Assignment 7-Side Pole Crash Simulation Challenge

#16 // Assignment 7- Side Pole Crash Simulation Challenge.

AIM: Side Pole Crash Simulation of Dodge Neon BIW using RADIOSS solver and Pre-processing using HyperMesh / HyperCrash.

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 out on the deformation and the forces created as a result of the crash Neon side crash- BIW.

Neon side crash -BIW

• 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.
• Initial velocity - 20mph, as per the standards.
• Use model checker to ensure good quality.
• Timestep:0.5 to 0.1 microseconds.
• Run 80ms.

Output requests:

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

INTRODUCTION:

• Assume that you tried to steer your car at high speed at turning but the speed was enough to outwit the Tires’ resisting force and you hit the rigid cylindrical object like a tree. So, in this and many other cases like a side car accident, slipping on a snowflake, etc. can cause damage to the passenger if the car is not designed with great care. This is where the side-impact standard comes into the role. The standard has been devised by a standard makers like FMVSS (214, 201), EURO NCAP, US NCAP, and IIHS. Again, for this project, the car with the simplified model is taken for analysis purposes. The model is prepared following the guidelines suggested by the FMVSS 214 standard. The analysis is executed to check the intrusion made inside the car, intrusion inside the fuel tank (for hybrid electric vehicles, battery-package system, which is more dangerous), and how much the B pillar is affected.
• According to the standard, relative displacement (intrusion) must be small before the inflation of the airbag. Indeed, the strength of the B pillar and other surrounding structures should be high enough to bear the impact force and should not deform at least for a small duration of time. The major component which is going to play a major role in this impact is the B pillar, rocker, Door outer, Door beam, Door support, roof rail, roof bow, front header, and cross rail. So, let our discussion start from the preparation of the model, and simulation to the analysis of the result and validation.
• In different parts of the world, there are several vehicle safety assessment programs that perform a crash test in order to increase vehicle safety and ensure that vehicle has good occupant and pedestrians safety. These programs focus on improving the crashworthiness of motor passenger vehicles and reducing the number of injuries. In Europe, there is the New Car Assessment Program (NCAP), based on the program introduced in 1979 by the NHTSA (National Highway Traffic Safety Administration) in the USA. the Euro NCAP frontal crash test standards are followed in India.

Going through the FMVSS standards: https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/tp214p-01.pdf

• Here in this simulation, we are going to take the angle of inclination as 90 degrees instead of 75 degrees and the initial velocity as 20 mph as per the given, requirements.

Load path for the side impact ->

PROCEDURE:

• Check for Unit system.
• Import model in HYPERCRASH.
• Check for penetration and intersection.
• Add masses to reach a target weight of 700kg.
• Export changes file and import in HYPERMESH.
• Create Self Interface contact.
• Create a rigid wall.
• Add Initial velocity to the model.
• Create cross-sections to find sectional forces on the cross members.
• Create springs to check intrusion in different positions.
• Assign property to springs.
• Create TH for section forces, intrusion springs, interface contacts.
• Create cards.
• Run Model checker and correct errors if any.
• Run the Analysis.

1. Import the Model

• First, we will import “0000.rad” starter file of the model which is named neon_side_reduced_0000.rad in Radioss using the Import Solver Deck option.

> Reduced Model for Side Crash Analysis…

2. CHECK FOR UNIT SYSTEM:

• Now in order to check the unit system of the model. we can go Model browser, and in Cards, check BEGIN_CARD or we can just open the Neon_front_0000.rad in a notepad, where we will be able to check the units.

• So, for this model, we will see that the unit system followed is [kg mm ms].
• 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.
• Go to Application > Hypercrash > Select the unit system > open.

• Select the Neon starter file and drag it to the hyper crash application to open the model.

3. CHECK FOR PENETRATION AND INTERSECTION:

• Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that pass completely through one another. All models and especially impact models should be checked for penetrations and intersections and De penetrated to ensure the integrity of the model. Penetrations adversely affect results and should be removed.
• To check penetration and intersection, Go to Quality > Check all solver contact interfaces > Select parts > Click on check penetration.

