Week - 5 - Modelling Spotwelds

#6 / Week _ 5 - Modelling Spotwelds.

AIM: To simulate the spotweld created using a beam and solid element and run the model to compare them.

ABSTRACT: In this challenge, we will compare the models first by creating the spot weld using a beam element and then by creating the element using the solid hexa element. after running we will also compare the post-processing results.

THEORY:

Spot welding is a type of resistance welding technique that comes under the fusion welding category where heat and pressure both are applied to join two parts. The Heat produced is due to the resistance of the current flow through the material air gap. The heat generated is equal to I2R and nugget formation happens. Then when held for a few fractions of seconds the fusion between the part happens.

METHODOLOGY:

To run the simulation we need to follow certain steps

1. Open the keyword file in the LS Pre-post environment.
2. Create the beam element for spotweld.
3. Define the Material card and section card for spotweld as well as for the plate to be welded.
4. Assign the section and material for the weld beam part and also for the plates.
5. Define the contact type between the plate and plot weld as well as for the plate self-impact.
6. Create the initial velocity card for the parts as 50kmph or 13.889 mm/ms.
7. Create the planer rigid wall 20 mm away.
8. Define the DATABASE cards such as D3PLOT, ASCII, NODE HISTORY, SWFORCE, ...etc.
9. Define the control card Termination.
10. Save as a keyword then RUN the file to create the output file into the solver.
11. Analyze the post-simulation results.
12. Run the same by changing the welding element to solid(hexa) and a new section with the same material card.

PROCEDURE:

Open the keyword file in the LS Pre-post environment.

open the keyword file on ls pre-post to set the deck file. once we open the file, we can see two plates that needed to be welded. using beam element and then using hexa solid element.

/ Create the beam element for spotweld.

Create the beam element to represent the spot weld between two plates. to create that go to element generation and under beam section and Beam By [Two_Node_sets] pick the node-set 1 select the node and then pick node set 2 select the second node.

In a similar way create 5 sets of the beam elements. (As shown below).

Define the Material card and section card for Spotweld as well as for the plate to be welded.

• To define the material card for the spotweld select MAT 100 to give the steel properties. (gm, ms, mm)
• The best simulation should have a failure at half of the termination time. So, put TFAIL time half of End Time in Control Termination.

Define the material card for plates with an ELASTIC card MAT001 using steel properties.

Define the section for the beam using the SECTION_BEAM card with 'ELFORM 9' for spotweld.

Define the section for the Top & Bottom Plates using the SECTION_SHELL card with ELFORM 16 for a fully integrated shell element.

Assign the section and material for the weld beam 'part' and also for the Top & Bottom plates.

/ reate a part card for assigning spot weld element material and section.

/ Create a part card for assigning Shell Top & Bottom Plates element material and section.

Define the contact card for spotweld with TIED_SHELL_EDGE_TO_SURFACE and AUTMOATIC_SINGLE_SURFACE for plate self-Impact.

/ Set the plates under part-set and assign them as slaves by selecting SSTYP as 2 & MSTYP as 0 for self-contact.

/ For CONTACT_TIED_SHELL_EDGE_TO_SURFACE -> Set the part-set for the beams and assign them as slave and master as plates using SSTYP as 2 and MSTYP as 2.

Create the planer rigid wall 10 mm away.

/ Create a rigid wall using create an entity and give a distance of 10mm from the part.

Create the initial velocity card for the parts as 50kmph or 13.89 mm/ms.

/ Create an initial velocity card using the Create entity and assign 13.89 mm/ms speed to all components.

Define the DATABASE cards such as D3PLOT, ASCII, NODE HISTORY, SWFORCE, ...etc.

Define all the cards necessary for viewing the result during post-processing such as BINARY_D3PLOT, ASCII_OPTION, and HISTORY_NODE.

Check the ELOUT, GLSAT, MATSUM, SWFORC, and NODEOUT with DT value as '0.1'.

Also, insert the node for which we need output data in HISTORY_NODE CARD.

Define the control card Termination.

set the termination END TIME as 10 ms similar to the previous challenge.

// Case 2 For Hexa solid spotweld element

For case 2 for solid hexa spotweld element create the element using the element editing option and select 8 node points.

Use the Material card same as for steel created for beam element but change the Section card as SECTION_SOILD and ELFORM 1.

CONTACTs ->

Define the contact type for Spotweld in solid element as CONTACT_SPOTWELD create as a set of part and define Spotweld as slave and plate as master.

Post-processing Results:

Beam Element Case 1:

Axial Forces ->

As we can see in the case of the beam element the axial force Maximum reaches 6.96e+03N at 1.2ms.

Shear Forces ->

As we can see in the case of the beam element the shear force Maximum reaches 1.01e+04N at 0.9ms.

Solid Element (Hexa) Case 2:

Axial Forces ->

As we can see in the case of the Solid(Hexa) element the axial force Maximum reaches 2.65e+03N at 4.8ms.

Shear Forces ->

As we can see in the case of the beam element the shear force Maximum reaches 7.22e+03N at 1.7ms.

Failure plot ->

/Beam Element Case 1:

For Beam element spotweld initially in around 1ms 3 beams failed & last 2 beams failed at 5ms.

/Solid Element (Hexa) Case 2:

In Solid element spotweld, we see that all solid elements failed at 5ms.

From the analysis of Spotweld, we can observe that solid elements are more accurate than beam element spotweld.

Acceleration plot ->

/Beam Element Case 1:

As we can see for the beam element the acceleration of node 502655(Top plate), and 508233(Bottom plate) maximum of 4.71e+03 mm/ms2 at 2.4ms.

/Solid Element (Hexa) Case 2:

As we can see for the beam element the acceleration of node 502655(Top plate), and 508233(Bottom plate) maximum of 3.01e+03 mm/ms2 at 6.6ms.

The internal energy of the solid element is more so the solid element absorbs more energy than the beam element but as the spotweld fails there is will huge displacement in sheet metal which as solid element spotweld this huge displacement results in more acceleration at the mid-node during spotweld failure.

Energy plot ->

Beam Element Case 1:

As we can see that the K.E is at a maximum at initial (impact time) then drops down and converts to internal energy (strain energy) and T.E is almost constant but lost has sliding energy loss.

Solid Element (Hexa) Case 2:

As we can see that the K.E is at a maximum at initial (impact time) then drops down and converts to internal energy (strain energy). T.E. is almost constant but has sliding energy loss.

All energy values are higher in solid element spotweld than beam element spotweld. So, we can observe that solid element spotweld is stiffer than beam element spotweld.

Effective stress in Animation :->

Beam Element Case 1:

Solid Element (Hexa) Case 2:

Comparison:

Axial & Shear Force ->

SPOTWELD	Axial Force	Shear Force
Beam element Spotweld ->	6.96e+03	1.01e+04
Solid (Hexa) element Spotweld ->	2.65e+03	7.22e+03

Here beam element is a 1D element with some approx. thickness which is less than the solid element the tensile resistance is maximum in the beam element compared to the solid element that’s why the axial force is more in the beam element spot-weld

Since Shear Stress Depends on the thickness of the element and we know the solid element is thicker and the beam element is lesser thick so, the solid element will have more shear strength than the beam element.

Conclusion:

• We have Model Two types of Spotweld in the sheet metal separately and compared the results.
• The Spotweld failure criteria values were calibrated according to the failure at half of the termination time.
• As we saw The Solid element spotweld experiences more stress than the beam Element and The Internal energy of the Solid element is very higher than the beam element.
• And we can also conclude from the result that the solid element is stiffer than the beam element and offer great resistive force against the loss.
• So the Solid element is preferable for a realistic condition.