Side crash Analysis using HyperMesh & Radioss

Aim:

To run and analyse a Side crash with the BIW component add the mass up to 700kg and run the crash with given parameters.

Objective:

Side crash-BIW

• Check 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 reference model.
• Compare the model weight with the reference model and use added masses to reach target weight 700kg while getting CG about the required range.
• Initial velocity as shown in the picture.
• Use model checker to ensure good quality.
• Timestep :0.5 to 0.1 microseconds.
• Run 80ms.
• Sectional force in the cross member.
• The intrusion at B pillar, hinge pillar and fuel tank region. Provide recommendation on what can help to reduce Fuel tank intrusion.
• Peak velocity of the inner node of the door.

Introduction:

Explicit dynamics:

1. Explicit dynamics approach is used for solving high deformation and high energy producing models.
2. Used to determine the dynamic response of a structure due to stress wave propagation, impact or rapidly changing time-dependent loads.
3. Momentum, Non-linearity effects and inertial effects are usually taken into consideration.
4. The explicit method has many pros like Conditional stability, Dynamic and shock problems, Element by element calculation, Relatively low in cost, Timestep is too small and High Robustness

Equation:

`[M] {(d^2u)/(dr^2)}+C{(du)/dt}+K {U}={Fext(t)}`

Where,

M= Mass matrix

C= Damping matrix

K= Stiffness matrix

Crash Testing Requirements:

Regulatory testing: FmVss,ECE,AU,JS,BNVSAP

Consumers testing: NCAP

• The regulatory test provides an answer to the question, whether the car passes or fails If injury recorded in dummy is less than the standard value then it is said to be passed.
• Consumer testing will give a star rating based on the injury results. They will also give a rating based on individual component performance from the car.
• The results from the above testing drive the overall business decisions as well.

Procedure:

1. In this case, we have to add mass to the given model and then set the given parameters.

Add mass to the model up to 700kg while getting CG about the required range.

The red dot represents COG point which is at the centre of the car by distributing the mass evenly.

In this mass tab, we can view the total mass added to the BIW model.

2. To Create the contact interface Type 7 with friction 0.2 and recommended parameters.

Igap=2 (set the variable gap to take into account the true distance between parts.)

Gapmin = 0.5 mm (Specify minimum thickness of the model to avoid numerical issues.)

Inacti = 6 (Remove initial penetration where possible. Elsewhere, reduce to less than 30% of the defined gap value and adjust the gap with Inacti)

Istf= 4 (Set stiffness of interface based on the softer of master and slave)

Stmin = 1000N/mm (specify a minimum stiffness in the contact to avoid too soft contact)

Idel =2 (Removes the slave node from contact because of element deletion)

Iform = 2 (Sliding forces are computed using stiffness parameters of the interface. Usually results in bigger time step)

3. Now to check any penetration and intersection in the model.

The output of the run shows zero collision found.

4. To create a rigid wall we have to create a rigid wall card in the model and mention the parameters for front crash the friction is set to 0.1, geometry type is set to the Cylinder and Dsearch is set as recommended.

• Here For the Cylinder wall, we have to align the wall equally with the car in Hypercrash by defining the axis position manually.

Before Aligning the Rigid Pole:

After Aligning the Rigid Pole:

5. In solver create a new initial velocity card for the parameters create a new set in a set group and select the new set in gmd_ID. and for velocity, the units are in m/s so from the given 20 mph is converted to 8.94 m/s.

6. The model checker shows there are no errors in the model. There are few unused sets which will cause an error in crash simulation It has to be deleted.

7. In Solver the Timestep DT/NODA is set to 0.0005.

8. To set the run-time edit the engine run card Tstop as 80 seconds.

9. To get the output data on a particular part, Section is created along with the frame and added to the output block. Sections are created in two cross members one on the driver side and in B-pillar.

10.To get the compression distance Intrusion are created at B pillar, hinge pillar and fuel tank region.

11.To get Peak velocity of the inner node of the door TH/NODE is created and for the output translation velocity graph is been mentioned.

