Fiber and bundle orientations, matrix rich regions, and mechanical properties of fiber reinforced composites using thermal digital image correlation

1. A method for assessing a characteristic of a composite material or a joint between two materials, the method comprising:

applying indicia to a surface of the composite material or the joint;

exposing the composite material or the joint to a temperature change;

imaging the composite material or the joint at a plurality of time points before, during and/or after the temperature change using one or more optical cameras to measure strain and a thermal camera to measure spatially resolved temperatures of the composite material or the joint comprising the indicia, thereby monitoring a surface mechanical strain tensor while the composite material is undergoing the temperature change; and

assessing the characteristic of the composite material or the joint based on the imaging.

2. The method of claim 1 , wherein the composite material comprises a fiber-reinforced composite material.

3. The method of claim 2 , wherein the composite material comprises a fiber-reinforced polymeric, metallic, or ceramic composite.

4. The method of claim 1 , wherein the composite material comprises a laminate/fabric based multi-layer composite material or a molded discontinuous fibers/bundles/platelets based composite material.

5. The method of claim 1 , wherein the composite material comprises a material selected from the group consisting of a thermoset-based carbon fiber, a thermoplastic-based carbon fiber, a glass fiber, a basalt fiber, a natural fiber, and combinations thereof.

6. The method of claim 5 , wherein the thermoset-based carbon fiber comprises a material selected from the group consisting of an epoxy, a vinyl ester, a polyester, a phenolic resin-based polymer, and combinations thereof.

7. The method of claim 5 , wherein the thermoplastic-based carbon fiber comprises a material selected from the group consisting of polyphenylene sulfide (PPS), polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polypropylene, polycarbonate, polybutylene terephthalate (PBT), polyethylene, polyvinyl chloride (PVC), nylon, and combinations thereof.

8. The method of claim 1 , wherein the joint is selected from the group consisting of a hybrid joint and an adhesively bonded joint.

9. The method of claim 1 , wherein exposing the composite material to a temperature change comprises heating and/or cooling the composite material.

10. The method of claim 9 , wherein cooling the composite material comprises allowing the composite material to cool after manufacturing.

11. The method of claim 1 , wherein the imaging comprises identifying spatially varying temperatures, identifying measured surface strains, or a combination thereof.

12. The method of claim 1 , wherein the indicia comprise a contrasting black and white (B/W) pattern.

13. The method of claim 1 , wherein the imaging comprises using two optical cameras to measure strain.

14. The method of claim 1 , wherein the assessing the characteristic of the composite material based on the imaging comprises assessing fiber orientation of continuous fibers through a volume of the composite material.

15. The method of claim 1 , wherein assessing the characteristic of the composite material based on the imaging comprises identifying spatially varied fiber orientations, matrix rich regions, corresponding mechanical properties, or combinations thereof.

16. The method of claim 1 , wherein assessing the characteristic of the composite material comprises assessing manufacturing process control, quality assurance and/or control; predicting thermal behavior and/or mechanical behavior; and/or evaluating a repair.

17. The method of claim 1 , wherein the imaging further comprises obtaining multiple magnified optical images of a cross-section of the composite material or joint; and the method further comprises determining fiber orientation for a cross-section of the composite material or the joint using a variation of grey-scale intensity in the cross section of the composite material or the joint.

18. The method of claim 15 , wherein the cross-section is a non-circular cross-section.

19. A method for assessing fiber orientation in a composite material or a joint between two materials, the method comprising:

exposing a cross-section of the composite material or the joint to a light source;

obtaining multiple magnified optical images of the cross-section of the composite material or the joint;

detecting differences in grey-scale intensity values from the multiple images; and

assessing the fiber orientation for the cross-section of the composite material or the joint based on the differences in grey-scale intensity values in the cross-section of the composite material or the joint.

20. The method of claim 19 , wherein the cross-section of the composite material or the joint comprises a reinforcing element or material having a non-circular cross-section.

21. A method of manufacturing a composite material, the method comprising:

during manufacturing of the composite material, applying indicia to a surface of the composite material and exposing the composite material to a temperature change;

imaging the composite material comprising the indicia using one or more optical cameras to measure strain and a thermal camera to measure spatially resolved temperature at a plurality of time points before, during and/or after the temperature change, thereby monitoring a surface mechanical strain tensor while the composite material is undergoing the temperature change; and

assessing a characteristic of the composite material based on the imaging.

22. The method of claim 21 , comprising controlling the manufacturing of the composite material based on the assessing of the characteristic of the composite material.