1D Element Creation Challenge

 

 

Objective:

 

Mesh the Given component with the Size of 5 Units. Create 1D elements on the following component with given cross-section and DOF

a. Rod element:- Translational DOF should be Constrained with RBE2 link

Cross-Section: BOX- Dimension a= 12 mm

                              dimension b=10 mm

                              Thickness t= 0.75 mm

b. Beam element:- All DOF should be constrained with 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:-  Constrain only x and y DOFs With RBE3 link

Cross-section: X 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 the RBE2 link

f. Join the two components with Spring elements  

 

 

 

Solution:

 

Here we are going to create a 1D element on the given component and mesh accordingly. But before we proceed we need to take a look at what are 1D elements. And we are going to get the idea from few research paper.

 

While working with 1D elements sooner or later you will come across the following element types:

• CROD
• CBAR 
• CBEAM

In brief, CROD elements support (allow) tension and compression only, whereas CBARS and CBEAMS allow bending as well. A CBAR element is a kind of simplified CBEAM element and should be used whenever the cross-section of the structure and its properties is constant and symmetrical.
The CBAR element requires that its shear center and the neutral axis coincide. Due to this requirement CBAR elements are not useful for modeling structures that may warp, such as open channel-sections. This limitation is not present in CBEAM elements.

Thus, CBEAM elements are used to model more “complicated” geometries with varying cross sections. Important to note, in CBEAM elements the neutral axis and shear center are noncoincident. Overall, this type of element demands a deeper understanding of beam theory.

Furthermore, we recommend the beginner to use the predefined 1D element cross-sections available with the OptiStruct library (provided you are using OptiStruct/RADIOSS as your finite element solver). Another benefit of employing the cross-sections available with the OptiStruct library is that the stress recovery points which are needed for postprocessing stress results are predefined already. Of course, in addition to the cross-sections depicted further below (OptiStruct library) you can create your very own and general 1D cross-sections with HyperMesh.

 

CROD Elements In the following the general modeling building process based on CROD elements is documented. Most of working the steps can also be applied to CBAR and CBEAM elements, too.

This element “understands” tension and compression loads (axial forces) only. In other words, the nodes of a CROD element only have translation degrees of freedom (still this element has a torsional stiffness).

 

Simple beams with constant properties (symmetrical and constant cross-section), may be modeled with CBAR or CBEAM elements. However, what you need to recall is that in CBAR elements the origin of the element coordinate system is centered at the shear center of the crosssection (shear center and neutral axis coincide). Any offsets between the neutral axis and the shear center is not accounted for. As a consequence, CBAR elements are not useful for modeling beams that warp as it may be the case with open channel sections. Thisis because,the cross-sections of CBAR elements remain plane. In other words, whenever you are modeling open or nonsymmetrical sections be especially cautious with the element type you are going to use.

 

 

The cross-sectional properties, shear flexibility factors, and stress recovery points (C, D, E, and F) are then computed using the TYPE and DIMi as shown below. As the CBAR and CBEAM elements also account for bending the orientation of the element and thus of its cross-section becomes important (as it automatically defines the location of the pre-defined stress recovery points; see discussion below).

 

 

As mentioned earlier, care must now be taken regarding the orientation of the cross-section (orientation of the element and thus “location” of the stress recovery points)

 

The local element x-direction is given by its first (A) and second node (B). Its overall orientation i.e. the local xy plane (Plane 1) of the element is then defined by a vector v and the local x-axis. The v vector is defined with respect to the global coordinate system, however.
Note, more information is also available in the help documentation helphwsolvershwsolvers.htm, then Index > CBEAM or CBAR)

 

Now we are going to setup our component with 1D elements. And for that we are going to extract the model and import it in hypermesh.

 

Once we imported the geometry then we are going to start working on geometry.

 

 and again here we are going to get the geometry loaded in wireframe mode then we can use a tool to give a visual display of the solid surface.

 this is the tool we can use to get the desired view.

 

 Now we are going to perform mid-surface and assign the property along with it. The geometry is called Bracket, so we named the lower and upper bracket as BRACKET_1 and BRACKET_2.

 

 

 

 

Now that we created the mid surface, we are going to delete the solid components which are 3D. so only the sheet surface is left with 1d view.

 

 

we change the color for references for the brackets so that it would be easy to understand the differences.

 

now we are going to add material type t0 bracket1 & 2, which is STEEL, and then add a washer around the circled holes of the components.

 

 

now adding washer from washer split tool.

 

 

moving onto meshing the whole component to Mixed mesh with tetra and Hexa elements. If there is less number of nodes compared to the bigger concentric washer then we can level up the same by decreasing and increasing the nodes.

 

 

This is what it looks like after editing the mesh part.

 

 

now we are going to add RBE2 and RBE3 Links according to our objective.

 

for RBE2 we are going to go for rigids

for RBE3 we have rbe3

 

 

this is how we get RBE2 and eventually RBE3 links. Always try to select the BY PATH method to multi-select all nodes at once.

 

 

a. Rod element:- Translational DOF should be Constrained with RBE2 link

Cross-Section: BOX- Dimension a= 12 mm

                              dimension b=10 mm

                              Thickness t= 0.75 mm

 

We can add these 1D elements in Hyperview where we can create and modify the elements according to our needs or you can select from Standard selection and then from there Hypermesh or Optistruct selection for cross elements.

 

here we select Thinned walled box

 

 

we have setup the elements and we are gong to give proper dimension too for the same.

 

 

 

b. Beam element:- All DOF should be constrained with 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:-  Constrain only x and y DOFs With RBE3 link

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

                                             Thickness DIM2= 1.2 mm

                                             Dimension DIM3= 10 mm

                                             Thickness DIM4= 1.2mm

 

Here you can select the CROSS from the OPTISTRUCT section

 

 

 

 

after adding the elements we are going to create properties for them and then assign them accordingly.

 

 

This is how it looks like when we complete adding our elements and assigning them.

 

 

 here we assign their properties and edit the physical parameters that affect the geometry.

 

 

 

Now we selected a 2D representation of the geometry and we get to see the elements assigned correctly onto the componenets.

 

 

 

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

 

Element types can be selected as CMASS1

 

 

f. Join the two components with Spring elements

 

 

 

 

Now this is our complete and finish product.

 

 

 

 

References:

1D_Elements_Extract.pdf (altairuniversity.com)