Assignment 7-Side Pole Crash Simulation Challenge

Side Pole Crash Simulation

AIM:

Side Pole Crash Simulation of Dodge Neon BIW using RADIOSS solver and Preprocessing using HyperMesh / HyperCrash.

OBJECTIVE:

The following are the requirements for this project:

• Check 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 Pole 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 is 35 mph.
• Use a model checker to ensure good quality.
• Timestep :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.

PROCEDURE:

We will be using Hypercrash and Hypermesh to set up the model. Some checks will be done in Hypercrash and some in Hypermesh. First, we will import the model into Hypercrash and check for Penetration and make sure the units are in Kg mm ms.

The unit check can be done without opening the model. We can just open the Neon_front_0000.rad in a notepad where we will be able to check the units.

Go to Neon_side_reduced_0000.rad file >> Open >> check the unit system

We can see that the Units are in Kg mm ms. Now we will open Hypercrash and perform a penetration check and also will be adding mass to the body.

To open hyper crash we have to first open hyper mesh.

Now go to Application >> hyper crash>> Select the unit system >> Open

Once Hypercrash is opened we will be checking for Penetration and Intersection.

Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another.

All models and especially impact models should be checked for penetrations and intersections to make sure there is no penetration and intersection. Penetrations adversely affect results and should be removed.

To check penetration and intersection

Got to Quality>> Check Intersection on tree >> Select parts > Click on check penetration

We can clearly see from the above figure there are no penetrations and intersections are present in the model.

COG and Additional Mass:

In the next step, we will be adding masses to the setup. Since this is a reduced model the vehicle's weight and COG are not at the required point. So we will be adding some masses keeping the full model as a reference and will be bringing the COG at the required point.

The reduced model's weight while importing was 166kg so we will be adding massed to bring it up to 700kg in the appropriate places so that the COG is at the center of the CH-CBN-SEAT-REINF-FT.

From the below image you can see the Weight and the position of the COG in the reduced Model.

Once the Additional masses are added we can see that the total weight is 700kg and the correct position of the COG.

CONTACT INTERFACE:

Type-7 Node to surface contact is used in this model. Both the Slave nodes and the Master nodes will be the same for this simulation since there is self-intersection between the parts while it simulates.

The recommended properties are as following:

1. Igap = 2 (Variable Gap took into account.)
2. GAPmin ≥ 0.5mm (minimum thickness to avoid the numerical issue.)
3. Inacti = 6 (remove initial penetrations wherever possible, else reduce to less than 30% of the defined gap)
4.Istf = 4 (Stiffness based on softer Segment)
5.Stmin = 1 kN/mm (Minimum stiffness in contact to avoid too soft contact.)
6. Idel = 2 (remove slave nodes from contact because of element deletion)
7.Iform = 2 (Frictional Forces are calculated based on the Stiffness parameter.)

Before creating this contact make sure to delete the previous contacts.

RIGID POLE:

A rigid wall is a nodal constraint applied to a set of slave nodes to avoid node penetration to the wall. If contact is detected, then the slave node acceleration and velocity are modified. Mainly to constrain the movement of a moving body after impact, we will be using a plane wall. An infinite plane wall is a plane that extends to infinity. It is defined with two points.

Rigid wall entities provide a method for treating a contact between a deformable body's rigid surface and nodal points. In the Radioss user profiles, rigid walls can be created in the Model and Solver browsers.

To create an RWALL

Go to Solver browser >> Create >> Rwall >> Cylinder

We need a reference node to create an RWALL so we can select a node at the position where we need the pole.

Based on the reference node we can just adjust the wall in such a way that it is not in contact with the car and there is a small gap between the wall and the vehicle.

We will be providing the contact interface as Sliding with friction with a frictional coefficient of 0.1. The Diameter of the pole is 254mm.

The D-search distance we can use around the range of 500 mm. All the Nodes within this distance will be considered as salve nodes for the contact between the car and the Rigid Wall.

INPUT VELOCITY:

The velocity input for this simulation as per the Standards is 35mph so when we convert it to m/s the input velocity is 15.6464m/s.

To create a velocity

Go to solver browser >> Create >> boundary conditions (BC) >> Inivel

Define the Node group on which specified initial velocities are applied (grnd_ID1). For our simulation, we will be selecting the whole vehicle setup.

The velocity type is selected as Translation velocity and it is provided in the y-direction as shown in the above image.

CREATING SECTIONS:

We will be Creating Sections at the cross members to Study the sectional forces. We have to know how the forces are transmitted from the Bumper to the Dashboard and the rate of deformation. It is done to ensure the safety of the passenger.

Certain components have to deform more than the other so that the forces are distributed correctly leaving very little force left to transmit inside the cabin.

Before creating a Section we need to create a moving frame, This frame will be assigned to the section.

We will be using these moving frames to create a section as shown below.

We will be creating a TH file separately for both of these sections so that we can view the transfer of force through them.

CREATE SPRINGS:

We are creating spring elements to study the intrusions(The deformation in those regions). Create 3 parallel spring elements.

Springs can be created from the 1D Panel > Springs

We can see the yellow springs in the Model. The Spring at the Front end of the car will show us the intrusion experienced by the hinge pillar. The Spring in the middle will show the intrusion of the B-Pillar and the one at the rear end of the vehicle will show the intrusion at the Fuel Tank.

