Engineering

main imageProblem Statement

A 3D solid model for the cover of a pressure cylinder is designed which can hold up a pressure of 0.5 MPa. The model is made up of aluminum alloy. It is required to find alternative material to manufacture pressure cylinder cover. This case deals with material – Engineering Plastic being substituted for aluminum alloy.

 

Objective:

The purpose of the simulation is to assess the possibility of replacing the aluminum alloy by a new type of engineering plastic.

 

Area of Interest:

In this case study various parameters and technical segments come into picture which will form our areas of interest.
1. Circularity
2. Cylindrical Coordinate System
3. Mesh Refinement
a) Tetrahedral Meshing
i. Patch Conforming
ii. Patch Independent
b) Multi zone Meshing
i. Hex/Hex-Dominant Method
c) Sweep Method
d) Skewness mesh metric
4. Silvers.

 

Circularity:

Circularity of a model is defined as the difference between the radii of two concentric circular areas. It is used to control the roundness of circular parts or features. The circularity should be less than 10 micrometer; excess of circularity beyond this value may impair the tightness and cause the gas leakage.

 

Model:

 

model 1

 

 model 2

 

At the onset static structural analysis is carried out with default mesh settings, a 0.5 MPa pressure is applied on the inner faces of the circularity and the frictionless support is applied to the space provided for the bolt at all four corners of the geometry. The problem was solved for Total deformation, Equivalent Stress, Structural error and Directional deformation.

 

Meshed Model:

The boundary conditions and the mesh parameters were same for both the cases and the problem was solved one by one for both materials.

 

meshed model 

 

Results:

 

For Aluminum Model:

 

Total deformation:

 

figure 4 

 

Equivalent Stress:

 

figure 5

 

Structural Error:

 

figure 6

 

Directional Deformation:

 

figure 7

 

 

For Engineering Plastic Model:

 

Total Deformation:

 

figure 8

 

Equivalent Stress:

 

figure 9

 

Structural Error:

 

figure 10

 

Directional Deformation:

 

figure 11

 

When the analysis was carried out both using Aluminum Alloy and Engineering Plastic without mesh refinement, we could observe similar results with the circularity criterion satisfied. However the mesh doesn’t seen to be appropriate so as to provide a final conclusion, therefore the analysis with Engineering Plastic is further carried out after refining the mesh appropriately as discussed in the section below:

For mesh refinement, first off all the model of the pressure cylinder cover is divided into 5 sub-parts so that each part will be meshed separately and the surface distortion will be avoided.  The geometry of the 5 parts is shown in fig. 12.

 

figure 12

 

In the next step the contacts between all five parts defined accordingly, then “Sweep” meshing method is provided to four parts, {i.e. 4 plates and one inlet except wall} and the wall is meshed with the “Patch Independent with tetrahedron” method, after generating the mesh with the above mentioned methods, we found the mesh discontinuity on inlet in the form of “silver”, so we repaired this mesh defect in “Design Modeler” and then re-meshed the cover and we found that all the silver defects were removed and the mesh was appropriate. The meshed model of the cover with mesh details is shown below in fig. 13.

 

figure 13

 

After mesh refinement the number of nodes and elements were reduced and the maximum value of skewness mesh metric was 0.89 which was less than 0.95, it means the mesh is appropriate.

The problem is solved again for the same results and the results are shown below:

 

Total deformation:

 

total deformation

 

Equivalent Stress:

 

equivalent stress

 

Structural Error:

 

structural error 

 

Directional Deformation:

 

directional deformation

 

Final Deduction:

After analyzing all the above results for Aluminum Alloy and Engineering Plastic, we observed that the directional deformation of the circularity region reduces in case of engineering plastic which also reduces the risk of gas leakage and the value of 0.001375mm is much lesser than the value of 10 micron.

Hence the Engineering Plastic material is safe for the cover of pressure cylinder and it can easily replace the aluminum alloy.