Assignment 7-Side Pole Crash Simulation Challenge

# Assignment 7

Side Pole Crash Analysis on BIW Model

Aim: To create a deck setup for SIDE POLE CRASH OF BIW model and request for TH (Time History file), and by observing the simulation give suggestion for what can help for reducing fuel tank intrusion.

Objectives:

The objective of this project is to find-out the various outcomes as shown below

• Sectional Forces in the crossmember.

• Intrusion at B-Pillar, Hinge-Pillar, fuel tank region, Provide, recommendation what can help to reduce Fuel tank Intrusion.

• Peak velocity of Inner node of the Door.

Things need to be taken care off:

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

• Create appropriate interface friction 0.2 and recommended parameters.

• Make sure of no penetration and intersection, correct rigid body if any issue.

• Create rigid wall with friction 1.0

• Add mass to reach target weight of 700kg while getting CG about the required range.

• Initial Velocity = 20mph as per FMVSS standards.

• Time step 0.5 to 0.1 microseconds.

• Run time 80ms

Theory:

A crash Test for Vehicle safety is a type of destructive testing undertaken to ensure that standards for safe design with regards to crash compatibility and crashworthiness are followed for different Transport modes.

Crashworthiness is the ability of vehicle to safe or protects its occupant, Occupant protection can be achieved by ability of vehicle to absorb crash energy by controlled vehicle deformation.

Type of Crash Tested:

There are majorly three types of crash named as frontal, side and roof crash.

Side crash:

Side crashes account for the second highest frequency of death and serious injuries compared to frontal impact, there is very little space inside the vehicle interior in which to absorb energy and severe injuries to the Head and chest are common.

Side Impact Protection

Due to the virtually non-existent deformation zones on the side of car, occupants are particularly vulnerable in a side crash. Since the bodywork at this point offers, unlike the front and rear sections, very little scope of absorbing energy by means of crumple zone, the sides must be needed to design with maximum stability, so that passenger side will deform as little as possible. SEAT uses different protective mechanism in the side of the car, which sustainably reduces the risk of injury.

• Side impact bars increase the rigidity of the Doors and distribute the energy in the event of a side-on-crash.

• Large door overlaps with columns increases the deformation strength. The forces that occur in the event of a crash can therefore be better absorbed into the floor and the roof.

• Stable A, B and C columns

Side Mobile barrier crash

Source: IIHS

Some side impacts involve a vehicle travelling sideways into rigid roadside objects such as trees or poles. Often this is the result of a loss of control on the part of the driver, owing to speeding, misjudgement of a corner or because of a skid in slippery conditions. Such accidents are severe and the frequency of death or serious injury is high.

SOME SIDE IMPACTS INVOLVE A VEHICLE TRAVELLING SIDEWAYS INTO RIGID ROADSIDE OBJECTS SUCH AS TREES OR POLES.

In Euro NCAP’s test, a car is propelled sideways at 32 km/h against a rigid, narrow pole. The car is placed at right angles to the direction of motion, or as is done from 2015 onwards, at a small angle away from the perpendicular. Where a vehicle is equipped with a centre airbag to protect against the front seat occupants hitting each other, two average male side impact dummies are placed in the front seats. Where there is no centre airbag, single dummy is placed on the driver’s seat.

BIW terminologies:

Side Door

Procedure:

1. Import the file by using import option in Hyper-mesh.

Extracted BIW component of the car (NEON SIDE)

2. SETUP for the Side Pole crash

• Check unit system and either follow [Mg mm s], [Kg mm ms].

To check unit system either we can open the 0000.rad file (Starter file) in notepad or either we can check the imported units in BEGIN-card.

Checking unit system in BEGIN_CARD

• Create appropriate interface, friction 0.2 and recommended parameters.

Here we have to create the interface as self-contact interface (TYPE7) for all the model, Here we have already previously created interfaces, we can’t use them because in the above model some parts are missing and it cause and confusion to solver that’s why we can’t use these interfaces, we simply delete them, after deleting the interface we create the Type 7 interface as self-contact interface with recommended parameters.

Recommended Parameters for TYPE7 interface

• To create an interface, go to solver browser right click and create interface and select as TYPE 7, define the slave nodes and master elements. Along with that set the recommended parameters which is suitable for crash application.

Defining Recommended parameters

TYPE7 Interface has been created

• Make sure of no penetration and intersection, connect rigid body if any issue.

