Week - 5 - Modelling Spotwelds

Objective :

To create spotweld connections for the given model using the beam amd hexa element in the LS-Dyna.

Procedure :

Step 1: Import the given model to the ls-dyna which is in the keyword format and it is meshed.

Step 2: Now we can see the two different thin plates which are together but doe not have connections. Here we need to create a spotweld connection for the model. To do that first we need to create a required elements between the plates and then we need to give spotweld material to that element.

Step 3: First we are following the beam type spotweld, to create beam go to the the element and mesh deck in that select the element generation and with help of two nodes we can create a beam element.

Step 4: To turn beam element as a spotweld we need material card and connection card, so go to the material card and select the mat 100 spotweld card and give the steel properties to it and also mention the failing criteria for the spotweld. Cretae a section to the beam elements which is beam keyword and mention the beam card id and material card id in the part section.

Step 5: To create connection go to the contact keyword and selct the tied shell edge to the surface and here we need to create a master and slave id for the contact. To create them go to the create entity and select the set option and create a slave set using the beam node set id and master set using the entire part set id and give this id number in the contact keyword and accept it.

Step 6: Now we have created a complete spotweld connection for the given model but we need to create a crash test for the model using the rigidwall.

Step 7: To create the crash test first we need to have contact connection to the rigidwall, to create that go to the contact keyword and select automatic single surfacee. Here we need to give slave set id using entire shells of the model, create the shell set using the set option and give the id number in the contact keyword and accept it.

Step 8: To move the model we need to have a velocity card, to create got to create entity and select the velocity card and select the entire elements of the model and specify the direction of the model with speed 13.888 mm/ms and accept it.

Step 9: Now create a material card for the model using the mat 001 elastic card and give the steel properties to the card.

Step 10: NOw create a rigidwall using the create entity option and selct the rigidwall planar and select the N1 and N2 nodes and it shows the rigidwall and accept it.

Step 11: Now a crash test model is completed but get the results we need to give the database keywords like ASCii, Binary d3plot, History node set and crossection. Give the control termination time as 6ms.

Step 12: Now go to the ls manager and run the keyword file and it gives normal termination it means our crash test model is coreect.

Step 13. To extract the results again open the new tab in ls prepost and open the file of d3plot and we here we can see the all the results.

Step 14: Now we are going to use solid or hexa element for the spotweld instead of beam. To create solid element go to the element generation deck and select the element editing and create the hexa or solid element by selecting the two shell elements between the plates, like this we will create the six hexa elements.

Step 15: For this also we need to create contact keyword. To create go to contact keyword manager and for hexa element we will select the spotweld contact. To this also we need to create aa slave set id and master set id as we done for the beam spotweld method and give the id for the spotweld contact and accept it.

Step 16: Like above steps from step 7 we need to follow same steps for the solid spotweld method and run the keyword in ls manager to extract the results.

Results and Discussion:

Here we extracted the results for both beam spotweld and hexa spotweld and we can see the stres values from the figures.

Here we can extract the two types of stress values or simulationos a. Beam element will not file due to larger time value of failure criteria and b. Beam element will fail due to small time value of failure criteria. For above simulations beam is not failed due to the above mentioned condition (a).

b. Here we can see that beam brakes or fails and does not crashes to the wall and stress is created here is low when compared to the above mentioned method and time value is tfail = 6ms.

Here we can see the solid element has higher stress value when compared to the beam spotweld this is due to less abosrption of stress from hexa element.

Section force:

Here we are going to find the section force both the simulations

i. Beam type

From the plot we can see that middle section of the shell elemnts is shearing from 15N to -15N due to the beam elements.

ii. Solid element

From the plot we can see that shearing at start is more and it is reduced to low with the help of the hexa spotweld weld when comparing to the beam spotweld element.

Node velocity and acceleration at the section:

I. Beam spotweld:

From the plots we can see that after hitting the wall direction of velocity is reversed due to the spotweld connection beam and we can see that velocity becomes zero at the section of the part.

II. Solid spotweld element:

From the plot we can see that velocity is reversed same as the beam element spotweld but here velocity is not reduce to the zero and it continous to the negative X-axis -5mm/ms.

Energy plots:

From the both the plots we can see that energy is distributed equally from internal energy to kinectic energy where hourglass and total energyies are constant. More energy is released in the beam element spotweld when compared to the solid element spotweld.

Conclusion :

Thus we created two types of connections for the model i.e, Beam and Hexa elements and we run a simulations for both the methods and extracted the results successfully.