Crashworthiness Analysis using HyperMesh and Radioss Assignment 7 - Side Pole Crash Simulation Challenge

OBJECTIVE

To perform a crash analysis on the left side of a Dodge Neon BIW, also known as a side crash. The analysis is to be carried on the deformation and the forces created as a result of the crash at a speed of 35 mph. Along with the analysis, certain output requests were to be generated and they are as follows:

• Sectional force in the cross members.
• Intrusion at B pillar, hinge pillar, and fuel tank region(Also provide recommendations on what can be done to help reduce fuel tank intrusion)
• Peak velocity of a node on the inner door panel.

BACKGROUND

The crash test is a virtual reconstruction that replicates the same forces and speeds that would occur if the vehicle was to be involved in an actual crash. In this type of testing, since nothing is physically impacting the Body-in-White (BIW), no physical deformation or damage occurs to the body’s structure, allowing multiple crashworthiness tests to be conducted in succession. This type of simulation is an integral part of the design process and can help save both time and money since it can be implemented instead of costly, destructive testing programs.

source: https://www.simuleon.com/simulia-abaqus

MODEL IMAGE

PROCEDURE

The model is imported through the 'import via solver deck' option on either Hypermesh. The first thing we need to verify is the applied interface, which is type 7. We need to ensure that it has all the proper settings.

There are multiple type 7 cards for this model - they can all be deleted by right-clicking them all and selecting 'delete' in the model browser. We can go ahead and create a new interface card by right-clicking in the model browser section > create > contact. We shall be creating a type 7 card with the following properties:

For the slave and master node settings, all the components in the model are selected. Therefore, this interface card will cover all the components in the model.

Moving on to the other requirements,

CREATION OF RIGID WALL

For this, the model was imported to Hypercrash. To switch to Hypercrash, we need to go to Applications > Hypercrash from the Hypermesh window.

A rigid wall is an object that is used to define an interaction between a non-deformable entity and a deformable entity. Nothing can go beyond it and it is non-yielding. There are multiple types, like infinite plane, infinite cylinder, spherical, and parallelogram. But for this case, we shall be using the infinite cylinder option, which creates a pole with a specified diameter at a specified location.

To create a rigid wall in Hypercrash, we can go to the top toolbar and access LoadCase > Rigid Wall. In the Rigid Wall panel, we can select the create new object button and select 'Cylinder' (the same process can be carried out by right-clicking the panel's interface and going through the same options).

The created rigid wall is given the following properties (with the requirement of friction of 0.1):

To understand the co-ordinates XM, YM, ZM & XM1, YM1, and ZM1,

M0 is defined by XM, YM, and ZM whereas M1 is defined by XM1, YM1, and ZM1. This helps create a normal for the rigid wall and hence orient it properly with respect to the model. The furthest point on the model, which would be a point on the bumper, is picked as a reference for M0. To allow a gap between the wall and the model, we can edit the y-coordinate, since the movement will be along that axis. The same concept is used to define M1, where we will use a different x-coordinate value again and that helps define the normal.

APPLICATION OF INITIAL VELOCITY

To add initial velocity to the system in Hypercrash, we need to go to LoadCase > Initial Velocity. For [Gnod_id] Support, we shall be selecting all the nodes in the model. The required velocity is 35 mph but the units are in mm/ms, which would be 15.6464 mm/ms. As discussed in the previous section, movement is along the y-axis, so this value will be entered in [Vy] Y Velocity. All other velocity values would be 0.

After entering the values, we can click save at the bottom of the panel.

MASS BALANCING

The target mass of the model is supposed to be 700 kgs. We can check what the current mass is by accessing Mass > Balancing from the top toolbar in Hypercrash.

As we can see, it says the current mass is 166 kgs. It also shows where the current center of gravity is. The above image also shows where the center of gravity ought to be moved to, based off the full car model provided. Understandably, we need to add more mass and balance the additional weight to change these parameters. To do so, we can go to LoadCase > Added Mass. Then we can click the 'create a new object' icon in the panel to add an entity. We are to then select the 'type' of mass to be added, and we shall pick type 1. In addition to that, we are to assign a mass to this entity and select the nodes that would come under it.