To check penetration, we can use both Hyper-mesh and Hyper-crash, Hyper-crash are more sophisticated than Hyper-mesh, so we are using Hyper-crash to check penetration, also we can simply check in the Hyper-mesh as well.

To check Penetration and Intersection in Hyper-mesh go to Tool >> Penetration check, if any penetration occurs use auto penetration fix option to fix the penetration.

No Penetration found

There are no issue present in the model and also there is no issue with the rigid bodies, but there are some where connections are missing, we have to create the connections in that region.

• Create Rigid wall (Cylindrical rigid wall) with friction 0.1.

To create rigid wall, go to Solver >> Create >> R-wall >> cylinder, define the sliding friction value and give search distance of 1000.

..

Defining a node at B-Pillar region

Here as you see the rigid wall is intersecting with BIW structure of car, we have to remove them, for that we have to change the distance in the Y direction.

Defining a parameter for Rigid wall (Cylindrical

Defining Cylindrical rigid wall / Consider as Pole

• Mass Balancing and Added mass to reach target weight 700 kg while getting CG about the required range.

• To add mass, go to Solver >> Create >> Add mass

• Here we have to distribute the mass in such a way that our COG will lie at proper location and the overall weight should be we equal to 700 kg.

Adding mass at the desired locations

Position of COG with overall weight 700Kg

• Initial velocity 35mph

Now we have to create the initial velocity in the Hyper-mesh, for that go to Solver >> create Boundary condition >> INVEL, in order to move car towards rigid wall we are defining the initial velocity to it, we have given initial velocity of 20mph, but we have to convert it into the mm/ms which is equal to 8.9 mm/ms. We have to define it in a Side pole direction.

Defining a Parameters for Initial Velocity

Initial velocity is defined properly

• 0Time step: 0.5 to 0.1ms

Input run time is 80ms that is the simulation time, for run in the engine card ENG_RUN, Time step defaults for all element which is 0.003ms (Solver >> create >> DT) DT is the time step of simulation, Here, to control the Time step ENG_DT_BRICK, ENG_DT_INTER, ENG_DT_NODA is already defined, with CST option which is constant time step during simulation by adding some mass.

ENG_DT_NODA is defined

Output Request:

• Sectional Forces in the crossmember.

• Intrusion at B-Pillar, Hinge-Pillar, fuel tank region, Provide, recommendation what can help to reduce Fuel tank Intrusion.

• Peak velocity of Inner node of the Door.

• Sectional Forces in the cross-member:

• To create section first we have to create the frames (Moving frames)

FRAME: Frame is type of reference co-ordinate system where the quantities defined follow its own origin. Here, unlike the moving skew, the moving frame is attached with the nodes which is selected as origin. calculates the motion of the body relative to frame defined. Frames are used only in notable option like imposed velocity, imposed displacement, TH/node etc.

To create frame, go to solver >> Frame >> Mov frame

define the origin node and then define the z axis with second node which is in the direction of crash and the define the third node for plane.

Defining a node to create frame

• After creating the frame, now we can create the Sections around the parts so that we can know the forces receive by that section. So, to create the section go to Solver Browser >> Create >> SECT, here we have to define the frame and also we have to define the nodes and elements to create a section.

Creating a section at the cross-member

Here we create the section at both the cross-member and also, we create one more section at the Roof Rail.

• Now we have to be measures Intrusion on the Side Door / Hinge Joint / Fuel tank region.

To measure intrusion, we create the spring among the nodes and then do calculation that how much spring displaced, this is equal to the intrusion of the door or Hinge, kindly make sure that spring weight should be very small and also stiffness of spring also needs to take small.

After creating the spring, we also need to be create the Spring property and then we need to define it to the springs that we created to measure intrusion.

Defining a Property for the spring

Springs are created on the Hinge-Pillar, B-Pillar and also region near to the Fuel tank.

• Peak velocity on the Inner-node of the Door

To find the Peak velocity simply we request for the TH of the node in output block with default results, so that it should show all the default results that are associated with the nodes, or simply you can define one particular desired result that you want.

For that go to Output Block >> Create >> TH >> define a node for which you want to extract the result.

Defining a node

• After defining all of those things, our job is not yet done, we need to extract the results from the Sections and Springs.

