The composite system is bonded to the prepared surfaces of structural members by a structural adhesive. As the structural member is exposed to fatigue loading, the system accepts a portion of the load. Because many details are particularly fatigued in bending, the added local structural thickness substantially improves stiffness, even though the material stiffness of the system may be considerably lower than the underlying material. Eventually, fatigue levels in the structure will reach the point of bond line failure, which will occur at prescribed strain and/or cycle levels. As the fatigue level is reached, the composite material will crack through and essentially unzip the from the surface of the structure, exposing an indicator. The indicator then alerts the engineers to the exact location and fatigue levels being encountered at a specific structural detail.

File Number: 09KU010L