Side Pole Car Crash simulation of Dodge Neon BIW using Radioss and HyperCrash

AIM:

Side pole carcrash simulation of Dodge Neon BIW using RADIOSS solver and Preprocessing using HyperMesh / HyperCrash

OBJECTIVE:

The following are the requirements for this project:

1. Import the model of the Neon Dodge ie, the FEA model in such a way that the required output requests can be post-processed from it.
2. The required output requests are Sectional force in the cross members.
3. The intrusion at B pillar, hinge pillar, and fuel tank region. And Give a recommendation on what can help to reduce Fuel tank intrusion.
4. Peak velocity of the inner node of the door

Setup Request:

• Check the unit system and either follow [Mg mm s] or [Kg mm ms].
• Create an appropriate interface, friction 0.2, and recommended parameters.
• Make sure of no penetration and intersections.
• Create a rigid wall with friction 0.1 as per the reference model.
• Compare the model weight with the reference model and use added masses to reach the target weight of 700kg while getting CG about the required range.
• The initial velocity of 35 mph.
• Use model checker to ensure good quality.
• Time step: 0.5 to 0.1 microseconds.
• Run 80ms.

Output requests:

• Sectional force in the cross member.
• The intrusion at B pillar, hinge pillar, and fuel tank region. Provide recommendations on what can help to reduce Fuel tank intrusion.
• Peak velocity of the inner node of the door.

Steps to achieve the task

• Import the model into Radioss/ Hypercrash.
• Setup the boundary conditions as given.
• Remove all the unwanted and used components, property cards, sets, groups, joints, etc.
• Check for penetration and intersections
• Setup the output request and check the necessary card status eg. ANIM/DT, ENGINE_RUN, etc.
• Run the model checker and debug the errors and warnings.
• Generate the Radioss file for animation and time history plots.

Theory:

Fig: Sidepole crash test (Source: Google Images)

During a car crash, energy is transferred from the vehicle to the rigid wall/pole it hits. This transfer of energy, depending on variables that alter states of motion, can cause injuries and damage cars and property. The object that was struck will either absorb the energy thrust upon it or possibly transfer that energy back to the vehicle that struck it. Focusing on the distinction between force and energy can help explain the physics involved.

Car crashes are clear examples of how Newton's Laws of Motion work also referred to as the law of inertia, asserts that an object in motion will stay in motion unless an external force act upon it. Conversely, if an object is at rest, it will remain at rest until an unbalanced force act upon it.

Consider a situation in which a car collides with a static, unbreakable wall/pole. The situation begins with the car traveling with velocity (v) and, upon colliding with the pole/wall, ending with a velocity of 0. The force of this situation is defined by Newton's second law of motion, which uses the equation of force equals mass times acceleration. In this case, the acceleration is (v - 0)/t, where t is whatever time it takes car A to come to a stop. The car exerts this force in the direction of the pole/wall, but the wall, which is static and unbreakable, exerts an equal force back on the car, per Newton's third law of motion. This equal force is what causes cars to accord up during collisions.

In the case of a car, if it slams into the wall and comes to an immediate stop, that would be a perfectly inelastic collision. Since the wall doesn't break or move at all, the full force of the car into the wall has to go somewhere. Either the wall is so massive that it accelerates, or moves an imperceptible amount, or it doesn't move at all, in this case, the force of the collision acts on the car, and deformation occurs.

Crashworthiness

Crashworthiness is the ability of a structure to protect its occupants during an impact. This is commonly tested when investigating the safety of aircraft and vehicles. Depending on the nature of the impact and the vehicle involved, different criteria are used to determine the crashworthiness of the structure. Several criteria are used to assess crashworthiness prospectively, including the deformation patterns of the vehicle structure, the acceleration experienced by the vehicle during an impact, and the probability of injury predicted by human body models. Injury probability is defined using criteria, which are mechanical parameters (e.g., force, acceleration, or deformation) that correlate with injury risk. A common injury criterion is the Head impact criterion (HIC).

Procedure

1. Import model

On importing the _0000.rad file into Hypercrash we get this partial reduced BIW model for performing side impact test. It contains 95 components, 94 material cards, and 7 contact interfaces.

Fig: Model opened in HyperCrash

This is the partial BIW view of the full vehicle (300k element) so that it can get open into Hyper Crash (student version). Once importing the _0000.rad deck file into Hyper crash or Hyper works environment we can see it consist of 96 components, 92 material cards, 6 interfaces, and redundant spherical and translational joints. The total weight of the car is 188.4 kg with a COG point located near the dashboard base.

Check the unit system and either follow [Mg mm s] or [Kg mm ms].

By checking the _0000.rad file we see the unit system which is followed is [kg mm ms].

