Assignment 6-Frontal Crash Simulation Challenge

Aim-

• To perform the frontal crash on car model given and study about deformation and stresses developed in the model.

Objective-

• First to check the unit system.
• Create type-7 contact with friction value 0.2 with recomended parameters.
• To check for penetration and intersections ini the model if present.
• Check for rigid body if any, means make sure all component connected properly.
• Create planer rigid wall with 0.1 friction value.
• Add mass on given body to reach target of 700kg and make COG align approximately with seat rail.
• Give initial velocity of 35mph(mile per hour) which is 15.6464 m/s in x direction.
• Give time step of 0.0001 for Brick Noda and Inter.
• Give run time of 80 ms in run card.

Request for additional TH output-

• Sectional force in the rails at location of indicated node 174247.
• Axial force received on the rails from bumper.
• Shotgun cross sectional forces.
• A pillar cross section.
• Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
• Intrusions on the dash wall 66695,66244.

Abstract:

Crash test is virtual reconstruction that replicates the same force and sped that would occurs if the vehicle was to be involved in an actual crash.Iin this type of testing, since nothing is physically impacting the body-in-white (BIW), no physical deformation or damage occurs to the body's structure, allowing multiple crashworthiness tets to conduct in succession.

• Frontal crash test.
• Side impact crash test.
• Roof crash test.

In this particular challenge we will discuss about the frontal crash,

Since in frontal crash test, there are multiple standards use on which we have to focus.

FMVSS 208-

• Federal Motor Vehicle Safety Standard 208 (FMVSS 208) regulates automotive occupant carsh protection in the United States. Like all other Federal Motor Vehicle Safety Standards, FMVSS 208 is administered by the United states Departmenet of Transpotatio's National Highway Traffic Safety Administration.
• This test procedure is used to determine whether a vehicle meets the conditions,requirements, and injury criteria specified in Federal motor vehicle safety standard (FMVSS) No. 208, Occupant crash protection.
• In this test according to FMVSS 208 we give the intial velocty of 35mph(mile per hour)or 56km/h or 15.56m/s to the Car body.

Euro NCAP-

• Euro NCAP tests cars against a rigid barrier with full overlap at a test speed of 50 km/h. A small female frontal impact dummy is seated in the front driver’s seat and in the rear passenger side seat.
  

• In this we perform carsh and we give initial velocity as 31mph(mile per hour) or 50km/h.
• This test places high demands on the restraint systems in front and rear seating positions. Strict limits are placed on the decelerations of the chest and on the degree of chest deflection and this, in turn, encourages manufacturers to fit more sophisticated restraints.
• The test complements the offset deformable test as a balance must be found between a restraint system that is stiff enough to restrain a male dummy in the frontal offset test and one that is compliant enough not to put injuriously high deceleration forces on a small female.
• In this tets overall we make car strucrure stiffer,wo it can help to reduce lower leg and head injury.

How frontal crash looks from outside-

How frontal crash looks from inside-

Procedure:

1. Check for units both in Hypermehs and Hypercrash.
2. Import the model in hypercrash.
3. Perform mass balancing in hypercrash.
4. Export model in hypermesh.
5. Give time step for Brick,Noda and Inter as 0.0001 milisecons with respective scale factors.
6. Check for initial penetrarion and intersection.
7. Give initial velocity of 35mph(mile per hour) or 15.6464 mps(meter per second).
8. Create type-7 interface contact with friction value as 0.2.
9. Create Infinite plane rigid wall with friction 0.1.
10. Create intrusion spring on dasboard position to measure the deformation.
11. Create sections on bumper,rails and A-piller.
12. Request for TH file as required for this challenge.
13. Perform model checker.
14. Run the simulation.
15. Post-processing

1.Check for units both in Hypermehs and Hypercrash:

Hypermesh

Go to Solver>cards>Begin card

Hypercarsh:

• In hypercrash while opening itself it will ask to select unit where we will choose as shown below.

2(a).Import the model in hypermesh.

