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Fracture Matlab GUI

I am creating a Matlab GUI toolbox for fracture analysis: vibrationdata_fracture.zip

vibrationdata_fracture.m is the main script. The remaining scripts are supporting functions.

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Functions:

1. Stress intensity factor for a through crack, at right angles, in an infinite plane, to a uniform uniaxial stress field
2. Stress required to propagate a partial through-the-thickness, crack-like discontinuity

More later…

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References:

http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_lefm_Kc_Matl.cfm

http://academic.uprm.edu/pcaceres/Courses/INME4011/MD-5B.pdf

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- Tom Irvine

Fatigue Survey

I recently sent out a survey asking engineers which fatigue methods that they use.

If anyone else would like to reply, then please send me an Email. I will then update the survey.

Survey Results

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See also:

Rainflow Fatigue

Dirlik Method

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Tom Irvine
Email: tom@irvinemail.org

PowerPoint Slides:

Webinar_38_circuit_board_fatigue_part_2.ppt

Reference Paper:

Extending Steinberg’s Fatigue Analysis of Electronics Equipment Methodology to a Full Relative Displacement vs. Cycles Curve

electronic_rd_n.pdf

extending_Steinberg.pptx

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Matlab script: Vibrationdata Signal Analysis Package

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See also:

Webinar 32 – Circuit Board Fatigue

Thank you,

Tom Irvine

Wind Tunnel Testing

Here are some notes on the basics of wind tunnel testing:  wind_tunnel_notes.pdf

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- Tom Irvine

PowerPoint Slides:

webinar_37_acoustic_fatigue.pptx

Audio/Visual File:

AcousticFatigue.wmv

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References:

Rainflow Fatigue Posts

Acoustic Fatigue of a Plate

Acoustic Power Spectra

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Matlab script: Vibrationdata Signal Analysis Package

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See also: Vibrationdata Webinars

Thank you,

Tom Irvine

emb145

Figure 1.  ERJ (EMB) 145 Aircraft

Rolls-Royce_AE_3007_2

Figure 2.  Rolls-Royce AE 3007 Series Turbofan Engine

emb145_fft

 

Figure 3.  Fourier Magnitude, ERJ 145 Climb-out

 

I recently flew as a passenger in an EMB 145 jet similar to the one shown in Figure 1.

This aircraft has two Rolls-Royce AE 3007 series turbofan engines turbofan engines, as shown in Figure 2.

Here are the rotational speeds for each rotor.

Fan Speed                       7903 RPM   (132 Hz)
Gas Generator Speed   16013 RPM   (267 Hz)

Note that there are several variants of this engine with slightly different rotor speeds.

I made an audio recording from within the aircraft cabin during climb-out, while hearing some distinct sine tones against the background random noise. The audio file is: emb145.wav

A Fourier transform of the sound file is shown in Figure 3.  Spectral peaks occur at 133 and 267 Hz, which agree with the specifications for the engines.

Again, this recording was made from inside the cabin. So the fuselage walls would have attenuated some of the engine-generated acoustic energy, particularly at higher frequencies.

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- Tom Irvine

02-2014-nissan-versa-note-fd

versa

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I recently drove a Nissan Versa rental car similar to the one shown above.

The Versa made a strong throbbing sound when I drove down a highway at 65 mph with the front side windows closed and the rear windows open.

Here is the sound recording that I made with my Samsung Android: Versa Sound

Please listen to the sound file using a headset with good low frequency response to hear the full effect.

The Fourier transform is shown above with its fundamental frequency at 21.2 Hz and integer multiples thereof.

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Dr. Stephen Granade explains:

That “whum whum WHUM WHUM” noise happens because the wind passing over the small window opening… forms tiny tornadoes as it moves past the front edge of that opening. When those tornadoes, or vortices, reach the opening’s back edge, they make a wave of pressure that pushes air into and out of the car.

Since sound is nothing more than waves of pressure, this makes noise… The vortices keep pressing on the air in your car just at the right time to make big pressure waves that we can feel and hear.

The technical term for this effect is the Helmholtz resonance, though car people call it “side window buffeting”…

…As you drive faster, the rate at which the whums occur speed up and the loudness goes up.

Interestingly enough, Granade goes on to theorize that “It’s more noticeable in modern cars because they’re more aerodynamic,” the thinking being that cracking a window is more disruptive to a smoothly-tuned airflow. If that’s true, it would mean cars with boxy shapes would suffer less from Hemholtz resonance.

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A more technical explanation is:

Buffeting (also known as wind throb) is an unpleasant, high-amplitude, low-frequency booming caused by flow-excited Helmholtz resonance of the interior cabin. Vortex shedding in the shear layer over the cavity opening (side window) couples with the cabin acoustics, leading to a self-sustained oscillation of shear layer and cabin pressure.

Reference

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- Tom Irvine

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