This video details the spectacular failure of the ninth test firing of a 3D printed rocket engine combustion chamber, part of NASA's long-life additive manufacturing program. While the carbon-carbon nozzle extension failed first due to a known defect, the focus of the analysis, as detailed in a recently published paper, is the subsequent disintegration of the combustion chamber. The video visually tracks the chamber failure, showing a crack initiating and propagating around the structure, leading to explosive separation and propellant leakage. The analysis of the failed part and test prints revealed that print interruptions during the laser powder bed fusion manufacturing process, coupled with potential issues like unmelted powder, contaminants, and possibly laser attenuation due to dust buildup, created weak points. The paper concluded that a combination of these issues, leading to localized increases in defect rates, caused the catastrophic failure, highlighting the critical need for stringent process controls in additive manufacturing for high-stress applications like rocket engines.
Summary:
0:06 Failed Rocket Test: Video shows the ninth test firing of a 3D printed rocket engine combustion chamber designed for three tons of thrust, which fails spectacularly.
0:23 Initial Nozzle Failure: The carbon-carbon nozzle extension disintegrates first; this failure was expected due to an existing defect and is not the focus of the detailed analysis.
0:25 Combustion Chamber Breakup: Seconds after the nozzle fails, the combustion chamber breaks apart, spraying fuel. This is the primary subject of the analysis discussed in the video.
0:34 NASA Program: The test was part of NASA's program focused on using 3D printing (additive manufacturing) for rocket engines.
0:40 Paper on Failure Cause: A recently published paper investigates specifically why the combustion chamber test failed.
1:18 Chamber Crack Propagation: Analysis of slower footage shows a crack starting at the 8:00 position and developing around the chamber before it separates.
1:26 Propellant Behavior: Post-failure, liquid methane fuel, used for cooling the chamber walls, is sprayed outwards, while liquid oxygen oxidizer flowing through the middle stops relatively quickly. Shutting off oxidizer first is a safety measure against metal fires.
3:20 3D Printing for Rocketry: Fuel is flowed through the walls of the combustion chamber for cooling, which is facilitated by the complex geometries enabled by 3D printing.
3:26 Laser Powder Bed Fusion: The chamber was printed using this method, involving laying down thin layers of metal powder and selectively melting them with a laser to build the part layer by layer.
3:57 Copper Alloy: The chamber was made with a special copper chromium niobium alloy for better heat transfer.
4:06 Failure Analysis: Engineers analyzed the failed part, finding a thin line corresponding to a print layer and an interruption in the build cycle.
4:25 Print Interruptions: Documented interruptions during the printing process, including power outages and opening the machine for maintenance, were linked to the failure location.
4:43 Interruptions Visible: These interruptions were visible in three of the printed combustion chambers tested. One chamber with similar visible lines failed after 51 successful firings.
5:08 Post-Processing (HIP): Parts undergo Hot Isostatic Pressing (HIP) to reduce porosity and increase material strength by heating and squeezing them under high-pressure gas.
6:02 Findings from Analysis: Microscopic analysis revealed unmelted powder and contaminants near
Error: Column.new() missing 6 required positional arguments: 'cid', 'name', 'type', 'notnull', 'default_value', and 'is_pk' hypothesis suggests dust accumulating on optics might attenuate the laser power as the print progresses, reducing melting effectiveness.
8:15 Conclusion on Failure Cause: The failure wasn't due to a single problem but a combination of issues related to print interruptions, leading to increased defect rates in specific layers, emphasizing the need for stringent process controls.
8:27 Engineering Margins: The video concludes by highlighting that rocket engineering is challenging due to very small margins for failure, where even a small increase in defect rate can be catastrophic.