PERFORMING FRONTAL CRASH ANALYSIS OF A CAR

PERFORMING FRONTAL CRASH ANALYSIS OF A CAR

OBJECTIVES

1. To understand the different Kinematic Conditions.
2. To understand the different Loading Conditions.
3. To assign recommended contact interfaces parameters for crash analysis.
4. To understand the Timestep Control for crash analysis.
5. To learn about the Output Requests for post processing.
6. To learn about the Check Debug for post processing

7. To plot the different contours formed with use of various contact interfaces and parameter change.

Check with the unit system, either use [Mg mm s] or [kg mm ms]

• This can be done using the starter _le neon_front_0000.rad in notepad as shown below.

• Import the file neon_front_0000.rad
• It will appear in wireframe mode.
• Click on the shaded mesh to view the surfaces in shaded form.

Create an appropriate interface, friction 0.2 and recommended parameters.

• There are different contact interfaces are present for each part. But it is good to have lower number of interfaces so that we will get faster simulation.
• Delete the available interfaces in the original model, and create a new one with the Type 7 interface.
• Recommended properties as follows

• To create the interface of Type 7 you can create in Hypermesh or Hypercrash
• To create in Hypermesh right-click > create >contact>Type 7, apply appropriate properties and friction as 0.2

• Igap (Determines how the size of the gap is calculated): 3 Variable gap + gap scale correction of the computed gap + size of the mesh is taken into account to
• Avoid initial penetrations during self-contact.
• Fscale_gap(Gap scale factor) : 0.8
• Gapmin(Minimum gap for activation of the interface ): 0.5
• Inacti(Action to take if initial penetrations exist): 6 Gap is variable with time but initial penetration is computed
• Istf(Affects how the stiffness of the interface is calculated): 4 Kmin=(Km, Ks)
• Iform(Friction formulation): 2 Stiffness
• Stmin(Minimum stiffness to use in the interface): 1
• Idel(What to do with slave nodes and master segments if an element fails (deleted) that they are attached to): 2 when an element is deleted, the corresponding segment is removed from the master side of the interface
• Fric(coefficient of friction ): 0.2

Make sure of no penetrations and intersections

• To run the analysis, we should make sure that there is no intersection and penetrations between two bodies of parts
• To check for penetrations and intersections in a hypermesh.

• As there are no penetrations and intersections available in a model. We can run the analysis. If the quality check shows any intersection or penetration we can fix it by using an auto fix tool.
• If the auto fix is failed to clear the penetrations or intersections then we have to correct as per the manual method.

Check rigid bodies if any issues

As checked in the model, there are no issues with the rigid bodies in the given model.

Create a rigid wall with friction 0.1

• We can create in both Hypermesh and Hypercrash
• To create a rigid wall in Hypermesh go to Create> Rigid Wall
• Select the type of the rigid wall you want as a cylinder, infinite plane, or sphere.
• For this application, we need an infinite plane type of rigid wall.
• Select the base node from which you want to create the rigid wall.
• Enter the value for D search as 1500 and friction as 0.1.

Comparing the weight with a full-scale model for weight balancing

• The weight of the full car model is 1216.55 kg as shown in below image.
• The weight of the reduced car model is 188 kg.
• The center of gravity of the model should be in line with the C.G of the full car, because in order to compare with the full model we should have the C.G in the same place. The location of the C.G is at the position when the line from the bottom of the driver seat meets with the central line. So in order to get the C.G we have to arrange the mass in certain way.

• The total mass of the Full car model is 700kg, so we need to match these mass in our model and attain the C.G at Correct place by Distributing those mass in front and rear.
• The current model as the total mass of 187kg still 513kg has to be added to the model.

• We can add the remaining mass on the floor panel 200kg is added to the rear part of the floor and 100kg is added to the front part on driver side and 100Kg is added to Co-passenger side. For attempting 700Kg challenge and remaining 52Kg in Gearbox Assy Section so that C.G lies inline from the bottom of the driver seat meets with the central line.

Apply initial velocity if 35mph

• As we are following the system [kg mm ms] we need to input the value of velocity in mm/ms.
• So after conversion the velocity 35mph= 15.65mm/ms.
• In Hypercrash go to Load Case > Initial Velocity > Select the whole model and apply velocity in X-Direction as 15.65mm/ms as shown in the below image.

• In Hypermesh go to Boundary Condiotions > Initial Velocity > Select the whole model and apply velocity in X-Direction as 15.65mm/ms as shown in the below image.

