Modelling Spotwelds using LS DYNA
Aim:
To model the spot-weld for the given assembly parts using beam and solid elements separately. Also, perform the crash analysis for the same and compare the output results of the beam and solid spot-welds.
Abstract:-
Spot welding is also known as resistance spot welding is a resistance welding process. This welding process is used primarily for welding two or more metal sheets together by applying pressure and heat from an electric current to the weld area. It works by contacting copper alloy electrodes to the sheet surfaces, whereby pressure and electric current are applied and heat is generated by the passage of current through resistive materials such as low carbon steels.
Procedure:-
1. Open the spotweld-assignment. k file in LS-PrePost.
2.The File Only Consists of the nodes and elements of the Mobile phone and the table.
3.The Unit system Followed here is gm, mm, ms
4. To perform the Simulation, materials, Section, initial velocity, Contact Interface, Boundary conditions, Weld elements. Output For the Following Must be Specified.
1.Creation Of BEAM Elements:-
1.The spot weld modeled using beam element is created by selecting the Mesh > Element Generation > Beam > New Part ID > Select Beam by-Two_Node_Sets >Select any 2 Desired nodes from the Parts > Create > Accept > Done.
2. Select 5 to 6 Beam elements In Different places to see the behavior.
2.Section Creation:-
Delete Auto-created Section cards Which Are created After Creating Beam Elements.
1.Two Different sections Must be Created. One for the Beam Elements And the Shell Parts.
2. For Defining Section Go to Keyword manager > All > Section > Shell
3. For the Bottom and top Sheet metals Section SHELL is created and Thickness is assigned as 1.5mm
4. The element formulation is Given as 16- Fully Integrated.
5.For The Beam Elements SECTION_BEAM are Created And A thickness of 2mm Is assigned.
6.The element formulation is Given as 9 for the Spot weld.
7. Totally 6 Beam elements were Created So 6 Sections were Assigned to Each Beam element.
3.Assigning Materials:-
1. For Defining materials go to Keyword Manager > All> MAT > Select the Material card and define the material properties like mass density, Young’s modulus, Poisson’s ration, Yield point stress value, and other required quantities. For the Sheet metal Parts, The Material card MAT_001_ELASTIC is Assigned with the Properties of Steel.
Massdensity(RO)=0.00785gm/`mm^3`
Young'sModus(E)=2.1⋅105gm/`mm*ms^2`
Poisson'sratio(PR)=0.3
Yieldstress(SIGY)=310gm/`(mm*ms)^2`
2. For The Beam, Elements MAT_100_SPOTWELD is Assigned with the same Properties.
3. Conditions Like TFAIL, EFAIL, Time-Dependent Failures, Force Dependent Failures With respect to Axial and Stress and resultant forces, And Moment-based Failures to the Beam elements were assigned.
4. As we need to Solve This problem based On Time Based Failure All other Failures except Time are Comparatively High.
4.Specifying the Material and Section ID to the respective part IDs.
1. In parts, we basically assign material and sections with their proper ID for every part individually.
2. Assign the Section-Id and Materials Individually
3. For Creating part Go to Keyword manager> Model > Part and assign the Materials and Sections of the Sheet metals and Beam elements.
4.Individual Parts For Sheet Metals are Created as Top part and Bottom Part And their respective section and Mat_Elastic was Assigned.
5.Since there are 6 Beam elements, 6 parts Were created Individually, And MAT_SPotweld and respective Section created to the Beam elements was Assigned.
5. CONTACT INTERFACE:-
1. For the beam element, (*CONTACT_TIED_SHELL_EDGE_TO_SURFACE) Contact Type is Used.
2. As we need to Know the Reactions Of the Beam It is defined as a slave And the Sheet metal parts as Master.
3. For defining the Slave select beam nodes Set, The Beam nodes set is created by Entity Create > SetData > *SET_NODE > Pick the nodes > Apply.
4. For Master The Part Set is created Entity Create > SetData > *SET_PART > Pick the nodes > Apply.
5. Assign both the slave-set and the master-set as created by the above technique to the contact card. *CONTACT_TIED_SHELL_EDGE_TO_SURFACE card. Select Slave-type - Node set ID and Master-type - Part set ID
6.Similarly Automatic_single_surface contact card Is created for the parts as after the Spotweld Breaks the parts shouldn't come in contact with each other.The Parts are selected as Slaves Here.
6.Boundary Conditions:-
1. An SPC Set was Created at One end And The Nodes are Locked In All DoF's.
2.The End is Fixed
3.An node-set Is created At the Other End as prescribed Motion Node set for Displacement
4.Prescribed Motion Set was Created by Keyword > Boundary > Prescribed Motion set and select the Node set Created As Nset_id and accept.
