Alcoa's Keensert inserts and studs, shown here, along with Inconel 718 bolts and standard hexagon nuts, went to Mars on the Curiosity Rover. In spacecraft and aircraft, Keenserts provide high resistance to torque-out and pullout loads.
The lightning strike issue isn't about frequency so much as it is about catastrophic results. If you've only got a (for example) 1% chance of something happening, but that something has catastrophic results--people dying, lawsuits--then that's something you've got to protect against, or at least not encourage, in your materials and assembly process selection.
I never thought that lightening strikes on aircraft was so common. I read that it happens 2 times per year on average, per airplane. I have seen electrical discharge responsible for fastener loosening and in some cases, ejecting.
There is a downside to composite pieces, price. Bolting parts together will always be around. I designed a mechanical system that ended up having over 60 bolts.. it was cheaper than with none, that was for sure.
Glad you liked the article. The whole issue of the grounding of composites used in aircraft has been widely misunderstood, so I thought it was a good idea to include some clear discussion on that issue. Could you clarify your question about comparisons between fasteners for composites and fasteners for metal? What sort of comparisons do you have in mind?
Excellent post Ann. I know the longevity of any fastener is dependent upon the application and use. Relative to composite fasteners, do we know how they "stack up" relative to metal fasteners? I have seen no data that tries to correlate life cycles of either type. Great point also about the grounding of composites. I know this must be a huge issue but not talked about too much in the literature.
That's true of course. The question is, given an increase in composite use, whether fasteners will be used in high enough quantities in repair to make up for the lower overall quantities in manufacturing.
Artificially created metamaterials are already appearing in niche applications like electronics, communications, and defense, says a new report from Lux Research. How quickly they become mainstream depends on cost-effective manufacturing methods, which will include additive manufacturing.
SpaceX has 3D printed and successfully hot-fired a SuperDraco engine chamber made of Inconel, a high-performance superalloy, using direct metal laser sintering (DMLS). The company's first 3D-printed rocket engine part, a main oxidizer valve body for the Falcon 9 rocket, launched in January and is now qualified on all Falcon 9 flights.
Lawrence Livermore National Laboratory and MIT have 3D-printed a new class of metamaterials that are both exceptionally light and have exceptional strength and stiffness. The new metamaterials maintain a nearly constant stiffness per unit of mass density, over three orders of magnitude.
Smart composites that let the material's structural health be monitored automatically and continuously are getting closer to reality. R&D partners in an EU-sponsored project have demonstrated what they say is the first complete, miniaturized, fiber-optic sensor system entirely embedded inside a fiber-reinforced composite.
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