High-speed helicopter drive shaft hydrogen cracking

Post-break Q&A continuation. Warehouse inventory center in North Carolina etched a unique identifier code into high-speed steel drive shafts; the etching introduced hydrogen into the high-strength steel and 100% of the etched parts failed in fatigue simulation. Subsequent move to laser scribing produced the same problem by a different route (rapid surface melt → high hardness → brittle initiation). Pulled together with the PMI (positive materials identification) serialization-of-parts program of the 1970s–80s.