Detection of foreign materials in prepregs

Fiber-reinforced polymer prepreg materials are supplied in the form of tape, tow, fabric, etc. During the cutting and lay-up processes, some of the backing material (release film) remains on the material. Composite parts manufactured using such prepregmaterials can fail since the backing material prevents a good bond between individual plies.Menon and Associates proposes to demonstrate a magnetic resonance (MR) system to detect the backing material. MR principle is based on exciting the hydrogen atoms inside the material being inspected. Depending on the state of hydrogen we receive a uniquesignal. For example, the resin used inside the prepreg and the polyethylene or paper backing material have hydrogen atoms. However, the state of the hydrogen atoms in these two are different. We have a hand-held MR probe that can measure relaxationtimes of the hydrogen atoms in prepreg materials. This will detect any remaining backing material. In addition, if the backing material is aluminum, the MR field gets distorted and this also gives a good response. Using MR (similar to MRI in medicalimaging) we can potentially measure wrinkles and voids at different depths by monitoring drastic variations in the signal from the hydrogen atoms from inside the composite.The capability of the proposed MR sensor for early flaw detection will result in a) improved fabrication and thus capability, b) increased life-time of the composite structure, and c) increased cost effectiveness. The commercialization potential is notlimited to military uses but also includes civilian applications. Examples are the civilian aerospace industry, the automobile industry and sports industry.