Assignment 6-Frontal Crash Simulation Challenge

Project 1 : Frontal crash simulation with given BIW frame in RADIOSS

 

Aim :-  To perform a frontal crash simulation with the given BIW frame in Radioss and request for outputs as mentioned in problem statement.

Software used :- Altair hyper-works student version 2020 and Hyper-Crash 2020

Problem statement :-

Frontal crash-BIW

• 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 penetrations and intersection.
• Correct rigid bodies if any issues.
• Create rigid wall with friction 0.1.
• Compare the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.
• Initial velocity 35 mph.
• Use model checker to ensure good quality.
• Time-step :0.5 to 0.1 microseconds.
• Run 80 ms.

Output requests:

• Sectional force in the rails at location of indicated node 174247.
• Axial force received on the rails from bumper.
• Shotgun cross sectional forces.
• A pillar cross section.
• Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
• Intrusions on the dash wall 66695,66244.

 

 

Introduction :- The model setup is a reduced version of a full car FE model for the frontal crash. There is a front bumper component which is meshed with solid elements along with a rail attached with it. There is a shotgun shaped component attached in the side portion of the BIW. There is also a suspension shock tower where the front suspension is mounted. Attached to the suspension shock tower is the side fender assembly. Following that, we have the A and B pillars along with connected roof lines and a floor panel. The floor panel has two cross members and two longitudinal members. 

Crash analysis is an integral part of safety analysis and is often completed at intersections and corridors. The crash analysis can help assess concerns and help determine potential improvement options. A Crash test is a form of destructive testing usually performed in order to ensure safe design standards.

New Car Assessment Program (NCAP):  

It is a government car safety program tasked with evaluating new automobile designs for performance against various safety threats.

Standard crash tests performed by NCAP:

1: Frontal offset testing (64 km/h proposed)

2.Side-impact testing

3.Pedestrian protection testing

4.Rear impact testing

5.Child dummy dynamic crash testing

 

FMVSS ( Federal Motor Vehicle safety standards)

Federal Motor Vehicle Safety Standards (FMVSS) are US federal Vehicle Regulations specifying design, construction, performance, and durability requirements for motor vehicles and regulated Automobile safety-related components, systems, and design features. They are the U.S. counterpart to the UN Regulations developed by the World Forum For Harmonization of Vehicle Regulations and recognized to a varying degree by most countries except the United States.

BIW (BODY IN WHITE)

Body in white (BIW) is the stage in Automobile Manufacturing in which a car body's frame has been joined together, that is before painting and before the motor, chassis sub-assemblies, or trim (glass, door locks/handles, seats, upholstery, electronics, etc.) have been integrated into the structure. Assembly involves different techniques such as Welding (spot, MIG/MAG), Riveting, clinching, bonding, and laser Brazing.

 

 

 

Solution :-

 

Step 1 :- Intersection and penetration checking :-

1. Before opening model check units for further results from starter input file.

 

2. 2. Import the given model "neon_front_0000" into Hypermesh. And open the same model "neon_front_0000” in Hypercrash as well with the unit system "Kg mm ms".

 

3. To check for penetrations in the model, we will go to Toolsmenu on Menu bar and click on Penetration Checkoption. In Penetration check panel, we will select all the components and click on Check command. The software will check for penetrations and then display the results as shown below,

There are no penetration or intersection error found.

Step 2: - Balancing COG: -

1. The BIW model doesn't consist of the exact weight of the vehicle so Additional mass should be added to the BIW model considering the weight of the Body after manufactures e.g. with the weight of the seats, the weight of the persons and all other weights in realistic condition.
2. For adding mass, three major types are used here,0 (Type 0 = Mass is added to each node of the node group, Type 1 = Mass is distributed to each node of the node group, Type 3 = Additional mass distributed on the part group)
3. The targeted weight is given 700kg where the actual mass before adding external weight is 180kg.
4. To Add the mass, Click on added mass, and to create a new object Select Type0 - Mass is distributed to each node of the node group, and click save
5. Check  COG, Simultaneously after giving the mass in the balancing menu.
6. Add mass according to the needs till the point reaches the centre and till the mass attains the target value. Below, image show that COG is present on required location i.e. under the driver seat.

 

Step 3: - Creating contact surfaces.

1. A contact interface should be defined to view the contact energy. Here the type-7 Contact is used (Node to Surface), because of its high accuracy and correct physical representation. The self-impact is defined in the Contact interface as the body acts as both master and Slave.
2.  Interface properties Changed to recommended conditions as per mentioned in problem statement and create another interface for bumper and rail contacts. which is shown in image below.

 

Step 4 : -  Rigid wall

1. Now we will be creating a rigid wall with friction 0.1. This can be done by right-clicking in the solver tab and creating a R-wall of the required type. For this frontal crash scenario, we are using a plane-type R-Wall.

Step 5 :- Initial velocity :-

1. The initial velocity is given as 35 mph which is converted into 15.6464 mm/ms as the solver follows this unit system.
2. The velocity is defined in the X-axis where the body should move in that direction. 

Step 6 :- Section creation. :-

1. The cross-section is created to observe the forces Distributed in various components such as Rails, Shotguns, and A-pillars.
2. The cross-section must be Created in such a way that the Normal force observed in the component should be opposite to the velocity Applied.
3. For creating a cross-section a new set is defined as A-pillar, Shotgun, and Rails.
4. Give the card image as Grshell and Select a set of elements in the entity id where the cross-section might be placed and click proceed.
5. Follow the same procedure for Shotgun and Rails.

