Missing single seat chopper and pilot, NW of W.A.
Join Date: Jul 2008
Location: Australia
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I am astounded that bond failures are the accepted "norm"
Oleary
I am astounded that bond failures are considered the be part of the risk of flight, and I know of your case because we discussed it some time ago. Bond failures can be prevented. There are really only two causes of bond failures: bad production processes or bad design and certification processes.
The simple fact is that examination of the bond failure surfaces can clearly tell you what is the cause. If it fractures the adhesive and leaves large amounts of adhesive on both surfaces, then it is a cohesion failure and the fault is a design and certification issue. Such failures usually occur at high loads. For film adhesives failure usually occurs through the carrier cloth, a light open weave material used to facilitate handling.
If the bond fails at the interface or near the interface the it is indicative of degraded bond strength at the interface and failures usually occur at or near the interface between the adhesive and the substrate to which the bond is formed. These are always failures at a much lower strength and are directly associated with production processes. For metals, the failure is almost invariably driven by hydration of the oxide layer on the metal surfaces where the adhesive is bonding. A similar mechanism applies to some bonds to fibre composites but there may also be some other factors.
I wish I could have access to the wreckage in many crashes involving bonded parts because i know that the level of knowledge of adhesive bond failure forensics within the regulators and crash investigators is exceptionally low, and this is not a reflection on the personnel involved, it is a recognition that the available level of understanding and training is deficient. If you don't know that you don't know then what you do know becomes the accepted explanation even if it is wrong.
Regards Blakmax
I am astounded that bond failures are considered the be part of the risk of flight, and I know of your case because we discussed it some time ago. Bond failures can be prevented. There are really only two causes of bond failures: bad production processes or bad design and certification processes.
The simple fact is that examination of the bond failure surfaces can clearly tell you what is the cause. If it fractures the adhesive and leaves large amounts of adhesive on both surfaces, then it is a cohesion failure and the fault is a design and certification issue. Such failures usually occur at high loads. For film adhesives failure usually occurs through the carrier cloth, a light open weave material used to facilitate handling.
If the bond fails at the interface or near the interface the it is indicative of degraded bond strength at the interface and failures usually occur at or near the interface between the adhesive and the substrate to which the bond is formed. These are always failures at a much lower strength and are directly associated with production processes. For metals, the failure is almost invariably driven by hydration of the oxide layer on the metal surfaces where the adhesive is bonding. A similar mechanism applies to some bonds to fibre composites but there may also be some other factors.
I wish I could have access to the wreckage in many crashes involving bonded parts because i know that the level of knowledge of adhesive bond failure forensics within the regulators and crash investigators is exceptionally low, and this is not a reflection on the personnel involved, it is a recognition that the available level of understanding and training is deficient. If you don't know that you don't know then what you do know becomes the accepted explanation even if it is wrong.
Regards Blakmax
