Sad news. (Leonard) John Hart-Smith has recently passed away in Melbourne Australia. John was a strident pioneer in adhesive bonding technologies and composite structures. He will be sadly missed.
Regards
Blakmax
Tugboat, it is not possible to model interfacial degradation due to hydration.
3DDave. The reason for addressing hydration is that it results in one of the most common forms of bond failure.
ALL adhesive bond design methods inherently assume that the bond is sound and the processes are...
Tugboat
You are exactly like you say. The same oxidisation occurs with aluminium, where this is the exact mechanism that causes interfacial (adhesion) failure in aviation structures. We have experience with epoxy silanes to prevent hydration on aluminium surfaces with very significant results...
Oh dear:
Tugboat says: Whatever the analysis states, the only part of the sub we have seen are the titanium domes. There was ZERO adhesive attached to the domes which means the failure occurred between the adhesive and the titanium. We all saw the video of the gluing process, the surface was...
This is a surface preparation issue. To achieve an adhesive bond the surface:
1. must be clean (we all know that).
2. must be chemically active. (not so well known).
Unless the adhesive reacts strongly with the ahderends, you must undertake measures to get the surface chemically active...
Hi again Spagett
Just a further comment. Repairs using autoclave heating is not the panacea that may be commonly assumed because all of the structural panel is heated, so ANY moisture trapped in the panel will result in damage due to the steam pressure created. I have seen structural damage...
Hi Spagett
Is the structure uniform, or are there changes in thickness (spars, ribs etc). within the structure? If so, where were the thermocouples located? Many SRM use generic layouts which totally ignore substructure. The configuration of heat sources and theermocouples can greatlt influence...
Hi JP
Before you change adhesives, firstly assess the failure mode for the existing bonds. My bet is that the adhesive breaks away, leaving a shiny metal surface. In which case, your problem may not be the type of adhesive but the process used to treat the metallic surface prior to bonding...
I started my career as a metal machinist, then returned to high school and ended up doing a degree in Mech Eng. I studied part time for a Masters in engineering, and then applied for a research position in materials science that required a PhD. By chance, there were no other applicants so I got...
TugboatEng
SwinnyGG's comments about yield/ultimate are correct, if a little blunt (a bit like my responses at times [bigglasses]). In general, composites are considered to be linear elastic to failure if loaded on the fibre direction, but there may be some features that resemble yielding but...
Having read the attached link, I make the point that in both the bolt hole specimen and the ILS specimen in the reference work, there is no possibility of a glossy surface such as would occur in production defects such as probably were referenced in the previous description of the post...
Tomth
I've been in the industry for longer than most but I have yet to see a VALID test result that shows that strength can be restored through a few drill holes. I have tons of evidence that the injection repair for bonded joints in metallic structure simply does not work. Since these bonds...
Tomfh
My assertion that injection repairs are ineffective is based on over 50 years of aircraft maintenance of bonded structures, and I have seen thousands of injection repairs inmetal bonded structure that have resulted in bond failure in later service. Like you, my assertion was challenged by...
3DDave,
what would have helped even more was a better composite failure criteria than the commonly accepted Tsai Hill or Tsai Wu criteria that are widely programmed into many FEA packages. FROM MEMORY: (and it is a 75 year old memory!!) there was a widespread assessment of composite failure...
I'm wth you SWComposites. There is a lot we don't know but what we do know is very curious indeed. Your most telling comment was :
As previously discussed I don't think the passengers would have had time to discuss the last acoustic indication of structural activities.
There are3 so many...
Hi MintJulep
In 2006, I was engaged as a consultant to a helicopter crash in Fiji. It occurred on the same day as there was a military coup and therefore the Australian and New Zealand governments withdrew the usual formal investigative support from government organisations, so CAAFI engaged a...
Wow.
I didn't mean to kill the discussion with my last posting!!! Sorry Guys and Gals.
My background: I have been working in composites and adhesive bonding since 1972. (I think Moses was still in shorts then.) I am well and truely retired but I have extensive experience and expertise in...
I have had a week off travelling... a benefit reserved for the retired. I note the simulation provided by IRStuff, and I make the comment that this representation depends yet again on the composite failure theory used in the model. Again, if it is the Tsai-Hill or Tsai-Wu model the results is...
Read my previous posting on adhesive bond failure mechanisms and interfacial hydration. Salt exacerbates hydration. So if their surface preparation is deficient, the operating environment will definitely find the deficiencies.
Another issue from the adjacent discussions: There will be thermal...
