Week - 3 Drop test Challenge

Objective/Aim:

The objective of this assignment is to prepare/build a complete LS-Dyna deck for drop test of a mobile phone from scratch using just the finite element model of the mobile phone and the drop surface.

Explanation:

Case setup/ Deck Setup (Keywords): mm,ms,Kg,KN Unit system

The keywords created are mentioned below.

1. Section- SECTION_SHELL and SECTION_SOLID

Shell and solid sections are created using the above-mentioned key words and selectively reduced shell and solid elements are used as they are economical from a computation perspective.

2. Material- MAT_PIECEWISE_LINEAR_PLASTICITY

Two materials are used here.

Aluminum is assigned for the phone and a hypothetical material with high strength is used for imitating the hard ground surface since the object of interest is only the phone.

Since the objective of this assignment is just to create a working simulation, the ground is kept as it is.

But from an FEA perspective, removing the brick and shell elements used to model the ground and replacing it with a rigid wall will help reduce computational time and resources.

3. Part definition - PART_PART

The created section ID and Material ID are then entered in PART card.

4. Loads and load curve- INITIAL_VELOCITY, LOAD_GRAVITY_PART and DEFINE_CURVE

The loads applied here are Initial velocity and gravity.

Load curve need not be provided for initial velocity and hence a node set is created using all the nodes of the phone and an initial velocity of 4mm/ms is applied.

For gravity, DEFINE_CURVE keyword is used to input the following values that constitute the curve.

Then LOAD_GRAVITY_PART keyword is used to define the gravitational load

5. Boundary conditions -BOUNDARY_SPC_SET

Since the ground surface should always be stationary, the boundary condition SPC is used to constrain the nodes of the elements that constitute the ground surface.

6. Contact- CONTACT_SURFACE_TO_SURFACE

The contact keyword is created to define a contact to make sure that the phone does not pass through the ground while doing the simulation.

Usually, the hard surface or body with coarse mesh is chosen as the master surface and the body with fine mesh is chosen as slave.

Hence, in this model, the ground is chosen as master surface and the phone is chosen as slave surface.

Since there are solid and shell elements in the ground, contact is also defined for the shell and solid elementsts in the ground.

7. Control- CONTROL_ENERGY, CONTROL_HOURGLASS and CONTROL_TERMINATION

The CONTROL_ENERGY is used to make sure that the hourglass energy and sliding energies are calculated for the energy balance check.

The CONTROL_HOURGLASS card is used to make sure that the hourglass effect is minimal or nonexistent.

The CONTROL_TERMINATION card is used to input the simulation run time as 10ms and minimum time step as 0.01ms.

8. Database- DATABASE_ASCII_option and DATABASE_BINARY_D3PLOT

The DATABASE_BINARY_D3PLOT keyword is used to mention the time interval between outputs.

The DATABASE_ASCII_option is used to request the ELOUT (element output), NODOUT (Nodal outputs), GLSTAT, etc at interval of 0.05ms

Plots & Contours:

Von-Mises Stress contour at the time of Impact:

Internal Energy:

1. Since the phone is dropped from a hight, initially, the internal energy is zero.

2. After the phone hits the ground, the reaction force imparts energy to the phone and thus internal energy increases to achieve the maximum value.

3. After the phone bounces off the ground, the fluctuations in internal energy can be noted due to the impact loading.

Kinetic Energy:

1. Since an initial velocity is given to the phone, the kinetic energy is maximum at the begining.

2. Kinetic energy becomes zero the moment the phone touches the ground and then increases from zero as the phone bounces off the floor

Hourglass Energy:

1. Due to the nature of selectively reduced shell and solid elements, hourglass effect is not produced.

Total Energy:

1. Total energy is the sum of all the energies like Internal energy, hourglass energy, kinetic energy, external work etc.

Result:

The drop testing of a phone was done in LS-Dyna and the contours are successfully plotted.

Conclusion:

The given meshed model was successfully used to build a LS-Dyna keyword deck and the drop test was successfully simulated with normal termination.