Hmm, right away it doesn't strike me as much damage for an engine that was supposed to come apart in flight. Maybe we aren't seeing everything, but usually catastrophic failures of the turbine blades causes a lot more damage, both shooting through the engine and parts flying out the exhaust. Although there is usually a ring around the engine to "catch" the blades as they are ejected during a catastrophic failure, at full power and spinning, the damage is usually much more massive when it fails at full power/RPM. The ring that is suppose to "catch" everything bears little resemblance in that condition to what it started out looking like and the damage is generally on a fairly massive scale. In practice, it attenuates the energy enough that anything that does escape doesn't pose a further danger, but it's usually torn to shreds.
You should watch some of the chicken-shooting videos where they test jet engines. It's amazing how much they flex and move around when subjected to a shock. They are not the rigid structures they seem to be. This is why when there is an accident, even if it had nothing to do with the engine, the engine will often tear itself apart on some scale, just not the scale that would indicate a catastrophic internal failure. Remember that these are very carefully balanced engines that spin at tens of thousands of RPM, which means when something internally does "go", it tears itself apart in sometimes less than a revolution. That's a massive amount of energy. I don't really see those energy signatures in these pictures, but again, we aren't seeing everything.
Again, as I said via PM, we can't look at the fatigue cracks (if present) on a microscopic scale, which is what the labs do to determine fatigue failure vs. overload failure. Overload means the entire thing was subject to far more stress than it was designed to handle, like running it up way past 100%, and in that case there should be additional heat signatures to show it was operating above what it should. Turbine engines are pretty sensitive to temps and over-temp operations leave some pretty good signatures. Much more common in almost every failure is a flaw of some kind or locally under-designed area, which causes a crack that propagates with each cycle until the structure can no longer hold itself together, and then it catastrophically fails. Things just don't fail unless they are either subjected to more load than they are designed to handle, or they fail below that level, but if that's the case, it doesn't happen at once. It happens over time. This is sometimes visible to the trained eye without excessive magnification, but it also sometimes takes extreme magnification, beyond what scanning electron microscopes can do (into the area of transmission electron microscopes). This is why labs are used extensively to test and determine fatigue failures. This is where I'd be looking carefully to eliminate a catastrophic failure of the turbine disc/blades. If the disc was recovered, the signature of a fatigue crack would be there.
05-14-2017
