Week 5 Bending of iPhone

SIMULATION OF IPHONE BENDING USING ANSYS WORKBENCH

OBJECTIVE

To simulate the bending of iPhone for the following case study,

1. Case (1): To simulate the model with bottom fingers in their pre-defined position.
2. 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:

a. Glass.

b. Polyethylene.

c. Aluminum Alloy NL.

d. Structural steel.

Fig.2.2 Material property details of iPhone bending model.

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 frictionless contact.

2.3.2 Joint Details:

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:

a. Face sizing of contact region of frame and fingers.                                     b. Meshed model.

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. The total number of nodes and elements generated are 23270 and 10944 respectively.

Note: The academic version of software has the problem size limit of 128k nodes or elements.

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 Y-direction 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 7.931 mm at the lower side of hole region for side button and reduces as the load is removed and reaches to a value of 5.474 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 577.73 MPa near the hole region for side button.

c. Equivalent Elastic Strain in Frame:

The maximum equivalent elastic strain developed in frame is 0.0083094 near the hole region for side button.

d. Fatigue Safety Factor of Frame:

The fatigue safety factor for the aluminum alloy NL material of frame is 0.27695, which is less than 1, hence material cannot sustain the applied load and eventually leads to failure.

e. Fatigue Life of Frame:

The maximum fatigue life of frame is 1e8 cycles. The minimum life of frame is 0 cycles which is observed near the region of side button hole, hence there is possibility of crack propagation and failure of the component.

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):

The maximum deformation of frame along Y-axis reaches a maximum of 7.9597 mm at the middle and reduces as the load is removed and reaches to a value of 4.3334 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 359.67 MPa near the hole region for side button.

c. Equivalent Elastic Strain in Frame:

The maximum equivalent elastic strain developed in frame is 0.005329 near the hole region for side button.

d. Fatigue Safety Factor of Frame:

The fatigue safety factor for the aluminum alloy NL material of frame is 0.44486, which is less than 1, hence material cannot sustain the applied load and eventually leads to failure.

e. Fatigue Life of Frame:

The maximum fatigue life of frame is 1e8 cycles. The minimum life of frame is 77910 cycles which is observed near the region of side button hole, hence there is possibility of damage of the component after attaining minimum life.

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.

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.

The minimum fatigue life of frame for case (1) is 0 cycles, hence there is possibility of crack propagation and failure of the component.

The minimum fatigue life of frame for case (2) is 77910 cycles, hence there is possibility of damage of the component after attaining minimum life.

4. ANIMATION OF RESULTS:

4.1 Case (1): Bottom fingers in their pre-defined position.

a. Directional Deformation in the Y-axis:

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

c. Equivalent Elastic Strain in Frame:

d. Fatigue Safety Factor of Frame:

e. Fatigue Life of Frame:

4.2 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:

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

c. Equivalent Elastic Strain in Frame:

d. Fatigue Safety Factor of Frame:

e. Fatigue Life of Frame:

CONCLUSION

1. Simulation of bending of iPhone was carried out successfully for the following case study,

1. Case (1): Bottom fingers in their pre-defined position.
2. 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.

4. The minimum fatigue life of frame for case (1) is 0 cycles, whereas, for case (2) is 77910 cycles, hence there is possibility of damage of the component after attaining minimum life.