Week - 5 - Modelling Spotwelds

AIM:

      To create a simulation file using input parameters to perform a Crash box simulation by using spotweld beam, solid spotweld & plot the results.

OBJECTIVE:

For the particular simulation, the required input paramters are;

Title card, section, material card, part, initial velocity, spotweld(beam & solid element) contact, control card 

Input .k file and output files (d3plot, glstat, sleout, rcforc)

• Animation of the final simulation
• Cross-sectional force generated in the middle of the crashbox (along its length)
• Acceleration plot of a node  in the middle of the crashbox (along its length)
• Maximum directional stress and strain along the length of the crashbox (X strain, Y strain etc)
• Plot of all energies (total, internal, kinetic, hourglass, sliding)
• Compare axial and shear force among beam and solid elements.

PROCEDURE:

• Import the particular model in LS-Prepost.
• Once the model is imported, Set the input parameters.

• Once the model is imported, Set the input parameters.

• Create a suitable title for the simulation by using keyword manager.

• To create a section for shell & solid element using keyword manager.
• To create a material for shell by using keyword manager go to material-elastic.

• To create a part by using the part option in keyword manager then assign the section & material ID

• To create a rigid wall by using create entity option rigid wall & select the planar option & select a node on a crash box to create a rigid wall.
• By using tran option assign the distance of the rigid wall away from the crash box.

• To create a initial velocity for a crash box by part select initial velocity & pick the part.

• The spot weld can be modeled a beam & shell elements by using various techniques

• For the beam element, the material card is assigned as the MAT_*100 for spot weld material.
• Then the values are asigned & it may take sometime for time-dependent failure concepts like effective plastic strain, maximum axial stress, maximum shear stress, force resultant, torsional moment resultant, moment resultant. Thus for other terms, we can give higher value.
• For the beam element section property is assigned by using *SECTION_BEAM card. Then assign (ELFORM) element formulation as 9, while MAT_*100 applies only for (ELFORM)  formulation in the case of beam element. The cross section is picked as tubular, since default cross section is rectangle it gives zero during simulation. The thickness of the beam at both the ends are given as 3mm.
• *Contact_Tied_Sheel_Edge_To_Surface  is used for the beam element. Part & slave id's will be nodes of beam weld element. To define slave select beam nodes. For defining master select both the parts.

• Then we need to create *Contact_Automatic_Single_Surface contact card for the parts to ensure that after the spot welds breaks the parts come to each other, which shouldn't penetrate.
• By using solid element Spot weld modeled is created. By picking four nodes from bottom & top of the model.
• For the solid element section property is assigned by using *SECTION_SOLID card. We need to assign element formulation (ELFORM) *MAT_100 spot weld material only applies for ELFORM1 formulation in the case of solid element.

• For the solid element, the material card is assigned as the MAT_*100 for spot weld material.

• Then the values are asigned & it may take sometime for time-dependent failure concepts like effective plastic strain, maximum axial stress, maximum shear stress, force resultant, torsional moment resultant, moment resultant. Thus for other terms, we can give higher value.

• For solid element contact type to be used is *CONTACT_SPOTWELD card. the master set id will be part id & slave id will be nodes of solid weld element. To define slave set select solid nodes to create the set. For defining the master select both the parts. It is used to create contact interface for the beam element.
• Create a control card using keyword manager, Time to end the simulation can be calculated analytically by using distance between the rigid wall & the component, so we can able to calculate the time. But extra time is consisdered after the simulation, while crashing & bouncing back of the crash box.

• To generate sectional force in the middle of the crash box, create a cross section. 
• Create a output request to obtained plot results from the crash box simulation. We can set the time, d3 plot, ASCll & select GLSTAT to set dt values for energy plot.
• 
• Finally check for the model for errors & warnings using keyword manager by using model check option.

• Once the model checking is done, We can run the simulation using LS-Dyna option. The file should be imported in the LS-Run for simulation.

ANIMATION:

Von-misses stress

For Spotweld beam:

For Spotweld solid:

• The effective stress(Von-misses stress) is used to predict the yielding of materials under complex loading from the results of uniaxial tensile stress.It satisfies the property where two stresses with equal distortion energy have an equal von misses stress.

PLOTS:

ENERGY FOR SPOTWELD BEAM

ENERGY FOR SPOTWELD SOLID:

• From the above obtained plots beam & solid weld as they impacted with the rigid wall. We can see that kinetic energy has been decreased, where initial energy is been increased. Hourglass energy constantly remains at zero. The total energy remains constant.

SECTIONAL FORCE FOR SPOTWELD BEAM

SECTIONAL FORCE FOR SPOTWELD SOLID:

• The cross sectional force is created for the middle of the crash box & we can see the force value of the Y & Z direction is very low after the impact. Since the velocity value is in the X direction. During impact time we can observe that force value in the x direction is at its peak and it varies up & down after the bounce back of the crash.

AXIAL & SHEAR FORCE FOR SPOTWELD BEAM:

AXIAL & SHEAR FORCE FOR SPOTWELD SOLID:

• By oberving the splot weld is process on various parts & it connects together. we can see that axial forces are higher than the shear force. The force value drops to zero, once spot weld fails. The force acting on the spot weld is in transverse direction. therefore solid element gives force resisting ability.

RESULTS:

• Thus crash box model has been set & spotweld has been created.
• Vonmisses stress animation is created & graphs has been plotted for energies, crosssections, axial & shear force.