ultrasonic Nondestructive Evaluation of Damage in Continuous Fiber Comnposites /I"

IS. A i! ~ 4 C ealmev.. e.e " onde,cddent-ty by *toeb mulusbert tis well-known that composite materials develop a complex damage state when the! are subjected to monotonic or fatigue loading. The damage has, in general, two effects on the propagation of an ultrasonic wave: it decreases the stiffness and increases the attenuation. The central objective of this work has been to correlate damage states with changes in the t" ' ultrasonic paramete~rs (wavespeed and attenuation). We have developed a new technique for measuring the wavespeed and attenuation in the thickness direction, in extremely thin laminates. We have also developed a technique for the excitation and detection of Lamo waves in the len~thwise direction. Thus, both the in-plane and out-of-plane measuremerts can be made. Damage in the form of transverse cracking in cross-ply graphite/epoxy laminates has been studied by the use of these twu techniques. For through-the-thickness measurements the stiffness was found to be insensitive toutransverse cracking. The attenuation