Week - 5 - Modelling Spotwelds
OBJECTIVE :
1) To model the spotweld using the beam elements and solid elements in two seperate cases.
2) To run the simulation for the beam spotweld and solid spotweld using the same *MAT_SPOTWELD using the steel properties.
3) To compare the axial and shear forces of both beam and solid spot welds and calibrate the data for the failure of both the welds.
4) To ensure that the best simulation has the failure at half the time of the termination.
Fig 1 Model
CASE SET UP :
Creating the rigid wall
The rigid wall is created using the Rigid Wall card in the keyword manager. The Normal to the Rigid wall is created in such a way that it's direction is opposite that of the Intial velocity of the plates.
Fig 2 Creating the Rigid Wall
CASE 1 :
1. Creating the Spot welds using the beam elements
The beam elements are created using the element edit tool under the element tool bar. In the element gen tool, the beam elements are created by picking the nodes between which the beam elements are to be created.
Fig 3 Creating the beam elements
2. Creating the Material cards for the plates and the Spotwelds
i. The Material card for the plates
The material card used for the plates is *MAT_ELASTIC. All the properties of the STEEL are fed into the card.
ii. The material card for the spotweld
The material card used for the spotweld is *MAT_SPOTWELD. All the properties of the steel are fed into the card.The values for the NRA, NRS and NRR are fed to be extreme.
Fig 5 Material card for the spotweld
3. Creating the section card for the Plates and beam elements
The section cards are created for the plates in the keyword manager and the thickness of the elements are entered. The elementform 2 is chosen.
Fig 6 Creating the section for the Plates
Similarily, the beam section card is created for the beam elements and the elementform 9 is chosen for the beam element section. The tubular form is chosen as the beam form.
Fig 7 Creating the Section for the Beam
4. Assigning the Material and the section card to the Part ID
The material and the section card created are assigned to the respective Part ID's i.e, Plates and the spotwelds.
5. Creating the Intial Velocity card
The Intial velocity card is created in the keyword manager and the intial velocity is applied by selecting all the nodes of the plates and entering the value of 50 kmph.
Fig 8 Creating the Initial Velocity card
6. Creating the Contact cards
i. The Automatic surface to Surface contact for the plates
The automatic Surface to Surface contact card is created for the self contact in case of the plates.
Fig 9 Creating the Self contact card for the Plates
ii. Tied Contacts between the Spot welds and the Plates
The Tied contacts between the spotwelds and the plates are created by creating the tied Shell edge to surface card in the keyword manager. The nodeset id for the spotweld beam elements are selected as the slaves where as the Part set ID created out of both the plates is selected to behave as the master.
Fig 10 Creating the Tied Contact between the Beam and the Plates
7. Giving the ouput requests
The Output requests are given by creating the Following cards under the keyword database
i. ASCII
Under the ASCII card the following requests for the output plots are checked :
a) GLSTAT for the energy plots such as Internal Energy, Kinetic Energy, Total energy, resultant Energy etc
b) MATSUM for the different material energy plots
c) RWFORC for the Rigid wall forces
d) SWFORC for the Spotweld forces such as the Axial forces, Shear forces, Netresultant forces.
ii. Binary D3plot
8. Creating the Control termination card.
The ENDtime for which the simulation has to be run is entered in the Control termination card.
CASE 2 :
1. Creating the Spot welds using the solid elements in place of the Beam Elements
The solid elememts are created by Hexa elements by selecting the four nodes of one plate and another set of four nodes form the second plate in the element edit tool thus creating the solid (Hexa) element between the two plates.
Fig 11 Creating the solid spotwelds
2. Creating the Contact cards
i. The Auto matic surface to Surface contact for the plates remain unchanged
ii. Tied Contacts between the Spot welds and the Plates
The Tied contacts between the spotwelds and the plates are created by creating the tied Shell edge to surface card in the keyword manager. The nodeset id for the spotweld solid elements are selected as the slaves where as the Part set ID created out of both the plates is selected to behave as the master.
Fig 12 Creating the Tied contact between the Solid spotwelds and the Plates
3. The Other cards such as the material,section card , Intial Velocity card , control termination card remains unchanged with respect to the CASE 1.
EXECUTION :
The Keyword files formed for the both the cases are run in the LS-RUN.
RESULTS :
1. Axial Spot weld forces for the Spoweld Beam
Fig 13 Axial Forces in case of the Spotweld Beam elements
Inference: The maximum force at the time of the contact is 3480N for one of the Spotweld beam element which is in the middle . Hence, any force bigger than this will cause the welds to fail during the contact with the rigid wall.