> In HyperWorks..

> In HyperCrash..

• As you can see in the image below there are no penetrations or intersections present in the model.

4. Compare the model weight with the full-scale 300k nodes model and use added masses to reach a target weight of 700kg while getting CG about the required range:

• A vehicle’s center of gravity, or CG, is the theoretical point where the sum of all the masses of each of its individual components effectively acts. In other words, from a physics perspective, a vehicle behaves as if its entire weight resides at this one point. Carrying weight up high, such as a panoramic sunroof will raise a vehicle’s CG while placing heavy subsystems low in a vehicle, such as a battery pack, will work to lower it. Lower is better from a handling standpoint, as it reduces weight transfer during cornering and braking, and it also reduces the propensity to roll over.

Add Masses ->

• Mass balancing: In order to maintain the CG of a car we have to add mass for the given components, In the given model there are so many parts are missing because of the node limits in the student version
• To check the CG, Go to Menu > Mass > Balancing > Show CG point.

> Initial Position of COG ->

Current weight: 166 kg

Target weight: 700 Kg

• In order to bring CG to our required position, the masses should be added to the nodes.
• For adding the masses, "Added mass" option in the Loadcase is chosen as shown in fig,

• After selecting that, by right-clicking on the Mass browser select Create New. In that, Type 1 is selected.
• In order to distribute the given mass to each node of the node group selected.
• then we added mass to different components as shown in the table below in the BIW structure in order to obtain the required mass of 700 kg and to place CG at the required location.

• Now, we added mass to different components in the BIW structure in order to obtain the required mass of 700 kg and to place CG at the required location.

• // Now export the radios file from Hypercrash and import it into HyperMesh to do the rest of the case setup. //

/ OR, In HyperWorks_Radioss, We also do the same add mass process like,

> First we check the initial mass of the model & initial COG of it.

• Opening mass summary -
  Go to Menu bar > tools > mass details > mass, cog, inertia.
  We can see that the mass is less as it should be around 700 kg.

Also, the position of COG is currently closer to the dashboard region whereas it should be near to the driver seat region.

Now to shift the COG to the desired area, some masses are added to the rear part.

The added mass will account for the fuel tank, passengers’ weight, additional luggage load, etc.

• To Add mass, ADMAS option is used under the solver browser,
• Go to Create > ADMAS.

• STEP 3: Adding mass to increase the overall weight of the car.
  Go to Solver browser > ADMAS > create > extra mass > give GRNODE ID > give mass value.

/ Note- right click on "grnd_ID" to create GRNOD, then select nodes under "Entity IDs" & proceed. I select "Mass type" as "1. Mass/N is added to each node of node group". So, I simply add 535kg to make it a 700kg target weight. /

Then, the mass and COG is checked in Hypermesh. To view the COG position, a point is created with the obtained COG coordinates.

Hence the mass is corrected to 700kg to represent a real-life mass of a vehicle, and also the position of COG is now relocated to the desired position.

5. Defining Initial Velocity:

To define an initial velocity of 20mph (8.9408 mm/ms) under the solver browser:

The required velocity is 20 mph but the units are in mm/ms, which would be 8.9408 mm/ms. and the vehicle is moving along the y-axis, so this value will be entered in [Vy] Y Velocity. All other velocity values would be 0.

Go to Create > Boundary Conditions > INIVEL.

/Note- right click on "grnd_ID" to create GRNOD, then select nodes under "Entity IDs" & (all Components) proceed. /

6. Create Contact Interfaces:

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

• For this model, we will create Type 7 interface for all the components of the model as it is self-impacting or the nodes and elements of the model will have contact between them. Interface TYPE7 is a multi-usage impact interface, modelling contact between a master surface and a group of slave nodes. It is also possible to consider heat transfer and heat friction.
• We will go to the Solver browser and we will delete all the existing interfaces.
• Now to create a new contact, go to model browser > Right-click > Create > INTER > TYPE7 > Rename as Self contact > Select slave node and master components > Enter Type 7 recommended properties.

