Frontal Car Crash Test Using Hypermesh And Radioss

Frontal Car Crash Test Using Hypermesh And Radioss

Introduction:-

Car Simualtion is a recreation of the real life car crash (we do in labs) with the help of computers inorder to understand the safety of the car and people inside it. This is mainly used in automobile industry while making a new model. In car simulation we give the car model real life condition and give it a load or velocity, make it hit on rigid wall and analyse the deformation happen to it. The kinetic energy is converted to deformation of the car. Studying the deformations we can understand the safety of the car, like how much load can the car withstand, will the load reach the passenger inside..etc. The car should alway deform upto the standard values so that the passengers are safe. Like in real life the car crash, which is done using dummies, Air bags and seat belts, Now car simulation is also using these saftey measurses virtually.

Objective:-

To perform frontal crash of the given car model with the given conditions and study the BIW model after crash.

Conditions:-

• Check unit system and either follow[Mg mm s] or [Kg mm ms].
• Create appropriate interface ,friction 0.2 and recommended parameters.
• Make sure of no penetrations and intersection.
• Correct rigid bodies if any issues.
• Create rigid wall with friction 0.1.
• Compare the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.
• Initial velocity 35 mph.
• Use model checker to ensure good quality.
• Time-step :0.5 to 0.1 microseconds.
• Run 80 ms.

Procedure:-

1. Check the unit system followed:-

a. Click on Cards>BEGIN CARD from model browser.

b. Check the entity editor in which unit system is used in this model.

c. Here we use the units kg-mass, mm-length, ms-time.

2. Creating appropriate interfaces:-

a. We create a type 7 interface on the car body to study self intersection.

b. Right click on Groups in model browser> click on create.

c. In card image choose Type 7

d. Choose the slave nodes in Grnod_Id(S) and master elements in Surf_id(M).

e. Give value of friction as 0.2

f. Then fill the parameters with recommended parameters.

Recommended Parameters:-

Igap=2 :- Set variable gap to take into account the true distance between parts

Gapmin> 0.5mm :-Specify minimum thickness of the model to avoid numerical issues.

Inacti=6 :- Remove the initial penetrations where possible.

Istf=4 :- Set stiffness of interface based on the softer of master and slave.

Stmin=1 kN/mm :- Specify a minimum stiffness in the contact because of element deletion

Idel=2 :- Remove slave nodes from contact because of element deletion

Iform=2 :- Sliding forces are computed using stiffness parameters of the interface. Usually results in bigger time steps.

3. Check for penetrations and intersection :-

a. Its is to check these in hypercrash so we can also open hypercrash.

b. Import the model in hypercrash.

c. Go to Quality > Check all solver contact interfaces

d. A quality tab appears and in that we can see that Intersection and penetration are zero.

4. Create rigid wall :-

a. For creating rigid wall in hypercrash we need to go to Loadcases > Rigid Wall.

b. Now a new module Rigid Wall appears near tree and other modules. Right click on the white area Create New > Rigid walls > Plane.

c. In title give a name.

d. Give a distance in distance for slave search.

e. In Sliding change to 2.Sliding with friction.

f. For friction give value .1

g. In [XM,YM,ZM]M define the tail of the normal direction.

h. In [XM1,YM1,ZM1]M1 define the head of the normal direction.

i. Click on Save.

5. COG and Mass adjestment :-

a. To see the COG point go to Mass > Balanceing .

b. Click on the spectacle icon you can see the location of COG point now.

c. If it is not at the center, we need to shift it to the center. Also the total mass should be 700kg. The masses should be divided to different areas so that it should never exceed 700kg.

d. We can change the COG by adding Masses.

e. For adding mass go to LoadCases > Added Mass.

f. Right click on the Added mass area> Create New> Select Type 1- Mass is distributed to each of node group.

g. In title give a name.

h. In Added Mass give the mass to add.

i. In grnod_ID , pick the nodes to which the mass should be distributed.

j. Click on Save.

k. Like that add masses at different places of the car body and position the COG at center.

6. Give an Initial Velocity of 35mph (15.6464 m/s) :-

a. In browser tab Right Click > Creat New > I-L > Initial velocity.

b. In the INVEL tab edit the values .

c. Type is translational because there is no rotation motion.

d. Only X velocity is given because there is only movement in the X direction.

e. In Grnod_id select the whole nodes of the car.

