Challenge 5 - Modelling Spot welds

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Good job on completing the challenge. Your report looks great!!

                                             Modelling Of Spotweld 

OBJECTIVE: To model spotwelds for the given assembly of parts and to run a crash test and to compare the axial and shear force between beam and solid element spotweld.

PROCEDURE(case set up and execution)

CASE I: Modelling with beam elements.

The file is loded to Ls-Prepost and 7 beam elements are created in a symmetric manner

• *Section cards are created for both Shell elements and beam elements . For shell part, I have assigned a thickness of 2mm with ELFORM 16, CST as tubular and for Beam parts, i have assigned an ELFORM value of 9, QR/IRID=4 and thickness as 2mm.

• Materials are being created. For all the parts, i have assigned the material properties for steel. I have assigned *MAT_PIECEWISE_LINEAR_PLASTICITY (MAT024) For the shell part and i have choosen MAT100 spotweld for beam elements.

Failure time for the beam elements are defined as 5ms, Effective plastic strain=10

Steel properties: E=2.1e5, Density=7.85e-3, Pr=0.3, σy=1000 and ETAN=10000 (g,mm ms)

• Sections and materials are assigned to the respective parts in Parts sections.

• In boundary conditions, SPC for arresting the one side is defined and Prescribed_motion_set is defined on the other end with displacement. For defining displacement, load curve data is also defined with Abscissa values as (0,0) (10,10) (10.01,10).

• Control Termination has been given to the model with DT=10 ms. Hourglass is also taken into consideration in the Control energy card.

•  Database Binary D3plot card has been given to the model with DT=1 ms so that the output data will be written every 1 milli second of the total run time (10 ms).

•  Database ASCII is also written with GLSTAT, MATSUM, NODOUT, RCFORC, SECFORC, SWFORC with DT as 1 ms. 

•  Database History node is also defined for the nodes of all the beam elements so that the results can be obtained for those nodes.

• Database cross section is also defined so that the cross sectional force can also be determined. For that, a node set and a shell set is defined and SECFORC card is opt in the database ASCII options. 

•  Contact has been defined with the card Automatic_single surface by defining slave as the shell parts. contact tied_shell_edge_to_surface is also defined with shell parts as Master and beam nodes as the slave nodes.

• The model is checked with "model checking" tab and the the file has been saved as Keyword file (.k).

• The Key file is being loaded into ls-program-Manager and is allowed to run. At the end, beam elements got failed at 5.0 ms and normal termination has occured and D3 plots are automatically written and saved to the folder.

• The D3 plot file is opened in ls-prepost and the output has been checked.

CASE II: Modelling with solid elements (HEX).

Here, the procedures are almost the same except here i have used hex elements instead of beam elements. Changes are mentioned below.

• For the solid parts, i have assigned an ELFORM value of 1.
• contacts are changed to spotweld by giving solid parts as slaves and the shell parts as the master.

RESULTS OBTAINED:

1. Cross Sectional Force

BEAM ELEMENT

The maximum cross sectional force in x direction is around 494 N  

SOLID ELEMENT

The maximum cross sectional force in z direction is around 1620 N  

2. AXIAL AND SHEAR FORCE

1.AXIAL FORCE

Axial force is the force in the beam acting parallel to it's longitudinal axis.

1.1 Solid Elements

The maximum axial force reached is 3060 N. Since the elements are in an inclined position at the initial stage, the axial forces were getting reduced. Once the elements attained 90 degree inclination, the axial force reached zero and while the parts were getting pulled, the force kept on rising until the TFAIL(5ms) reached. When the elements got failed, the forces went back to zero.

1.2 Beam Elements

The maximum axial force reached is 1830 N. Here the force were falling and rising beacuse of the inclination of the beam elements. once it reached the TFAIL value, the elements got failed and the forces went back to zero.

2. SHEAR FORCE

Shear force is the force in the beam acting penperdicular to it's longitudinal axis.

2.1 Solid Elements

When the inclination of the elements reached 90 degree, the shear force reached it's maximum value and as shearing happens the inclination went down and so the force. Once it's reached the TFAIL value, all the elements got failed and the forces went back to zero.

The maximum shear force reached is 7.16e3 N.

2.2 Beam Elements

The maximum shear force reached is 1.81e3 N. Once the elements reached the TFAIL value, all the elements got failed and the forces went back to zero.

3. ACCELERATION OF A MID NODE (near the weld region)

Solid Spotweld.

The maximum acceleration reached for the node:501667 is 646 mm/ms2 at 7ms.

Beam Weld.

The maximum acceleration reached for the node:501566 is 259 mm/ms2 at 4ms.

4. ENERGY (K.E,I.E,T.E,Sliding Energy)

Solid Elements

Here from the graph, the Hourglass energy remains within the zero value.Internal and total energy kept rising until the elments got failed and remains almost constant. Sliding energy is zero since there is no conctact happened between the parts in the simulation. The kinetic enegry kept varying between 0 and 3000 Nmm.

Beam Elements

Sliding and Hourglass energy is zero. I.E and T.E kept rising until it reaches the TFAIL. K.E kept on varying between 0 and 2500 Nmm.

5. DIRECTIONAL STRESS AND STRAIN ALONG THE LENGTH (X diection)

Directional stress of beam weld (Along x axis) just before the failure of welds is 701 Pa

Directional strain of beam weld just before the failure of welds is 7.28e-05

Directional stress of Solid Spotweld (Along x axis) just before the failure of welds is 1093 Pa

Directional strain of Solid Spotweld just before the failure of welds is 6.9e-3

CONCLUSION

Spotwelds modeling for the given assembly of parts are done and a crash test is ran and the axial and shear force between beam and solid element spotweld are compared and the results are plotted. From the results beam elements were showing a less stress results which helps the part from avoiding failure.

There are other ways also to determine the weld failure like using *constrain_spotweld or using *constrain_generalized_weld_spot where we need to provide the axial or shear force to fail the weld.

weld failure is detremined for simulations as the parts are more important while a crash happens and we are not interested in weld or it's behaviour.

* All the necessary files are attached with this report.

Thanks,

Rakesh