One-dimensional model for the ultrasonic response of resin-filled gaps in automated tape layup composites

摘要

Automated tow placement has become a widely-used fabrication technique, especially for large aerospace structures. Robotic heads lay down strips of pre-impregnated fiber (called tows) along programmed paths. While the intention is to lay adjacent tows abutted to one another, occasionally a tow is placed leaving a non-zero gap between it and the previously-placed tow. In order to preserve the intended stiffness properties in the finished composite, it is important to control gap formation, to keep gaps below a certain width. If a gap between tows exists, it tends to fill with resin during the cure, forming a fiber free (resin-rich) volume. In immersion ultrasonic pulse-echo measurements of a cured laminate, the gap can be observed to produce a noticeable echo, lacking the image “texture” of the surrounding fiber-filled resin. Furthermore, the gap does not appear to significantly attenuate the sound, as indicated by the reflection from the far surface of the laminate.