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An Analysis of Structural Strength of a Compact Disc

CD Explosion

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The Laser is refracted through the polycarbonate layer and then reflects off of the thin Aluminum layer

Inside a Compact Disc

Investigate strength and properties of Compact Discs under high rpm

1. Determine if a disk could fail inside a high speed CD-ROM drive.

2. Determine RPM of fracture in CD-ROM drive environment. 3. RPM of fracture of a CD with typical defect.

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Goal:

Challenges:

1.To run an analysis in Ansys we needed material properties (we assumed that majority of material strength is from polycarbonate using MatLab.

2. How to model scratches (assume axis-symmetric)

3. Applying forces and creating other physical properties in Ansys

Results:

1. Convergence Test: 30,000 elements sufficiently modeled the physics

Von Mises Stress under 27,500 RPM (ANSYS)

CD without Scratch Sensitivity Analysis

30.5

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31.5

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32.5

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33.5

0 10000 20000 30000 40000 50000 60000

# of Elements

Ma

x V

on

Mis

es

Str

es

s

Von Mises Stress Distribution

Nodal Displacement

Von Mises Stress under 36320 RPM (ANSYS)

2. CD without a defect: failure @ 36,230 rpm > 27,500 rpm of a modern CD-ROM

36,230 rpm at which stresses in an un-flawed CD equal Ultimate Tensile Strength

Ultimate Tensile Strength of Poly Carbonate: 55-75 Mpa (99.97% material Poly Carbonate)

3. CD with a crack 0.3 mm wide 2 cm long and .15mm deep.

•Failure @ ~21,000 rpm (about same as Myth Busters)

•Crack propagation

Videos on youtube.com and Myth Busters also show the CD exploding as low as 23,000 RPM. These videos use rotary tools which clamp the disk down, forcing the vibrations caused by unbalanced center of mass to be directed entirely into the disk.

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References:

www.Howstuffworks.comwww.youtube.com

Computer Softwares:

Ansys SolidworksMat LabMicrosoft Excel

Any Questions?

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Myth Busted: Enjoy your CD without any fear