Week 5 Challenge: Modelling Spotwelds Challenge

Course: LS-DYNA for Structural Mechanics/ FEA

Submitted by: Amanpreet Singh Whan

Supervisor: Tholkappiyan D

July 18, 2021

Table of Contents

1 Introduction.

2 Aims.

3 Methodology.

4 Results.

5 Conclusion.

6 Appendix.

1 Introduction

LS-DYNA is an advanced general-purpose multiphysics simulation software package developed by the former Livermore Software Technology Corporation (LSTC), which was acquired by Ansys in 2019. While the package continues to contain more and more possibilities for the calculation of many complex real-world problems, its origins and core competency lie in highly nonlinear transient dynamic finite element analysis (FEA) using explicit time integration. LS-DYNA is used by the automobile, aerospace, construction and civil engineering, military, manufacturing, and bioengineering industries.

The purpose of the challenge is to perform a crash test of the two rectangular brackets (surfaces) welded with beam and solid elements spot welds. Also, analyze how the forces and moments behave when the brackets hit the rigid wall with an initial velocity of 50 km/hr (13.8 mm/ms).

2 Aims

1. Create a simulation setup to perform the crash test of the given two rectangular brackets CAD model welded with beam and solid elements spot welds for the scenario where the brackets crash into the rigid wall and rebound back completely.
2. Analyze the force, maximum directional stress, strain, and other results obtained from the simulation while and after the brackets hit the rigid wall.
3. Compare the axial and shear force results of both the beam and solid elements spot welds crash test.

3 Methodology

The section describes different stages that were performed to set up the simulation file using an engineering tool LS-DYNA for the completion of the Week 5 Challenge task. These stages can be broadly categorized into creating an input deck containing different cards such as contact, control, database, element, hourglass, initial (velocity), keyword, MAT, node, part, section, and title.

Since LS-DYNA does not have a default system of units, therefore, the user needs to input material properties and physical dimensions according to a consistent system of units as per their choice. Considering the challenge requirements of simulating a crash test of two rectangular brackets (spot-welded) into the rigid wall, g mm ms were assumed to be the most appropriate units.

What follows hereafter is the set of images representing the process followed to create different cards and values assigned to their key parameters.

Contact:

The keyword CONTACT provides a way of treating interaction between disjoint parts. For the given rectangular brackets, Automatic Single Surface Contact was defined to avoid penetration of the brackets into each other during the crash test. Also, Tied Shell Edge to Surface and Contact Spotweld contacts were defined respectively for beam and solid elements spot welds.

Control:

The keyword control cards can be used to change defaults. The control energy and control termination cards were created for the challenge purposes.

Database:

The database definitions are necessary to obtain output files containing results information. The binary D3Plot and ASCII options were selected for the challenge purposes.

Hourglass:

Hourglass (HG) modes are nonphysical, zero-energy modes of deformation that produce zero strain and no stress. Hourglass modes occur only in under-integrated (single integration point) solid, shell, and thick shell elements.

Initial:

The keyword INITIAL provides a way of initializing velocities and detonation points. The velocity node option was selected, and the assigned value of velocity is presented in the following card.

Mat:

The keyword MAT helps in defining and assigning different types of materials to a part as per requirements. For this challenge MAT 001 steel (elastic) was selected for the two rectangular brackets. Also, the MAT 100 spotweld was selected for both beam and solid elements spotweld connections. The values assigned to material card parameters are presented in the following card.

Section:

Under section, the element formulation, integration rule, nodal thicknesses, and cross-sectional properties are defined. Shell section, beam section, and solid section were created as per challenge requirements, and assigned values for their parameters are presented in the following picture.

Part:

Here define combine material information, section properties, hourglass type, thermal properties, and a flag for part adaptivity.

4 Results

After setting up the input deck and saving the file. K format, the first and foremost step is to perform a model check and then run the simulation using LS-Run software. Once normal termination is achieved, the results can be viewed and analyzed using LS-PrePost software.

What follows hereafter is the pictures illustrating the beam elements and solid elements spot welds created at certain locations as per challenge requirements.

The following images representing the results of the crash analysis of the two different scenarios.

• Rectangular brackets welded with beam elements hit the rigid wall and rebound back.
• Rectangular brackets welded with solid elements hit the rigid wall and rebound back.

Results of the crash test of brackets welded with Beam elements.

Figures 20-23 represents effective stresses, energy plots, axial force plots, and shear force plots of the crash analysis of the rectangular brackets Cad model welded with beam elements spot welds. The maximum effective stress was found to be 2876 g/(mm* ms^2). From figure 21, it can be seen that when the crash box hits the rigid wall, there is a reduction in the kinetic energy of the box while there is an increment of the internal energy of the wall and after that both energies become constant. This validates the principle of conservation of energy which states that energy can neither be created nor destroyed but can be converted from one form of energy to another. Moreover, from the plot, it can also be seen that the hourglass energy remains nearly 0 indicating a good selection of both the hourglass and element formulation for the simulation setup. Figure 22 shows that the maximum tension experienced by a beam element is 4000 newtons while maximum compression is about 3200 newtons. Figure 23 displays the variation in the shear force experienced by the beam elements over the entire period of simulation.

Results of the crash test of brackets welded with Solid elements.

Figures 24-27 represents effective stresses, energy plots, axial force plots, and shear force plots of the crash analysis of the rectangular brackets Cad model welded with beam elements spot welds. The maximum effective stress was found to be 1557 g/(mm* ms^2). From figure 25, it can be seen that when the brackets hit the rigid wall, there is a reduction in the kinetic energy of the box while there is an increment of the internal energy of the wall and after that both energies become constant. This validates the principle of conservation of energy which states that energy can neither be created nor destroyed but can be converted from one form of energy to another. Moreover, from the plot, it can also be seen that the hourglass energy remains nearly 0 indicating a good selection of both the hourglass and element formulation for the simulation setup. Figure 26 shows that the maximum tension experienced by a beam element is 2100 newtons while maximum compression is about 4000 newtons. Figure 27 displays the variation in the shear force experienced by the beam elements over the entire period of simulation.

5 Conclusion

The main aim of the Week 5 challenge was to create an input deck or setup file to perform the crash analysis of rectangular brackets welded with beam and solid elements using LS-DYNA software and analyze the behavior of stress-strain and other results while and after brackets hits the rigid wall. The crash simulations were performed for two different scenarios; brackets welded with beam elements spot welds connections hit the rigid wall and rebounds back completely and the second case where brackets welded with solid elements hit the rigid wall and rebounds back. From the GLSTAT plots, it was found that the simulation setup follows and validates the principle of conservation of energy expressing loss of kinetic energy of crash boxes conversely leads to the gain of internal energy of the rigid wall.

6 Appendix

Simulations of the crash test of brackets welded with Beam elements.

Simulations of the crash test of brackets welded with Solid elements.