Week - 3 Drop test Challenge

LS DYNA – Phone_Drop_Analysis

By Enos Leslie

Mechanical Engineer

29^th March 2021

Question:

In this assignment, we provide you with a file having just nodes and elements of two parts, a simplified cellphone, and a plate mimicking ground.

• You need to create a complete simulation file from this to perform a drop test. *INITIAL_VELOCITY card is to be used to give velocity specifications for the cellphone.

• We are not interested in how the phone travels from your hand to the plate, but only the period when the impact happens and a few milliseconds after that. Therefore, we will keep the two parts very close and provide an appropriate magnitude of velocity.

• The orientation of the cellphone is also important and there are specific guidelines on how to orient the products but for this assignment, we will ignore that.

• Based on what you have learned till now, use your judgment, manuals, and the previous simulations that are shown to create a complete input file for a drop test.

A typical large engineering firm will have three distinct departments handling simulation work. The first two departments will handle CAD modeling and meshing. The third group will be specialists for different stimulation jobs such as static, dynamic, and thermal. These specialists will not be working on meshing much unless they need to modify it for a specific purpose. We will cover some meshing guidelines later but otherwise, we will concentrate on how to use LS-DYNA and debug

OBJECTIVE

The objective of this assignment is not to get a correct simulation but to get a feel of creating an input deck from scratch. I have been provided with a mesh file and a complete simulation of the drop test is made and analysed below.

PROCEDURE

IMPORT

The K. file is imported into LS- Prepost where an input file is going to be made to be solved by LS-Dyna. The is a 3D part which is the phone and a solid ground with a 2D shell over it. The solid part is deleted so must have just the 2D wall.

MATERIAL

Firstly, a material card is created for both parts. Linear plasticity MAT 024 is used for the phone with unit system of (g/mm/ms). A rigid material MAT 020 is assigned to the wall. The details of the material can be seen in the image below.

SECTION

Sections are created for the phone and wall. This is done by using the section keyword. Wall being a 2D element is specified a ELFORM of 2 and thickness of 6mm. The phone being a solid is assigned an ELFORM of 2.

PART

The part keyword is opened and section, material and PID is assigned to their respective parts as seen below.

BOUNDARY CONDITION

The nodes on the edges of the wall are selected to be fixed in all DOFs. An SPC set is created.

A part list is created to highlight the nodes on each of the part. The solid and shell parts are created separately.

CONTACT

A contact is defined from the contact keyword. Contact automatic surface to surface is used.

SSTYPE and MSTYPE is placed on the number 2 to allow the possibility to assign parts as master and slave. SSID and MSID are assigned by making the phone the slave and wall the master.

INITAIL VELOCITY

The orientation of the phone is ignored as this is just a demonstrational exercise. The initial velocity of free fall is assumed to be 5mm/ms. This is assigned to the phone using the part node set and specified in the negative Z direction.

CONTROL TERMINATION

This keyword controls the end time of the simulation. DT is specified to 5ms.

OUTPUT

Output files are requested using database keyword. D3plot is requested with a time of 0.5ms. Similarly, we request for ELOUT, GLSAT, and MATSUM is requested to be analyzed.

POST-PROCESSING

After the simulation is successful, the animation plot is opened and analyzed.

Conservation of energy, principle of physics according to which the energy of interacting bodies or particles in a closed system remains constant. The first kind of energy to be recognized was kinetic energy, or energy of motion. In certain particle collisions, called elastic, the sum of the kinetic energy of the particles before collision is equal to the sum of the kinetic energy of the particles after collision.

The same theory applies here. When the phone is in free fall and about to hit the wall, the is kinetic energy which is maximum until 3ms when collision happens. The energy upon hitting the wall is transferred to internal energy was minimum until 3ms and then rises as the body losses its kinetic energy. The energy upon crush causes the phone to rebound because of the elastic nature of the crush

 The total energy of the body remained the same which validates the theory of conservation of energy. Also, no hourglass controls were needed as there is not much deformation in this experiment. The hourglass energy is practically nonexistent as no occurrence of hourglass is seen.

CONCLUSION

This simulation helped demonstrate the creation of a typical LS-Dyna solver deck input file. The simulation was successful, and the conservation of energy was demonstrated during the drop test.