I added masses to include that of the cross member under the front seats and that of the doors on the pillars on the right. The following shows the current mass and location of the centre of gravity, which was what we were going for:

ADDING SECTIONS

Firstly, we will be creating moving frames for each of these regions. To do so, we go to the solver browser and right-click > create > frame > mov.

Doing so brings up the moving frame attribute window on the bottom. We are to define a plane basically. The origin node is going to be the node that will be part of the section that is to be defined. The next two will define the plane. They are selected as shown in the above screenshot.

After creating the moving frame, we can move on to defining the section. In the same solver browser, we are to right-click > create > sect > sect.

N1 is going to be the same as the origin node defined in the moving frame setting. N2 & N3, again, will help define the plane. Frame_ID will be the corresponding moving frame that was created earlier. grshel_id will be a selection of two rows of elements, of which the nodes are a part.

After creating the section, we can move to the model browser and right-click 'Output Blocks' > Create. With this, we shall create an output request for the sections we previously created. We can edit the output block in the entity editor on the bottom left.

For the entity IDs, we shall be selecting all the crosssections that were created (which is 2).

Screenshot with all the crosssections visible:

ADDING INTRUSIONS

The first step is to create a moving skew for these intrusions. To create a moving skew, we need to go to the solver browser, right-click > Create > Skew > Mov.

Doing so brings up the moving skew attribute window on the bottom. We are to define a plane basically. The origin node is going to be the node at which the intrusion is to be measured (nodes at positions: B-Pillar, Hinge Pillar and Fuel Tank). The next two will define the plane. They are selected as shown in the above screenshot.

Then we can switch to the model browser and create an output block for this newly created skew. Right-clicking 'Output Blocks' and selecting 'create' brings up an entity editor on the bottom left.

The entity ID is going to be the node where the intrusion is to be measured and the lskew is going to be the corresponding skew system.

PEAK VELOCITY

A node on the inner panel of the driver's door is where peak velocity is going to be measured (node 337773). Just as we did previously, we can go ahead and define a moving skew on this exact node. (Node 337773 is going to be the origin node).

The next step is to create a Time History (TH) output specifically for this. For that, we can switch to the model browser and create a new output block, this time for peak velocity (right-click > create > output blocks). The entity ID is going to be just the one node - node 337773 and for lskew, we shall be selecting the skew created previously.

PENETRATION CHECK

Then, we can run a penetration check by going to Tools > Penetration Check from the upper toolbar in Hypermesh.

We will need to click the 'Invoke Penetration Check Setup Widget' within its browser to access options for the process. With the entity type as 'Components', we can select all of the components in the model for the 'selection' option. The algorithm gives the result on the panel in the bottom-left. As we can see, there were 0 penetrations in the model.

SIMULATION TIME

In the model browser, we can go to cards > ENG_RUN to change the simulation time. In the entity editor, T_stop is given the value of 80ms.

Time step did not require editing since the default values were in the 0.5 to 0.1 microsecond range.

ERRORS

Finally, before carrying out the RADIOSS analysis, an error check was run on the file through Hypercrash. The model check tool can be accessed through Quality > Model Checker > Run from the upper toolbar.

As we can see, there were no errors in the model, just warnings. We can choose to fix or ignore warnings as they wouldn't affect the analysis. I ignored them.

In addition to that, if there are any unsupported cards in the model browser, they can be deleted.

RUNNING THE ANALYSIS IN RADIOSS

Switching to Hypermesh, moving to Analysis > radioss, we can click 'save as' to save the file if it hasn't been saved yet. Care must be taken to include '_0000.rad' in the file name since it's the starter file. After that, we can check the connectors option and input '-nt 4' in the options bar before clicking 'Radioss'. This starts the Radioss simulation.

ANALYSING THE OUTPUT FILE

The next step is to carry out energy error and mass error checks and this is done by analyzing the RADIOSS engine output file. This can be accessed from the same directory as the starter and engine files and is denoted by the '.out' extension. The file in question contains '_0001.out' and can be accessed using any text editor - such as Notepad.

