Week - 3 Drop test Challenge

Objective :

To analysis the smart phone when it hits the ground and to check the stress and total energy of the smart phone using Ls - Dyna.

Procedure :

Step 1: Open the model which is in .k format into the ls dyna and we can see the model of drop test where smart phone is above the ground, to do analysis and to get stress and energy values we need to create material card, boundary and connections cards for the model.

Step 2: As we can see the they are three parts in the model i.e, smart phone, ground has two parts i. plate type and ii. solid ground. Here we want only a ground and phone so we deleting the solid ground part and analysisng the ground and phone parts and create part cards. The reason I took plate type part is here we have two type of meshing solid mesh and shell mesh so I took both type of mesh parts.

Step 3: Now we gave to create material cards for the model for two parts we are taking two different materials i. Aluminium for smart phone and ii. Steel for the ground. To create aluminium material card go to keyword manager > select all > mat > '024 piecewise linear ealsticity' > give required values as shown in below figure and create individual maerial id. Same apply to steel material card but take '020 rigid' card. Before giving the values we need to give values as gm mm ms units because phone is in grams and length is in milli meters and fall frrom space to ground will happen in milli seconds.

Step 4: Now we have to create section id for two type of mesh smart phone has solid section id card and ground has shell section id card and ELform as '2'.

Step 5: After creating both material and section id cards go to parts and give section id number and material id number in the part card and accept it. Here we have just defined which part has which material and which mesh, now we need to cretae boundary conditions for the model.

Step 6: We need create contact boundary this will help to hit the smart phone to ground. To create this go to keyword manager > all > contact > select automatic surface to surface > here we need to create set part id for both phone and ground this also known as slave segment set id and create master segment id. This will help to create a contact boundary for the model.

Step 7: Now we have to give another condition that is velocity, when smart phone is falling it has some velocity. To give velocity go to the create entity > intial > velocity > and at 'Vz' give -5 as velocity this is calculate from the formulae `V = (2gh)^(1/2)`which is the form of kinectic energy > select the part > accept.

Step 8: Now we have to create a Hourglass energy this, will help to plot different type of energies when we plot the graphs.

Step 9: Now we have to create a control termintion card which will help to create the end time of the analysis and also create energy card and keep Hgen as 2 this will include the hourglass energy in the plots.

Step 10: After that create a database cards d3plot and ASCII (glstat,elout,matsum,sleout). d3plot card help to calculate the stress,strain data values and ascci helps to plot the graphs. With this each every boundary conditions are given to the model.

Step 11: Now save the file in the format of .k and open this in ls manager application this will help to sove the problem and gives the data of stress and data of energies. In th end solver shows normal termination this means solving is done with no errors. Save the file.

Step 12: Now again open another tab of the ls dyna and select the d3plot file and open it. When we open this file it will automatically opens from the post procees. Here we need to create a stress data so go the stress tab and select the von misses and accept. This will give the complete stress values of the model when it falls on the ground.

This is the time when smart phone hits the ground as we can see that more stress is created near the bootom and stress is distrubuting through whole body.

When phone starts to rebound from ground we can see that stress is slowly reducing at the bottom and highly concentrated at the top of the smart phone, this is due to the impact at the ground and it is being absorbed by the smart phone.

At last we can see that stress is realised at the top and bottom of the smart phone and only concentrated at the middle. This due to the material behaviour where the total energy is absorbed by the smart phone.

Step 13: Now we need to plot the graph for energies to do that go to ascii option and selct the glstat and selct the internal energy,kinectic energy and hourglass energy and select the plot it will shows the graph.

In the graph we can see that internal energy, kinectic energy, total energy and hourglass energy. Here red line represents the kinectic energy and green line represents internal energy and blue line represents total energy and light blue line represents hourglass energy. From the graph we can clear see the law of conservation that total energy of the model is constant through out thetest where as kinectic energy is reduced and it converted as a internal energy when phone hits the ground and when it rebound internal energy is reduce and it converted as the kinectic energy. Thus we can see that energies are plotted and shows clear data of the model.

Conclusion : Thus we have performed a drop test for the smart phone using Ls Dyna and collected the data of stress and the energy values and we plotted the graph to understand clearly.