We have to provide the springs with their respective properties.

Go to model Browser >> Create >> Property >> Rename as Springs

After creating a property, a new tab will open there we have to select CARD image as P4 SPRING and Mass as 0.001, and Stiffness as 0.001 and assign all these properties to the spring.

Make sure to create a Time History file for these Springs Individually so that we can view the intrusions.

CHECKS:

These checks can be done via both Hypermesh and Hypercrash but it is recommended to check via the Hypercrash module. Before exporting the model we will be checking for Unused and Empty. Also, make sure all the parts are connected, or once the simulation is done the results will be wrong with parts flying.

Tools>>Unused and Tools>>Empty and delete the unwanted data in the model and export them.

From both the images, we can see that there are no Errors and they show only warnings. We can now run the Simulation and view the results.

RESULTS:

We can see the Maximum Stress formation is in the B-pillar as it comes in contact with the pole first and from there we can see the transfer of stress and deformation to the connecting parts.

Once the simulation is run we can check the Output files for Energy errors and Mass errors.

OBSERVATION:

The Energy Error is Negative and has been linearly increasing up to -1.7% only, which is acceptable. Mass error is zero which is acceptable We can conclude that there are no errors in the analysis.

Energy and Force Graphs:

The tools to plot the graph are available on Hypergraph.

Hypergraph 2D >> Data File >> FIRST_RUNT01 >> Apply

A hypergraph is a data analysis and plotting tool that represents the FEA from the simulation in graphs to the selected unit system.

As the vehicle is moving with a certain velocity (Say 15.646 m/s for the Model), the initial kinetic Energy will be High (Refer to Above Graph). Once the car is hit by the rigid cylinder, the vehicle starts deforming results in absorbing the Surrounding Energy and stored it. Thus, internal Energy starts increasing. At the Maximum deformation, the Velocity will become Zero and thus the kinetic energy will also be dropping down to zero resulting there is no energy to absorb in the system. Thus, Internal Energy Remains Constant thereafter.

The above graph shows that the Hourglass energy is almost negligible since we have used improved integrated element formulation (QEPH).

Our Requirement from an Ideal Simulation is that we have minimal Contact energy and maximum Energy absorption/Deformation in the elements. We can check the Energy error in the Engine output file, which has maxed out at -1.7% which is within the limits for it to be. Our Mass error is also 0 % which means that the solver did not need to add mass onto the nodes to reduce the time step to further avoid the Hourglass Error.

PEAK VELOCITY:

As we all know, when the car hits the pole, the first impact will be the door and due to the deformation, the inner portion of the door might hit the passengers inside the car and lead to injuries. Hence it is important that the Peak velocity at the door region is to be calculated.

From the Graph, the peak velocity of the node on the door is 17.606 m/s. As we saw from the above graph there are fluctuations in the shock waves this is because of vibration that occurred during the crash of the vehicle.

INTRUSION SPRINGS:

Here in this graph, we can see that the B pillar has the maximum intrusion, then come to the fuel tank and the least intrusion is seen at the hinge pillar.

Here the red curve indicates the B-Pillar intrusion, Blue indicates the Hinge Pillar, and the last green indicates the Tank intrusion.

Here at the B-Pillar, the spring elongation of 716 mm. The B-pillar touches the rigid pole and the other side is crushed towards it, so its intrusion is so high. For the Fuel tank, the spring elongation is 406 mm and for the Hinge Pillar, it shows an elongation of 210 mm.

Since due to the Node limitation in the software, we don’t have the full-scale model and many missed components like the rear axle, Fuel tank, etc. But in real condition, the rear axle, wheels, and the fuel tank give much more stiffness to the car and this might help to reduce the intrusion in a good manner. To reduce the intrusion in this model we can add one cross member near to the Fuel tank region

The cross members are the parts that transfer the force from one side to another side when the impact occurs. The max section force at the B-pillar cross member is 16.6 KN and the driver cross member is 2.88 KN. When the car hits the rigid pole, the force is transferred from the B pillar to cross members and then to the other side. In the above graph, we can see a rise in curves this is due to the force acting on the cross members, due to this force the cross members get bent, and the force passing through the cross members get reduced that is why we see the drop in resultant force in the graph.

Learning Outcome

• Learned how to set up a side crash test.
• Learned how the rigid wall interface works and can lead to incompatible Kinematic conditions.
• Learned how Sectional forces are generated.
• Learned how the distribution of forces among the components during a side crash.
• Learned how some components are designed to deform in such a way to ensure the safety of the passengers inside the cabin.
• Learned how to check for Energy, mass, and momentum balance.
• Learned how to Debugging errors in order to get the right results.
• Learned how to place a node to see his peak velocity.

CONCLUSION:

The given model was simulated for the side crash using Radioss and the results obtained were validated. The graphical results were plotted for all the test cases. From the simulation, it can be observed that there was maximum deformation in the cabin, and also maximum intrusion was found in the cabin area. This is due to the limited number of nodes in the student version some of the BIW, engine blocks, suspension system, etc., are removed, so the results are not as in real condition. After understanding these we will get to know what all things we should do on this car to make it safer. For example to decrease the amount of intrusion in the Fuel tank region we can introduce a cross member there.