• Go to File> import>Import solver deck> select the file from folder.
• Or, we can drag down(by shift+right click) the 0000.rad file and release on hypermesh GUI.

2(b).Import the model in hypercrash.

• Go to File>import >Radioss>select the file from folder.
• Or, we can drag down(by shift+right click) the 0000.rad file and release on hypercrash GUI.

3.Perform mass balancing in hypercrash.

• For mass balancing first we will check the initial mass of the model for that,
• Go to Mass > Mass balancing , It will show the initial mass as shown below as 188.4 kg.

• So reach to mass value to 700kg we need to add 511.6 kg mass more.
• For mass addition we will use ADMAS option.

For Add mass

Go to Loadcase > Added mass

• We will choose type-1, it will distribute the mass over the nodes which we give as shown below.

• Similarly we will add mass over floor panel to reach 700kg mass.
• And to place COG at right place on rail.

• Now we can see the COG location and and target mass as 700 kg.

5.Give time step for Brick,Noda and Inter as 0.0001 milisecons with respective scale factors.

To give time step go to Model browser> cards > ENG_DT_BRICK

• Give CST type and add value for scale factor and time step.

• Simmilarly we will do for NODA.
• But here we wuill give scale factor 0.67.

• Now we will give time step for interface and we will choose DEL here.
• DEL will activate delete element command if time step going below given time step.

6.Check for initial penetrarion and intersection.

• Here we will check for initial penetrtion in the model.

For that go to tool > Penetration check > Select group > Check

• After selecting groups, hit on check it wil show the result below.

• Here we can see that 0 collision found.

7.Give initial velocity of 35mph(mile per hour) or 15.6464 mps(meter per second).

Create > Boundary condition > INVEL

• Now here in INVEL card give velocity of 15.64 in global x-axis.
• Select all component because we are going to give the initial velocity for whole BIW parts.

8.Create type-7 interface contact with friction value as 0.2.

Go to create > INTER > Type-7

• Select all the recomended parameter for Type-7 contact.
• Select all the conponent in slave and master as well to give self contact.

9.Create Infinite plane rigid wall with friction 0.1.

Go to Create > RWall > Plane

• Click on blue arrow it will allow to select node manually on FE.
• After selecting node co-ordinates of node will display as below.

• Now to move rigid wall plane in x direction to give space between rigid wall and car body.
• Manually put the value for x co-ordinate as 4600 so rigid will move approximately 12 mm.
• Also give -1 normal in x-directon to make rigid wall perpendicular from point of contact.
• Slide option give a slside with friction with friction value of 0.1.

• Infinite planner Rigid wall created now

10.Create intrusion spring on dasboard position to measure the deformation.

• Here we will deploy intrusion spring to measure the deformation.
• Means how much spring length will change, will tell length of BIW defomed in passenger compartment.

Go to Geometry > Temp node > select nodes > add.

• Now deploy spring connection between nodes,

Go to 1D > Spring >Spring2 > Select nodes

• Create different collector for this intrusion spring so that we can assign property for this spring.
• Now create property card for intrusion spring.

• Select as P4 spring and mass value as 1gm and stiffness 1N/mm.

11.Create sections on bumper,rails and A-piller.

• we are creating sections to analyze the amount of force is travelling from that region.

• Select nodes in a way that the frame z axis should come perpendicular to global co-ordinate system.

• Frame is created now.

Now affter frane we will create section,

• We can select the N1,N2 and N3 in the same way we selected the nodes for frame.
• Then we can see the red blu and green arrrow which is showing the section plane.
• Then in frame id select the frame which we have created erlier.
• Now select the elements in region where we are going to create section, for that right click on gshell_id and create and edit and select elements.
• Put the factors value of deltaT=0.001 and alpha=0.67.

• Hit on proceed and we can see the section is created successfully.

• Now simmilarly we will create frame and sections for right shotgun, for rails according to the node id given and for Apiller and for bumper as well.

