Preparation of electrodes on CFRP composites with low contact resistance comprising laser-based surface pre-treatment

1. A method for bonding an electrode to a carbon fiber reinforced polymer (CFRP), the method comprising:

selecting an average power P ave and a scanning speed v of a laser system;

preparing a pretreated target area on the carbon fiber reinforced polymer (CFRP) composite surface by using laser pulsed irradiation from the laser system so that at least 75% of carbon fibers of the CFRP composite are exposed;

forming an electrode directly to the exposed carbon fibers in the pretreated target area; and

bonding lead wires to the electrode with a conductive epoxy adhesive,

wherein the average power P ave and the scanning speed v of the laser system are selected to achieve the at least 75% exposed carbon fibers.

2. The method of claim 1 , wherein the electrode includes a silver paste and a copper layer.

3. The method of claim 1 , wherein the electrode has a contact resistance of 0.1 ohms or less.

4. The method of claim 1 , wherein the electrode exhibits a uniform bonding over the pretreated target area.

5. The method of claim 1 , comprising:

preparing a plurality of pretreatment target areas on the CFRP composite surface using laser pulsed irradiation; and

bonding a plurality of electrodes to corresponding ones of the plurality of pretreatment target areas.

6. The method of claim 1 , wherein the at least 75% exposed carbon fibers in the pretreated target area of the CRFP composite are fully exposed by the laser pulsed irradiation.

7. The method of claim 6 , wherein exposure of the carbon fibers is evaluated using Raman mapping of the pretreated target area.

8. The method of claim 1 , wherein the electrode is mechanically interlocked with fully exposed fibers in the pretreated target area during bonding.

9. The method of claim 1 , wherein forming the electrode comprises applying silver paste to the pretreated target area.

10. A method for monitoring a structural health of a carbon fiber reinforced polymer (CFRP) composite, the method comprising:

positioning the CFRP composite for pretreatment of a target area of a CFRP surface;

selecting an average power P ave and a scanning speed v of a laser system;

preparing the pretreated target area by irradiation with a pulsed laser beam along a series of paths in the target area, wherein the pulsed laser beam is generated by the laser system so that at least 75% of carbon fibers of the CFRP composite are exposed; and

forming an array of electrodes directly to the exposed carbon fibers in the pretreated target area;

measuring associated impedances of the array of electrodes at a domain boundary of a given domain of the CFRP composite; and

reconstructing the given domain based on the measured impedances using a computed tomographic technique, for monitoring the structural health of the CFRP composite,

wherein the average power P ave and the scanning speed v of the laser system are selected to achieve the at least 75% exposed carbon fibers.

11. The method of claim 10 , wherein the series of paths are a plurality of parallel paths.

12. The method of claim 10 , wherein the pulsed laser beam has a focused beam diameter (d s ) of 25 μm on the CFRP surface.

13. The method of claim 10 , wherein the series of paths have a minimum line spacing (p) of 30 μm.

14. The method of claim 10 , wherein the pulsed laser beam has a frequency (f) of 30 kHz and traverses the series of paths at the scanning speed (v) of less than or equal to 500 mm/second, and with the average power (P ave ) being less than or equal to 30 Watts.

15. The method of claim 14 , wherein the scanning speed (v) is less than 100 mm/second and the average power (P ave ) of the laser is equal to or less than 7.5 Watts.

16. The method of claim 14 , wherein the scanning speed (v) is equal to or greater than 50 mm/second and the average power (P ave ) of the laser is greater than 4.5 Watts.

17. The method of claim 16 , wherein the average power (P ave ) of the laser is greater than 6.75 Watts when the scanning speed (v) is greater than 75 mm/second and the average power (P ave ) of the laser is equal to or less than 6.75 Watts when the scanning speed (v) is equal to or less than 75 mm/second.

18. The method of claim 16 , wherein the average power (P ave ) of the laser is greater than 5.25 Watts when the scanning speed (v) is equal to or greater than 60 mm/second.

19. The method of claim 10 , wherein a pulse duration (τ p ) of the pulsed laser is greater or equal to 10 nanoseconds.