ATPMBA wrote
I think heat has an affect on bonding materials. The MidEast can be an oven.
Heat does have significant effects on adhesives. The stress to failure is lower, but the adhesive bcomes more ductile, and again remembering that the strength of the joint depends on the area under the strsss-strain curve, the adhesive load capacity is often slightly higher at elevated temperature. There is an upper limit to adhesive performance, known as the "Glass Transition Temperature". Above that temperature the adhesive passes from being a relatively hard glassy material to a soft, compliant rubbery material. Stength and performance fall away above that temperature. As a general rule, the higher the processing temperature for the adhesive the higher the Tg. My observation of the close-up photos I have seen indicate that AW used a film adhesive which means it was cured at least 120C (250F) and may have been cured as high as 175C (350F) in which case the Tg should be adequate even in the sand pit.
My observations from the photos is that there is extensive micro-voiding present in the samples I have seen. Micro voids occur when volatiles are released during cure of the adhesive during production. They cause a significant reduction in strength for lap-shear joints and I would expect a similar reduction in core to skin bond strength. I suspect that this may have contributed to the DOH failure.
Because of the number of causes of micro-voiding and the fact that this feature has been observed from two separate samples from two different areas of the boom, it is reasonable to expect that this may not be isolated to one aircraft and may not be isolated to only the disbond area from which the sample was taken.
Regards
blakmax