2. Axial Spot weld forces for the Solid elements
Fig 14 Axial Forces in case of the Spotweld solid elements
Inference: The maximum force at the time of the contact is 1515 N for one of the Spotweld solid element which at the left corner. Hence, any force bigger than this will cause the welds to fail during the contact with the rigid wall.
3. Comparison of the Axail Spotweld forces between the Spotweld Beam elements and the Spotweld Solid elements.
Fig 15 Comparison axial forces between the Beam elements Solid Elements
Inference : The axial force is more in case of the beam elements as compared to the solid elements.
4. Shear Spot weld forces for the Spot weld Beam
Fig 16 Shear Force in case of the Spotweld Beam Element
Inference : The maximum shear force at the time of impact is 1359 N at the time of the contact with the rigid wall . The middle beam element has the Maximum shear force at the time of the contact with the rigid wall.
5. Shear Spotweld fores for the Spot weld Solid
Fig 17 Shear Force in case of the Solid Spotweld elements
Inference: The maximum shear force at the time of the contact with the rigid wall is 7210N in case of the solid spotweld element.
6. Comparison of the Shear Spotweld forces between the Solid Spotweld elements and the Beam spot weld elements
Fig 18 Comparison of the Shear Force between Solid and the beam Spotweld Element
Inference : The Shear force in case of the Solid elements is nearly 6 to 7 times more as compared to the shear force in case of the beam elements.
7. Energy plots
i. Kinetic Energy Plot
Fig 19 Comparison of the Kinetic energy between the Spotweld Beam Element and the Spotweld Solid Element
Inference : The Kinetic energy in both the cases are approximately simillar at all the timesteps.
ii. Internal Eenergy Plot
Fig 20 Comparison of the Internal Energies Between the Beam Spotweld Elements and the Solid Spotweld Elements
Inference : The Increase in the Internal energy is more in case of the Plates with the Solid Spotweld Elements as compared to the Plates with beam spotweld elements.
iii. Total energy Plot
Fig 21 Comparison of the Total energies between the Beam Spotweld elements and the Solid Spotweld elements
Inference : The Total energy is more in case of the plates with the solid Spotwelds as compared to the plates with the beam spotwelds.
8. Rigid Wall Forces
Fig 22 Comparison of the Rigid Wall Forces
Inference : The rigid wall force is more in case of the plates with Solid Spotwelds as compared to the plates with the Beam Spotwelds.
CALIBRATION OF AXIAL AND SHEAR SPOTWELD FORCES FOR FAILURE
i. Calibrating the Spotweld Axial force for the failure of the beam spotweld element
The value from the plotted result showed that the minimum value of the axial force generated is 410N . Any value of the Axial force below this value will cause it to fail during the simulation. Hence, entering the value of the axial force as 350N in the MAT_SPOTWELD card will cause the spotweld beam element to fail as seen in the simulation run.
ii. Calibrating the Spotweld Shear force for the failure of the beam spotweld element
The value from the plotted result showed that the minimum value of the shear force generated is 400N. Any value of the shear force below this value will cause it to fail during the simulation. Hence, entering the value of the shear force as 350N in the MAT_SPOTWELD card will cause the spotweld beam element to fail as seen in the simulation run.
iii. Calibrating the Spotweld Axial force for the failure of the solid spotweld element
The value from the plotted result showed that the minimum value of the axial force generated is 455N . Any value of the Axial force below this will value cause it to fail during the simulation. Hence, entering the value of the axial force as 375N in the MAT_SPOTWELD card will cause the spotweld solid element to fail as seen in the simulation run.
iv. Calibrating the Spotweld Shear force for the failure of the solid spotweld element
The value from the plotted result showed that the minimum value of the shear force generated is 5155N . Any value of the shear force below this will value cause it to fail during the simulation. Hence, entering the value of the shear force as 4000N in the MAT_SPOTWELD card will cause the spotweld solid element to fail as seen in the simulation run.
v. Calibrating the Spotwelds to fail for half the time of the simulation run time
The value for the Tfail is entered in both the cases so that the spotwelds fail at half the simulation time .
Note:
All the calibrated simulations could be found in the attached Power point presentation.
CONCLUSION :
- The simulation and comparison for the spotweld beam element and the spotweld solid elements were carried out successfully.
- The spotweld beam elements and the spotweld solid elements were calibrated for the failure due to the axial force and the shear force.
- The spotwelds were also calibrated for the TFAIL i.e, they were made to fail at half the time of the total simulation.
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