13 ms·

I'm no expert, but I do know there's anything fundamentally flawed about polymer composites (including carbon fibre composites) in place of metals. Composite p

by ra 3y ago

I'm no expert, but I do know there's anything fundamentally flawed about polymer composites (including carbon fibre composites) in place of metals. Composite properties can be fairly accurately measured and tested, just like any other material including plate steel or aluminium. If a structural failure has occurred, it's related to a design, manufacture or maintenance issue. For example, not enough layers, or a weakness around a joint or fitting.

JumpCrisscross 3y ago
> Composite properties can be fairly accurately measured and tested, just like any other material including plate steel or aluminium Metals are uniform and broadly predictable. Composites vary cure to cure. We simply don’t have the deep engineering tables that let you know how a material will behave without destructive testing.
- californical 3y ago
  Then there’s also the issue of minor failures cascading. I’m by no means a structural engineer, but with bike parts — in steel or aluminum, if you get a tiny 1mm chip in the material, you can more-or-less just treat it as if the steel is 1mm thinner. With engineering tolerances it is irrelevant. But in a carbon fiber, that 1mm chip could be totally unnoticed for months, while slowly causing an invisible hairline crack, until the entire component suddenly explodes with no warning. Maybe someone can verify if that is possible at a larger scale, but I feel like it must be to some extent.. especially if there is an invisible manufacturing imperfection due to the higher precision required in carbon fiber
  - dredmorbius 3y ago
    NB: Aluminium is rather notorious for its tendency to develop invisible hairline fractures which fail suddenly. Particularly around high-stress regions. The BOAC Comet failures (cracks propagating from squared-off window corners) is a notorious example, with multiple total hull losses in flight. I've experienced somewhat less significant failures of bicycle components (though they could easily have proved far worse). It's a good idea to replace components after a wreck or even hard-cornering of a crankset.
    - pfdietz 3y ago
      The window corner thing is an urban legend. https://www.youtube.com/watch?v=-DjnG74DDno https://www.youtube.com/watch?v=-DjnG74DDno The cracks actually started on the top of the plane, at cutouts for radio antennas. The windows always had rounded corners (although they made them even rounder later, which may have led to the confusion.)
      - dredmorbius 3y ago
        Interesting, and a good explanation from Mentour Pilot as well. Thanks!
- rkagerer 3y ago
  Didn't it take us thousands of years of working with metals (Bronze Age through Modern) to get them to the uniform quality we see today (at least speaking on a commoditized basis)? I'm sure the story around composites will improve in due time.
- midoridensha 3y ago
  >Metals are uniform and broadly predictable. That's not true at all: metals have a grain structure, and how those grains are oriented can change the metal's properties in different directions. >Composites vary cure to cure. Metal castings can vary from cast to cast.
  - omniglottal 3y ago
    Forging and heat treatment are processes to introduce uniformity of metallic grain structures. These have been perfected over hundreds of years. I challenge you to find a single structural component in a safety-critical context which is made of cast metal.
    - durundal 3y ago
      https://www.investacast.com/industries/safety-critical/ https://www.investacast.com/industries/safety-critical/ These folks, among others, make a lot of them. You are also incorrect about forging being used to introduce uniformity into the grain, it is typically (though not always, as some forging operations may just be for establishing shape) to stretch the grains such that they are oriented along the load path, resulting in higher allowable stresses. Look up highly loaded aircraft parts like landing gear, they are typically forged to establish the grain direction and then machined to final dimension. Nothing stops you from heat treating metal after it has been cast, either. Some heat treatments are also expressly to produce nonuniform conditions in the metal, case hardening for example.
      - jacquesm 3y ago
        As well as chemical treatments.
mardifoufs 3y ago
Composites can be tested. Not as easily as metals can be, and it involves a lot more software analysis and even AI, but it's still possible. I work on flaw detection/segmentation with ultrasounds -and I have not directly worked with metal scans so I can't exactly compare- but we can already get some pretty good results with the right probes and scanners. The other major issue is that NDT on composites needs more care and time from the inspectors on the ground, and might need a lot more organizational resources to track and make sense of the data. But now that i think about it, I have no clue about performance or even feasibility of testing carbon composites. I'll have to ask around, but I'm pretty sure we have clients that use our hardware for Carbon! :)
- jacquesm 3y ago
  How does that work? Shouldn't the device be certified for such an application?
  - mardifoufs 3y ago
    Yes! Sorry if I wasn't clear enough. I meant that they use the devices because they are compliant and certified for carbon composites. I just wasn't sure since the devices are usually not for a single purpose so it's hard to keep track of all certified use cases from my PoV. But sometimes they are! We have a few scanners specifically for pipelines and even robots for wind blades, yet even then the probe usually uses the same detection technology (ultrasounds, eddy currents, etc). The magic happens on the signal processing side when it comes to the difference between the scanners, and the trend is towards multipurpose all in ones. Our most recent industrial scanner has an FPGA that is explicitly there to allow for extensibility so that it fits most applications. FPGAs have been used quite often in the field but usually merely to implement some specific signal processing, not to be extensible! I'm rambling here but my point is that some devices can be used for pretty much any application (the Omniscan for example), process specific devices are more for large scale industrial workflows! The probes can be the only thing you need to change to use the same scanner to do stuff as varied as hydrogen poisoning analysis on steel to composite flaw detection on windblades! Here is an example, again with the Omniscan : https://www.olympus-ims.com/en/scanners/aerospace-wind-blade-inspection-scanners/ https://www.olympus-ims.com/en/scanners/aerospace-wind-blade...