Here we have to define the output blocks. In the output block there is previously created Blocks, we don’t need that so we delete it,

Now to define the section in output block, create the new output block and define the Entity id by cross-section and then select all the Sections that we created, and then click ok to define it.

INVEL = 8.9 mm/ms

Defining Sections for the result in Output Block

In similar manner we have to define the result for Spring and also need to define a Output block for R-wall as well.

• After defining all the output-blocks, we can check whether there is any error present in the model or not, for that we can either use Model checker or either we can do a Dry run, by setting the Stop time to 0ms, Here by this there is no generation of any Animation and Time history file.

Here we have no errors but some warning found on Model checker, warning doesn't hurts a lot, but if you don't know about the issue behinds these warning, don't play with them otherwise it will ruin your result.

DRY-RUN

• After a Dry run we got 0 Errors, but it shows us some warning, we can neglect that warning, also it shows us Normal Termination at the end of the Simulation which indicates that our simulation is run without any error.

Deck is setup properly for Side Pole crash

• Now we can run the simulation, for that go to Analysis panel >> RADIOSS >> select the input file >> save it in different folder and name it >> Run, also setting the -nt 3, whereas nt is number of threads or number of cores used to solve the problem is 3.

• After completing the simulation, the RADIOSS will popup a solver window stating RADIOSS job completed, which indicates simulation has been finished, also showing the total number of cycle and Elapsed time, means time required to solve the problem.

End of solver Output

To check the value of Energy error and Mass error, open the 0001.out file in Note pad

Energy Error:

• If energy error is negative, it means some energy is dissipated. This dissipation can be of any type for example in case of under-integrated elements, the Hourglass energy can explain a negative energy error since it is not counted in the energy balance. The acceptable amount of Hourglass energy is about 10-15%
• If energy error is positive there is energy creation. In case of QEPH elements the solution is calculated accurately as there is no hourglass energy is produced. A positive energy error of 1-2% is acceptable.
• If energy error is -99% the computation has diverged, this happen due to false energy balance that is created due to improper model definition.

Mass Error:

• Non Zero value of mass error is printed because of mass added to meet specific time step

Mass Balancing: Mass of whole model needs to be consistent throughout the model simulation. There shouldn't be any change in the mass, we need to be carefully and need to checked where it will be coming from, when we try to control the time step we allow some certain type of mass addition, If we added mass then mass is going to increase, and make sure that mass variation should be smaller than 1%.

If mass variation is b/w 1 to 3%, you have to check if nodes with added mass are moving or not. if this is the case then added mass will result in increase in kinetic energy. So for more than 3% of variation in mass results are probably bad.

Both Energy error and Mass error is in acceptable range.

Mass error is occur because of mass addition to make the Time-step constant.

• After that we need to visualize it. For that we need to switch to the Hyper-view utility, in hyper-view we need to import the h3d file that was generated during solving. Now to display the result we need to select the result plot we required, here we check von-misses contour by selecting Global variable as Von-misses, and here we use averaging method as simple to visualize the result.

Von-Misses stress contour plot

• To plot the graph, we need to switch to the Hypergraph 2D. we can switch to it using the same client selector option in toolbar, also in single window we can split it into number of windows, where we can plot the different plots. To plot the graph, we required the T01 file to upload to see the graphs. This file is available in same directory where we have .out files, h3d files, here we can plot different graphs like Rigid wall forces, Internal energy, Kinetic energy, Hourglass energy, Total energy to compare and visualize the result.

Overall Results

Graph 1.0 this shows the Internal energy / Kinetic energy / Hourglass energy / contact energy / Total energy

• Initially Internal energy is Zero, as simulation time increases, it increases with time until the crash complete, as you see here the Kinetic energy is high at initial, and decreasing with time, this is because kinetic energy is directly proprtional to velocity, so kinetic energy is maximum at initial stage, and with time Kinetic energy is lossed because the energy is absorbed during deformation, and this is nothing but the internal energy (du = q /w), which is increasing with time as the deformation goes on increasing, and it stop increasing when the deformation stops,(Kinetic energy becomes 0).

• Total Energy = Internal energy + Kinetic energy + External work, Here Total energy is not depending upon external work because there is no any force actiong on the car BIW , only the car is moving with the initial velocity, with time Internal energy increasing, and kinetic energy is decreasing in same path, so the Total energy remains almost constant, there is small decrease in TE because of contact energy, which is nothing but energy acting opposite to system to prevent penetration acting on the system due to applied velocity.

