Week 2 Bevel Gear Challenge

OBJECTIVE

Perform a gird dependency test for the bevel gear simulation for the mesh sizes of 6,5,4 mm Evaluate the different results for von misses Stress Equivalent elastic strain and total deformation

PRODECURE

What is a grid dependency test and its use ?

Grid or mesh generation is the basic step in any simulation .In practice of finite element stress analysis the engineer first needs to know if key stress are converging and second if they have converged to a reasonable level of accuracy .In order to achieve results that are reliable when using the finite element method it must be ensured that an acceptable mesh is used with the respect to the shape and size of the elements .Mesh quality and mesh density values are directly linked with the solution accuracy.

Grid dependency test is done by varying the mesh size from coarse to fine and checking the output result for each mesh .When varying the meshdoes not affect the results much then we can stop and select that maximum mesh size for our final solution output.

Grid dependancy test grid independence test and mesh refinement test are the synonyms and they all mean the same . The aim of this test is to find the best possible mesh size for the solution .In other words a coarse grid will not capture all the features and finer mesh will give a solution of a little higher accuracy than required but at the expense of computational power and time . The results are generally kept in the range of 3-5% variation as acceptable .The difference between the stress component and stress considering the discretization in the local area of high stress must be less than 5%.

• Create Static Structural analysis and in engineering data select the material as structural steel.

• Import the geometry and check in Spaceclaim for any irregularties.
• Then open ansys mechanical and rename the gears.

Contacts Contact created between the both bevel gears .The contact type is frictional with the mating surface of gears selected as contact and target .The behaviour is changed to symetric and the formulation type used in Augmented Lagrange .The interface treatment is set to adjust to touch.

• Joints Joint set for both the gears as the revolute and bodyground

• Analysis Setting The simulation runs for 6 steps So the number of step is set as 6 , Define by time and large deflection is set to on.

• Joint Load One of the gears is given rotation for six time steps and the other is given a constant moment .
• Joint load Rotation.

Now for the different mesh sizes the bevel gear meshed.

• Case 1 - 6mm
• Case 2 - 5mm
• Case 3 - 4mm

For the face of bevel gear use face sizing option and mesh with element size of 1.75mm in all cases.

Result The analysis runs successfully and results obtained for all the cases.

Case 1 6mm

Mesh

Equivalent Stress Max - 1.9778Mpa

Equivalent Elastic Strain Max 1.1463e-5 mm/mm

Total Deformation Max - 47.872mm

Case 2 5mm

Mesh

Equivalent Stress Max - 4.0314Mpa

Equivalent Elastic Strain Max - 2.0996e-5mm/mm

Total Deformation Max - 47.843mm

Case 3 4mm

Mesh

Equivalent Stress Max - 3.8873 Mpa

Equivalent Elastic Strain Max - 2.0835e-5 mm/mm

Total Deformation Max - 47.843mm

CONCLUSION

Grid dependacy test perfomed for all the three cases where mesh size used as 6mm , 5mm , 4mm while the face sizing kept at 1.75mm for all the three cases.

Element Size Equivalent Stress Max Mpa Equivalent Elastic Strain Max mm/mm Total Deformation Max mm

6 mm 1.9778 1.1463e-5 47.872

5 mm 4.0314 2.0996e-5 47.843

4 mm 3.8873 2.0835e-5 47.843

• It is observed that there is no major change in total deformation
• As expected from the grid dependancy test as the mesh was changed from Coarse the fine the accuracy in the results Equivalent Elastic strain from 6mm to 5mm. And from 5mm to 4mm there is small or minor change in value of equivalent stress and equivalent elastic strain.
• Thus on refining the mesh getting more accurate results.

MODEL LINK : https://drive.google.com/file/d/1K5uGsrci9oG8_giSnXGYsYGOWDxs7dgc/view?usp=sharing