7. Check the model, eliminate errors and minimize warnings :-

a. To check the quality go to Hypermesh and Tools > Model Checker > Radioss Block

b. Click on Run Checks, When the check is finished it will be show on the bottom.

c. If we have errors Click on Auto Correct, it will eliminate almost most of the errors.

d. Still errors persist we need to look manually and correct it.

8. Give Time step and Run time :-

a. In Hypermesh from model browser choose Cards

b. From cards open ENG_RUN

c. In that give the value of Tstop as 80.

d. To give the time step value open the ENG_DT card.

e. In that give the value .0003 for Tmin.

Output requests :-

• 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

Procedure for creating Output requests :-

1. Creating Cross sections at rails, shotgun, A pillar :-

a. For createing section we need to define skews so first we create skew.

b. Go to solver tab Right click> Create > Skew > MOV

c. Then we need to select the nodes to define the planes for getting direction of the skew.

d. First select the node to show origin, then choose an axis and select the nodes to define a plane.

e. Click on create.

f. Now we can create a section. Go to model tab Right click > Create > Cross section.

g. In the Entity editor Give the parameters correctly.

h. Give a Name to the crosection.

i. Select 3 nodes to define the x-axis and x-y plane.

j. In Frame_ID select the skew that we created.

k. In deltaT give .1 and for alpha give 1.67

l. In grshel_id select the set of elements. Where we want to see the section force.

m. Like this we need to create sections and skews in 6 areas. (Left and right rails, shotgun and a pillar)

n. 174247, 139604, 103242 these are the nodes where we need to create section on Left side.

o. So we create a temp node in each point and do.

p. For right side we need to reflect these nodes to find the nodes there.

2. Axial forces can be identified by creating interfaces on both rails and bumper :-

a. We need to create 2 interfaces, Left and right . With the bumper and rails.

b. The interfaces should be made with Type 7 Card and with recomended parameters.

c. Master will be rail elements and the slave should be bumper nodes.

3. Intrusions on the dash wall 66695,66244 :-

a. Intrution is measured using 2 spring from each of the given node and the middle cross beam.

b. For creating spring we go to 1D > springs > select the nodes between where we want to create the spring.

4. Creating Accelerometer for acceleration curve :-

a. Right click on the model browser area Create > Accelerometer

b. In the Entity editor in node_ID Select the node where we want to place the accelerometer.

c. Click on proceed.

5. For ploting graphs, add TH as required :-

a. Go to solver tab.

b. Right click on TH, Select option as we needed.

INTER- Interfaces

ACCEL- Acceleration

SPRING- spring elongation

PART- For each parts forces

SECTIO- sectional forces

c. First we select INTER for ploting forces.

e. In Entity ID select the interface of which we need to plot tge graph.

f. In NUM_VARIABLES select number of variables (How many forces you need to plot in y axis)

g. In INTER select which all forces you need to plot.

h. Like this create TH of ACCEL, SPRING, PART, SECTIO ... etc

Simulation explanation:-

In the animation we can see the car BIW is hitting the rigid wall and getting crushed. The deformation is happening in a way that front is getting crushed more and as going backwards the deformation gets decreases.While checking the resultant forces on rails, shotgun and a pillar on both sides we can see the same. The Rails are placed at the front most side so they are getting the maximum resultant force. Some of the force made some deformation there so the force transfered to the shotgun is lesser than the force in Rails. Again the force decreses while we go to the a pillar.

Energy Graph:-

For the car components, we used Ishell=24 QEPH formulation so only a small presence of the Hourglass energy is present . The contact energy is formed only when there is penetration, at the begining there is no penetration. But at the end there is some penetration so some contact energy is created. Initially the K.E energy is high and will reduce as the car moves forward and get crushed. The K.E energy is absorbed by the car and deformations occur. So the kinetic energy is converted to internal energy . That is why when we look at K.E and internal energy graphs we can see that the reduction in kinetic energy curve is just the opposite of increasing internal energy curve. The total energy is the sum of all energy so the curve is like a straight line.

