MIL-STD-167-1A
APPENDIX A
IDENTIFYING RESPONSE PROMINENCES TO BE INCLUDED IN ENDURANCE TESTING A.1 SCOPE
A.1.1 Scope. This appendix details the procedures for identifying response prominences to be included in endurance testing. This appendix is not a mandatory part of the standard. The information contained herein is intended for guidance only.
A.2 PROCEDURE
A.2.1 Determining and displaying transmissibility. Transmissibility information should be presented using the output responses and prescribed inputs. The transmissibility magnitudes for both exploratory and variable frequency tests are to be used for response prominence determinations.
A.2.1.1 Transmissibility magnitudes. Transmissibility magnitudes are to be developed by dividing the measured output amplitudes by the input amplitudes using consistent units (e.g., acceleration in g's or inches/sec2).
A.2.1.2 Transmissibility and frequency. Transmissibility information is to be presented in linear-linear format. Plots or tabulations are acceptable. Both the transmissibility and frequency information must be presented in linear units (i.e., no logarithms or dB of either frequency or transmissibility are to be used to compute or display the data used for response prominence determinations).
A.2.2 Identifying response prominences. Regardless of whether or not the transmissibility exceeds 1.0, find all local maxima in the transmissibility magnitude-frequency data and include the frequency endpoints in the list of maxima.
a. For each of these maxima, determine if there is reason to believe that the maximum is attributable to an instrumentation error, a fixture resonance or from a numerical error related to computation of the transmissibility (round-off errors may appear as maxima). Any maxima that are attributable to an instrumentation error, fixture resonance, or numerical errors must be discarded as a potential response prominence. Fixture resonances are not permitted and refixturing must be employed to eliminate such resonances.
b. Examine the end points for indications that a resonance may exist outside the test frequency range.
c. An initial decrease in transmissibility with increasing frequency above the frequency of the lower end point suggests a potential response prominence outside the lower bound of the test frequency range. If this condition is observed and is not attributed to shaker problems at low frequencies, include the lower
endpoint in the candidate list of endurance test frequencies noting whether or not it affects functional or structural integrity. If this condition is not observed, the lower bound test frequency may be discarded as a potential response prominence. At these low frequencies, noticeable displacement magnitude amplifications may occur if a true response prominence exists below the lower frequency bound of testing and this fact may be used to help determine the nearby presence of a true response prominence.
d. Similarly, an increase in transmissibility with increasing frequency near the upper bound test frequency suggests a potential response prominence outside the upper bound of the test frequency range. If this condition is observed, include the upper endpoint in the candidate list of endurance test frequencies noting whether or not it affects functional or structural integrity. If it is not observed, this frequency cannot be excluded from the list of endurance test frequencies unless other response prominence frequencies are found.
e. Observe whether or not equipment function (if permitted by the ordering data) or structural integrity is affected at any of the frequencies used in exploratory or variable frequency testing. Include those frequencies at which equipment functional or structural integrity is affected in the candidate list of endurance test frequencies. Also include frequencies at which maxima occur in the candidate list of endurance test frequencies if the impact on functional/structural performance cannot be established.
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