Ok, I remember. Old dogs, new tricks. I finally worked out how to post these photos.
This one shows a spar to adhesive failure which was NOT the cause of the crash. However, given that the adhesive is 10 times stronger than the core we should be seeing core attached.
Now here is a lower magnification of the matching surface.
Got a nice carpet in my house, yeah?
Note the adhesive has completely separated from adjacent to the spar. This is PROBABLY because of moisture (humidity) contamination during the bond curing process. Moisture at the interface has prevented adhesion.
Now given the evidence I have seen on the AW139 boom failures, it appears that at least some of the AW bonding is performed in less than optimum controlled environments which has probably led to moisture contamination of the bond and subsequent disbonding due to weakened core to adhesive bonds caused by micro-voids. Now I have worked out this photo-linking stuff, here is a photo of a good bond which fails by fracture of the core and tearing of the fillet bonds. Note the absence of micro-voids compared to the next photo.
Here is a photo of an AW139 boom disbond.
Note the number of small bubbles, and the number of shiny surfaces in the fractured core areas. These are also micro-voids. As I said on the AW139 thread, there is published data which shows that similar micro-void levels typically cause a 50% strength loss in overlap joints and I would expect a similar loss of flatwise tensile strength for core bonds, See my postings on the AW139 tail boom failure thread.
Hence, if similar core to spar bond failures as shown in the first two figures are evident in the AW109 event, there may be a common link. I hope that the investigators read this posting before assigning the event to "ground resonance". The possibility of a structural failure should not be excluded from consideration just yet. Again, I make no definitive conclusions. I simply suggest that this failure mode be investigated and if appropriate, eliminated.
Regards
Blakmax