Quasi-static Roof crash analysis with an impactor.

Problem statement:

Quasi-static Roof crash analysis with an impactor.

Objectives:

Pre-processing:

1. Import car and Impactor.
2. Transformation operations to locate the impactor above the B pillar.
3. Create Interfaces with appropriate properties.
4. Imposed boundary conditions.
5. Check control cards.
6. Use a constant nodal time step.
7. Print time history every 0.0001 seconds.
8. Solve for 200 ms.
9. Create an animation file every 0.005 seconds.
10. 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.

Post-processing:

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

I. Pre-processing:

1. Unit System

Unit system used in this simulation is 'kg ,mm, ms.'

Fig 1: Unit System.

2. Import Model:

The car structure and an impactor is imported from 2 different file. The below figure shows imported models.

Fig 2: Car models.

3.Transformation operations to locate the impactor above the B pillar:

After importing models the impactor should be translate to the B pillar. For this following operations were used.

1. This will require (in order).
2. A 180° rotation about the global z-axis.
3. A 5° rotation about the axis through axis AB.
4. A 25° rotation about the axis through axis AC

The following figure shows the details of the above points on the impactor.

Fig 3: Impactor (source: skill-lync website).

This Impactor is placed over B pillar. as shown below

Fig 4: Car model.

4. Interfaces:

There are two groups of type 7 created. The first interface all the interface in the car component are connected together. In the second group whole car and impactor are connected together. The following fig shows the properties used while defining type 7 contact. In this the master element is impactor while slave are car components.

Fig 5: properties of type 7 contact.

5. Boundary conditions:

Since it is Quasi-static Roof crash analysis there are boundary condition defined which are as follow:

1. The free end of the spring of the impactor is fixed.
2. Master node of a rigid body of a impactor imposed velocity is defined. It is defined as the 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.
3. Suspension point are locked in Z direction by creating rigid body.
4. The rigid body master node is fixed in all direction.
5. A moving skew is defined for imposed velocity direction on the impactor.

Fig 6: Imposed velocity function.

6. Control cards:

There are 25 control cards used including

1. /ANALY card
2. /DEF_SHELL card
3. /DEF_SOLID card
4. /IOFLAG card
5. /SPMD card
6. /TITLE card

For printing time history every 0.0001 seconds inputs are given in a card ENG_TFILE. as shown below.

Fig 7: Card ENG_TFILE.

The run time is set to 200ms. as shown below.

Fig 8: Run time.

7. Selected output in animation files:

There are some output request which are as follow:

1. Elemental Energy.
2. Elemental equivalent plastic strain.
3. Elemental hourglass energy.
4. Elemental von Mises stress.
5. Nodal added mass.
6. Turn on parallel arithmetic.

Fig 9: Output request.

Nodal added mass following card is used.

Fig 10:Nodal added mass card.

For turning on parallel arithmetic the following card is used.

Fig 11: Parallel arithmetic card.

II. Processor (Solver):

There are some factors which helps us to predict the solution is accurate and precised so in this section we are going to check it.

From roof_crash_0001.out file, The Total number of cycles was 200000. The energy error is -12.50% which is in acceptable limit. The mass error is 4.6% which also less than 5% it is accepted. There is increase in mass which is due to reduction in time step at that node, to maintain time step the mass is increased. The run was "normal terminated" which implies the was successfully completed. There was no sudden changes in energy as well as in error. As shown below.

Fig 12: roof_crash_0001.out file.

Fig No. 13: Energy graph

Since it is Quasi-static Roof crash analysis initially in both the graphs energy starts from zero. As impactor is in contact with the roof the energy starts increasing. The kinetic energy is not zero at the start due to imposed velocity of the impactor and hourglass energy is also zero. So the graph justices the elevation in energies. So we will check mass and inertia of the system.

Fig No. 14: Total final mass and inertia from out file.

Fig No. 15: Total initial inertia, C.G. and mass.

From both values from out file and hypermesh file are same so it is correct annd we can move to post processing.

Fig 16: Error.

III. Post-processing:

1. Von-Mises stress:

Fig 17: Von-Mises stress.

The maximum stress developed in the roof is 226 MPa.

2. Displacement:

Fig 18: Displacement.

The maximum Displacement is 483mm.

3. Plastic strain:

Fig 19: Plastic strain.

The maximum Plastic strain is 1.201e-02.

4. Force vs Displacement:

Fig 20: Force vs Displacement.

There was a problem in ploting the graph for 200mm but Since here the important factors is peak Force so at t= 84ms. the maximum force is 1.9kN. According to FMVSS 216 target load of 47,000 N (= 3 * GVW) has been met. So the weight of the car structure in this case is apporoximately 174kg. to convert this in newton

174 x 9.81 = 1706.94 N

Now according to FMVSS 216 target load of 47,000 N (= 3 * GVW) which will be,

1706.94 x 3= 5120.82

which is 5.12kN since the maximum force is 1.9kN which is less than 5.12kN the is satifying the criteria.

Conclusion:

1. There was increase in energy error due to some of the free parts present in the assembly.

2. The maximum stress developed in the roof is 226 MPa.

3. The maximum Displacement is 483mm.

4. The maximum Plastic strain is 1.201e-02.

5. The maximum force is 1.9kN which is less than 5.12kN the is satifying the criteria.