To perform random testing, a random test spectrumneeds to be defined. | FEMCI BOOK
We cannot input these values directly into NASTRAN because it will not accept a slope in dB/Oct. | REFERENCES
The safety factor is usually applied to the amplitude. With a finite element model, a random vibration analysis can be performed to predict acceleration responses from 20 Hz to 2000 Hz. Generally the random vibration spectrum profile is displayed as a power spectal density (PSD) plot. Customer can prefer to use either sinusoidal sweep or random vibration profile as vibration test specification of an automotive part. Generally, the random vibration spectrum profile is defined as a power spectral density (PSD) plot. PSD refers to the actual plot generated during testing, which simply reads the power output from the accelerometers.). * NOTE: 3dB (3.01dB to be exact) is a factor of 2 for ASD curves (g2/Hz) while 6dB is a factor of 2 for grms values. Finally, solve for the ASD at the desired frequency: Or, for those of you who want a more expanded and complete version (where m is the slope in dB/Oct): I'll leave it up to you to use the example given in the graph above to prove that the equations work. | WORKSHOP
Keep in mind that an octave is the doubling of the frequency. Some random vibration tests are intended to simulate the maximum expected environment, which may include a safety factor. Real-time data acquisition utilizes spectrum-averaging to produce a statistical approximation of the vibration spectrum. The typical aircraft random vibration test profiles are between 30 minutes and 6 hours per axis, with 3 hours being a common choice in the absence of specific knowledge of the transportation profile. | MINUTES
Unfortunately, this spreadsheet needs the frequency and ASD values as inputs. The IEC 60068-2-64 package testing standard addresses structural integrity. Most random vibration testing is conducted using Gaussian random suppositions for both measurement and specification purposes. Thanks to Bob Coladonato and Dr. Bill Case, both retired from Goddard, and Jaap Wijker of University of Technology Delft in the Netherlands for their assistance with this page. Often truck random vibration profiles are testing in conjunction with aircraft profiles to represent transport before and after air transport. | LINKS
So going from 1Hz to 2Hz is an octave and going from 1000Hz to 2000Hz is also an octave. Presentations
Presentations
SPECIFICATION: Per Saint Technologies Test Plan TP-100 REQUIREMENTS: Nuts do not move due to vibration. Random vibration testing is one of the more common types of vibration testing services performed by vibration test labs. Developing Amgen’s Random Vibration Test Standards This paper describes the collaboration of science, engineering, industry, academia, and consultants to develop testing profiles to meet your qualification needs. Individual points in G2/Hz vs. Hz are required. (Note that regardless of popular opinion, G2/Hz is actually an acceleration spectral density (ASD), not a power spectral density (PSD). | PRIVACY. … This response is in turn used as a template to derive a test level specification. One purpose for performing a random vibration analysis is to create a component test level specification. With Gaussian assumptions, there is no definable maximum amplitude, and the amplitude levels are measured in RMS (root-mean-squared) values. For components less than 100 lbs (45.4 kg), NASA uses these values from. For example, reducing a peak ASD value of 12g2/Hz -3dB would give you 6g2/Hz; reducing a value of 12grms -3dB results in a value of 8.48grms and reducing it -6dB results in a value of 6.0grms. An Excel 95 version, grms95.xls, is also available. Links
But once you've calculated your ASD values, you can input them into this spreadsheet as a check to see if you did your math correctly. Use these guidelines to create the spec. Fh and FL are 100Hz and 600Hz, respectively. References
Creating a Random Vibration Component Test Specification. This response is in turn used as a template to derive a test level specification. Enclose response curve inside test spec curve using the following rules: Slopes should be less than + 25 dB/oct or greater than - 25 dB/oct. | MINUTES
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IEC 60068-2-64 Vibration Testing.
| PRESENTATIONS
A set of testing standards, including BS EN 60068-2-64 (broadband random vibration), -27 (shock), -32 (simulates falls during handling), – 78 (heat and humidity), – 52 (salt mist), -53 (combined temperature/humidity with vibration/shock), -50 (combined cold and sinusoidal vibration).