Week - 5 - Modelling Spotwelds

Aim:

To model, a Spotweld connection between two sheet plates and their axial and shear force should be compared among beam and solid elements

Theory:

Spotweld is a common welding method used to join two or more metal components at a particular spot, unlike other welding methods where the weld is created along a line. In FEA, spotweld is used as a connection to connect multiple parts. It is modelled as either a 1D joint or a 3D (Hexa) joint. Modelling a spotweld as a 1D element, reduces the computational time and cost, while the 3D joint gives more freedom in the actual representation of the weld, but at the expense of time and cost.

Procedure:

• Import the keyword file from the downloads and check the model for any sort of issues
• The given model consists of two shell parts (meshed)
• The unit system we're going to use is gm, mm, ms

Create the Material for the Sheet Metal Plates, here MAT_ELASTIC was used

Create the Material for the SpotWeld Beam Elements, here MAT_SPOTWELD was used. In that Material, we specified the Tfail value, to make Beam Elements gets failed by the time of 5 ms. 

Since we don't have the exact data of yield stress value, Axial force resultant, Force resultant and Torsional moment resultant. We defined the Tfail value to eliminate the Weld Elements by the time of 5 ms. Create the Section/Properties for the Sheet Metal Plates, here SECTION_SHELL was used

Since the Sheet Metal Plate meshed with 2D Elements, we specified the Shell Element properties. Create the Section/Properties for the Beam Elements, here SECTION_BEAM was used.

Assume the Thickness of the Spotweld is 3 mm, we specified the value, and the Element formulation should be 9, which should be selected, when we are using the Material as a spotweld beam, see *MAT_SPOTWELD (Type 100). Create the Section/Properties for the Beam Elements, here SECTION_SOLID was used.

For Solid Weld Element, we have to specify the Section as solid with constant stress solid element (default)

Assign all Material and Section to the corresponding parts, which is listed as shown:

 Create the RigidWall to make the Crash scenario, ensure the Normal of the RigidWall should be opposite to the Sheet Metal Plate and maintain some decent gap between the RIGID WALL and Model. 

Assign an Initial Velocity to the Model, so then the Sheet Metal Plate with Spotweld will be projected towards the Rigidwall to experience the Crash scenario.

Create a valid contact between the components available on this model. For that here, AUTOMATIC_SINGLE_SURFACE contact was created between the Sheet Metal Plates, to serve as a self contact between them

TIED_SHELL_EDGE_TO_SURFACE contact was created between the Spotweld beam and Sheet Metal Plates to enhance the behaviour between them

CONTACT_SPOTWELD type contact was created between the Spotweld Solid and Sheet Metal Plates to enhance the behaviour between them

Now, we need to define the CONTROL_ENERGY, which will give controls for energy dissipation options

Define the CONTROL_TERMINATION, to inform the exit time of the simulation

Finally, create the DATABASE card to call out all the results.

• In ASCII_Option: ELOUT, GLSTAT, MATSUM, SLEOUT, NODOUT, SECFORC, SWFORC
• To define the frequency of animation file creation, we need to create the BINARY_D3PLOT

 To evaluate the amount of force that gets transmitted towards a certain area, we need to define a Cross Section on the model as shown

 To know the results of the Beam Element Spotwelds, we need to define a separate DATABASE_HISTORY_BEAM Card for Beam Elements.

Results and Observations:

After the simulation went well, now we need to Post Process the results, that we obtained:

Energy Outputs for Beam Element Spotweld:

 BEAM ELEMENT:

  SOLID ELEMENT:

 Sliding and Hourglass Energy Plot:

 BEAM ELEMENT:

  SOLID ELEMENT:

Cross Section Resultant Force Comparison:

From this, we can understand, how much force gets transmitted, when the Sheet Metal Plate made an impact with the RigidWall:

 BEAM ELEMENT:

SOLID ELEMENT:

Von Mises Stress:

BEAM ELEMENT:                                                                                    

 SOLID ELEMENT: 

Stress along X-axis:

BEAM ELEMENT: 

SOLID ELEMENT: 

 Axial Force Comparison:

The axial forces induced in the Spot welds for both the Beams and the Solid were plotted from the 'ASCII option' from the 'post' tab. For that, we need to tick the check box in "SWFORCE in ASCII_Option" itself. The overall/average axial force was higher in the Solid_Element Spotweld since the Solid_Element has higher tensile strength and thus takes higher tensile loads.

Shear Force Comparison:

Similarly, the shear forces were also plotted for the Beams and the Solid SpotWeld. Since Solid_Element Spotweld has more strength to absorb the shear force.

Conclusion:

In this challenge, the Sheet Metal Plate was connected using the two types of spot welds that were analyzed successfully and the results were plotted. The types of spot welds used for structural analysis are of 2 types viz. 1D spotweld and 3D spotweld. 1D spot welds are generally modelled using the beam elements while the solid spot welds are modelled using the hexahedral elements. The failure of both the spot welds were scheduled at half of the termination time (6ms) and behaved as desired.