Side Pole Impact simulation on the CAR BIW structure using Radioss / Hypercrash Workbench.

AIM:- Side Pole Impact simulation on the CAR BIW structure using Radioss/Hypercrash.

OBJECTIVES:-

• 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.
• Deploy Initial velocity in the appropriate direction.
• Use model checker to ensure good quality.
• Timestep :0.5 to 0.1 microseconds.
• Run 80ms

METHODOLOGY

• Import the model in Radioss/Hypercrash workbench. (each platform has there individual PROs and CONs)
• Check the model through Solver(Radioss) or browser (Hypercrash) deck.
• Isolate/ delete the unwanted data from the model.
• Set up different Boundry conditions, Kinematic conditions, interfaces, etc parameters.
• Also, set up the Output request related to the simulation post-process phase.
• Run the model checker (Hypercrash is recommended). and debug the errors and warnings before the simulation.
• RUN the simulation and examine the data collected in the form of graphs and animation.

Crashworthiness

Crashworthiness is the ability of any given structure to protect its occupants from getting severely injured during an impact or collision in the case of a moving structure. So for that, the Car main Structure also known as skeleton / BIW should be made up of a material that can easily absorb the impact forces and avoid unwanted injuries on both passenger and driver side. Material is not the only criterion other than that the structure geometry, connectivity between two parts, Vehicle velocity during impact, Force distribution of the force generated are also important factors.

Crashworthiness analysis can give approximate data regarding the vehicle’s structural ability to plastically deform and yet maintain a sufficient survival space for its occupants involving crashes.

Old times when actual models are made and push through this sort of harsh condition which we are gone look in short times. What happened is that after each crash-test body got damaged so severely that the prototype cant is used again. So this is a time as well as money consuming process also the data we get from these physical tests is not accurate.

Crashworthiness helps to Desing Optimization.

Side Crash Test (Pole compact test):-

-Under this project, we are working on a Side Crash using the BIW structure. The Side Crash Analysis is very important for the occupant as well as passenger safety. If the holding structure is not good, all the impact force may travel into the main compartment and injured the occupant very badly. In side-impact, there are no many components (Engine, transmission, etc.) that are available in between the occupant and the car body for indirect protection. The only thing is to stand between the occupant and the impacted body is the Car outer panel and Main Frame (A-pillar, Bipiller, Intermediate components, etc.)To avoid that, A structure, as well as a full-scale model, should go through the testing by applying different real event-based loading conditions.

Doing this sort of testing using the Experimental method is costly as well and you cant guarantee that the result would be 100% accurate. We can perform this sort of analysis using Solvers like radioss and then discuss the data for a better result. With the Analysis software, we will get approximately the same result as a real-world scenario. We can update the respective parts or strengthen some parts or change the material over some parts for better results. In the End, Occupant safety is an important factor that all vehicle manufacture consider to the topmost.

[NOTE:- In the Lab, they do an actual model testing using a pole of 254mm dia, also the car is impacted on the pole at an angle of 75 degrees during the Test.]

PROCEDURE:-

-I had got the model as you can see in the below image in this Project. As you can see the model is not a Full Body model because of the NODE Processing Limitation In the Student Version of a HypweWorks. The Student Version of Radioss only can handle the 100k nodes and the Hypercrash 10k nodes and the full-body consist of more number than that as it contains so many parts and sub-assemblies.

There are lots of components in this image also, Out of which I just pointed out some that we are gone to work on our further simulation.

1) A-pillar

2) B-Pillar

3) Door

4) Cross-member

5) Rocker

I had imported the Starter file (0.rad) in both the Radioss and Hypercrash. [Hypercrash with gave the user a better graphical interface with detailed options]

Unit Check

I had started the Hypercrash in kg, mm, ms, KN unit system, and my starter file not asked me if I want a unit conversion, so I assumed that the starter file comes with the same unit system. Only for confirmation, I had checked the starter file by opening it in the NOTE pad and find the same unit system. It's necessary to check the unit system before went ahead with further simulation because it can cause of the wrong result in the feature.

Check for Connectivity

-The next important thing is to check if there are any free parts in the assembly or not. Free parts may cause some problems in simulation results therefore get rid of them its important.

We can check the connectivity with the "Check the connectivity of tree section " option which is available in the Quality menu of Hypercrash.

Hypercrash --> Quality --> Check the connectivity of tree section

After checking I have found out there are three parts that are not connected properly. If I had run the simulation as it is these parts may cause unexpected results. As these parts are not bound together they may fly out of the simulation, which is not a good representation.

-The three unconnected parts I have found out are the strengthening elements, so they have significant importance in our simulation. In the normal circumstance, I may have deleted these parts but because of their importance in our simulation, I had the plan to keep them and deploy necessary connections between them.

-These three parts are free which is not good for our simulation, so we have to fix that as soon as possible. I had used the same property card and 1D element to define the connection on these parts.

Inappropriate card or the connection data Check

-After the unit and connectivity check, I had checked for any inappropriate card or the connection data that is available. Like in this model the concerned person already deleted Nos. of parts but sometimes what happens is the connection for that part is remains in the system info. and that may cause some error because the parent surface already gets deleted.

