Week 5 Bending of iPhone

SIMULATION OF IPHONE BENDING USING ANSYS WORKBENCH

OBJECTIVE:

To simulate the bending of iPhone for the following case study,
i. Case (1): To simulate the model with bottom fingers in their pre-defined position.
ii. Case (2): To move the bottom fingers from their defined position to the given position X= 22.5mm & Z= 10mm and obtain the results for the simulation.To define the S-N curve for the Aluminium Alloy material for frame as per values given below and determine the fatigue life
results for the same.

1. THEORY
1.1 iPhone Bending:
The iPhone 6, particularly the iPhone 6 Plus, was the subject of many criticisms and jokes when it was discovered to bend almost too easily to pressure applied by nothing more than regular hands or placing them in the back pockets of tight jeans and sitting in different angles repeatedly.

Fig.1.1 iPhone bending.
Some say that extra-tight jeans are to blame, but it's really an issue of building materials the iPhone 6 and 6+ feature an aluminum chassis spread over a wider area than any previous iPhone. Aluminum is a naturally soft metal; with enough pressure and leverage, it's going to bend. Apple was said to have improved the build of its iPhone 6s and 6s Plus, this time utilizing 7000 Series aluminum.

In this project, an iPhone model is made to bend using thumb fingers placed just below the volume button and in the next case, the thumb fingers are placed at the middle of the bottom side of the phone.

2. ANALYSIS SETUP
2.1 Geometry:

a. Case (1): Initial position of pushing fingers.

b. Case (2): Pushing fingers moved to defined position.

c. Different components of iPhone bending assembly.

Fig.2.1.1 3D model of iPhone bending.

The given 3D model of iPhone bending assembly is imported into SpaceClaim. The iPhone assembly consists of display, frame, inside parts, pushing fingers and supporting fingers. For case (1), the position of pushing fingers is as shown in fig. 2.1.1 (a).

For case (2), the pushing fingers are moved from their defined position to the given position X= 22.5mm & Z= 10mm using move option in SpaceClaim.

a.Flexible.

b. Rigid.

Fig.2.1.2 Stiffness behavior.

The stiffness behavior of components highlighted with green color in fig. 2.1.2 (a) is set as flexible and in fig.2.1.2 (b) is set as rigid.

2.2 Material Properties:

The material assigned for the following components are, (i) Display; Glass, (ii) Frame; Aluminum Alloy NL, (iii) Inside part; Polyethylene, (iv) Fingers; Structural Steel.

2.3 Connection Details:
2.3.1 Contact details:

a.Contact between display and frame.

b. Contact between display and fingers.

Fig.2.3.1 Contact details of iPhone bending.

Contact between, (a) display and frame is assigned as bonded contact and (b) display and fingers are assigned as frictionlesscontact.

2.3.2 Joint Details:

We have to define each joint seperately for each finger. All finger joints are fixed and pushing finger joints are translational.

a.Fixed joint applied for supporting fingers.

b. Translational joint applied for pushing fingers

Fig.2.3.2 Joint details of supporting fingers and pushing fingers.

The fixed type of joint is assigned for supporting fingers to hold the display with connection type being body-ground. The translational type of joint is assigned for both pushing fingers with connection type being body-ground, since the pushing fingers has to move upward in order to bend the iPhone.

2.4 Meshing:

b. Meshed model.

a. Face sizing of frame 

Fig.2.4 Meshing details of iPhone bending model.

The element size of bottom surface of frame and contact surface of pushing fingers is set as 4 mm using face sizing option.

2.5 Boundary Conditions:
2.5.1 Analysis settings:

Fig.2.5.1 Analysis settings.
In the analysis settings the number of steps considered is 8. In solver controls, the solver type selected is ‘Direct’, with weak spring set as ‘Program controlled’ and large deflection is set to ‘On’. Under the nonlinear controls, the stabilization is set as constant with energy dissipation ratio being ‘0.1’ and activation for first sub-step set as ‘Yes’.

2.5.2 Boundary condition for iPhone bending:

a.Fixed support applied on surface of inside part.

b. Displacement applied on frame along Y-axis.

c. Translational joint load applied to both pushing fingers along Y-axis.
Fig.2.5.2 Boundary conditions for iPhone bending.

The fixed support is applied on the surface of inside part of iPhone on both sides. In order to move the iPhone in upward Ydirection
while pushing, the displacement is set to free in Y-direction and constrained in other direction. In order to bend the iPhone, the translational joint load is applied on both pushing fingers as shown in fig. 2.5.2 (c).

3. RESULTS AND DISCUSSIONS
3.1 Case (1): Bottom fingers in their pre-defined position.
a. Directional Deformation in the Y-axis (Frame):

The maximum deformation of frame along Y-axis reaches a maximum of 7.7 mm at the lower side of hole region for side button and reduces as the load is removed and reaches to a value of 5.04 mm at the end of step 8. Hence, it is observed from plot that the frame deforms plastically and does not regain its original shape and position.

b. Equivalent (v-m) Stress in Frame:

The maximum v-m stress developed in frame is 370 MPa near the hole region for side button.

c. Equivalent Elastic Strain in Frame:

The maximum equivalent elastic strain developed in frame is 0.0057026 near the hole region for side button.

3.2 Case (2): Bottom fingers moved from their defined position to the given position X= 22.5mm & Z= 10mm.
a. Directional Deformation in the Y-axis (Frame):

b. Equivalent (v-m) Stress in Frame:

c. Equivalent Elastic Strain in Frame:

3.3 Comparison of Results:
From the table, it is observed that the max. deformation along Y-axis, v-m stress and equivalent elastic strain for case (1) is more than compared to case (2), because the load applied through pushing fingers for case (2) is at the middle of frame.

CONCLUSION

1. Simulation of bending of iPhone was carried out successfully for the following case study,
i. Case (1): Bottom fingers in their pre-defined position.
ii. Case (2): Bottom fingers moved from their defined position to the given position X= 22.5mm & Z= 10mm.

2. The values of max. deformation along Y-axis, v-m stress and equivalent elastic strain for case (1) is more compared to case (2),
because the load applied through pushing fingers for case (2) is at the middle of frame.
3. The minimum fatigue safety factor for aluminum alloy NL material of frame in both cases is less than 1, hence material cannot sustain the applied load and eventually leads to failure.