Week - 3 Drop test Challenge

Drop test challenge

Aim :- To perform drop test challenge on mobile by providing proper inputs by using Ls-dyna and conclude the results.

Software Used :- Ls-Pre-Post V4.7.17

Introduction :-

The most common failure of mobiles is probably the impact due to accidental drop, so the manufacturers aim to develop products that are impact resistant and can survive the drop test from specific height. At the design stage, FE method plays a more important role since actual drop test can only be conducted at the end of design cycle and provides little feedback to improve the design. The FE simulation will help designers understand how components interact in the assembly and how the failure mode and mechanism is developed under the impact loading.

Here, The given model has meshed by shell and solid elements which has to be simulated by performing the drop test by giving an initial velocity of 10 m/s to mobile. In this model units system used is [Kg mm ms Mpa N-mm)

Procedure :-

1. Import given file: In order to open a file use file>open>LS-DYNA keyword file > Select file > Open option.

2. Create Boundary by (Model and Part>Boundary(all)>SPC) and for SPC set create node set by selecting floor nodes and constrain it to all DOF and press accept. Change the node set and SPC boundary condition abel as a Floor node set.

3.Material Creation: For every part the material is necessary in order to run simulation also, the material properties should be in consistent unit system.

1. Here the unit system is kg-mm-ms, all the data which is input must be in same unit system.
2. Create material for a floor which is rigid and for mobile here considered as aluminium.((Model and Part>MAT(all)>020_rigid(plate ) and 024_picewise_linear_plasticity)

4. Section Keyword: In order to distinguish between the type of element we have to define the section keyword. for shell and solid

a. Section is created by (Model and Part > section (all) > shell). here we have to define thickness and type of element formulation here it's not important because all nodes are fixed in all direction so there is no element undergo displacement.

b. Section is created by (Model and Part>section(all)>solid).

5. Assign Material and section to the PART :-

Assign those Section and Material to the parts by directly clicking on part in (Model and Part>part) so we can see part list and each part has the option to select for Section ID and MATID.

6. Initial velocity: In order to move the mobile towards floor we are providing the velocity of 10 mm/ms in negative direction as per problem statement. here select the node set and input velocity in which direction it should move as shown in image below.

7. Define Contact: In order to simulate impact take place between mobile and floor there should be contact definition or else phone will simply pass through plate.

here we select all nodes of mobile are slave and all floor nodes are master nodes.

8. Control Keyword: The keyword control cards are optional and can be used to change defaults activate solution options such as mass scaling adaptive remeshing and an implicit solution however it is advisable to define the CONTROL_TERMINATION card. This key word is used to control simulation by time, 5ms

9. Output Request: Using data base pannel we can request such as animation file energy data,contact forces etc.

BINARY3DPLOT - The complete state dump interval as given in *DATABASE_BINARY_D3PLOT serves as the time step to be used in the material model driver run. Plotting information is saved in core for the interactive plotting phase.

ASCII_option- This option is used to read the data of following

ELOUT - This latter option will output all integration point data or extrapolated data to the connectivity nodes in a file call eloutdet.

GLSTAT - Reade the energy like KE, PE, IE

MATSUM - Every material part energy due to deformation

RCFORCE - contact force b/w them

SLEOUT - sliding force due to contact

SPCFORCE - single point contact force.

LS-Run: Here, the file imported and run the simulation, after the simulation plot the effective stress.

Contour plot of Von-mises stress :-

Due to the impact, the max von mises stress developed in the cellphone part is 0.1823 N/m2 at 2ms which is formed at the tip of the cell phone part.

Plot Energies Vs. Time :-

The above plots show the energy involved in the energy balance and how those energies are utilized or consumed by the simulation. At the time 2ms, the kinetic energy is reduced and internal energy is increased when the mobile comes into contact with the floor which is rigid surface. There is no hourglass energy formed because of fully integrated.

Conclusion :-

Thus, the drop test simulation performed successfully by providing proper inputs such as boundary conditions, Initial velocity, Material, section and contact. The max von misses stress is developed at the bottom which is 0.1823 N/m2.