Greg M
Do you have first hand knowledge of the use of 9309 as a "filler"? Was it used to fill dents or was it used as effectively an "injection" repair to repair disbonds?
I actually conduct courses on adhesive bond failure forensics and with better close up photos I could probably provide a more reasoned assessment. However, the different colour on the core at the outer end would make me suspect moisture ingress, and the absence of core separation towards the leading edge would make me suspect adhesion (interfacial) failure. The change in colour of tyhe leading edge bond is probably a transition from weak adhesion failure at the leading edge to mixed mode failure aft of the leading edge. Such failures are typical of hydration of the metal oxides on the leading edge due to hydration in service. This does not necessarily match with the overheat theory, but that could be verified by metallurgical analysis of the metal in the region.
I suggest you look at this file
I agree totally that the vast number of technical and engineering personnel in many organsations including OEMs do not have even a modest level of competency in management of heat distribution in complex structure during repair processes, especially using point source heating devices such as heat lamps. As a simple demonstration of this assertion, there is a common perception that because an arbitrarily located thermocouple reaches a designated set point temperature, then the repair has been adequately heated. Reality: move the sensor or change the location of the heat source, the result will be totally different.
Heat sources must be configured to match the individual structural heat sinks, the sensors must be located to measure the hottest point under each heat source to prevent overheat damage, but they also must be located where the anticipated COLDEST point will occur so that there is assurance of full adhesive cure.
Happy to accept PMs to discuss this further.
My name is on the attached document.
Regards
Blakmax