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.

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See also:

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Tom Irvine

Email: tom@irvinemail.org

Posted in Fatigue on November 14, 2014 | 4 Comments »

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.

* * *

See also:

* * *

Tom Irvine

Email: tom@irvinemail.org

Posted in Acoustics, Fatigue, webinars on November 7, 2014 | Leave a Comment »

PowerPoint Slides:

webinar_37_acoustic_fatigue.pptx

Audio/Visual File:

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References:

Rainflow Fatigue Posts

Acoustic Fatigue of a Plate

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Matlab script: Vibrationdata Signal Analysis Package

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See also: Vibrationdata Webinars

Thank you,

Tom Irvine

Posted in Fatigue on October 6, 2014 | Leave a Comment »

NASA-STD-5019, Fracture Control Requirement for Spaceflight Hardware (excerpt)

4.1.1.12 Low-Risk Part

This section addresses parts that can be classified non-fracture critical because of large structural margins and other considerations that make failure from a pre-existing flaw extremely unlikely.

a. For a part to be classified low risk, it shall be constructed from a commercially available material procured to an aerospace standard or equivalent.

b. Aluminum parts shall not be loaded in the short transverse direction if this dimension is greater than 7.62 cm (3 in).

c. A part whose failure directly results in a catastrophic hazard shall be excluded from being classified low risk, except when the total (unconcentrated) stresses in the part at limit load are less than 30 percent of the ultimate strength for the material used and requirements (1) through (3) and either (4) or (5) are met.

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Thus fatigue and fracture analyses are not required for parts with peak stress less than 0.3*ultimate.

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- Tom Irvine

Posted in Acceleration, Fatigue, Matlab on August 5, 2014 | Leave a Comment »

Rainflow fatigue cycles can be easily calculated for a single-degree-of-freedom subjected to a sine or sine sweep base input. The reason is that each pair of consecutive positive and negative response peaks forms a half-cycle.

The relative fatigue damage can then be calculated from the rainflow cycles.

Here are Matlab scripts for performing the rainflow and damage calculations. rainflow_sine.zip

rainflow_sine.m is for the case where the natural frequency is known.

rainflow_sine_fds.m gives the fatigue damage spectrum for a family of natural frequencies.

The remaining scripts are supporting functions.

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See also:

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- Tom Irvine

Posted in Acoustics, Fatigue on July 22, 2014 | 1 Comment »

Here is a paper showing how fatigue damage can be calculated from a stress response PSD for a plate excited by an acoustic pressure field: acoustic_fatigue_plate.pdf

The calculation method is given at:

Fatigue Damage for a Stress Response PSD

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The Matlab scripts for calculating the plate responses are included in the vibroacoustics section of the Vibrationdata GUI package, available at: Vibrationdata Signal Analysis Package

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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

Steady-State Vibration Response of a Plate Fixed on All Sides Subjected to a Uniform Pressure: fixed_plate_uniform_pressure.pdf

Aircraft Fuselage Fluctuating Pressure

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- Tom Irvine

Posted in Fatigue, Matlab, Power Spectral Density on July 3, 2014 | 5 Comments »

Here is a paper.

Estimating Fatigue Damage from Stress Power Spectral Density Functions: estimate_fatigue_psd.pdf

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This following Matlab program calculates the cumulative rainflow fatigue damage for an input stress PSD using the following wideband methods:

1. Wirsching & Light

2. Ortiz & Chen

3. Lutes & Larsen, Single-Moment

4. Benasciutti & Tovo, alpha 0.75

5. Dirlik

6. Zhao & Baker

Reference:

Random Vibrations: Theory and Practice (Dover Books on Physics)

The stress PSD and the fatigue strength coefficient must have consistent stress units.

The input PSD must have two columns: freq(Hz) & stress(unit^2/Hz)

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Main scripts:

Vibrationdata Signal Analysis Package

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The following values are “For Reference Only.”

m = fatigue exponent

A = fatigue strength coefficient

Aluminum 6061-T6 with zero mean stress

m=9.25

A=9.7724e+17 (ksi^9.25)

A=5.5757e+25 (MPa^9.25)

Butt-welded Steel Joints

m=3.5

A=1.255e+11 (ksi^3.5)

A=1.080e+14 (MPa^3.5)

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See also:

Mrsnik, Janko Slavic, Boltezar, Frequency-domain methods for a vibration-fatigue-life estimation – Application to real data: mrsnik_article_vib_fatigue.pdf

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- Tom Irvine

Posted in Fatigue on June 25, 2014 | 1 Comment »

Here is an empirical method for directing calculating a fatigue damage spectrum from a shock response spectrum: srs_fds.pdf

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See also:

Using Random Vibration Testing to Cover Shock Requirements

- Tom Irvine

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