Results from finite element analysis of fatigue fuse geometries. The philosophy is that the fuse need not necessarily be attached to the structure but can be cyclically stressed at a remote location where it can be optically monitored. Cyclic fatigue is often the nemesis. These periodic stresses can cause atomic vacancies, small voids, and dislocations to merge and form high stress regions that initiate crack movement. The fatigue fuse can be subjected to millions of cycles and give warning of the potential origins of failure.
Photoelastic measurements permit visualization of the strains.
Most commonly, optical fiber sensors have been employed for more than a decade. They are attached to a structure and monitor strains by measuring the optical polarization. The literature is extensive in various aspects of optical fiber smart structures. But here again, as with the strain gauge, the internal integrity of a structure may not be reliably recorded by a surface optical fiber even if the attachment is firm. Finally, there is the concept of the sensored composite, a bundle of high-strength fibers, stronger than steel, that are bonded together with an epoxy and become the entire structural members of a device.