Week 5 Bending of iPhone

OBJECTIVE

To carry out a static-structural analysis on an iPhone bending simulation to determine the capacity of the material used to make the frame of the iPhone (Aluminium Alloy NL). The analysis will involve two cases differentiated by the location of thumbs that will be the source of load on the iPhone. The following outputs are to be requested:

 

• Directional deformation within the model
• Safety Factor of Aluminium Alloy NL
• Life of the Aluminium alloy for the case

MODEL IMAGE

PROCEDURE

1. After opening ANSYS Workbench, we are met with the Project Schematic window. Here, we can select the 'System Structural' analysis system on the left. Doing so creates a new project. Here, we can rename the project and also change the material if needed. We will need to right-click 'Geometry' and select 'import'. The file provided for this project should be selected. 

Now, we can add the materials right here and make our job easier for later. To do that, we need to double-click Engineering Data'. This opens up the list of inserted materials. We can pick materials we need from the repository listed here. The materials we need to add are Aluminium Alloy NL and Polyethylene, which should be available in the General Non-Linear Material and General Material repositories respectively. After that, we simply need to click the yellow '+' symbol on the material's corresponding 'add' column to add this specific material to the project. Then, we need to add the S-N curve to the added Aluminium Alloy NL material, by simply dragging 'S-N Curve' from the toolbox on the left as shown. We can then enter its values on the property window on the top right:

We also need to duplicate the polyethylene material (option is available when right-clicking it) to create a glass material card. Renaming the duplicated material, we can then edit the properties as shown below:

We can then exit out of the engineering data tab and return to the project schematic window, where we can right-click geometry and select 'edit'. This will bring the model up in the SpaceClaim interface.

2. To improve simulation time and reduce the number of elements, we can merge certain faces on the fingers of the model using the merge faces tool in the repair tab as shown:

After selecting the tool, we simply need to select the surfaces by using ctrl+left-click. After selecting, we simply need to press 'enter' and the algorithm merges the faces.

Merging will only be done once for both cases. But in the second case, we will need to move the position of the thumbs. To do that, we can make use of the move tool which lets us specify the magnitude and direction of displacement of the particular body that requires moving:

For the second case, we are to move both thumbs by 22.5mm in the X direction and 10mm in the Z direction. The option to select the entire body is available when right-clicking the selected surface.

Once we are done, we can simply close SpaceClaim and right-click 'model' and select 'update', since we have made changes to the geometry. We can then right-click 'model' again and click edit to bring up the mechanical interface.

3. In the mechanical interface, in the outline, under geometry, we can rename each of the components if needed. We shall be naming the fingers and the parts of the phone (Screen, Frame, Internal Components). Each of these will be assigned materials as well (Screen - glass, Frame - Aluminium Alloy NL, Internal Components - Polyethylene). In addition to that, all the fingers except the right thumb will have a rigid stiffness.

The fingers will be assigned the standard material of structural steel.

4. For the contacts under connections, they shall all be renamed based on definition (option available on right-clicking contacts). Two of the automatically generated contacts will be between fingers so they can be deleted. All the contacts except the one between the screen and the frame will have a frictionless type contact. Whereas, the contact between the frame and screen will be bonded.

5. Next, we can add fixed joints for all the fingers except the thumbs. To do that, we can simply Right-click the Contact entity, we can then go to Insert > Joint. They are going to be body-ground and fixed type. For the geometry, we can simply select one surface on the body, then press shift+F2 to select the entire body. We can then click 'apply' on the geometry attribute to create the joint. This process is repeated for the remaining 7 fingers.

We will now be creating translational joints for both the thumbs. The same process is repeated except in this case, we need to ensure the translation direction is towards the phone. If it isn't, we need to align the principal axis in the right direction as shown:

6. Moving on to the mesh, we can selectively refine the mesh in the regions of contact - namely certain surfaces on the thumbs and the frame surface. We shall be using the sizing option and the sizing will be of 4mm. Also, for the general mesh settings, the mesh smoothing should be low.

7. Next, we shall work on the analysis settings. The number of steps would be 8. Selecting all the steps, we can assign the following attributes:

All output controls should be enabled as well.

8. Moving on, we can insert the boundary conditions. For that, we go to Static Structural > Analyses Settings. Right-click analysis settings > insert > fixed support. Both sides of the internal component are selected as shown (after hiding the frame):

We can then similarly add the displacement condition. For this, we shall be selecting 4 faces on either side of the frame. The X and Z components are constrained.

Next, we need to right-click static structural > Insert > Joint Load. This will be created for both the translational joints on the thumbs. The x displacement values are entered in the tabular column as shown:

9. Now we can generate the outputs. To do this, we can right-click Solution > Insert > Strain > Equivalent (Von-Mises) (for equivalent strain) and right-click Solution > Insert > Stress > Equivalent (Von-Mises) (for stress) and right-click Solution > Insert > Deformation > Directional (Y Axis). For directional deformation, we can specify the geometry to be just that of the frame body.

We also need to insert a fatigue tool through the same process. After creating a fatigue tool, we can right-click 'fatigue tool' and insert 'life' and 'safety factor'. For each of these outputs, we should specify the frame again.

Now, all we need to do is right-click solution again and click 'Evaluate all results'. It must be reiterated that after reaching the solution, we should save the model and go back to SpaceClaim and make the changes for the second case as discussed earlier. After that, we will need to evaluate the results again and save it as a separate file.

Finally, when the analysis is done, we can view the results by simply clicking each of these solution entities we created, in the Outline menu.

OUTPUTS

CASE 1

Stresses on Phone Frame

Strains on Phone Frame

Directional Deformation in Y Direction (Entire phone)

Directional Deformation in Y Direction (Phone Frame only)

Maximum & Minimum Deformations on Phone Frame

Safety Factor Output for Phone Case

Life Output for Phone Case

CASE 2

Stresses on Phone Frame

Strains on Phone Frame

Directional Deformation in Y Direction (Entire phone)

Directional Deformation in Y Direction (Phone Frame only)

Maximum & Minimum Deformations on Phone Frame

Safety Factor Output for Phone Case

Life Output for Phone Case

OBSERVATIONS

Going by hard numbers, we can see that in case 1, even though the extreme deformation values were more than that of case 2, the average numbers stayed low. This is due to the location of the load application. Most of the load applied on the edge of the frame meant more load being transferred to other connected parts, like, possibly the screen. More stresses would be generated along the rim of the case. Whereas, in case 2, a large chunk of the force generated would be experienced by the centre region of the frame, which is flat. With this region experiencing more stresses, it ended up experiencing more deformations as well. This resulted in a higher average deformation in the case in particular but lower maximum and minimum values due to most of the frame absorbing the load.

Even so, the minimum number of cycles in both cases is 0, meaning the phone case will invariably fail in both cases. There will be permanent deformation.

As for safety factor, case 1 has a region with a lower safety factor, which means case 1 experiences higher stresses than in case 2 (also proven by outputs in the previous section: maximum stress experienced in case 1 was 606.9 MPa whereas in case 2 it was 418.55 MPa). That does not mean case 2 is any better. Both cases have minimum safety factors below 1, meaning the phone case will fail in both cases.

RESULT

Static-structural analysis was carried out on an iPhone case made of a Non-Linear Aluminium Alloy material undergoing bending. Two cases involving different load locations were simulated, analysed and compared. It was established that the case would fail in both instances. Nevertheless, from a safety point of view, case 2 exhibited better numbers in terms of stresses and deformation generated.