Week - 5 - Modelling Spotwelds
AIM:
To model spot weld for the given assembly of parts by using 1-D beam elements and 3-D Hexa elements.
THEORY:
Spot welding is one of the oldest welding methods for joining metal plates using strong current and is widely used in all industries such as automobile, ship building and aerospace sectors. In this simulation the spot weld is modelled as beam and hexa element and results are compared for both case.
PROCEDURE:
1.The given LS-DYNA keyword file is imported.
Spotweld Modeling:
Beam Element:
1.Goto Mesh> EleGen > Beam > Two_Node_sets.
Hexa Element:
1.Goto Mesh > EleEdit > Create > Hexa
Part Definition:
The part is defined by assinging the section properties and material properties. In this model there are three parts. They are Top bracket, Bottom bracket and Spotweld.
Section Properties:
1.Goto Keyword Manager > Section > Shell.
2.The sectopm properties of brackets are assigned as shell element with 1.5mm thickness and ELFORM=16, Fully integrated shell element.
3.The section properties of spot weld in the first case are assigned as beam element with 3mm thickness and ELFORM = 9.
4.The section properties of spot weld in the second case are assigned as solid element and ELFORM = 1, constant stress solid element.
MATERIAL PROPERTIES:
1.The brackets and spot welds are assigned with steel material.
For steel material
1.MAT24 material card is used to assign the steel material properties to the assembly of parts. The MAT24 represent Piecewise linear isotropic plasticity.
For spotweld material
1.The material model applies to beam element type 9 and to solid element type 1. The failure models apply to both beam and solid elements.
BOUNDARY CONDITIONS:
Rigid Wall:
1. Goto Create entity > Rigid wall > cre > Planar > in+NL
2.The rigid wall is created at a distance of 10mm away from the brackets.
Initial Velocity:
1.Goto Keyword manager > Intial > Velocity
2.The brackets are assigned with intial velocity of Vx = 13.88mm/ms is applied along x direction to crash against the rigid wall.
Contact Condition:
1.Goto Keyword manager > Contact > Automatic_Single_surface
2.The Automatic single surface contact type is assigned for the contact between rigid wall and brackets.The FS and FD that are static and dynamic friction coefficient with a value of 0.08 is entered in the contact card.
3.Goto Keyword manager > Contact > Tied_shell_Edge_to_surface
4.This contact type is assigned for the contact between spotweld beam elements and brackets.
5.Goto Keyword manager > Contact > Spotweld
6.The spotweld contact type is assigned for the contact between spotweld solid elements and brackets.
CONTROL FUNCTION:
1.Goto Keyword manager > Control > Energy
2.The control energy function is enabled for computing the hourglass energy, stonewall energy and sliding energy.
3.Goto Keyword manager > Control > Termination
4.The control termination function is enabled to specify the end time of simulation. The termination time is set for 5ms to capture the effects of brackets striking the rigid wall.
DATABASE OPTION:
1.Goto Keyword manager > Database > Binary_D3Plot
2.The time step value of 0.1 ms is given for the Binary_D3plot and 0.01.
3.Goto Keyword manager > Database > Cross_section_plane
4.This card is used to compute the sectional force of the model.
OUTPUT:
For Using beam element:
1.Von-Mises stress contour:
2.Effective Plastic Strain contour:
3.Plot of Axial force in spotweld:
4.Plot of Shear Force in Spotwelds:
5.Plot of Resultant force in Spotwelds:
6.Plot of Length of Spot welds:
7.Global energy plots:
8.Sectional Force Plots:
9.Acceleration plot of a node:
10.Plot of v-m stress vs effective plastic strain:
For Using Hexa element:
1.Von-Mises stress contour:
2.Effective Plastic Strain contour:
3.Plot of Axial force in spotweld:
4.Plot of Shear Force in Spotwelds:
5.Plot of Resultant force in Spotwelds:
6.Plot of Length of Spot welds:
7.Global energy plots:
8.Sectional Force Plots:
9.Acceleration plot of a node:
10.Plot of v-m stress vs effective plastic strain:
COMPARISON:
1.For axial force in spotweld, for beam element the axial force is transferred to the spot weld gradually fluctuates with a maximum value of 1.65 kN.
For the hexa element the axial force is transferred to the spot weld rapidy fluctuates with a maximum value of 0.848kN which is comparatively less than beam element. So that spotweld is modeled as solid hexa element is rigid compared to beam element.
2.For shear force in spotweld, for beam element the shear force generated during collision increases suddenly to value of 1.06kN and thereafter decreases gradually.
For the hexa element the shear force generated during the collision increases suddenly to value 1.9kN and thereafter fluctuates till rebounding.
3.For Resultant force in spotweld, for Beam element the resultant force generated in the spot weld gradually increases during collision and fluctuates with maximum value of 1.79kN.
For hexa element the resultant force generated in the spot weld increases suddenly during collisison and fluctutates with a maximum value of 1.91kN.
4.For length of spotweld, for beam element the length of the spot weld is gradually increasing till a time of 2.8ms, since the spot weld is modeleld as 1-D beam element.
For hexaa element the length of the spot weld is remains constant since it is modeled as solid hexa and is able to withstand the force generated during the collision.
5.For global energy plot, for beam element the kinetic energy is reduced during the time of collision to a value of 73.9*10^3N-mm and the internal energy is increased to a value of 68*10^3N-mm.
For hexa element the kinetic energy is reduced during the time collision to a value of 72.7*10^3 N-mm and the internal energy is increased to a value of 67.9*10^3N-mm.
6.For sectional force plots, for beam element a resultant sectional force of 5.7KN is developed during the collision with rigid wall and increases to a maximum of 9.81KN at time 1.67ms and decreases while the crash box is rebounced.
For hexa element resultant sectional force is 10.4KN us developed during the collision with rigid wall and increases to a maximum of 10.8KN at time 1.69ms and decreases while the crash box is rebounced.
7.For acceleration plot of a node, for bema element resultant acceleration of 106mm/ms^2 is developed during the collision with rigid wall and increases to a maximum of 733mm/ms^2 at time 3.54 ms and decreases while the brackets are rebounced.
For hexa element resultant accelelration of 358mm/ms^2 is developed during the collision with rigid wall and incrreases to a maximum of 1060mm/ms^2 at time 4.78ms and decreases while the bracketts are rebounced.
RESULT:
Thus the model spot weld for the given assembly of parts by using 1-D beam elements and 3-D Hexa elements is performed sucessfully.
GOOGLE DRIVE LINK: https://drive.google.com/drive/folders/1jM8u0H5RC2izCHV5aExGf2hqkiaNGl-1