I had one terrific Summer. I hope you enjoyed it as much as I did.
One highlight of the Season was the analysis of a meter-class optical window to assure safe operation over a 15 year service life in transport-type aircraft. Safe means zero chance for failure over 15 years (no Weibul statistics for these folks!). Fortunately, they had selected a glass for which there is good engineering data, i.e. the fracture toughness, the crack propagation rates and the stress-corrosion effects of moisture had been well defined and quantified. My job was to define the proof test for the new windows that would assure the product safety for 15 years and another proof test to be used at the periodic reinspections.
procedure is a deterministic one. The engineer integrates the crack
propagation velocity repeatedly over the time of the stress transient until the
crack grows to critical size at which time complete fracture occurs
instantaneously. I use MSC/Nastran
finite element code to define the stress transient and I use AEH/Jade brittle fracture software to perform
the numerical integration. AEH/Jade
allows me to easily vary the initial crack size and the integration time
step. The latter allows me to demonstrate convergence in the time domain
which may be very important in complicated stress transients.
Once an acceptable initial crack size has been determined the defining proof test becomes a piece of cake.
Well, that was one of this Summer’s adrenalin highs.
I’m sorry for having been away so long, but I was having way too much fun! More later, I promise.
Look out! All Hallow’s Eve awaits you.