Cell Phone Drop Test under the Military Standard 810G

Cell Phone Drop Test

Objective: Cell phone drop test is to be conducted by creating all the necessary input keywords starting from

1. Material creation,
2. Section creation,
3. Assigning material and section to their respective parts.
4. Defining Boundary conditions and specifying the Initial velocity to the Cell Phone.
5. Creating contact definition between Cell phone and rigid plate.
6. Model Termination time has to be assigned
7. Database (BINARY_D3PLOT and ASCII_option) and finally
8. Plotting the results.

This Drop test of transit equipment (cell phones) follows Military Standard (MIL-STD-810G) (516.6) Procedure IV

Steps:

First of all, the cell phone is measured for its total length and found to be 150.4 (which is obvious that this unit is in ‘mm’) units as the smart phones in the present age range their length from 5.5-6 and odd ‘inches’ and the distance between a node on the phone and the nearest node on rigid plate has been noted down as 20.178 units (nearest nodes).

In LS-DYNA there is no specific unit system deck available so it is important that the user need to define all the parameters in a specific unit system.

The unit system taken in here is ‘kg, mm, ms, kN, GPa’

1. Material keyword creation:

Model and Part> Keyword Manager>All>MAT> Give values >Accept>Done

The model has a shell (rigid plate) and a solid (cell phone). The surface (rigid plate) material on which the cell phone drop test is conducted is taken a ‘steel’, usually these surfaces will be taken as concrete and the cell phone body (frame) is taken as ‘Aluminium’. Usually the cell phone frames as made of Aluminium alloys and plastics (mostly polycarbonate). So is the reason to take the cell phone frame as Aluminium.

· MAT-20-Rigid has been assigned for the Shell (rigid plate) with the parameters and their values are as follows

·

MAT-24-Piecewise_Linear_Plasticity has been attributed to solid(phone).

2. Section creation:

Model and Part> Keyword Manager>All>Section> Give values >Accept>Done

· Section_Shell is taken for the rigid plate and

· Section_solid for the phone has been created.

3. Part keyword assignment:

Model and Part> Keyword Manager>Model>Part> Select part>Give values >Accept>Done

With the material and the Section keywords created now is the time to assign the respective (numbered) keywords to their respective Part keywords.

4.Boundary Conditions:

Model and Part> Create Entity>Boundary>spc>Create>set>Select parts>Pick area> Selection of nodes based on the choice (by node or by path or by edge) > Apply> Done

A Boundary_spc keyword has been created to fix the rigid plate edges from moving during the impact

Initial Velocity: Initial velocity (velocity nodes) for all the nodes of the cell phone has been assigned.

The velocity has been calculated using the formula V=\sqrt(2*g*h). The distance between the bottom most node of the cell phone and its nearest node to the rigid plate as said above is 20.178.

When calculated the velocity value becomes

V= \sqrt(2*9.86*10-3*20.178) =0.629 mm/ms (acceleration due to gravity is w.r.t the unit system) towards the negative z-axis. But, with this small velocity it is difficult to make the impact simulation within some milliseconds of time (5 ms which can be seen in Control_Termination ).

So, sticking to the MIL-standard- 810G velocity has been calculated where the cell phone is dropped from a height of 180 cm = 1800 mm.

V=\sqrt(2*9.806*10-3*1800)= 5.94 mm/ms towards the negative z-axis.

5. Contact creation:

Model and Part> Keyword Manager>All>CONTACT>give values> Accept>Done

While selecting the slave and Master it is important that Slave segment set or node set type

An Automatic_Surface_To_Surface has been created between the Cell phone and rigid plate with Cell phone being the slave and Rigid plate taken as Master.

6.Control creation:

Model and Part> Keyword Manager>All>Control> Select required keyword>Give values >Accept>Done

· Control_Energy keyword has been created with HGEN-Hourglass generation and SLNTEN-Sliding Energy

· Control_Termination keyword is created when to end the termination and End time is set to 5ms.

7. Database Creation:

· BINARY_D3PLOT - In this keyword the frequency with which the animation is to be created will be given and is set to 0.1ms and-

·

ASCII_option keyword- In this keyword

1. ELOUT- Element Data

2. GLSTAT- Global Data

3. MATSUM- Material Energies and

4. SLEOUT – Sliding Interface Energies.

the same animation frequency has been applied for these keywords too.

Model-Check: After assigning all the keyword check the model using the model checker and make sure that the file is error free.

Save the keyword with a name of required interest with an extension ‘. k ‘so that, the LS-DYNA Solver will recognize when it is run.

One can change the Title of the model by editing the '.k' file in text editor. The change of the title is user's interest, it is not a mandatory.

Run the FILE in the solver if it’s ends as a Normal Termination then model is correct

8. Post-Processing (Results):

Animation of Cell phone drop test

Fringe Component>stress>VonMises Stress

This is the VonMises stress where the Cell phone hits the rigid plate at 34^th frame of the simulation.

Here at 34^th frame it can be seen that the stress develops at the side edges along the length of the phone and it proceeds till the end of it. It depicts a proper stress distribution.

Stress at 52^th frame

The VonMises stress at the final frame is 2.272 E-2 GPa

In order to get the Global data click - ASCII>glstat*>Load. Select the energies of interest and plot them

The graph for the Internal , Kinetic and Total Energies have been plotted with IE=0.278 J, KE = 5.01 J and TE= 5.29 J respectively at the end (5 ms) of the simulation

In order to get the Sliding Interface Energy data click - ASCII>sleout*>Load>select body slave and master energy by pressing Ctrl+LMB to select.

Save the keyword with a name of required interest with an extension ‘. k ‘so that, the LS-DYNA Solver will recognize when it is run. The master energy is zero indicating that the body is rigid and there is only a small amount of Energy created that is 0.734 J which is same as that of the sliding energy.

Conclusion:

1. All the keywords has been created right from scratch and model checked.
2. The whole purpose of this challenge is to make the user get familiarize with the GUI, to learn from the LS-DYNA manual, creating keywords and running the simulation.