Damage evaluation system and method using optical fibers

A fiber reinforced composite material, which comprises:

• a plurality of layers of reinforcing fibers, with the reinforcing each two adjacent layers extending in one direction within that layer, and a polymer binding the reinforcing fibers together;
• a plurality of damage sensing optical fibers extending generally parallel to one another and spaced apart from one another between said two layers of reinforcing fibers with the optical fibers extending at the largest possible angle relative to the reinforcing fibers of each of said two layers, and with the angle between the optical fibers and the reinforcing fibers of one of said two layers being substantiall,y equal to the angle between the optical fibers and the reinforcing fibers of the other of said two layers.

A composite material as claimed inclaim 14 or 15 wherein the transition parts are such as to provide minor perturbations and/or cracking of the surfaces of the damage sensing portions, to give a desired reduction in the fracture strength of the damage sensing portions.

A fiber reinforced composite material, which comprises:

• a plurality of layers of reinforcing fibers, with the reinforcing fibers of each of two adjacent layers extending in one within that layer, and with the reinforcing fibers of the two layers being at an angle to one another, and a polymer binding the reinforcing fibers together;
• a plurality of optical fibers extending generally parallel to one another and spaced apart from one another between said two layers, with the optical fibers extending perpendicularly to the reinforcing fibers of one of said two layers.

A fiber reinforced composite material, which comprises:

• a plurality of layers of reinforcing fibers, and a polymer binding the layers of reinforcing fibers together;
• a plurality of volume backscattering optical fibers located between two adjacent layers of reinforcing fibers and extending across a predetermined area, with the optical fibers comprising a first group of optical fibers which extend across one edge of a predetermined area to a second, generally opposite edge of the predetermined area, and a second group of optical fibers which extend across said second, generally opposite edge to said one edge and which are interdigitated with the first group optical fibers.

A fiber reinforced composite material which comprises:

• a plurality of layers of reinforcing fibers and a polymer binding the reinforcing fibers together;
• a plurality of optical fibers extending between two adjacent layers of reinforcing fibers and across a predetermined area for detecting damage therein;
• a light source, a directional coupler having an input connected to the light source and an output, a DMD connected to the output of the directional coupler and to each of the optical fibers, a reference photodetector magnitude of the light from the light source, and a return signal photodetector connected to the directiona-4 coupler, for detecting the magnitude of return light back from each optical fiber, the light source and the DMD operating together to illuminate each of the optical fibers individually and successively, and the DMD and the return signal photodetector operating together to interrogate .the optical fibers individually and successively.

A fiber reinforced composite material which comprises:

• a pIuralityof layers of reinforcing fibers and a polymeer binding the reinforcing fibers together;
• a pluralityof volume backscattering optical fibers extending, spaced apart from one another between two adjacent layers of reinforcing fibesrs, each optical fibesr including a damage sensing portion comprising a plurality of first parts, a plurality of second parts having a smaller diameter than the diameter of the first parts and alternating therewith, ad a plurality of transition parts extending between the first and second parts, the transition parts being such as to provide substantial stress concentrations and sufficiently weaken the optical fibers to give the optical fibers a reduced fracture strength relative to optical fibers of uniform diameter and similar material, and the transition parts locking the optical fibers to the composite material, whereby the optical fibers are subjected to the same strain as the compoeite mterial;
• illumination and interrogation means connected to both ends of each optical fiber, for alternately illuminating each end of each optical fiber, to determine the location of a fracture of the optical fiber.

An optical fiber which includes, a damage sensing portion comprising a plurality of first parts, a plurality of second parts having a smaller diameter than the diameter of the first parts and alternating therewith, and a pIurality of transition parts extending between the first and second parts, the transition parts being such as to provide substantial stress concentrations and sufficiently weaken the optical fibers to give the optical fibers a reduced fracture strength relative to optical fibers of uniform diameter and similar material, and the transition parts being capable of locking the optical fibers to an object, whereby the optical fibers are subjected to the same strain as the object.

A damage evaluation system for anobject, the damage evaluation system comprising a plurality of damage sensing optical fibers for bonding to the object, each of which optical fibers includes a damage sensing portion oomprising a plurality of first parts, a pluralityof second parts having a smaller diameter than the diameter of the first parts and alternating therewith, and a plurality of transition parats extending between the first and second parts, the transition parts being such as to provide substantial stress concentrations and sufficiently weaken the optical fibers, to give the optical fibers a reduced fracture strength relative to optical fibers of uniform diameter and similar material, and the transition parts being capable of locking the optical fibers to the object, whereby the optical fibers are subjected to the same strain as the object.