To: beanie
Following the lightning strike, the blade was returned to the manufacturer for evaluation before it was returned to service. Currently the investigation team is gathering more information about the history of this blade. At this stage, there is no evidence to link the lightning strike to the fatigue failure, however, this is one of the variables still under active consideration.
Let’s assume your are correct in stating that the spar is made of titanium alloy. If that were true the point of lightning attachment would have been seriously discolored.
Titanium has a strange property in that it will form colored oxides on the surface of the material when an electrical current is passed through it. The color can be varied with the increase or decrease in current level and all colors of the spectrum can be achieved with this variance. The voltage can vary from several volts to 50-100 volts in order to achieve the surface color change. If this relatively low voltage can effect the surface in forming the colored oxides then imagine what several million volts at very high amperage can do not only to the surface but the internal matrix as well.
