Week 5 Bending of iPhone
Simulation of Bending of iPhone
OBJECTIVE
To simulate the bending of the I-phone using ANSYS workbench.
Case 1. When bending action is performed from one of the longitudinal side of phone.
Case 2. When bending action is performed from center position.
Assign Aluminum alloy NL to the frame of the phone and define S-N curve for the material using following tabular data:
And from the simulation, determine the directional deformation of model along the direction of bending action & compare the fatigue life and safety factor of frame for the above two cases.
ANALYSIS PROCEDURE
1. Material Selection
Below is the list of materials used in the following simulation:
- Glass material is assigned to the phone screen.
- Aluminum alloy NL to phone frame.
- Polyethylene material for content inside phone.
- Structural steel for fingers
2. Geometry
Geometry consisting of assembly of fingers & i-phone is directly imported in the workbench from the available sources.
Fig. Detailed Geometry
Fig. Geometry for Case 1 Fig. Geometry for Case 2
3. Meshing
- Finer mesh element is introduced in the region of force application (i.e. region where pushing fingers press I-phone) using face sizing.
Fig. Faces selected for Face sizing
- While program controlled mesh with element size of 10mm is applied all over the assembly.
Fig. Meshed Geometry
STATISTICS
Total No. of Elements : 7637
Total No. of Nodes : 16444
Avg. Mesh Element Quality : 0.34271
4. Setup
i. Contacts
- Bonded contact is created between Display screen & Frame.
- While all other interfaces between Display screen, fingers & frame are assigned with frictionless contacts.
Below figures shows the various contacts which are established for the simulation.
Fig. Bonded Contact between Display screen & Frame
Fig. Frictionless contact between Display screen & Inside
Fig. Frictionless contact between Frame & inside component of I-phone
Fig. Frictionless contact between Holding fingers & Display screen
Fig. Frictionless contact between Frame & Holding fingers
Fig. Frictionless contact between Frame & Pushing finger
ii. Joints
In joints, fixed joint is assigned to all the holding fingers while translational joints is assigned to pushing fingers.
Fig. Fixed Joint assigned to each holding fingers
Fig. Translational joint assigned to both pushing fingers
iii. Boundary Condition
- Fixed Support is provided as boundary condition to the transverse side of phone inside material.
Fig. Fixed support on transverse side of Inside material
- While planar motion of phone frame is constrained using Displacement boundary condition.
Fig. Displacement Boundary condition for constraining planar motion
- Both the Translational joints are provided with perpendicular displacement so as to carry out bending action.
Fig. Displacement Boundary condition on pushing fingers( Displacement is provided in X-axis)
iv. Analysis Setting
- Simulation is made to undergo in steps of 8 time steps.
- Solver type is changed to Direct Solver.
- Settings for Weak spring, Auto-time Stepping is enabled to program controlled & Large deflection is also enabled
- Stabilization is turned on and set to constant in non-linear control. A value of 1 is provided in Energy dissipation ratio with 0.2 as Stabilization force limit.
Fig. Analysis Setting
RESULTS AND DISCUSSION
1. Directional Deformation (along axis perpendicular to planar surface of screen which is Y-axis)
Results are presented at the end of 8th time step.
Case 1. When bending action is performed from one of the longitudinal side of phone
Fig. Directional Deformation for whole system (along Y-axis)
Fig. Directional Deformation of Frame (along Y-axis)
Case 2. When bending action is performed from center position.
Fig. Directional Deformation for whole system (along Y-axis)
Fig. Directional Deformation of Frame (along Y-axis)
Results of Directional deformation are complying with the given displacement boundary condition. Graph shows the initial linear increase in Directional deformation and it reaches to a peak value of 8mm approximately. After that as the loads are removed, deformed region tends to return back to its initial state because of its elastic behavior. About 2mm deformation is disappeared during this event and the left amount i.e. approx. 6mm remained in the component as plastic deformation.
Comparison of results of the two cases shows similar trend however, deformation present at the end of 8th time step is higher when bending action is performed from one of the longitudinal side. This indicates that more plastic defomration is occured in the first case.
2. Equivalent Stress
Results are presented at the end of 8th time step.
Case 1. When bending action is performed from one of the longitudinal side of phone
Fig. Stress Distribution in whole system
Fig. Stress Distribution in frame
Case 2. When bending action is performed from center position
Fig. Stress Distribution in whole system
Fig. Stress Distribution in frame
Results of Equivalent stress, shows the development of higher stresses when phone is bended from one of its longitudinal sides compared to first case in which phone is bended from center. This is because of the geometric shape at the corner region, bending from a region close to one-side increases the moment of area of the geometry which basically means more force is required to bend the phone & hence more stress is developed in response to it.
3. Fatigue Life
Case 1. When bending action is performed from one of the longitudinal side of phone
Fig. Fatigue life of Frame
Case 2. When bending action is performed from center position
Fig. Fatigue life of Frame
As expected, regions which are under high stresses, are having minimum fatigue life. In first case, region in proximity to edge is under threat with minimum fatigue life of zero that means it may break during the process. While in second case, central region is found to have minimum fatigue life.
4. Safety Factor
Results are prsented for Design life of 1 million cycles i.e. 1E+06 cycles
Case 1. When bending action is performed from one of the longitudinal side of phone
Fig. Safety Factor for frame
Case 2. When bending action is performed from center position
Fig. Safety Factor for frame
Results of Safety factor further clarified the above results, as similar distribution is seen in both the cases. Safety factor is significantly low in the regions of high stresses.
ANIMATION