Utility of a probability-density-function curve and F-maps in composite-material inspection - The development of an inspectability criterion based on probability-density functions

The use of probability-density-function analysis, an important topic in statistical analysis, is studied in this paper with respect to its utility in nondestructive testing. In addition to the mathematical concepts, several sample problems in composite-material inspection are presented. A feature map (or F-map) is introduced as a new procedure that gives us a new way to examine composite materials. A probability-density function is basically a plot of number of times a particular value per unit value occurs vs. the value itself. A feature is defined as a parameter measured or calculated from an ultrasonic waveform. Some examples are center frequency, rise time, pulse duration, attenuation at frequency f, and so forth. Probability-density curves are estimated for each of the features derived from a waveform. These curves are then used to assist in the production of F-maps. Sample problems in graphite-polyimide structures and boron-aluminum materials using these curves and F-maps are given. An inspectability parameter based on feature probability-density-function analysis is introduced for a compositematerial fabrication process that makes damage detection more reliable. F-maps are then used to determine the extent of damage.