Assignment 5

Objective :

• To mesh the given bumper assembly according to the required criteria.
• To perform the given simulations according to the conditions required and notice the change in results.

Procedure :

Import the model bumper into the hypermesh pre-processor. Using geometry cleanup fix any duplicate surfaces that may be present or cleanup the geometry.

Move all the surfaces into 2 component collectors, namely bumper & bumper_support.

2d Mesh : Mesh both components individually with a mesh size of 6mm. Using remesh and quality index option, remove all the tria elements from the mesh so that only quad elements remain.

Bumper

Bumper_support

After both components have been mesh they can be connected using 1d connectors-->spot-->weld

Hereby both components have been connected using spot welds as shown below.

Running the simulations

The second part of the question has been answered using the 4 parameters given in the question

• Plot RWALL forces ,contact forces,internal energy and Create TH/PART for all parts and compare results for all cases.

To create TH/PART for the components go to output block-->create new-->select components-->choose entity IDs-->choose the 4 components and click enter.

1. Sim_1(as is)

Rwall forces/Stress:

Contact energy :

Internal Energy v/s Kinetic Energy:

2. Sim_2 (inacti = 6)

Rwall forces/Stress:

Contact Energy:

Internal Energy :

3. Sim_3 (type 11):

Adding type 11 type interface(edge to edge) is done twice.

First time keeping Igap, Inacti = 0and rest all at default

Rwall forces/Stress:

Contact Energy:

Internal Energy v/s Kinetic energy:

Second time keeping Igap = 1, Inacti = 6 and rest all at default

contact energy :

rwall force/stress :

timestep:

The comparison is drawn using different types of parameters in type 11 as shown above

4. Sim_4 (no notch no boundary condition):

Rwall/Stress:

Contact energy :

IE v/s KE:

5. Sim_5 (centre notch):

Rwall/Stress:

Contact Energy :

IE v/s KE:

6. Sim_6 (opposite sides notch) :

Rwall/Stress :

Contact Energy :

IE v/s KE:

• Difference in Energies :

The difference in energies is mainly visible in the total translational energy:

Sim_1:

In the first case, with the default notches, as the tube begins compressing the notches first compress, namely the central one first followed by the one near the wall and by the end of the cycles the whole tube is presses against the wall.

Sim_2:

In the second case, the total stress is the same as the first, only the initial penetrations if any get reduces and scaled down according to the size of mesh. As the tube begins compressing the notches first compress, namely the central one first followed by the one near the wall and by the end of the cycles the whole tube is presses against the wall.

Sim_3 :

In the third case, as we have added the type 11 contact we see that the edge to edge interfaces are handled by this and we see a difference in the translational energy graph as compared to the rirst two cases. Also what is visible is a reduction in the total stress on the tube as more of it is getting dissipated due to more accurate modelling of the contact interfaces.

Sim_4:

This case scneario experiences the least amount of stress and translational energy change as the simulation progresses in to the absence of notches and boundary conditions, this reduces the absorbtion of energy by the tube and allows more of it to be transmited thereby causeing a smooth flow of energy.

Sim_5:

This case has the most stresses being generated due to the presence of a large notch in the centre of the tube thereby increasing stress concentration at a crucial point. We also see that the translational energy drops steeply at the begining of the simulation followed by a staggered drop as the simulation progresses.

Sim_6:

This simulation has again a lowered stress due to the presence of small notches at the begninig of the tube. there is also a somewhat staggered graph for translational energy as the case above.

• How does the notch affect the results?

Notches are point of stress concentration in a body that is getting deformed and may also change the deformation characteristics of a particular body depending on their placement. We will discuss the effect of notch on a case-by-case basis.

Sim 1 & 2 :

In both these cases the notch is in the same position and the only difference in the two simulations is the addition if initital penetration control paramter inacti = 6 which reduces the penetration according to the size of penetrated gap and mesh size. The stresses generated in both cases are identical (0.6964 GPa).

As we can see the deformation accumulates at the notch first due to stress concentration at these points.The notch fully gets compressed by the flaps formed on both sides causing a stress concentration as shown below.

Sim 3:

In the third case, as we have added the type 11 contact we see that the edge to edge interfaces are handled by this and we see a difference in the translational energy graph as compared to the rirst two cases. Also what is visible is a reduction in the total stress (0.649 Gpa)on the tube as more of it is getting dissipated due to more accurate modelling of the contact interfaces.

As we can see the mechanism of deformation is similar to Sim_1 and Sim_2 only difference is that the stress getting generated is reduced by a bit

Sim 4:

In this Simulation, there is no notch and there are also no boundary conditions. The fewer the boundary conditions to adhere to, the lesser the stresses are absorbed by the component and a larger percentage of it gets transmitted.

In this simulation there are no particular stress concentration points, the tube undergoes buckling under normal circumstances and develops least amount of stresses.

Sim 5:

In this simulation there is a large notch provided in the centre, which is a critical position to place a notch for a body that is undergoing complete deformation. As a result there is major concentration of stresses at this point.

This is a comparsion of central notch with no notch simulation. As we can see the tube instead of compressing near the wall, starts compressing near the notch first. The stresses are also elevated due to this.

Given above is a velocity variation curve in z-axis for central notch v/s no notch.

Notice the difference between translational energies of both cases. For no notch it is more linear as compared to central notch.

Sim 6 :

For this simulation 2 notches are provided at the start of the tube on opposite faces to study the effect of position of notch in a crash tube. As this notch is rather small there is not much pronounced stress concentration in these areas and they get compressed only towards the end of the simulation due to their location.

As we can see it remains intact throughout most of the simulation. The stresses are also kept to a minimum when compared to central notch.

Please note that in the above simulation the wall is to the left of the tube. We can see from the above picture which is notch at the beginning v/s no notch, its position affects the deformation towards the end. As we can see their is widening of the section in y-direction at the z-co-ordinate of the notch due to notch compression at the end. Whereas for no notch the tube folds onto itself in a normal fashion as was the case earlier. Pls note that in the above simulation the wall is to the left of the tube.

We can notice the deviation in translational energy towards the end of the curve due to the notch being at the start of the tube in the graph on the left.

In this way the notch affects the deformation characteristics of the tube, by creating stress concentration points, accumulating the stress before compressing thereby causing spikes in energy after they get compressed.

• Comparison of total energies :

Sim 1:

Sim 2 :

Sim 3 :

Sim 4 :

Sim 5 :

Sim 6 :

As we can see in all the above graphs, the total energy of the system decreases linearly, goes into a downward peak and comes back up. The upward curve from the lowest point begins when the tube and been fully compressed and begins to expand again due to spring-back effect, followed by the curve flattening out till the end of the simulation. The depth of this doward curve is different for all the above simulations with the deepest down-ward dip (highest spring-back) being for sim 3 (type 11 enabled) and the least springback being for Sim 5(central node).

Conclusion : The characteristics of the different interface cards along with varying notch position have been studied with respect to a crash simulation.

Result : Assignment_5