OUTPUT REQUEST

Control_Termination : this keyword specifies the duration of the simulation ,in this case we assume the impact occurs with in a time period.

CONTROL_ENERGY :This keyword is used to specify the various energies that need to be considered and computed during the simulation.for this analysis we have a rigid wall present we can compute the stone wall energy ,similarly reqire the hourglass energy.

CONTROL_ACCURACY : Control parameters that can improve the accuracy of the calculation.

ASCII :

GLSTAT : globel statistics involving KE,IE,hourglass etc

NODOUT : nodal properties like displacement ,acceleration etc.

RCFORCE: interface force

RWFORCE : rigid wall force .

SLOUT : sliding interface energies

SECFORCE : cross sectional forces

POST PROCESSING

von-mises 1.2mm thickness

the effective stress or von mises stress in crash box for 1.2 mm .the highest value 1.2 mm thickness shell is 410 mpa at time 1.099

plastic starin 1.2mm thickness

hourglass 1.2mm thickness

step t=1 strain is 0.0059068, time step =5 the strain is 0.0095 ,in this time the material deformation occur.the total deformation is 0.0096 at the end of time step

ENERGY 1.2 THICKNESS

The kinetic energy of the system tends to behave in an opposite manner internal energy thus decreasing with respect to time.the crash box model produces significantly small amount of strain the hourglass energy remain zero.

SECTIONAL FORCE 1.2MM THICKNESS

NODEOUT 1.2 MM THICKNESS

the maximum resultant accleration is found tobe 14 at time 9ms

CASE 2 : 1.5 mm THICKNESS

in case 2 the creation of material ,initial velocity,rigid wall,ascii ,database,contact and sectional forces is follwed the same procedure of the case 1 .only the change in difference crash box shell elem 1.5mm thickness.

section creation

Shell formation so we assign the elform=2 and the thickness =1.5mm.

post-processing

vonmises 1.5mm thickness

stress at 5 ms 321.2mpa ,it indicate the stress is distributed along the part that there is a stress reduction.

plastic strain 1.5mm thickness

hourglass 1.5mm thickness

step t=1 strain is 0.005849, time step =5 the strain is 0.008604 ,in this time the material deformation occur.the total deformation is 0.00859 at the end of time step

enegy 1.5 mm thickness

The kinetic energy of the system tends to behave in an opposite manner internal energy thus decreasing with respect to time.the crash box model produces significantly small amount of strain the hourglass energy remain zero.

sectional force 1.5 mm thickness

nodeout 1.5mm thickness

stress along x axis stress

1.2mm thickness

1.5mm thickness

stress along y axis stress

1.2mm thick

1.5mm thickness

CONCLUSION

• A simulation on crash box impacting a rigid wall with 13.88 m/s (50 kmph) velocity performed using ls dyna.
• it can be seen from the simulation that the crash box bounces backward after hitting the rigidwall.
• the simulation carried out for crash box shell thickness of 1.2mm and 1.5 mm and the postprocessing result are analyzed.
• from the obtained result stress level for both the cases it found that the crash box wih thickness 1.5mm has better and energy absorption rate as stress increases during impact than that of 1.2mm thickness

https://drive.google.com/file/d/1iuOwzCPNgGXQFeUcOd6ojB2OjWnjVilO/view?usp=sharing