Sectional Force at Rails :-

To study the sectional force at rails I plot graph with X-axis as Time and Y axis as Resultant force. We can see from the animation that the rails Almost at the front most area, So maximum force will be felt there. When we compare left and right rails we can see that the force is more on right rail which is 41.6317kN at 18ms and left rail have 34.7447kN at 18ms. When we look in the animation we can see that at the maximum force, at that time the right rail and left rail starts buckling. Thats why after that point the force is reduced. Also you can see that the right rail is buckled and moving But the left rail is buckled and then again get crushed with the wall. So in the graph the right rails curve is going down and left rails curve is staying in between a range. The difference in force felt initially is different due to the difference in connections given there and also a hole is present in the right side of the car.

Sectional Force at Shotgun :-

Plotted the graph with X-axis as Time and Y axis as Resultant force on shotgun. Initially the force felt on the shotguns are the force which are coming from the rails. That is why the Left shotgun has a slight increase in the force than the right shotgun. Due to the presence of the hole, the right rail is deformed more and force is absorbed. So lesser force will be transmitted to the right shotgun. Then the forces on both shotguns increases till they buckle, after buckle the forces decreases. At time 40ms we can see a sudden increase in force on the left shot gun this is because at that time the left shotgun directly hits the rigid wall. Also at time 46ms the right shotgun will also directly touch the wall so an increase in force can be seen there. After the direct hitting on the wall boths force will reduce due to buckling. And again at 65ms we can see both shotgun's buckled parts touching the wall directly at that time also we can see an increase in forces.

Sectional Force at A pillar :-

Plotted the graph with X-axis as Time and Y axis as Resultant force on A pillar. The passenger cabin will starts with the A Pillar so the force affecting this region should be less. As the force applied made lot of deformations on the rails and shotgun, only a small amount of force will be transfered to the A pillar. The left A Pillar have max of 5.26533kN and the right A pillar have max of 3.20333kN. On the left A pillar curve we can see 4 ups this is due to the buckling of each parts that are in front of the A Pillar. Like when we explained the shotgun it was seen that the buckling of parts will make a dip in curve and when the buckled part again hit the wall a hike in the force is seen, so how the force is recived in the rails and shotgun like the same will be recived in a pillar but will be of a lesser magnitude. In case of right A pillar the buckled parts are not hitting the wall again much. After the buckling the bended parts move upwards , so there is less force on the right A Pillar.

Axial force recived from the bumper to the rail:-

The axial force is the force applied by the bumper to the rail in lengthwise . At the beganing when the wall touches the bumper and bumper touches the rail there will be high axial force. At that time compression of parts occurs, after that the rail bends due to buckling and the force recived in the axial direction will be reduced. The maximum Axial force recived by the left rail is 16.4081kN and right rail is 17.7867kN.

Acceleration curve ( Based on accelerometer at base of B pillar) :-

1 New ACCEL1= Right side & 2 New ACCEL2= Left side.

To make the acceleration curve, we put two accelerometer at the base of B pillar on the rocker. The accelerometer on the right side gave a max value of 1.99651 mm/ms2 and the left side give a max value of 7.71274mm/ms2.

Intrusions on the dash wall (66695,66244):-

Intrusions are one of the important parameter, while checking the passenger saftey in crash. It can be used to know how much of the car part came inside the passenger cabin during the impact. Here to measure the intrusions at two points i have created 2 springs with stiffness 1kN/mm. By measuring the elongation we get the intrusion. Here 66695 is having an intrusion of 121.467mm and the 66244 have 106.87mm.

Von Mises Animation :-

Here we can see that the maximum stress is 3.785E-01 and it is at the right side front area. This is because the right side front part is crushed more other than bending like the left side.

Energy Error and Mass Errors:-

If the enery error value negative and decreasing, also is less than 15% it is acceptable. For Mass error, it should be less than 5% of the total model mass. Our mass error is 0.2970E-01 which is less than 5% of the total mass so its acceptable.

Results:-

We have done simulation on Dodge Neon 1996 model car's BIW. The deck setup was done as the given condition. Simulation is done and all the graphs are ploted.

Conclusion :-

From the simulation we understand how a front car crash is done, what all things should be checked while the crash test is done. How the car cash in simulation works and compare it to real experimental car crash, what are the difference in real condition and simulation. From the graphs we understood many things like, from the sectional force graph we can exactly study the transfering of force from the rails to shotgun and from shotgun to the A Pillar. How the force decreases from one part to other.