ASTMD4728_2001

that occur according to the Gaussian distribution, it is called“Gaussian random vibration.” Gaussian random vibration hasthe property that the rms level is equal to the standarddeviation, or 1 sigma, and that the amplitude will fall within 3sigma, or 3 times the rms level, 99.7 % of the time.3.2.12 root-mean-square (rms)—the square root of themean-square value. In the exclusive case of a sine wave, therms value is 0.707 times peak value.3.2.13 sigma drive signal clipping—a condition where themaximum amplitude of the drive or output signal to a vibrationsystem is limited to a sigma value, or multiple of the rms value.For drive clipping at the 3 sigma level, the maximum ampli-tude will not exceed 3 times the rms value.3.2.14 sinusoidal vibration—a periodic oscillation having asinusoidal waveform of only one frequency.3.2.15 spectrum—a definition of the magnitude of thefrequency components within a specified frequency range.3.2.16 statistical degrees of freedom (DOF)—as related toPSD calculation, the degrees of freedom is a measure of thestatistical accuracy of the PSD estimation. The number of DOFis determined by the analysis bandwidth (frequency resolution)and total time of the sample (determined by frequency resolu-tion and number of averages). It is defined by the formulaDOF = 2BT, where B is the analysis bandwidth in Hz, and T isthe total record length in seconds.3.2.17 transfer function—the dynamic relationship betweenoutput and input. In terms of a vibration system, it is the ratioof output response to a constant input over a defined frequencyrange.4. Signifi cance and Use4.1 Shipping containers are exposed to complex dynamicstresses in the distribution environment. Approximating theactual damage, or...