Week - 3 Drop test Challenge

Title : Drop Test on Mobile Phone Dummy on a floor

Problem Description : This study involves structural impact analysis of a Mobile Dummy on a floor. Free fall of mobile is considered. The stresses in the component is checked in yield for failure.

Input:

The input .k file for the analysis is used to import the geometry and mesh in LS-Dyna. For the free fall condition gravity is considered hence 9.8 mm/ms is the input velocity for Mobile Dummy. The unit system considered here is kg-KN-mm-ms .

FEM Model Setup (LS Dyna)

Following are the *keywords cards used to setup the model in LS Dyna which results a *keyword file as input file to run the simulation.

1. TITLE

Initially the default card is generated the Title for the simulation is changed for better understanding.

2. PART

The different auto created Parts are renamed to their corresponding nomenclature, i.e Mobile and Floor.

3.SECTION

We have Solid elements used in our simulation for Mobile Dummy and Floor, section should be defined for this elements, following image shows the SECTION card for solid elements that is defined. The Section id is given as 2, with Element formation type 1, i.e constant stress solid element.

4. MAT

In this card we have defined two different material cards, one is MAT20 (Rigid) and MAT24 (Piecewise Linear Plasticity). The initial one is defined to floor and the later one for the Dummy Mobile. Following figure show the Cards and their corresponding material information. For MAT24 only single strain rate is considered.

5. INITIAL

In this card we have given the input velocity to the Dummy Phone, the entire Mobile Phone is provided with the input velocity.

6. BOUNDARY

In this card the bpundary condition for the floor is encorporated, the Node Set for the floor is created and this node set is provided with the Boundary condition i.e all the DOF are restricted for the floor.

7.CONTROL TERMINATION

In this card we provide the time of simulation, i.e the end time, in this study the simulation is ran for 5ms.

8. DATABASE

The use of this card is for reading the outputs, so the required outputs are requested here, the requested outputs are d3plot with time interval of 0.1ms and for ASCII Output, ELOUT, MATSUM and GLSTAT with all time interval as 0.1ms.

9. CONTACT

This card plays a vital role in defining the contact between the Dummy (Slave) and the Floor (masters). The type implemented here is Automatic Surrface to Surface type as shown below.

The file is then ran in LS Run and the post processing is done,

Post Processing:

Following are the Outputs that are studied,

We can see that the stresses developed in the Mobile Dummy are below the Yield Strength. This might not result into permanent deformation in the dummy, but has might have impact on the phone.

It can be seen that Total Energy remains constant, which indicates the law of conservation of energy is followed by our simulation and at the time of impact there is sudden rise in Internal Energy and Decreace in Kinetic Energy.

So such a simple problem provides the scope of FEM and commercial softwares like LS Dyna in the Pre Design phase of any Component in the industry, which would result in saving of huge amount of time, effort and money but a major care should be taken that the credibility of analysis is high, i.e the Validation and Verification of simulation is must.