Week 6 - Creating connection for Rear door

AIM:

To implement connections for a Rear Door FE model.

DESCRIPTION:

• Understand car rear door assembly
• Understand different types of connections and 1D elements.
• Perform connections for a FE model.

PROCEDURE:

• Methodology for giving connections
• Import the FE model
• Understand the geometry and mechanism
• Give connection to all the bolt holes
• Given the connections to the overlapping surface.
• Give the necessary connection to the areas where it feels necessary as per your analysis requirement. eg. weather-seal strip,
  handle, spot welds, etc.

Introduction:

Car Rear Door Assembly

Connection and 1D Elements

There are mainly 5 types of connection
1. Weld
2. Adhesives
3. Bolt
4. Area contact
5. Replace part

1D Element:

One of the dimension is very large compared to the other two If a large number of bolts are to be modeled, then the use of solid element

representation can be far too burdensome in terms of setup time, contact complexity, and computational cost. An alternative is to use a 1D beam

element representation. This can also use a similar preload method.

There are many different implementations of this approach, but we will focus on a method which uses a rigid element to spider out the head and

nut tend of the bolt to the top and bottom plate respectively, and can connect to 2D or 3D element representation.

They are simply the connection between nodes. There are few working elements majorly used:

a) Non-rigid Links
1. CROD
2. CBAR
3. CBEAM

b) Rigid Links
1. RB2
2. RB3

CROD:

• This element only 'understand' "tension & compression" loads (only axial force only).
• They only have translational DOF.

CBAR:

• Simple beam with constant properties (symmetrical and constant cross-section).
• Shear center and neutral axis should consider, any offset between the neutral axis and the shear center is not accounted
• Not useful to model beam that warps (open channel section).

CBEAM:

• The cross-sectional properties are tapered.
• The neutral axis and shear axis does not coincide
• The effect of cross-sectional warping on torsional stiffness is critical
• The difference in the mass center of gravity and shear center is significant.

Rigid Elements

A rigid element is a link from one node to one or more other nodes, where the motion of the node(s) is governed by the "degrees

of freedom" you choose to connect. A rigid element is actually a constraint equation rather than an actual element.

• Bolt pre-load at a critical interface needs to be modelled, but does not need the bolt to be modelled with any more detail than as a "bar" or "beam" element. An RBE2 can be used to connect the end node of the "bolt" element to the multiple nodes which represent the washer area over which the bolt load acts.
• To model the dynamic behavior of a vehicle, the engine can be modelled as a mass element connected by an RBE2 rigid element to the engine's multiple mounting locations. This makes the reasonable assumption that the engine is "very stiff" compared to the body structure and so the engine does not need to be modelled in detail. The mass is located at the centre of gravity of the engine, and the rigid element links the engine mass to the rubber mounts (eg. springs or bushes) whose stiffnesses are typically much more relevant.

Note:

Both elements "look" the same, in that they have a single node connected to one or (usually) multiple other nodes. The difference is that

the RBE2 element adds (infinite) stiffness to the structure, while RBE3 elements "distribute forces" around the connected nodes, without adding.

any stiffness.

Connectors

These are the geometrical representations of the connection between the entities. The advantage of connectors is the ability to create multiple

connections at a single time.

Spot

• connection at a point
• spot weld, rivet, etc.

Bolt

• connection at the hole locations.
• eg. Bolts
  

Seam

• connection along the length
• seam weld
• connect geometry only
  

Area

• Connection of areas
• Adhesives

Role of a seal in the NVH behavior of a car

Automotive weather seals are typically dual extrusion bulbs of sponge and dense rubber that are attached to either the door or the car body in

order to seal the passenger compartment. The seals can be held in place in several manners, e.g. intermittent pushpins, continuous carriers, etc.,

and have a vast variety of shapes with a height of approximately 10-30 mm. The seal wall thickness is typically a few millimeters to provide a

maximum sealing area at a low compression force.

The seal strip induces some residual stiffness and viscoelastic contribution to the door support conditions and plays a role in the way exterior noise

and vibration can be transmitted to the interior of the car. The initial use of seals in automotive applications was aimed at accommodating

construction variations.

