Roof crash analysis of a BIW car using Hypermesh, Hypercrash, Radioss, Hyperview, and Hypergraph.

Objective: To perform roof crash analysis on the given model and obtain the required output requests.

Given Question:

Roof Crush - BIW:

Import

• Car
• Impactor

Transforms

• This will require (in order)
• A 180° rotation about the global z-axis
• A 5° rotation about the axis through axis AB
• A 25° rotation about the axis through axis AC
• A translation to put point A at global ( -2145.26, 584.822, 1343.06)

Reference image ( Full Vehicle Model ) 

Interfaces

• Create a Type 7 contact interface between the impactor and the car
• choose an appropriate stiffness definition
• choose an appropriate minimum gap
• change the coefficient of friction to 0.2
• choose the appropriate friction penalty formulation
• Save the data from the interface to the time history file.

Gravity and boundary condition

Apply gravity to whole model but keep the suspension shock tower nodes
locked in Z.

Impactor Boundary Conditions

• The impactor assembly contains a spring attached for stability. Create a BCS
collector to fix the free end of the spring.
• Create a moving SKEW to define the direction normal to the impactor’s
face.
• Create a BCS collector to guide the master node of the impactor rigid body
so that it is free to translate normal to the face of the impactor, but is fixed
in all other DOFs.

Imposed Displacement

• Impose the velocity of the impactor starting from 0 mm/s at t = 0. The
displacement of the impactor should be 200 mm @ 200 ms.
• Avoid abrupt changes in the acceleration of the impactor.

Control Cards

• /ANALY card
• /DEF_SHELL card,
• /DEF_SOLID card, and
• /IOFLAG card
• /SPMD card
• /TITLE card

Engine File

• Use a constant nodal time step
• Print time history every 0.0001 seconds
• Solve for 200 ms
• Create an animation file every 0.005 seconds

Include selected output in animation files:

• Elemental Energy
• Elemental equivalent plastic strain
• Elemental hourglass energy
• Elemental von Mises stress
• Nodal added mass
• Turn on parallel arithmetic

Solution and Results Post Processing

• Run the model
• Plot force vs. displacement. Check that the FMVSS 216 target load of
47,000 N (= 3 * GVW) has been met.
• Plot the energy vs. time curves

Case set up and Execution:

Procedure:

  • Open the given 'neon_roof_0000.rad' file in Hypermesh and Hypercrash.
  • Keep the unit system as 'kN mm ms kg' in Hypercrash.
  • Import the impactor 'FMVSS_216_ROOF_IMPACTOR_coarse_0000.rad' file and give the transforms in given order.
  • A 180° rotation about the global z-axis
  • A 5° rotation about the axis through axis AB
  • A 25° rotation about the axis through axis AC
  • A translation to put point A at global ( -2145.26, 584.822, 1343.06)

  • Run the model checker in Hypercrash and do the changes in Hypermesh and make sure that there are no penetrations and intersections.

  • Create boundary conditions.

  • Now delete all the previous interfaces and create 2 new interfaces of Type 7 card with the below-mentioned properties.

   

  • Now assign the slave nodes and master surface to the above-created contact interface cards as shown below.

  • Masses are added and we reach 716kg which is very close to our target weight 700kg while getting CG in the required range.

  • Create imposed displacement card.

  • Create a function card with the imposed displacement curve.

  • Create and add new material and property cards to already present materials and properties cards.

 

  • Create rigid bodies with mentioned parameters.

  • Assign slave nodes [Gnod_id] for different RBODY as mentioned below keeping remaining parameters constant as shown above.
  • No name - ID 1 - [70] NULL.8
  • New RBODY 9900037 - ID 9900037 - [1139] RBODY_group_1139_of_NODE
  • New RBODY 1 - ID 9900038 - [5] RBODY_group_3_of_GRNOD
  • No name - ID 9900041 - [1143] rigid184786nodeset
  • No name - ID 9900042 - [1144] rigid184787nodeset
  • No name - ID 9900043 - [1145] rigid184788nodeset

  • In the system card, give skew as shown.

  • The timestep has been set by changing the following parameters and run time to 200 ms.

  • The final browser tree is shown below.

  • Now we run the model using radioss analysis.
  • After a successful run check for errors where energy error is -12.7% and mass error is 0.0052%. 
  • We also get the .h3d animation file in Hyperview and .T01 file for plotting graphs in Hypergraph 2D.

Output requests:

Energy curve plots:

  • Internal energy absorbed is 755.7 KN-m.
  • Hourglass energy is 0 KN-m.
  • Contact energy is 113.16 KN-m.
  • We know that K.E. coverts to I.E. during the crash as elements get deformed and absorbs the energy.
  • If more energy is absorbed then fewer elements will get deformed which increases the safety of the car. 
  • Contact energy increases gradually.
  • Initially, there was a slight increase in hourglass energy but after a few ms it became constant.

Roof crush resistance:

  • This is Force vs Time graph.
  • The maximum force exerted is 8.35 KN.

Displacement:

  • This is the Displacement vs Time graph.
  • The maximum displacement is 201.604 mm.

Inference:

As per FMVSS 216 standards, a force of 1.5-3 times the Gross Vehicle Weight is to be achieved within 130mm of the impactor stroke.

  • Assuming the full model mass to be 1400kgs:
    Required force = (3*1400*9.81) N= 41,202 N = 41.202 KN
  • From the graph, it can be seen that a maximum force of 8.35 KN or 8354 N has been achieved within 130mm displacement of the impactor, which is way below the FMVSS target load.

Improving Roof Crush Resistance:

  • Geometric Approach: Increase the thickness of Roof, Roof Rail, Panel B-pillar inner rail, Side Panel, Inner Rocker panel, Floor channel, Front floor, Rear Floor and Trunk Floor.
  • Material Approach: Use of Composite Body Solutions (CBS) such as Foams, Plastics, Alloys, and non-ferrous metals. CBS Materials like Foam have a high Strength to Weight Ratio which increases the Force absorption capacity of the structure hence the roof is able to withstand higher forces for a given deformation.

Result and Conclusion:

  • COG location and mass of the car are very important.
  • We observed the deformations happening, which means more robust components and materials must be used at these locations.
  • The reason for such low roof crush resistance is the reduced model which does not include all of the components of the BIW to offer proper geometric resistance to the impactor displacement.
  • Material approach is preferred over the Geometric approach due to space constraints in the passenger compartment as well as weight limitations.

Thus, the roof crash analysis of a BIW car is successfully carried out using Hypermesh, Hypercrash, Radioss, Hyperview, and Hypergraph.


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