by ra 3y ago

JumpCrisscross 3y ago

> Composite properties can be fairly accurately measured and tested, just like any other material including plate steel or aluminium Metals are uniform and broadly predictable. Composites vary cure to cure. We simply don’t have the deep engineering tables that let you know how a material will behave without destructive testing.

californical 3y ago
Then there’s also the issue of minor failures cascading. I’m by no means a structural engineer, but with bike parts — in steel or aluminum, if you get a tiny 1mm chip in the material, you can more-or-less just treat it as if the steel is 1mm thinner. With engineering tolerances it is irrelevant. But in a carbon fiber, that 1mm chip could be totally unnoticed for months, while slowly causing an invisible hairline crack, until the entire component suddenly explodes with no warning. Maybe someone can verify if that is possible at a larger scale, but I feel like it must be to some extent.. especially if there is an invisible manufacturing imperfection due to the higher precision required in carbon fiber
- dredmorbius 3y ago
  NB: Aluminium is rather notorious for its tendency to develop invisible hairline fractures which fail suddenly. Particularly around high-stress regions. The BOAC Comet failures (cracks propagating from squared-off window corners) is a notorious example, with multiple total hull losses in flight. I've experienced somewhat less significant failures of bicycle components (though they could easily have proved far worse). It's a good idea to replace components after a wreck or even hard-cornering of a crankset.
  - pfdietz 3y ago
    The window corner thing is an urban legend. https://www.youtube.com/watch?v=-DjnG74DDno https://www.youtube.com/watch?v=-DjnG74DDno The cracks actually started on the top of the plane, at cutouts for radio antennas. The windows always had rounded corners (although they made them even rounder later, which may have led to the confusion.)
    - dredmorbius 3y ago
      Interesting, and a good explanation from Mentour Pilot as well. Thanks!
rkagerer 3y ago
Didn't it take us thousands of years of working with metals (Bronze Age through Modern) to get them to the uniform quality we see today (at least speaking on a commoditized basis)? I'm sure the story around composites will improve in due time.
midoridensha 3y ago
>Metals are uniform and broadly predictable. That's not true at all: metals have a grain structure, and how those grains are oriented can change the metal's properties in different directions. >Composites vary cure to cure. Metal castings can vary from cast to cast.
- omniglottal 3y ago
  Forging and heat treatment are processes to introduce uniformity of metallic grain structures. These have been perfected over hundreds of years. I challenge you to find a single structural component in a safety-critical context which is made of cast metal.
  - durundal 3y ago
    https://www.investacast.com/industries/safety-critical/ https://www.investacast.com/industries/safety-critical/ These folks, among others, make a lot of them. You are also incorrect about forging being used to introduce uniformity into the grain, it is typically (though not always, as some forging operations may just be for establishing shape) to stretch the grains such that they are oriented along the load path, resulting in higher allowable stresses. Look up highly loaded aircraft parts like landing gear, they are typically forged to establish the grain direction and then machined to final dimension. Nothing stops you from heat treating metal after it has been cast, either. Some heat treatments are also expressly to produce nonuniform conditions in the metal, case hardening for example.
    - jacquesm 3y ago
      As well as chemical treatments.

mardifoufs 3y ago

Composites can be tested. Not as easily as metals can be, and it involves a lot more software analysis and even AI, but it's still possible. I work on flaw detection/segmentation with ultrasounds -and I have not directly worked with metal scans so I can't exactly compare- but we can already get some pretty good results with the right probes and scanners. The other major issue is that NDT on composites needs more care and time from the inspectors on the ground, and might need a lot more organizational resources to track and make sense of the data. But now that i think about it, I have no clue about performance or even feasibility of testing carbon composites. I'll have to ask around, but I'm pretty sure we have clients that use our hardware for Carbon! :)

jacquesm 3y ago
How does that work? Shouldn't the device be certified for such an application?
- mardifoufs 3y ago
  Yes! Sorry if I wasn't clear enough. I meant that they use the devices because they are compliant and certified for carbon composites. I just wasn't sure since the devices are usually not for a single purpose so it's hard to keep track of all certified use cases from my PoV. But sometimes they are! We have a few scanners specifically for pipelines and even robots for wind blades, yet even then the probe usually uses the same detection technology (ultrasounds, eddy currents, etc). The magic happens on the signal processing side when it comes to the difference between the scanners, and the trend is towards multipurpose all in ones. Our most recent industrial scanner has an FPGA that is explicitly there to allow for extensibility so that it fits most applications. FPGAs have been used quite often in the field but usually merely to implement some specific signal processing, not to be extensible! I'm rambling here but my point is that some devices can be used for pretty much any application (the Omniscan for example), process specific devices are more for large scale industrial workflows! The probes can be the only thing you need to change to use the same scanner to do stuff as varied as hydrogen poisoning analysis on steel to composite flaw detection on windblades! Here is an example, again with the Omniscan : https://www.olympus-ims.com/en/scanners/aerospace-wind-blade-inspection-scanners/ https://www.olympus-ims.com/en/scanners/aerospace-wind-blade...