Strain mapping by hyperspectral imaging

1 . A strain mapping system for producing a strain map of an object, comprising:

a nanomaterial configured to be applied to a surface of the object as a film,

an imager configured to acquire a background image and a plurality of spectrally indexed object images, the imager comprising;

a polarized light source configured to irradiate the film with polarized light,

a camera configured to record a fluorescence of a light emitted from the film,

a tunable spectral filter configured to pass a range of wavelengths of the light emitted from the film,

one or more image processing algorithms configured to determine an induced strain value at each pixel in each image of the plurality of spectrally indexed object images by subtracting a reference strain value of the background image and dividing by a stress gauge factor; and

one or more computer processors communicatively coupled to the imager;

wherein the stress gauge factor is calculated as γ=−δ(λ (7,6) −λ (7,5) )/δ ε where γ is the stress gauge factor, SE is a change in the object strain, λ (7,6) is a first wavelength peak and λ (7,5) is a second wavelength peak of the light emitted from a test film;

wherein the strain mapping system is configured to produce a strain map of the object, wherein the strain map, ε(x, y), is obtained by ε(x, y)=[δ 1 (x, y)−δ 0 (x, y)]/γ where δ 0 (x,y) is a reference strain map of the object that is obtained from the background image, δ 1 (x,y) is an object strain array based on the induced strain value at each pixel in each image of the plurality of spectrally indexed object images and γ is the stress gauge factor.

2 . The strain mapping system of claim 1 , wherein the polarized light source is an excitation laser configured to emit polarized light within a predetermined wavelength band.

3 . The strain mapping system of claim 2 , wherein the predetermined wavelength band is within an infrared wavelength range.

4 . The strain mapping system of claim 1 , wherein the strain mapping system is configured to produce the strain map for a plurality of angles of polarization of the polarized light source.

5 . The strain mapping system of claim 4 , wherein the strain map obtained from the plurality of angles of polarization determines a strain anisotropy.

6 . The strain mapping system of claim 1 , wherein the film further comprises a multi-layer coating wherein the multi-layer coating comprises an opaque base layer, a high gloss primer layer, a sensing layer, and a protective top layer.

7 . The strain mapping system of claim 1 , wherein the tunable spectral filter further comprises a wide band pass filter and a narrow band pass filter.

8 . The strain mapping system of claim 1 , wherein the background image and the plurality of spectrally indexed object images capture an area of the object.

9 . The strain mapping system of claim 1 , wherein the nanomaterial comprises single-walled carbon nanotubes (SWCNTs).

10 . A method for producing a strain map of an object using a strain mapping system comprising a nanomaterial, a camera, a polarized light source, a tunable spectral filter, one or more image processing algorithms and one or more computer processors communicatively coupled to the imager, the method comprising:

acquiring, with the camera, a background image;

irradiating, with the polarized light source, a film of the nanomaterial disposed on a surface of the object wherein a fluorescence of a light is emitted from the film in response to irradiating the object;

acquiring, with the camera, a plurality of spectrally indexed object images of the object wherein the plurality of spectrally indexed object images has a calibration dataset of spatial and spectral calibration data;

correcting, with the one or more image processing algorithms, intensities of the plurality of spectrally indexed object images using the background image and the calibration dataset;

identifying, with the one or more image processing algorithms, a spectral index with a maximum intensity for a plurality of pixels in the spectrally indexed object images;

determining, with the one or more image processing algorithms, an interpolated index of a true maximum intensity;

determining, with the calibration dataset, a reference wavelength of the interpolated index of the true maximum intensity;

calculating, using the reference wavelength and a spectral gauge factor, a plurality of local strain values comprising a strain value at each pixel in each image of the plurality of spectrally indexed object images determined by subtracting a reference strain value of the background image and dividing by a stress gauge factor;

producing, with the one or more image processing algorithms and the plurality of local strain values, a strain map of the object, wherein the strain map, ε(x, y), is obtained by ε(x, y)=[δ 1 (x, y)−δ 0 (x, y)]/γ where δ 0 (x,y) is a reference strain map of the object that is obtained from the background image, δ 1 (x,y) is an object strain array based on the induced strain value at each pixel in each image of the plurality of spectrally indexed object images and γ is the stress gauge factor; and

storing, on the one or more computer processors, the strain map of the object;

wherein the stress gauge factor is calculated as γ=−δ(λ (7,6) −λ (7,5) /δε where γ is the stress gauge factor, δ ε is a change in the object strain, λ (7,6) is a first wavelength peak and λ (7,5) is a second wavelength peak of the light emitted from a test film.

11 . The method of claim 10 , wherein determining an interpolated index of a true maximum intensity further comprises:

fitting, with the one or more image processing algorithms, a curve for a plurality of intensities versus a plurality of index points;

wherein the curve is a second-order polynomial function or a third-order polynomial function.

12 . The method of claim 10 , wherein calculating a plurality of local strain values further comprises:

correlating the fluorescence of the light emitted from the film to a presence of strain; and

determining a wavelength of the light emitted from the film;

wherein a shift of the wavelength of the light emitted from the film indicates a local strain.

13 . The method of claim 10 , wherein producing a strain map of the object is repeated for a plurality of angles of polarization of the polarized light source.

14 . The method of claim 13 , wherein the strain map obtained from the plurality of angles of polarization determines a strain anisotropy.

15 . The method of claim 10 , wherein the polarized light source is an excitation laser configured to emit polarized light within a predetermined wavelength band.

16 . The method of claim 15 , wherein the predetermined wavelength band is within an infrared wavelength range.

17 . The method of claim 10 , wherein the background image and the plurality of spectrally indexed object images capture an area of the object.

18 . The method of claim 10 , wherein the film further comprises a multi-layer coating wherein the multi-layer coating comprises an opaque base layer, a high gloss primer layer and a sensing layer.

19 . The method of claim 10 , wherein the nanomaterial comprises single-walled carbon nanotubes (SWCNTs).