ULTRASONIC MONITORING OF FLAW GROWTH IN GRAPHITE/EPOXY LAMINATES UNDER FATIGUE LOADING.

In the reported experiments, ultrasonic techniques were used to monitor flaw growth in graphite/epoxy laminates containing four types of initial flaws and subjected to fully reversed spectrum fatigue loading, including temperature and moisture variations. The specimens were graphite/epoxy (AS3501-5A) coupons of left bracket (0/ plus or minus 45/90)//s right bracket //2 and left bracket O//2/ plus or minus 45 right bracket //2//s layups. It was found that flaw growth was much more pronounced in the specimens exposed to environmental fluctuations in addition to the load spectrum, than in those tested in an ambient environment. Flaw growth was also greater in specimens of left bracket (O/ plus or minus 45/90)//s right bracket //2 layup than in those of left bracket O//2/ plus or minus 45 right bracket //2//s layup. No significant reduction in residual tensile strength (in general less than ten percent) was observed for any of these groups of specimens.