Week 10 Bullet penetrating a Bucket Challenge

OBJECTIVE

To set up a simulation and carry out an explicit dynamic analysis of a bullet penetrating a bucket. Three different cases involving different non-linear materials for the bucket is to be carried out and compared. The outputs to be generated are as mentioned in the video - equivalent stress and total deformation. In addition to that, the equivalent strain will be generated as well.

MODEL IMAGE

PROCEDURE

1. After opening ANSYS Workbench, we are met with the Project Schematic window. Here, we can select the 'Explicit Dynamics' analysis system on the left. Doing so creates a new project. Here, we can rename the project and also input the material. We will need to right-click 'Geometry' and select 'import'. The file provided for this project should be selected. 

Now, we can add a material for the analysis. To do that, we need to double-click Engineering Data'. This opens up the list of inserted materials. We can then pick materials we need from the repository listed in the Engineering Data Sources. This challenge requires the use of non-linear materials so we shall pick three from the non-linear material source - Stainless Steel NL, Aluminium Alloy NL and Copper Alloy NL. It also requires Tantalum, which should be available in the explicit materials source.

After that, we simply need to click the yellow '+' symbol on the material's corresponding 'add' column to add this specific material to the project. Similarly, we need to pick 'Tantalum' from the 'explicit materials' source. Once we are done, we can simply close the tab.

We can then exit out of the engineering data tab and return to the project schematic window, where we can right-click geometry and select 'edit'. This will bring the model up in the Mechanical interface.

2. In the mechanical interface, in the outline, under geometry, we can rename each of the components. We also need to assign the material to the bucket. (This material is to be changed and simulation is to be run again).

The bullet is assigned the tantalum material and a stiffness behaviour of 'rigid' since no analysis would be carried out on it.

4. Moving on to meshing, we can assign a sizing attribute to the bucket splits (the regions of penetration and exit of the bullet). To do so, we need to right-click mesh > insert > sizing. We can give it a size of 6mm.

5. Moving on to the analysis settings, we shall be entering an end time of 0.01s as shown. We can also assign a maximum energy error of 5.

6. Next, we need to right-click Explicit Dynamics > Insert > Velocity. We need to select the bullet's body for this. Then, we need to enter tabular data for the direction of velocity application, which is the negative x coordinate in this case. The value would be -139000 mm/s. All the other components are constrained.

Then, we can assign the fixed support on rim surface of the bucket as shown (via right-clicking Explicit Dynamics > insert > fixed support).

7. Now we can generate the outputs. To do this, we can right-click Solution > Insert > Stress > Equivalent (Von-Mises) (for stress), right-click Solution > Insert > Deformation > Total (for total deformation), right-click Solution > Insert > Strain > Equivalent (Von-Mises) (for strain).

Now, all we need to do is right-click solution again and click 'Evaluate all results'.

Finally, when the analysis is done, we can view the results by simply clicking each of these solution entities we created, in the Outline menu.

To reiterate, this analysis needs to be run again a second and third time after saving the case 1 file and changing the material of the bucket.

OUTPUTS

CASE 1 - STAINLESS STEEL NL

EQUIVALENT STRESS

Maximum & Minimum stress

TOTAL DEFORMATION

Maximum & Minimum deformation

Maximum & Minimum directional deformation in x-axis

EQUIVALENT STRAIN

Maximum & Minimum strain

CASE 2 - ALUMINIUM ALLOY NL

EQUIVALENT STRESS

Maximum & Minimum stress

TOTAL DEFORMATION

Maximum & Minimum deformation

Maximum & Minimum directional deformation in x-axis

EQUIVALENT STRAIN

Maximum & Minimum strain

CASE 3 - COPPER ALLOY NL

EQUIVALENT STRESS

Maximum & Minimum stress

TOTAL DEFORMATION

Maximum & Minimum deformation

Maximum & Minimum directional deformation in x-axis

EQUIVALENT STRAIN

Maximum & Minimum strain

OBSERVATIONS

In the simulations, we can see that the impact of the bullet results in the ejection of deleted elements from the bucket. They are ejected a fair distance and this is picked up by the directional deformation outputs, which explains the excessive minimum deformation values. They are ejected in the negative x-direction, which is why they are in negative. On the other hand, the total deformation conveys a different story, in that the bullet undergoes the most deformation when in reality, it covers the most ground due to the nature of this interaction.

Compared to aluminium alloy and copper alloy, stainless steel variants have higher universal tensile strength, ranging between 500-600 MPa on average. Whereas many aluminium alloys are in the 100-300 MPa range and copper alloys are in the 350-500 MPa range. This is proven through these outputs - stainless steel on average generates the highest amount of stress followed by copper alloy and aluminium alloy respectively.

Going to strain, we can see that stainless steel has lower strains generated compared to similar numbers for aluminium alloy and copper alloy - probably due to their superior ductility properties.

RESULT

The explicit dynamic analysis was carried out on a model involving a bullet penetrating a bucket. Three cases using different non-linear materials for the bucket were analyzed and their outputs were compared.