Researchers at NASA’s Marshall Space Flight Center have analyzed what is likely the most spectacular 3D print failure ever seen.
The failure occurred during hot fire testing of an additively manufactured GRCop-42 copper-alloy combustion chamber. The rocket engine was fired in a horizontal orientation, as is customary for test fires.
During the test, the engine bell literally blew off, and the combustion chamber split open — right along a witness line. If there has ever been a more spectacular 3D print failure, I don’t know what it could be.
The failure was analyzed in considerable detail by researchers at Marshall, who determined a number of factors were involved in the negative outcome:
- Build interruptions are risky. The failure originated at a witness line created during one of several build interruptions during the print job.
- Porosity was three orders of magnitude higher at the failure site than in well-manufactured components, dramatically reducing mechanical properties, especially elongation and tensile strength.
- The failed combustion chamber showed elevated oxygen levels and an imbalanced Cr/Nb ratio, likely reducing high-temperature strength and creep resistance.
- Hot isostatic pressing (HIP) was insufficient. Although all parts were HIP’d, surface-connected and internal porosity remained due to poor fusion during build interruptions.
The researchers found that properly managed build interruptions can be safe. They tested replica tensile and fatigue test bars, produced with controlled interruptions, which showed no degradation in mechanical performance. This suggests that interruption protocols, not the interruptions themselves, were the failure cause.
In the end, they concluded that the failure was the result of a combination of poor restart procedures, lens contamination, and possible powder oxidation — none of which were detected by the machine logs alone.
This scenario suggests several actions should be taken by those producing critical metal parts with additive manufacturing systems, including mandatory witness line inspection, much stricter process controls around build interruptions, optical system health monitoring, real-time monitoring of oxygen levels and other parameters, and non-destructive testing of printed parts.
These are all important findings that should be considered by any operation producing metal parts, particularly those being used for critical applications.
Finally, this paper was analyzed by the Internet’s favourite space YouTuber, Scott Manley. Manley provides some interesting commentary on the situation, along with slow-motion views of the incident.
Fly safe!
Via Science Direct
