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Avionics components in aircraft and launch vehicles may be mounted to surfaces which are exposed to high intensity acoustic excitation. The external acoustic pressure field causes the panel and shell surfaces to vibrate. This vibration then becomes a base input to any component mounted on the internal side. Components must be designed and tested accordingly.

The component vibration input levels can be derived via analysis and testing for a given sound pressure level.

Acoustic testing of the structure can be performed in a reverberant chamber or using a direct field method. There is some difficultly in testing, however, because the simulated acoustic field in the lab facility may be different in terms of spatial correlation and incidence than that of the flight environment even if the sound pressure level can be otherwise replicated.

The vibroacoustic analysis techniques include finite element and boundary element methods, as well as statistical energy analysis. These are powerful tools, but they require numerous assumptions regarding external acoustic pressure field type, coupling loss factors, modal density, impedance, radiation efficiency, critical and coincident frequencies, distinguishing between acoustically fast and slow modes, etc.

As an alternative, simple empirical methods exist for deriving the structural vibration level corresponding to a given sound pressure level. Two examples are the Franken and Spann techniques. These methods may be most appropriate in the early design stage before hardware becomes available for lab testing and before more sophisticated analysis can be performed.

The Spann method provides a reasonable estimate of the acoustically excited component vibration environments when only the areas exposed to the acoustic environment and mass are known.

Spann_vibroacoustic_method.pdf

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The scripts for performing this calculation are given at:
Vibrationdata Signal Analysis Package

>> vibrationdata > Acoustics & Vibroacoustics > Vibroacoustics

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- Tom Irvine

oblique

The Steady-State Response of a Baffled Plate Simply-Supported on All Sides Subjected to Harmonic Pressure Wave Excitation at Oblique Incidence:

ss_plate_oblique_incidence.pdf

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The scripts for performing this calculation are given at:
Vibrationdata Signal Analysis Package

>> vibrationdata > Acoustics & Vibroacoustics > Vibroacoustics

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See also:

Steady-State Response of a Rectangular Plate Simply-Supported on All Sides to a Uniform Pressure:  ss_plate_uniform_pressure.pdf

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- Tom Irvine

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

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