Week 3 Challenge: Drop Test Challenge

Course: LS-DYNA for Structural Mechanics/ FEA

Submitted by: Amanpreet Singh Whan

Supervisor: Tholkappiyan D

June 30, 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.

2 Aims

1. Create a simulation setup to perform the drop test of the cell phone.
2. Analyze the stress, strain, and other results obtained from the simulation while and after the cell phone hits the ground.

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 3 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 cell phone drop on a plate mimicking ground, kg 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. The Automatic_Surface_To_Surface Contact option was selected for the challenge purposes.

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.

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 20 (Rigid) and MAT 024 (piecewise linear plasticity) were selected for Baseplate (ground) and cell phone respectively. The values assigned to the parameters of both materials are presented in the following cards.

Section:

Under section, the element formulation, integration rule, nodal thicknesses, and cross-sectional properties are defined. Two separate sections of shell and solid were created and assigned values for their parameters are presented in the following pictures.

Part:

Here define combine material information, section properties, hourglass type, thermal properties, and a flag for part adaptivity. Since the given model contains two different parts, therefore the above-mentioned properties must be defined separately for both parts.

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.

From the plot, it can be seen that at 1 ms, when the cell phone hits the ground, there is a reduction in the kinetic energy of the mobile phone while there is an increment of the internal energy of the plate 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.

5 Conclusion

The main aim of the Week 3 challenge was to create an input deck or setup file to perform the drop test of a cell phone using LS-DYNA software and analyze the behavior of stress-strain and other results while and after the cell phone hits the plate (mimicking ground). The maximum effective stress at the time of impact was found to be 2.771 e-01 kg/(mm*ms^2). 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 mobile phone conversely leads to the gain of internal energy of the plate (ground).

6 Appendix