Fiber Optic Sensors for Flow and Health Monitoring of Resin Transfer Molded Composite Structures

1. Fiber Optic Sensors for Flow and Health Monitoring of Resin Transfer Molded Composite Structures Casey Keulen, AfzalSuleman and MehmetYildiz CSME Forum 2010, Victoria, B.C. June 8, 2010

2. Outline: • Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG • Conclusions -2- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

3. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction • Composite materials becoming increasingly more valuable for many applications • Drawbacks of composite materials include difficulty in processing and damage assessment • Resin Transfer Molding (RTM) is a particularly attractive processing technique • Embedded fiber optic sensors can help to mitigate these drawbacks -3- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

4. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction RTM and Composite Material Issues • RTM has many advantages over alternative manufacturing methods, however it has it’s issues • Advantages: • Produces repeatable, high quality product • Little post processing required • Limited operator interaction, can be automated • Disadvantages: • Critical that mold is fully saturated with resin • Skill required to design manufacturing system • Difficult to asses the presence or extent of damage -4- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

5. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Resin Transfer Molding • Falls into the category of liquid composite molding • Process involves: • Loading a fully enclosed mold with fiber preform • Closing and securing the mold • Injecting resin into the mold until fully saturated • Allowing resin to cure • Removing part from mold and post processing -5- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

6. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Resin Transfer Molding -6- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

7. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Fiber Optic Sensors • Fiber optics are thin glass fibers extensively used in telecommunications industry since the 1960’s • Have the ability to transfer light extremely long distances with minimal loss • A fiber optic is analogous to a water pipe, it consists of a core that carries light and a cladding that contains the light in the core • Numerous types of fiber optic sensors exist for a variety of applications and measurements -7- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

8. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Fiber Optic Sensors • Fiber optic sensors relative to composites: • Fiber Bragg gratings (FBG) • Etched fiber sensor (EFS) • FBG are becoming very common, wide range of applications, generally used to measure temperature and strain • EFS are not very common, only applicable to fluid detection • Both types can be multiplexed on a single fiber -8- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

9. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Fiber Bragg Grating Sensors • FBG is a periodic variation of the refractive index in the core of a fiber optic • An FBG reflects a narrow band allowing a broadband to pass • This narrow band is centered around the Bragg wavelength • To obtain such a wavelength the following condition must be met: • Where: is the Bragg wavelength, is the effective index of refraction and is the grating spacing -9- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

10. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Fiber Bragg Grating Sensors -10- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

11. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Etched Fiber Sensors • EFS consists of a small section of optical fiber where the cladding is etched away allowing light to escape • When that section comes in contact with resin, which has a lower refractive index more light escapes -11- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

12. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Etched Fiber Sensors -12- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

13. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Introduction Embedded Fiber Optics • Due to their small diameter and flexibility fiber optics can be embedded in composite materials • Embedded fiber optic sensors can be used to detect many properties related to RTM’d composite materials • Presence of fluid during injection • Degree of resin cure • Strain in composite • Presence and extent of damage -13- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

14. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work -14- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

15. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Ingress/Egress Issues • Fiber diameter is small, therefore difficult to seal without permanent sealant • Tapered silicone stopper used to seal around fiber • Optical fiber is delicate, must maintain minimum bend radius • A hypodermic tube placed around fiber to protect it and maintain radius -15- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

16. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Ingress/Egress Issues -16- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

17. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work • Objective: • to investigate performance of EFS and their ability to multiplex with FBGs • to detect strain in composite with embedded FBG • Three EFS and two FBG sensors were multiplexed on a single fiber optic • EFS were used to detect presence of resin, verified by visual monitoring through glass • FBG were later used to detect strain in composite -17- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

18. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Flow Monitoring -18- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

19. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Etched Fiber Sensors -19- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

20. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Flow Monitoring -20- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

21. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work EFS Output • A plot of transmitted light intensity vs. time during injection -21- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

22. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Experimental Work Characterization of Embedded FBGs -22- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

23. Introduction • Resin Transfer Molding • Fiber Optic Sensors • Embedded Fiber Optics • Experimental Work • Fiber Ingress/Egress • Flow Monitoring • Characterization of FBG Conclusion • These experiments have shown: • FBGs and EFS may be multiplexed on a single fiber • FBGs embedded with this technique still perform as strain sensors • To achieve these results a number of issues were resolved: • Experimental RTM apparatus was developed • Ingress/egress technique was developed • EFS employed in a novel manner (looped) -23- June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada

24. Fiber Optic Sensors for Flow and Health Monitoring of Resin Transfer Molded Composite Structures Casey Keulen, AfzalSuleman and MehmetYildiz June 8, 2010 CSME Forum 2010 Victoria, B.C., Canada