Week 4- Challenge

Aim :

Creat 1D elements on the following component with given cross-section and DOF

a. Rod element:- with only translational DOF and RBE2 link

Cross-Section: BOX- Dimension a= 12 mm

dimension b=10 mm

Thickness t= 0.75 mm

b. Beam element:- with all DOF and RBE3 link

Cross-Section: I Section- Dimension a= 8 mm

Dimension b= 10 mm

Dimension c= 8.5 mm

Thickness t1= 0.75 mm

Thickness t2= .6 mm

Thickness t3= .6 mm

c. Bar element:- with only x and y DOFs With RBE3 link

Cross-section: CROSS section- Dimension DIM1= 5 mm

Thickness DIM2= 1.2 mm

Dimension DIM3= 10 mm

Thickness DIM4= 1.2mm

d. & e. apply the mass of magnitude 10 with RBE2 link

f. Join the two components with Spring elements

Solution:

Midsurface:

Creating a mid-surface shell model is still favourable as :

Accuracy of the end result can be way off with solid mesh elements
Whether you have followed a basic course from a CAD-integrated FEA software, or from a stand-alone High-End FEA software, they will all teach you to create shell meshes for thin-walled parts. Even if you setup a simple thin-walled beam and let it suffer under bending, you already see differences in both stress and displacement for a solid mesh versus a mid-surface shell mesh. Particularly when the solid mesh approach is a course mesh, the effects are even bigger. When you refine the solid mesh, the results will become more accurate, but you will need quite some iterations to have mesh convergence.

The solid mesh approach, which needs 3 to 4 elements across the thickness, results in huge amount of elements and long running times
If you do decide to take the solid mesh approach, please be aware that you need a minimum of 3 to 4 elements across the thickness to capture all bending and stiffness effects to generate an accurate solution. For products that don’t look like a simple beam, it can potentially create huge number of elements, resulting in large running times. If you think of injection moulded parts with ribs, draft angles and fillets and other types of typical geometry, the necessary amount of elements will be enormously and therefor the running times will be huge. We have seen differences for injection moulded parts with a shell approach that take 1 hour to run, while with a proper solid mesh including 3 to 4 elements across the thickness the running time could potentially be somewhere between 5 to 10 days per simulation run.

The shell mesh approach creates a fast running accurate simulations
Since the amount of elements is less for the shell approach, because the wall thickness is captured as a mathematical value instead of actually modelling the thickness, there will be less equations to solve. This results in simulations that run in minutes or an hour instead of days to weeks. That also means that a shell mesh approach can be easily used to perform iterative simulations. Another benefit is that changing the wall thickness in your simulations with the shell approach are easy, and you will see the results of those changes in a very short time.

Creation of Mid Surface :

Using the mid surface command a midsurface was created and than the surface was moved over to the component surface and the remaining components were deleted.

Creation of Washer Surface with 5 mm offset:

Using the quick edit tool , a washer surface with an offset of 5mm was created in all the holes so that a proper mesh is generated and the curvature of the holes is captured .

Creation of 2D Automesh:

Creation of RBE2 and RBE3 bodies :

The following holes have the following elements :

Hole A : RBE2 with only Translational DOF

Hole B: RBE3 with all DOF

Hole C : RBE3 with x and y translation DOF

Hole D : RBE2

Hole E : RBE2

Hole F :RBE2

Creation of mass at e and d holes as shown below :

At holes D and F , mass of 10 units is added as shown above.

Creation of Sections as shown below :

Using the hyperbeam tool sections of cross ,box and I were created .

Creation of Bar elements :

The following holes have the following type of connections :

Hole A : CROD

Hole B: CBEAM

Hole C : CBAR

Hole D : SPRING

Hole E : SPRING

Hole F :SPRING

Creation of Sections :

The sections were assigned by using the update command and after selecting properties and assigning the sections as follows :

Hole A : CROD with BOX section

Hole B: CBEAM with I section

Hole C : CBAR with cross section

Conclusion:

Hence all the DOF,sections and elements have been assigned using the tools in hypermesh