A thermographic technique was developed to measure the extent of fatigue damage in composite materials during fatigue loading.

Heat generated by cyclic loading of fatigue damaged material raised surface temperatures. These temperatures were measured with an infrared camera and were used as boundary conditions in a finite element heat transfer program, which was developed especially to calculate the extent of the heat generation zone, and thereby to define the fatigue damage zone. The finite element program was verified by comparing calculated heat generation with the actual heat generation for a simple heat transfer problem that had a closed form solution. The program was also checked by analyzing the thermogram of a composite specimen with an external heat source of known dimensions.

From thermograms of specimens, damage zones were calculated for (0₈), (45/90/-45/0)_s, and (45/0/-45/0)_s boron/epoxy fatigue specimens. Calculated damage zones were compared with damage detected by C-scan, X-ray, and scanning electron microscope (SEM) examination. The analysis was effective in locating the boundaries of the fatigue damage zones.