- The above two images are one of the remaining files I am talking about. This Time history and contact interface are given to the model when it is a full-scale model and the intension of these parameters are for that simulation, But for our simulation, we don't need all these parameters. All these additional files only increase the computational time and the result of these conditions gives are not that we want either, so the best option is to remove them and set conditions as per our own requirement.

-I had removed these set conditions along with some others like Unsupported card, Engine card that we won't require for this simulation, etc.. For that, we can directly delete the part if those parts don't have any important role in the simulation. Another way is to correct that by deploying the appropriate connections.

COG modification / Mass Balancing

-Now its time to Condition set up, But before that Mass and COG check is important, As in our model Nos. of parts are missing The COG and mass is not appropriate for the simulation as you can see in the below image.

As you can see in the above image the Total mass noted by Hypercrash is 166 kg which is much lesser than the indicated 700kg mass. If we RUN the simulation as it is we will face a really BAD result as COG is already shifted towards the left and rear side of a CAR body. In normal circumstances, the COG is near the seat and in our case, we can say it should be near the cross member.

-ADMASS is the term in the MASS BALANCING in which we add some masses over the body so it can perform as a real body. I had used that Added Mass option to add mass over the body so we can achieve our target weight and COG. I especially used TYPE 1 to Added Mass option because it will distribute the mass over the selected set of nodes and most suitable for our simulation. Under the Added Mass TYPE 1 option we only have to select the node on which we want to do a mass addition and define the Mass we want to deploy. By using this option I had added the mass on the right side of the car body where the door panel and some of the support elements missing due to model size-reduction. Also added some mass over the front side cross member to balancing the overall weight and move the COG a little bit on the frontal side. Added the mass over the rear side where the Fuel tank should be located.

As a result, I get the desire Mass and COG at the desired position as you can see in the above image.

Contact Interface Deployation & Penetration Check

-After Mass Balancing I had moved forward for a Penetration check, But it's not valid to do a penetration check without defining the appropriate Interface connection, AS we Know that during a crash scenario the parts collide with a rigid wall as well as themselves. For that, it's mandatory to define an appropriate interface between them.

For the next step, I had decided to go with the TYPE7 interface type which is recommended and more frequently used to defined ELasto-Plastic material interface connections. For that, I had open the Interface browser in the Hypercrash and select the TYPE 7 interface [Load Case --> Contact Interface] and go with the all ideal values that are suitable for our simulation purpose.

After that, I had checked for Initial Penetration in my model and removed them. To check the penetration using Hypercrash is simple and we get a shortcut button inside the Contact interface BOX as you can see in the above image extreme left. By clicking on that button we can easily check for Penetration.

In Hypercrash Steps are as follows Menu Bar --> Tool --> Penetration check

After this, I had Set up My own condition related to our simulation like Initial velocity, Timestep, simulation time, animation time, and frequency, Section forces, etc.

Kinematic Conditions

1) Initial Velocity:- as we are performing a crash test it's mandatory our moving body would collide with the rigid wall for that we have to provide our model an Initial velocity with which it can collide with the Rigid wall and we will get the result we are looking for.

to set initial velocity In hypercrash --> Load Case --> Initial velocity

-As you can see in the above image the Initial velocity I had set up was 15.65 mm/ms which is 35mph. Also, I had defined the Velocity along the Y-axis using a global coordinate system only.

2) Rigid Wall set up

-After the initial velocity set-up I had created the Rigid wall. The rigid wall allows an easy way to define an interface between the Rigid Surface and nodes of a deformable body. Here I had used an Infinite Cylinder type Rigid wall because Side crash tests are performed using the Vehicle body and Rigid pole. So Cylinder type rigid body is most suitable for our Side Crash scenario.

-I had defined search distance here, the nodes within this search distance behave as a slave and help to replicate the actual crash scenario of the car against the wall. The Search distance for this simulation is 1000 and the Pole Diameter is 254 mm which is the Standard value for Side impact test simulation.

Section Setup for Section force calculation & Intrusion Point setup

-Now is time to setup Section Forces, we can do that by using both the Hypercrash and Radioss but I had to go with Hypercrash of this as its user interface to make it easy to create the Sections.

Hypercrash-->> Data History --> Section

To create the section we first have to select the part for which we want to calculate the section forces, by using Three nodes we have to define the section, and then we can edit the section card easily by double-clicking on as we want.

-As you can see in the above image I had created 2 Cross Sections for force distribution study on both of the cross members, so at the end, we will get the 2 sections.

-To get the data from these to define sections we have to define the TH output block, One one good thing about the Hypercrash is it will automatically create the Output block for us. But if we did this in Radioss we have to do the output request separately. so this is one of the advantages of using Hypercrash.

-After that, I had set up some Intrusions so we will get the idea about how much displace meant is happening over the impact zone.

-The tree blue lines you can see in the above image are nothing but intrusion points I had defined using spring (2Nodes). Also, set up the Time History request for the output of these intrusions.

