Frontal Crash Analysis on the Neon Dodge Surrogate Model

AIM

To do the FRONTAL CRASH on a surrogate model of Neon Dodge based on the Federal Motor vehicle safety standards.

OBJECTIVE

Import the preprocessed model of the Neon Dodge surrogate model and model the FEAmodel in such a way that the required output requests can be postprocessed from it.The required output requests are

• Sectional force in the rails at location of indicated node 174247.
• Axial force received on the rails from bumber.
• Shotgun cross sectional foces.
• 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.

CASE SET UP AND EXECUTION

We are using the Hypercrash to FEA model the file.So Open the Hypercrash and import the model into it.We can see the model is a surrogate file of the Full model of neon dodge .This surrogate model is used because of the limitation of elements in student edition of hypercrash.Parts in the vehicle model connected with CWELD elements as spot weld. The CWELD element is a wellknown 1D element used widely for simulate the spot weld connections in the finite element method. The CWELD element fulfills the main requirements that it can connect non congruent meshes as well as congruent and the weld area is considered.

First we need to create a self contact in the model,before that we need to delete the contact already applied in the model this is because the since we are defining a self contact.we dont want a type 7 contact with the same components already in self contact.This is because two contacts defined for the particular components will leads to increase in simulation time and also it will affect the Interface time step as well.

So for defining a Self contact we are using a TYPE 7 contact which is a node to suirface contact.In that we will check the self contact and we will give the recommended paramters to the type 7 contact and select the whole model as master .In the end we need a Contact force between the bumber and the rails.Inorder to obtain that we need to create a contact in between the bumber and the rails.This is also a type 7 contact and here we select the rails as the slave and bumber as master since we need to obtained the force on rails.So component under study is rails.So we define Rails as slave.

Fig 1 Type 7 contact definition

Then Penetrations need to be checked and we made sure that the penetrations and intersections are zero.Since the Penetrations can leads to energy error and intersections can leads to run terminations.If we see some penetrations ,There is always auto depenetrate option to remove the penetrations.

Rigid wall Creation

Rigid wall is the body is having high stiffness and we made the model to collide with the rigid wall.We here use a infinite plane rigid wall.For defining the rigid wall, first select the tail cordinate as a node in the bumber and copy those cordinates to head .Then we can tweak with the value of the cordinates in the normal direction of the plane to get the Rigid wall at a distance from the model.Here we shouldn't move the Rigid wall very far away from the model.This is because if we do that the time taken for the car to run and reach the rigid wall is actually a wastage of cpu time,We dont want any results from that motion.So rigid wall should be only a little apart from the model Bumber.Here we need a friction with rigid wall with sliding friction of 0.1 .So specify that as well.Then the search distance for the slave nodes should be given a particular value.Atleast it should search the nodes till A pillar,because upto that region the nodes may get interacted with the wall.

Rigid body Issues

If we check the connectivity of tree using Model>Check Tress connectivity.It will show a list of free party and free joints.These are the parts and joints which are not connected to any of the any parts.So compare with the full model and check whether the part where the joints are connected to are presented in the surrogate model,If not then delete those joints.And if some parts are free then connect it to it respective component using some sort of simple springs .Always make the model a single connected one .Other wise run issues will occurs.

Centre of Gravity adjustment

Then centre of gravity of the model should be inline with the C.G of the the full car ,because inorder to compare with the full model we should have the C.G in same place .The location of the C.G is at the position when the line from bottom of the driver seat meets with the central line.So inorder to get the C.G at that place ,we need to add mass on it.For that we can make use of added mas option in the Hypercrash.We can add the mass of 700 kg .We need to add those mass sensibly and realistcally to get the C.G at the place we want.So here we applied the mass at the places where the passenger seat are.

Fig 2 Added Mass

Intial Velocity application

We need to create an intial velocity and input the Grnodes as all the node of the surrogate model.Then give the value of velocity as 15.6 mm/ms in the X direction.This makes the frontal crash possible.35mph is equal to 15.6 m/s or mm/ms.

Fig 3 Intial Velocity

We are going to let this crash happen for 80ms so the run time will be 80 ms.So create the run Control card and input the value as 80.Also Provide the minimum time step as .5 microsecond in element time step and 0.1 as nodal time step ,for the CST ,which will add mass and stablize the time step when the time step drops below a minimum value.

We are intrested in getting the value of sectional forces through the left and right A pillar,Left and right shortgun and the sectional forces at node 174247.To get this values ,what we have to do is ,first make a section at these places and we need to put those sections in time history.Then only we can extract the results like sectional forces.

To create a section ,in hypercrash go to Data history>section>Default sections>choose the parts through which we need to create the ring of the sections(means the hypercrash will select the nodes and eleements through those elements to create a ring over it to create the section)>Then we need to select the normal axis >then place the radio button in 3 nodes>select the nodes in such a way that the first two selection in required x axis direction >and third selection will define the XY plane.While defining the section what we need to take care is that the normal of the section we created should not be in the same direction as that of the shock wave instead it should be in opposite direction of that of shockwave.

