Hello
Are high altitude and low pressure conditions a main cause for failures of composite structures, mainly with honycombs?
Are there any known examples for such failures?
What are the best solutions for this? I have heard about ventilized honycomb, but could not find any information on it.
Thank You
Avi
I always wondered about this. Most space bound things use honeycomb core. I will ask around and see if I can get info.
Depends what kind of failure.
In my understanding, the low pressure scenario is not a primary cause of failure as long as the structure; it is the cyclical nature of high pressure, low pressure, etc experienced by aircraft going up and down that will cause, for example, porosity to initiate a crack or just to grow an existing crack. However, if there is air trapped within the honeycomb during manufacturing for example, where the air hasn’t been evacuated properly, then there will obviously be a considerable pressure differential between the internal pressure in the honeycomb and the external high altitude environment. Therefore, this can also cause internal stresses and initiate a crack around an air bubble for example. Is combatting thei problem what you mean when you talk of ventilized honeycomb? You can of course use a spiked roller for example during lay-up to assist with air removal from the honeycomb during manufacture
What is the standard inspection for checking if all the air form the honeycomb was taken out?
I wonder if when vacuum laminated, and then the cells are sealed off from earth atmosphere pressure, in space there is ultimate vacuum, but the ratio of the cell pressure, and spac pressure isn’t enough to cause problems.
Which, when traveling between altitudes as well, is the same thing…there is a good half-way point in pressure in the cells.
So i guess that calculations must be done in order to deside if the cells in the honeycomb are suitable for this issue.
We cannot count on the vacum in the manufacturing process to take out all the trapped air in the honeycomb cells?
We have shipped Americas yacht hulls all over the world within an Antonov’s fuselage… The consequences of not pressurising the load bay to save fuel on one trip caused the inside skin to blow off in a small area on one boat!
leaky bag around that area? 
Astute, that is unfortunate but interesting at the same time! What do you do now to limit this, just pressurise the loading bay or have you changed manufacturing?
Pressurise the bay, for sure!..
That said- The standard within the marine industry has jumped up considerably over the last 10 years especially within the Cup and Volvo circuit. With NDT being the norm now, it is in the teams interest to know before the boat leaves the shed that your processes are up to spec.
The term is “Perforated” and I have used alloy core that was perforated on a wing mast build…
Every failure I have seen in an aircraft part, excluding impact or lightning strike, was due to moisture intrusion and freezing.