Shock and Vibration Severity Thresholds for Structures and Equipment

Launch vehicle and spacecraft equipment must withstand pyrotechnic shock from stage separation and other flight events.   Civil engineering structures and equipment must survive seismic events.  There are many other examples where military, automotive, telecommunication and other equipment must be designed and tested to meet shock requirements derived from field or flight data.  The likelihood that a structure or equipment piece will fail a shock environment is often expressed in terms of a severity threshold.  The threshold may be expressed in terms of a base input or response level.  The purpose of this paper is to compile severity acceleration and velocity thresholds for both equipment and buildings into a single document for comparison purposes.

Link:  shock_vibration_severity_thresholds.pdf

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See also:
Shock Severity Limits for Electronic Components
Dr. Howard Gaberson’s Papers
Stess-Velocity Relationship

– Tom Irvine

Hypersphere SRS

hsrs

Figure 1. El Centro Earthquake 1940, Peak Pseudo Velocity, 36.4 in/sec
 
Launch vehicle and spacecraft equipment must withstand pyrotechnic shock from stage separation and other flight events. Civil engineering structures and equipment must survive seismic events. There are many other examples where military, automotive, telecommunication and other equipment must be designed and tested to meet shock requirements derived from field or flight data. The specification is commonly given as a shock response spectrum (SRS). An SRS may be calculated for each orthogonal input axis, assuming the availability of triaxial accelerometer data. Each axis may thus have a separate specification. Alternatively, a maximum envelope can be drawn over the three SRS curves and then applied as a uniform specification to each orthogonal axis.

The uniform enveloping method, however, can underestimate the maximum resultant shock when all possible orthogonal axes sets are considered. The purpose of this paper is to introduce a hypersphere method to achieve a true maximum SRS.

Paper link:  hypersphere_SRS

The Matlab script for this calculation is included in the GUI package at:
Vibrationdata Matlab Signal Analysis Package

– Tom Irvine

 

Vibration Analysis of Structures with Composite Materials

Natural Frequencies of Composite Beams: compbeam.pdf

A function for composite beams is included in: Vibrationdata Matlab Signal Analysis Package

The function can be accessed via:

>> vibrationdata > Miscellaneous Functions I > Structural Dynamics > Beam Bending > General Beam Bending, Composite Laminates

Plates & shells later…

– Tom Irvine

Peak Response to Random Vibration with Probability of Exceedance

An important parameter in random vibration analysis is the peak response, which can be the maximum relative displacement, velocity, acceleration, stress or strain. The peak response can then be compared with the threshold for yielding, ultimate failure, etc. The peak is also important for fatigue analysis, particularly for materials with higher exponents. A common approach is to consider that the peak response is 3σ, where 1σ is the standard deviation. But higher responses often occur > 3σ.

This paper presents a method for estimating the peak response for a desire probability of exceedance.  peak_response_random.pdf

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The equation is included in: Vibrationdata Matlab Signal Analysis Package

The function can be accessed via:

vibrationdata > Miscellaneous Function I > SDOF Response: Sine, Random & Miles > SDOF Response: Peak Sigma for Random Base Input > Risk of Overshoot, XRS, URS

This function may also be used for MDOF systems if the positive slope zero-crossing rate is used in place of the natural frequency.

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See also:

European Cooperation for Space Standardization, Mechanical Shock Design and Verification Handbook, ECSS-E-HB-32-25A

Equivalent Static Loads for Random Vibration

– Tom Irvine

European Space Agency Shock Handbook

clampband

LV/SC Clampband Release Test

Here is an excellent reference on shock testing and analysis:

European Cooperation for Space Standardization, Space engineering, Mechanical Shock Design and Verification Handbook, ECSS-E-HB-32-25A, 14 July 2015  download link

The Shock Handbook was covered in several presentations at the ESA 2nd Workshop on Spacecraft Shock Environment and Verification, 2015   presentation link

Tom’s Summary Slides

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See also:

SRS Educational Animation

Vibrationdata Matlab Signal Analysis Package

Vibration Testing & Analysis Standard References

Pyrotechnic Shock

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– Tom Irvine

Bird Songs

carolina_wren_1

I made a recording of a bird in my backyard in Madison, Alabama.  The bird was up in a tall pine tree, and I could not see it.  But I was able to identify it from its song with the help of someone on the WhatBird website forum.  It turned out to be a Carolina Wren, which is the State Bird of South Carolina.  The image above is a stock photo of this species.

More bird songs later…

– Tom Irvine

Earthquake Conference

vafb_launch

Rocket vehicles mounted on launch stands at Vandenberg AFB, California must be designed and analyzed to withstand potential earthquakes originating on the nearby San Andreas Fault.  The vehicles behave as long, slender cantilever beams prior to liftoff.

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I am going to present a paper at the

16th World Conference on Earthquake Engineering
January 9-13, 2017, Santiago, Chile

The title is:

Seismic Analysis and Testing of Equipment using Historical Strong Motion Data Scaled to Satisfy Shock Response Spectra Specifications.  Preliminary Draft.

This paper has application for launch vehicles, power substations, telecommunication equipment, buildings, etc.

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See also:

Webinar 47 – Shock Response Spectrum Synthesis, Special Topics

Matlab script: Vibrationdata Signal Analysis Package

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– Tom Irvine

Fatigue Group & Conferences

Howdy!

If you are interested in vibration fatigue please send me a reply.
Email: tom@irvinemail.org

I am creating a mailing list specifically for fatigue. Topics will include rainflow cycle counting, spectral methods, applications, etc.

My current fatigue offerings are posted at: https://vibrationdata.wordpress.com/?s=fatigue&submit=Search

Also, I am going to present papers at the following upcoming conferences. Please let me know if you will be able to attend one or more. Or I may be able to visit you at your workplace if you are nearby.

ESTECH, Glendale, Arizona, May 2-5, 2016

Spacecraft and Launch Vehicle Dynamic Environments Workshop, El Segundo, California, June 21-23, 2016

MOVIC & RASD 2016, Southampton UK, July 3-6, 2016

European Conference on Spacecraft Structures Materials and Environmental Testing, Toulouse, France, September 27-30, 2016

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Here is paper that Curtis Larsen and I presented in Prague:

A review of spectral methods for variable amplitude fatigue prediction and
new results  download link

3rd International Conference on Material and Component Performance
under Variable Amplitude Loading, VAL2015

Thank you,
Tom Irvine

Modifying Spectral Fatigue Methods for S-N Curves with MIL-HDBK-5J Coefficients

Here is a paper: spectral_methods_MILHDBK5J.pdf

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The example problem in the paper was performed via the Matlab software posted at Matlab GUI package

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See also

Fatigue Damage for a Stress Response PSD

Rainflow Fatigue Cycle Counting

MIL-HDBK-5J

MMPDS-01

More later….

Tom Irvine