Lately, the isolation issue became important, and the design was oriented to better isolate the passenger compartment from dust, water, and air

leakage. Nowadays the general trend in seal design is mainly oriented on the isolation of the passenger compartment from noise and vibration. For

automotive applications the material requirements aspect, such as resilience, weather resistance (including ultraviolet radiation effects), bonding

strength, tear, abrasion resistance, etc. also need to be considered when designing for optimal weather seals.

At a certain driving speed, the pressure difference between the interior and the exterior of the car pushes the seal outward. If the resultant

pressure is higher than the frictional forces at the contact area, separation occurs. The occurrence of separation is influenced by the compression

rate and the friction coefficient of the rubber to the metal contact area. When separation occurs, an open path for direct noise is created and

turbulence at the door edge is generated. The turbulence is due to the interaction between the escaping air fluxes from the passenger compartment, encountering the air fluxes at the exterior of the car.

The damping, stiffness, and the mass distribution influence the car door vibration levels and the mechanism of energy transmission from the door

to the car body. The support and isolation characteristic of the seal becomes important performance factors that should be taken into account in

seal design and analysis.

PROCEDURE:

1.Import FE model

The FE model is in a .nas format so we need open by using 'input' shown below

Rear Door FE Model

Once you open the model understand the mechanism and necessary areas that need to rigidised or made connected.

Firstly, we will cover all bolt connections through the RB2 stem element. we will perform this connection by using the auto-mode for the selection

of nodes.

2.Next create new PIDs goto Mesh→Macros→Set PID→Faces/Shells→Select the shells→New→P shell as shown below.

3.Next see the properties it shows as shown below.

4.Follow the above steps created the different PIDs for different components as shown below.

5.Next Check the Geometry and observe were give the connections were found.

6.See the above image there is a lot of holes so I'am created the RBE2 connection.

7.Goto the Decks→Nastran→Elements→RBE2→Many nodes as shown below.

8.Follow the above steps create RBE2 connections as shown below.

9.Next create the bolts at the hinge area as shown below.

10.create a 3D point goto the Topo→Points→on COG as shown below.

11.Next convert the 3D point to bolt go to Assembly→Convert→3D Points→Select the 3D point→Bolt→Ok as shown below.

successfully completed 3D point is converted into the bolt as see the image it shows bolt symbol.

12.Next goto Assembly→Connection Manager as shown below.

once you are done with assigning values then apply and realize the connection.

Do the same with all other bolt holes and this can be done for all the holes by selecting them in a one GO process.

Note: surface selection(P1, P2,etc.) by modify-> then use F1 key-> then after selecting press twice Enter key

Hinge connection

connect the surface of the overlapping surface with the help of RB2 cluster element.

Once the cluster RB2 elements are assigned the rotating link is made using a two-node RB2 element where the CM parameter represents the DOF

here we assign 12345. As it is to be noted that 6 is intentionally not provided to allow rotation DOF about Zaxis. Therefore DOF in all directions is

arrested to expect rotational motion about Z_axis, so as to allow the opening movement of the door.

13.Now we have to finally make connections for weather seal strip and window glass. To do so we need to follow certain steps.

1) Hide the FE model except for the glasses.

2) construct the curve all around the glass edge using Fea2curve tab. Select each edge of the glass one by one to do so.(as shown below)

CONCLUSION:
After the completion of the challenge, it can be concluded that for any type of model the understanding of the mechanism is very important. As the

mechanism will decide in analysis ways to make decisions regarding assigning connections. The connection procedure is moreover the same for

any type of model but the requirement to assign the connection may differ from model to model with the requirement of the analysis. So for the

NVH analysis, the weather seal was important to capture and is captured in a pretty good way with help of CBUSH element. Most of the areas are

covered and are been rigidised as well as connected as per the requirements.

LEARNING OUTCOME:
1. 1D element and types of connection.

2. Different types of methods to make connections.

3. Assigning mass to the Rigid body

4. Aware of the working mechanism of the car door.

5. assigning spot and seam weld to the surface

6. Arresting required DOF of the element.