Triboluminescent damage sensors

Details Triboluminescent damage sensors Triboluminescent damage sensors

1998-03-30

1999-05-18

Font, Frank G.

Radiant energy

Inspection of solids or liquids by charged particles

250307, 73105, 2523016F, G01N23/00

Patent

active

059052600

DESCRIPTION:

BRIEF SUMMARY
This invention relates to damage sensors in which materials capable of responding to physical damage are embedded in or attached to structures such as aircraft parts, buildings, or bridges subjected to abnormal loads including earth movements.
Presently, a number of techniques are used to monitor stress within structures and include, pressure sensitive foil sensors and in some cases embedded fibre optics, where stress leads to a definite change in capacitance, resistance, or optical signal respectively.
Structures such as plastic composites in aircraft can be subjected to impacts which cause hidden damage leading to failure if not detected, repaired or replaced. It is often a time consuming process to locate the exact area where damage has occurred, particularly in large structures such as aircraft in order that repair can take place.
The above problem is solved according to this invention by the use of triboluminescent (TL) materials embedded within or attached to structures, together with light guiding means for directing light output from the TL material to detectors.
Triboluminescent material give off light when stressed to fracture levels. Thus by detecting the amount of light, a measure of damage to adjacent structures may be determined.
According to this invention a damage sensor in combination with a structure requiring damage detection comprises at least one triboluminescent material element located at an area of the structure requiring damage detection and at least one light detector together with light guiding means connecting between the element and the detector, the arrangement being such that both location and amount of hidden damage between a predetermined known threshold value and observable failure of the structure may be determined.
The light sensor may be connected directly to the triboluminescent material or via light guiding means such optical fibres.
The sensor may be embedded within a structure, such as a composite plastics material, or fixed externally to such structure. Several sensors may be embedded within one structure. Light output from the triboluminescent material may be detected directly, or such light output may be absorbed by photo excitable dye material whose subsequent luminescence is detected. Different triboluminescent material and or different dyes may be used in different parts of a structure so that damage location is readily determined from the wavelength of emission. The detector may be directly connected to each different triboluminescent or dye material, or one or more detectors used with filters or wavelength detection means to determine the location of damage at several sites.
Additionally the damage site may be located by timing receipt of pulses. The intensity of emission may also be measured to give an indication of the severity of impact and hence damage.
The light guiding means may be single or multimode optical fibres, optical transparent sheet or slab within a composite material. The sheet material may have waveguides defined by rib, indiffusion, or etching etc. and may contain secondary emitters.
The detectors may be photo multipliers, photo diodes, as single detectors or in arrays.
The invention will now be described, by way of example only, with reference to the accompanying drawings of which:
FIG. 1 is a sectional view of a sensor embedded within a structure;
FIG. 2 is similar to and a variation of FIG. 1;
FIG. 3 is a sectional view of two sensors embedded within a structure, with optical fibre readout to a single detector;
FIG. 4 is a sectional view of a sensor mounted on a surface of a structure;
FIG. 5 is a sectional view of several triboluminescent materials and a light guiding layer embedded within a structure:
FIG. 6 is similar to that of FIG. 5, but in addition has a different photo excitable dye associated with each triboluminescent material;
FIG. 7 is a perspective view of a sensor employing three differently doped fibres each directing light from several triboluminescent materials to a single detector.
FIGS. 8, 9, and 10 are views of three

REFERENCES:
patent: 4772417 (1988-09-01), Pappalardo et al.
patent: 5581082 (1996-12-01), Hansma et al.

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