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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

ObjectiveIdentify the root causes of failureEngineering solutions

LimitationThis 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, Screen discoloration on the surface of an LCD

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Methodology

Step 1Define a bench mark

Step 2Investigating the characteristics of LCD

Step 3Finite element analysis

ANSYSPro|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 arrangement hence 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 analysisPro| MechanicaANSYS

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 pressure results.This option is only available if the Single Pass Adaptiveconvergence method is requested.Friction between parts are not allowedLess control of mesh

FactSingle pass adaptive convergence is valid for small deflection theorySmall deflection theory becomes invalid when the model bends beyond 5 degrees.geometric nonlinear analysis (large deflection theory).

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Contact Analysis ANSYS

CapabilityAllows us to refine mesh on contacting surfaces-more accurate resultsLarge deflection theory is valid for contact analysisAllows friction between the mating parts

Factcontact elements use a "target surface" and a "contact surface" to form a contact pair

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Challengecontact 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 the location of contact beforehand

Node to surface contact elementswell-suited for point-to-point, point-to-surface, or edge-to-surface contact applications

Surface to surface contact elementsProvide better contact results needed for typical engineering purposes, such as normal pressure and friction stress contour plots 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 2Define element type

Structural solid-brick 8 node 185

---Contact Analysis

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step 3Meshing

Adaptive volume meshing Triangular mesh (both LCD casing and LCD module)

LCD moduleLCD cover

---Contact Analysis

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Step 4Selecting contact surfaces

use contact managersurface to surface analysis

---Contact Analysis

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Step 5Choose contact element types

The target surface is modeled with Target170 3-D target surface element

The contact surface is modeled with elements Conta1743-D contact surface element

---Contact Analysis

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step 6specify solution controls

Large displacement staticAutomatic 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 the top of LCD assembly

---Contact Analysis

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Result ANSYS FEA result depicts the

experimental result accurately in areas of interest

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Result

Areas of deflection (>3.8043mm) on the LCD depicts T and P failure areas on the LCD panel

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Result - contact stress

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Result- contact stress

Areas of Higher contact stress (>4.89MPa) depicts the three types of failure

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Solution specificationEngineering solutions will be based on the following parameters (sustaining)

Thickness of the magnesium panelThickness of the magnesium panel recommended for the market is 2mm; however this thickness can be changed to +0.5mm/-0.5mm. Due to product feature requirements the shape of the panel need not to be changed.

The Gap between the LCD and the PanelThis parameter can be changed to the desired level, or can be stuffed with material as long as it wouldn’t give an extra of 0.5lb in overall weight of the product.

The type of material to be used for the LCDThis 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 distance between the LCD Module and the Mg panelResult

Decreasing the gap shows high resistance for a specific load

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Thickens ChangeAnalysis base

Keep the gap distance between the Mg panel and LCD module constant

Bench: 2mm Gap

Vary the Mg panel thickness

ResultIncreasing the thickness of the Mg panel shows less deflection for a specific load

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Changing material typeDue 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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ConclusionEngineering 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 also decrease 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