Week 6
Objective: To use and apply various types of connections in the given component using ANSA.
Different types of connections used in ANSA:
Connection Entities are ANSA entities that contain the engineering information of a weldment between two or more parts. Such information is the type of the connection (spotweld, seamweld etc), the geometrical information such as diameter, width or height and connectivity information (which parts participate in the connection). In order to support the various types of weldings (1D, 2D and 3D connections), ANSA supports the following type of
welds:
- 1D connections: spot welds, gumdrops, bolts
- 2D connections: spot weld lines, seamlines, adhesive lines, hemmings
- 3D connections: adhesive surfaces
This information in maintained in the ANSA database and is managed by the Connections Manager. These connections can be realized into FE entities of any type, when the model becomes solver and discipline specific. ANSA can read a variety of standard connection point formats such as MCF (xml), vip, vip2.
RBAR and RBE2 Elements:
The RBAR or RBE2 element can be used for connecting two nodes to model a ‘rigid’ welded type connection, with all 6 DOFs, or a pinned connection with 3 translational DOFs.
The RBE2 element can also be used to model a wagon wheel type connection between the independent and the dependent nodes. RBAR and RBE2 elements artificially add stiffness by constraining the system to follow a one to one linear displacement and/or rotational relationship between the connected nodes.
RBE3 Elements:
Comparing RBE2 Vs RBE3 elements, RBE3 on the other had is not a ‘rigid’ element so to speak. The motion at the ‘dependent’ node is a weighted average of the motion at the ‘independent’ nodes. This is why it is also known as an ‘interpolation’ R element. RBE3 elements do not add artificial stiffness to the structure like the RBAR or RBE2 elements do.
CBUSH Elements:
CBUSH Elements: Is a 6DOF customizable pseudo‐beam element. It has all the advantages of a beam element with the ability to dial in spring values.
CBAR ELEMENTS: a bar element is known as a CBAR. The CBAR element is a general purpose beam that supports tension and compression, torsion, bending in two perpendicular planes, and shear in two perpendicular planes. The CBAR uses two grid points and can provide stiffness to all six DOFs of each grid point. With the CBAR, its elastic axis, gravity axis, and shear center all coincide. The displacement components of the grid points are three translations and three rotations.
CBEAM ELEMENTS: The beam element includes extension, torsion, bending in two perpendicular planes, and the associated shear. The CBEAM element provides all of the capabilities of the CBAR element, plus additional capabilities.
Procedure:
The component is imported into ANSA and geometry clean-up is performed.
Various connections like spot welds, bolts, seam welds re used in order to connect the different parts present in the car door assembly.
1) Single cluster connections:
All the bolt connections are to be connected through the RBE2 stem element and lock their degrees of freedom. This is done under the NASTRAN module, with the help of elements tab
2) Spider connections: These types of connections re used where independent holes are present. It makes the hole rigid and hence voids unnecessary movements.
3) RBE2 two node connections: These are used in the door hinges. Under the RBE2 option, two nodes option is selected and the required nodes for the connection are chosen. In the info option from the elements tab, the two nodes which were created are selected and the degrees of freedom are locked.
4) For door connections: In this type of RBE2, two master nodes of two spider connections of the holes are connected so as to form COG. Then using the CONMi option the mass for COG is specified s 100 grams or 10^-4 tonnes.
5) Bolt connections: When bolts re needed to be fitted in the rear door model, bolt connections re to be used. This is done by first creating a 3D point using the ONCOG option under the points tab in the topo module. Then this 3D point is converted into bolt washer points using the convert option in the assembly tab.
Then under the assembly tab, select the connection manager and select the required points. In the connectivity list, the parts where these connections are required are selected. After this, under the FE representation tab, bolt is selected, and zones selected as in/out (to fi the ones rigidly). These settings are applied, and the realized option is also selected.
6) Spot weld connections: Spot weld connections are done wherever spot welding is required. Same as above, a 3D point is created using the ONCOG option under the points tab in the topo module. Then this 3D point is converted into spot welds points using the convert option in the assembly tab.
Then under the assembly tab, select the connection manager and select the required points. In the connectivity list, the parts where these connections are required are selected. After this, under the FE representation tab, RBE3-HEXA-RBE3 is selected and the search distance value is specified. In order the keep the spot weld locked, RBE3 pinflags are used. These settings are applied, and the realized option is also selected.
7) Bushing connections for windows:
Curve is created using the perimeter of the window. Then these curves re converted into spot lines.
Windows re connected with soft bending so that they can absorb shock without breaking.
Then under the assembly tab, select the connection manager and select the required points. In the connectivity list, the parts where these connections are required are selected. After this, under the FE representation tab, RBE3-CBUSH-RBE3 is selected and the search distance value is specified. Under the bush ID the stiffness constant is provided to the bushing.
The cbush elements are the aligned with respect to the local coordinate system.
Conclusion: The connections were obtained for the given component, rear door of a car. Various connections like RBE, bolt, spot weld and bushing connections were made.