Early Fatigue Damage Detection in Composite Materials

Detection of early fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass/Epoxy, and ±45°/0° Graphite/Glass/Epoxy. Dynamic axial modulus and temperature were monitored continuously with a correlation between temperature rise and modulus decrease observed. The modulus decrease and temperature rise are indicative of irreversible damage in these materials. Torsional modulus measurements and coin tap tests were performed at 0, 10 ⁶ , 5 × 10 ⁶ , and 10 ⁷ cycles, on all fatigue specimens. Other NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-Ray radiography were performed on two specimens of each material to evaluate their effectiveness in detecting fatigue damage. Ultrasonics and holography proved to be effective; however, at this time, no clear quantitative correlation beween structural properties and NDI measurements has been determined.