12.Output Request:

Create Accelerometer

• We will request TH file for acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).'

For that First create accelerometer,

• First create the node on which we will deploy accelerometer.
• Now in below picture we wil select that node in node_ID and name this accelerometer as right accelerometer.

• similarly we will do for left accelrometer as well.

a).Now request for TH file for accelerometer,

• Create new card for accelerometer TH file.
• Select both left and right accelerometer in Entity IDs.

b).Now request for TH file for Interface-

• Here we have only one type-7 contact (all other type of contact deleted already).
• So request for this only.

c).Now request for TH file for sections-

• Select all sections we had created.

d).Now request for TH file for intrusion spring-

Run the simulation:

• To run the simulation go to Analysis > Radioss.

• After clicking Radioss click on input file and save it in new folder as Test-1 as shown below figure.
• Check the include connectors and option as -nt 4.
• N indicated the how many cores will involve to run the simulation.
• It will make simulation faster.

• After that click on Radioss it will start the simulation.
• And wait untill the new window popup and show as Radioss job completed.

• After running the simulation we will get animation file, h3d file and also T01 file.
• Check for all the files.

• Now open 0001.out file and check all the details.
• Here we can see all variable in the out file about energy error and mass error also.
• So for checking the maximum loss check the last cycle details.

• Here in in last cycle of the simulation we have maximum energy losses where,

Energy error = 2.2 % Acceptable (Range is -15% to +5%)

Mass Error = 0 Acceptable (Range is 0 to 2%)

So the resultent energies are,

1. Internal Energy 0.3987E+5
2. Kinetic Energy 0.4237E+5
3. External work -1158
4. No of cycles 388900

Post processing-

• Review the simulation using Hyperview.
• Plot the graphs using Hypergraph-2D

1.Review the simulation using Hyperview.

Split the screen in two part-

• Now after splitting the sreen open hyperview after switching into in 2nd screen.

• In hypergraph window import the h3d file for simulation run.

Animation-

• Now after importing the h3d file on hyperview GUI go for contour activation.
• In contour it will show the simulation graphically and contour lines of load and other properties variation.
• To activate contour go to Tool bar > contour as shown below.
• Go to Contour > Displacement > apply contour.

• From above simulation we can see that the deformation is start taking place from bumper component.since this is the component which is coming in contact first.And here in bumper some amount of kinetic energy will get stord in internal energy as deformation take place.
• After that remaining Energy will transfer to further component which are side rails and hence side rails start deforming and it will also absorb some amount of energy.
• Then Shotgun start deforming with and it will also abosorb some amount of energy then finally A-piller will deform.
• So according to the above discussion we can understand that all the impact should abosorb within the front section means before passenger compartment.
• Deformation we can see that is not proper and realistic means BIW is kind of going down is just because of there no chassis and suspension and wheel system present in this model.

• simillarly for Von-mises:

• Stress distribution over the model is quite good as we can see there is only few region in bumper system have stress concentration.
• Otherwise stress is distributed all over the BIW model.

Intrusion spring:

[Note-I have not selected the node ID for left spring according to node ID given in challenge]

Spring with node_ID 66706-

• From below fig we can see that initially the lenght of the spring was 766.51mm.

• And at end of simulation final length of spring is 665.493mm.

'

• So now the change in length is 766.51-665.493=101.017mm.

Spring with node_ID 66244-

• From below fig we can see that initially the lenght of the spring was 781.409mm.

• And at end of simulation final length of spring is 645.531mm.

• So now the change in length is 781.409-645.531=135.878mm.

2. Plot the graphs using Hypergraph-2D

• Now split the window in 3Part and open hypergraph-2D in new window.
• After opening the hypergraph windoe import the T01 file in Hypergraph.

First we will plot the graph which we have requested,

A).Section forces-

1.Bumper sections

• Since we know that the impact will come on bumper first so forces will also come highest on bumper.
• On both left and right bumper forces will be same approximately as shown below graph.