Here both Hourglass energy and Contact energy is less than 15% of Total energy, which is good. So Here we want that structure need to absorb energy, But the problem is that we don't have enough structure to absorb energty, and we don't allow the structure to deform much, because high intrusion cause the more chances of injuries to the passenger, because here overall passenger cabin is striking with pole or deformable barrier, so we want our passenger cabin to intact don't deform much.

RIGID WALL FORCES:

Here as we see the rigidwall forces is maximum initially, at 5.50ms the reaction force or rigidwall force is about 40.02KN, because initially the structure is intact and with time the rigidwall forces declines as the structure or side pillar is going to deform,

Sectional Forces:

Total resultant force of Floor crossmember (Front), at time = 17.5ms the Total resultant force = 4.71KN

Total resultant force of Floor crossmember (Rear), at time = 39.0ms the Total resultant force = 3.60 KN

Total resultant force at Roof Rail, at time = 18ms the total resultant force is 0.7KN

The total resultant forces or normal forces that pass through the roof rail is low because instead of transfering force it simply bend or buckled, and not able to transmit that force to other side of pillars. also the Base or Floor cross-member is not able to take or transfer large amount of forces, because it also buckle during crash, and there is progressive deformation in these cross-members, that will lead to large intrusion toward passenger cabin.

Intrusion at B-Pillar, Hinge-Pillar, fuel tank region

Intrusion at RockerPillar=307.35mm

Intrusion at fuel tank region = 276.25mm

Intrusion at B-Pillar = 185.3mm

Intrusion at Hinge-Pillar = 86.51mm

Peak Velocity of Node and Inner side of door

Resultant velocity of node at inner side of door

• As body is moving with some initial velocity the node is also having some initial velocity, when the body impact with pole the velocity reduces and node velocity strat decreasing at arround 8ms.

Recomendation for Reducing Fuel tank Intrusions:

Side crashes account for the second highest frequency of death and serious injuries compared to frontal impact, there is very little space inside the vehicle interior in which to absorb energy and severe injuries to the Head and chest are common.

During side Impact, the door comes first in contact with the hitting vehicle and pole or may be tree. As the space available between the occupant inside the vehicle is limitted and there is no space for energy absorption as compared to front end collision, Therfore Design of Side impact beam inside the door should be such that it sustain high load or transfer high load or forces with smaller displacement. An anti-intrusion bar or beam is a saftey device, installed in most of cars and other ground vehicles, which must protect the passenger from side impacts.

• The location of Impact is very close to Passenger, and there might be chances of high fatal injuries to the occupant that is sit inside the car.

• In side impact collision some time the impacting vehicle may be large trailers , Tree (consider as rigid), so at that situation there is high chances of injuries because of large deformation or intrusion in the car.

The role of Anti-intrusion bar is to absorb kinetic energy of the colliding vehicle and convert partially into internal work of the members involved in crash, Therefore increasing the side door strength by adding more anti-intrusion bar, we can reduce the overall amount of intrusion.

But as we see in the simulation our Cross-members and roof rail is going to bend / Buckled during the crash, due to this the overall structure of passenger cabin is deformed a lot, so we have to increase the stength of the both roof rails and cross-members so that it transfer all the forces to other members without much having large deformation, by this we can overall protect or we can overall reduce the intrusion and deformation of Passenger or Occupant cabin.

To reduce the Fuel Tank intrusion we can add one more cross-member nearer to fuel tank, or either we can design a cross-member in such a way that it can't buckle during side crash and maintain the stability during crash.

Also to reduce the chances of injuries, vehicle needs to equiped with Center airbags and Side airbags to reduces the impact and protects the Occupant Heads during crash.

Conclusion:

This is a very severe test of a car’s ability to protect the driver’s head. As the loading on the car is so localised, that deformation can be very high and the pole can penetrate deeply into the passenger compartment. Without effective protection, the pole would strike the head resulting in serious injuries. Head protection airbags – often curtain airbags mounted above the side windows but sometimes seat-mounted thorax/head airbags – have become a common solution but great care is needed to ensure effective performance of such devices.

Learning Outcomes:

• Understanding about the overall deck setup for Side pole crash analysis on BIW model.

• Understanding about the Side crash and why it need to tested.

• Understanding abou various saftey aspect that is related to Side Crash.