      6. In The solver, area Create a new section by right-clicking > create > SECT.

      7. Create a Frame for each section created.

      8. Frame is created by right-clicking > create > FRAME > MOV

      9. Assign the frame system to the respective Cross-section and give the value of the nodes in the frame.

      10. Assign the set created in the model area in grshel_id

 

Step 7 :- Run model checker to ensure good quality

 

 

Step 8 :- Output request

1. Create accelerometer on rocker under B-piller for creating accelerometer click create > ACCEL in the Solver area and select a node.

     2. Create Intrusions on the dash wall at the node given 66695,66244

 

3. 3. Specify the time step = 0.0005 and time-frequency = 1.6 and runtime = 80ms.

 

4. Create TH for Rigid wall, nodes (Intrusion), contact interface, all sections and accelerometers as shown in image below.

 

 

RUN THE SIMULATION:

1. Click on the analysis panel in the Hyper mesh.
2. Save the model in the local directory.
3. Type -nt 4 in option and click on Radioss.

 

From Front_crash_0001.out file, the Total number of cycle was 159500. The energy error is -2.0% which is acceptable limit. The mass error is 0.01287% which also less than 5% it is acceptable. The run was “normal terminated’ which implies the processor successfully completed. There was no sudden changed in energy as well as in error. as shown below

 

Simulation in Hyperview:

Animation of the crash simulation is as follows:

Displacement contour plot :-

 

Von mises stress :-

 

the left side rail, shotgun and the bumper buckled heavily more than the right side of the vehicle symmetrically. The maximum von mises stress is built up on the rail component on both the sides because the normal force acting against the car motion in the bumper causes it to transfer all its force to the neighbouring component

Plots in Hyperview 2D :

                The plots like energy differences, displacements, velocity and the normal forces are analysed.

TOTAL ENERGY OF THE SYSTEM:

 

The internal energy and the kinetic energy curves are mirror images of each other. It is because the internal is gain during deformation is from the kinetic energy and conserve the energies. But it's seen that there is a drop in energy as the simulation progress, this is because of the loss of energy in the form of contact energy. The gain in contact energy is the same as the loss in total energy. The deformation increases the intersection of the shell elements and to avoid the intersection the contact energy is absorbed by the nodes which move out of the intersected shell. The hourglass energy is zero because of the shell formulation used in the model. QEPH shell formulation is used in this model which eliminates the hourglass effect in the shells during deformation.

When objects collide, contact forces transfer energy so as to change the objects' motions. When two objects interact, each one exerts a force on the other, and these forces can transfer energy between them. Fields contain energy that depends on the arrangement of the objects in the field. The max energy formed as 1300 KG-mm²/ms².

Acceleration Curves

• The accelerometer are placed at the bottom of the B pillar on rocker components
• In left side accelerometer the maximum accelerations is 348mm/ms2 at t= 1ms and then falls suddenly and goes decreasing further. This jerk is caused due to the impact of the car to rigid wall.
• In Right side accelerometer the maximum accelerations is 154m/s at t= 2ms and then falls suddenly and goes decreasing further.
• It observed that there are more jerk observed in left side than right side

Force received on created sections :-

1. Axial force received on the rails from bumper.

 

We have created type 7 contact between rails and bumper on both sides. So we get the axial force on the right side (Passenger side) higher as compare to the left side. The maximum axial force on the left side was 290 N and on the right side, it was 950 N. The total maximum force exerted on bumper is 8500 N which is on left side (Driver side) of bumper.

2. Sectional force in the rails

 

The graph shows forces acting at the cross-section on both the rails (RH and LH). The animation shows left side of the structure is having a larger displacement in the z-direction, this can be justified by the sectional force plot. It's clearly seen that the RH rail experiences a larger amount of force compared to the LH (Driver side) rail. The maximum force experienced on right rail is 4550N

3. Shotgun cross sectional forces

 

On comparing the cross sectional forces on the left & right sides on shotguns, we can see that on the left side, the forces are higher than on the right side. The maximum force was generated is 3400 N on left side (Driver side) of shotgun.

4. A pillar cross section.

In the A pillars there is no hike in force till t = 8 ms, the maximum force of 850N was generated in left side A-pillar. At the end of the simulation, the force decreases.

5.Intrusions on the dash wall 66695,66244.

 The intrusion of the selected nodes in the dashwall component is simulated using hyperview. It is noted that the displacement increases over time, which indicates that the force is directly distributed on the nodes. Node 66244 is displaced more than node 66695 which is almost 900 mm and 700 mm respectively at 80ms.

6. Rigid wall force :-

 

The maximum impact force exerted on rigid wall is 125 KN at 15ms

CONCLUSION :

From the above project, the frontal crash analysis is performed on the BIW frame. The appropriate contact interfaces are defined along with a self-contact with type 7 contact. Rigid wall is created with required parameters and initial velocity is set to 35 mph. The model weight is kept at 700 kg. The model is checked for penetrations & intersections and the analysis is performed for 80 ms.

After the analysis was performed following outputs were obtained from the analysis:

• The simulation results are not that accurate because the complete model is missing, but it gives a brief idea of how the impact affects the vehicle at critical locations.
• After studying the simulation results it can be concluded that the Bumper which experiences the impact which transfers energy to the rails. The bumper absorbs impact energy to a higher extent compared to other parts. 
• The rails and other crush tubes absorb energy further reduction in energy before the passenger experiences any shock. This structure is more important as it reduces the overall impact on the person in the vehicle.
• The A-pillar experiences the least forces, indicating that most of the forces are absorbed by the bonnet area. 
• The intrusion nodes which are actually absorption of a higher amount of the forces by the bonnet area, it undergoes displacement. That means that the crushing of legs is possible.
• So overall the front part of the vehicle must be designed crucially considering the type of materials to be used which would reduce the impact on the passenger and ensure safety.