• As we can see from simulation that the bumper is coming first into contact with the rigid wall so the amount of force also will be more on bumper that is 45.497KN on left side of bumper and 45.53KN on right side of the bumper.

2.Rail sections

• After bumper force will travel through rail. so the secondary component which coming in contact with rigid wall will be rail section.

• Amount of force travelling by the left rail section is 23.30KN and 30.10KN from right rail section.

3.shotgun sections-

• Shotgun section will be next after rail section.

• From graph we can see that the value of force which should go thorugh the shotgun section approximately equal to graph value.
• From left shotgun section 11.7KN and from right shotgun 8.65KN of force travelling.

2.A-piller sections

• In front crash we should take care of one point that, least amount of force should travel from A-piller to keep passenger compartment safe.
• Which is displayed in below graph in left 2.9425N and in right 3.01356N.

• Here is the cumulutive graphical representation of all the forces travelling through the section.

B).Spring Elongation-

Spring elongation of spring with node id 66706:

• These intrusion of spring show that how much leg area of passenger is safe.
• Means the spring should not be compressed more the 150mm of 15cm.
• according to graph we can see that the maximum intrusion is 100.56mm and 134.73mm respectively.

Interface-

• This graphis showing the force generated due to self contact with resepect to time.
• So the maximum amount of force generating due to sel contact is 121.004KN.

Accelorometer graph

• Accelerometer graph is showing the maximum acceleration recived by the B-pillar section due to this crash.
• Since we had deployed accelerometer to both side on B-pillar base so there is two graph which is showing both accelerometer value.

• In left accelerometer the amount of acceleration observed is 159.774 mm/ms^2 and in right side 181.37 mm/ms^2.
• These value are in acceptable range.

Global Energies-

• Now we will study the energy variation throughout the simulation.
• Here is the cumulutive graphical variation of all type of energies involved in the simulation.

Internal Energy-

• At time t=0 internal energy will be zero, and as impact begins the amount of force causing the stress due to which starin start taking place and deformation happens.
• So due to deformation some internal energy will start storing whithin the body and keep increasing as defomartion increses in the body.

kinetic Energy-

• Since we have given a initial velocity to the car body 0f 15.6464 m/s and car body itself having its mass so according to he kinetic energy formula.
• 1/2 mv^2 = 85683.44kJ(kilo joule)
• The value shown by graph below is less than calculated value is just because of energy error.

Contact Energy-

• Contact energy is due to self contact of FE elements of car body.
• So according to graph the maximum value of contact energy is 1471.33KJ.

Hourglass Energy-

• Since we already used shell parametrs, insead of that we observe some amount of hourglass energy.
• This hourgalss happenes in some region where goes below iven timestep of due to stress concentration in course mesh.
• For that we particularly work on that region to refine the the mesh.
• But here the value is 212.593KJ less than 10% of the internal energy value(10% of 39695.7 is 3969.57KJ).
• So this hourglass value is acceptable.

Total Energy-

• Total enrgy is combination of all energies present here,
• Maximum value of total energy is found 85263.6KJ.

Result-

• Mass balancing is done for the given BIW for final value of 700kg.
• Created Typ-7 Interface contact for BIW self contact.
• Created rigid wall with friction value as given.
• Time step value is given for all type of elements and contacts.
• Initial velocity is also given to the BIW body.
• Intrusion spring is created to measure the deformation or to ensure safety for passenger leg area.
• Accelerometer is inatalled at base of B-Pillar.
• All TH file requested for output and then run the model checker.
• Run the simulation and post-processed in hyperview and hypergraph.

Learning Outcome-

• In this challenege i came to know that how to balance mass in hypercrash.
• How to create rigid wall for frontal crash.
• How to create interface contact and set all the required parameters.
• How to give initial velocity and time step values for brick shell and interface.
• How to request fo TH file which will be used in post-processing of the simulation.
• Learned how to create frame and section to determine sectional forces and its importance.
• Get to know what are standards use for crash analysis like FMVSS,Euro-Ncap etc.