Introduction:

When performing crash analysis, one of the common tests that engineers perform is check the integrity of the rear car door. In this project, we will perform the same test using a simulation. This project deals with analysis of a rear door of a car crashing into a pole.

Objective:

To simulate the movement of a car rear door crashing into a pole and analyse the motion to understand the deformations, the material worthiness, stress distribution and the energy curves on the car door.

Steps to be done:

  • Clean up the geometry
  • Meshing
  • Specify the element quality criteria
  • Post processing

Geometry Cleanup:

Software used – HyperMesh

The lines which have more proximity to each other are toggled together. When the model is cleaned up then the model is converted into a midsurface.

For this project, we chose a symmetrical model of the car door and split it into two halves. We then moved one half of the door to a new component and the geometry is cleaned up.

Meshing of Geometry:

Once the midsurface is cleaned, then the meshing of the midsurface is done. When a meshed geometry is impacted with a force, the force vector travels through the geometry like a wave and affects every finite element. This is called as mesh flow. Since we are studying the impact of force on a component, it is important to ensure that the model has a good mesh flow. For this purpose, we chose a Mixed mesh type to ensure that the model has the better mesh flow.

It is important to ensure that this force travels without being deflected by the shape of the finite elements. To not compromise the mesh flow, we use tria elements on only 10% of the mesh since the tria elements are stiffer than the quad elements.

                 One half of the Meshed door components

Element Quality Criteria:

Parameter Value
Warpage 15
Aspect 5
Skew 60
Chord Dev. 0.1
Cell Squish 0.5
Length 6
Minimum length 4
Maximum length 8
Jacobian 0.7
Equia. Skew 0.6
Area Skew 0.6
Taper 0.5 degrees
Tria minimum angle 20 degrees
Tria maximum angle 120 degrees
Quad minimum angle 45 degrees
Quad maximum angle 135 degrees

 

Once every finite element passes the Element quality criteria, the geometry is duplicated and reflected to the other half to obtain a complete model.

Fully Meshed Door

Property Card

The P1_Shell is set as the property card to specify the properties of the door designed and the thickness of 0.7484mm in assigned.

Parameter Value
Ishell 24
Ish3l 2
N 5
Ithick 1
Iplas 1

 

Material Card

The M2_Plas_Johns Zeril i.e., law2 is assigned to the model with aluminium as the material. The unit system used is Kg KN mm ms.

Parameter Value
Density 2.7e-006
Young’s modulus 71
Poisson ratio 0.3
Plastic Yield Stress (a) 0.29
Plastic Hardening (b) 0.5623
Hardening Parameter (n) 0.63
Plasticity Maximum Stress 0.425

 

Seam Weld

The seam weld is a continuous weld and it is created along the edges of the components. The card used for the seam weld is Type 2 (Spring Single Rows) with spacing and tolerance as 5.

 

 

Two components were welded using seam weld

Contact

Contact is defined as the point or the area where two geometries come into contact. This can happen during collision, welding etc. The type 7 contact is assigned to the model so that finite elements can interact during the crash. The contact parameters are listed below.

Parameter Value
Istf 4
Igap 3
Idel 2
Gapmin 0.5
Lacti 6
Iflorm 2

 

Rigid Pole

The pole is created by assigning the Rwall card and the geometry set as Cylinder. The radius is given as 127 mm. The pole is created at the distance of 30 in the negative X direction i.e. against the direction of the velocity for the impact to happen.

Load Collector

The load collector is used to specify the loading conditions. In this model, the velocity is assigned to the model through the BC manager with the INVEL card. The velocity is given as 8.3mm/ms. The velocity is added in positive X direction.

Output Block

The output block is created to request default result parameters like displacement, velocity etc.

Control Cards

The control cards are used to control the simulation by specifying the run time, the number of animation file to be generated, the desired output parameters needed, the time history files that are to be controlled etc. Once the control cards are set, the simulation is made to run.

Now the simulation is made to run on the Radioss Solver.

Post Processing

Software used: HyperView

Now the output file is examined. The animation file is loaded in the HyperView and the parameters specified earlier are observed visually. Here are a few snapshots showing the plastic strain and Von-Mises stress acting on the car door:

Plastic Strain

 

Von Mises Stress

Then the graph is studied in Hypergraph by opening the T0 file. The Internal energy, Kinetic energy and the Total energy is plotted. The Total energy remains constant and the Internal energy increases while the Kinetic energy drops during the impact.

You can view the animation of Von-Mises stress acting on the car door here:

Result

Deformation = 0.102 mm

The maximum Von mises stress obtained = 0.39 N/mm2

The UTS of the material = 0.425 N/mm2

Factor of safety = Uts / Maximum Von Mises Stress

= 0.425/0.399 = 1, which indicates the material and the design is moderately safe to use as long as human lives are not involved.

Conclusion:

By calculating the amount of forces acting on a back door during a crash event, we can understand the areas of high impact and low impact. Accordingly, we can design the model to withstand forces durably. Also, the model has a safety factor of 1, which is not safe enough to protect humans inside the vehicle in the event of a crash. By using numerical methods like the one we did here, we can redesign the model to be more safe-proof and fail-proof.

Project submitted by,

Sathesh C


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