As we can see, the energy error is -1.8%. It is definitely acceptable due to its proximity to 0% error. In addition to that, the mass error is 0.0099, which means that a negligible quantity of mass of around 10 grams was added during the simulation, possibly for the sake of time step control/stabilization. It is a rather low amount so it's still acceptable.

Total Simulation Time: 4387.64s
No. of cycles: 80000

VIEWING THE SIMULATION

To view the simulation, we can switch to Hyperview through the client selector.

In Hyperview, we will need to import the h3d variant of the file. After importing, we can then select the 'contour' tool to switch to the Von Mises contour so we can analyze the stresses that form within the BIW in the simulation. This is what the simulation looks like:

GENERATING THE PLOTS

After generating the simulation, we can then go ahead and generate the plots. Using the same client selector, we can switch to Hypergraph. In the Hypergraph client, we are asked to import the required file, which is the T01 variant of the file.

On importing, we can build the plots using different variables. We shall first look at general plots of energies and rigid wall forces generated in and by the entire BIW respectively.

Energies

The changes in kinetic and internal energies occur at the exact moment the BIW makes contact with the rigid cylindrical wall. Understandably, the BIW loses kinetic energy throughout the simulation due to the obvious decrease in velocity. At the same time, it absorbs the forces, and this results in an increase in internal energies, and as a result, the deformations also occur.

Taking a look at the contact energy graph:

Contact energy is a type of energy that is formed when one element comes in contact with the other or neighbouring elements. The opposing force created by this element forms the contact energy. In this case, it takes off after 7 ms, at this point the model starts deforming in such a way that penetration of nodes occurs. When certain regions of the model press on themselves, buckled elements are forced into contact.

The increase in contact energy affects the overall energy of this system, which is why there is a decrease in the total energy over the course of the simulation - it is a comparatively negligible decrease though. The magnitude of contact energy generated is much lower compared to that of the energies in the previous plot.

Rigid Wall Forces

Taking a look at the rigid wall forces generated:

There is an initial spike of around 75 kN, which is the point of first impact. After that, the forces generated stabilize between 30 and 45 kN, due to forces (as a result of the collision) causing the deformations in other regions of the BIW.

Sectional Forces in cross members

Intrusions
B-Pillar

Hinge Pillar

Fuel Tank Region

Peak Velocity - Inner Door

OBSERVATIONS

In the case of the cross members, cross member 2 receives the first jolt of force at around 25 ms understandably due to it being situated at the B-Pillar. Once the deflection on the side members reach cross member 1, it absorbs the brunt of the incoming force, thus resulting in the reduction of force generated in cross member 2 (at around 50ms mark).

Regarding intrusions, the fuel tank region received the least displacement, followed closely by the B-Pillar, then the Hinge Pillar. Admirably, the B-Pillar was able to absorb a lot of the impact due to multiple reinforcement members attached to it and in its vicinity, despite being one of the first regions of impact in the crash. The hinge pillar did not have any reinforcements and hence suffered the most displacement.

From the peak velocity graph, we can see that the peak velocity (almost 16 m/s) is during the initial impact. This is, as a matter of fact, the same as the initial velocity given to the model (15.6464 m/s). After impact, there is a steep drop and then a small rise, probably due to the folding deformation created as the crash progressed (due to inertia). As time passes, we can see the velocity gradually decreasing.

RESULT & CONCLUSION

Side crash analysis was carried out on the given BIW model of the Dodge Neon as per requirements. The output requests were also generated after the creation of cross-sections in each of those regions. Peak velocity and intrusion values were also measured at certain points of the model.

Fuel tank intrusion and intrusions, in general, could be reduced by using anti-intrusion beams (or side-impact beams) between the pillars. They increase the rigidity of the doors and distribute the energy in the event of a side-on crash. The model already does have such beams as shown:

There may be stronger options for anti-intrusion bars but there is the weight-to-cost factor that might be a major factor. There are multiple materials other than steel such as aluminium and composites being tested that are lightweight but effectiveness is more or less comparable. If more bars can be used, that could be an option as well.

Otherwise, another option is to simply add an extra cross member next to the fuel tank to reinforce that region.