Model Checker

-Now is time to RUN the Model checker, so we can identify any hidden error in this huge model. For that in

Hypercrash --> Quality --> Model checker-->RUN

Radioss --> Tools --> Model Checker --> Radioss Block

-I don't find any errors in this model but some warnings are there. All the Warnings are not harmful but the Error should be taken care of before proceeding towards the Analysis. Out of All the warnings I had got The last two may cause some issue so I had deleted that Unused GRNOD and Surfs. The others are acceptable and we don't have to worry about them as they won't affect my simulation.

- I had set up the RUN time to 80ms and time step 0.001ms.

-After done with all the changes and condition definition I had Exported the file and open it in Radioss. go through all the parameters again and RUN the simulation for 80ms.

ENGINE OUTPUT FILE

-As per the Standard Energy Error should be between +5 to -15 %. and the -ve sing indicated energy dissipation, and you can see the Energy error we are getting at the end of the simulation is -1.1% which is good and acceptable. In the intermediate, this Energy error reaches the +0.0%, which means energy is added to the system and after some time again starts to decrease. This indicates a stable simultaion.

-The Imposed time step which was 0.001 is larger than the nodal time step inside the Engine out file (0.00021) to compensate that the mass is added on the nodes and registered as MAss error. As per the standard mass error must be less than 1% and during our simulation its 0.0089% which is a good indicator of stable simulation.

-The Total simulation time I had noticed was 1hr 16min and 23 sec.

ANIMATION RESULT

1) Von Mises stress development over the body

-As you can see in the above animation result Max Von misses stress developed inside the body is 0.34GPa. This result also shows that the body is badly deforming due to the impact, In a real-life situation, you can't find a deformation like this. The main reason for this deformation is that Nos. of intermediate components and sub-assemblies are missing here, so the animation /simulation not behaving as a real-life scenario.

2)Displacement contour animation

3)Intrusion points Behavior.

-As you can see in the animation as well as in the above image the intrusion is happening all the set intrusion points. All points are displaced as the animation moved forward. The first image is showing the starting animation frame where you can see the initial values at every point. The second image representing the last frame in the simulation and you can clearly see the new displacement values achieve by intrusion points.

Animation Result over the Inner BEAM SECTION

- In the above simulation keep your eye on the inner side of the door. BEAM inside the rear door undergoes massive deformation. there is very less force experienced at the front BEAM. the impact has happened over the B-pillar section. If the impact happened a little bit of the front or rear side than there is a chance that the BEAMS will be helpful to damping that.

PLOTTED RESULT FROM HYPERGRAPH WORKBENCH

1) Energy Plot

-As you noticed in the plot the increase and decrease in the Internal Energy and Kinetic Energy respectively is linear, which means that all the KE absorbed by the system is converted into IE. So the behavior is satisfying the Law of Conservation of Energy which is a good indication. You can find here the steady total energy plot. The contact energy is also noted here but it's very small.

2) Sectional force in the cross member

-As we can see in the plot the max force is traveled through the cross member -A from the start of the impact to the very END. The cross member -B is also experiencing the impact force but less as compared to cross member -B.

If you compare it with the Animation results we get than you noticed that the even though the large amount of force experienced by the Cross member-A the deformation is very less as for Cross-member -B it is deforming very badly with the less amount of forces as compared to cross member -A. The reason may be the structural stiffness or material property. There is one support element (support part) at the bottom side of the cross-section-A, which is providing this strength to it against the deformation. you can see this part in the "Check for Connectivity" section in this report.

3) Intrusion points Results Plot

-Here you can see the displacement happen of the Intrusion points. I have verified this result by comparing it with the animation results

-Intrusion B-pillar is 226.78 mm

-Intrusion at Hinge is 492.56 mm

-Intrusion at Fuel tank Region is 581.16 mm

-Intrusion B-pillar is 334.43 mm

-From the result, we can conclude that the max displacement happens near the Fuel Tank and it's not good at all. In a real-world scenario if this sort of deformation ever happens it, will puncher, the fuel tank and may cause an explosion also as it's deforming very badly. The missing parts in the model may be the cause of this result but for safety, we can increase the strength of the support element near the Fuel tank region (By changing the material or by adding a small support bracket over that region), We can also introduce a cross member over there to absorb the impact force.

4)Peak velocity of the inner node of the door.

-This plot helps to understand, with how much the actual inner side of the door moves in the direction of the Driver during the pole impact.

-The peak Velocity measure at the inner door point is 15.84mm/ms2 at 18.50ms. after that, the speed is starting to reduce to a great extend.

CONCLUSION

-After reviewing the Starter & Engine Output file and the Animation as well as Plot data result I can conclude that the simulation is pretty stable but the data is not accurate due to the missing components and assemblies. But still enough to conclude that Cross-members A and B are playing important role in the Impact force absorption. So improving the cross member material or adding some extra support element near the cross member can improve there performance, Also for the Fuel tank side as we discuss earlier need some reinforcement.

-We can also work on the B-pillar property improvement as it's the 1st part whos comes in the contact with the force during the impact. The changes I am suggesting can be implemented by either improving material or the strengthening elements or joints.