Abebaw Final

8/4/2019 Abebaw Final

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Dell Confidential

Client EngineeringClient Engineering

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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

Abebaw Final

Documents

Transcript of Abebaw Final