>Review->

7. CREATE A CYLINDRICAL RIGID WALL:

• To create a cylindrical rigid wall at the left side of the car, we will need the outermost node at the front left door of the car. So, we will create the outermost node on the element edge using temp nodes Then we will right-click in the solver browser and navigate to Create > RWALL > CYL.
• In the RWALL panel, under Engineering data will specify the coordinates of the pole which will be at some distance from the outermost node on the side door. Then we will give the normal direction to the pole in the Z-axis and the diameter of the pole to be 254 mm. The FRIC value will be “0.1” and Dsearch value will be 1000 as shown below.

> Properties of Rigidwall..

8. Create Time-step: 0.5 to 0.1 microseconds. ->
   CASE_1 -> Go to Model browser > Cards > ENG_ANIM_DT > Tfreq = 5.0

CASE_2 -> Go to Model browser > Cards > ENG_DT_NODA > Tmin = 5.0/1000 = 0.0005 // (> Tscale=0.9)

> Timestep Control:

// NOTE- we convert the Time-step value 0.5 microseconds to 0.5 / 1000 = 0.0005 ms. & Put it in Tmin. /

9. Running 80 ms. ->
   Go to Model browser > Cards > ENG_RUN > Tstop= 80.0

10. Output requests: ->

• 1// Sectional force in the cross member.

1. Creating Cross Section –

• The results which we want on required cross-sectional parts will be calculated based on a frame of reference. So before creating a cross-section, we will create moving frames on a particular node of that section. Now as we must create the moving frames which are also called as local axis, we must perfectly align our local axis to the global axis.
• Now we can create a moving frame using these nodes. In the Solver browser, we will right-click and navigate to Create > FRAME > MOV. So here, we will create frame by node reference and select the nodes for z-axis and yz plane and then click on create.

• Thus, a moving frame will be created. Now we will create a cross-section for this frame. To create a cross-section, we will right-click on the Solver browser and navigate to Create > SECT > SECT. In the section panel, we will specify the Frame_ID & node_ID 1/2/3 as N1, N2, and N3 as the moving frame. We right-click and create grshel_id, then we will select the elements where we want the cross-sectional results.

• 2// Intrusion at B pillar, hinge pillar, and fuel tank region. Provide recommendations on what can help to reduce Fuel tank intrusion.

1. To Measure Intrusions –

• Here, we need to find the intrusions at B-pillar, hinge pillar, and fuel tank. So, to find the results at the specified parts, we need to create a spring between the left and right parts of the B-piller, Hinge-piller, and fuel tank, for creating spring go to 1D > SPRINGS > SPRING2 and select 2 nodes as shown in the figure below.

> Spring created as shown in the figure below,

• Now we have to create a property card for spring and assign it to the spring element created
• Go to model Browser > Create > Property > Rename as Intrusion Springs.
• After creating a property, a new tab will open there we have to select CARD image as P4 SPRING and Mass as 0.0001, and Stiffness (K) as 0.001
• And Then assigned the property & materials (here I select default one 'M2_PLAS_JHONS') card to the component card for Intrusion Spring.

• 3// Peak velocity of an inner node of the door.

1. Peak velocity of an inner node of the door –

• To find the peak velocity at the inner node of the door, we will create a moving frame at the node location by using right-clicking on solver browser > create > skew > MOV.

• select the required node as the origin node then select a node to define the x-axis and XY-plane. as shown in the figure below,

REQUESTING TH (Time History files) FOR INTRUSION SPRINGS, PEAK VELOCITY NODE, SECTION FORCE:

output files requested are as shown in the table below,

MODEL CHECKER:

Finally, before carrying out the RADIOSS analysis, an error check was run on the file through HyperWorks. The model check tool can be accessed through

Tools > Model Checker > RadiossBlock > Run from the upper toolbar. (fix if any errors are there manually)

RUNNING THE ANALYSIS IN RADIOSS ->

In 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.

Or we can analyze through ‘Altair Compute Console View’ after the simulation is completed.