Use model checker to ensure good quality.

• Before going to the actual run we should ensure the quality of the model.
• In Hypermesh go to Tool> Model checker> Radioss Block > Then the system will show the error and warning. Try to find out the error and correct then or use the autocorrect tool.

• In Hypercrash go to Quality> Model checker> Run. Then the system will show the error and warning. Try to find out the error and correct then or use the autocorrect tool.

Timestep changes, Runtime, Animation Frequency changes.

• A constant nodal time step
• T_scal:0.67
• Time step:0.5
• Termination Time: 80ms.
• Before running the simulation is better to do the model checker and make sure there is no error in the simulation

Output request

• Sectional force in the rails at the location of indicated node.
• The axial force received on the rails from the bumper.
• Shotgun cross-sectional forces.
• A pillar cross-section forces.
• Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
• Intrusions on the dash wall
• To get the forces mentioned in the sections we need to create the sections at those places.

Section Creation

In Hypercrash go to Data History> section> select component> select 3 nodes to create a section.

Debugging

• For debugging we have to see FRONTAL_CRASH_0001 file

The Energy Error computed by RADIOSS is a percentage.

• If the error is negative, it means that some energy has been dissipated.
• Negative Energy Error since it is not counted in the energy balance. The normal amount of Hourglass energy is about 10% to15%.
• If the error is positive, there is an energy creation. In case of using QEPH shell formulation or fully integrated elements, the Energy
• Error can be slightly positive since there is no Hourglass energy and the computation is much more accurate. An error of 1%or 2% will be acceptable.

The Mass error is 0.1334E-02 which is acceptable as no change is happened to mass.

The Simulation time for frontal crash is much more.

• Action to take if initial penetration. Removal of initial penetration where possible. Elsewhere, reduce to less than 30% of defined gap value and adjust the gap by using in Inacti.
• When we are not using no failure criteria simulation time required is quite less as compared to others.

As per the above image, the energy error is -2.0% and mass error is 0.1334E-02. So we can go for results as the values are in an acceptable range.

RESULTS

• Max Stress: 0.4060GPa

• Displacement: 1273mm

• Plastic Strain: 1.245mm

• Specific Energy:62190J

All Energies

• Mass

• Acceleraton

• Acceleration on Right Rail LH- 5 mm/(ms)²
• Acceleration on Right Rail RH – 1 mm/(ms)²

• Sectional Forces

• Section Force at A Pillar RH = 0.25KN
• Section Force at A Pillar RH = 0.18KN

• Section Force at shortgun RH = 1.2KN
• Section Force at shortgun LH= 8KN

• Section Force at Front Rail RH = 8KN
• Section Force at Font Rail LH=  8KN

• Maximum energy absorbed by right bracket is 6KN
• Maximum energy absorbed by left bracket is 16KN

• Section Force at Lower Rail RH = 2.5 KN
• Section Force at Lower Rail LH = 2KN

CONCLUSION:

1. Learn about how to change the different Kinematic Conditions of Radioss solver.
2. Studied the different Loading Conditions.
3. Learn to assign contact interfaces parameters for crash analysis
4. Understood the Timestep Control control for crash analysis
5. QEPH cell formation for fully integrated elements the energy error can be slightly positive since there is no hourglass energy and the computation is much more accurate.
6. The energy error and mass error are in an acceptable range.
7. The Mass error is 1334E-02 i.e 0.13% which is acceptable as no change has happened to mass.
8. To plot the different contours formed with the use of various material laws and parameter change.
9. The sectional forces in the bumper to rail for both RH and LH side plays an important role in absorbing the max impact.
10. The role of shotgun design also plays an important role to keep the impact less transmitting to the interior parts of the vehicle.
11. The max impact is taken by the frontal cross-sections hence the forces in the A-pillar section for both RH and LH side are very less.
12. The position of the Center of Gravity of a vehicle is vital in the crashworthiness, so maintaining the weight balancing of a vehicle is the skill of design engineer.
13. As we are using the half model and with added masses, if we can go for full vehicle body analysis then more realistic results can be obtained.

 NOT UPLOADING - FRONTAL_CRASH.h3d - File size should be <200MB

FOR DETAILS  PLEASE CLICK ON BELOW LINK

https://drive.google.com/file/d/1gFBJfyfy_s8YkLuxSu7vc-_n6-aLCf7X/view?usp=sharing