2. Create an appropriate interface, friction 0.2, and recommended parameters.

Here 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 since we are defining a self-contact. We don’t want a type 7 contact with the same components already in self contact. This is because two contacts defined for the particular components will lead to an 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 surface contact. In that, we will check the self-contact and we will give the recommended parameters to the type 7 contact and select the whole model as a master. All parameters provided are as recommended shown below.

Fig: Self-contact (Type-7)

3. Make sure of no penetrations, intersection, and Proper connectivity between parts(ie, No free parts)

To check for the intersections and penetrations of the parts using tree-selection can be done by selecting Quality > Check Intersections of Tree Selection

Before moving to the next step we will make sure there are no intersection or penetration of elements. If any, fix them by using the tools provided in Hyper-crash / Hyper-Works, since there was no penetration or intersection during the check we can proceed further.

Fig: Intersection check

Fig: Penetration check

Note: Now we need to check for the connectivity of the parts

To check for the connectivity of the parts using tree-selection can be done by selecting Quality > Check Connectivity of Tree Selection. It will show a list of free parts and joints. These are the parts and joints which are not connected to any of any parts. To 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 its respective component using some sort of simple springs. Always make the model a single connected one or otherwise run issues will occur.

Fig: Connectivity check

5. Rigid wall Creation

The rigid wall is the body is having high stiffness and we made the model collide with the rigid pole. We here use a cylindrical rigid wall. For defining the rigid wall, first, select the tail coordinate as a node in the rocker and copy those coordinates to the head. Then we can change the values with the value of the coordinates in the normal direction of the plane to get the Rigid pole at a distance from the model. Here we shouldn't move the rigid pole very far away from the model. This is because if we do that the time taken for the car to run and reach the Pole is actually a wastage of CPU time. We don’t want any results from that motion. So rigid walls should be only a little aside from the model.

Here we need a frictional rigid wall with sliding friction of 0.1. Then the search distance for the slave nodes should be given a particular value. At least it should search the nodes till A-pillar because up to that region the nodes may get interacted with the wall or we can select the parts or nodes by box selection but here we opted for the search distance method as 1000mm. The diameter of the pole should be given as 254 mm, Reference: Euro NCAP(New Car Assessment Program)

Fig: Rigid Pole creation

6. Compare the model weight with the reference model and use added masses to reach the target weight of 700kg while getting CG about the required range.

On checking the mass balancing in the Hyper-Crash we see the total weight of the model is 166.3 kg and COG somewhere near the B-pillar cross member mid-region (as shown below) and so as to make the mass near to the 700kg we need to add mass so we added the 534 kg to the rocker cross beam so as to make the COG point over near to the rocker cross beam. As shown in the figure below.

Fig: Mass added at the different parts

Fig: Positioned the COG of the model after mass addition

7. Set up Initial Velocity and Gravity load

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

Fig: Card defined for Initial Velocity

From the gravity point of view, we need to define a function that should be a time-dependent gravity acceleration value, since we know that the value of gravity will be the same for whatever be the time. The negative value of acceleration is due to the downward direction (ie, negative z-axis)

Fig: Function defined for Gravity

Same as the above card definition for initial velocity, we need to input the Grnodes as all the nodes of the model. Then give the value of acceleration due to gravity as -0.00981 mm/ms^2 in the Z-direction.

Fig: Card defined for Gravity

8. Cross-section setup for cross members.

To know the sectional force over the areas such as cross members we need to give section over the elements as shown below. The sections are provided using a moving frame. Here in the moving frame, we need aware of the following data,

• N1-node for the origin of the local coordinate.
• N2-node for the x-axis of the local coordinate.
• N3-node for the y-axis of the local coordinate and marks the x-y plane
• Direction - specifies the N1-N2 node direction

Fig: Shows the defined control cards and requested Time History output

Fig: The sections are created using a moving frame.

9. Intrusion nodes and velocity at the door part

To know the intrusions over the area of crash impact we need to set the TH node for the area as shown below.

Fig: Time History card for node

10. Output TH request and Engine cards

Once we are done providing the setup request we have to request the TH output. Such as accelerometer, sections, rigid wall, etc. After we are done with TH output we need to provide engine cards for animation and contour capturing eg. ANIM/DT, ANIM/VECT, ENG_RUN ETC.

Fig: Shows the defined control cards and requested Time History output

Note:

To get the crossectional force in the part that we have taken for study using a local coordinate system where we can specify the output using the local data from the options. Here we selected the local data as the output since the global data that is actually not required. The below card defined only for the right side A-pillar but we need to do the same for every part whose crossectional force is taken for the study like A-pillar, Shotgun, and Support-rail. When compared the local axis normal values with the global axis normal force values we got nearly the same results and finally gone with plotting the values with the global axis.

