abebaw final
TRANSCRIPT
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Amanuel M Abebaw
Advisor: Dr. El-MounayriDepartment of Mechanical Engineering
Purdue School of Engineering and Technology, IUPUI
Co-Advisor: Phil GilchrestDell inc.
August 30th 2005
Failure analysis of an LCD assembly
ME 597 Project I
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Outline
Objective
Identify the root causes of failure
Engineering solutions
Limitation This study only analyze the LCD assembly (the Mg
cover and LCD module) of the Notebook computer
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Back ground
Definition of failure
Paint lines , Paint spots, Scratches (light ,deep), dents, Screendiscoloration on the surface of an LCD
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Methodology
Step 1 Define a bench mark
Step 2
Investigating the characteristics of LCD
Step 3Finite element analysis
ANSYS Pro|Mechanica
Step 4Identify failure causes
Step 5Suggest design improvement
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Step 1- Defining a bench Mark
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Step 2- Investigation of LCD
LCD
Polarized filters are most commonly made of a chemical film applied
to a transparent plastic or glass surface
Molecules in Nematic phase have definite order and arrangementhence external load (temperature and pressure) to this moleculesaffect the pattern and arrangement
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STEP 3-Finite Element Analysis
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Finite Element Analysis
Identifying resources
contact analysis
Pro| Mechanica
ANSYS
Pro| LCD cover
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Contact Analysis
Pro|Mechanica Capability
MECHANICA allows you to refine the elements on the
contacting surfaces in order to improve contact pressureresults.
This option is only available if the Single Pass Adaptiveconvergence method is requested.
Friction between parts are not allowed
Less control of mesh
Fact
Single pass adaptive convergence is valid for small deflectiontheory
Small deflection theory becomes invalid when the modelbends beyond 5 degrees.
geometric nonlinear analysis (large deflection theory).
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Contact Analysis
ANSYS Capability
Allows us to refine mesh on contacting surfaces-more accurateresults
Large deflection theory is valid for contact analysis Allows friction between the mating parts
Fact
contact elements use a "target surface" and a "contact surface"to form a contact pair
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Challenge
contact element type
Node to node contact elements
node-to-node contact elements is an extremely precise
analysis of surface stresses
To use node-to-node contact elements, you need to know thelocation of contact beforehand
Node to surface contact elements
well-suited for point-to-point, point-to-surface, or edge-to-surface contact applications
Surface to surface contact elements
Provide better contact results needed for typical engineeringpurposes, such as normal pressure and friction stress contourplots
Have no restrictions on the shape of the target surface
---Contact Analysis
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Steps used for the analysis
step 1:
Create the model geometry in ANSYS / Import from Pro|
Engineer using IGES
step 2
Define element type
Structural solid-brick 8 node 185
---Contact Analysis
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step 3
Meshing
Adaptive volume meshing
Triangular mesh (both LCD casing and LCD module)
LCD module
LCD cover
---Contact Analysis
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Step 4
Selecting contact surfaces
use contact manager
surface to surface analysis
---Contact Analysis
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Step 5
Choose contact element types
The target surface is modeled with Target170
3-D target surface element
The contact surface is modeled with elements Conta174
3-D contact surface element
---Contact Analysis
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step 6
specify solution controls
Large displacement static
Automatic time stepping It allows ANSYS to determine appropriate sizes to break the load steps
---Contact Analysis
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Step 7
Apply constraints on the LCD assembly and run the analysis
Apply loads (up to 25lbf)
Apply structural constraints( zero DOF at the edges of the LCD
assembly)
Step 8
Post process and view the result
Zero degree of freedom
at the edge of LCD
assembly
Force distribution at thetop of LCD assembly
---Contact Analysis
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Result
ANSYS FEA result depicts theexperimental result accurately inareas of interest
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Result - contact stress
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Result- contact stress
Areas of Higher contact stress (>4.89MPa) depictsthe three types of failure
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Solution specification
Engineering solutions will be based on the following parameters(sustaining) Thickness of the magnesium panel
Thickness of the magnesium panel recommended for the market is 2mm;however this thickness can be changed to +0.5mm/-0.5mm. Due to productfeature requirements the shape of the panel need not to be changed.
The Gap between the LCD and the Panel This parameter can be changed to the desired level, or can be stuffed with
material as long as it wouldnt give an extra of 0.5lb in overall weight of theproduct.
The type of material to be used for the LCD This parameter is very restricted, at this moment the magnesium can only be
substituted with BPL 1000 Plastic panel.
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Gap
Analysis base Keeping Mg panel
thickness constant Bench: 2mm Mg
Varying the gap distancebetween the LCD Moduleand the Mg panel
ResultDecreasing the gap shows
high resistance for aspecific load
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Thickens Change
Analysis base Keep the gap distance
between the Mg panel andLCD module constant
Bench: 2mm Gap
Vary the Mg panelthickness
Result
Increasing the thickness
of the Mg panel shows
less deflection for aspecific load
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Changing material type Due to product cosmetic and DFC issues changing
material type was not an applicable option
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Conclusion
Root cause for failure
Failures are caused due to structural deflection (>3.8043mm) Contact stress (>4.89Mpa) between the Mg panel and the LCD module
create screen discoloration on the LCD surface
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Conclusion
Engineering solution based on the given controlled design parameters Increasing the Mg panel thickness from a 2mm to a 2.5mm on the product will
decrease deflection of the assembly
Decreasing the gap distance from a 2.0mm gap to a 0.5mm gap distance will alsodecrease the LCD assembly deflection.
N.B.High deflection creates more stress contact between the LCD assembly and the Key
board of the Note book
Recommendation for Further study
Determining the amount of stress that is developed during LCD contact with the
Keyboard
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Thank you