12. To get the output results in the graph we have to create TH for all the new cards.

Result:

The car is moving at a velocity of 32.18 kmph which hits the rigid pole, due to this impact some parts get huge deformation as shown in the animation. The maximum stress is developed as 378.6 Mph in 80 s.

Internal and Kinetic energy:

The kinetic energy is constant for 15s because the object is not in contact with the rigid pole. After 15s, the kinetic energy is decreasing from 28000 to 18000 due to frontal crash impact the internal energy increases from 0 to 9000.

Total Energy=IE + KE + RKE + CE + HE (RKE-Rotational kinematic energy, CE-Contact ENery, HE-Hourglass Energy) and the total energy must remain constant or can decrease very slightly.

Contact and Hourglass energy:

When the parts collide, The contact force transfer energy through the parts which intersect each other, and transfers energy between them. The maximum energy formed is 450 J. The hourglass energy at maximum energy deformation of the elements is 25 J.

The intrusion at B pillar with node:

Maximum displacement on the B-pillar node is 300mm

The displacement of nodes is displaced this is due to the absence of components in the passenger compartment.

The parts like seats, the floor in the passenger compartment will absorb energy from crash pole since these parts aren't there, the force is directly transferred to B-pillar

By increasing the material grade and thickness of the Cash pole component will increase the stiffness and reduce the intrusion.

The intrusion at Hinge pillar with node:

Maximum displacement on Hinge pillar node is 455 mm

The displacement of nodes is due to the force of pole crash at speed 32.18 kmph.

The hinge pillar is connected with B-pillar but the deformation happened here is acceptable.

The parts like seats, the floor in the passenger compartment will absorb some energy from crash pole since these parts aren't there, the force is directly transferred to Hinge.

By increasing the material grade and thickness of the Cash pole component will increase the stiffness and reduce the intrusion.

The intrusion at fuel tank with node:

The displacement of nodes is due to the force of pole crash at speed 32.18 kmph.

The fuel tank node receives Maximum displacement on Fule tank node is 275 mm

The parts like seats, the floor, in the passenger compartment will absorb some energy from crash pole since these parts aren't there, the force is directly transferred to the fuel tank part.

By increasing the material grade and thickness of the Cash pole component will increase the stiffness and reduce the intrusion.

B-pillar and Driver side cross member section force:

Maximum Sectional force on the B-pillar cross member is 8.5 KN

Maximum Sectional force on is driver side cross member 6.4 KN

B-pillar cross member receives only 20% of the total force transfer remaining is transferred to the floor panel of the car that's why the section force of both pillars is less compared to other components.

Peak velocity of the inner node of the door:

From the simulation, we can analyse the maximum velocity achieved by the inner door from this we can conclude that at the speed of 32.18 kmph. the maximum displacement is 9.1mm/ms.

Conclusion:

The frontal crash analysis is done with the student version of Hyperworks. The Improper meshing leads to some errors which are in an acceptable range.

We have obtained the value of the sectional force at cross member and have created type 7 interface to the model. Obtained the Intrusion on particular nodes and peak velocity as well.

The B-pillar, Chassis and door which are the component in the crash zone they absorb more energy and transfer energy to passenger section that's why a section of the cross member receives high force.

The energy error obtained as -1.7%, Mass error obtained is 0.7760e-04 No of cycles is 160000.

By improving the Components in the crash zone will help in protecting the occupants.

• The energy error and mass error are in an acceptable range.
• The sectional force in cross members for both RHS and LHS plays an important role in absorbing the max impact.
• The B-pillar design also plays an important role in keeping the impact less transmitting to the interior parts of the vehicle.
• The position of the centre of gravity of the vehicle is vital in the crashworthiness, so maintaining the weight balancing of the vehicle is the skill of design engineer.
• As we are using the half model and with added masses, if we can go for full vehicle body analysis then more realistic results can be obtained.

Reference:

https://skill-lync.com/knowledgebase/section-creation-in-radioss

https://en.wikipedia.org/wiki/Federal_Motor_Vehicle_Safety_Standards