As we can see, the energy error is -1.5%. It is definitely acceptable due to its proximity to 0% error. In addition to that, the mass error is 0.3457E-05 to 0.4245E-05, which is very less and acceptable.

SIMULATION ANIMATION ->

• To view the simulation, we can switch to Hyperview through the client selector.
• Or, in Console Solver view results we directly open Hyperview.

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:

> Displacement contour plot-

In the above crash simulation of the vehicle, we can see the vehicle BIW is impacting a Pole. After the impact, the frame of the vehicle deforms and the vehicle body gets contracted around the pole with the left B-Pillar as the pivot point. The CG of the vehicle is in the same axis or direction of the pole, so we can see even deformation of the frame around the pole.

> Von Mises stress contour plot-

From the Von Mises stress plot, we can say that the stress distribution is quite good in the vehicle after the crash. There are very few areas where we can see stress concentration. Generally, the stress is more in B-pillar and cross members as B-pillar takes the initial impact, and then the impact is transferred to the cross members.

From the simulation, we can see that initially, the car is hitting the R-wall cylinder with a velocity of 20mph, while the first impact is with B-Pillar then the forces going to transferred to the left and right and front direction in the roof rail and cross members in the bottom as shown in below figure. In each stage, the transfer of force is going to reduce because energy absorbed by the components.

GENERATING OUTPUT PLOTS ->

• After generating the simulation, we can then go ahead and generate the plots. Using the same client selector, we can switch to Hypergraph 2D. In the Hypergraph client, we need to import time history file‘T01’ 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.

Global Variable – Energies -

• The changes in kinetic and internal energies occur at the exact moment the BIW contacts 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, deformations also occur.

Contact Energy Graph –

• Contact energy is a type of energy that is formed when one element meets the other or neighboring elements. The opposing force created by this element forms the contact energy. In this case, it takes off after 17 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.
• From the above graph, we can see that the Hourglass energy is almost negligible since we have used Improved integrated element formulation (QEPH).

Rigid Wall Forces -

Take a look at the rigid wall forces generated:

• As it can be seen in the starting, the rigid wall force generated is zero till 15 ms of simulation because of no contact, but at 19.5 ms there is a peak rise in the wall forces to a value of 35.27KN which is the point another first impact, Then rigid wall force decreases.

Sectional force on Cross-member –

• Cross-members are very crucial in the side-impact analysis as these components prevent the body to shrink or deform inward. When the car hits the rigid body maximum amount of forces will pass through the cross member of the base and roof. This component along with the door bar and support, door outer, B pillar, and rocker are also involved in the majority to prevent deformation. But the forces acting on every other component eventually pass from the cross member.
• The max sectional force at the B-pillar cross member (C2) is 2.5 KN at 38.5 ms and for the driver seat cross member (C1) it is 8.29 KN at 39 ms.

Peak velocity at Inner Door -

• As we all know that when the car hits the pole 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 9.8 mm/ms at 20 ms. The velocity of the node is almost constant before hitting the rigid cylindrical wall (up to 16.5 ms). 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.

Intrusion inside the car at B pillar, hinge pillar, and fuel tank –

• The intrusion or deformation of the component can harm the occupants and the inner part of the car like a fuel tank. From the above plot, it is obvious that intrusion near the Hinge Spring (A-Pillar) is 75mm which is substantial and at the fuel tank it is around 144 mm, at the B pillar it is 287 mm which may damage the cabin, and the passengers inside.
• The A-Pillar spring received the least displacement than B_Pillar & Fuel tank. Admirably, the B-Pillar was able to absorb a lot of the impact because the COG and the pole are sides by side for B-pillar.

CONCLUSIONs:

The overall objective of this project was to simulate a Side Pole Crash and validate the results of the simulations obtained from the crash test. The simulation was performed using the Radioss software package.

• All the required graphical results are obtained and discussed
• Due to the limited number of nodes in the student version some of the BIW, engine blocks, suspension system, etc are removed, so results are not as in real condition.
• From all the results we can say that the cabin is mostly deformed which is not acceptable. We can prevent this by providing additional cross-members at the top and bottom.