Fig 4 Section Creation

Along with the sectional forces ,we need the intrusion at 66695,66244 nodes .For calculating intrusion we need to define a referance node and we need to measure the distance the node moved before and after crash.So we Create a time history for those nodes.For that create > time history>Th of nodes>choose the node>Then define a fixed skew at part opposite to that node(Here we define the skew at Cross beam).Fixed skew will not move and the displacement of the node will be given by the TH of nodes.

Also in addition to this the accelerations of the node below the B pillar rocker is also needed.So in order tio get this ,Place an accelerometer at on eof the node in B pillar rocker on both the sides.And put the accelerometer into time history.The data saving time is given as 0.080 so that we can get the 1000 points in the graph so that the graph will be accurate.

Fig 5 Time History

At the final stage ,Run the quality model checker .If there are no errors then we proceed to export the file to a fiolder.Then we can import that file to Hypermesh.

Fig 6 Model Checker

After importing the file in Hypermesh we can run the analysis in radioss solver.After the analysis is done .Switch the hypermesh to hypergraph.Results based on the output requests are follows:

Fig 7 Resultant Force at Node 1724247

At the node 174247,The maximum sectional force is obtained about 5.78 kN.This is a node in the front rail.After the bumber gets dformed the forces starts to transmitt to the rails ,That is why the value of force starts to raise after a time after 0 millisecond.

Fig8 Bumber to front Rail Axial Force

Bumber to rail contact force ia about 13kN.So this much force is being tansmitted to the front rail.This is the force through both the rails .Total impacting force is splitted across the shortgun and rails.

From crashworthiness point of view, a car is divided into two distinct zones: safety zone and crushing zone.The safety zone includes the occupant compartment, which must be rigid to resist plastic deformation and to prevent intrusion into the occupant compartment.Material requirement for the safety zone is high strength and that for the crushing zone is high toughness. Because the tougher material is the one which absorbs most of the energy coming to it before fracture. As the crash worthiness point of view ,we also want the crushing zone to absorb all the kinetic energy thereby protect the passengers from the shock.Body structures evolved to include progressive crush zones to absorb most of the kinetic energy resulting from a crash. The kinetic energy is spent in the plastic deformation of the crush zones.

Fig 9 Short gun sectional Forces

Sectional Force through the left short Gun is 8.6 KN and that of through right shortgun is 16.1kN.The force begans to rise just after some time after T =0.This indictaes that the bumber done its job properly and it deforms as soon as the collision happens,so that the transmission of energy is lower than the impact energy. Generally Short gun are made of advanced high strength materials which are having high strength as well as high toughness ,So that the shortgun absorbs all of the Force and deforms and buckles so that the energy transmission to the occupant area will be less.

Fig 10 A pillar Forces

Left Shortgun imparts the force to left A pillar and and the sectional force through the left A pillar at the section we created is 3.1 kN and that of through the right A pillar is 1.98kN.

Fig 11 Displacement of the nodes 66244,66695

Intrusion is basically the displacement of the node with respect to some referance node.So to find these values we defined a Fixed coordinate system at the cross beam in floor panel and then we put the nodes 66244 and 66695 in time history.The values we obtained is pretty high.This is due to the fact that our model is not having any engine and other components in the front crushing area.

Fig 12 Acceleration at the left and right b pillar rocker

The accleration values at the B pillar rocker are obtained.These values depicts the value of acceleration sustained by the occupant when the collision happens.The mmaximum value of the accelration is at the Right B pillar rocker is 2.51 mm/ms^2 and that at left B pillar rocker is 0.38 mm/ms^2.

Maximum Sectional force through the Node 174247 is 5.8 kN

Maximum Sectional force through left short gun is 16.1 kN

Maximum Sectional force through right short gun is 8.6kN

Similarly the Sectional forces through the right A pillar is 1.98 kN and the sectional forces through the left A pillar is 3.1 kN.

And the intrusion at 66244 is 919.96 mm and that of at 66695 is 893.2 mm.

The accleration values obtained at the Left B pillar rocker is 0.38 mm/ms^2 and that at the right b pillar is 2.51 mm/ms^2.

CONCLUSION

Surrogate model of the neon Dodge Car is made to analyse the frontal crash and we obtained the values of the sectional forces at the A pillar,Shortgun and front Rails.We obtained the intrusion and accelerations as well.The crushing area components absorbs a lot of energy while deforming.These regions are made with the materials having good toughness character so that it shows good strain hardening nature as well and since they are tougher they will absorb a lot of energy from collison and at the same time these material are ductile as well, so they deform plastically while absorbing the forces.Thereby it helps in crashworthiness.The occupant area is rigid and it should be free from plastic deformation to protect the occupants.So the occupant area is build by such materials like the high strenth steel which have large strength and low elongation capacity.

LINK FOR THE FILES

https://drive.google.com/drive/folders/1gtmbiYlNrjlWstRlDE3xA0B9S-R3d4z2?usp=sharing