a true mean BFD (µpop) less than 42.7 mm will pass FAT. Furthermore, under these conditions a design that just passes FAT with µpop = 42.7 mm will cause 10 percent of the individual body armor plates to experience BFDs image 44 mm. In fact, 5 percent of the plates will have BFDs image 44.3 mm and 1 percent will have BFDs 45 mm.

This effect can be illustrated as follows. First consider a hypothetical armor system that has negligibly small variance in true performance. If the backing material exhibits a variance characterized by a standard deviation σbckmatl, then the true population of BFDs will be


where µpop is the mean BFD for that particular armor system (which depends on the mechanical response of the armor and the elastic recovery in the backing material) and σpop= σbckmtl. For µpop = 42.7 mm and with σpop = 1 mm, Figure G-1 shows the distribution of BFDs for the hypothetical population of body armor.


FIGURE G-1 Plot of normally distributed BFDs from a design that just meets the 90 percent upper tolerance limit requirement with µop = 42.7 mm and σpop = 1 mm.

The impact of employing a measurement technique that adds significant variability is illustrated in Figure G-2. In this illustration, we assume the

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement