dibble777
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Damage To Fuselage Aluminium Vs Carbon Fibre

Sat Jul 13, 2013 5:19 am

In the case of damage to a fuselage by a truck or by fire how does repair of an aluminium skin and underlying structure compare with the repair of a carbon fibre skin? In terms of time/cost/feasibility.
 
Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 10:13 am

One thing I'm wondering about: With thermal damage in the crown area on the ET 787, how do you determine the exact extent of the skin area to replace, assuming that the heat spread beyond just the area where external damage actually became visually apparent?

How do you know how far the composite structure is actually damaged? Do you cut out pieces and subject them to microscopic and chemical testing?

How would you determine the extent of such damage with aluminium skin?
 
fr8mech
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 3:01 pm

Quoting Klaus (Reply 1):
How would you determine the extent of such damage with aluminium skin?

Eddy current conductivity testing and sometimes hardness testing.
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Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 4:06 pm

Quoting fr8mech (Reply 2):
Eddy current conductivity testing and sometimes hardness testing.

Okay... so external sample testing is usually not required even after a partial fire?
 
fr8mech
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 4:12 pm

Quoting Klaus (Reply 3):
Okay... so external sample testing is usually not required even after a partial fire?

We've never done it.

But, we always follow engineering's lead in these matters and they'll typically talk to the manufacturer.
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Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 6:20 pm

Quoting fr8mech (Reply 4):
We've never done it.

If that procedure has been validated properly, there shouldn't be a problem with it.

Quoting fr8mech (Reply 4):
But, we always follow engineering's lead in these matters and they'll typically talk to the manufacturer.

Makes sense.

Are repair procedures for the 787 already known? I would expect that to be the case at least at the existing operators.
 
KPWMSpotter
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 8:14 pm

Quoting Klaus (Reply 1):
How do you know how far the composite structure is actually damaged? Do you cut out pieces and subject them to microscopic and chemical testing?

There are a handful of established non-destructive inspection methods for composite laminates. Most maintenance checks only specify a general visual inspection for damaged fibers on the surface of the laminate. A more detailed first check is a "sonic tap test", where a trained mechanic will tap a heavy metal coin against the component, listening for any change in sound across the part where there may be damage. Where there is large delamination it is very easy to tell by the tap test (a good laminate will have a sharp tapping sound, a delaminated part will make more of a dull thud). Boeing's inspection manuals (at least for the 737, 757, and 767, possibly others too) provide guidelines for a proper tap-test, down to the required size and weight of the "coin" used to tap the part.

Where damage is suspected, inspectors can utilize thermal, ultrasonic, or X-Ray inspection. Thermographic inspection is used where moisture ingression is suspected. The part is heated in an oven, then brought out to cool at room temperature. Composite structure will cool rapidly, but trapped moisture will remain hot and show up on a thermal camera.

Ultrasonic is the best method to find exact damage. A tool is used which emits a sonic pulse and measures the return echo (very similar to SONAR, but on a smaller scale). Changes in the return pattern can indicate voids, defects, or damage.

I'm sure there are other inspection methods available, but these methods have been in place for decades to inspect composite components. The 787 requires inspection on a much larger scale, so Boeing may have developed entirely new procedures.
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Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Sun Jul 14, 2013 9:08 pm

Quoting KPWMSpotter (Reply 6):
Boeing's inspection manuals (at least for the 737, 757, and 767, possibly others too) provide guidelines for a proper tap-test, down to the required size and weight of the "coin" used to tap the part.

Sounds a bit... unscientific, though, doesn't it...?

Quoting KPWMSpotter (Reply 6):
I'm sure there are other inspection methods available, but these methods have been in place for decades to inspect composite components. The 787 requires inspection on a much larger scale, so Boeing may have developed entirely new procedures.

I was asking because if the crown area in question was indeed open without a crew rest module up there, the heat should have spread out across a larger area, with decreasing intensity.

Given the very tight tolerances for the fuselage, Boeing must have specified and certified safe damage limits for the material. They will need to have quantifiable tests for whether a fix / replacement is required in a certain area.

I guess the actual repair will be documented to the public to some extent. It would just be interesting to have a look into the repair manuals right away...
 
dynamicsguy
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Mon Jul 15, 2013 9:14 am

Quoting Klaus (Reply 7):
Sounds a bit... unscientific, though, doesn't it...?

Sounds it, but it's actually really effective, even for an untrained chump like me. An Australian 20 cent piece is about right.

Quoting Klaus (Reply 7):
I guess the actual repair will be documented to the public to some extent. It would just be interesting to have a look into the repair manuals right away..

This repair won't be in any manual - it'll have to be designed. I can't see how they'll be able to get away with anything other than cutting out a fairly large section and splicing in a new one. It will be very intersting to see how much gets replaced and how the section is manufactured.
 
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bikerthai
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Mon Jul 15, 2013 2:22 pm

Quoting Klaus (Reply 7):

I was asking because if the crown area in question was indeed open without a crew rest module up there, the heat should have spread out across a larger area, with decreasing intensity.

Yes, except the thermal insulation blanket in that area does impact how much heat damaged is spread. (That is if the blanket didn't catch fire themselves  )

Quoting dynamicsguy (Reply 8):
Sounds it, but it's actually really effective, even for an untrained chump like me. An Australian 20 cent piece is about right.

Deja Vu . . . could have sworn I read this comment from you a couple of years ago when we were discussing composite repair 

bt
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Mon Jul 15, 2013 3:58 pm

Quoting dynamicsguy (Reply 8):
Sounds it, but it's actually really effective, even for an untrained chump like me. An Australian 20 cent piece is about right.

No disrespect intended or implied – I'm sure this works well.

But doesn't that test detect only actual delaminations and not merely weakened resin that just hasn't delaminated yet (but might still do so once stressed again)?

Would there be enough of a safety margin even in a highly critical part like a pressurized fuselage barrel to accept that possibility?
 
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bikerthai
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Mon Jul 15, 2013 6:59 pm

Quoting Klaus (Reply 10):
But doesn't that test detect only actual delaminations and not merely weakened resin that just hasn't delaminated yet (but might still do so once stressed again)?

True. What they will probably have to do is take specimen along the area beyond the visible damage and do flex tensile test.

Good flex tensile test should tell you that the material have not experienced heat damage.

bt
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
Klaus
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Mon Jul 15, 2013 7:57 pm

Quoting bikerthai (Reply 11):
Good flex tensile test should tell you that the material have not experienced heat damage.

Does that mean stressing it mechanically and then checking whether any delaminations have developed?
 
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bikerthai
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RE: Damage To Fuselage Aluminium Vs Carbon Fibre

Tue Jul 16, 2013 6:49 pm

Quoting Klaus (Reply 12):

Nope. I believe they are checking for modulus. Changes in modulus will show that the composite is compromised even no decontamination occurs. This will specially be true for heat damage.

bt
Intelligent seeks knowledge. Enlightened seeks wisdom.

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