Fig: TH/SECTION card defined for the cross beam part

11. Run the model checker and debug the errors and warnings.

Finally before generating the radioss simulation and file we need to do the final check i.e. model check. On running the model check we see that it showed a few errors and warnings so we need to check and fix them. The error can be due to unused group nodes, shells, surfaces, etc. It can be also due to the incompatible kinematic condition or wrong definition of rigid connection, etc. By working on the errors, finally, we got the debugging correct and manage to fix all errors. Here the warning will not affect the simulation of our file and this arises due to the better definition of the cards for the proper simulation.

Fig: Debug the errors

Note: To make the material card for front and rear door window glass

To make the glasses of the car window to show the brittle nature and breakage effect we need to change the material card to PLAS_BRIT (Law-27) type with properties of glass as shown below.

Here Material is defined with the following parameters for young's modulus, poisson's ratio, and yield stress for the glass

Fig: Material card defined for front and rear window

After defining the material card we explained the Fail card defined especially for the crack formulation rather than the element deletion. Herewith the function card, we are inputting the stress-strain data for the failure of the glass material.

Fig: Fail-keyword defined

Fig: Failure function defined

POST PROCESSING

On opening the _0001.out file, we can see the energy error to be -1.2% and mass error to be 0.009605 which is acceptable and can consider an as a good model with total no. of the cycle as 80001 with time duration of 1:17:07 or 4627 sec.

ANIMATION FILE

1) Von-Mises stress plot

Here we can see the value of von-mises stress generated during the impact with the side pole, the max value of 0.5391 Kg/mm ms^2 generated at shell 121291.

From the side view, we can analyze the stress flow path during the impact absorbed by the B-pillar, sill beam, cross members, and A-pillar.

2) Displacement contour plot

The maximum displacement achieved is 1443mm at node 439169

TH plots

1) Energy plot

As we can see the kinetic energy at the start of the simulation is at 86KJ and reduces gradually with the impact into the rigid wall (velocity reduced). Internal energy starts at 0 and increases to a value of 36.9KJ at the end of simulation due to the deformation and conversion of K.E to the I.E. The value of hourglass energy is zero throughout the simulation due to the use of recommended shell properties and contact energy is insignificant.

2) Rigid pole forces

As we can see the plot below shows the normal force in Y -direction variation w.r.t simulation time. As it can be seen in the starting the pole force generated is zero till 2ms of simulation because of no contact but at the 4 ms, there is a peak rise in the wall forces to a value of 68KN. Then from 10 ms to 50 ms, the value remains almost constant in between 40-45 kN value. After that from 50 ms to 70 ms the value remains in the 55 kN but there was an increase in between due to contact of later parts in the BIW. Finally, we reached the maximum normal force value that is 95.2 kN, due to contact of later parts in the BIW.

3) Section Force Rocker beam

The variation in section force at the Rocker beam is shown below. it starts with the value of 0 till 6ms and then shows a much variation between 20 to 40ms with a max value of 12.5 KN at 41ms. Finally, it has shown ups and dips and ups to get a maximum value of 21.59 kN at 73 ms

4) Section Force cross member

The variation in section force at the B-pillar cross beam is shown below. it starts with the value of 0 till 5ms and then shows a much variation between 5 to 50ms with a max value of 9.6 KN at 48ms. Finally, it was having a greater dip in the cross-section force due to failure or break in the weld connection since it is carrying a very low load value with a high peak at the region of 50 to 80 ms as 4.3 ms.

5) Intrusion on nodes at different sections

The Intrusions are measured by taking the node under consideration at location 123293 - fuel tank, 123412 - B-pillar, 123255-rocker arm. So as to get the displacement in Y-axis we need to measure the just before the impact and at the end of the simulation therefore we get

Node 123293: 122.4 mm (fuel tank)

Node 123412: 137.7 mm (B-pillar)

Node 123255: 177.3 mm (hinge rocker arm)

So to reduce the intrusion at the fuel tank area the cross members and the sill beam need to be more robust (rigid) which can resist deformation and play a major role in occupant safety too.

7) Peak velocity of the node at the inner door

The peak value of the inner door panel node (337773) velocity is 16.26 mm/ms at 6ms of simulation then drops down after 18 ms at a value of 6 mm/ms. Between 20 to 80 ms the velocity value fluctuates between 4-8 mm/ms.

CONCLUSION:

By completing this project we can see maximum deformation and by that maximum energy, the absorption is done on the B-pillar and the cross members. Side impact bars helps in reducing the intrusion happens to the B pillar and Fuel tank regions. B pillar plays a major role in reducing the side-impact and protecting the passengers from its effect, it redirects the force to the roof and the cross beams so that the shock is reduced and the passengers are protected. Here these regions are made with high toughness material such that they absorb a lot of energy from the collision and such that it helps in the occupant safety and moreover the occupant side parts will be made of the proper rigid material. The results and plots obtained are relevant to the actual condition of crash analysis.