5.The Displacement for The Nodes are Defined By a Curve. Initial and Final displacement is fed with respect to time and choose Plot
6.Input the Load curve In LCID Prescribed Motion Set.
Procedure For SOLID-ELEMENTS:-
1.Creation Of Solid Elements:-
1.The spot weld modeled using beam element is created by selecting the Element tools > Element edit > Create > Element type:Hexa > select 8 nodes > Accept > Done.
2. SInce Element Type- Hexa is selected, 8 nodes are selected From the element where The solid elements to be Formed In between. Create 5 elements at different places.
2. Section Creation:-
The Same Section is assigned for The Sheet metal plates.
1.For The Solid Elements SECTION_SOLID is Created.
2.The element formulation is Given as 1
3. Assigning Materials:-
The Material Assigned for the Sheet metal plates remains the same.
1. For the solid, Elements MAT_100_SPOTWELD is Assigned with the same Properties.
2. Conditions Like TFAIL, EFAIL, Time-Dependent Failures, Force Dependent Failures With respect to Axial and Stress and resultant forces, And Moment-based Failures to the Beam elements were assigned.
3. As we need to Solve This problem based On Time Based Failure All other Failures except Time are Comparatively High`
4. Specifying the Material and Section ID to the respective part IDs.
1. In parts, we basically assign material and sections with their proper ID for every part individually.
2. Assign the Section-Id and Materials Created For Solid elements
3. For Creating part Go to Keyword manager> Model > Part and assign the Materials and Sections of the Solid Elements
5. CONTACT INTERFACE:-
The Contact Created Remains the same for the Sheet metal plates.
1. For the Solid element, CONTACT_SPOTWELD is used.
2. As we need to Know the Reactions Of the Solid elements It is defined as a slave And the Sheet metal parts as Master.
3. For defining the Slave select Solid nodes Set, The Beam nodes set is created by Entity Create > SetData > SET_NODE > Pick the nodes > Apply.
4. For Master The Part Set is created Entity Create > SetData > *SET_PART > Pick the nodes > Apply.
5. Assign both the slave-set and the master-set as created by the above technique to the contact card. *CONTACT_TIED_SHELL_EDGE_TO_SURFACE card. Select Slave-type - Node set ID and Master-type - Part set ID
All Other Boundary Conditions And Displacement Curve Remains the same.
Control cards:-
1. Control cards such as Control Termination, Control energy are specified.
2.Termination time defined by using *CONTROL_TERMINATION card
3.Set Model and Part > Keyword Manager >Control> Termination to 10ms
OUTPUT REQUEST:-
1. To view the results of Simulations Following Steps are Specified.
2.The time interval between the outputs is 1 is defined in D3plot
3. Go to Keyword Manager > Database > ASCII select GLSTAT, SWFORC, NODOUT with DT 1
4.As In the DataBase NODOUT is defined The Nodes of the beam and Solid Elements are Defined, In the History Node Option
5. To View Nodout Go to Database > History Node Enter the Node Id Of beam and Solid Individually In the ID check box.
Run the Simulation:-
1. Save The Keyword for Both Solid And Beam elements Separately In Different Folder And Run the Simulation.
2. From The Output, file Check the Time in which Solid and Beam Elements failing With the Time Specified in the TFAIL.
Output for Beam elements:-
As we gave The TFAIL=5ms The element gets deleted at 5ms
Von mises Observation:-
The Effective Von-mises stress is Maximum of 2.887e03gpa At element 101266 and a Minimum of 0.000 at element11011
Energy graph:-
Due to the Displacement using the prescribed Set The Displacement is less till it reaches The Maximum value.
Spotweld Forces:-
From the above graph, we can see that the Axial and Shear forces of Beam elements Getting deleted at 5ms which is assigned as the TFAIL value
Output for SOLID elements:-
As we gave The TFAIL=6 ms The element gets deleted at 6ms
Von-mises Observation:-
Energy Graph:-
Spotweld Forces:-
From the above graph, we can see that the Axial and Shear forces of Beam elements Getting deleted at 6ms which is assigned as the TFAIL value.
Inference:-
The Beam element Created Takes load axially More than Shear force
The force acting on the spot weld is in the transverse direction (perpendicular to the axis) since the solid element gives the force-resisting ability in the transverse direction, higher shear force values are notices for a solid element than beam element.
Conclusion:-
Thus the Spotwelds are Modelled using beam and solid elements for the Same Component and Their results are Compared and Plotted.