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posted by martyb on Thursday February 20 2020, @03:14AM   Printer-friendly
from the all-you-need-to-do-is-climb-that-wind-turbine-and-check-its-blade-for-defects-with-this-microscope dept.

A team at the National Institute of Standards and Technology (NIST) has developed a tool to monitor changes in widely used composite materials known as fiber reinforced polymers (FRPs), which can be found in everything from aerospace and infrastructure to wind turbines. The new tool, integrated into these materials, can help measure the damage that occurs as they age.

[...] Since the 1960s, scientists have been experimenting with ways to make FRPs lighter and stronger. This has often meant testing the bond between fiber and resin. As reported in a previous publication, the NIST team added small molecules that fluoresce after the impact of mechanical force. These molecules, called "mechanophores," change color or light up, helping identify tiny nanometer-sized openings or cracks between the fiber and resin.

The NIST team has taken this technology to the next level by incorporating the mechanophore throughout the composite resin. Although not noticeable to the naked eye, the newest approach allows scientists to use special microscopy imaging techniques to measure FRP damage. The approach incorporates a minute amount (less than 0.1% mass) of a fluorescent dye called rhodamine that causes no appreciable changes in the material's physical properties.

If the new mechanophore is embedded in structures made of FRP, field testing for fatigue could be done inexpensively and on a regular basis. Structures like wind turbines could frequently be scanned easily for interior cracks, even years after they've been erected.

Journal Reference:
Jeremiah W. Woodcock et al. Damage sensing using a mechanophore crosslinked epoxy resin in single-fiber composites, Composites Science and Technology (2020). DOI: 10.1016/j.compscitech.2020.108074

Original Submission

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  • (Score: 3, Informative) by khallow on Thursday February 20 2020, @11:56AM

    by khallow (3766) Subscriber Badge on Thursday February 20 2020, @11:56AM (#960256) Journal
    Searching around, I found some technical details [] of the setup. Basically, it shoot a 140 femtosecond laser pulse (that's 140 quadrillionths of a second! appears to be infrared with 800 nm wavelength?) at the material (in a scanning pattern), and then looks at the resulting fluorescence with both a spectrometer and "lifetime" counters which apparently measure the total radiated fluorescence over a small band of frequencies. Fluorescence is very short as well, on the order of nanoseconds. As the material comes under stress, this apparently causes changes in the fluorescence.

    Presently, I don't see how the present setup could be adapted to use in the field. It appears you need a very dark environment and very extreme levels of stability. But you could stress test parts in a lab and get additional information on how things degrade and fail in the part.

    I know from my limited experience in composites, that the materials are finicky and can vary wildly in reliability based on how you lay the strands of the embedded fiber, presence of flaws like air bubbles in the resin, and factors that my group at the time just never figured out. Often if something broke under too little stress, we just added more material to the failed section for the next part in the hope that would solve the problem. Fortunately, most of our parts didn't need to endure a lot of stress and probably were way overbuilt for their intended purpose.

    It would be great to be able to say that we need less material or material structured a different way. It'd save time and material as well as making for a lighter structure overall.
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